Giuseppe Di Giovanni

Abstract: Episodic ataxia type 1 (EM) is an autosomal dominant neurological disorder characterized by myokymia and attacks of ataxic gait often precipitated by stress. Several genetic mutations have been identified in the Shaker-like K+ channel Kv1.1 (KCNA1) of EA1 individuals, including V408A, which result in remarkable channel dysfunction. By inserting the heterozygous V408A, mutation in one Kv1.1 allele, a mouse model of EA1 has been generated (Kv1.1(V408A/+)). Here, we investigated the neuromuscular transmission of Kv1.1(V408A/+) ataxic mice and their susceptibility to physiologically relevant stressors. By using in vivo preparations of lateral gastrocnemius (LG) nerve-muscle from Kv1.1(+/+) and Kv(1.1V408A/+) mice, we show that the mutant animals exhibit spontaneous myokymic discharges consisting of repeated singlets, duplets or multiplets, despite motor nerve axotomy. Two-photon laser scanning microscopy from the motor nerve, ex vivo, revealed spontaneous Ca2+ signals that occurred abnormally only in preparations dissected from Kv1.1V(408A/+) mice. Spontaneous bursting activity, as well as that evoked by sciatic nerve stimulation, was exacerbated by muscle fatigue, ischemia and low temperatures. These stressors also increased the amplitude of compound muscle action potential. Such abnormal neuromuscular transmission did not alter fiber type composition, neuromuscular junction and vascularization of LG muscle, analyzed by light and electron microscopy. Taken together these findings provide direct evidence that identifies the motor nerve as an important generator of myokymic activity, that dysfunction of Kv1.1 channels alters Ca2+ homeostasis in motor axons, and also strongly suggest that muscle fatigue contributes more than PNS fatigue to exacerbate the myokymia/neuromyotonia phenotype. More broadly, this study points out that juxtaparanodal K+ channels composed of Kv1.1 subunits exert an important role in dampening the excitability of motor nerve axons during fatigue or ischemic insult. (C) 2012 Elsevier Inc. All rights reserved.

Abstract: Oxidant molecules generated during neuronal metabolism appear to play a significant role in the processes of aging and neurodegeneration. Increasing experimental evidence suggests the noteworthy relevance of the intracellular reduction-oxidation (redox) balance for the dopaminergic (DA-ergic) neurons of the substantia nigra pars compacta. These cells possess a distinct physiology intrinsically associated with elevated reactive oxygen species production, conferring on them a high vulnerability to free radical damage, one of the major causes of selective DA-ergic neuron dysfunction and degeneration related to neurological disorders such as Parkinson�s disease. Tyrosine hydroxylase (tyrosine 3-monooxygenase; E.C. 1.14.16.2; TH) activity represents the rate-limiting biochemical event in DA synthesis. TH activity, metabolism and expression are finely tuned by several regulatory systems in order to maintain a crucial physiological condition in which DA synthesis is closely coupled to its secretion. Alterations of these regulatory systems of TH functions have indeed been thought to be key events in the DA-ergic degeneration. TH has seven cysteine residues presenting thiols. Depending on the oxido-reductive (redox) status of the cellular environment, thiols exist either in the reduced form of free thiols or oxidized to disulfides. The formation of disulfides in proteins exerts critical regulatory functions both in physiological and in pathological conditions when oxidative stress is sustained. Several reports have recently shown that redox state changes of thiol residues, as consequence of an oxidative injury, can directly or indirectly affect the TH activity, metabolism and expression. The major focus of this review, therefore, is to report recent evidence on the redox modulation of TH activity and expression, and to provide an overview of a cellular phenomenon that might represent a target for new therapeutic strategies against the DA-ergic neurodegenerative disorders.

Abstract: Metabotropic glutamate receptors (mGluRs) play a crucial role in regulation of phasic inhibition within the visual thalamus. Here we demonstrate that mGluR-dependent modulation of interneuron GABA release results in dynamic changes in extrasynaptic GABA(A) receptor (eGABA(A)R)-dependent tonic inhibition in thalamocortical (TC) neurons of the rat dorsal lateral geniculate nucleus (dLGN). Application of the group I selective mGluR agonist dihydroxyphenylglycine produces a concentration-dependent enhancement of both IPSC frequency and tonic GABA(A) current (I(GABA)tonic) that is due to activation of both mGluR1a and mGluR5 subtypes. In contrast, group II/III mGluR activation decreases both IPSC frequency and I(GABA)tonic amplitude. Using knock-out mice, we show that the mGluR-dependent modulation of I(GABA)tonic is dependent upon expression of delta-subunit containing eGABA(A)Rs. Furthermore, unlike the dLGN, no mGluR-dependent modulation of I(GABA)tonic is present in TC neurons of the somatosensory ventrobasal thalamus, which lacks GABAergic interneurons. In the dLGN, enhancement of IPSC frequency and I(GABA)tonic by group I mGluRs is not action potential dependent, being insensitive to TTX, but is abolished by the L-type Ca2+ channel blocker nimodipine. These results indicate selective mGluR-dependent modulation of dendrodendritic GABA release from F2-type terminals on interneuron dendrites and demonstrate for the first time the presence of eGABA(A)Rs on TC neuron dendritic elements that participate in �triadic� circuitry within the dLGN. These findings present a plausible novel mechanism for visual contrast gain at the thalamic level and shed new light upon the potential role of glial ensheathment of synaptic triads within the dLGN.

Abstract: Several recent studies have emphasized a crucial role for the nitrergic system in movement control and the pathophysiology of the basal ganglia (BG). These observations are supported by anatomical evidence demonstrating the presence of nitric oxide synthase (NOS) in all the basal ganglia nuclei. In fact, nitrergic terminals have been reported to make synaptic contacts with both substantia nigra dopamine-containing neurons and their terminal areas such as the striatum, the globus pallidus and the subthalamus. These brain areas contain a high expression of nitric oxide (NO)-producing neurons, with the striatum having the greatest number, together with important NO afferent input. In this paper, the distribution of NO in the BG nuclei will be described. Furthermore, evidence demonstrating the nitrergic control of BG activity will be reviewed. The new avenues that the increasing knowledge of NO in motor control has opened for exploring the pathophysiology and pharmacology of Parkinson�s disease and other movement disorders will be discussed. For example, inhibition of striatal NO/guanosine monophosphate signal pathway by phosphodiesterases seems to be effective in levodopa-induced dyskinesia. However, the results of experimental studies have to be interpreted with caution given the complexities of nitrergic signalling and the limitations of animal models. Nevertheless, the NO system represents a promising pharmacological intervention for treating Parkinson�s disease and related disorders.

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Abstract: The interaction between serotonin (5-HT) and dopamine (DA)-containing neurons in the brain is a research topic that has raised the interest of many scientists working in the field of neuroscience since the first demonstration of the presence of monoamine-containing neurons in the mid 1960. The bulk of neuroanatomical data available clearly indicate that DA-containing neurons in the brain receive a prominent innervation from serotonin (5-hydroxytryptamine, 5-HT) originating in the raphe nuclei of the brainstem. Compelling electrophysiological and neurochemical data show that 5-HT can exert complex effects on the activity of midbrain DA neurons mediated by its various receptor subtypes. The main control seems to be inhibitory, this effect being more marked in the mesocorticolimbic DA system as compared to the DA nigrostriatal system. In spite of a direct effect of 5-HT by its receptors located on DA cells, 5-HT can modulate their activity indirectly, modifying gamma-aminobutyric (GABA)-ergic and glutamatergic input to the ventral tegmental area (VTA) and substantia nigra pars compacta (SNc). Although 5-HT/DA interaction in the brain has been extensively studied, much work remains to be done to clarify this issue. The recent development of subtype-selective ligands for 5-HT receptors will not only allow a detailed understanding of this interaction but also will lead to the development of new treatment strategies, appropriate for those neuropsychiatric disorders in which an alteration of the 5-HT/DA balance is supposed.

Abstract: Nicotine, the main psychoactive ingredient in tobacco, stimulates dopamine (DA) function, increasing DA neuronal activity and DA release. DA is involved in both motor control and in the rewarding and reinforcing effects of nicotine; however, the complete understanding of its molecular mechanisms is yet to be attained. Substantial evidence indicates that the reinforcing properties of drugs of abuse, including nicotine, can be affected by the nitric oxide (NO) system, which may act by modulating central dopaminergic function. In this study, using single cell recordings in vivo coupled with microiontophoresis and microdialysis in freely moving animals, the role of NO signaling on the hyperactivation elicited by nicotine of the nigrostriatal system was investigated in rats. Nicotine induced a dose-dependent increase of the firing activity of the substantia nigra pars compacta (SNc) DA neurons and DA and 3,4-dihydroxyphenylacetic acid (DOPAC) release in the striatum. Pharmacological manipulation of the NO system did not produce any change under basal condition in terms of neuronal discharge and DA release. In contrast, pretreatments with two NO synthase (NOS) inhibitors, N-omega-nitro-l-arginine methyl ester (l-NAME) and 7-nitroindazole (7-NI) were both capable of blocking the nicotine-induced increase of SNc DA neuron activity and DA striatal levels. The effects of nicotine in l-NAME and 7-NI-pretreated rats were partially restored when rats were pretreated with the NO donor molsidomine. These results further support the evidence of an important role played by NO on modulation of dopaminergic function and drug addiction, thus revealing new pharmacological possibilities in the treatment of nicotine dependence and other DA dysfunctions.

