[3H]paroxetine binding is altered in the hippocampus but not the frontal cortex or caudate nucleus from subjects with schizophrenia

A Novel Method to Estimate Levels of Receptors Using an Allosteric Modulator: Focus on Muscarinic M1 Receptor

This chapter outlines some of the general principles that need to be considered when developing a radioligand binding assay to measure the affinity and density of radioligand binding to a receptor in tissue or on cells. In addition it describes an innovative step forward in using radioligand binding assays to measure levels of muscarinic M1 receptors in human postmortem CNS, using both membrane binding and in situ radioligand binding. These examples show how, using receptor-specific allosteric modulators, it is possible to gain an estimate of the density of a single receptor using a radioligand that is not totally specific to the target site of interest. Given there is a growing understanding that there are problems with antibodies not showing specificity to their supposed target protein, well-characterized radioligand binding techniques still provide an important tool when studying receptor density in tissues and cells.

Serotonin modulation of hippocampal functions: From anatomy to neurotherapeutics

The hippocampal region receives a dense serotoninergic innervation originating from both medial and dorsal raphe nuclei. This innervation regulates hippocampal activity through the activation of distinct receptor families that are expressed in excitatory and inhibitory neurons, terminals of several afferent neurotransmitter systems, and glial cells. Preclinical and clinical studies indicate that hippocampal dysfunctions are involved in learning and memory deficits, dementia, Alzheimer's disease, epilepsy and mood disorders such as anxiety, depression and post-traumatic syndrome disorder, whereas the hippocampus participates also in the therapeutic mechanisms of numerous medicines. Not surprisingly, several drugs acting via 5-HT mechanisms are efficacious to some extent in some diseases and the link between 5-HT and the hippocampus although clear remains difficult to untangle. For this reason, we review reported data concerning the distribution and the functional roles of the 5-HT receptors in the hippocampal region in health and disease. The impact of the 5-HT systems on the hippocampal function is such that the research of new 5-HT mechanisms and drugs is still very active. It concerns notably drugs acting at the 5-HT_1A,_2A,_2C,_4,6 receptor subtypes, in addition to the already existing drugs including the selective serotonin reuptake inhibitors.

Comparing the effect of the subcategories of atypical antipsychotic medications on cognition in schizophrenia using a meta-analytic approach

OBJECTIVES

The aim of this study was to compare the two most commonly prescribed classes of atypical antipsychotic medications (i.e., -pines and -dones) with regard to their effects on cognition in patients with schizophrenia.

DATA SOURCES

Ovid Technologies web-based software was used to search the Medline and PsycINFO computerized databases to identify articles that met the inclusion criteria.

REVIEW METHODS

The search was limited to papers published after 1990, written in English, employing human subjects, using atypical antipsychotics, using a within-subjects design or control group of patients with schizophrenia for comparisons, using participants aged from 18-65, and employing standardized neuropsychological measures.

RESULTS

A total of 996 eligible studies were identified, and of these 19 were finally analyzed. Nine domains of cognitive functioning were assessed. The two groups of agents produced equivalent overall effects (-dones = .254 versus -pines = .202). The -pines were found to improve the domains of attention/working memory, executive functioning, fluency, nonverbal memory, processing speed, and verbal memory, each with a significant, small effect size. The -dones were found to improve attention/working memory, executive functioning, motor function, nonverbal memory, processing speed, and verbal memory, each with a significant, small effect size. Failsafe N was robust for all of the domains for the -pines, but only for the verbal memory domain for the -dones, suggesting that the significant findings for the other domains with the -dones are more tenuous.

CONCLUSION

The results indicate that the agents were largely equivalent and that there was no clear evidence that the pattern of cognitive effects differed as a result of the agent applied. The effects themselves, while statistically significant, were small, indicating that some or all of the differences may be attributable to practice effects on the instruments employed.

