Abstract: Synaptic dopamine is mainly regulated by presynaptic dopamine transporter (DAT) activity. We hypothesized that variations in synaptic dopamine are reflected by variations of DAT radioligand binding. The effect of haloperidol, which increases synaptic dopamine concentrations, was therefore assessed in the rat striatum using (123)I-N-omega-fluoropropyl-2beta-carbomethoxy-3beta-(4-iodophenyl)-nortropane ((123)I-FP-CIT) as a DAT radioligand. METHODS: Striatal (123)I-FP-CIT binding was measured in 24 rats under baseline conditions (no pretreatment) and at 1 h after injection of haloperidol or a vehicle (1 mg/kg) using a small-animal SPECT camera. RESULTS: Baseline equilibrium ratios (V(3)'') were 1.32 +/- 0.24 (mean +/- SD). After the haloperidol injection, V(3)'' decreased to 0.99 +/- 0.38 (P(2-tailed) < 0.0001), corresponding to a mean reduction of DAT binding by 25%. CONCLUSION: Our results are indicative of competition between the DAT ligand (123)I-FP-CIT and synaptic dopamine elevated by haloperidol, suggesting that the assessment of (123)I-FP-CIT binding may be suitable to study variations in synaptic dopamine in vivo.
Abstract: This review gives an overview of those in vivo imaging studies on synaptic neurotransmission, which so far have been performed on patients with movement disorders and/or dementia. Thereby, the focus is on disease-related deficiencies within the functional entity of the dopaminergic, serotonergic, cholinergic, glutamatergic, GABAergic or opioid synapse. In vivo investigations have yielded highly consistent results on the dysfunction of synaptic constituents in the majority of diseases covered by this overview. Findings show presynaptic dysfunctions in idiopathic as well as early-onset Parkinson's disease with decreases in striatal dopamine synthesis (57 out of a total of 59 reports on both types of Parkinson's disease), storage (nine out of nine reports), release (two out of three reports) and transporter binding (95 out of 95 reports). In contrast, the "Parkinson plus" syndromes multiple system atrophy and progressive supranuclear palsy are characterized by both pre- and postsynaptic deficiencies with reductions in striatal dopamine synthesis (11 out of a total of 11 reports on both types of "Parkinson plus" syndromes), storage (four of four reports), and transporter binding (27 out of 27 reports) as well as D1 (two out of two reports) and D2 receptor binding (34 out of 36 reports). This does not hold for the "Parkinson plus" syndromes dementia with Lewy bodies and corticobasal degeneration. For these diseases, for the time being, firm evidence of alterations in D1 and/or D2 receptor binding is lacking. In patients with Huntington's disease, mainly postsynaptic dysfunctions with reductions of striatal D1 (six out of six reports) and D2 receptor binding (15 out of 15 reports) were observed. Alzheimer's disease is characterized by both pre-and postsynaptic deficiencies of the cholinergic system with decreases of cortical acetylcholine storage (one out of two reports) and both musarinic (seven out of 10 reports) and nicotinic cholinergic receptor binding (three out of six reports). Moreover, reductions in cortical (one out of three reports) and limbic 5-HT1A (three out of three reports) and cortical (four out of four reports) and limbic 5-HT2A receptor binding (one out of two reports) were observed. Moreover, there is evidence for a cortical (four out of six reports) and cingulate (three out of three reports) increase of peripheral benzodiazepine receptor binding indicative of microglial activation. In the majority of investigations on patients with Alzheimer's disease, no alterations of presynaptic dopamine function were found, whereas all other forms of dementia including corticobasal degeneration, dementia with Lewy bodies, Parkinson's disease dementia and frontotemporal dementia were characterized by presynaptic dopaminergic deficiencies with reductions in striatal dopamine synthesis (10 out of a total of 10 reports on these types of dementia), storage (four out of four reports) and transporter binding (29 out of 29 reports). Taken together, in vivo imaging methods can be employed for the diagnosis of idiopathic and early-onset Parkinson's disease as well as "Parkinson plus" syndromes and Huntington's disease. Moreover, differentiation is feasible between, firstly, Parkinson's disease and the "Parkinson plus" syndromes multiple system atrophy and progressive supranuclear palsy, secondly, multiple system atrophy/progressive supranuclear palsy and the other "Parkinson plus" syndromes dementia with Lewy bodies and corticobasal degeneration, and, thirdly, Alzheimer's disease and other forms of dementia.