Abstract: It has been recently shown that the substantia nigra pars reticulata (SNr) of 6-hydroxydopamine (6-OHDA)-lesioned rats, under urethane anaesthesia, manifests a prominent low frequency oscillation (LFO) of around 1 Hz, synchronized with cortical slow wave activity (SWA). Nevertheless, it is poorly understood whether these electrophysiological alterations are correlated only with severe dopamine depletion or may also play a relevant pathogenetic role in the early stages of the dopamine denervation. Hence, here we recorded SNr single units and electrocorticogram (ECoG) in two models of dopamine denervation: (i) acute dopamine denervated rats, obtained by injection of tetrodotoxin (TTX), (ii) chronic dopamine depleted rats, 2 weeks after 6-OHDA lesioning. Both TTX and 6-OHDA were infused into the medial forebrain bundle (MFB). The acute TTX-mediated dopamine depletion caused a fast developing occurrence of a SNr/ECoG coherence, peaking between 0.48 and 1.22 Hz, parallel with a consistent decrease of firing rate (from 22.61 +/- 7.04 to 15.35 +/- 9.04 Hz) homolateraly to the infusion. Strikingly, this abnormal 1 Hz synchronization, TTX-mediated was qualitatively similar to the ECoG/SNr synchronization detectable in the 6-OHDA lesioned hemisphere (LH). In addition, TTX infusion in the un-lesioned hemispheres (UH) of 6-OHDA treated rats, produced ECoG/SNr synchronization qualitatively similar to that recordable in the LH. Hence, our data support the proposition that LFO, is tightly correlated to cortex, and represent a critical hallmark of a basal ganglia (BG) failure from the early stages of dopamine denervation. (C) 2010 Elsevier Inc. All rights reserved.

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Abstract: Parkinson�s disease (PD) is the second most common neurodegenerative disease, which unfortunately is still fatal. Since the discovery of dopamine (DA) neuronal cell loss within the substantia nigra in PD, the past decades have seen the understanding of the pathophysiological mechanisms underlying the degenerative process advance at a very impressive rate. Nevertheless, there is at present no cure for PD. Although there are no proven therapies for prevention, a large body of evidence from animal studies has highlighted the paramount role of dietary factors in counteracting DA degeneration. Consistently, associations between the risk of developing PD and the intake of nutrients, individual foods, and dietary patterns have been recently shown. Therefore, promoting healthy lifestyle choices such as a Mediterranean diet might be the key to reducing the risk of PD.

Abstract: There is extensive evidence that oxidative damage of dopamine (DA)-containing neurons in the substantia nigra pars compacta (SNc) may contribute to the pathogenesis of Parkinson�s disease (PD). We evaluated the potential neuroprotective effect of diets enriched with wild-type Red Setter (RS) tomato or transgenic High Carotene (HC) tomato, rich in beta-carotene, obtained by the activation of lycopene beta-cyclase (tlcy-b), in an animal model of PD. Male Fischer 344 rats were fed for 14 days with standard Altromin(MT) diet, 5% RS- or 5% HC-enriched diet. Seven days after the beginning of this diet regimen, the rats were lesioned by 6-hydroxydopamine (6-OHDA) injected into the left SNc. After further 7 days, the rats were sacrificed, and DA and 3,4-dihydroxyphenylacetic acid (DOPAC) levels in both the left (ipsilateral) and the right (contralateral) striata were measured. Striatal DA levels were reduced by 86.5 +/- 5.0% in control, 86.2 +/- 5.0% in HC-, and 56.0 +/- 9.0% in RS- fed group. Striatal DOPAC was decreased by 85.6 +/- 5.0% in controls, 83.0 +/- 6.0% in HC-, and 58.9 +/- 10.0% in RS- fed group. Blood was obtained from the rats on day 14 and the plasma level of licopene and beta-carotene was measured by liquid chromatography-atmospheric pressure chemical ionization-mass spectrometry (LC-APCI-MS) for the determination of lycopene and beta-carotene levels. The plasma level of lycopene was 4.7 +/- 0.2 ng/ml in 5% RS- fed rats, while it was undetectable (< 2.5 ng ml(-1)) in control and HC- fed rats. The efficacy of RS diet to preserve striatal dopaminergic innervation can be attributed to the ability of lycopene to prevent the degeneration of DA-containing neurons in the SNc.

Abstract: 6-Hydroxydopamine (6-OHDA) is a neurotoxic compound commonly used to induce dopamine (DA) depletion in the nigrostriatal system, mimicking Parkinson�s disease (PD) in animals. The aim of the present study was to evaluate the 7-day effect of unilateral nigral lesion on rat brain monoamine neurochemistry. Five brain regions were examined: the brain stem, cerebellum, hippocampus, striatum, and cortex. 6-OHDA-unilateral lesion dramatically modified DA, serotonin (5-HT) and their metabolites contents in both sides of the different brain nuclei. Furthermore, unilateral 6-OHDA lesion reduced DA and 5-HT contents and produced a robust inversion of their turnover in the nonlesioned side compared to sham-operated rats. These data suggest that 6-OHDA unilateral nigral lesion produces bilateral monoamine level modifications, and this piece of evidence should be taken into account when one interprets data from animal models of unilateral PD.

Abstract: Parkinson�s disease (PD) is a progressive neurodegenerative disorder that is primarily characterized by the degeneration of dopamine (DA) neurons in the nigrostriatal system, which in turn produces profound neurochemical changes within the basal ganglia, representing the neural substrate for parkinsonian motor symptoms. The pathogenesis of the disease is still not completely understood, but environmental and genetic factors are thought to play important roles. Research into the pathogenesis and the development of new therapeutic intervention strategies that will slow or stop the progression of the disease in human has rapidly advanced by the use of neurotoxins that specifically target DA neurons. Over the years, a broad variety of experimental models of the disease has been developed and applied in diverse animal species. The two most common toxin models used employ 6-hydroxydopamine (6-OHDA) and the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine/1-methyl-4-phenilpyridinium ion (MPTP/MPP(+)), either given systemically or locally applied into the nigrostriatal pathway, to resemble PD features in animals. Both neurotoxins selectively and rapidly destroy catecolaminergic neurons, although with different mechanisms. Since in vivo microdialysis coupled to high-performance liquid chromatography is an established technique for studying physiological, pharmacological, and pathological changes of a wide range of low molecular weight substances in the brain extracellular fluid, here we review the most prominent animal and human data obtained by the use of this technique in PD research.

Abstract: The present study was undertaken to explore the involvement of nitric oxide (NO) in the 6-hydroxydopamine (6-OHDA) experimental model of Parkinson�s disease (PD) in rats. The effect of pharmacological manipulation of the NO system was evaluated on striatal dopamine (DA) level decrease produced by the toxin. 7-nitroindazole (7-NI, 50 mg/kg i.p.; n = 5) pretreatment significantly restored the striatal DA contents. Conversely, 40 mg/kg i.p. of molsidomine (MOL, it = 5), an NO donor, significantly worsened the neurodegeneration (n = 5) and completely counteracted the neuroprotective effect of 7-NI (n = 5). Thus, a crucial role for NO in 6-OHDA induced neurodegeneration is suggested together with a protective benefit for inhibitors of NOS in the treatment of PD.

Abstract: Tumor necrosis factor (TNF)-alpha is a proinflammatory cytokine acting on two distinct receptor subtypes, namely p55 and p75 receptors. TNF-alpha p55 and p75 receptor knockout mice were previously shown to display a decreased or enhanced susceptibility to seizures, respectively, suggesting intrinsic modifications in neuronal excitability. We investigated whether alterations in glutamate system function occur in these naive knockout mice with perturbed cytokine signaling that could explain their different propensity to develop seizures. Using Western blot analysis of hippocampal homogenates, we found that p55(-/-) mice have decreased levels of membrane GluR3 and NR1 glutamate receptor subunits while GluR1, GluR2, GIuR6/7 and NR2A/B were unchanged as compared to wild-type mice. In p75(-/-) mice, GluR2, GluR3, GluR6/7 and NR2AJB glutamate receptor subunits were increased in the hippocampus while GluR1 and NR1 did not change. Extracellular single-cell recordings of the electrical activity of hippocampal neurons were carried out in anesthetized mice by standard electrophysiological techniques. Microiontophoretic application of glutamate increased the basal firing rate of hippocampal neurons in p75(-/-) mice versus wild-type mice, and this effect was blocked by 2-amino-5-phosphopentanoic acid and 6-nitro-7-sulfamoyl-benzo(f)quinoxaline-2,3-dione denoting the involvement of N-methyl-D-aspartic acid and AMPA receptors. In p55(-/-) mice, hippocampal neurons responses to glutamate were similar to wild-type mice. Spontaneous glutamate release measured by in vivo hippocampal microdialysis was significantly decreased only in p55(-/-) mice. No changes were observed in KCl-induced glutamate release in both receptor knockout mice strains versus wild-type mice. These findings highlight specific molecular and functional interactions between p55 and p75 receptor-mediated signaling and the glutamate system. These interactions may be relevant for controlling neuronal excitability in physiological and pathological conditions. (C) 2009 IBRO. Published by Elsevier Ltd. All rights reserved.