Altered interregional correlations between serotonin transporter availability and cerebral glucose metabolism in schizophrenia: A high-resolution PET study using [11C]DASB and [18F]FDG

The purpose of the present study was to investigate the patterns of interregional correlations of serotonin transporter (SERT) availability with glucose metabolism using 7-Tesla magnetic resonance imaging (MRI) and high-resolution positron emission tomography (PET) with ¹¹C-3-amino-4-(2-dimethylaminomethylphenylthio)benzonitrile ([¹¹C]DASB) and [¹⁸F]fluorodeoxyglucose ([¹⁸F]FDG) in antipsychotic-free patients with schizophrenia in order to shed new light on the disrupted functional connectivity in schizophrenia. Nineteen patients with schizophrenia and 18 healthy controls underwent high-resolution PET and MRI. The binding potential (BP_ND) of [¹¹C]DASB and standardized uptake value ratio (SUVR) of [¹⁸F]FDG were obtained. In SERT availability, the region of interest (ROI)-based analyses showed no significant group differences in any region, except for the anterior hippocampus where the SERT availability was lower in patients with schizophrenia than in controls. The ROI- and voxel-based analyses revealed that the [¹⁸F]FDG SUVR values were significantly lower in patients than in controls in the right superior frontal gyrus and medial part of the left superior frontal gyrus. Regarding the interregional correlations of [¹¹C]DASB BP_ND with [¹⁸F]FDG SUVR, more widespread positive correlations across the brain regions were observed in control subjects than in patients with schizophrenia. Notably, the patients and control subjects showed statistically significant differences in correlations between the SERT availability in the parietal and temporal cortices and the glucose metabolism in the posterior cingulate cortex. These results suggest abnormal functional connectivity between the higher-order cortical regions in schizophrenia and a possible important role of the posterior cingulate gyrus and its related circuitry in the pathophysiology of schizophrenia.

A review of genetic alterations in the serotonin pathway and their correlation with psychotic diseases and response to atypical antipsychotics

Serotonin is a neurotransmitter that plays a predominant role in mood regulation. The importance of the serotonin pathway in controlling behavior and mental status is well recognized. All the serotonin elements - serotonin receptors, serotonin transporter, tryptophan hydroxylase and monoamine oxidase proteins - can show alterations in terms of mRNA or protein levels and protein sequence, in schizophrenia and bipolar disorder. Additionally, when examining the genes sequences of all serotonin elements, several single nucleotide polymorphisms (SNPs) have been found to be more prevalent in schizophrenic or bipolar patients than in healthy individuals. Several of these alterations have been associated either with different phenotypes between patients and healthy individuals or with the response of psychiatric patients to the treatment with atypical antipsychotics. The complex pattern of genetic diversity within the serotonin pathway hampers efforts to identify the key variations contributing to an individual's susceptibility to the disease. In this review article, we summarize all genetic alterations found across the serotonin pathway, we provide information on whether and how they affect schizophrenia or bipolar disorder phenotypes, and, on the contribution of familial relationships on their detection frequencies. Furthermore, we provide evidence on whether and how specific gene polymorphisms affect the outcome of schizophrenic or bipolar patients of different ethnic groups, in response to treatment with atypical antipsychotics. All data are discussed thoroughly, providing prospective for future studies.

Serotonin transporter availability in thalamic subregions in schizophrenia: a study using 7.0-T MRI with [(11)C]DASB high-resolution PET