Abstract: This review gives an overview of those in vivo imaging studies on synaptic neurotransmission, which so far have been performed on patients with mental and affective disorders. Thereby, the focus is on disease-related deficiencies within the functional entities of the dopaminergic, serotonergic, cholinergic, histaminergic, glutamatergic, or GABAergic synapse. So far, in vivo investigations have yielded rather inconsistent results on the dysfunctions of specific synaptic constituents in the pathophysiology of the diseases covered by this overview. Among the more congruent results are the findings of increased synthesis (8 out of a total of 12 reports) and release of dopamine (4 out of 4 reports) in the striatum of schizophrenic patients, which supports the dopamine hypothesis of schizophrenia. Results on both dopaminergic and serotonergic neurotransmission are inconsistent in both major depressive disorder and bipolar illness, and fail to clearly agree with the dopamine and/or serotonin hypothesis of depression. The majority of in vivo findings suggest no alterations (25 out of a total of 50 reports on serotonin synthesis, transporter as well as receptor binding) rather than a deficiency (merely 13 out of these 50 reports) of cortical serotonergic neurotransmission in major depression, whereas a decrease of cortical serotonergic neurotransmission (3 out of a total on 5 reports) can be assumed in bipolar illness. In borderline personality disorder, an increased binding of serotonin transporter binding was observed (merely 1 report). Due to the limited evidence, this result only with due caution may be interpreted as an indication for increased availability of serotonin in the synaptic cleft. Patients with Tourette syndrome exhibited increases of DAT binding in the neostriatum (5 out of 10 reports) increases of dopamine storage and dopamine release in the ventral striatum (1 report, each). Moreover, striatal D2 receptor binding was found to be decreased in advanced stages of the disease. Results, tentatively, may be interpreted in terms of an increased dopaminergic neurotransmission in the mesolimbic system. There is limited evidence of decreased dopamine synthesis in both children and adults with attention-deficit/hyperactivity disorder (4 out of a total of 10 reports). These findings as well as the reduction of striatal dopamine release observed in adults (merely 1 report) are in line with the notion of mesocortical dopaminergic hypofunction in attention-deficit/hyperactivity disorder. Thereby, however, in children, results on dopamine synthesis indicate a deficiency in the ventral tegmentum rather than in the prefrontal cortex, whereas, with increasing age, the prefrontal cortex rather than the sites of origin of DAergic innervation become predominantly affected (merely 1 report, each). In anxiety disorders, varying results have been obtained for both pre- and/or postsynaptic dopaminergic, serotonergic and GABAergic binding sites. Thereby, results on posttraumatic stress disorder are homogenous reporting a decrease of GABA A receptor binding in all investigated brain regions including striatum, thalamus, neocortex and limbic system (2 out of 2 reports, each). Moreover, patients with obsessive-compulsive disorder displayed increases of dopamine transporter binding (2 out of 4 reports) and decreases of both D1 (merely 1 report) and D2 receptor binding (4 out of 5 reports), respectively. These findings, tentatively, may be interpreted in terms of an increased availability of synaptic dopamine in the neostriatum, which is compensated for both pre- and postsynaptically by increasing dopamine reuptake into the presynaptic terminal, and decreasing (inhibitory) signal transduction of efferent fibers. The observed reduction of GABA A receptor binding in frontocortical neurons (in 11 out of a total of 21 reports on anxiety disorders) is in line with this assumption. The inconsistency (and, partially, also incompleteness) of in vivo findings on mental and affective disorders constitutes a major result of this overview. Discrepancies indicate that the regulation state of synaptic constituents may not only vary between the subtypes of disorders but also between subject cohorts and, even, individual patients depending on variables such as the predominance of symptoms, medication status or onset and duration of disease. This, for the time being, limits the application of in vivo imaging methods for differential diagnosis of mental and affective disorders. In vivo imaging results on anxiety disorders, however, are of possible interest with regard to psychoanalysis, as they offer a neurochemical correlate for Freud's theories on the pathogenesis of anxiety- and compulsion-related disorders.
Abstract: OBJECTIVE: This study investigated dopamine transporter blockade in the rat striatum after treatment with various doses of methylphenidate using a high-resolution small animal SPECT ('TierSPECT') and I-FP-CIT. METHODS: I-FP-CIT was administered intravenously 1 h after intraperitoneal injection of methylphenidate (3 mg.kg, 10 mg.kg) or vehicle. Rats underwent scanning 2 h after radioligand application. From the spatial resolution of the imaging system and the size of the rat striatum followed that 'true' radioactivity concentrations were underestimated by approximately 50%. From cerebellar and partial volume corrected striatal radioactivity concentrations, striatal equilibrium ratios (V3'') were computed as estimations of the binding potential. RESULTS: Vehicle-treated animals yielded striatal V3'' values of 3.5+/-0.9 (mean+/-SD). After pre-treatment with 3 mg.kg and 10 mg.kg methylphenidate, striatal V3'' values were reduced to 2.4+/-0.8 (independent t-test, two-tailed, P=0.026) and 1.7+/-0.6 (P<0.001), respectively. CONCLUSIONS: This first in-vivo study of rat dopamine transporter binding after pre-treatment with various doses of methylphenidate showed a dose-dependent reduction of striatal dopamine transporter binding. Results indicate that in-vivo quantification of dopamine transporter binding is feasible with I-FP-CIT and the TierSPECT method. This may be of future relevance for investigating in-vivo binding properties as well as pharmacological profiles of novel agents acting at the dopamine transporter binding site. Moreover, alterations of striatal transporter densities may be investigated in animal models of neurological and psychiatric diseases such as attention-deficit/hyperactivity disorder and Parkinson's disease.