Abstract: Nitric oxide (NO) plays an important role in the integration of information processed by the basal ganglia nuclei. Accordingly, considerable evidence has emerged indicating a role for NO in pathophysiological conditions such as Parkinson�s disease (PD) and other neurodegenerative disorders. Despite these recent advances, the nitrergic modulation of the dopamine (DA) nigrostriatal system is still unclear. In order to fill this gap, in this study we used in vivo electrophysiology and ex vivo neurochemical analysis to further investigate the effect of NO signaling in rat substantia nigra pars compacta (SNc) and the striatum. Acute and subchronic (4 days) pharmacological manipulation of the NO system using 7-nitroindazole (7-NI, 50 mg kg(-1) i.p.) and molsidomine (MOL, 40 mg kg(-1) i.p.) treatment caused significant changes in both DA SNc neurons electrophysiological properties and striatal DA and 3,4-dihydroxyphenylacetic acid (DOPAC) levels. It is worth noting that acute inhibition of NO production decreased DA nigrostriatal neurotransmission while its subchronic inhibition was instead excitatory. Thus, a crucial role for NO in the modulation of nigrostriatal DA function is suggested together with a potential role for inhibitors of NO sythase in the treatment of PD.

Abstract: The impact of serotonergic neurotransmission on brain dopaminergic pathways has substantial relevance to many neuropsychiatric disorders. A particularly prominent role has been ascribed to the inhibitory effects of serotonin 2C receptor (5-HT(2C)R) activation on physiology and behavior mediated by the mesolimbic dopaminergic pathway, particularly in the terminal region of the nucleus accumbens. The influence of this receptor subtype on functions mediated by the nigrostriatal dopaminergic pathway is less clear. Here we report that a null mutation eliminating expression of 5-HT(2C)Rs produces marked alterations in the activity and functional output of this pathway. 5-HT(2C)R mutant mice displayed increased activity of substantia nigra pars compacta (SNc) dopaminergic neurons, elevated baseline extracellular dopamine concentrations in the dorsal striatum (DSt), alterations in grooming behavior, and enhanced sensitivity to the stereotypic behavioral effects of D-amphetamine and GBR 12909. These psychostimulant responses occurred in the absence of phenotypic differences in drug-induced extracellular dopamine concentration, suggesting a phenotypic alteration in behavioral responses to released dopamine. This was further suggested by enhanced behavioral responses of mutant mice to the D(1) receptor agonist SKF 81297. Differences in DSt D(1) or D(2) receptor expression were not found, nor were differences in medium spiny neuron firing patterns or intrinsic membrane properties following dopamine stimulation. We conclude that 5-HT(2C)Rs regulate nigrostriatal dopaminergic activity and function both at SNc dopaminergic neurons and at a locus downstream of the DSt.

Abstract: Previous neurochemical and behavioral studies suggest that muscarinic receptor antagonism has an excitatory effect on the nigrostriatal dopamine (DA) system. Using in vivo extracellular single unit recording, this study examined whether blockade of the muscarinic receptor by scopolamine alters the firing properties of DA neurons in the substantia nigra (SN). Scopolamine was administered either systemically or locally to DA neurons using microiontophoresis. Surprisingly, scopolamine did not cause any significant change in either the firing rate or pattern of the spontaneously active DA neurons. However, systemic injection of scopolamine significantly increased the number of active DA neurons in the SN. Local infusion of scopolamine into the pedunculopontine tegmental nucleus (PPT) mimicked the effect induced by systemically administered scopolamine, significantly increasing the number of active DA neurons without altering the firing rate and pattern. These results suggest that the reported increase in striatal DA release induced by scopolamine is in part mediated by activation of silent nigral DA neurons. The experiments with PPT local infusion further suggest that part of the effect of scopolamine may be due to its blockade of the inhibitory muscarinic autoreceptors on PPT cholinergic cells. The latter effect may lead to activation of quiescent DA neurons by increasing acetylcholine (ACh) release in the SN or in other brain areas providing inputs to DA neurons. Further understanding of the mechanism of action of scopolamine may help us further understand the role of ACh in both the pathophysiology and treatment of DA-related disorders including schizophrenia and Parkinson�s disease. Synapse 63:673-680, 2009. (c) 2009 Wiley-Liss, Inc.

Abstract: The cellular mechanisms underlying typical absence seizures, which characterize various idiopathic generalized epilepsies, are not fully understood, but impaired gamma-aminobutyric acid (GABA)-ergic inhibition remains an attractive hypothesis. In contrast, we show here that extrasynaptic GABA(A) receptor-dependent �tonic� inhibition is increased in thalamocortical neurons from diverse genetic and pharmacological models of absence seizures. Increased tonic inhibition is due to compromised GABA uptake by the GABA transporter GAT-1 in the genetic models tested, and GAT-1 is crucial in governing seizure genesis. Extrasynaptic GABA(A) receptors are a requirement for seizures in two of the best characterized models of absence epilepsy, and the selective activation of thalamic extrasynaptic GABA(A) receptors is sufficient to elicit both electrographic and behavioral correlates of seizures in normal rats. These results identify an apparently common cellular pathology in typical absence seizures that may have epileptogenic importance and highlight potential therapeutic targets for the treatment of absence epilepsy.

Abstract: In this review, the most relevant data regarding serotonin (5-hydroxytryptamine, 5-HT)/dopamine (DA) interaction in the brain, as studied by both in vivo and in vitro electrophysiological methods, are reported and discussed. The bulk of neuroanatomical data available clearly indicate that DA-containing neurons in the brain receive a prominent innervation from 5-HT originating in the raphe nuclei of the brainstem. Furthermore, this modulation seems to be reciprocal; DA neurons innervate the raphe nuclei and exert a tonic excitatory effect on them. Compelling electrophysiological data show that 5-HT can exert complex effects on the electrical activity of midbrain DA neurons mediated by the various receptor subtypes. The main control seems to be inhibitory, this effect being more marked in the ventral tegmental area (VTA) as compared to the substantia nigra pars compacta (SNc). In spite of a direct effect of 5-HT by its receptors located on DA cells, 5-HT can modulate their activity indirectly, modifying gamma-amino-n-butyric acid (GABA)-ergic and glutamatergic input to the VTA and SNc. Although 5-HT/DA interaction in the brain has been extensively studied, much work remains to be done to clarify this issue. The recent development of subtype-selective ligands for 5-HT receptors will not only allow a detailed understanding of this interaction but also lead to development of new treatment strategies, appropriate for those neuropsychiatric disorders in which an alteration of the 5-HT/DA balance is supposed.

Abstract: Several recent studies have emphasized a crucial role for the interactions between serotonergic and dopaminergic systems in movement control and the pathophysiology of basal ganglia. These observations are supported by anatomical evidence demonstrating large serotonergic innervation of all the basal ganglia nuclei. In fact, serotonergic terminals have been reported to make synaptic contacts with both substantia nigra dopamine-containing neurons and their terminal areas such as the striatum, the globus pallidus and the subthalamus. These brain areas contain a high concentration of serotonin (5-HT), with the substantia nigra pars reticulata receiving the greatest input. In this chapter, the distribution of different 5-HT receptor subtypes in the basal ganglia nuclei will be described. Furthermore, evidence demonstrating the serotonergic control of basal ganglia activity will be reviewed and the contribution of the different 5-HT receptor subtypes examined. The new avenues that the increasing knowledge of 5-HT in motor control has opened for exploring the pathophysiology and pharmacology of Parkinson�s disease and other movement disorders will be discussed. It is clear that these avenues will be fruitful, despite the disappointing results so far obtained by clinical studies with selective 5-HT ligands. Nevertheless, these studies have led to a great increase in the attention given to the neurotransmitters of the basal ganglia and their connections.

