Abstract: Inter-organelle signaling plays important roles in many physiological functions. Endoplasmic reticulum (ER)-mitochondrion signaling affects intramitochondrial calcium (Ca(2+)) homeostasis and cellular bioenergetics. ER-nucleus signaling attenuates ER stress. ER-plasma membrane signaling regulates cytosolic Ca(2+) homeostasis and ER-mitochondrion-plasma membrane signaling regulates hippocampal dendritic spine formation. Here, we propose that the sigma-1 receptor (Sig-1R), an ER chaperone protein, acts as an inter-organelle signaling modulator. Sig-1Rs normally reside at the ER-mitochondrion contact called the MAM (mitochondrion-associated ER membrane), where Sig-1Rs regulate ER-mitochondrion signaling and ER-nucleus crosstalk. When cells are stimulated by ligands or undergo prolonged stress, Sig-1Rs translocate from the MAM to the ER reticular network and plasmalemma/plasma membrane to regulate a variety of functional proteins, including ion channels, receptors and kinases. Thus, the Sig-1R serves as an inter-organelle signaling modulator locally at the MAM and remotely at the plasmalemma/plasma membrane. Many pharmacological/physiological effects of Sig-1Rs might relate to this unique action of Sig-1Rs.
Abstract: Activation of the newly identified σ(1) chaperone protein is involved in several aspects of the psychostimulant and addictive effects of cocaine. The development of ligands that selectively target the σ(1) protein may lead to putative potent anti-cocaine agents. We report here a new and more convergent synthetic pathway to amino side chain substituted hydantoins. Twenty new analogs of our lead compound were synthesized. None of them showed better in vitro affinity for σ(1) receptor than our lead compound. Nevertheless, three of them, obtained as racemates, showed high in vitro affinity and selectivity for σ(1) receptor. A preliminary in vivo evaluation of their pharmacological activity identified compound 22 as one that increases cocaine-induced locomotor stimulation and therefore acts as a potential efficient σ(1) agonist.
Abstract: p300/CREB binding protein-associated factor (PCAF) regulates gene expression by acting through histone acetylation and as a transcription coactivator. Although histone acetyltransferases were involved in the toxicity induced by amyloid-beta (Abeta) peptides, nothing is known about PCAF. We here analyzed the sensitivity of PCAF knockout (KO) mice to the toxic effects induced by i.c.v. injection of Abeta(25-35) peptide, a nontransgenic model of Alzheimer's disease. PCAF wild-type (WT) and KO mice received Abeta(25-35) (1, 3 or 9 nmol) or scrambled Abeta(25-35) (9 nmol) as control. After 7 days, Abeta(25-35) toxicity was measured in the hippocampus of WT mice by a decrease in CA1 pyramidal cells and increases in oxidative stress, endoplasmic reticulum stress and induction of apoptosis. Memory deficits were observed using spontaneous alternation, water-maze learning and passive avoidance. Non-treated PCAF KO mice showed a decrease in CA1 cells and learning alterations. However, Abeta(25-35) injection failed to induce toxicity or worsen the deficits. This resistance to Abeta(25-35) toxicity did not involve changes in glutamate or acetylcholine systems. Examination of enzymes involved in Abeta generation or degradation revealed changes in transcription of presenilins, activity of neprilysin (NEP) and an absence of Abeta(25-35)-induced regulation of NEP activity in PCAF KO mice, partly due to an altered expression of somatostatin (SRIH). We conclude that PCAF regulates the expression of proteins involved in Abeta generation and degradation, thus rendering PCAF KO insensitive to amyloid toxicity. Modulating acetyltransferase activity may offer a new way to develop anti-amyloid therapies.
Abstract: Depression is potentially life-threatening. The most important neuroendocrine abnormality in this disorder is hypothalamo-pituitary-adrenocortical (HPA) axis hyperactivity. Recent findings suggest that all depression treatments may boost the neurotrophin production especially brain-derived neurotrophic factor (BDNF). Moreover, BDNF is highly involved in the regulation of HPA axis activity. The aim of this study was to determine the impact of chronic stress (restraint 3h/day for 3weeks) on animal behavior and HPA axis activity in parallel with hippocampus, hypothalamus and pituitary BDNF levels. Chronic stress induced changes in anxiety (light/dark box test) and anhedonic states (sucrose preference test) and in depressive-like behavior (forced swimming test); general locomotor activity and body temperature were modified and animal body weight gain was reduced by 17%. HPA axis activity was highly modified by chronic stress, since basal levels of mRNA and peptide hypothalamic contents in CRH and AVP and plasma concentrations in ACTH and corticosterone were significantly increased. The HPA axis response to novel acute stress was also modified in chronically stressed rats, suggesting adaptive mechanisms. Basal BDNF contents were increased in the hippocampus, hypothalamus and pituitary in chronically stressed rats and the BDNF response to novel acute stress was also modified. This multiparametric study showed that chronic restraint stress induced a depressive-like state that was sustained by mechanisms associated with BDNF regulation.
Abstract: RATIONALE: Trilostane is a competitive inhibitor of 3β-hydroxysteroid dehydrogenase (3β-HSD), which notably converts pregnenolone into progesterone or dehydroepiandrosterone into androstenedione. Trilostane shows antidepressant-like properties in the forced swimming test (FST). The compound, however, induced only moderate effects on neuroactive steroid levels that could be related to its behavioral efficacy. METHODS: We compared the behavioral effect of trilostane with the other 3β-HSD inhibitor, cyanoketone, and analyzed the putative involvement of the β-type estrogen receptor (ERβ) in its antidepressant effect. RESULTS: Trilostane reduced immobility in the FST significantly at 12.5 and 25 mg/kg subcutaneously (s.c.), whereas cyanoketone (0-100 mg/kg s.c.) was ineffective. The negative ER modulator fulvestrant (ICI 182780) dose-dependently blocked the effect of trilostane (25 mg/kg). Trilostane increased circulating estradiol levels in the 12.5-50 mg/kg dose-range, and this effect was unaffected by stress and not shared by cyanoketone (25 mg/kg). The trilostane (25 mg/kg) treatment increased the ERβ mRNA expression in adrenals (+100%) and centrally, in the hippocampus (+330%). Stress and cyanoketone failed to affect ERβ mRNA levels in periphery or in the brain. CONCLUSIONS: These data demonstrate that the antidepressant-like potential of trilostane is not due to its 3β-HSD inhibiting activity, since it is not shared by cyanoketone, but rather to its estrogenic activity. The compound, which releases estradiol and up-regulates ERβ receptors, could be used as a therapeutic tool to allow an estrogenic facilitation of antidepressant efficacy.
Abstract: P300/CBP associated factor (PCAF) acts as an acetyltransferase that acetylates specific lysine residues in histones, thereby remodelling chromatin structure. The possible involvement of PCAF in learning and memory processes or mood disorders was recently assessed by characterizing the behavioural phenotype of PCAF KO mice bred on a CD1 background and revealed short-term memory deficits that evolved with age towards long-term memory alteration and an exaggerated response to stress [10]. PCAF KO mice have been backcrossed on a C57BL/6j strain for 15 generations and we report here the first data regarding their behavioural phenotype. PCAF KO mice bred on a C57 background showed short-term memory deficits in terms of decreased spontaneous alternation and absence of acquisition of a daily changing platform position in the water-maze. Acquisition of a fixed platform location or passive avoidance response was preserved. PCAF KO mice showed no difference with WT C57BL/6j controls in their performances in the forced swimming and light/dark exploration box, suggesting no particular phenotype on anxiety and stress responses. We therefore evidenced marked phenotypic differences in PCAF KO mice depending on the genetic background strain confirming that PCAF histone acetyltransferase is involved lifelong in the chromatin remodelling necessary for memory formation but differentially involved in anxiety and response to stress.
Abstract: In drug discovery, structural modifications over the lead molecule are often crucial for the development of a drug. Herein, we reported the first in vivo bioisosteric effect of phosphinolactone function in relation to the lactol group constituting the bioactive molecule: Hydroxybupropion. The preparation of phosphinolactone analogues and their antidepressant evaluation towards forced swimming test in mice showed that biological activity was regained and even strengthen.
Abstract: Beta-amyloid (Abeta) deposition is one important pathological hallmark in Alzheimer's disease (AD). However, low levels of Abeta may modify critical endogenous protection systems before neurodegeneration occurs. We examined the time-course effect of sublethal concentrations of Abeta on total BDNF (panBDNF), BDNF transcripts (I, II, IV and VI), trkB.FL, trkB.T1 and p75(NGFR) mRNA expression in cultured cortical neurons. We have shown that Abeta exhibited a dual response on BDNF mRNA, i.e. an increase at short times (3-5 h) and a dramatic decrease at longer times (24 or 48 h). The early increase in BDNF expression seems to be driven by increased expression of transcripts I and IV. The BDNF drop was specific since did not occur for other mRNAs examined. The BDNF protein content showed a similar profile but did not follow the dramatic reduction as its encoding mRNA. These observations may help to explain cognitive deficits observed at initial stages of AD.
Abstract: Decrease in the expression or activity of acetylcholinesterase (AChE) enzymatic activity results in increased cholinergic tonus in the brain and periphery, with concomitant regulations of nicotinic and muscarinic receptors expression. We generated AChE knockout mice and characterized the behavioral phenotype of heterozygous animals, focusing on learning and memory functions. Male and female, AChE+/- and AChE+/+ littermate controls (129 sv strain) were tested at 5-9 weeks of age. AChE activity was significantly decreased in the hippocampus and cortex of AChE+/- mice, but butyrylcholinesterase activity was preserved. AChE+/- mice failed to show any difference in terms of locomotion, exploration and anxiety parameters in the open-field test. Animals were then tested for place learning in the water-maze. They were trained using a 'sustained acquisition' protocol (3 swim trials per day) or a 'mild acquisition' protocol (2 swim trials per day) to locate an invisible platform in fixed position (reference memory procedure). Then, during 3 days, they were trained to locate the platform in a variable position (working memory procedure). Learning profiles and probe test performances were similar for AChE+/- and AChE+/+ mice. Mice were then treated with the muscarinic receptor antagonist scopolamine (0.5, 5 mg/kg) 20 min before each training session. Scopolamine impaired learning at both doses in AChE+/+ mice, but only at the highest dose in AChE+/- mice. Moreover, the intracerebroventricular injection of amyloid-beta25-35 peptide, 9 nmol, 7 days before water-maze acquisition, failed to induce learning deficits in AChE+/- mice, but impaired learning in AChE+/+ controls. The peptide failed to be toxic in forebrain structures of AChE+/- mice, since an increase in lipid peroxidation levels was measured in the hippocampus of AChE+/+ but not AChE+/- mice. We conclude that the increase in cholinergic tonus observed in AChE+/- mice did not result in increased memory functions but allowed a significant prevention of the deleterious effects of muscarinic blockade or amyloid toxicity.
Abstract: Microcebus murinus, a mouse lemur primate appears to be a valuable model for cerebral aging study and for Alzheimer's disease model since they can develop beta-amyloid plaques with age. Although the biological and biochemical analyses of cerebral aging are well documented, the cognitive abilities of this primate have not been thoroughly characterized. In this study, we adapted a spatial working memory procedure described in rodents, the sequential choice task in the three-panel runway, to mouse lemurs. We analyzed the age-related differences in a procedural memory task in the absence or presence of visual cues. Sixty percent of young adult and 48% of aged lemurs completed the exploratory, choice habituation and testing phases at the beginning of the procedure. Young adult lemurs showed a higher level of perseverative errors compared with aged animals, particularly in the presence of visual stimuli. Over trials, old animals made more reference errors compared to young ones that improved quickly their performances under random level. No significant improvement was observed in young adults and old ones over sessions. This study showed that behavioural performances of M. murinus assessed on the sequential choice task in the three-panel runway markedly differ from the previously reported abilities of rodents. The behavioural response of young adult lemurs was influenced by novelty-related anxiety that contributed to their performance in terms of perseverative errors. Conversely, aged lemurs showed less perseverative errors, a rapid habituation to the three-panel runway maze, but made more memory errors. Overall, these findings demonstrate the feasibility to use the three-panel runway task in assessing memory performance, particularly in aged mouse lemurs.
Abstract: Tetrahydro-N,N-dimethyl-2,2-diphenyl-3-furanmethanamine hydrochloride (ANAVEX2-73) binds to muscarinic acetylcholine and sigma1 (σ1) receptors with affinities in the low micromolar range. We characterized its anti-amnesic and neuroprotective potentials in pharmacological and pathological amnesia models. Spatial working memory was evaluated using spontaneous alternation in the Y-maze and non-spatial memory using passive avoidance procedures. ANAVEX2-73 (0.01-3.0 mg/kg i.p.) alleviated the scopolamine- and dizocilpine-induced learning impairments. ANAVEX2-73 (300 µg/kg) also reversed the learning deficits in mice injected with Aβ25-35 peptide, a non-transgenic Alzheimer's disease model. When the drug was injected simultaneously with Aβ25-35, 7 days before the tests, it blocked the appearance of learning impairments. This protective activity was confirmed since ANAVEX2-73 blocked the Aβ25-35-induced oxidative stress in the hippocampus. This effect was differentially sensitive to the muscarinic receptor antagonist scopolamine or the σ1 protein antagonist BD1047, confirming the mixed muscarinic/σ1 pharmacological action. Finally, its unique demethyl metabolite, ANAVEX19-144, was also effective and ANAVEX2-73 presented a longer duration of action, effective 12 h before Aβ25-35, than its related compound ANAVEX1-41. The neuroprotective activity of ANAVEX2-73, its mixed cholinergic/σ1 activity, its low active dose range and its long duration of action together reinforce its therapeutic potential in Alzheimer's disease.
Abstract: Activation of the newly identified sigma(1) chaperone protein is involved in several aspects of the psychostimulant and addictive effects of cocaine. The development of ligands that selectively target the sigma(1) protein may lead to putative potent anti-cocaine agents. Here, we synthetized substituted hydantoins with high affinity for the sigma(1) protein and evaluated their behavioral efficacy. Two pure enantiomers were designed and synthesized: tetrahydroisoquinoleine-hydantoin fused compounds 3 and 4. They increased cocaine-induced locomotor stimulation or sensitization. The most active enantiomer 4, facilitated CPP acquisition but failed to substitute for cocaine. When CPP was acquired with cocaine and then extinguished, 4 provoked reactivation of CPP. These observations showed that compound 4 shows a typical profile of sigma(1) protein activator, facilitating cocaine-induced behavioral effects. Preliminary ADME properties are in favour of an optimal therapeutic development. Such Tic-hydantoin compound may serve as a new effective agonist therapy in cocaine addiction.
Abstract: The antiamnesic and neuroprotective activities of the new aminotetrahydrofuran derivative tetrahydro-N,N-dimethyl-5,5-diphenyl-3-furanmethanamine hydrochloride (ANAVEX1-41), a nonselective muscarinic receptor ligand and sigma(1) protein activator, were examined in mice injected intracerebroventricularly with amyloid beta(25-35) (Abeta(25-35)) peptide (9 nmol). Abeta(25-35) impaired significantly spontaneous alternation performance, a spatial working memory, and passive avoidance response. When ANAVEX1-41 (1-1000 mug/kg i.p.) was administered 7 days after Abeta(25-35), ie, 20 min before the behavioral tests, it significantly reversed the Abeta(25-35)-induced deficits, the most active doses being in the 3-100 mug/kg range. When the compound was preadministered 20 min before Abeta(25-35), ie, 7 days before the tests, it prevented the learning impairments at 30-100 mug/kg. Morphological analysis of corticolimbic structures showed that Abeta(25-35) induced a significant cell loss in the CA1 pyramidal cell layer of the hippocampus that was prevented by ANAVEX1-41 (100 mug/kg). Increased number of glial fibrillary acidic protein immunopositive cells in the retrosplenial cortex or throughout the hippocampus revealed an Abeta(25-35)-induced inflammation that was prevented by ANAVEX1-41. The drug also prevented the parameters of Abeta(25-35)-induced oxidative stress measured in hippocampus extracts, ie, the increases in lipid peroxidation and protein nitration. ANAVEX1-41, however, failed to prevent Abeta(25-35)-induced caspase-9 expression. The compound also blocked the Abeta(25-35)-induced caspase-3 expression, a marker of apoptosis. Both the muscarinic antagonist scopolamine and the sigma(1) protein inactivator BD1047 prevented the beneficial effects of ANAVEX1-41 (30 or 100 mug/kg) against Abeta(25-35)-induced learning impairments, suggesting that muscarinic and sigma(1) targets are involved in the drug effect. A synergic effect could indeed account for the very low active doses measured in vivo. These data outline the therapeutic potential of ANAVEX1-41 as a neuroprotective agent in Alzheimer's disease.Neuropsychopharmacology advance online publication, 3 December 2008; doi:10.1038/npp.2008.212.