Abstract: Dopaminergic synaptic function may be assessed either at the presynaptic terminal or at the postsynaptic binding sites using molecular in vivo imaging methods. Apart from the density of binding sites, parameters such as alterations in dopamine synthesis, dopamine storage or dopamine release can be quantified either by application of specific radiotracers or by assessing the competition between the exogenous radioligand and endogenous dopamine. The performance of animal studies allows the induction of specific short-term or long-term synaptic conditions via pharmacological challenges or infliction of neurotoxic lesions. Therefore, small laboratory animals such as rats and mice have become invaluable models for a variety of human disorders. This article gives an overview of those small animal studies which have been performed so far on dopaminergic neurotransmission using in vivo imaging methods, with a special focus on the relevance of findings within the functional entity of the dopaminergic synapse. Taken together, in vivo investigations on animal models of Parkinson's disease showed decreases of dopamine storage, dopamine release and dopamine transporter binding, no alterations of dopamine synthesis and DA release, and either increases or no alterations of D2 receptor binding, while in vivo investigations of animal models of Huntington's disease. showed decreases of DAT and D1 receptor binding. For D2 receptor binding, both decreases and increases have been reported, dependent on the radioligand employed. Substances of abuse, such as alcohol, amphetamine and methylphenidate, led to an increase of dopamine release in striatal regions. This held for the acute application of substances to both healthy animals and animal models of drug abuse. Findings also showed that chronic application of cocaine induced long-term reductions of both D1 and D2 receptor binding, which disappeared after several weeks of withdrawal. Finally, preliminary results yielded the first evidence that acute pplication of haloperidol might induce a reduction of dopamine transporter binding, indicating an enhancement of dopamine release into the synaptic cleft. It is remarkable to what degree the findings obtained with small animal imaging devices correspond to the results of clinical and experimental studies on humans. This agreement underlines the validity of small animal imaging methods and demonstrates the feasibility of further investigations on animal models of human diseases.
Abstract: Dopaminergic synaptic function may be assessed either at the presynaptic terminal or at the postsynaptic binding sites using molecular in vivo imaging methods. Apart from the density of binding sites, parameters such as alterations in dopamine synthesis, dopamine storage or dopamine release can be quantified either by application of specific radiotracers or by assessing the competition between the exogenous radioligand and endogenous dopamine. Investigations of humans in both clinical and experimental settings have yielded evidence that disturbances of dopaminergic function may be associated with numerous neurological and psychiatric conditions, among which are movement disorders, schizophrenia, attention-deficit hyperactivity disorder, depression and drug abuse. This article gives an overview of those studies, which so far have been performed on dopaminergic neurotransmission in humans using in vivo imaging methods. We focus on disease-related deficiencies within the functional entity of the dopaminergic synapse. Taken together, in vivo findings yield evidence of presynaptic dysfunctions in Parkinson's disease with decreases in striatal dopamine synthesis, dopamine storage, dopamine release and dopamine transporter binding. In contrast, 'Parkinson plus' syndromes (multiple system atrophy, progressive supranuclear palsy, corticobasal degeneration, dementia with Lewy bodies) are characterized by both pre- and postsynaptic deficiencies with reductions in striatal dopamine synthesis, dopamine storage, dopamine release, and dopamine transporter, as well as D, and D, receptor binding. In patients with Huntington's disease, postsynaptic dysfunctions with reductions of striatal D1 and D2 receptor binding have become apparent, whereas attention-deficit/ hyperactivity disorder is mainly characterized by presynaptic deficits with increases in dopamine transporter binding. Interestingly, findings are also consistent with respect to drug abuse: cocaine, amphetamine, methylphenidate, heroin, alcohol and nicotine invariably act via enhancement of dopamine release in dorsal and/ or ventral striatal regions. In vivo findings additionally suggest that not only D2 receptor binding but also the extent of dopamine release is lower in individuals with a history of drug abuse. Findings become inconsistent with increasing complexities of psychiatric conditions. As yet, there is no clear evidence as to the contributions of the individual presynaptic and postsynaptic constituents of the dopaminergic synapse to the pathophysiologies of schizophrenia and depression. As these diseases can be conceived as the result of a variety of dysfunctions and dysregulations within an intricate network of neurotransmitter systems, regional investigations of one single pre- or postsynaptic constituent may not reach far enough to disentagle the interrelationships between the constituents of one let alone a variety of neurotransmitter systems.
Abstract: BACKGROUND AND AIM: Dopamine transporters are the target of psychostimulants used for treatment of attention-deficit/hyperactivity disorder (ADHD). Therefore, the present study aimed to evaluate striatal dopamine transporter density in adult patients with ADHD. METHODS: Twenty patients (11 female, nine male; mean age 35+/-7 years) and 20 control subjects (11 female, nine male, mean age 32 +/- 8 years) were examined with SPECT using the specific radiotracer 123I-FP-CIT. The ratio of striatal to cortical radioactivity concentration was used for semiquantitative evaluation of dopamine transporter binding potential (V3''). There was a significant influence of age (P < 0.001) and a trend towards an influence of gender (P = 0.053) on V3''. An ANCOVA with these covariates showed a slightly higher V3'' in the patients than in the control subjects (4.24 +/- 0.48 vs. 4.03 +/- 0.56; P = 0.02). CONCLUSION: This study provides further in-vivo evidence for an involvement of the dopamine transporter in ADHD. However, compared to previous studies, the increase of dopamine transporter density in the patient group is less pronounced here.