The serotonin transporter (SERT) is an integral protein that provides an index of serotonergic innervation. Until recently, few studies have investigated SERT binding in thalamic subregions in schizophrenia. The purpose of this study was to examine SERT availability in thalamic subdivisions (anterior nucleus, mediodorsal nucleus, and pulvinar) using 7.0-T magnetic resonance imaging (MRI) and high-resolution positron emission tomography (PET) with (11)C-3-amino-4-(2-dimethylaminomethylphenylthio)benzonitrile ([(11)C]DASB) in schizophrenia. Antipsychotic-free patients with schizophrenia (n=12) and healthy controls (n=15) underwent PET and MRI scans. For SERT availability, the binding potential with respect to non-displaceable compartment (BPND) was derived using the simplified reference tissue model (SRTM2). The analysis revealed that there were no significant differences in SERT availability between the two groups. In patients with schizophrenia, the severity of negative symptoms had a negative correlation with SERT availability in the anterior nucleus of the left thalamus. The present study did not reveal significant differences in SERT availability in thalamic subdivisions between patients with schizophrenia and control subjects. The association of SERT availability in the anterior nucleus with negative symptoms may suggest a role for the anterior thalamic nucleus in the pathophysiology of symptoms of schizophrenia. The ultra-high resolution imaging system could be an important asset for in vivo psychiatric research by combining structural and molecular information.

Alterations in the serotonin system in schizophrenia: a systematic review and meta-analysis of postmortem and molecular imaging studies

Serotonergic dysfunction is thought to contribute to the pathophysiology of schizophrenia but the evidence has not been systematically synthesised before. We therefore systematically reviewed postmortem and in vivo molecular imaging studies of serotonin function in schizophrenia. We identified fifty relevant studies investigating eight different serotonin receptor systems in a total of 684 patients and 675 controls. Meta-analysis of postmortem studies found an elevation in prefrontal 5-HT1A receptors with a moderate to large effect size (N=8, 85 patients and 94 controls, SMD=0.60; CI: 0.17-1.03; p=0.007) and a reduction with a large effect size in prefrontal 5-HT2A receptors (N=8, 168 patients and 163 controls, SMD=-0.73; CI: -1.33, -0.12; p=0.019) in schizophrenia vs healthy controls. The evidence for alterations in serotonin transporter availability or other serotonin receptors (5-HT1B; 5-HT1D; 5-HT3; 5-HT4; 5-HT7) is limited. There are fewer studies investigating 5-HT receptors in schizophrenia with neuroimaging. Findings indicated possible 5-HT alterations at psychosis onset, although due to the limited number it was not possible to combine studies in a meta-analysis. Further in vivo studies, particularly in drug naive patients using radiotracers that can index high affinity states, will help determine if the postmortem findings are primary or secondary to other factors.

Synapse regression in depression: the role of 5-HT receptors in modulating NMDA receptor function and synaptic plasticity

Depression is accompanied by an increase in activity in the amygdala and a decrease in the rostral anterior cingulate cortex (rACC), with the former attributed to a failure of the latter to exert its normal inhibitory influence. This failure is likely due to regression of synaptic connections between the rACC and the amygdala, a process reversed in part by selective serotonin reuptake inhibitors (SSRIs). The present work presents a hypothesis as to how SSRIs might bring about this process and hence normalization of activity, at least in patients that are responsive to SSRIs. Serotonin receptors of the excitatory 5-HT(2A)R class increase N-methyl-D-aspartate receptor (NMDAR) efficacy, while those of the inhibitory 5-HT(1A)R class decrease NMDAR efficacy. A decrease of 5-HT transporter (5-HTT) efficacy, either during human development through functional polymorphisms, or in animals through 5-HTT transgenic knockouts, is accompanied by a decrease in 5-HT(1A)R and hence an increase in excitability and NMDAR efficacy which drives an increase in synaptic spines in the amygdala. As the limbic region of the brain normally possesses high levels of 5-HT(1A)R the effect of loss of these is to increase excitation in this region, as is observed. Changes in the level of extracellular 5-HT in adult animals also modulates the density of synaptic spines, with these increasing with an increase in 5-HT, possibly as a consequence of increases in 5-HT(2A)R activity over that of 5-HT(1A)R. Increasing extracellular levels of 5-HT with SSRIs would then lead to an increase in excitability and in synaptic spines for afferents in the dorsal rostral anterior cingulate cortex but not in the ventral regions such as the amygdala that have few 5-HT(2A)R. This allows dorsal regions to once more exert their inhibitory influence over ventral regions. In this way, SSRIs may exert their effect in normalizing dorsal hypometabolism and ventral hypermetabolism in those suffering from depression.