Abstract: In this review, the functional interactions between serotonin (5-HT) and dopamine (DA) neuronal systems are discussed with the focus on microdialysis studies in the rodent brain (mainly rats). 5-HT by itself is involved both directly and indirectly via actions on complex neuronal circuitry, in the regulation of DA release through multiple 5-HT receptors, playing a critical role in the development of normal and abnormal behaviours. Recent evidence suggests that dysfunction of dopaminergic and serotoninergic neurotransmitter systems contributes to various disorders including depression, schizophrenia, Parkinson�s disease and drug abuse. Here we summarize recent neurochemical works that have extensively explored the role of 5-HT receptors in the control of DA central systems in both basal and drug-induced conditions, using in vivo microdialytic techniques. Several 5-HT receptor subtypes, including the 5-HT(1A), 5-HT(1B), 5-HT(2A), 5-HT(3) and 5-HT(4) receptors, act to facilitate DA release, while the 5-HT(2C) receptor mediates an inhibitory effect of 5-HT on DA release. Taken together, neurochemical approaches using microdialysis can not only contribute to clarification of the physiological role of the serotonergic neuronal systems but may also be a powerful pharmacological approach for the development of therapeutic strategies to the treatment of depression, schizophrenia, Parkinson�s disease and drug abuse.

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Abstract: Parkinson�s disease (PD) is the second leading age-related degenerative brain disease in the world affecting millions of people. This neurological disorder disrupts the quality of life of patients and their families, exerts an enormous emotional and physical strain on caregivers, and has a large cost for society. Moreover, the increasing numbers of elderly people in the population will result in a sharp increase in the prevalence of PD. The understanding of its pathophysiology and treatment has advanced at a very impressive rate during past decades. Nevertheless, PD is still fatal and there is at present no cure for it. Furthermore, there are no proven therapies for prevention of PD and although evidence exists of risk and protective factors, this is not strong enough to warrant specific measures in an attempt to diminish risk or enhance protection. Drug development programmes are engaged in finding neuroprotective and neurorestorative therapies or, even better, discovering drugs able to rejuvenate the dopaminergic neurons. The latest developments in this promising field will be discussed with reference to the current literature together with the advantages and pitfalls of suggested drugs. Finally, an analysis of the role of various dietary recommendations, lifestyle, environmental and other factors in reducing the risk of PD is carried out.

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Abstract: Nicotine, the major psychoactive agent present in tobacco, acts as a potent addictive drug both in humans and laboratory animals, whose locomotor activity is also stimulated. A large body of evidence indicates that the locomotor activation and the reinforcing effects of nicotine may be related to its stimulatory effects on the mesolimbic dopaminergic function. Thus, it is now well established that nicotine can increase in vivo DA outflow in the nucleus accumbens and the corpus striatum. The stimulatory effect of nicotine on DA release most probably results from its ability to excite the neuronal firing rate and to increase the bursting activity of DA neurons in the substantia nigra pars compacta (SNc) and the ventral tegmental area (VTA), and from its stimulatory action on DA terminals in the corpus striatum and the nucleus accumbens. The neurochemical data are consistent with neuroanatomical findings showing the presence of nicotinic acetylcholine receptors (nAChRs) in the SNc, the VTA, and in projection areas of the central dopaminergic system such as the corpus striatum and the nucleus accumbens. Several lines of evidence indicate that the reinforcing properties of drugs of abuse, including nicotine, can be affected by a number of transmitter systems which may act by modulating central dopaminergic function. In this paper, the neurobiological mechanisms underlying nicotine addiction will be reviewed, and the possible strategies for new pharmacological treatments of nicotine dependence will be examined.

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Abstract: Parkinson�s disease (PD) is known to be a chronic and progressive neurodegenerative disease caused by a selective degeneration of dopaminergic (DAergic) neurons in the substantia nigra pars compacta (SNc). A large body of experimental evidence indicates that the factors involved in the pathogenesis of this disease are several, occurring inside and outside the DAergic neuron. Recently, the role of the neurron-glia interaction and the inflammatory process, in particular, has been the object of intense study by the research community. It seems to represent a new therapeutic approach opportunity for this neurological disorder. Indeed, it has been demonstrated that the cyclooxygenase type 2 (COX-2) is upregulated in SNc DAergic neurons in both PD patients and animal models of PD and, furthermore, non-steroidal anti- inflammatory drugs (NSAIDs) pre-treatment protects against 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) or 6 hydroxydopamine (6-OHDA)-induced nigrostriatal dopamine degeneration. Moreover, recent epidemiological studies have revealed that the risk of developing PD is reduced in humans who make therapeutical use of NSAIDs. Consequently, it is hypothesized that they might delay or prevent the onset of PD. However, whether or not these common drugs may also be of benefit to those individuals who already have Parkinson�s disease has not as yet been shown. In this paper, evidence relating to the protective effects of aspirin or other NSAIDs on DAergic neurons in animal models of Parkinson�s disease will be discussed. In addition, the pharmological mechanisms by which these molecules can exert their neuroprotective effects will be reviewed. Finally, epidemiological data exploring the effectiveness of NSAIDs in the prevention of PD and their possible use as adjuvants in the therapy of this neurodegenerative disease will also be examined. (c) 2007 Elsevier Inc. All rights reserved.

Abstract: Since the 1950s, when serotonin (5-HT) was discovered in the mammalian central nervous system (CNS), all enormous amount of experimental evidence has revealed the pivotal role of this biogenic amine in a number of cognitive and behavioural functions. Although 5-HT, is synthesized by a small group of neurons within the raphe nuclei of the brain stem, almost all parts of the CNS receive serotonergic projections. Furthermore, the importance of 5-HT modulation and the fine-tuning of its action is underlined by the large number of 5-HT binding sites found in the CNS. Hitherto, up to 15 different 5-HT receptors subtypes have been identified. This review was undertaken to summarize the work that has explored the pathophysiological role of one of these receptors, the 5-HT2c receptor, that has been emerged as a prominent central serotonin receptor subtype. The physiology, pharmacology and anatomical distribution of the 5-HT2c receptors in the CNS will be firstly reviewed. Finally, their potential involvement in the pathophysiology of depression, schizophrenia, Parkinson�s disease and drug abuse will be also discussed.

Abstract: The neuropathological hallmark of Parkinson�s disease (PD) is the selective degeneration of dopaminergic (DAergic) neurons in the substantia nigra pars compacta (SNc). In this study, using a microdialysis technique, we investigated whether an inhibitor of neuronal nitric oxide synthase (nNOS), 7-nitrindazole (7-NI), could protect against DAergic neuronal damage induced by in vivo infusion of 1-methyl-4-phenylpiridinium iodide (MPP+) in freely moving rats. Experiments were performed over 2 days in three groups of rats: (a) nonlesioned, (b) MPP+-lesioned, and (c) 7-NI pretreated MPP+-lesioned rats. On day 1, control rats were perfused with an artificial CSF, while 1 mM MPP+ was infused into the striatum for 10 min in the other two groups. The infusion of the MPP+ produced a neurotoxic damage of the SNc DA neurons and increased striatal DA levels. On day 2, 1 mM MPP+ was reperfused for 10 min into the striata of each rat group and DA levels were measured as an index of neuronal cell integrity. The limited rise of DA following MPP+ reperfusion in the MPP+-lesioned rats was due to toxin-induced neuronal loss and was reversed by pretreatment with 7-NI (50 mg/kg, intraperitoneally) on day 1, indicating a neuroprotective effect by inhibiting NO formation. These results indicate that neuronally derived NO partially mediates MPP+-induced neurotoxicity. The similarity between the MPP+ model and PD suggests that NO may play a significant role in its etiology.

Abstract: The basal ganglia are a highly interconnected group of subcortical nuclei in the vertebrate brain that play a critical role not only in the control of movements but also in some cognitive and behavioral functions. Several recent studies have emphasized that serotonergic pathways in the central nervous system (CNS) are intimately involved in the modulation of the basal ganglia and in the pathophysiology of human involuntary movement disorders. These observations are supported by anatomical evidence demonstrating large serotonergic innervation of the basal ganglia. In fact, serotonergic terminals have been reported to make synaptic contacts with dopaminc (DA)-containing neurons and gamma-aminobutyric acid (GABA)-containing neurons in the striatum, globus pallidus, subtlialamus and substantia nigra. These brain areas contain the highest concentration of serotonin (5-HT), with the substantia nigra pars reticulata receiving the greatest input. Furthermore, in these structures a high expression of 5-HT different receptor subtypes has been revealed. In this paper, evidence demonstrating the serotonergic control of basal ganglia functions will be reviewed, focusing on the role of the 5-HT2C receptor subtype. In addition, the involvement of 5-HT2C receptors in neurological disorders such as Parkinson�s disease and other related motor disorders, and their management with drugs blocking the 5-HT2C receptor will be discussed.