Abstract: Changes in neuro(active)steroid levels are involved in depressive states and mood disorders. For instance, dehydroepiandrosterone or pregnenolone sulfate showed anti-stress and antidepressant activity in rodents and regulation of allopregnanolone levels appeared to be one of the consequence of an effective antidepressant therapy in patients. 4alpha,5-Epoxy-17beta-hydroxy-3-oxo-5alpha-androstane-2alpha-carbonitrile (trilostane) inhibits the activity of 3beta-hydroxysteroid dehydrogenase (3beta-HSD) that, in particular, converts pregnenolone into progesterone. We examined whether systemic administration of trilostane affects the response to stress and depression. An acute treatment with trilostane (6.3-50mg/kg SC injected twice -16 and -2h before the measure) increased 3beta-HSD mRNA levels in the hippocampus and adrenals, but had little effect on protein levels. The trilostane treatment failed to affect open-field, locomotor or exploratory behaviors, but significantly reduced the immobility duration in the forced swimming test, measuring antidepressant-like activity, and increased the time spent in open arm in the elevated plus-maze, measuring anxiety response. The antidepressant-like effect of trilostane was effective after a repeated treatment (2.5-20mg/kgSC twice-a-day during 7 days) or in mice submitted to a restraint stress during 21 days and showing several behavioral and physiological parameters of depression (decreased body weight, increased adrenal glands weight and anhaedonia). Trilostane also reduced stress-induced increase in plasma corticosterone and ACTH levels, showing direct effect on HPA axis activity. These observations suggest that the 3beta-HSD inhibitor trilostane present antidepressant-like activity, putatively by regulating brain and peripheral levels of neuroactive steroids.
Abstract: Originally considered an enigmatic protein, the sigma-1 receptor has recently been identified as a unique ligand-regulated molecular chaperone in the endoplasmic reticulum of cells. This discovery causes us to look back at the many proposed roles of this receptor, even before its molecular function was identified, in many diseases such as methamphetamine or cocaine addiction, amnesia, pain, depression, Alzheimer's disease, stroke, retinal neuroprotection, HIV infection, and cancer. In this review, we examine the reports that have clearly shown an agonist-antagonist relationship regarding sigma-1 receptors in models of those diseases and also review the relatively known mechanisms of action of sigma-1 receptors in an attempt to spur the speculation of readers on how the sigma-1 receptor at the endoplasmic reticulum might relate to so many diseases. We found that the most prominent action of sigma-1 receptors in biological systems including cell lines, primary cultures, and animals is the regulation and modulation of voltage-regulated and ligand-gated ion channels, including Ca(2+)-, K(+)-, Na(+), Cl(-), and SK channels, and NMDA and IP3 receptors. We found that the final output of the action of sigma-1 receptor agonists is to inhibit all above-mentioned voltage-gated ion channels, while they potentiate ligand-gated channels. The inhibition or potentiation induced by agonists is blocked by sigma-1 receptor antagonists. Other mechanisms of action of sigma-1 receptors, and to some extent those of sigma-2 receptors, were also considered. We conclude that the sigma-1 and sigma-2 receptors represent potential fruitful targets for therapeutic developments in combating many human diseases.
Abstract: We examined the potential protective effect of BDNF against beta-amyloid-induced neurotoxicity in vitro and in vivo in rats. In neuronal cultures, BDNF had specific and dose-response protective effects on neuronal toxicity induced by Abeta(1-42) and Abeta(25-35). It completely reversed the toxic action induced by Abeta(1-42) and partially that induced by Abeta(25-35). These effects involved TrkB receptor activation since they were inhibited by K252a. Catalytic BDNF receptors (TrkB.FL) were localized in vitro in cortical neurons (mRNA and protein). In in vivo experiments, Abeta(25-35) was administered into the indusium griseum or the third ventricle and several parameters were measured 7 days later to evaluate potential Abeta(25-35)/BDNF interactions, i.e. local measurement of BDNF release, number of hippocampal hilar cells expressing SRIH mRNA and assessment of the corpus callosum damage (morphological examination, pyknotic nuclei counting and axon labeling with anti-MBP antibody). We conclude that BDNF possesses neuroprotective properties against toxic effects of Abeta peptides.
Abstract: We examined the sensitivity of AChE(+/-) mice to the amnesic effects of scopolamine and amyloid beta peptide. AChE(+/-) and AChE(+/+) littermates, tested at 5-9 weeks of age, failed to show any difference in locomotion, exploration and anxiety in the open-field test, or in-place learning in the water-maze. However, when treated with the muscarinic receptor antagonist scopolamine (0.5, 5mg/kg s.c.) 20 min before each water-maze training session, learning impairments were observed at both doses in AChE(+/+) mice, but only at the highest dose in AChE(+/-) mice. The central injection of Abeta(25-35) peptide (9 nmol) induced learning deficits only in AChE(+/+) but not in AChE(+/-) mice. Therefore, the hyper-activity of cholinergic systems in AChE(+/-) mice did not result in increased memory abilities, but prevented the deleterious effects of muscarinic blockade or amyloid toxicity.
Abstract: Prenatal infection is a major stressful experience leading to enhanced susceptibility for mental illnesses in humans. We recently reported in rats, that oxidative stress and glutathione (GSH) shortage occurred in fetal male brain after lipopolysaccharide (LPS) to the dams and that these responses might be involved in the neurodevelopmental deficits observed in adolescent offspring. Furthermore, pretreatment with N-acetylcysteine (NAC) before LPS avoided both delayed synaptic plasticity and mnesic performance deficits. Since NAC is one of the few medications permitted in pregnant women, this study evaluated the ability of NAC to serve as a protective therapy even after the LPS challenge. Pregnant rats received a single ip injection of E. coli LPS, two days before delivery, and were given NAC in their tap water after the LPS. GSH was evaluated at the time of its expected drop in the hippocampus of male fetuses, whereas long-term potentiation (LTP) in the CA1 area of the hippocampus and spatial memory in the water-maze were recorded in 28-day-old male offspring. Post-treatment with NAC, four hours after the LPS challenge fully prevented the drop in the GSH hippocampal content. LTP, as well as spatial learning were completely protected. NAC administration at delivery also partially restored the LTP whereas post-treatment two days later was inefficient. Another set of dams were supplemented with alpha-tocopherol prior to LPS exposure, enhancing the alpha-tocopherol levels in fetal hippocampus. This treatment did not prevent the LPS-induced synaptic plasticity impairment. These results point to fetal hippocampal GSH as a major target of the detrimental effects of in utero LPS challenge. The therapeutic window of NAC extends up to birth, suggesting that this drug might be clinically useful even after an immuno-inflammatory episode.
Abstract: Abstract The interest in understanding healthy aging has prompted scientist to look for animal models presenting this feature. Lou/C rats, an inbred strain of Wistar origin, is an animal model of successful aging with a longer lifespan and preserved memory capacities than most laboratory rat strains. In an attempt to shed light on this remarkable aging feature, we investigated the hippocampal patterns (mRNA and proteins) of some protective and plasticity-related molecules, i.e., brain-derived neurotrophic factor (BDNF), its precursor proBDNF, and its receptors (i.e., TrkB.FL, TrkB.T1, TrkB.T2, and p75). Using different experimental approaches, we compared these characteristics in young and aged Lou/C versus matched Wistar rats (the most appropriate controls). Data showed that young and aged Lou/C rats had higher amounts of BDNF and proBDNF content than Wistar rats. In contrast, proBDNF content was reduced in aged Lou/C rats and increased in aged Wistar rats. With aging, Lou/C rats showed a weaker decrease in TrkB.FL receptors than Wistar rats and no changes in TrkB.T1 receptors, which, contrarily, were increased in aged Wistar rats. Overall, these observations could account for the preserved cognitive performances and memory-dependent mechanisms, such as the unaltered long-term potentiation (LTP), throughout the lifespan recently reported in the Lou/C strain. Data suggest that boosting the expression or activity of these endogenous protective systems may be a promising alternative for combating some age-related cognitive declines. Therefore, Lou/C rats represent an interesting model of healthy aging for studying plasticity-related processes that evolve from youthfulness to aging.
Abstract: Chromatin remodeling by posttranslational modification of histones plays an important role in brain plasticity, including memory, response to stress and depression. The importance of H3/4 histones acetylation by CREB-binding protein (CBP) or related histone acetyltransferase, including p300, was specifically demonstrated using knockout (KO) mouse models. The physiological role of a related protein that also acts as a transcriptional coactivator with intrinsic histone acetylase activity, the p300/CBP-associated factor (PCAF), is poorly documented. We analyzed the behavioral phenotype of homozygous male and female PCAF KO mice and report a marked impact of PCAF deletion on memory processes and stress response. PCAF KO animals showed short-term memory deficits at 2 months of age, measured using spontaneous alternation, object recognition, or acquisition of a daily changing platform position in the water maze. Acquisition of a fixed platform location was delayed, but preserved, and no passive avoidance deficit was noted. No gender-related difference was observed. These deficits were associated with hippocampal alterations in pyramidal cell layer organization, basal levels of Fos immunoreactivity, and MAP kinase activation. PCAF KO mice also showed an exaggerated response to acute stress, forced swimming, and conditioned fear, associated with increased plasma corticosterone levels. Moreover, learning and memory impairments worsened at 6 and 12 months of age, when animals failed to acquire the fixed platform location in the water maze and showed passive avoidance deficits. These observations demonstrate that PCAF histone acetylase is involved lifelong in the chromatin remodeling necessary for memory formation and response to stress.
Abstract: Chronic alcohol consumption is associated with increased risk of gastrointestinal cancer. High concentrations of ethanol trigger mucosal hyperregeneration, disrupt cell adhesion, and increase the sensitivity to carcinogens. Most of these effects are thought to be mediated by acetaldehyde, a genotoxic metabolite produced from ethanol by alcohol dehydrogenases. Here, we studied the role of low ethanol concentrations, more likely to mimic those found in the intestine in vivo, and used intestinal cells lacking alcohol dehydrogenase to identify the acetaldehyde-independent biological effects of ethanol. Under these conditions, ethanol did not stimulate the proliferation of nonconfluent cells, but significantly increased maximal cell density. Incorporation of phosphatidylethanol, produced from ethanol by phospholipase D, was instrumental to this effect. Phosphatidylethanol accumulation induced claudin-1 endocytosis and disrupted the claudin-1/ZO-1 association. The resulting nuclear translocation of ZONAB was shown to mediate the cell density increase in ethanol-treated cells. In vivo, incorporation of phosphatidylethanol and nuclear translocation of ZONAB correlated with increased proliferation in the colonic epithelium of ethanol-fed mice and in adenomas of chronic alcoholics. Our results show that phosphatidylethanol accumulation after chronic ethanol exposure disrupts signals that normally restrict proliferation in highly confluent intestinal cells, thus facilitating abnormal intestinal cell proliferation.
Abstract: Cystinosis is a lysosomal storage disorder characterised by progressive cystine accumulation. The causative gene, CTNS, encodes cystinosin, the lysosomal cystine transporter. Neurological deterioration is one of the last symptoms to appear and the least well characterised. Visuospatial memory deficits have been documented in patients. To determine whether the cystinosis mouse model presents similar anomalies, we studied the learning and memory abilities of young and middle-aged Ctns(-/-) mice. We did not detect deficits in young Ctns(-/-) mice. In contrast, spatial reference and working memory deficits were detected in middle-aged Ctns(-/-) mice. Elevated cystine levels were detected in the hippocampus, cerebellum, forebrain and brainstem of all Ctns(-/-) mice, which increased with age and were consistent with the appearance of impairments. Our results strongly suggest that the cystinosis-associated CNS anomalies are due to progressive cystine accumulation. Furthermore, the Ctns(-/-) mice serve as a model to investigate the evolution of these anomalies and test the efficiency of existing and novel treatments to cross the blood-brain barrier and reduce lysosomal cystine levels.
Abstract: We showed that dextromethorphan (DM) provides neuroprotective/anticonvulsant effects and that DM and its major metabolite, dextrorphan, have a high-affinity for sigma(1) receptors, but a low affinity for sigma(2) receptors. In addition, we found that DM has a higher affinity than DX for sigma(1) sites, whereas DX has a higher affinity than DM for PCP sites. We extend our earlier findings by showing that DM attenuated trimethyltin (TMT)-induced neurotoxicity (convulsions, hippocampal degeneration and spatial memory impairment) in rats. This attenuation was reversed by the sigma(1) receptor antagonist BD 1047, but not by the sigma(2) receptor antagonist ifenprodil. DM attenuates TMT-induced reduction in the sigma(1) receptor-like immunoreactivity of the rat hippocampus, this attenuation was blocked by the treatment with BD 1047, but not by ifenprodil. These results suggest that DM prevents TMT-induced neurotoxicity, at least in part, via sigma(1) receptor stimulation.
Abstract: Growing evidence suggests a role for sigma(1) (sigma(1)) receptors in cognitive function, anxiety, depression, regulation of stress responses, and, recently, the appetitive effects of cocaine as measured by conditioned place preference. This study was designed to extend understanding of the role of sigma(1) receptors in addiction-relevant conditioned effects of cocaine by testing the effects of a potent and selective sigma(1) receptor antagonist, BD1047, on conditioned reinstatement of cocaine-seeking. To determine whether modification of conditioned reinstatement by BD1047 is selective for drug-directed behavior or reflects general suppressant effects on motivated behavior, BD1047 was tested also on reinstatement induced by stimuli conditioned to a natural reward, sweetened condensed milk (SCM). Additionally, because sigma(1) receptors have been implicated also in processes linked to the acute reinforcing actions of cocaine, tests of the effects of BD1047 on cocaine self-administration-including a comparison with the sigma(1) antagonist effects on SCM self-administration-were conducted as well. Cocaine self-administering male Wistar rats were trained to associate a discriminative stimulus (S(D)) with the availability of cocaine or SCM, and then subjected to reinstatement tests following extinction of cocaine or SCM-reinforced behavior. BD1047 (1-30 mg/kg) reversed response reinstatement induced by the cocaine S(D) at 20 and 30 mg/kg but did not modify SCM S(D)-induced responding at all but the highest 30 mg dose, at which responding was reversed to extinction levels. BD1047 did not modify responding reinforced directly by SCM or cocaine. The findings support a role for sigma(1) receptors in regulating conditioned responses to cocaine-related contextual stimuli and identify this receptor as a potential treatment target for the prevention of craving and relapse.
Abstract: Aging leads to alterations in the function of the hippocampus, a brain structure largely involved in learning processes. This study aimed at examining the basal levels and the impact of a learning-associated task on brain-derived neurotrophic factor (BDNF), on BDNF full-length catalytic receptor (TrkB.FL) and on the truncated forms (TrkB.T1 and TrkB.T2) receptor expression (mRNA and protein) in the hippocampus of young (2-month-old) and aged (24-month-old) Wistar rats. Spatial memory was evaluated using a water-maze procedure involving visible and invisible platform location learning. Aged rats showed higher latencies during the first two training days but rapidly exhibited learning performances similar to patterns observed with young rats. Real-time PCR measurements showed that aged rats had significantly higher levels of trkB.FL mRNAs than young rats under basal conditions. In situ hybridization analysis indicated that the highest level of trkB.FL mRNA (mRNA encoding for TrkB.FL receptor) was noted in the dentate gyrus, and in the CA2 and CA3 hippocampal layers. In contrast, there was no marked difference in trkB.T1 signal in any hippocampal region. Training induced a significant reduction in trkB.FL mRNA levels solely in aged rats. In contrast, in young and aged rats, trkB.T2 mRNA levels were significantly increased after training. Measurements of proteins revealed that learning significantly increased TrkB.FL content in aged rats. Untrained aged rats presented higher levels of BDNF and brain-derived neurotrophic factor precursor (proBDNF) proteins than young rats. Training strongly increased precursor BDNF metabolism in young and aged rats, resulting in increased levels of proBDNF in the two groups but in old rats the mature BDNF level did not change. This study shows that Wistar rats present age-related differences in the levels of BDNF and TrkB isoforms and that spatial learning differentially modifies some of these parameters in the hippocampus.
Abstract: Cystinosis is a lysosomal storage disorder characterized by abnormal accumulation of cystine, which forms crystals at high concentrations. The causative gene CTNS encodes cystinosin, the lysosomal cystine transporter. The eye is one of the first organs affected (corneal lesions and photophobia in the first and visual impairment in the second decade of life). We characterized the ocular anomalies of Ctns-/- mice to determine whether they mimic those of patients. The most dramatic cystine accumulation was seen in the iris, ciliary body, and cornea of Ctns-/- mice. Consistently, Ctns-/- mice had a low intraocular pressure (IOP) and seemed mildly photophobic. Retinal cystine levels were elevated but increased less dramatically with age. Consistently, the retina was intact and electroretinogram (ERG) profiles were normal in mice younger than 19 mo; beyond this age, retinal crystals and lesions appeared. Finally, the lens contained the lowest cystine levels and crystals were not seen. The temporospatial pattern of cystine accumulation in Ctns-/- mice parallels that of patients and validates the mice as a model for the ocular anomalies of cystinosis. This work is a prerequisite step to the testing of novel ocular cystine-depleting therapies.