Abstract: During the recent years, in vivo imaging of small animals using SPECT has become of growing relevance. Along with the development of dedicated high-resolution small animal SPECT cameras, an increasing number of conventional clinical scanners has been equipped with single or multipinhole collimators. This paper reviews the small animal tomographs, which are operating at present and compares their performance characteristics. Furthermore, we describe the in vivo imaging studies, which have been performed so far with the individual scanners and survey current approaches to optimize molecular imaging with small animal SPECT.
Abstract: PURPOSE: The aim of this study was to investigate the feasibility of assessing dopamine transporter binding after treatment with methylphenidate in the rat using a recently developed high-resolution small animal single-photon emission computed tomograph (TierSPECT) and [123I]FP-CIT. METHODS: [123I]FP-CIT was administered intravenously 1 h after intraperitoneal injection of methylphenidate (10 mg/kg) or vehicle. Animals underwent scanning 2 h after radioligand administration. The striatum was identified by superimposition of [123I]FP-CIT scans with bone metabolism and perfusion scans obtained with 99mTc-DPD and 99mTc-tetrofosmin, respectively. As these tracers do not pass the blood-brain barrier, their distribution permits the identification of extracerebral anatomical landmarks such as the orbitae and the harderian glands. The cerebellum was identified by superimposing [123I]FP-CIT scans with images of brain perfusion obtained with 99mTc-HMPAO. RESULTS: Methylphenidate-treated animals and vehicle-treated animals yielded striatal equilibrium ratios (V''3) of 0.24+/-0.26 (mean +/- SD) and 1.09+/-0.42, respectively (t test, two-tailed, p<0.0001). Cortical V''3 values amounted to 0.05+/-0.28 (methylphenidate) and 0.3+/-0.39 (saline, p=0.176). This first in vivo study of rat dopamine transporter binding after pre-treatment with methylphenidate showed a mean reduction of 78% in striatal [123I]FP-CIT accumulation. CONCLUSION: The results can be interpreted in terms of a pharmacological blockade in the rat striatum and show that in vivo quantitation of dopamine transporter binding is feasible with [123I]FP-CIT and the TierSPECT. This may be of future relevance for in vivo investigations on rat models of attention deficit/hyperactivity disorder. Furthermore, our findings suggest that investigations in other animal models, e.g. of Parkinson's and Huntington's disease, may be feasible using SPECT radioligands and small animal imaging systems.
Abstract: This paper presents the performance of a new small-animal camera (TierSPECT) devised for the in vivo measurements of radiolabeled substances in small laboratory animals such as mice and rats. In a scatter medium, the camera has a tomographic spatial resolution of 2.87 mm and a sensitivity of 22 cps/MBq in a usable Field-of-View (FOV) with a diameter of 82 mm. The planar homogeneity amounts to 3.3%, the tomographic homogeneity lies between 3.2% and 3.5%. The deviation between filled and measured concentration of activity in a cylindrical 4-chamber-phantom was smaller than 2.6%. Using a novel rat head phantom with chamber volumes in the order of magnitude of the spatial resolution (between 0.065 ml and 0.19 ml) it could be demonstrated that studies of the rat neostriatal dopaminergic system are feasible under observance of physiological conditions. In vivo studies using [99mTc]diphosphonato-1,2-propandicarbonic acid (99mTc-DPD) and [123I]N-omega-fluoropropyl-2beta-carbomethoxy-3beta-(4-iodophenyl)-nortropane (123I-FP-CIT) proved that bone metabolism and dopamine transporter binding can be visualized with the TierSPECT. The fusion of 99mTc-DPD and 123I-FP-CIT images allowed the differentiation between intra- and extracerebral structures. Pretreatment with methylphenidate resulted in blockade of striatal dopamine transporter binding.
Abstract: PURPOSE: This study assessed [123I]iodobenzamide binding to the rat dopamine D2 receptor in competition with haloperidol and endogenous dopamine using a high-resolution small animal SPECT. METHODS: Subsequent to baseline quantifications of D2 receptor binding, imaging studies were performed on the same animals after pre-treatment with haloperidol and methylphenidate, which block D2 receptors and dopamine transporters, respectively. RESULTS: Striatal baseline equilibrium ratios (V3'') of [123I]iodobenzamide binding were 1.42+/-0.31 (mean+/-SD). After pre-treatment with haloperidol and methylphenidate, V3'' values decreased to 0.54+/-0.46 (p<0.0001) and 0.98+/-0.48 (p=0.009), respectively. CONCLUSION: The decrease in [123I]iodobenzamide binding induced by pre-treatment with haloperidol reflects D2 receptor blockade, whereas the decrease in receptor binding induced by pre-treatment with methylphenidate can be interpreted in terms of competition between [123I]IBZM and endogenous dopamine. Findings show that multiple in vivo measurements of [123I]iodobenzamide binding to D2 receptors in competition with exogenous and endogenous ligands are feasible in the same animal. This may be of future relevance for the in vivo evaluation of novel radioligands as well as for studying the interrelations between pre- and/or postsynaptic radioligand binding and different levels of endogenous dopamine.