Abstract: The effect of aspirin on dopaminergic neuronal damage induced by in vivo infusion of 1-methyl-4-phenylpiridinium iodide (MPP+) and 6-hydroxydopamine (6-OHDA) was studied in rats, using microdialysis. Rat striata were perfused with 1 mM MPP+ or 6-OHDA for 10 min, causing peak levels of dopamine (DA) in the dialytic fluid, after 40 min. After 24 h, I mM MPP+ was perfused again for 10 min and DA levels measured in the dialytic fluid, as an index of neuronal cell integrity. Pretreatment with Aspidol (lysine acetylsalicylate), 180 mg/kg i.p., I h before MPP+ or 6-OHDA perfusion, did not modify DA extracellular output, on day 1, but restored MPP�-induced DA release on day 2, indicating a neuroprotective effect of Aspidol. Conversion of 0.5 mM 4-hydroxybenzoic acid (4-HBA) to 3,4-dihydroxybenzoic acid (3,4-DHBA) was measured as an index of reactive oxygen species (ROS). 6-OHDA, but not MPP+, significantly enhanced 3,4-DHBA levels in the perfusion fluid. Aspidol (180 mg/kg, i.p.) reduced 6-OHDA-dependent increase of 3,4-DHBA levels. Meloxicam (50 mg/kg, i.p.), a specific cyclooxygenase-2 (COX-2) inhibitor, was ineffective against both neurotoxins. These data suggest that the protective effect of aspirin is due to different mechanisms of action according to the neurotoxin used, and it is independent from COX-2 inhibition. (c) 2006 Elsevier B.V. All rights reserved.

Abstract: Background: Nitric oxide (NO) and cholecystokinin (CCK) are involved in the modulation of several neurotransmitter systems in the basal ganglia, and a functional interaction between their modulatory effects could be hypothesised. Materials and Methods: We studied the effects exerted by the administration of 7-nitroindazole (7-NI) (50 mg kg(-1) i.p.), a selective inhibitor of neuronal NO synthase, on the depth EEG activity of the striatum and of the globus pallidus in both not pre-treated and sulphated CCK octapeptide (CCK-8S)-treated (100 nM kg(-1) i.p.) rats. Striatal and pallidal depth EEG power spectra were examined by means of a Fast Fourier Transform analysis. Results: Striatal depth recordings showed a marked increase of % power of slow standard rhythms after 7-NI systemic treatment. In contrast, pallidal recordings revealed an increase of % power of rapid standard rhythms after i.p. injection of 7-NI. The same modifications were not evidenced in CCK-8S pre-treated rats after 7-NI administration. Conclusion: The results show an influence exerted by peripheral CCK on the nitrergic modulation of the bioelectric activities of the striatum and of the globus pallidus. This effect could be of particular interest in the light of NO and CCK involvement in the neuroprotective mechanisms.

Abstract: It is now well established that nitric oxide (NO) acts as a neuromodulator in the central nervous system. To assess the role of NO in modulating striatal activity, single-unit recording was combined with iontophoresis to study presumed spiny projection neurons in urethane-anesthetized male rats. Striatal neurons recorded were essentially quiescent and were therefore activated to fire by the iontophoretic administration of glutamate, pulsed in cycles of 30 sec on and 40 sec off. In this study, iontophoresis of 3-morpholinosydnonimine hydrochloride (SIN 1), a nitric oxide donor, produced reproducible, current-dependent inhibition of glutamate-induced excitation in 12 of 15 striatal neurons, reaching its maximal inhibitory effect (76.2 +/- 5.6% below baseline) during the application of a 100 nA current. Conversely, microiontophoretic application of N-omega-nitro-L-arginine methyl ester (L-NAME), an inhibitor of nitric oxide synthase, produced clear and reproducible excitation of glutamate evoked firing in 7 of 10 cells (51.4 +/- 2.3%, at 100 nA). To evaluate the involvement of cyclic guanosine monophosphate (cGMP) in the electrophysiological effects produced by the NO donor, the effects of methylene blue, an inhibitor of guanylyl cyclase, on the responses of nine neurons to SIN 1 were tested. In six of nine neurons the effect of SIN 1 was significantly reduced during continuous iontophoretic administration (50 nA) of methylene blue. Taken together, these data show that NO modulates the striatal network and that inhibitory control of the output neurons is involved in this effect. These results also suggest that the effects of nitric oxide on striatal neurons are partially mediated via cGMP. (C) 2003 Wiley-Liss, Inc.

Abstract: We have chosen to study the effects of both nitric oxide (NO) and cholecystokinin neuromodulatory systems in some motor structures that are frequently involved in excitotoxic phenomena. In particular, 7-nitroindazole, a selective inhibitor of neuronal NO synthase, was administered in control and sulfated cholecystokinin octapeptide-treated rats. Cortical surface, striatal and pallidal depth bioelectric activities were examined through Fast Fourier Transform analysis. Cortical and pallidal recordings revealed an increase of rapid standard rhythms after the inhibition of neuronal NO synthase; in contrast, striatal depth recordings showed a marked increase of slow standard rhythms. All these effects were completely abolished by chronic pre-treatment with sulfated cholecystokinin octapeptide. The results suggest a functional cooperation between cholecystokinin and NO systems in the modulation of the bioelectric activity of all the motor structures examined, and the possibility of preventing excitotoxic damages induced by an anomalous balance between excitatory and inhibitory neurotransmitters in these areas. (C) 2003 Elsevier Inc. All rights reserved.

Abstract: Single units were recorded in the striatum and in the globus pallidus (GP) of urethane-anesthetized rats under microiontophoretic administration of either Nomega-nitro-L-arginine methyl ester (L-NAME, inhibitor of nitric oxide synthase), or 3-morpholino-sydnonimin-hydrocloride (SIN-1, nitric oxide, NO donor). A steady baseline firing of sporadically discharging striatal neurons (basal firing rate <0.1 spikes/s) was evoked by a pulsed microiontophoretic ejection of glutamate. On striatal neurons, microiontophoretic application of SIN-I induced a current-dependent inhibition (11/13), whereas L-NAME administration produced a clear excitation (9/9). On GP cells, the administration of SIN-1 had excitatory effects (10/15), whereas the administration Of L-NAME reduced the neuronal activity (6/6). We hypothesize that NO could exert an intrinsic regulatory action on the activity of both striatal and GP cells. (C) 2003 Elsevier Science Ireland Ltd. All rights reserved.

Abstract: Clozapine and risperidone are two atypical antipsychotic drugs which bind, among other receptors, to 5-HT2c receptor subtypes. They inhibit the basal inositol phosphate production in mammalian cells expressing rat or human 5-HT2c receptors. This biochemical effect is indicative of inverse agonist activity at these receptors. There is evidence that 5-HT2c receptors are involved in the control of the activity of central dopaminergic system. Therefore, the effects of clozapine (5 mg, kg ip), risperidone (0.08 mg/kg ip) and of the typical antipsychotic haloperidol (0.1 mg/kg ip) were studied on the extracellular concentration of dopamine (DA) in the nucleus accumbens of chloral hydrate-anesthetized rats, using intracerebral microdialysis. When injected alone, clozapine, risperidone and haloperidol caused only small variations in DA efflux, However, clozapine and risperidone completely prevented the inhibitory action of RO 60-0175 (1 mg/kg ip), a 5-HT2c receptor agonist, on DA release. On the other hand, haloperidol did not affect RO 60-0175-induced decrease in DA release. Taken together, these data indicate that clozapine and risperidone, unlike haloperidol, are capable of blocking 5-HT2c receptors in the nucleus accumbens, It is concluded that the experimental model presented in this study might represent a simple and useful in vivo biochemical method to test the effect of putative atypical antipsychotic drugs on 5-HT2c receptors, (C) 2002 Elsevier Science Inc. All rights reserved.

Abstract: Rats treated with i.p. 7-NI showed a significant increase in cortical higher frequency EEG bands, associated with a corresponding and significant decrease in delta band activity. In the striatum, reduced levels of NO induced an increase in the low frequency band, and a decrease at higher frequencies. Pallidal depth recordings showed modifications to several frequency bands, similar to those found in the cortex. Altough 7-NI was administered at increasing doses (from 40 to 70 mg kg(-1)), it was not possible to demonstrate a relationship between modified band activities and the dose of 7-NI. As suggested indirectly by the quantitative EEG data reported in this study, NO plays a fundamental role in the modulation of several neurotransmitters that are functionally involved in the cortico-striato-pallidal interactions. In fact, striatal NO seems to integrate cortical-glutamatergic and nigral-dopaminergic inputs and to modulate the efferent pathway toward the globus pallidus.

Abstract: Previous observations have suggested a role for nitric oxide in the activity of the globus pallidus, but this functional involvement has not yet been tested in vivo. The extracellular activity of single units of the globus pallidus was recorded, and neuronal nitric oxide synthase was inhibited by systemically administering 7-nitro-indazole to a group of anaesthetised rats. Forty-five per cent of cells responded with a decrease in the firing rate. In another group of rats, the microiontophoretic administration of 3-morpholino-sydnonimin-hydrocloride (a nitric oxide donor) induced an increase in neuronal firing rate (24/28 cells), whereas the administration of Nomega-nitro-L-arginine methyl ester (a nitric oxide synthase inhibitor) reduced the activity of pallidal neurones (8/11 cells). No electrophysiological differences between drug-sensitive and -insensitive neurones were evidenced. An excitatory role of nitric oxide in controlling the level of spontaneous activity of globus pallidus neurones is suggested, without any influence upon the discharge pattern.