Abstract: Depression is characterized by hypothalamo-pituitary-adrenocortical (HPA) axis hyperactivity. In this major mood disorder, neurosteroids and neurotrophins, particularly brain-derived neurotrophic factor (BDNF), seem to be implicated and have some antidepressant effects. BDNF is highly involved in regulation of the HPA axis, whereas neurosteroids effects have never been clearly established. In this systematic in vivo study, we showed that the principal neuroactive steroids, namely dehydroepiandrosterone (DHEA), pregnenolone (PREG) and their sulfate esters (DHEA-S and PREG-S), along with allopregnanolone (ALLO), stimulated HPA axis activity, while also modulating central BDNF contents. In detail, DHEA, DHEA-S, PREG, PREG-S and ALLO induced corticotropin-releasing hormone (CRH) and/or arginine vasopressin (AVP) synthesis and release at the hypothalamic level, thus enhancing plasma adrenocorticotropin hormone (ACTH) and corticosterone (CORT) concentrations. This stimulation of the HPA axis occurred concomitantly with BDNF modifications at the hippocampus, amygdala and hypothalamus levels. We showed that these neurosteroids induced rapid effects, probably via neurotransmitter receptors and delayed effects perhaps after metabolization in other neuroactive steroids. We highlighted that they had peripheral effects directly at the adrenal level by inducing CORT release, certainly after estrogenic metabolization. In addition, we showed that, at the dose used, only DHEA, DHEA-S and PREG-S had antidepressant effects. In conclusion, these results highly suggest that part of the HPA axis and antidepressant effects of neuroactive steroids could be mediated by BDNF, particularly at the amygdala level. They also suggest that neurosteroids effects on central BDNF could partially explain the trophic properties of these molecules.
Abstract: BACKGROUND AND PURPOSE: Tetrahydro-N, N-dimethyl-5, 5-diphenyl-3-furanmethanamine hydrochloride (ANAVEX1-41) is a potent muscarinic and sigma(1) (sigma (1)) receptor ligand. The sigma (1) receptor modulates glutamatergic and cholinergic responses in the forebrain and selective agonists are potent anti-amnesic and antidepressant DRUGS. WE HAVE HERE ANALYSED THE SIGMA (1) COMPONENT IN THE BEHAVIOURAL EFFECTS OF ANAVEX1-41. EXPERIMENTAL APPROACH: Binding of ANAVEX1-41 to muscarinic and sigma (1) receptors were measured using cell membranes. Behavioural effects of ANAVEX1-41 were tested in mice using memory (spontaneous alternation, passive avoidance, water-maze) and antidepressant-like activity (forced swimming) procedures. KEY RESULTS: In vitro, ANAVEX1-41 was a potent muscarinic (M(1)>M(3), M(4)>M(2) with K(i) ranging from 18 to 114 nM) and selective sigma (1) ligand (sigma (1), K(i)=44 nM; sigma (2), K(i)=4 microM). In mice, ANAVEX1-41 failed to affect learning when injected alone (0.03-1 mg kg(-1)), but attenuated scopolamine-induced amnesia with a bell-shaped dose response (maximum at 0.1 mg kg(-1)). The sigma (1) antagonist BD1047 blocked the anti-amnesic effect of ANAVEX1-41 on both short- and long-term memories. Pretreatment with a sigma (1) receptor-directed antisense oligodeoxynucleotide prevented effects of ANAVEX1-41 only in the passive avoidance procedure, measuring long-term memory. ANAVEX1-41 reduced behavioural despair at 30 and 60 mg kg(-1), without involving the sigma (1) receptor, as it was not blocked by BD1047 or the antisense oligodeoxynucleotide. CONCLUSIONS AND IMPLICATIONS: ANAVEX1-41 is a potent anti-amnesic drug, acting through muscarinic and sigma (1) receptors. The latter component may be involved in the enhancing effects of the drug on long-term memory processes.
Abstract: Prenatal infection is a major risk responsible for the occurrence of psychiatric conditions in infants. Mimicking maternal infection by exposing pregnant rodents to bacterial endotoxin lipopolysaccharide (LPS) also leads to major brain disorders in the offspring. The mechanisms of LPS action remain, however, unknown. Here, we show that LPS injection during pregnancy in rats, 2 days before delivery, triggered an oxidative stress in the hippocampus of male fetuses, evidenced by a rapid rise in protein carbonylation and by decreases in alpha-tocopherol levels and in the ratio of reduced/oxidized forms of glutathione (GSH/GSSG). Neither protein carbonylation increase nor decreases in alpha-tocopherol levels and GSH/GSSG ratio were observed in female fetuses. NMDA synaptic currents and long-term potentiation in CA1, as well as spatial recognition in the water maze, were also impaired in male but not in female 28-day-old offspring. Pretreatment with the antioxidant N-acetylcysteine prevented the LPS-induced changes in the biochemical markers of oxidative stress in male fetuses, and the delayed detrimental effects in male 28-day-old offspring, completely restoring both long-term potentiation in the hippocampus and spatial recognition performance. Oxidative stress in the hippocampus of male fetuses may thus participate in the neurodevelopmental damage induced by a prenatal LPS challenge.
Abstract: Chronic alcohol consumption (CAC) provokes intense neurobiological alterations, which lead, notably, to an important abstinence syndrome upon withdrawal with deleterious cognitive consequences. We here examined the effect of activation or inactivation of the sigma(1) receptor during CAC withdrawal on the cognitive abilities of Swiss mice. Animals consumed an alcohol 10%/sucrose 30 g/l solution during 4 months. Control groups consumed only the sucrose vehicle solution. Then, animals experienced a progressive, 16 days long, CAC withdrawal, during which they were administered once daily with saline, igmesine (10 mg/kg i.p.), a sigma(1) receptor agonist, or BD1047 (10 mg/kg i.p.), a sigma(1) antagonist. Mice were then tested using an object exploration task, to evaluate their locomotor and exploratory activities and reactions to object habituation, spatial change or novel object presentation. CAC-treated animals showed augmentation of locomotion, anxiety and object exploration, which impeded correct reaction to object habituation, spatial change or novelty. Treatment with the sigma(1) ligands, ineffective in control groups, resulted in decrease of the hyper-responsiveness and restored habituation. However, correct reactions to spatial change and novelty were only produced by the sigma(1) agonist treatment. Moreover, the sigma(1) receptor hippocampal expression was increased in CAC-treated mice. Treatments with both sigma(1) ligands regulated its expression, but subcellular fractionation experiments revealed that the agonist treatment increased [(3)H](+)-pentazocine binding to sigma(1) sites in the plasma membrane fraction, while the antagonist maintained it only in the microsomal, putatively endoplasmic reticulum, fraction. In conclusion, CAC increased the sigma(1) receptor expression in the hippocampus of mice. Regulation of its expression during withdrawal, notably using a selective agonist, allowed not only to attenuate the CAC-induced hyper-responsiveness, but also to restore correct cognitive abilities.
Abstract: Naturally occurring polyphenols are potent antioxidants. Some of these compounds are also ligands for the GABA(A) receptor benzodiazepine site. This feature endows them with sedative properties. Here, the anxiolytic activity of the green tea polyphenol (-)-epigallocatechin gallate (EGCG) was investigated after acute administration in mice, using behavioral tests (elevated plus-maze and passive avoidance tests) and by electrophysiology on cultured hippocampal neurons. Patch-clamp experiments revealed that EGCG (1-10 muM) had no effect on GABA currents. However, EGCG reversed GABA(A) receptor negative modulator methyl beta-carboline-3-carboxylate (beta-CCM) inhibition on GABA currents in a concentration dependent manner. This was also observed at the level of synaptic GABA(A) receptors by recording spontaneous inhibitory synaptic transmission. In addition, EGCG consistently inhibited spontaneous excitatory synaptic transmission. Behavioral tests indicated that EGCG exerted both anxiolytic and amnesic effects just like the benzodiazepine drug, chlordiazepoxide. Indeed, EGCG in a dose-dependent manner both increased the time spent in open arms of the plus-maze and decreased the step-down latency in the passive avoidance test. GABA(A) negative modulator beta-CCM antagonized EGCG-induced amnesia. Finally, state-dependent learning was observable after chlordiazepoxide and EGCG administration using a modified passive avoidance procedure. Optimal retention was observed only when animals were trained and tested in the same state (veh-veh or drug-drug) and significant retrieval alteration was observed in different states (veh-drug or drug-veh). Moreover, EGCG and chlordiazepoxide fully generalized in substitution studies, indicating that they induced indistinguishable chemical states for the brain. Therefore, our data support that EGCG can induce anxiolytic activity which could result from an interaction with GABA(A) receptors.
Abstract: Steroids from peripheral sources or synthesized in the brain, i.e. neurosteroids, exert rapid modulations of neurotransmitter responses through specific interactions with membrane receptors, mainly the gamma-aminobutyric acid type A (GABA(A)) receptor and N-methyl-d-aspartate (NMDA) type of glutamate receptor. Progesterone and 3alpha-hydroxy-5alpha-pregnan-20-one (allopregnanolone) act as inhibitory steroids while pregnenolone sulfate or dehydroepiandrosterone sulfate act as excitatory steroids. Some steroids also interact with an atypical protein, the sigma(1) (sigma(1)) receptor. This receptor has been cloned in several species and is centrally expressed in neurons and oligodendrocytes. Activation of the sigma(1) receptor modulates cellular Ca(2+) mobilization, particularly from endoplasmic reticulum pools, and contributes to the formation of lipid droplets, translocating towards the plasma membrane and contributing to the recomposition of lipid microdomains. The present review details the evidences showing that the sigma(1) receptor is a target for neurosteroids in physiological conditions. Analysis of the sigma(1) protein sequence confirmed homologies with the ERG2/emopamil binding protein family but also with the steroidogenic enzymes isopentenyl diphosphate isomerase and 17beta-estradiol dehydrogenase. Biochemical and physiological arguments for an interaction of neuro(active)steroids with the sigma(1) receptor are analyzed and the impact on physiopathological outcomes in neuroprotection is illustrated.
Abstract: BACKGROUND AND PURPOSE: The acetylcholinesterase inhibitor, donepezil, is also a high affinity sigma(1) receptor agonist. We examined the involvement of sigma(1) receptors in its anti-amnesic and neuroprotective properties against amyloid beta(25-35) peptide-induced toxicity in mice. EXPERIMENTAL APPROACH: Mice were given an intracerebroventricular (i.c.v.) injection of Abeta(25-35) peptide (9 nmol) 7-9 days before being tested for spontaneous alternation and passive avoidance. Hippocampal lipid peroxidation was measured 7 days after Abeta(25-35) injection to evaluate oxidative stress. Donepezil, the sigma(1) agonist PRE-084 or the cholinesterase (ChE) inhibitors tacrine, rivastigmine and galantamine were administered either 20 min before behavioural sessions to check their anti-amnesic effects, or 20 min before Abeta(25-35) injection, or 24 h after Abeta(25-35) injection and then once daily before behavioural sessions, to check their pre- and post-i.c.v. neuroprotective activity, respectively. KEY RESULTS: All the drugs tested were anti-amnesic, but only the effects of PRE-084 and donepezil were prevented by the sigma(1) antagonist BD1047. Only PRE-084 and donepezil showed neuroprotection when administered pre i.c.v.; they blocked lipid peroxidation and learning deficits, effects inhibited by BD1047. Post i.c.v., PRE-084 and donepezil showed complete neuroprotection whereas the other ChE inhibitors showed partial effects. BD1047 blocked these effects of PRE-084, attenuated those of donepezil, but did not affect the partial effects of the other ChE inhibitors. CONCLUSIONS AND IMPLICATIONS: The potent anti-amnesic and neuroprotective effects of donepezil against Abeta(25-35)-induced toxicity involve both its cholinergic and sigma(1) agonistic properties. This dual action may explain its sustained activity compared to other ChE inhibitors.
Abstract: The role of nitric oxide (NO) and lipid peroxidation (LPO) processes in the physiological deficits induced by in utero cocaine exposure was examined in rats. NO generation in the hippocampus and cortex was detected using the electron paramagnetic resonance and LPO products were measured as thiobarbituric acid reactive species (TBARS). Pregnant Sprague-Dawley rats received a daily intraperitoneal injection of 20 mg/kg cocaine (IUC) or saline solution for control dams (IUV) between E17-E20. NO level was lower in the brain of IUC rats at postnatal day 1 and 2, but not 4, as compared with IUV rats. TBARS content was increased at day 1-4. Animals were used for behavioral testing at 25 days of age. Both NO and TBARS were elevated in the hippocampus of IUC rats as compared with IUV rats. Juvenile IUC rats developed significant learning impairments in the water-maze, as revealed by probe test retrieval deficits. Behavioral sessions resulted in a significant increase of TBARS levels only in IUV animals. Therefore, IUC rats showed a significant oxidative stress in basal conditions that may be related to their impaired learning ability. We did not find direct correlation between the changes in NO generation and intensity of LPO processes. It may probably mean that changes in intensity of LPO processes observed during prenatal cocaine exposure are not directly linked to NO pathway activation.
Abstract: Donepezil is a potent acetylcholinesterase inhibitor that also interacts with the sigma1 receptor, an intracellular neuromodulatory protein. In the present study, we analyzed the antiamnesic and neuroprotective activities of donepezil in a mouse hypoxia model induced by repetitive CO exposure, comparing donepezil's pharmacological profile with other cholinesterase inhibitors tacrine, rivastigmine, and galanthamine, and the reference sigma1 agonist igmesine. CO exposure induced, after 7 days, hippocampal neurodegeneration, analyzed by Cresyl violet staining, and behavioral alterations, measured using spontaneous alternation and passive avoidance responses. When injected 20 min before the behavioral tests, i.e., 7 to 8 days after CO, all drugs showed antiamnesic properties. Preadministration of the sigma1 receptor antagonist N-[2-(3,4-dichlorophenyl)ethyl]-N-methyl-2-(dimethylamino)ethylamine (BD1047) blocked only the igmesine and donepezil effects. The neuroprotective activity of the drugs was tested by injection 20 min before the first CO exposure (preinsult protection) or by injection 1 h after the last CO exposure (postinsult protection). All drugs alleviated the hypoxia-induced neurodegeneration and behavioral impairments when injected before CO exposure. Preadministration of BD1047 blocked both the igmesine and donepezil effects. However, when injected after CO exposure, only igmesine and donepezil induced effective neuroprotection, and the morphological and behavioral effects were BD1047-sensitive. These results showed that donepezil is a potent antiamnesic and neuroprotective compound against the neurodegeneration induced by excitotoxic insult, and its pharmacological actions as both an acetylcholinesterase inhibitor and sigma1 receptor agonist contribute to its marked efficacy. In particular, the drug is a more potent postinsult protecting agent compared with more selective cholinesterase inhibitors.
Abstract: Steroids synthesized in the periphery or de novo in the brain, so called 'neurosteroids', exert both genomic and nongenomic actions on neurotransmission systems. Through rapid modulatory effects on neurotransmitter receptors, they influence inhibitory and excitatory neurotransmission. In particular, progesterone derivatives like 3alpha-hydroxy-5alpha-pregnan-20-one (allopregnanolone) are positive allosteric modulators of the gamma-aminobutyric acid type A (GABA(A)) receptor and therefore act as inhibitory steroids, while pregnenolone sulphate (PREGS) and dehydroepiandrosterone sulphate (DHEAS) are negative modulators of the GABA(A) receptor and positive modulators of the N-methyl-D-aspartate (NMDA) receptor, therefore acting as excitatory neurosteroids. Some steroids also interact with atypical proteins, the sigma (sigma) receptors. Recent studies particularly demonstrated that the sigma1 receptor contributes effectively to their pharmacological actions. The present article will review the data demonstrating that the sigma1 receptor binds neurosteroids in physiological conditions. The physiological relevance of this interaction will be analyzed and the impact on physiopathological outcomes in memory and drug addiction will be illustrated. We will particularly highlight, first, the importance of the sigma1-receptor activation by PREGS and DHEAS which may contribute to their modulatory effect on calcium homeostasis and, second, the importance of the steroid tonus in the pharmacological development of selective sigma1 drugs.
Abstract: The present series of experiments examined the involvement of the sigma(1) receptor and related neuroactive steroids in the memory state induced by a very low dose of cocaine. Using a modified passive avoidance procedure in mice, we examined whether cocaine induces state-dependent (StD) learning. Animals trained and tested with saline or the same dose of cocaine (0.1 or 0.3 mg/kg) showed correct retention, measured using two independent parameters: the retention latency and a ratio between the retention latency and the last training latency. Animals trained with cocaine (0.1 mg/kg) and tested with saline or cocaine (0.03, 0.3 mg/kg), or trained with saline and tested with cocaine, showed altered retention parameters, demonstrating that StD occurred. Therefore, cocaine administered before training produced a chemical state used as an endogenous cue to insure optimal retention. Since sigma(1) receptor activation is an important event during the acquisition of cocaine reward, we tested several sigma(1) ligands and related neurosteroids. The sigma(1) agonist igmesine or antagonist BD1047 failed to produce StD, but modified the cocaine state. Among neuroactive steroids, pregnanolone and allopregnanolone, positive modulators of the gamma-aminobutyric acid type A (GABA(A)) receptor, produced StD. However, steroids also acting as sigma(1) agonists, dehydroepiandrosterone (3beta-hydroxy-5alpha-androsten-17-one (DHEA)), pregnenolone, or antagonist, progesterone, failed to induce StD but modified the cocaine state. Furthermore, optimal retention was observed with mice trained with (igmesine or DHEA)+cocaine and tested with a higher dose of cocaine, or with mice trained with (BD1047 or progesterone)+cocaine and tested with vehicle. This study demonstrated that: (i) low doses of cocaine induce a chemical state/memory trace sustaining StD; (ii) modulation of the sigma(1) receptor activation, although insufficient to provoke StD, modulates the cocaine state; (iii) neuroactive steroids exert a unique role in state-dependent vs state-independent learning, via GABA(A) or sigma(1) receptor modulation, and are able to affect the cocaine-induced mnesic trace at low brain concentrations.