Haplotype analysis confirms association of the serotonin transporter (5-HTT) gene with schizophrenia in the Han Chinese population

Serotonin transmission has long been suspected as being involved in the pathogenesis of schizophrenia. 5-HTT is a promising candidate gene for schizophrenia due to its critical role in regulating serotonin transmission and role in the mechanism of the atypical antipsychotic drugs. A common polymorphism STin2 VNTR in the 5-HTT gene has been extensively investigated in the genetic association studies, but the results are conflicting. Meanwhile, the SNPs of the 5-HTT gene have been much less explored. We therefore conducted a case-control study of the association between STin2 VNTR and three tagging SNPs in 5-HTT and schizophrenia in the Han Chinese population based on a cohort of 329 schizophrenic patients and 288 control subjects. No association was found in the single locus, but haplotype-based analyses revealed significant association between two haplotypes with schizophrenia even after Bonferroni correction (P=0.00000538 and 0.011).

The serotonin transporter 5-HTTPR polymorphism is associated with current and lifetime depression in persons with chronic psychotic disorders

OBJECTIVE

Variation in the serotonin transporter gene (SLC6A4) promoter region has been shown to influence depression in persons who have been exposed to a number of stressful life events.

METHOD

We evaluated whether genetic variation in 5-HTTLPR, influences current depression, lifetime history of depression and quantitative measures of depression in persons with chronic psychotic disorders. This is an association study of a genetic variant with quantitative and categorical definitions of depression conducted in the southwest US, Mexico and Costa Rica. We analyzed 260 subjects with a history of psychosis, from a sample of 129 families.

RESULTS

We found that persons carrying at least one short allele had a statistically significant increased lifetime risk for depressive syndromes (P < 0.02, odds ratio 2.18, 95% CI 1.10-4.20).

CONCLUSION

The 'ss' or 'sl' genotype at the 5-HTTLPR promoter polymorphic locus increases the risk of psychotic individuals to develop major depression during the course of their illness.

Binding of paroxetine to the serotonin transporter in membranes from different cells, subcellular fractions and species

The binding of [(3)H]-paroxetine to membrane serotonin transporter (SERT) has been studied in membranes from different sources and subcellular fractions. From rat were membranes from venous blood platelets, brain total cortex, brain microsomes, brain crude and purified synaptosomes. Membranes were obtained from venous blood platelets from human volunteers and from brain cortex tissue from neurosurgery (cerebral lobectomies following craniocerebral injuries). The main finding was that the K (D) of paroxetine binding to the SERT was the same for platelet and nerve ending (synaptosomal) membranes. That parameter was significantly lower in membranes from brain microsomes and cortex total tissue. No species related difference was found, where comparison was possible, between human and rat tissue. The equality of K (D) of paroxetine binding to blood platelet membranes and to membranes from nerve endings appears to encourage the use of such membranes as a model for brain SERT. Binding at two different temperatures for several of the fractions suggests that paroxetine-SERT interaction is entropy-driven.

Increased levels of serotonin 2A receptors and serotonin transporter in the CNS of neuregulin 1 hypomorphic/mutant mice

Changes in neuregulin 1 expression have been reported in the CNS from subjects with schizophrenia. As neuregulin 1 is important in cortical development we postulated that changes in neuregulin 1 expression may contribute towards changes in cholinergic, glutamatergic and serotonergic markers that are well documented in the CNS of subjects with that disorder. To begin to test this hypothesis, we used in situ radioligand binding to measure levels of muscarinic M1/M4 receptors, the kainate receptor, the NMDA receptor, the serotonin 2A receptor, the serotonin 1A receptor and the serotonin transporter in the CNS from heterozygous transmembrane domain neuregulin 1 mutant mice. The major outcomes from these studies was the demonstration of an overall increase in levels of the serotonin 2A receptor (F=11.3, d.f.=3,1,72, p=0.0012) and serotonin transporter (F=5.00, d.f.=1,3,72, p<0.05) in the mutant mice. Levels of the other receptors did not vary in the mutant mice compared to their wild type-like litter mates. These data are the first evidence to suggest that NRG1 gene expression may be involved in regulating the development of the serotonergic system in the mammalian CNS.