Abstract: The activity of single units in the striatum of urethane-anesthetized rats was recorded before and after the systemic administration of 7-nitro-indazole (7-NI; 50 mg/kg intraperitoneally), a selective inhibitor of neuronal nitric oxide (NO) synthase. Two neuronal types were clearly distinguishable electrophysiologically, on the basis of either discharge frequency pattern or features of the individual spike waveform (spike duration, negative phase/total duration ratio, and negative phase/total amplitude ratio). Only sporadically discharging neurons (basal firing rate, <0.1 spikes/s) were influenced by 7-NI, which caused a statistically significant increase in their firing rate. In contrast, the activity of continuously discharging neurons (basal firing rate, 4-6 spikes/s) was not affected. We hypothesize that NO neurotransmission could exert a tonic inhibitory influence upon sporadically discharging striatal neurons, which are presumably striatal output neurons. (C) 2002 Elsevier Science Ireland Ltd. All rights reserved.

Abstract: In vivo electrophysiological techniques were used to study the effect of m-chlorophenylpiperazine, a non-selective serotonin-2C receptor agonist, on the activity of non-dopaminergic neurons in the substantia nigra pars reticulata and the ventral tegmental area of anesthetized rats. Intravenous administration of m-chlorophenylpiperazine (5-320 mug/kg) caused a dose-dependent increase in the basal firing rate of a subpopulation of nigral neurons which do not respond to a footpinch stimulus [P(0) neurons], whereas it did not affect the activity of neurons which are responsive to the footpinch [P(+) neurons]. However. m-chlorophenylpiperazine (5-320 mug/kg) excited all non-dopaminergic neurons sampled in the ventral tegmental area. Moreover, microiontophoretic application of m-chlorophenylpiperazine (10-40 nA) caused an excitation of P(0) nigral and ventral tegmental area neurons. Pretreatment with the selective serotonin-2C receptor antagonist SE 242084 (200 mug/kg, i.v.) completely blocked the excitatory effect of i.v. m-chlorophenylpiperazine (5-320 mug/kg), both in the substantia nigra pars reticulata and in the ventral tegmental area. It is concluded that stimulation of serotonin-2C receptors by m-chlorophenylpiperazine activates non-dopaminergic (presumably GABA-containing) neurons in the substantia nigra pars reticulata and ventral tegmental area. (C) 2001 IBRO. Published by Elsevier Science Ltd. All rights reserved.

Abstract: The hydromethanolic extract of Hypericum perforatum has been shown to be an effective antidepressant, although its mechanism of action is still unclear. In this study, in vivo microdialysis was used to investigate the effects of Hypericum perforatum-CO2 extract on dopamine (DA), 3,4-dihydroxyphenylacetic acid (DOPAC), serotonin (5-HT), and 5-hydroxyindoleacetic acid (5-HIAA) release in various areas of brain. Administration of Hypericum perforatum extract (1 mg/kg, p.o.) caused a slight, but significant increase of DA outflow both in the nucleus accumbens and the striatum. The maximal increase of DA efflux (+19.22 +/- 1.93%, relative to the control group) in the nucleus accumbens occurred 100 min after administration of Hypericum perforatum, In the striatum, the extract maximally enhanced DA outflow (+24.83 +/- 7.49 %, relative to the control group) 80 min after administration. Extraneuronal DOPAC levels were not significantly affected by Hypericum perforatum treatment. Moreover, Hypericum perforatum (1 mg/kg, p.o.) did not produce any significant effect on either 5-HT or 5-HIAA efflux in the ventral hippocampus. This study shows for the first time that Hypericum perforatum extract is capable of increasing in vivo DA release.

Abstract: Previous studies of conventional tricyclic and non-tricyclic antidepressants have suggested that a number of these drugs display considerable pharmacological activity at 5-HT2C receptors in the brain. There:ls evidence that 5-HT2C receptors are involved in the control of the activity of the central dopaminergic system. Therefore, the effects of amitriptyline (5 mg/kg and 10 mg/kg i.p.) and of the atypical antidepressant mianserin (2.5 mg/kg and 5 mg/kg i.p.) were studied on the extracellular concentration of dopamine (DA) in the nucleus accumbens of chloral hydrate-anesthetized rats, using intracerebral microdialysis. Amitriptyline and mianserin significantly increased DA release (+31.1+/-7.9% and +33.6+/-4.3%, respectively) at the higher doses. In addition, lower doses of mianserin (2.5 mg/kg i.p.) and amitriptyline (5 mg/kg i;p.) blocked the inhibitory action of RO 60-0175 (1 mg/kg i.p.), a selective 5-HT2C receptor agonist, on DA release. The effect of RO 60-0175 (1 mg/kg i.p.) was completely blocked by SE 242084 (2.5 mg/kg i.p.), a selective and powerful 5-HT2C receptor antagonist. Taken together, these data indicate that amitriptyline and mianserin increase DA release in the nucleus accumbens by blocking 5-HT2C receptors.

Abstract: Electrophysiological and in vivo microdialysis were used to investigate and compare the effect of tonic activation of serotonin(2C/2B) (5-HT2C/2B) receptors on nigrostriatal and mesolimbic dopaminergic (DA) function. Thus, extracellular single unit recordings of neurochemically-identified DA neurons in the SNc and the VTA, as well as simultaneous monitoring of striatal and accumbal DA release were performed following the administration of the unselective 5-HT2C/2B agonists, mCPP (m-chlorophenylpiperazine) and MK 212 [6-chloro-2-(1-piperazinyl)piperazine]. Both mCPP (5-320 mu g/kg i.v.) and MK 212 (5-320 mu g/kg i.v.) dose-dependently decreased the firing rate of VTA DA neurons. The maximal effect was reached at the cumulative dose of 320 mu g/kg mCPP and MK 212, which caused a decrease of 42.6 +/- 12.8% and 56.4 +/- 12.6%, respectively. In addition, the total number of events in bursts and the number of bursts of VTA DA cells were significantly reduced by both mCPP and MK 212. On the other hand, mCPP (5-320 mu g/kg i.v.) and MK 212 (5-320 mu g/kg i.v.) induced a slight decrease in the basal firing rate, but not in bursting activity of SNc DA neurons. Consistent with electrophysiological data, dialysate DA levels in the nucleus accumbens decreased significantly, reaching the maximum of 26.6 +/- 9.6% below baseline levels 120 min after mCPP (1 mg/kg i.p.) administration, and of 25.2 +/- 5.5% 140 min after MK 212 (1 mg/kg i.p.) injection. DA outflow in the striatum was unaffected by both drugs. The inhibitory effect of both mCPP and MK 212 on VTA DA cell activity was blocked completely by pretreatment with the selective 5-HT2C antagonist SE 242084 6-chloro-5-methyl-1-[2-(2-methylpyridyl-3-oxy)pyrid-5-yl carbamoyl] indoline (200 mu g/kg), given intravenously 10 min before the first injection of the 5-HT2C/2B agonists. SE 242084 (2.5 mg/kg i.p.) antagonized also the decrease in DA release induced by mCPP and MK 212 in the nucleus accumbens. Taken together, these data indicate that mCPP and MK 212 selectively inhibit mesolimbic dopaminergic function by acting on 5-HT2C receptors. Therefore, selective 5-HT2C receptor agonists might be useful in clinical conditions where it is necessary to reduce the mesolimbic dopaminergic activity without affecting the nigrostriatal function. Synapse 35:53-61, 2000. (C) 2000 Wiley-Liss, Inc.

Abstract: In vivo microdialysis and electrophysiological techniques were used to elucidate the role of the 5-HT2 receptor family on the control of mesolimbic dopaminergic system exerted by serotonin (5-HT). Administration of RO 60-0175 (1 mg/kg, i.p.), a selective 5-HT2C receptor agonist, significantly decreased dopamine (Dh) release by 26+/-4% (below baseline) 60 min after injection. Moreover, RO 60-0175 (80-320 mu g/kg, i.v,) dose-dependently decreased the basal firing rate of DA neurons in the ventral tegmental area (VTA), reaching its maximal inhibitory effect (53.9+/-15%, below baseline) after the dose of 320 mu g/kg. The selective 5-HT,, receptor antagonist SE 242084 completely blocked the inhibitory action of RO 60-0175 on accumbal DA release and on the firing rate of VTA DA cells. On the contrary, both (+/-)-DOI, a mixed 5-HT2A/2C receptor agonist, and the selective 5-HT2B agonist BW 723C86, did not affect either DA release in the nucleus accumbens or the firing rate of VTA DA cells. Taken together, these data confirm that central 5-HT system exerts an inhibitory control on the mesolimbic DA system and that 5-HT2C receptors are involved in this effect. (C) 2000 Elsevier Science B.V. All rights reserved.