Abstract: In the present study, we examined the interaction of (+/-)-2,3-dihydro-5,6-dimethoxy-2-[[1-(phenylmethyl)-4-piperidinyl]-methyl]-1H-inden-1-one hydrochloride (donepezil), a potent cholinesterase inhibitor, with two additional therapeutically relevant targets, N-methyl-d-aspartate (NMDA) and sigma(1) receptors. Donepezil blocked the responses of recombinant NMDA receptors expressed in Xenopus oocytes. The blockade was voltage-dependent, suggesting a channel blocker mechanism of action, and was not competitive at either the l-glutamate or glycine binding sites. The low potency of donepezil (IC(50) = 0.7-3 mM) suggests that NMDA receptor blockade does not contribute to the therapeutic actions of donepezil. Of potential therapeutic relevance, donepezil binds to the sigma(1) receptor with high affinity (K(i) = 14.6 nM) in an in vitro preparation (Neurosci Lett 260:5-8, 1999). Thus, we sought to determine whether an interaction with the sigma(1) receptor may occur in vivo under physiologically relevant conditions by evaluating the sigma(1) receptor dependence effects of donepezil in behavioral tasks. Donepezil showed antidepressant-like activity in the mouse-forced swimming test as did the sigma(1) receptor agonist igmesine. This effect was not displayed by the other cholinesterase inhibitors, rivastigmine and tacrine. The donepezil and igmesine effects were blocked by preadministration of the sigma(1) receptor antagonist N-[2-(3,4-dichlorophenyl)ethyl]-N-methyl-2-(dimethylamino) ethylamine (BD1047) and an in vivo antisense probe treatment. The memory-enhancing effect of donepezil was also investigated. All cholinesterase inhibitors attenuated dizocilpine-induced learning impairments. However, only the donepezil and igmesine effects were blocked by BD1047 or the antisense treatment. Therefore, donepezil behaved as an effective sigma(1) receptor agonist on these behavioral responses, and an interaction of the drug with the sigma(1) receptor must be considered in its pharmacological actions.
Abstract: We examined whether significant oxidative stress is induced in the brain of juvenile rats exposed in utero to cocaine, and contributes to their mnesic difficulties. We measured nitric oxide generation, using electron paramagnetic resonance, and the thiobarbituric acid reactive species as specific indexes of lipid peroxidation. Both nitric oxide and lipid peroxidation were elevated in the hippocampus of in-utero cocaine-exposed rats as compared with control animals. In-utero cocaine-exposed rats developed significant learning impairments in the water-maze, shown by probe test retrieval deficits. In parallel, behavioural sessions resulted in increases of thiobarbituric acid reactive species levels only in control animals. Therefore, in-utero cocaine exposure resulted in a significant oxidative stress in basal conditions, which may be related to impaired learning ability.
Abstract: The sigma1 receptor is a unique intracellular receptor whose activation results in an efficient modulation of several neurotransmitter responses. Its role as a target for the rapid nongenomic effects of neuro(active)steroids and the age-related diminutions in steroid levels suggested that targeting the sigma1 receptor might allow alleviation of age-related neuronal dysfunctions. We examined here the expression and behavioral efficacy of sigma1 receptors in the senescence-accelerated (SAM) mouse model. The sigma1 receptor mRNA expression was measured by using comparative RT-PCR in the olfactory bulb, hippocampus, hypothalamus, cortex, or cerebellum of senescence-prone SAMP/8 and senescence-resistant SAMR/1 control animals. No difference was observed between substrains in 6-, 9-, and 12-month-old (m.o.) mice. The sigma1 protein expression was analyzed by using immunohistochemical techniques. Labeling was intense in the olfactory bulb, hippocampus, hypothalamus, and midbrain of both SAMR/1 and SAMP/8 mice, and the distribution appeared unchanged in 6-, 9-, and 12-m.o. animals. The receptor's in vivo availability was examined by using in vivo [3H](+)-SKF-10,047 binding. No age-related difference was observed in the olfactory bulb, hippocampus, hypothalamus, cortex, cerebellum, and brainstem of 6- or 12-m.o. SAMR/1 or SAMP/8 mice. The antidepressant efficacy of the selective agonist igmesine was examined in the forced-swimming test. The compound decreased significantly the immobility duration at 60 mg/kg in 6- and 12-m.o. SAMR/1 and in 6-m.o. SAMP/8 mice. In 12-m.o. SAMP/8 mice, the drug efficacy was facilitated; a significant effect was measured at 30 mg/kg. Decreased neurosteroid levels, particularly of progesterone, were seen in 12-m.o. SAMP/8 mice that might explain the enhanced efficacy of igmesine. Preserved sigma1 receptor expression and enhanced behavioral efficacy of sigma1 agonists were measured in SAM animals, confirming the therapeutic opportunities for selective ligands against age-related mood disorders.
Abstract: Cocaine induces in the brain a drastic plasticity affecting numerous neurotransmission systems. In turn, the drug provokes a complex pattern of behavioral responses, including locomotor hyperactivity, stereotyped behaviors, sensitization, and appetitive and reinforcing properties that rapidly generate the addictive process. The involvement of sigma (1) receptors in cocaine effects has been suggested initially through the observation that sigma (1) antagonists could attenuate several acute effects induced by the drug, such as hyperlocomotion, stereotypies, convulsions and lethality. We will describe thereafter the recent results showing that activation of the sigma (1) receptor is also involved in the appetitive properties of cocaine, as measured using place preference conditioning in mice. Using selective sigma (1) antagonists or an in vivo antisense strategy, the role of the sigma (1) receptor in acquisition, expression and reactivation of conditioned place preference was demonstrated. The observation that repeated administration of cocaine rapidly provokes overexpression of the sigma (1) receptor outlines its major role in these first psychological steps of addictive processes. The physiological interaction between cocaine and sigma (1) receptors is detailed and the possibility that effective therapeutical strategies could target the sigma (1) receptor is considered.
Abstract: In utero cocaine (IUC) exposure results in offspring rats in complex neurochemical and behavioral alterations, particularly affecting learning and memory processes. We examined here the impact of IUC exposure on memory functions in male and female offspring rats and report that selective sigma(1) (sigma(1)) receptor agonists are effective in reversing the deficits. Dams received a daily cocaine, 20 mg/kg ip, injection between gestational days E17 to E20. Learning was examined in offspring between day P30 and P41 using delayed alternation in the T-maze, water-maze learning and passive avoidance. Both male and female rats prenatally exposed to cocaine showed delayed alternation deficits and impairments of acquisition of a fixed platform position in the water maze, as shown by higher acquisition latencies and diminutions of time spent in the training quadrant during the probe test. The acquisition of a daily changing platform position also demonstrated impaired working memory. Finally, passive avoidance deficits were observed. Pretreatment with the synthetic sigma(1) agonist igmesine (0.1-1 mg/kg ip) or the neuroactive steroid dehydroepiandrosterone (DHEA 10-40 mg/kg ip) reversed the prenatal cocaine-induced learning deficits in offspring rats for each test. The sigma(1) antagonist BD1063 (1 mg/kg ip) failed to affect performances alone but blocked the igmesine and DHEA effects, confirming the involvement of the sigma(1) receptor. IUC exposure thus results in marked memory deficits, affecting spatial and nonspatial short- and long-term memories in juvenile male and female offspring rats. The activation of the sigma(1) neuromodulatory receptor allows a complete behavioral recovery of the memory functions in prenatally cocaine-exposed rats.
Abstract: The sigma(1) receptor is a 223 amino acid protein sharing no homology with other mammalian protein. It is an intracellular protein present on the endoplasmic reticulum membrane, which can translocates to other organelles and plasma membranes after activation. Activation of the sigma(1) receptor results in modulation of calcium mobilization from inositol trisphosphate receptor-gated intracellular pools and, at the plasma membrane, in modulation of several neurotransmitter responses. Behaviorally, sigma(1) receptors are involved in learning and memory, response to stress and depression, psychostimulant-induced sensitization, vulnerability to addiction and pain perception. Numerous synthetic compounds bind to sigma(1) receptor, playing the role of activator/agonist or blocker/antagonist, and these include benzomorphans, neuroleptics, antidepressants, cocaine, peptides related to neuropeptide Y or calcitonin gene-related peptide. It is also the case of neuro(active)steroids, i. e., circulating neuroactive steroids and neurosteroids synthesized de novo by the brain, which appear as the most important endogenous modulators of sigma(1) receptor. Pregnenolone and dehydroepiandrosterone act as sigma(1) receptor agonists and progesterone is a potent antagonist. The present paper will review the molecular and biochemical features concerning the sigma(1) receptor and focus on the recent studies examining the impact of the neuro(active)steroid/sigma(1) receptor interaction on the antidepressant activity of sigma(1) receptor agonists in the context of neurodegenerative diseases.
Abstract: 1. Stress during pregnancy results in complex neurochemical and behavioral alterations throughout the offspring lifetime. We here examined the impact of prenatal stress (PS) on memory functions in male and female offspring and report the efficacy of a selective sigma(1) (sigma(1)) receptor agonist, igmesine, in alleviating the observed deficits. 2. Dams received an unpredictable 90-min duration restraint stress from gestational day E17 to E20. Learning was examined in offspring between day P24 and P36 using spontaneous alternation in the Y-maze, delayed alternation in the T-maze, water-maze learning and passive avoidance. 3. Both male and female PS rats showed impairments of spontaneous and delayed alternation performances. Acquisition of a fixed platform position in the water-maze was unchanged in PS rats, but the probe test revealed a diminution of time spent in the training quadrant. Acquisition of a daily changing platform position demonstrated impaired working memory for male and female PS rats. Finally, passive avoidance deficits were observed. 4. Pretreatment with the selective sigma(1) agonist igmesine (1-10 mg x kg(-1) i.p.) reversed the PS-induced learning deficits in offspring rats for each test. The sigma(1) antagonist BD1063 failed to affect performances alone but blocked the igmesine effect, confirming the involvement of the sigma(1) receptor. 5. PS thus induces delayed memory deficits, affecting spatial and nonspatial, short- and long-term memories in juvenile male and female offspring rats. Activation of the sigma(1) neuromodulatory receptor allows a significant recovery of the memory functions in PS rats.
Abstract: Pharmacological effects of amantadine on dopaminergic transmission are proposed to result from an uncompetitive antagonism at glutamate N-methyl-D-aspartate (NMDA) receptors. However, our previous studies examining amantadine-mediated dopamine receptor regulation in the rat striatum revealed a discrepancy from a direct interference with glutamate transmission. Preliminary in vitro binding data from the literature suggested the interaction of amantadine with the sigma1 receptor. Therefore, we have now further characterized the pharmacological properties of amantadine and memantine at this receptor and investigated its involvement in the modulation of striatal dopaminergic transmission. Our binding studies using [3H]-(+)SKF-10,047 indicated that amantadine and memantine behave as ligands of the sigma(1) receptor in rat forebrain homogenates (Ki values of 7.44 +/- 0.82 and 2.60 +/- 0.62 microm, respectively). In NG108-15 neuroblastoma cells, both drugs (amantadine (100 microm) and memantine (10 microm)) potentiated the bradykinin-induced mobilization of intracellular Ca2+, mimicking the effect of the sigma1 receptor agonist PRE-084 (1 microm). Finally, we previously showed that in striatal membranes from amantadine-treated rats, the functional coupling of dopamine receptors with G-proteins was enhanced. Similarly, PRE-084 dose-dependently increased the [35S]GTPgammaS binding induced by dopamine (Emax 28 and 26% of basal, 0.3 and 1 mg/kg PRE-084, respectively). By contrast, BD1047, which is without effect on its own, antagonized the effects of amantadine and PRE-084. Together, these data demonstrate that aminoadamantanes behave as sigma1 receptor agonists, and confirm an involvement of this receptor in modulating dopamine receptors exerted by therapeutically relevant concentrations of amantadine.
Abstract: RATIONALE: Cocaine-seeking behavior can be investigated in rodents using the conditioned place preference (CPP) paradigm, in which the drug-paired environment serves as a conditioned stimulus. Such approach allowed to previously demonstrate the importance of the neuromodulatory sigma1 (sigma1) receptor in acquisition of cocaine-induced CPP. CPP can be extinguished and then reactivated, notably using a cocaine challenge (i.e., priming). OBJECTIVES AND METHODS: In order to examine the role of the sigma1 receptor in reinstatement of Cocaine-seeking, Swiss mice acquired CPP with cocaine (30 mg/kg, i.p.) and then CPP was extinguished. RESULTS. A challenge cocaine priming (15 mg/kg) reactivated CPP up to 140% of the post-conditioning response. Pre-administration of the sigma1 receptor antagonist BD1047 (330 mg/kg, i.p.) or repeated treatment with an antisense probe targeting the sigma1 receptor prevented CPP reactivation. The sigma1 agonist igmesine (1-10 mg/kg, i.p.) or the steroid dehydroepiandrosterone (DHEA, 10-40 mg/kg, s.c.) reactivated CPP, in a BD1047-sensitive manner. Moreover, the in vivo [3H](+)-SKF-10,047 binding levels to the sigma1 receptor were increased after cocaine conditioning in numerous brain structures and these increases subsisted after extinction. Finally, cross-reactivation of cocaine-induced CPP was observed after phencyclidine (PCP), morphine, nicotine and ethanol administration. However, BD1047 blocked reactivation of CPP induced by PCP, morphine and nicotine but not ethanol. CONCLUSIONS: Since activation of the sigma1 receptor is not sufficient to sustain CPP in naive animals [Neuropsychopharmacology 26 (2002) 444], it is concluded that sigma1 receptor activation is a key event for relapse to drug seeking. Activation may occur via sensitization due to enhanced in vivo available of receptors.
Abstract: Stress during pregnancy results in neurochemical and behavioral alterations observed throughout adulthood and aging. We here examined the impact of prenatal stress (PS) on cognitive functions in juvenile-4-week-old-rats, focusing on putative sex differences. Dams received an unpredictable 90-min duration contention stress between gestational day E17 and E20. Locomotion and learning ability were examined in offsprings between day P24 and P29 using actimetry, spontaneous alternation in the Y-maze, delayed alternation in the T-maze, and passive avoidance. Both male and female PS rats showed increased activity. In the Y-maze, diminished spontaneous alternation (males: -20%; females: -29%) were seen for PS rats compared to non-PS rats. The number of arm entries was unchanged among groups. In the T-maze, PS rats failed to perform delayed alternation, as shown by equal time spent and number of entries in both the novel and previously explored arms. In the passive avoidance test, PS resulted in significant impairments for female offspring only of both step-through latency and percentage of animals to criterion. PS thus induced severe learning impairments affecting both short-term and long-term memories that could be observed early in lifetime, in 4-week-old, juvenile rats. In addition, marked sex differences were evidenced, particularly in the passive avoidance response that may reflect differential developmental neuroadaptations in precise brain structures.
Abstract: Treatment of depressive symptoms in patients suffering from neurodegenerative disorders remains a challenging issue, since few available antidepressants present an adequate efficacy during pathological aging. Previous reports suggested that selective sigma(1) receptor agonists might constitute putative candidates. We here examined the pharmacological efficacy of igmesine and (+)-SKF-10,047 and the sigma(1) receptor-related neuroactive steroid dehydroepiandrosterone sulfate, in rats infused intracerebroventricularly during 14 days with the beta-amyloid-(1-40) protein and then submitted to the conditioned fear stress test. Igmesine and (+)-SKF-10,047 significantly reduced the stress-induced motor suppression at 30 and 6 mg/kg, respectively, in beta-amyloid-(40-1)-treated control rats. Active doses were decreased, to 10 and 3 mg/kg, respectively, in beta-amyloid-(1-40)-treated animals. The dehydroepiandrosterone sulfate effect was also facilitated, both in dose (10 vs. 30 mg/kg) and intensity, in beta-amyloid-(1-40)-treated rats. Neurosteroid levels were measured in several brain structures after beta-amyloid infusion, in basal and stress conditions. Progesterone levels, both under basal and stress-induced conditions, were decreased in the hippocampus and cortex of beta-amyloid-(1-40)-treated rats. The levels in pregnenolone, dehydroepiandrosterone and their sulfate esters appeared less affected by the beta-amyloid infusion. The sigma(1) receptor agonist efficacy is known to be inversely correlated to brain progesterone levels, synthesized mainly by neurons that are mainly affected by the beta-amyloid toxicity. The present study suggests that sigma(1) receptor agonists, due to their enhanced efficacy in a nontransgenic animal model, may alleviate Alzheimer's disease-associated depressive symptoms.