Abstract: This article presents an overview of those animal studies which so far have been performed with dedicated small animal positron emission tomographs in the field of the neurosciences. In vivo investigations focus on energy metabolism, perfusion and receptor/transporter binding in rat models of reinforcement, learning and memory, traumatic brain injury, epilepsy, depression, cardiovascular diseases--such as ischemia and focal stroke--and neurodegenerative disorders such as Alzheimer's, Parkinson's and Huntington's disease. In the majority of studies, important novel aspects arise from the fact that the investigators made use of an option inherent to in vivo studies, namely to conduct longitudinal investigations on the same animals. Relevant findings pertain to the relationship of brain metabolism/perfusion and the cholinergic system, the regulation state of dopamine receptors upon cocaine administration and withdrawal, the regulation state of dopamine receptors and transporters in animal models of Parkinson's and Huntington's disease, and potential treatments of progressive dopaminergic depletion with adenoviral vectors, embryonic grafts, stem cells and nerve growth factors.
Abstract: Previous studies on hypothyroid subjects have indicated serious psychiatric symptoms affecting the patients' quality of life. The present prospective cross-sectional study's aim was to examine these symptoms in thyroid patients with different functional states. A total of 254 patients (age: 56 +/- 14 years [mean +/- standard deviation], 181 female, 73 male) referred to a hospital for radioiodine treatment of hyperthyroidism or for follow-up of differentiated thyroid cancer, respectively, were included. All patients underwent the twelve-item general health questionnaire, which is an instrument for detecting mood disturbances. Euthyroid and hyperthyroid patients did not differ significantly in their general health questionnaire score (11 +/- 5 vs. 11 +/- 7), nor did subclinical hyperthyroid (11 +/- 6) or subclinical hypothyroid subjects (12 +/- 5). In contrast, hypothyroid patients showed a significantly higher mean score (17 +/- 7, p < 0.001, ANOVA). Binary logistic regression revealed that hypothyroidism increases age and gender-adjusted risk for critical mood deterioration by seven-fold. Thus, hypothyroidism represents a widely underestimated functional condition that may severely affect mental health.
Abstract: A recent investigation showed that intracerebral radioactivity concentrations can reliably be quantified in vivo with a small-animal PET device. The purpose of the current study was to investigate the binding characteristics of the D(2) receptor radioligand (18)F-(3-N-methyl)benperidol ((18)FMB) in rat striatum by determining receptor density (B(max)) and affinity (K(d)) in vivo. For validation, K(d) and B(max) additionally were determined in vitro using storage phosphor autoradiography. METHODS: Striatal radioactivity was measured with PET in 8 Sprague-Dawley rats after injection of (18)FMB in increasing specific activities. Free radioligand concentrations were estimated from cortical radioactivity concentrations and were subtracted from striatal radioactivity concentrations to obtain specific binding. In vitro saturation experiments were performed on 7 further rats according to the isotopic dilution method. Specific binding was determined by both subtraction of (18)FMB binding in the presence of raclopride and subtraction of cortical radioactivity concentrations from total radioligand binding. Saturation binding curves were obtained by plotting specifically bound radioligand concentrations against free radioligand concentrations and were evaluated with regression analysis. RESULTS: PET yielded a K(d) of 6.2 nmol/L and a B(max) of 16 fmol/mg for the striatal D(2) receptor. In vitro, K(d) and B(max) amounted to 4.4 nmol/L and 84.1 fmol/mg (subtraction of (18)FMB binding in the presence of raclopride), respectively, and 7.9 nmol/L and 70.1 fmol/mg (subtraction of cortical radioactivity concentrations), respectively. CONCLUSION: K(d) values measured with PET and autoradiography agreed and corresponded to inhibition constants obtained in previous in vitro studies. B(max) values lay within the same order of magnitude. The results of in vitro saturation binding analyses also agreed, irrespective of the mode of determination of free radioligand concentrations. Thus, B(max) and K(d) may be determined with PET in analogy to the evaluation of in vitro binding data by regression analysis of bound-versus-free ligand concentrations. Our results show that small-animal tomographs are valuable tools for the in vivo characterization of receptor radioligands as an alternative to autoradiography.