Abstract: SE 242084 is the most potent and selective 5-HT2C receptor antagonist thus far available. Thus, SE 242084 has high affinity for the cloned human 5-HT2C receptor with a pK(i) of 9.0, a much lower affinity for the human cloned 5-HT2B (pK(i) 7.0) and 5-HT2A (pK(i) 6.8) receptors, and low affinity for other 5-HT, dopamine, and adrenergic receptors. In the 5-HT-stimulated PI hydrolysis model of 5-HT2C receptor function, SE 242084 was found to be a competitive antagonist with a pK(B) of 9.3. A series of in vivo studies have shown that SE 242084 is a very effective antagonist of behavioral responses mediated by 5-HT2C receptors such as penile erections, and the hypophagic and hypolocomotor effect of mCPP in rats. In addition, this compound has anxiolytic-like properties. Moreover, SE 242084 increases the basal activity of dopaminergic neurons in the VTA and the in vivo DA release in the nucleus accumbens, and it is capable of blocking the inhibitory effects of mCPP and RO 60-0175 on mesolimbic dopaminergic activity. These data are consistent with the evidence that 5-HT2C receptors exert an inhibitory control upon the mesolimbic dopaminergic system. Taken togheter, the available data on SE 242084 might have implication for the possible use of this compound in the treatment of anxiety, depression, and the negative symptoms of schizophrenia.

Abstract: Electrophysiological techniques and in vivo microdialysis were used to investigate the relative contribution of central serotonin-2C/2B and serotonin-2A receptor subtypes in the control of mesolimbic and nigrostriatal dopaminergic function. Thus, extracellular single-unit recordings were performed from neurochemically identified dopamine neurons in the ventral tegmental area and the substantia nigra pars compacta, as well as simultaneous monitoring of accumbal and striatal basal dopamine release in anesthetized rats following the administration of serotonin-2C/2B (SB 206553), serotonin-2A (SR 46349B) or serotonin-2A/2B/2C (ritanserin) antagonists. Administration of SE 206553 (40-160 mu g/kg, i,v.) caused a dose-dependent increase in the basal firing rate of ventral tegmental area and nigral dopamine neurons, reaching its maximum (45.2 and 28.5%, respectively) following 160 mu g/kg. Moreover, burst activity was significantly enhanced by SE 206553 in the ventral tegmental area only. In contrast, injection of SR 46349B (40-160 mu g/kg, i.v.), and ritanserin (40-160 mu g/kg, i.v.) did not cause any significant change in the basal activity of these neurons. Basal dopamine release was significantly enhanced in both the nucleus accumbens (42%) and the striatum (33%) following the intraperitoneal administration of 5 mg/kg SE 206553. In contrast, SR 46349B (0.5 mg/kg, s.c,) and ritanserin (0.63 mg/kg, i.p.) failed to affect basal dopamine output in both regions. Taken together, these data indicate that the central serotonergic system exerts a tonic inhibitory control of mesolimbic and nigrostriatal dopaminergic pathway activity and that the serotonin-2C/2B receptor subtypes are involved in this effect. Moreover, these findings might open new possibilities for the employment of serotonin-2C/2B receptor antagonists in the treatment of neuropsychiatric disorders related to a hypofunction of central dopaminergic neurons. (C) 1999 IBRO. Published by Elsevier Science Ltd.

Abstract: Neuropharmacological investigations aimed at understanding the electrophysiological correlates between drug effect and action potential trains have usually been carried out with the analysis of firing rate and bursting activity. In this study, a selective alteration of neural circuits providing inputs to ventral tegmental area dopaminergic neurons has been produced, and the corresponding electrophysiological correlates have been investigated by nonlinear dynamical analysis. The nonlinear prediction method combined with Gaussian-scaled surrogate data has been used to show the chaotic structure in the time-series corresponding to the electrical activity of ventral tegmental area dopaminergic neurons, extracellularly recorded in vivo. A decrease in chaos of ventral tegmental area dopaminergic neurons was found in a group of rats lesioned with 5,7-dihydroxytryptamine, a neurotoxin which selectively destroys serotonergic terminals. The chaos content of ventral tegmental area dopaminergic neurons in the control group and the decrease of chaos in the lesioned group cannot be explained in terms of standard characteristics of neuronal activity (firing rate, bursting activity). Moreover, in the control group a positive correlation has been found between the density-power-spectrum of the interspike intervals and the chaos content measured by nonlinear prediction S score; this relation was lost in the lesioned group. It is concluded that the impaired serotonergic tone induced by 5,7-dihydroxytryptamine reduces the chaotic behaviour of the dopaminergic cell firing pattern, while retaining many standard interspike interval characteristics. The functional role of this behaviour in a neuronal coding problem context and the implications for the pathophysiology of some mental disorders are discussed. (C) 1999 IBRO. Published by Elsevier Science Ltd.

Abstract: In this study, the nonlinear prediction method combined with Gaussian-scaled surrogate data was used to quantify, as a first goal, the chaotic behavior of the interspike interval of ventral tegmental area dopaminergic neurons, extracellularly recorded in vivo, in anesthetized rats. The second goal was to determine the differences in chaotic content as a function of age. Comparisons were made among three different groups of rag: young (two to four weeks of age), adult (three to four months of age) and aged (16-19 months of age). It has been found that the degree of complexity of action potential trains is reduced with aging. The chaotic content of ventral tegmental area dopamine neurons within each group and the decrease of chaos with aging cannot be explained in terms of standard characteristics of neuronal activity (firing rate, bursting activity). These data can be rationalized in the light of recent findings on the role of deterministic chaos in the functional behavior of complex biological systems, and suggests that nonlinear analysis may provide an additional method in characterizing neuronal activity. (C) 1999 IBRO. Published by Elsevier Science Ltd.

Abstract: Electrophysiological techniques and in vivo microdialysis were used to investigate the effect of SE 242 084, a potent and selective 5-HT2C, receptor antagonist in the control of nigro-striatal and mesolimbic dopaminergic function. Thus, extracellular single unit recordings were performed from neurochemically-identified dopamine (DA) neurons in the substantia nigra, pars compacts (SNc) and the ventral tegmental area (VTA), as well as monitoring of striatal and accumbal basal DA release in anesthetized rats following the administration of SE 242 084 and RO 60-0175. Administration of SE 242 084 (160-640 mu g/kg, i.v.) caused a dose-dependent increase in the basal firing rate of VTA DA neurons, reaching its maximum (27.8 +/- 6%, above baseline) after 640 mu g/kg. Moreover, bursting activity was significantly enhanced by SE 242 084 in the VTA. On the other hand, SE 242 084 (160-640 mu g/kg, i.v.) did not cause any significant change in the basal firing rate and bursting activity of DA neurons in the SNc. Injection of the 5-HT2c, receptor agonist RO 60-0175 (80-320% mu g/kg, i.v.) dose-dependently decreased the basal firing of DA neurons in the VTA but not in the SNc. RO 60-0175 exerted its maximal inhibitory effect (53.9 +/- 15.1%, below baseline) in the VTA at the dose of 320 mu g/kg. Basal DA release (34.8 +/- 9%, above baseline) and dihydroxyphenylacetic acid (DOPAC) efflux (19.7 +/- 7%, above baseline) were significantly enhanced in the nucleus accumbens following the intraperitoneal administration of 10 mg/kg SE 242 084. Intraperitoneal injection of 5 mg/kg SE 242 084 significantly increased DA release (16.4 +/- 6%, above baseline) in the nucleus accumbens, but did not affect DOPAC efflux. In the striatum, SE 242 084 (5 and 10 mg/kg, i.p.) only slightly increased DA release above baseline (3.5 +/- 3 and 11.2 +/- 6%, respectively), without affecting DOPAC efflux in this area. However, the effect of SE 242 084 in the striatum was rendered more evident by the fact that injection of the vehicle used to dissolve the drug in a group of control rats, significantly reduced basal DA output by 19.6 +/- 7%. Stimulation of 5-HT2C receptors by RO 60-0175 (1 mg/kg, i.p.) significantly decreased DA release in the nucleus accumbens by 26.1 +/- 4% (below baseline) 60 min after injection. On the other hand, RO 60-0175 (1 mg/kg, i.p.) did not cause any significant change of DA release in the striatum. However, DOPAC efflux was reduced by RO 60-0175 (1 mg/kg, i.p.) both in the striatum and the nucleus accumbens. Taken together, these data indicate that the central 5-HT system exerts a tonic and phasic inhibitory control on mesolimbic DA neuron activity and that 5-HT2C receptor subtypes are involved in this effect. Moreover, these findings might open new possibilities for the employment of 5-HT2C, receptor antagonists in the treatment of neuropsychiatric disorders related to a hypofunction of central DA neurons. (C) 1999 Elsevier Science Ltd. All rights reserved.