Abstract: The sigma(1) (sigma(1)) receptor represents a unique intracellular neuronal protein modulating several neurotransmitter responses with relevant effects on cognitive functions. We examined here its expression and behavioral efficacy during aging. The sigma(1) receptor expression was examined in young (2 months old) and aged (24 months old) C57BL/6 mouse brain using comparative RT-PCR and immunohistochemistry. The promnesic effect of PRE-084, a selective sigma(1) agonist, was assessed using a water-maze procedure. The sigma(1) mRNA expression was not affected during aging in the olfactory bulb, hippocampus, hypothalamus, cortex or cerebellum. The sigma(1) immunolabeling was intense in the olfactory bulb, hippocampus, hypothalamus and midbrain of the young mouse and the distribution appeared unchanged in the aged. The subcellular localization was similar in aged and younger animals, the protein being present on nuclear, mitochondrial, endoplasmic reticular and plasmic membranes. At the behavioral level, aged C57BL/6 mice showed deficits in the invisible platform learning, but not when the platform was visible. Animals subjected to a transfer test under repeated treatment with saline or PRE-084 significantly learned the new platform location. This study shows that sigma(1) receptor expression is preserved in aged animals and demonstrates the efficacy of a selective sigma(1) agonist against age-related memory deficits. Targeting this unique receptor may offer an original drug strategy during aging.
Abstract: The sigma1 receptor is critically involved in the rewarding effect of cocaine, as measured using the conditioned place preference (CPP) procedure in mice. Neuroactive steroids exert rapid neuromodulatory effects in the brain by interacting with GABA(A), NMDA, and sigma1 receptors. At the sigma1 receptor level, 3beta-hydroxy-5-androsten-17-one [dehydroepiandrosterone (DHEA)] and 3beta-hydroxy-5-pregnen-20-one (pregnenolone) act as agonists, whereas 4-pregnene-3,20-dione (progesterone) is an efficient antagonist. The present study sought to investigate the action of neuroactive steroids in acquisition of cocaine-induced CPP in C57BL/6 mice. None of these steroids induced CPP alone. However, pretreatment with DHEA or pregnenolone (5-20 mg/kg, s.c.) during conditioning with cocaine (10 mg/kg, i.p.) increased the conditioned score. On the contrary, pretreatment with either progesterone (10 or 20 mg/kg, s.c.) or finasteride (25 mg/kg, twice a day), a 5alpha-reductase inhibitor, blocked acquisition of cocaine (20 mg/kg)-induced CPP. A crossed pharmacology was observed between steroids and sigma1 ligands. The sigma1 antagonist N-[2-(3,4-dichlorophenyl)ethyl]-N-methyl-2-(dimethylamino)ethylamine blocked cocaine-induced CPP and its potentiation by DHEA or pregnenolone. Progesterone blocked cocaine-induced CPP and its potentiation by the sigma1 agonist igmesine. These results showed that neuroactive steroids play a role in cocaine-induced appetence, through their interaction with the sigma1 receptor. Therefore, neuroendocrine control of cocaine addiction may not involve solely glucocorticoids. The importance of neuroactive steroids as factors of individual vulnerability to drug addiction should, thus, be considered.
Abstract: In the present study, we examined the involvement of the sigma(1) (sigma(1)) receptor in several behavioral manifestations of ethanol addiction. Administration of ethanol (0.5, 1, and 2 g/kg) in Swiss mice dose-dependently induced locomotor stimulation, conditioned place preference, and conditioned taste aversion, which are considered as behavioral index of drug-induced reward. Pretreatment with the selective sigma(1) receptor antagonist N-[2-(3,4-dichlorophenyl)ethyl]-N-methyl-2-(dimethylamino)ethylamine (BD1047, 3-30 mg/kg) dose-dependently blocked ethanol (1 g/kg)-induced hyperlocomotion and taste aversion and ethanol (2 g/kg)-induced place preference. Pretreatment with the selective sigma(1) receptor agonist 2-(4-morpholino)ethyl 1-phenylcyclohexane-1-carboxylate (PRE-084, 1-10 mg/kg) before ethanol (0.5 g/kg) failed to affect the resulting locomotor stimulation, but dose-dependently enhanced the conditioned place preference. Each sigma(1) receptor ligand was devoid of behavioral effect by itself. These observations show that activation of the sigma(1) receptor is a necessary component of ethanol-induced motivational effects and suggest a new pharmacological target for alleviating ethanol addiction.
Abstract: RATIONALE: Activation of the neuronal sigma(1) (sigma(1)) receptor potentiates calcium mobilization, leading to effective modulation of postsynaptic responses to neurotransmitters. At the behavioral level, sigma(1) agonists modulate learning, response to stress and depression. In particular, the selective sigma(1) agonist igmesine reduced immobility in the forced swimming test. OBJECTIVES AND METHODS: We investigated the effect of modulators of Ca(2+) influx and mobilization, administered intracerebroventricularly at doses ineffective alone, on the igmesine effect. The tricyclic antidepressant desipramine was also studied for comparison. RESULTS: The calcium chelator EGTA blocked both igmesine and desipramine-induced decreases of immobility duration, indicating the importance of extracellular Ca(2+) influx in the initial action of each compound. Both L- and N-type voltage-dependent calcium channel (VDCC) appeared involved in the sigma(1) agonist effect. Verapamil, an L-type VDCC antagonist or omega-conotoxin GVI, a N-type VDCC antagonist, blocked whereas (-)-Bay K8644, a L-type VDCC agonist, potentiated the igmesine effect. Mobilization of intracellular Ca(2+) stores is involved selectively in the effect mediated by the sigma(1) receptor, since the membrane permeable intracellular Ca(2+) chelator EGTA/AM affected only the igmesine effect. Inositol 1,4,5-trisphosphate (InsP(3)) receptor-sensitive Ca(2+) pools appeared primarily involved, rather than Ca(2+)/caffeine-sensitive Ca(2+) pools. Indeed, the InsP(3) receptor positive modulator bradykinin potentiated, whereas the InsP(3) receptor antagonist xestospongin C blocked the igmesine effect. The ryanodine receptor agonist caffeine failed to affect the efficacy of igmesine, whereas the antagonist ryanodine reduced it. CONCLUSIONS: The sigma(1) receptor-mediated behavioral effect is dependent not only on rapid Ca(2+) influx, as observed for a classical antidepressant, but also on intracellular Ca(2+) mobilization.
Abstract: This study examined the antidepressant efficacy of the selective sigma(1) receptor agonists igmesine or PRE-084 in mice injected intracerebroventricularly (i.c.v.) with beta(25-35)-amyloid peptide and submitted to the forced swim test. Beta(25-35) peptide-injected animals developed memory deficits after 8 days contrarily to controls injected with scrambled beta(25-35) peptide or vehicle solution. In the forced swim test, the i.c.v. treatment failed to affect the immobility duration, but the antidepressant effect of the sigma(1) agonists was facilitated in beta(25-35) animals. Igmesine reduced immobility duration at 30 versus 60 mg/kg in control groups. PRE-084 decreased immobility duration at 30 and 60 mg/kg only in beta(25-35) animals. Desipramine reduced the immobility duration similarly among groups and fluoxetine appeared less potent in beta(25-35) animals. The beta(25-35) animals exhibited decreased progesterone levels in the hippocampus (-47%). The behavioural efficacy of sigma(1) agonists is known to depend on neuro(active)steroids levels synthesised by glial cells and neurones, which are affected by the beta-amyloid toxicity. This behavioural study suggests that sigma(1) agonists, due to their enhanced efficacy, may allow to alleviate the depressive symptoms associated with Alzheimer's disease.
Abstract: Cocaine is a highly addictive substance abused worldwide. Its mechanism of action involves initially inhibition of neuronal monoamine transporters in precise brain structures and primarily the dopamine reuptake system located on mesolimbic neurons. Cocaine rapidly increases the dopaminergic neurotransmission and triggers adaptive changes in numerous neuronal circuits underlying reinforcement, reward, sensitization and the high addictive potential of cocaine. Current therapeutic strategies focus on counteracting the cocaine effects directly on the dopamine transporter, through post-synaptic D(1), D(2) or D(3) receptors or through the glutamatergic, serotoninergic, opioid or corticotropin-releasing hormone systems. However, cocaine administration also results in the activation of numerous particular targets. Among them, the sigma(1) (sigma(1)) receptor is involved in several acute or chronic effects of cocaine. The present review will first bring concise overviews of the present strategies followed to alleviate cocaine addiction and animal models developed to analyze the pharmacology of cocaine addiction. Evidence involving activation of the sigma(1) receptor in the different aspects of cocaine abuse, will then be detailed, following acute, repeated, or overdose administration. The therapeutic potentials and neuropharmacological perspectives opened by the use of selective sigma(1) receptor antagonists in cocaine addiction will finally be discussed.
Abstract: The sigma(1) (sigma(1)) receptor exerts a potent neuromodulatory role in the brain with relevant consequences in memory processes, response to stress, depression and pharmacodependence. Its precise endogenous ligand is not yet identified but the sigma(1) receptor appears to be one target for the nongenomic rapid effects of neuroactive steroids in the brain. The aim of the present study was to establish whether differences in sigma(1) receptor-mediated behaviours could be observed among mouse strains, in relation with differences in either sigma(1) receptor expression or steroid levels. The sigma(1)-receptor immunohistochemical distribution appeared similar between Swiss and C57BL/6 strains in all the brain structures examined. The levels of in vivo [(3)H](+)-SKF-10 047 binding to sigma(1) receptors were lower in Swiss than in C57BL/6. Adrenalectomy/castration significantly increased [(3)H](+)-SKF-10 047 binding only in Swiss. The behavioural efficacy of the selective sigma( 1) agonists igmesine and PRE-084 -- reversion of the scopolamine-induced amnesia in the passive avoidance test; diminution of the immobility duration in the forced swimming test -- were significantly higher in C57BL/6 than in Swiss. Steroid levels were measured in the brain in basal conditions and after stress. C57BL/6 mice presented in both conditions, the lowest progesterone levels, this steroid acting as an endogenous sigma(1) antagonist. Collectively, the results suggested that strain differences in neuroactive steroid and particularly, progesterone, biosynthesis and sensitivity may contribute to the differential behavioural efficacy of sigma(1)-receptor ligands. Noteworthy, these observations are coherent with strain differences observed in the intensity of cocaine-induced reward properties, known to critically involve the sigma(1) receptor.
Abstract: Treating dementia of the Alzheimer's type is a terrible challenge that will require an innovative pharmacological strategy simultaneously addressing symptoms and causes of the complex neurodegenerative process involved in Alzheimer's disease. The present review will outline the most recent data, albeit restricted to preliminary preclinical studies, suggesting that the sigma(1) receptor agonist may present some efficacy. The sigma(1) receptor is a unique intraneuronal protein that modulates intracellular Ca(2+) mobilization and extracellular Ca(2+) influx, leading to a wide spectrum of neuromodulatory activity. At the behavioral level, sigma(1)-receptor agonists are antiamnesic and anti-depressant drugs. The sigma(1) receptor is also one of the receptors at which neurosteroids act to exert their rapid nongenomic effects in the brain. In particular, dehydroepiandrosterone (DHEA) is an endogenous sigma(1) agonist and progesterone, a potent antagonist of the sigma(1) receptor. The beta-amyloid protein-related toxicity induces important disturbances of neurosteroid syntheses and releases mechanisms, particularly by affecting the corticotropin-releasing hormone systems. In turn, sigma(1)-receptor agonists showed an enhanced efficacy in animal models of Alzheimer's disease-related learning impairments or depressive responses. In addition, selective sigma(1) agonists, as well as DHEA, showed marked neuroprotective activity in vitro against oxidative stress-related damages. Acting chronically through the sigma(1) receptor may indeed offer a new way to alleviate the cognitive disturbances observed in Alzheimer's disease and promote long-term improvements. (c) 2002 Prous Science. All rights reserved.
Abstract: 1. Sigma (sigma) receptors have generated a great deal of interest on the basis of their possible roles in various pathologies, including cytoprotection. Although the exact function of sigma-1 (sigma(1)) receptors is not yet known, their role in the regulation of intracellular Ca(2+) levels and sterol biosynthesis, functions that could be assigned to mitochondria, are the only mechanisms described. 2. Using preparations of purified rat liver and brain mitochondria we demonstrate herein the presence of sigma-like binding sites. [(3)H](+)-pentazocine, a sigma(1) radioligand was used to label these sites. 3. In the liver, [(3)H](+)-pentazocine labelled one class of binding sites with high affinity (K(d)=3 nM), similar to that observed in liver microsomes and synaptic membranes. These sites were located on the outer mitochondrial membranes and displayed high affinity for other sigma(1) ligands namely, haloperidol, ifenprodil, carbetapentane or 1,3-di(2-tolyl)guanidine (DTG). 4. The presence of sigma(1) receptors on liver mitochondria was confirmed using double fluorescence immunostaining. 5. [(3)H](+)-pentazocine binding sites were also found on brain mitochondria but they appeared pharmacologically distinct to the liver ones as [(3)H](+)-pentazocine and typical sigma(1) ligands displayed lower affinities for these sites. Nevertheless, [(3)H](+)-pentazocine binding on both liver and brain mitochondria was modulated by progesterone, a putative endogenous ligand for sigma receptors. 6. Our data demonstrates the presence of [(3)H](+)-pentazocine binding sites with pharmacological characteristics identical to sigma(1) receptors on rat liver mitochondrial membranes. The pharmacological significance of these sites and their role on mitochondrial function remain unknown.
Abstract: The involvement of the sigma(1) receptor on the rewarding effects of cocaine was examined using the conditioned place preference (CPP) procedure in C57BL/6 mice. Acquisition or expression of cocaine (20 mg/kg i.p.)-induced CPP was significantly decreased by pre-treatment with the selective sigma(1) receptor antagonists N,N-dipropyl-2-(4-methoxy-3-(2-phenylethoxy)phenyl)ethylamine (NE-100) or N-[2-(3,4-dichlorophenyl)ethyl]-N-methyl-2-(dimethylamino)ethylamine (BD1047), 1-10 mg/kg, i.p. The sigma(1) receptor agonists igmesine or 2-(4-morpholinoethyl-1-phenylcyclohexane-1-carboxylate hydrochloride (PRE-084) failed to induce CPP when injected alone. Moreover, the CPP induced by N-[1-(2-benzo(b)thiophenyl)cyclohexyl]piperidine (BTCP), a selective dopamine reuptake inhibitor, was blocked by treatments with the sigma(1) receptor antagonists as was similarly observed with cocaine. In addition, the repetitive treatment with cocaine during conditioning increased sigma(1) receptor mRNA expression in the nucleus accumbens, but not in the caudate putamen, prefrontal cortex or cerebellum. These data show that the sigma(1) receptor is not only necessary for acquisition of the cocaine-induced CPP, but that it is also implicated in its expression, confirming that activation of the sigma(1) receptor is induced during cocaine's early effects. The sigma(1) receptor is activated consequently to dopamine reuptake blockade and is not sufficient to induce CPP by itself. The mechanism of the sigma(1) receptor involvement in CPP and the selectivity toward the CPP-inducing drug remains however to be determined. These results show that strategies targeting the sigma(1) receptor with selective antagonists may allow effective attenuation of cocaine's rewarding properties and, in turn, offer new treatment strategies against drug addiction.
Abstract: The interaction of neuroactive steroids with the sigma(1)-receptor was investigated in Swiss mice submitted to the forced swimming test. The sigma(1)-agonists igmesine and (+)-SKF-10,047 and the steroid dehydroepiandrosterone sulfate (DHEAS) showed some antidepressant-like activity by shortening the immobility time, these effects being blocked by the sigma(1)-antagonist BD1047 or progesterone. The sigma(1)-agonist PRE-084 or pregnenolone sulfate failed to affect the immobility time. In adrenalectomized/castrated (AdX/CX) mice, the effects of igmesine and DHEAS were significantly potentiated, and PRE-084 or pregnenolone sulfate induced significant decreases of immobility time. The augmented effects in AdX/CX were fully blocked by BD1047. The effects of the classical antidepressants, desipramine or fluoxetine, were unchanged in AdX/CX mice. The effect of stress on the sigma(1)-receptor binding and neurosteroid levels was then examined in different brain structures, in terms of in vivo (+)-[(3)H]SKF-10,047 binding to sigma(1)-sites and neurosteroids levels. In the hippocampus, but not in the cortex or cerebellum, inhibition of in vivo (+)-[(3)H]SKF-10,047 binding was measured in parallel to the extent of progesterone levels according to the endocrine conditions. These data confirmed the antidepressant ability of sigma(1)-receptor agonists and revealed that the endogenous steroidal levels tonically interfere with the efficacy of the sigma(1)-system. It was observed that local modifications in progesterone levels are directly related to the changes of in vivo sigma(1)-binding. Such observations may be of major importance in view of the therapeutic use of selective sigma(1)-agonists in depression.