Abstract: Unilateral destruction of the substantia nigra by local application of 6-hydroxydopamine (6-OHDA) serves as an animal model for Parkinson's disease. In this study, the changes in neostriatal dopamine D(2) receptor density were investigated with a small animal positron emission tomograph (PET) before and after 6-OHDA lesion. PET scans were performed in 14 rats after injection of the D(2) receptor radioligand [(18)F] N-methylbenperidol. After the first scan (day 0), nigrostriatal pathways were lesioned by unilateral injections of 6-OHDA. Further PET scans were performed on days 2 and 14 post-lesion. For both striata, B(max) values were determined from saturation binding curves with non-linear regression analysis. In the striatum ipsilateral to the lesion, B(max) initially amounted to 19.3+/-1. 9 fmol/mg (mean+/-SD) and increased to 19.7+/-2.2 and 29.9+/-5.7 fmol/mg on days 2 and 14 post-lesion, respectively. Contralateral B(max) values increased from 19.2+/-2 fmol/mg prior to the lesion to 21.2+/-2.9 and 28.6+/-5.7 fmol/mg on days 2 and 14, respectively. On day 14, the ipsilateral saturation binding curve differed from the ipsilateral pre-lesion curve (P=0.04; F test). When the contralateral pre-lesion saturation binding curve was compared with the contralateral post-lesion curve on day 14, a P value of 0.08 was obtained. This first serial in vivo imaging study of 6-OHDA-lesioned rats showed a time-dependent increase in striatal D(2) receptor density on both sides, the increase being more pronounced ipsilateral to the lesion. This result implies that compensatory mechanisms in the intact hemisphere contribute to regenerative processes following nigrostriatal dopaminergic denervation. Overall, our findings show the feasibility of repetitive in vivo studies of striatal receptor density with a small animal tomograph. Moreover, the applied in vivo saturation binding technique provides a versatile method for the quantification of time-dependent changes in the concentration of receptor binding sites.
Abstract: AIM: The study presented here firstly compares the distribution of the binding potential of the serotonin-5HT2A receptor as measured in vivo with data of receptor density taken from literature. Secondly, the sensitivity of the method to detect gradual differences in receptor densities is evaluated. METHODS: Positron emission tomography (PET) studies were carried out in 6 healthy volunteers using the selective serotonin-5HT2A ligand 18F-altanserin. The binding potential was quantified in 12 regions using Logan's graphical method and the equilibrium method. These data were compared to the distribution of receptor density as taken from literature. RESULTS: The binding data in vivo correlated to autoradiography data (post mortem) with r = 0.83 (Pearson regression coefficient; p < 0.0001). A difference in the receptor density between two regions could be detected with p < 0.05 when it amounted at least to 18%. CONCLUSION: This study demonstrates a good agreement between in vivo data obtained with 18F-altanserin and PET in healthy volunteers and the true autoradiographically determined distribution of 5HT2A receptors in human brains. The in vivo method seems to be sensitive enough to detect changes in receptor density of more than 18%.
Abstract: Several groups have developed high-resolution PET systems and shown the feasibility of in vivo studies on small laboratory animals. In this investigation, one of these systems was validated for the performance of receptor imaging studies. For this, the radiotracer concentrations obtained in the same animals with PET and with autoradiography were quantified, and the correspondence between both methods was assessed by means of correlation analysis. METHODS: Striatal radioactivity was measured in 10 Sprague-Dawley rats after injection of 60 +/- 10 MBq of the dopamine D(2) receptor ligand (18)F-(N-methyl)benperidol in 6 time frames of 6 min each. On completion of the scans, animals were killed, and their brains were removed and sectioned using a cryostat microtome. Coronal slices were subjected to storage phosphor autoradiography with BaFBr:Eu(2+)-coated imaging plates. Striatal radioactivity was quantified in both modalities using region-of-interest analysis and activity standards. RESULTS: After partial-volume correction, the median of striatal radioactivity concentration measured with PET was 0.40 MBq/cm(3) (25th percentile, 0.32; 75th percentile, 0.44). Radioactivity concentrations determined by means of storage phosphor autoradiography amounted to 0.42 MBq/cm(3) (25th percentile, 0.24; 75th percentile, 0.51). Correlation of striatal radioactivity values yielded a Pearson correlation coefficient of 0.818 (P = 0.002). Radioactivity accumulation in Harder's glands led to an overestimation of striatal activity concentrations by approximately 5%. The median of striatal radioactivity concentration after spillover correction decreased slightly to 0.38 MBq/cm(3) (25th percentile, 0.30; 75th percentile, 0.43). Correlation of striatal radioactivity values after spillover correction yielded a Pearson correlation coefficient of 0.824 (P = 0.002). CONCLUSION: The results show a significant positive correlation between radioactivity values obtained with PET and storage phosphor autoradiography used as the gold standard. Because we applied a selective dopamine D(2) receptor radioligand and because radioactivity concentrations could be reliably quantified in the target region, we may infer that in vivo receptor binding studies will be possible in small laboratory animals.
Abstract: Prior studies have shown that the neurokinin substance P (SP) has anxiolytic-like effects when administered into the nucleus basalis (NB) area of the rat ventral pallidum. The present work was performed to examine whether the anxiolytic effects of SP in the nucleus basalis can be assigned its amino (N)- or carboxy (C)-terminal moiety. Using the elevated plus-maze model of anxiety in combination with unilateral injection of N-terminal SP(1-7) or C-terminal SP(7-11) into the NB region, we found that the treatment with either SP-fragment increased the number of entries into and time spent on the open arms as well as excursions into the end of the open arms, indicative of an anxiolytic-like profile. Furthermore, the effective doses of SP(1-7) (0.67 ng) and SP(7-11) (0.45 ng) were equimolar to the dosage of the whole SP molecule (1 ng), which was effective to reduce anxiety. Thus, the results support earlier findings that ventral pallidal injection of SP has anxiolytic-like effects and provide new evidence that fragments of SP, representing the N- and C-terminal domain of the peptide can reduce fear-parameters at a concentration similar to that of the parent peptide.