Abstract: The effects of mesulergine (100 and 200 mu g/kg s.c.), SB 206553 (1 and 2.5 mg/kg i.p.), RP 62203 (2.5 and 4 mg/kg i.p.) and ritanserin (630 mu g/kg i.p.) were studied on the extracellular concentration of dopamine (DA) and dihydroxyphenylacetic acid (DOPAC) in the nucleus accumbens of chloral hydrate-anesthetized rats, using intracerebral microdialysis. Mesulergine, a non selective serotonin(2c/2B/2A) (5-HT2C/2B/2A) receptor antagonist, significantly increased DA release, which reached a peak level (+ 20%) 60 min after drug injection and slowly returned back to baseline values. Mesulergine also caused a dose-dependent increase in DOPAC outflow. Pretreatment with mesulergine (200 mu g/kg) did not change the inhibition of DA release induced by apomorphine (100 mu g/kg), whereas it prevented the reduction of DOPAC outflow induced by apomorphine (100 mu g/kg). Administration of SB 206553, a selective blocker of 5-HT2C/2B receptors, dose-dependently increased DA outflow. The dose of 2.5 mg/kg SB 206553 caused a linear increase of DA output which reached a peak (+ 75%) 40 min after injection, while 1 mg/kg induced a more gradual increase of DA release which peaked (+/- 54%) 60 min after administration of the drug. Treatment with RP 62203, a selective 5-HT2A receptor antagonist, did not produce any significant effect on DA outflow. Administration of ritanserin, a mixed 5-HT2A/2C receptor antagonist, did not cause any significant change of DA and DOPAC outflow. Taken together, these data indicate that selective blockade of 5-HT2C/2B receptor subtypes increases DA release in the rat nucleus accumbens. (C) 1998 Elsevier Science Ltd. All rights reserved.

Abstract: Electrophysiological techniques were used to study the effects of amisulpride, a D-2/D-3 dopamine receptor blocker, on the activity of dopaminergic neurons in the substantia nigra pars compacta (SNc) and the ventral tegmental area (VTA). Administration of single bolus doses of amisulpride (8-32 mg/kg i.v.) induced a dose-dependent increase in the basal activity of dopaminergic neurons, in both the SNc and the VTA. The effect of amisulpride was more evident in the VTA, where it elicited a maximal excitation of 38.5 +/- 12%, whereas in the SNc it caused a peak excitation of only 22.1 +/- 9.8%. Amisulpride also increased the bursting activity of dopaminergic neurons in the VTA but not in the SNc, Microiontophoretic application of amisulpride (10-40 nA) into the SNc and the VTA caused an increase in the basal firing rate of the majority of dopaminergic neurons sampled. The excitation induced by 40 nA amisulpride was more marked in the VTA(36.1 +/- 21%) than in the SNc (25.0 +/- 18%). Moreover, microiontophoretic amisulpride (40 nA) increased the bursting activity of dopaminergic neurons in the VTA only. Repeated administration of amisulpride (20 and 50 mg/kg i.p.) for 21 consecutive days produced a significant decrease in the number of spontaneously active dopaminergic neurons in the VTA but not in the SNc. Repeated admistration of haloperidol (0.5 mg/kg i.p.) decreased the number of dopaminergic cells both in the SNc and the VTA. The effect of repeated admistration of amisulpride on the activity of VTA dopaminergic neurons was reversed by apomorphine, suggesting that these neurons were probably under a state of depolarization block. Taken together, these data confirm previous findings indicating that low doses of amisulpride preferentially increase dopaminergic transmission in the mesolimbic system. Moreover, results obtained from long-term experiments are consistent with clinical data indicating that amisulpride given at high doses is an effective antipsychotic agent, associated with a low incidence of extrapyramidal side effects.

Abstract: Electrophysiological techniques were used to study the effects of paroxetine, sertraline, and fluvoxamine on the basal activity of dopaminergic neurons in the ventral tegmental area (VTA) of rats. Acute i.v. administrations of paroxetine (20-1280 mu g/kg), sertraline (20-1280 mu g/kg), and fluvoxamine (20-1280 mu g/kg) caused a slight but significant reduction in the firing rate of the VTA dopaminergic cells studied. Paroxetine produced a maximal inhibitory effect of 10 +/- 11% at the cumulative dose of 160 mu g/kg. Sertraline induced a dose-related inhibition of VTA dopaminergic neurons, which reached its maximum (10 +/- 7%) at the cumulative dose of 1280 mu g/kg. The effect of fluvoxamine on the basal firing rate of VTA dopaminergic neurons was more pronounced as compared to that of paroxetine and sertraline, in that it produced a maximal inhibition of 17 +/- 12% at the cumulative dose of 1280 mu g/kg. Acute i.v. injections of paroxetine (20-1280 mu g/kg), sertraline (20-1280 mu g/kg), and fluvoxamine (20-5120 mu g/kg) caused a dose-dependent decrease in the basal firing rate of serotonergic neurons in the dorsal raphe nucleus (DRN), Paroxetine and sertraline stopped the spontaneous firing of serotonergic neurons at the cumulative dose of 1280 mu g/kg, whereas fluvoxamine reached the same effect only at the cumulative dose of 5120 mu g/kg, Pretreatment with the 5-HT1A receptor antagonist tertatolol (1 mg/kg, i.v.) reduced the inhibitory effects of paroxetine, fluvoxamine, and sertraline on the basal activity of serotonergic neurons in the DRN, Administration of tertatolol induced a 15-fold increase in the ED50 for fluvoxamine. The antagonistic effect of tertatolol was much less evident in blocking the inhibitory action exerted by paroxetine and sertraline on the activity of serotonergic neurons, Pretreatment with tertatolol (1 mg/kg, i.v.) potentiated the inhibitory effect of fluvoxamine on the basal activity of VTA dopaminergic neurons. Tertatolol did not affect the inhibitory action exerted by paroxetine and sertraline on these neurons. It is concluded that inhibition of the basal firing rate of dopaminergic neurons in the VTA is a common characteristic of selective serotonin reuptake inhibitors (SSRIs). The effects of SSRIs on VTA dopaminergic cell activity might be relevant for their therapeutic action and may explain the origin of the reported cases of akathisia, (C) 1998 Elsevier Science Inc.

Abstract:

Abstract: Central serotonergic and dopaminergic systems play a critical role in the regulation of normal and abnormal behaviours. Moreover, recent evidence suggests that the dysfunction of dopamine (DA) and serotonin (5-hydroxytriptamine, 5-HT) neurotransmission might underlie the pathophysiology of neuropsychiatric disorders, including depression, schizophrenia, attention deficit hyperactivity disorders, drug abuse, Gilles de la Tourette�s syndrome and Parkinson�s disease.

Abstract: Nitric oxide (NO) signalling plays an important role in the integration of information processed by the basal ganglia nuclei. Accordingly, considerable evidence has emerged indicating a role for NO in pathophysiological conditions such as Parkinson�s disease (PD), schizophrenia and drug addiction. To further investigate the NO modulation of dopaminergic function in the basal ganglia circuitry, in this study we used in vivo electrophysiology and microdialysis in freely-moving rats. Pharmacological manipulation of the NO system did not cause any significant changes either in the basal firing rate and bursting activity of the dopamine (DA) neurons in the substantia nigra pars compacta (SNc) or in DA release in the striatum. In contrast, the disruption of endogenous NO tone was able to counteract the phasic dopaminergic activation induced by nicotine treatment in both experimental approaches. These results further support the possibility that nicotine acts via a NO mechanism and suggest a possible state-dependent facilitatory control of NO on the nigrostriatal DA pathway. Thus, NO selectively modulates the DA exocytosis associated with increased DA functiov n.

Abstract: Serotonin (5-HT) is intimately involved in the modulation of the basal ganglia circuitry and in its pathologies. The 5-HT pivotal role is supported by anatomical evidence demonstrating a large serotonergic innervation throughout the basal ganglia, with the highest concentration of this indole in the substantia nigra (SN). Among all the 5-HT receptors present in the SN, the 5-HT(2C) receptor subtype seems to be one of the principal receptors through which 5-HT exerts its function. In this chapter, we present in vivo electrophysiology and microdialysis evidence showing that the selective activation of 5-HT(2C) receptors does not affect dopaminergic function whereas it has a profound impact on GABAergic function in the substantia nigra pars reticulata (SNr). 5-HT excites the neurons of the SNr by acting on 5-HT(2C) receptors, and this control seems to be phasic rather than tonic in nature. Consequently, activation of 5-HT(2C) receptors boosts the concentration of GABA in the SNr, likely increasing GABA somatodendritic release from SNr neurons and from other GABA-containing neurons projecting to the SNr as well. Therefore, drugs acting on 5-HT(2C) receptors may provide a novel non-dopaminergic target for improving therapies for some basal ganglia disorders such as Parkinson�s disease.