Abstract: Sigma(1) (sigma(1)) receptor agonists showed anti-amnesic properties in pharmacological amnesia models. We now investigated whether the selective sigma(1) receptor agonist, 2-(4-morpholinoethyl)-1-phenylcyclohexane-1-carboxylate hydrochloride (PRE-084), could ameliorate spatial learning in aged animals, using a water-maze procedure. Wistar rats, 3 or 24 months old, were trained to locate a visible platform and then an invisible platform. Finally, a transfer test was performed during saline or PRE-084 treatment. Aged, but not adult, animals showed learning deficits unrelated to visual impairments. The PRE-084 treatment allowed aged animals to learn the new platform location, in terms of decreased latencies to the platform during training and increased presence in the quadrant during retention. The results of these experiments suggest a potential of selective sigma(1) receptor agonists as cognitive enhancers during ageing.
Abstract: Steroids, synthesized in peripheral glands or centrally in the brain--the latter being named neurosteroids--exert an important role as modulators of the neuronal activity by interacting with different receptors or ion channels. In addition to the modulation of GABA(A), NMDA or cholinergic receptors, neuroactive steroids interact with an atypical intracellular receptor, the sigma(1) protein. This receptor has been cloned in several species, and highly selective synthetic ligands are available. At the cellular level, sigma1 agonists modulate intracellular calcium mobilization and extracellular calcium influx, NMDA-mediated responses, acetylcholine release, and alter monoaminergic systems. At the behavioral level, the sigma1 receptor is involved in learning and memory processes, the response to stress, depression, neuroprotection and pharmacodependence. Pregnenolone, dehydroepiandrosterone, and their sulfate esters behave as sigma1 agonists, while progesterone is a potent antagonist. This review will detail the physiopathological consequences of these interactions, focusing on recent results on memory and depression. The therapeutical interest of selective sigma1 receptor agonists in alleviating aging-related cognitive deficits will be discussed.
Abstract: The sigma1 (sigma1) receptor cDNA was recently cloned in several animal species, including the mouse. In order to firmly establish the implication of sigma1 receptors in memory, a phosphorothioate-modified antisense oligodeoxynucleotide (aODN) targeting the sigma1 receptor mRNA and a mismatched analog (mODN) were administered intracerebroventricularly for 3 days in mice. Scatchard analyses of in vitro (+)-[3H]SKF-10,047 binding to sigma1 sites showed that Bmax values were significantly decreased in the hippocampus (-58.5%) and cortex (-38.1%), but not in the cerebellum, of aODN treated mice, as compared to saline- or mODN-treated animals. In vivo binding levels were also significantly decreased after aODN treatment in the hippocampus and cortex but not in the cerebellum. The anti-amnesic effects of the selective sigma1 agonists PRE-084 or SA4503 were evaluated against the learning impairments induced by dizocilpine or scopolamine, respectively, using spontaneous alternation behavior and passive avoidance task. The anti-amnesic effects of PRE-084 or SA4503, observed after saline- or mODN-treatment, were blocked after aODN administration. These observations bring a molecular basis to the modulatory role of sigma1 receptors in memory processes.
Abstract: 1. The sigma(1) (sigma(1)) receptor cDNA was cloned in several animal species. Molecular tools are now available to identify its endogenous effectors, such as neuroactive steroids, and to establish its precise physiological role. In particular, the sigma(1) receptor is involved in memory processes, as observed in pharmacological and pathological rodent models of amnesia. 2. In order to establish the involvement of sigma(1) receptors in memory, a 16-mer oligodeoxynucleotide antisense to the sigma(1) receptor cDNA (aODN), and its mismatched control (mODN) were prepared and centrally administered into the mouse brain. The anti-amnesic effects induced by the selective sigma(1) agonist PRE-084 and the steroid dehydroepiandrosterone (DHEA) sulphate or pregnenolone sulphate were examined in ODN-treated animals. 3. The aODN treatment failed to affect the dissociation constant (K(d)) but significantly decreased the number of sigma(1) sites (B(max)) labelled with [(3)H]-(+)-SKF-10,047 in the hippocampus and cortex. In these structures, the in vivo binding levels were also diminished, according to the dose and number of injections, as compared with control animals injected with saline or mODN. 4. Cannulation and injections failed to affect the open-field behaviour of the animals. However, the anti-amnesic effects of PRE-084 and DHEA sulphate against the dizocilpine-induced impairments were blocked after aODN treatment in the short- and long-term memory tests. The anti-amnesic effects of pregnenolone sulphate remained unchanged. 5. These observations bring a molecular basis to the modulatory role of sigma(1) receptors in memory, and reveal that the anti-amnesic action of neuroactive steroids may not similarly involve an interaction with sigma(1) receptors.
Abstract: The neuroactive steroids pregnenolone (3beta-hydroxy-5-pregnen-20-one) and dehydroepiandrosterone (DHEA, 3alpha-hydroxy-5-androstene-17-one) are negative allosteric modulators of the GABA(A) receptors and positive modulators of acetylcholine, NMDA and sigma(1) receptors. Pregnenolone was recently shown to potentiate the neuronal damage induced by excessive glutamate in cell culture models, whereas dehydroepiandrosterone was reported to present some neuroprotective activity. The in vivo relevance of these effects was investigated in mice submitted to an hypoxic insult, the repeated exposure to carbon monoxide (CO) gas, a model that leads to neurodegeneration in the CA(1) hippocampal area and learning deficits. Recording spontaneous alternation behaviour in the Y-maze assessed short-term memory and long-term memory was examined using a passive avoidance task. After exposure to CO, mice showed a progressive deterioration of their learning ability, reaching significance after 3 days and being maximal after 7 days. Pregnenolone administered before CO significantly facilitated the hypoxia-related deficits, which could be measured 1 day after CO and appeared maximal after 3 days. Dizocilpine blocked the deficits in vehicle- and pregnenolone-treated CO-exposed animals, showing that pregnenolone selectively facilitated the NMDA receptor-dependent excitotoxicity. Dehydroepiandrosterone blocked the appearance of the CO-induced deficits, even after 7 days. Interestingly, the sigma(1) receptor antagonist N, N-dipropyl-2-(4-methoxy-3-(2-phenylethoxy)phenyl)ethylamine (NE-100) failed to affect the dehydroepiandrosterone-induced protection, showing the lack of involvement of sigma(1) receptors. Cresyl violet-stained sections of the mouse hippocampal formation showed that the neurodegeneration observed in the CA(1) area after exposure to CO was augmented by pregnenolone and blocked by dehydroepiandrosterone. These results show that pregnenolone and dehydroepiandrosterone, although being similarly involved in modulating the excitatory/inhibitory balance in the brain, do not equally affect the extent of excitotoxic insults.
Abstract: The sigma(1)-receptor is a one-transmembrane endoplasmic reticulum protein that binds neurosteroids and dextrorotatory benzomorphans. The roles of sigma(1)-receptors in regulating intracellular Ca(2+) in NG108 cells were examined in this study. sigma(1)-Ligands pregnenolone sulfate, (+)-pentazocine, and 2-(4-morpholino)ethyl-1-phenylcyclohexane-1-carboxylate hydrochloride modulate Ca(2+) signaling in NG108 cells via two modes of action. First, nanomolar concentrations of the ligands, without effect by themselves, potentiated the bradykinin-induced increase of the cytosolic free Ca(2+) concentration in a bell-shaped manner. This effect of sigma(1)-ligands was unaffected by depletion of Ca(2+) from perfusion buffer and was blocked by a 21-mer antisense oligodeoxynucleotide against the cloned sigma(1)-receptors. Second, after the cells were depleted of the endoplasmic reticulum Ca(2+) stores, the depolarization (75 mM KCl)-induced increase in cytosolic free Ca(2+) was potentiated by 2-(4-morpholino)ethyl-1-phenylcyclohexane-1-carboxylate hydrochloride, whereas it was inhibited by pregnenolone sulfate and (+)-pentazocine. These effects, albeit opposite in direction, were blocked by both the 21-mer antisense oligodeoxynucleotide and pertussis toxin. Western blotting indicates that sigma(1)-receptors are increased on the plasma membrane and the nuclear membrane in the presence of sigma(1)-ligand. These results suggest that Ca(2+) signaling via sigma(1)-receptors may represent a novel mechanism that affects intracellular Ca(2+) concentrations.
Abstract: In order to characterize the localization of the sigma(1) receptor in the adult rat central nervous system, a polyclonal antibody was raised against a 20 amino acid peptide, corresponding to the fragment 143-162 of the cloned sigma(1) receptor protein. Throughout the rostrocaudal regions of the central nervous system extending from the olfactory bulb to the spinal cord, intense to moderate immunostaining was found to be associated with: (i) ependymocytes bordering the entire ventricular system, and (ii) neuron-like structures located within the parenchyma. Double fluorescence studies confirmed that, throughout the parenchyma, sigma(1) receptor-immunostaining was essentially associated with neuronal structures immunostained for the neuronal marker betaIII-tubulin. In all rats examined, high levels of immunostaining were always associated with neurons located within specific regions including the granular layer of the olfactory bulb, various hypothalamic nuclei, the septum, the central gray, motor nuclei of the hindbrain and the dorsal horn of the spinal cord. In contrast, only faint immunostaining was associated with neurons located in the caudate-putamen and the cerebellum. Electron microscope studies indicated that sigma(1) receptor immunostaining was mostly associated with neuronal perikarya and dendrites, where it was localized to the limiting plasma membrane, the membrane of mitochondria and of some cisternae of the endoplasmic reticulum. At the level of synaptic contacts, intense immunostaining was associated with postsynaptic structures including the postsynaptic thickening and some polymorphous vesicles, whereas the presynaptic axons were devoid of immunostaining.These data indicate that the sigma(1) receptor antibody prepared here, represents a promising tool for further investigating the role of sigma(1) receptors.
Abstract: The sigma1 (sigma1) receptor constitutes a particular target of cocaine believed to be involved in some of its behavioral effects. In the present study, its involvement in the rewarding effect of cocaine was examined using the conditioned place preference (CPP) procedure. CPP was induced in C57Bl/6 mice injected repeatedly with cocaine (20 mg/kg, i.p.). The selective sigma1 receptor antagonists NE-100 and BD1047 (1-10 mg/kg, i.p.) significantly attenuated or blocked the cocaine-induced CPP. Animals treated centrally with a sigma1 receptor antisense oligodeoxynucleotide failed to develop cocaine-induced CPP, unlike mismatch controls. The sigma1 receptor thus appears to be critically involved in the development of the cocaine-induced CPP and, in consequence, may constitute a promising approach to blocking cocaine reward.
Abstract: Vimentin belongs to the family of intermediate filament (IF) proteins. During the nervous system development in mammals, it is transiently expressed in precursor cells of neuronal and glial lineages, and then it is progressively replaced by other types of IF proteins. Surprisingly, mice knock-out for vimentin develop and reproduce without any apparent defects (Colucci-Guyon et al. Cell 79:679-694, 1994). In adult rodents, Bergmann glia (BG) of the cerebellum continue to express vimentin together with glial fibrillary acidic protein (GFAP). A careful analysis of cerebellar morphology and ultrastructure in mutants showed poorly developed and highly abnormal BG, whereas the migration of granular neurons proceeded normally. Moreover, many Purkinje cells (PC) appeared stunted with a loss of spiny branchlets, and some of them were necrotic. Finally, impaired motor coordination was evidenced by behavioral tests. These observations demonstrate a role for vimentin in contributing to the normal development and morphology of BG and reveal a hitherto unreported functional relationship between BG and PC.
Abstract: The interaction between neurosteroids and sigma1 (sigma1) receptors may be of therapeutic interest during physiological or pathological ageing, particularly concerning their neuromodulatory role on cognitive functions. Neurosteroids modulate memory processes through a mechanism involving interactions with GABAA, N-methyl-D-aspartate and/or sigma1 receptors. To measure the contribution of endogenous neurosteroid levels to the antiamnesic effects of sigma1 agonists, we investigated the effects of inhibitors of key enzymes involved in neurosteroid synthesis, in adrenalectomized/castrated (AdX/CX) mice to avoid the effect of circulating steroids. Trilostane, a 3beta-hydroxysteroid-deshydrogenase inhibitor, blocks the pregnenolone to progesterone conversion and leads to a decrease of progesterone. Finasteride, a 5alpha-reductase inhibitor, blocks the progesterone to 5alpha-pregnane-3,20-dione conversion and leads to an accumulation of progesterone. The in vivo binding of (+)-[3H]SKF-10 047 to sigma1 sites was measured in the mouse hippocampus and cortex. The attenuating effect of the selective sigma1 agonist PRE-084 (0.1-3 mg/kg) against dizocilpine (0.15 mg/kg)-induced learning impairment was examined using spontaneous alternation behaviour, step-down passive avoidance and place learning in the elevated plus-maze. The in vivo (+)-[3H]SKF-10 047 binding appeared significantly increased in AdX/CX mice and after trilostane treatment (10 mg/kg twice a day, 7 days), compared with sham-operated animals. The finasteride treatment (25 mg/kg, 7 days) significantly decreased binding levels. The learning deficits induced by dizocilpine were not affected by the treatments. The antiamnesic effect of PRE-084 was facilitated in AdX/CX mice and even more after trilostane treatment, as several parameters for animals treated with both PRE-084 and dizocilpine returned to control values. The PRE-084 effect was blocked after finasteride. These results confirmed that endogenous neurosteroidal levels modulate sigma1 receptor-mediated behaviour directly, and revealed that, among neurosteroids, progesterone may be the main modulator of sigma1 receptors.
Abstract: Neuroactive neurosteroids, including progesterone, allopregnanolone, pregnenolone and dehydroepiandrosterone, represent steroid hormones synthesized de novo in the brain and acting locally on nervous cells. Neurosteroids modulate several neurotransmitter systems such as gamma-aminobutyric acid type A (GABA(A)), N-methyl-D-aspartate (NMDA) and acetylcholine receptors. As physiologic consequences, they are involved in neuronal plasticity, learning and memory processes, aggression and epilepsy, and they modulate the responses to stress, anxiety and depression. The sigma1-receptor protein was recently purified and its cDNA was cloned in several species. The amino-acid sequences are structurally unrelated to known mammalian proteins, but shared homology with a fungal sterol C8-C7 isomerase. The sigma1-receptor ligands exert a potent neuromodulation on excitatory neurotransmitter systems, including the glutamate and cholinergic systems. Consequently, selective sigma1 agonists show neuroprotective properties and beneficial effects in memory processes, stress and depression. The evidence of a direct interaction between neurosteroids and sigma1 receptors was first suggested by the ability of several steroids to inhibit the binding of sigma1-receptor radioligands in vitro and in vivo. A crossed pharmacology between neurosteroids and sigma1-receptor ligands was described in several physiological tests and behavioral responses. This review will detail the recent evidence for a common mechanism of action between neurosteroids and sigma1-receptor ligands and focus on the potential therapeutic interests of such interaction in the physiopathology of learning and memory impairments, stress, depression and neuroprotection.
Abstract: 1. Sigma (sigma) receptor ligands were previously reported to alleviate learning and memory impairments on several pharmacological and pathological rodent models of amnesia. Such effect was demonstrated as involving the sigma1 subtype of sigma receptor. 2. In this study, we characterized the pharmacological effect mediated by sigma ligands on two lesional models of amnesia in mice: (1) the hypoxia-related learning and memory impairment model induced by repeated exposure to carbon monoxide (CO) gas; and (2) the intoxication with trimethyltin (1 mg kg(-1)). 3. The selective sigma1 ligand PRE-084 (1 mg kg(-1)) or the non-selective sigma1/sigma2 compounds DTG (0.1 mg kg(-1)), BD1008 (3 mg kg(-1)), and haloperidol (0.1 mg kg(-1)) reversed significantly the spontaneous alternation deficits observed 7 days after exposure to CO or 14 days after intoxication with trimethyltin. 4. The selective sigma1 receptor antagonist NE-100 (1 mg kg(-1)) was ineffective by itself, but blocked completely the PRE-084 effects, partially the DTG effects, and did not affect the effects induced by BD1008 or haloperidol. 5. A similar pharmacological profile was observed in the step-down type passive avoidance test performed 8 days after exposure to CO. 6. These results show that, in contrast to the previously reported amnesia models, the impairments induced after exposure to CO or intoxication with trimethyltin could be alleviated not only by sigma1 receptor agonists but also by sigma2 agonists. The particular pattern of neurodegeneration observed in these lesional models may explain these differences.