Abstract: Reduction of neuronal activity in frontocortical and limbic circuits is considered a characteristic of depression. We aimed to test this hypothesis by pooling all available data from experimental literature. All investigations were included comparing regional cerebral blood flow (rCBF) or glucose metabolism (rCMRGlc) between acutely depressed unipolar major depressive patients and healthy controls. For cortical and subcortical regions we computed the percentage difference between depressives (n = 337) and controls (n = 321). In patients with unipolar major depression rCBF and rCMRGlc were lowered in left (-4.4%, P = 0.022) and right frontal (-3.2%, P = 0.053), left (-1.7%, P = 0.061) and right temporal (-3.0%, P=0.003), left (-6.5%, P = 0.002), and right parietal (-8.8%, P=0.001), and left (-6.6%, P = 0.083) and right occipital cortex (-4.2%, P = 0.02). Moreover, there were reductions in left (-6.3%, P = 0.029) and right basal ganglia (-4.8%, P = 0.002), left (-3.4%, P = 0.114) and right thalamus (-3.1%, P = 0.036), and left limbic system (-2.2%, P = 0.127). Parameters were increased by 1.0% (P = 0.714) only in the right limbic system. There were no hemispheric asymmetries (P > 0.05). Moreover, there was no indication for an anterior-posterior gradient (P > 0.05), and thus no 'hypofrontality'. In contrast to the current view, the data indicate a diffuse cortical rather than regionalized reduction of neuronal activity in unipolar major depression.
Abstract: The neurokinin Substance P (SP) is widely distributed in the central nervous system and has been extensively studied in various functional aspects. This review focuses on the behavioral relevance of SP. Here we show that SP can have memory-promoting, reinforcing and anxiolytic-like effects when administered systemically or into the nucleus basalis of the ventral pallidum. These effects seem to be mediated via the SP-preferring NK(1)receptor and differentially related to N- versus C-terminal fragments of the undecapeptide. Secondly, SP injection into the ventral pallidum can lead to increases of acetylcholine in frontal cortex and dopamine in nucleus accumbens, suggesting that the hypermnestic, positively reinforcing and anxiolytic effects observed upon basal forebrain injection of SP are mediated by activation of the nucleus accumbens-ventral pallidum circuitry. Furthermore, SP and certain SP-fragments may not only be considered to have beneficial behavioral effects in normal animals, but can also prevent lesion-induced functional deficits and improve the speed of recovery. This indicates that SP agonists might also have a neuroprotective capacity in parallel with recovery-promoting actions.
Abstract: The neurokinin substance P has reinforcing effects when administered into the nucleus basalis of the rat's ventral pallidum and these effects are encoded by its carboxy-terminal amino acid sequence. The present study examined the effect of prior treatment with the tachykinin NK1 receptor antagonist WIN51,708 on the conditioned place preference produced by intrabasalis injection of substance P and its carboxy-terminal heptapeptide analog dimethyl-C7. Pretreatment with WIN51,708 (10 and 20 mg/kg, i.p.) dose-dependently reversed the place preference produced by intrabasalis substance P (0.74 pmol). The carboxy-terminal analog dimethyl-C7 (0.74 pmol) was also found to act as a reinforcer following injection into the nucleus basalis region, but unlike for substance P, the behavioral effects of dimethyl-C7 could not be completely antagonized by joint administration of the NK1 antagonist. When injected alone, WIN51,708 did not influence the preference behavior. These findings suggest that the reinforcing effects of substance P in the nucleus basalis region might be mediated via NK receptive sites. The failure of WIN51,708 to completely antagonize the behavioral effects of dimethyl-C7 is interesting in the light of evidence, indicating that the carboxy-terminal substance P analog shows higher affinity for the tachykinin NK3 than for the NK1 receptor subtype.
Abstract: We reported previously that the neurokinin substance P has anxiolytic-like effects when administered into the nucleus basalis of the rat ventral pallidum. The present study aimed to determine the possible involvement of the neurokinin-1 receptor in the anxiolytic action of intrabasalis substance P injection. Behavioral testing was performed in the rat elevated plus-maze model of anxiety. Microinjection of substance P (1 ng) into the nucleus basalis increased sojourn times on the open arms, excursions into the end of the open arms and scanning over the edge of an open arm, indicative of an anxiolytic-like profile. The non-peptide neurokinin-1 receptor antagonist WIN51,708, administered i.p. 20 min prior to intrabasalis substance P injection, antagonized the anxiolytic effects of the neurokinin in a dose-dependent manner. WIN51,708 at 10 mg/kg diminished, while at the higher dose of 20 mg/kg the antagonist completely blocked, the effect of substance P on anxiety-related behaviors. These findings suggest that the anxiolytic-like effects of substance P in the nucleus basalis are mediated through neurokinin-1 receptive sites.