Abstract: The sigma1 (sigma 1) receptor agonists exert potent anti-amnesic effects, as they apparently block the learning impairments either induced by the muscarinic receptor antagonist scopolamine, the N-methyl-D-aspartate receptor antagonist dizocilpine or inherently due to the age-related deficits in senescence-accelerated mice. We recently described the amnesia induced by the beta-amyloid-related peptide beta 25-35, administered centrally in an aggregated form, in mice. The deficits were sensitive to cholinomimetics or to N-methyl-D-aspartate/glycine modulatory site agonists. Herein, we examined the effects of sigma 1 receptor ligands on the beta 25-35 peptide-induced amnesia. The effects of neuro(active) steroids, which interact in vitro and in vivo with sigma 1 receptors were examined in parallel. Mnesic capacity was evaluated seven days after administration of aggregated beta 25-35 peptide (3 nmol), using spontaneous alternation in the Y-maze for spatial short-term memory, or after 14 days, using the step-down type passive avoidance test for long-term memory. The sigma 1 receptor agonists (+)-pentazocine, PRE-084, or SA4503 attenuated, in a dose-dependent and bell-shaped manner, the beta 25-35 peptide-induced deficits on both tests. These effects were antagonized by haloperidol or BMY-14802, confirming the sigma 1 receptor pharmacology. Pregnenolone, dehydroepiandrosterone, and their sulphate esters, but not progesterone, also dose-dependently attenuated the beta 25-35 peptide-induced deficits. Progesterone blocked the beneficial effects of each other neurosteroid, behaving as an antagonist. Furthermore, haloperidol blocked the effects induced by neurosteroids, whereas progesterone antagonized the effects of the non-steroidal sigma 1 receptor agonists, showing a clear crossed pharmacology of different drug classes. These results demonstrate that: (i) the anti-amnesic effect of sigma 1 receptor agonists may be of therapeutic relevance in pathological states affecting the cholinergic and/or glutamatergic systems, such as in pathological aging; (ii) neurosteroids play an important role in learning processes and may collectively constitute a therapeutic target; (iii) the interaction between sigma 1 systems and neurosteroids appears indeed of behavioural relevance.
Abstract: Neurosteroids have been reported to modulate learning and memory processes in aged animals and in pharmacological models of amnesia. We report here the effects of dehydroepiandrosterone sulfate (DHEAS), pregnenolone sulfate (PREGS), and progesterone (PROG) on the learning impairment induced in mice by the muscarinic acetylcholine receptor antagonist, scopolamine. Spatial working memory was examined using the spontaneous alternation behavior in a Y-maze and long-term memory using place learning in a rectangular water-maze adapted for mice. Both DHEAS and PREGS (5-20 mg/kg, s.c.) prevented dose-dependently and significantly the scopolamine (2 mg/kg, s.c.)-induced alternation deficits. PROG (2-20 mg/kg, s.c.) failed to affect the scopolamine-induced deficits, but blocked, at 20 mg/kg, the beneficial effects induced by DHEAS or PREGS. In the water-maze, DHEAS (20 mg/kg) attenuated significantly the scopolamine-induced deficits, as observed during the acquisition sessions or the retention test. PROG (2, 20 mg/kg) did not affect the control or scopolamine-treated group performances, but blocked the ameliorating effect of DHEAS. Furthermore, in both tests, the selective sigma1 (sigma1) receptor antagonist NE-100 (1 mg/kg, i.p.) failed to affect the behaviors showed by the control or scopolamine-treated groups, but it blocked the ameliorating effects induced by DHEAS or PREGS. These results confirm the modulating role of neurosteroids in learning and memory processes and demonstrate that their modulation of the cholinergic systems involves an interaction with sigma1 receptors.
Abstract: 1. Although the physical nature of sigma (sigma) receptors have not yet been fully defined, several classes of selective ligands have been characterised, demonstrating a plethora of physiological actions. In the present review, the authors have set out to highlight two important aspects of the biological activities of sigma ligands, their neuroprotective and anti-amnesic effects. 2. The sigma ligands present a therapeutic potential as neuroprotective agents in brain ischemia. The neuroprotective activity of many non-selective sigma ligands is primarily a result of their affinity for the NMDA receptor complex. However, selective sigma ligands are also neuroprotective, possibly by inhibition of the ischemic-induced presynaptic release of excitotoxic amino acids. 3. The sigma 1 ligands prevent the experimental amnesia induced by muscarinic cholinergic antagonists at either the learning, consolidation or retention phase of the mnesic process. This effect involves a potentation of acetylcholine release induced by sigma 1 ligands selectively in the hippocampal formation and cortex. 4. The sigma 1 receptor ligands also attenuate the learning impairment induced by dizocilpine, a non-competitive antagonist of the NMDA receptor, and may relate to the potentiating effect of sigma 1 ligands on several NMDA receptor-mediated responses previously described in vitro and in vivo in the hippocampus. This effect is shared by NPY- and CGRP-related peptides and by neuroactive steroids, confirming the in vitro evidences of functional interactions between the sigma 1 receptors and these different systems. 5. Additional amnesia models also seem to be alleviated by sigma 1 ligands, such as phencyclidine-induced cognitive dysfunctions, and amnesia induced by the calcium channel blocker nimodipine, or by exposure to carbon monoxide. Furthermore, a preliminary study in an animal model of age-related memory deficits, the senescence-accelerated mouse, strengthened the therapeutic potentials of selective sigma 1 receptor ligands in aging-related pathologies.
Abstract: The beta-amyloid peptide-(25-35) fragment, but not beta-amyloid peptide-(1-28), shares with beta-amyloid protein-(1-42) the ability to self-aggregate and to induce neurotoxicity in vitro. This study examined the induction of amnesia in rats given intracerebroventricularly soluble or aggregated beta-amyloid peptide-(25-35) (5-45 nmol), or beta-amyloid peptide-(1-28) (15 nmol). Memory deficit in the water-maze test, examined 14 days after aggregated beta-amyloid peptide-(25-35) injection, was more pronounced than with soluble beta-amyloid peptide-(25-35). beta-Amyloid peptide-(1-28) only affected retention. These results confirm the direct amnesic properties of beta-amyloid peptides in the rat brain and showed that prior peptide aggregation markedly facilitates the appearance of amnesia.
Abstract: We previously reported that high-affinity sigma type 1 (sigma 1) ligands attenuate the learning impairment induced in mice by dizocilpine, a non-competitive N-methyl-D-aspartate (NMDA) antagonist. Neurosteroids, such as pregnenolone sulfate, progesterone and dehydroepiandrosterone sulfate (DHEAS), modulate NMDA-evoked responses in the central nervous system. Furthermore, some of them were reported to interact with sigma-receptors. This study was carried out to investigate whether DHEAS, a neurosteroid with memory-enhancing effects, attenuates the dizocilpine-induced learning impairment in mice, and, if so, by a mechanism involving sigma 1-receptors. Learning was evaluated using spontaneous alternation in the Y-maze for spatial working memory and step-down type of passive avoidance for long-term memory. At doses about 10-20 mg/kg s.c., DHEAS significantly attenuated dizocilpine (0.15 mg/kg i.p.)-induced impairment of learning on both tests. The enhancing effect of DHEAS (20 mg/kg s.c.) was antagonized by co-administration of the sigma-antagonist BMY-14802 (5 mg/kg i.p.) and suppressed by a subchronic treatment with haloperidol (4 mg/kg/day s.c. for 7 days). These results indicate that DHEAS attenuates dizocilpine-induced learning impairment via an interaction with sigma 1-receptors.
Abstract: The selective sigma1 receptor agonist 1-(3,4-dimethoxyphenethyl)-4-(3-phenyl propyl)piperazine dihydrochloride (SA4503) was reported to reverse the amnesia induced by the muscarinic receptor antagonist scopolamine at sub-mg/kg doses. We examined its effect on the learning impairment induced in mice by the non-competitive NMDA receptor antagonist dizocilpine. Learning capacities were evaluated using spontaneous alternation in the Y-maze for spatial working memory, and step-down type passive avoidance. SA4503 (0.03-1 mg/kg s.c.) attenuated the dizocilpine (0.15 mg/kg i.p.)-induced memory deficits following a bell-shaped curve in both tests. These effects of SA4503 were blocked by haloperidol (0.05 mg/kg i.p.), implicating sigma1 receptors. SA4503 also reversed the alternation deficit induced by N(omega)-nitro-L-arginine methyl ester (L-NAME, 100 mg/kg i.p.) at the same dosage, indicating that it acted on working memory through the nitric oxide (NO)-mediated signalling pathway. Furthermore, progesterone (2 mg/kg s.c.) blocked the SA4503 effects in the dizocilpine- and L-NAME-amnesia models, in accordance with the purported neurosteroids/sigma1 receptors interaction. These results demonstrate a promising neurobehavioural profile of SA4503, a ligand equally efficient to reverse the deficit in the glutamatergic as well as in the cholinergic amnesia model. Pertinent informations on the potential mechanism of the anti-amnesic effects of sigma1 receptor ligands were also obtained.
Abstract: It has been shown recently that low doses of sigma (sigma) receptor ligands like 1,3-di-(2-tolyl)guanidine (DTG), (+)N-allylnormetazocine [(+)SKF 10,047] and (+)pentazocine can antagonize learning impairments induced by dizocilpine (MK-801), a non-competitive antagonist at the NMDA receptor channel. This antagonism has been proposed to involve sigma receptor sites since it is blocked by the administration of purported sigma antagonists such as NE-100 and BMY-14802. It has also been demonstrated that peptides of the neuropeptide Y (NPY) and calcitonin gene-related peptide (CGRP) families modulate, in vivo, sigma labelling and electrophysiological effects in the hippocampal formation. Accordingly, we investigated if NPY- and CGRP-related peptides modulate cognitive processes by interacting with sigma sites in mice. In order to test this hypothesis, a step-down passive avoidance task was used. Interestingly, similarly to various sigma agonists, NPY, peptide YY (PYY) and the Y1 agonist [Leu31Pro34]NPY (but not NPY[13-36], a purported Y2 agonist), as well as hCGRPalpha and the purported CGRP2 agonist [Cys(ACM)2-7]hCGRPalpha (but not CGRP[8-37], a CGRP1 receptor antagonist), significantly attenuated learning impairments induced by MK-801. Furthermore, the effects of NPY, [Leu31Pro34]NPY, hCGRPalpha and [Cys(ACM)2-7]hCGRPalpha were blocked by the administration of the sigma antagonist, BMY-14802. The present data suggest that NPY- and CGRP-related peptides can indirectly interact in vivo with sigma receptors to modulate cognitive processes associated with NMDA receptor function.
Abstract: A beneficial effect of sigma (sigma) agonists was previously described on several pharmacological models of learning impairments. We examined this effect in senescence-accelerated mice (SAM), which has been developed as a murine model of aging and cognitive dysfunction. SAMP8/Ta (P8, senescence-prone substrain), 10-12 months of age, showed significant impairments in mnemonic capacities, as compared to age-matched SAMR1/Ta controls (R1, senescence-resistant substrain). Tests included open-field behavior, spontaneous alternation performances in the Y-maze, step-down passive avoidance and place learning after repetitive training in a water-maze. Pretreatment with the sigma agonists JO-1784 (igmesine) or PRE-084, at 0.1-3 mg/kg, s.c., significantly improved spontaneous alternation and passive avoidance performances in P8. JO-1784 or PRE-084, at 1 mg/kg, also improved place learning in the water-maze, and retention, in term of escape latency. The implication of sigma sites was indicated by the lack of significant effect of JO-1783, the inactive enantiomer of JO-1784, and by the ability of BMY-14802 (5 mg/kg, i.p.) to antagonize the effects on passive avoidance of JO-1784 (0.5 mg/kg) or PRE-084 (1 mg/kg). Subchronic treatments with JO-1784 (0.5 mg/kg/day) or PRE-084 (1 mg/kg/day) during 10 days, allowed a significant improvement of learning during training in the water-maze, but retention was not significantly ameliorated. These results confirmed the interest of the SAM substrains as an experimental model for senile memory impairment and showed that sigma agonists could improve the quality of learning, although they seem less effective on long-term memory retrieval upon chronic administration.
Abstract: Recent reports suggest an interaction between neuro-(active)steroids and sigma1 (sigma 1) receptors, affecting biochemical parameters as well as physiological responses mediated by sigma 1 ligands in the rodent brain. In this study, we examined the modulation by neurosteroids of the haloperidol-sensitive in vivo (+)-[3H]SKF-10,047 binding to sigma 1 sites in the mouse hippocampus and cortex. Progesterone (PROG; 2-40 mg/kg), pregnenolone sulfate (PREGS; 10-40 mg/kg), and dehydroepiandrosterone sulfate (DHEAS; 10-40 mg/kg) were administered systemically 10 min before the radioactive tracer. The total amount of (+)-[3H]SKF-10,047 bound in each structure was significantly affected by PROG and PREGS only at the highest dose tested and was unaffected by DHEAS. However, bound to free (B/F) radioactivity ratios were highly significantly decreased by 30-40% in each structure by PROG and PREGS. DHEAS, at 40 mg/kg, induced a significant 20% decrease in the hippocampus. Furthermore, the in vivo (+)-[3H]SKF-10,047 binding parameters were diminished in pregnant female mice compared to non-pregnant or male mice. These results confirm the in vitro binding results, bring a direct in vivo demonstration of the interaction between neurosteroids and sigma 1 receptors, and show that physiologic modulations of the steroidal concentrations affect the sigma 1 systems.
Abstract: The effects of D-cycloserine (DCS), a N-methyl-D-aspartate receptor-associated glycine site agonist, and milacemide (MIL), a glycine prodrug, were examined on learning impairments induced by administration of beta 25-35-amyloid peptide (3 nmol i.c.v.). Mice were examined for spontaneous alternation and step-down passive avoidance, 7 and 14 days after beta 25-35, respectively. The beta 25-35-induced deficits were reversed by DCS, 1-30 mg/kg i.p., or MIL, 3-100 mg/kg i.p., each drug being ineffective on control mice behaviours. These observations strengthen the therapeutic potential of glycine site agonists against the memory impairments induced by beta-amyloid peptides.
Abstract: Substantial evidences suggest that the increased cerebral deposition, and neurotoxic action of the beta-amyloid peptide, the major constituent of senile plaques, may represent the underlying cause of the cognitive deficits observed in Alzheimer's disease. Herein, we attempted to verify this hypothesis by inducing a potential Alzheimer's-type amnesia after direct intracerebroventricular administration of aggregated beta 25-35-amyloid peptide in mice. In this aim, mnesic capacities were evaluated after 6-13 days, using spontaneous alternation in the Y-maze, step-down type passive avoidance and place learning in a water-maze. Pretraining administration of aggregated beta 25-35 peptide induced dose-dependent decreases in both alternation behaviour and passive avoidance, at doses of 3 and 9 nmol/mouse. A reduced but still significant impairment was observed when the peptide was not aggregated, or 'aged', by preincubation for 4 days at 37 degrees C. The beta 1-28 peptide, at 3 nmol/mouse, also induced a marked decrease in step-down latency. Posttraining, but not preretention, administration of beta 25-35 peptide also significantly impaired learning. The beneficial effects of cholinergic agents on beta 25-35-induced amnesia was examined using the cholinesterase inhibitor tacrine (THA, 1.3 and 4.3 mumol/kg i.p.) and the nicotinic receptor agonist (-)-nicotine (NIC, 0.06 and 0.2 mumol/kg i.p.). Both drugs induced a dose-dependent abrogation of the beta 25-35-induced decreases in alternation behaviour and passive avoidance. Furthermore, THA, at 1.3 mumol/kg, and NIC, at 0.2 mumol/kg, also reversed the beta 25-35-induced impairment of place learning and retention in the water-maze. Histological examination of Cresyl violet-stained brain sections indicated a moderate but significant cell loss within the frontoparietal cortex and the hippocampal formation of mice treated with aged beta 25-35 peptide (9 nmol). Examination of Congo red-stained sections in the same animals demonstrated the presence of numerous amyloid deposits throughout these brain areas. These results confirm that the deposition of beta-amyloid peptide in the brain is in some way related to impairment of learning and cholinergic degeneration and suggest that the [25-35] fragment of the beta-amyloid protein, sufficient to induce neuronal death in cultures, also induces an Alzheimer's-type amnesia in mice.
Abstract: The peptides, histogranin and [Ser1]histogranin, were recently shown to modulate NMDA receptor function. In the present study, the effects of intracerebroventricular (i.c.v.) administration of [Ser1]histogranin and of the histogranin receptor antagonist, histogranin-(1-10), were examined on step-down type passive avoidance learning in mice. [Ser1]Histogranin (30-60 nmol) impaired retention, after post-training administration, but not when it was administered just prior to the retention assay. Histogranin-(1-10) (60 nmol) facilitated learning during training, without affecting retention. Co-administration of histogranin-(1-10) with [Ser1]histogranin (60 nmol each) led to a significant prevention of [Ser1]histogranin-induced learning impairment. These results indicate that [Ser1]histogranin impairs passive avoidance learning according to the pattern of NMDA receptor antagonists and involving specific histogranin sites.
Abstract: The high selectivity of the phencyclidine derivative PRE-084 for sigma (sigma) sites is demonstrated. We previously reported that this compound is able to markedly attenuate the impairment of learning induced in mice by the non-competitive NMDA antagonist MK-801, and the cholinergic nicotinic antagonist mecamylamine. In this study, we examined the effect of PRE-084 on the impairment of learning induced by acute administration of the calcium channel antagonist nimodipine. Nimodipine (0.3 mg/kg i.p.) impaired the spontaneous alternation behaviour in a Y-maze, decreased the step-down latency (SDL) in a passive avoidance task, and altered place learning and retention in a water-maze paradigm, with no marked effect on the motility observed using an open-field test. Preadministration of PRE-084 resulted in an attenuation of the impairment of alternation, in the 0.3-1 mg/kg s.c. range, in a marked increase in SDL, at 1-3 mg/kg, and improved place learning and retention in the water-maze, at 1 mg/kg. The effects on alternation behaviour and passive avoidance were completely prevented by co-administration of the purported sigma antagonist BMY-14802 (10 mg/kg i.p.), implicating the sigma sites. These results confirm the beneficial effect of the sigma ligand PRE-084 on pharmacological models of learning impairments, and indicate that sigma sites may modulate Ca2+ fluxes through VDCC, which may in turn bear some as yet unknown relationship to the previously described interaction with neurotransmitter systems.
Abstract: The effects of acute systemic administration of the Ca(2+) channel antagonist nimodipine were examined on learning capacities of adult Swiss mice. Tests included spontaneous alternation behaviour, for spatial working memory; and step-down passive avoidance and place learning in a water maze, for long-term memory. Nimodipine markedly impaired spontaneous alternation at doses of 0.3-1mg/kg i.p., and passive avoidance at doses of 0.3-3mg/kg i.p., as compared to the vehicle-treated animals. At 0.3mg/kg i.p., the drug did not alter motility in an open field, but significantly decreased performances in training trials and retention in the water maze. Subchronic nimodipine 0.3 and 1mg/kg once a day i.p. for 10 days) did not affect performances in the Y-maze and passive avoidance tests. These results show that acute nimodipine administration alters learning in adult mice, and argue for an involvement of voltage-dependent Ca(2+) channels in learning.
Abstract: The peptides, histogranin and [Ser1]histogranin, were recently shown to modulate NMDA receptor function. In the present study, the effects of intracerebroventricular (i.c.v.) administration of [Ser1]histogranin and of the histogranin receptor antagonist, histogranin-(1-10), were examined on step-down type passive avoidance learning in mice. [Ser1]Histogranin (30-60 nmol) impaired retention, after post-training administration, but not when it was administered just prior to the retention assay. Histogranin-(1-10) (60 nmol) facilitated learning during training, without affecting retention. Co-administration of histogranin-(1-10) with [Ser1]histogranin (60 nmol each) led to a significant prevention of [Ser1]histogranin-induced learning impairment. These results indicate that [Ser1]histogranin impairs passive avoidance learning according to the pattern of NMDA receptor antagonists and involving specific histogranin sites.
Abstract: The neuroprotective actions of cholecystokinin (CCK) peptides were investigated in a mouse hypoxia model, in which the animals were successively exposed to CO gas. Working memory impairment 5 days after CO exposure was examined by using a Y-maze test; delayed amnesia was examined 7 days after CO exposure, by using a step-down type passive avoidance test. Ceruletide (1-100 micrograms/kg, given s.c. 30 min before CO exposure) significantly prevented the CO-induced impairment of performance in both tests, the improvement being correlated with the severity of hypoxia. This severity was increased by maintaining the body temperature at 38 degrees C. Ceruletide was less effective when injected immediately after a single CO exposure. The order of potency of the CCK-peptides administered systemically was: ceruletide > CCK-8S > CCK-8NS >> CCK-4. Ceruletide (0.03-0.3 micrograms/mouse) and CCK-8S (0.03-1 microgram/mouse) prevented CO-induced amnesia after i.c.v. administration. Under all experimental conditions, dizocilpine [MK-801, (+)-5-methyl-10,11-dihydro-5H-dibenzo(a,d)cyclohepten-5,10-imine maleate, 500 micrograms/kg s.c. or 10 micrograms/mouse i.c.v.] prevented completely the CO-induced amnesia. The protective effects of systemic ceruletide were blocked, partially but significantly, by the preadministration of L-364,718 (3S-(-)-N-[2,3-dihydro-1-methyl-2-oxo-S-phenyl-1H-1,4- benzodiazepine-3-yl]-1H-indole-2-carboxamide, 1-10 mg/kg i.p.), a selective CCK-A receptor antagonist. L-365,260 ([3R-(+)-2,3-dihydro-1-methyl-2-oxo-5-phenyl-1H-1,4-benzodiazepine-3-yl] -N' - [3-methyl-phenyl]urea), a CCK-B antagonist, also decreased ceruletide-induced protection.(ABSTRACT TRUNCATED AT 250 WORDS)
Abstract: The potentiating effect of low doses of sigma ligands on the N-methyl-D-aspartate (NMDA)-induced excitation of pyramidal CA3 dorsal hippocampal neurons has recently been reported. In the present study, we investigated behavioral effects relevant to these findings in the experimental amnesia induced by the non-competitive NMDA antagonist, dizocilpine (MK-801), in mice. At doses below 1 mg/kg s.c., the sigma ligands, 1,3-di-(2-tolyl)guanidine (DTG), (+)-SKF 10,047, and (+)-pentazocine, but not their (-)-isomers, significantly decreased MK-801 (100 microgram/kg s.c.)-induced impairment of spontaneous alternation performances in 8-min sessions of a Y-maze exploration, an index of spatial working memory, without affecting the concomitant hyperlocomotion. The effect of DTG (100 micrograms/kg s.c.) was completely antagonized by the simultaneous administration of BMY 14802 (10 mg/kg i.p.) and NE-100 (1 mg/kg i.p.), two putative sigma antagonists, which had no effect by themselves. In long-term memory tests (step-down and step-through types of passive avoidance, elevated plus-maze), DTG exhibited a significant attenuation of MK-801-induced amnesia, at doses of 10 and 100 micrograms/kg s.c. In all tests of short- and long-term memory, the effects exhibited by the sigma ligands tested had a bell-shaped curve; no effect was seen at 1 mg/kg. DTG did not affect the impairment of alternation induced by CPP (5 mg/kg i.p.): the modulation may selectively target the blockade of NMDA receptor-associated ion channels. Moreover, DTG (1-1000 micrograms/kg) did not affect the impairment induced by scopolamine (1 mg/kg i.p.) or diazepam (4 mg/kg i.p.), but significantly prevented the impairment induced by mecamylamine (10 mg/kg i.p.). These results suggest that the potentiating effect of sigma ligands on NMDA receptor-mediated glutamatergic neurotransmission, already demonstrated electrophysiologically, may have some relevance to learning and memory processes in the hippocampus. A similar modulation may also affect cholinergic nicotinic systems.
Abstract: We investigated the effect of the sigma selective PCP derivative PRE-084 on the impairment of learning induced in mice by the noncompetitive NMDA antagonist MK-801. Learning capacities were evaluated using the spontaneous alternation in a Y-maze test for spatial working memory, the step-down passive avoidance and the elevated plus-maze test for long-term memory. At doses about 1 mg/kg IP, PRE-084 significantly attenuated MK-801 (0.2 mg/kg IP) induced impairment of learning. The dose-response curve was bell-shaped which is typical for cognition enhancers. The effect of PRE-084 was antagonized by BMY-14802 (10 mg/kg IP) and suppressed by a chronic treatment with haloperidol (4 mg/kg/day SC for 7 days). Furthermore, PRE-084 did not affect scopolamine (1 mg/kg SC) induced amnesia but significantly attenuated mecamylamine (10 mg/kg IP) induced amnesia. These results show that sigma sites mediate a modulation of the NMDA receptor complex-dependent learning processes and may similarly affect the cholinergic nicotinic memory processes. Moreover, the PCP derivative PRE-084, acting selectively at sigma sites, reverses the amnesia induced by a drug acting at the PCP site.
Abstract: MK-801 (30-100 micrograms/kg, SC) impaired spontaneous alternation behavior of mice, a behavior related to the spatial working memory. 1,3-Di-(2-tolyl)guanidine (DTG), (+)-pentazocine and (+)-SKF 10,047 (100 micrograms/kg, SC), putative sigma agonists, administered 10 min before MK-801, partially but significantly reversed the impairment, without affecting the concomitant hyperlocomotion. The antagonizing effects by DTG were prevented by BMY-14802 (5 mg/kg, IP), a purported sigma antagonist. These findings suggest that, at low doses, sigma ligands may modulate the N-methyl-D-aspartate dependent memory processes.
Abstract: This study examined the effect of low doses of sigma ligands on amnesia induced in mice by successive carbon monoxide (CO) exposure. Mice were exposed three consecutive times to CO (10 ml/min, 30-50 s) at 38 degrees C. Spatial working memory impairment was investigated 5 days later by monitoring spontaneous alternation behavior in a Y-maze. Delayed amnesia was examined 7 days after CO exposure by using a step-down passive avoidance test. The preadministration of the sigma ligand 1,3-di-(2-tolyl)guanidine (DTG), at doses of 1 to 1000 microgram/kg, s.c., 30 min before CO exposure did not affect the resulting amnesia in either test. However, when administered 30 min before the test, i.e., 5 or 7 days after CO exposure, this agent completely reversed the CO-induced decrease in alternation performance, at doses of 10 to 100 micrograms/kg. The same effect was observed with (+)-N-allylnormetazocine ((+)-SKF 10,047), at doses of 100 to 300 micrograms/kg, but not with (-)-SKF 10,047. DTG, at the same dose range that reversed the decrease in alternation, also totally reversed the CO-induced decrease in step-down latency in the passive avoidance test. The curve for these effects was bell-shaped; the effects were not observed at the dose of 1 mg/kg. Moreover, alpha-(4-fluorophenyl-2-pyrimidinyl)-1-piperazine butanol (BMY 14802), a putative sigma antagonist (1-10 mg/kg i.p.), did not affect CO-induced amnesia, but when simultaneously administered with DTG, it completely prevented its effect in both tests.(ABSTRACT TRUNCATED AT 250 WORDS)
Abstract: 1. [3H]N-[1-(2-Benzo(b)thiophenyl)cyclohexyl]piperidine ([3H]BTCP) labels in vivo the dopamine uptake complex in the mouse striatum. 2. In mice treated with gamma-butyrolactone (GBL, 400 mg/kg), [3H]BTCP specific binding was increased and ID50 values of BTCP and cocaine for the prevention of [3H]BTCP binding were significantly lowered. 3. In GBL-treated mice, cocaine (5 mg/kg, s.c.) had no effect on the BTCP ID50 value, whereas GBR 12783 (2 mg/kg, s.c.) increased it significantly. 4. Thus in vivo, endogenous dopamine and cocaine are competitive and non-competitive inhibitors, respectively, of the binding of [3H]BTCP.
Abstract: N-[1-(2-Benzo[b]thiophenyl)cyclohexyl]piperidine (BTCP) is a phencyclidine derivative highly selective for the dopamine (DA) uptake complex. Its effect on extracellular DA levels was studied by in vivo microdialysis on freely moving rats. In the striatum, BTCP induced a dose-dependent increase in DA levels, without affecting DA metabolites. In the nucleus accumbens, a lower increase in DA was observed, but with concomitant decreases in 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA). These experiments show that the effects of BTCP on extracellular DA levels are significantly different on extrapyramidal and mesolimbic dopaminergic terminals.
Abstract: The phencyclidine (PCP) derivative, [3H]N-[1-(2-benzo[b]thiophenyl)cyclohexyl]piperidine ([3H]BTCP), was used to label in vivo the dopamine uptake complex in mouse brain. The striatum accumulated the highest level of total and specific binding. Drugs which bind to the dopamine uptake site inhibited [3H]BTCP binding on an order similar to their in vitro affinities for the high-affinity [3H]BTCP site. Drugs which label selectively other monoamine uptake complexes. PCP, or sigma recognition sites were ineffective at doses up to 40 mg/kg. PCP bound to and dissociated from the dopamine uptake complex very rapidly. N-[1-(2-Thienyl)cyclohexyl]pideridine (TCP) and (+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine maleate (MK-801) had no effect at any time or at any dose. These results imply that the pharmacological effects of PCP are due to its simultaneous interaction with the dopamine uptake complex and the PCP receptor. Conversely, TCP and MK-801, which have the same behavioral properties as PCP, exert their action only through the interaction with the PCP receptor.
Abstract: The effects of N-[1-(2-benzo(b)thiophenyl)cyclohexyl]piperidine (BTCP) and desipramine on [3H]N-[1-(2-thienyl)cyclohexyl]piperidine ([3H]TCP) binding were investigated in vivo and in vitro. In the cerebrum, both drugs were competitive inhibitors of high-affinity [3H]TCP binding. Conversely, in the cerebellum, they were non-competitive inhibitors of low-affinity [3H]TCP binding. These results imply that the different [3H]TCP binding sites have distinct pharmacological properties, and show that, although chemically related to TCP, BTCP has an effect similar to that of desipramine.
Abstract: The modulation by dopamine of the binding of [3H]BTCP to the dopamine (DA) uptake complex was investigated in vivo (in control, reserpine- and L-DOPA-treated mice) and in vitro (on membrane preparations of the striatum of the rat). In both cases increasing doses of DA exerted a non-competitive inhibition of binding of [3H]BTCP, with a Ki value close to its K0.5, determined in competition experiments. Amphetamine and cocaine were also non-competitive inhibitors of the binding of [3H]BTCP, while GBR 12783 was competitive. In the presence of DA, the amount of cocaine required to inhibit the binding of [3H]BTCP was increased both in vitro and in vivo. These results suggest that inhibitors of the uptake of DA, such as BTCP or GBR 12783, modulate allosterically the uptake of DA, by binding to a site different from the DA recognition site. Cocaine, however, seems to share the same recognition site as DA.
Abstract: The phencyclidine (PCP) derivative N-[1-(2-thienyl)cyclohexyl]-piperidine (3H-TCP) was used to label in vivo the N-methyl-D-aspartate (NMDA) receptor-associated ionic channel in the mouse brain. After the injection of a tracer dose of 3H-TCP, a spread labeling throughout the brain was observed, but was the highest in the cerebellum. Preadministration of unlabeled TCP (30 mg/kg) resulted in a 90% reduction of 3H-TCP binding. PCP, TCP, MK-801, dexoxadrol, ketamine, and SKF 10,047 isomers dose-dependently prevented the in vivo 3H-TCP binding. ID50 determined in the cerebrum and the cerebellum were respectively correlated with K0.5 for 3H TCP high (rat cortex) and low affinity (rat cerebellum) sites in vitro. The pharmacological specificity of the 3H-TCP binding site in the cerebellum was significantly different from that in the cerebrum. ID50 values were generally higher than in the cerebrum and, particularly, MK-801, the most potent drug in the cerebrum, was without significant effect in the cerebellum, at any time and at doses as high as 30 mg/kg. N-[1-(2-benzo(b) thiophenyl)cyclohexyl]piperidine (BTCP), desipramine, and atropine showed a more efficient prevention of 3H-TCP binding in the cerebellum than in the cerebrum. The prevention of the binding by TCP or PCP, at doses close to their ID50 values, was rapid and then decreased slowly. The effect of MK-801 was long-lasting. This study confirm previous in vitro studies: 3H-TCP is an efficient tool for the labeling of the NMDA receptor-associated ionic channel.(ABSTRACT TRUNCATED AT 250 WORDS)
Abstract: We have previously demonstrated that exogenous ATP can give medullary thymocytes the calcium message required for the induction of their blastogenesis. In the present study, using the highly sensitive calcium indicator Indo-1, we have measured the effect of exogenous nucleotides on the cytosolic-free calcium concentration [Ca2+]i of thymocytes, and determined inositol phosphate (IP) formation in the same cells, in parallel assays. The results were compared to those obtained with the mitogenic lectin concanavalin A (ConA) in similar experiments. They show that ATP does not mobilize calcium from its internal stores but stimulates its influx from the extracellular medium. Nevertheless, these data do not rule out the possibility that the nucleotide acts through specific P2 purinergic sites.
Abstract: [3H]BTCP ([3H]N-[1-(2-benzo(b)thiophenyl)cyclohexyl]piperidine), a phencyclidine (PCP) derivative which binds with a high affinity to the dopamine (DA) uptake complex in vitro, has been tested for in vivo binding to mouse brain. Using [3H]BTCP as a tracer (5 microCi, i.v.) we found the striatum as the region which accumulated the largest amount of radioactivity (58 dpm/mg tissue). In other brain regions the radioactive level (about 20 dpm/mg tissue) was close to the non-specific binding determined by an injection of unlabeled BTCP (40 mg/kg, s.c.) 2 h prior to the [3H]BTCP injection. In the striatum [3H]BTCP binding was inhibited in a dose-dependent manner by unlabeled BTCP (ID50 = 6.34 mg/kg) and nomifensine (ID50 = 11.06 mg/kg). It was unaffected by the DA receptor antagonist haloperidol and by PCP or its analog TCP at doses of 10 mg/kg. These results suggest that [3H]BTCP binds to the dopamine uptake complex in the mouse brain in vivo. Thus, although PCP has no effect on [3H]BTCP binding in these experimental conditions, this in vivo binding model will be useful for the determination of the precise interaction of PCP and its derivatives with the striatal dopamine uptake complex in vivo independently of their interaction with the N-methyl-D-aspartate receptor-channel complex.