Abstract: The neuropeptide substance P is known to have mnemogenic and reinforcing actions and can exert neurotrophic and regenerative effects in vitro as well as in vivo. Furthermore, our previous work in the rat showed that either pre- or post-lesion treatment with substance P can promote functional recovery in cases of partial nigrostriatal dopamine lesions. Other work has provided evidence that the effects of substance P might be differentially encoded by its C- and N-terminal fragments. The C-terminal fragment was found to be reinforcing, whereas the mnemogenic as well as neurotrophic properties have been ascribed to the N-terminal sequences. Given these relations, we asked here whether pre-lesion treatment with either a C- or an N-terminal fragment of substance P might differentially affect the behavioral and neurochemical outcome of nigrostriatal dopamine lesions. Therefore, either substance P1-7 or substance P5-11 (37 nmol/kg each) was administered intraperitoneally daily for eight consecutive days before unilateral 6-hydroxy-dopamine lesions of the substantia nigra. Control rats received pre-lesion treatment with vehicle. Furthermore, we investigated the effects of pre-treatment with Boc-cholecystokinin-4 (0.91 nmol/kg), as we had found an increase in dopamine metabolism in animals that were pre-treated with cholecystokinin-8 in a former study. In accordance with our previous work, drug treatment effects were observed when excluding animals with most severe dopamine lesions: In animals with partial lesions (residual neostriatal dopamine levels of more than 10%), lesion-dependent asymmetries in turning behavior were observed in animals that were pre-treated with vehicle-, substance P1-7, or Boc-cholecysto-kinin-4, whereas turning after pre-treatment with substance P5-11 was not significantly asymmetrical. Furthermore, the ipsi- and contra-lateral neostriatal dopamine levels did not differ significantly in this group. Moreover, pre-treatment with substance P5-11 affected dopamine metabolism in the neostriatum and in the ventral striatum, as indicated by increased ratios of dihydroxyphenyllic acid to dopamine. The data provide the first evidence that the promotive effects of substance-P treatment in the unilateral dopamine lesion model might be mediated by its C-terminal and might depend on actions on residual dopamine mechanisms.
Abstract: The neuropeptide substance P (SP) has been implicated in the control of various neuro-behavioral functions including reinforcement and learning processes. It also exerts neurotrophic and regenerating effects in vitro and in vivo. A previous study indicated a potential therapeutic effect of SP in rats with partial 6-hydroxydopamine lesions of the nigrostriatal dopamine system when SP was administered after the lesion. The purpose of the present study was to determine whether prelesion treatment with SP would also interact with the effects of unilateral 6-hydroxydopamine lesion of the substantia nigra. Thus, SP (50 micrograms/kg) was administered i.p. on 8 consecutive days prior to unilateral lesion of the substantia nigra. Furthermore, we investigated the effects of prelesion treatment with cholecystokinin-8S (CCK; 1 microgram/kg), another neuropeptide, which is closely related to dopaminergic neurons, and which also can have neurotrophic and neuroprotective functions. Our results show that animals with partial neostriatal dopamine depletions (residual dopamine levels of more than 10%) did not show turning asymmetries when pretreated with SP, whereas animals pretreated with vehicle exhibited an initial ipsiversive asymmetry from which they recovered. In contrast, behavioral asymmetries were most pronounced in animals which had been pretreated with CCK. These peptide treatments did not affect the degree of neostriatal dopamine depletion; however, dihydroxyphenylacetic acid/dopamine ratios were enhanced in the neurostriatum of animals with partial dopamine damage after SP- and CCK-pretreatment, and in the ventral striatum of SP-pretreated animals. These data provide evidence that prelesion treatment with SP, but not with CCK, can alleviate functional deficits induced by a partial nigro-striatal dopamine lesion. This effect may be related to enhanced ventral striatal dopamine activity and/or to the peptide's known effects on learning, motivation, and emotion.
Abstract: Deficits in associative functions seen with senescence may be based, at least in part, on a decreased availability of trophic factors in the CNS. A reduced concentration of neurokinins, including undecapeptide substance P (SP), also accompanies aging. Thus, given the change in SP metabolism and the known mnemogenic as well as neurotrophic/neuroprotective effects of the peptide, it seems possible that age-related deficits in associative processes could be influenced by treatment with exogenous SP. In the present study, 30-month-old Wistar rats were injected daily with SP (50 or 250 micrograms/kg, intraperitoneally) starting 1 week before they were tested on the Morris water maze task and on motor coordination tests. Control groups included vehicle-injected old and adult (3-month-old) rats. Over the days of maze testing, application of the substances was performed 5 h after testing daily for 15 days and after the last drug delivery, maze testing was continued for 4 more days. The main finding of this study is that chronic administration of both dosages of SP (50 and 250 micrograms/kg) improved the maze performance of the old rats. This facilitatory effect of SP on performance was also evident after the drug treatment had been terminated in the course of maze testing. Furthermore, chronic application of SP in a dose range of 50-250 micrograms/kg was found to reduce age-related deficits in motor capacities.