Neuroreceptor imaging studies in schizophrenia

The ability of SPECT and PET to image specific biomolecules in the living brain provides a unique tool for clinical researchers. It is therefore not surprising that the use of neuroreceptor-imaging techniques has become more widespread over the past decade. This article reviews the application of these techniques to the study of schizophrenia. The design of neuroreceptor-imaging studies performed in the field of schizophrenia research can be broadly divided into two categories: (1) studies of pathophysiology and (2) studies of pharmacology. The former examines neuroreceptor and neurotransmitter parameters in individuals with schizophrenia compared to control subjects in order to provide a better understanding of the disease process. Studies of pharmacology seek to elucidate the mechanism of action for the treatments utilized in schizophrenia. This review will consider both studies of pathophysiology and pharmacology, with a discussion of the application of these techniques to drug development.

Alterations of serotonin transmission in schizophrenia

A role for serotonin alterations in the pathophysiology of schizophrenia has long been suspected because of the psychotogenic effects of serotonergic agonists and the therapeutic effects of 5-HT(2) antagonism. This chapter is a review of the evidence derived from pharmacological studies, postmortem, and imaging studies that have assessed the role of serotonin transmission in schizophrenia. While a clear picture of specific serotonergic alterations in schizophrenia has not emerged despite much research, this review reinforces a modulatory role of serotonergic agents on dopamine transmission in schizophrenia, which may contribute to the therapeutic effects of atypical antipsychotics.

Characterization of the serotonin transporter in lymphocytes and platelets of schizophrenia patients treated with atypical or typical antipsychotics compared to healthy individuals

A rapidly growing body of data suggests that abnormalities in serotonergic function might be involved in the pathophysiology of schizophrenia and that serotonergic mechanisms play a role in the therapeutic effects of antipsychotics. The activity of the serotonin transporter (5-HTT), as determined by [(3)H]5-HT uptake to blood lymphocytes, was measured in 38 medicated schizophrenia patients (15 of them treated with typical antipsychotics and 23 treated with atypical antipsychotics) and 15 healthy control subjects. In addition, the pharmacodynamic characteristics of platelet 5-HTT were assessed by [(3)H]citalopram binding. There were no significant differences in the density (B(max)) of platelet [(3)H]citalopram binding sites between the three groups. Similarly, the dissociation constant (K(d)) values were indistinguishable. There were no significant differences in the maximal uptake velocity (V(max)) of [(3)H]5-HT to fresh lymphocytes between the three groups. The affinity (K(m)) values of 5-HT to the 5-HTT were significantly higher in schizophrenia patients treated with typical antipsychotics compared with control subjects. The K(m) values in schizophrenia patients treated with atypical antipsychotics were significantly lower compared with those observed in the group of schizophrenia patients treated with typical antipsychotics; however, they were comparable to values in the control group. The high values of K(m) associated with typical antipsychotic treatment may be relevant to the high risk of developing extrapyramidal side effects (EPS). The role of the various components of the serotonergic system in the etiopathology of schizophrenia and the mechanisms by which antipsychotics achieve their therapeutic effects need to be further evaluated.

Fatty acids differentially affect serotonin receptor and transporter binding in the rat brain

The aim of this study was to examine the influence of different fat diets on serotonin receptor and transporter binding. Male Sprague-Dawley rats were fed a diet of either high saturated fat, omega-6 polyunsaturated fatty acid, omega-3 polyunsaturated fatty acid or low fat (control) for eight weeks. Using Beta-Imager quantification techniques, [(3)H]ketanserin, [(3)H]mesulergine and [(3)H]paroxetine binding to serotonin (5-HT)(2A), 5-HT(2C) receptors and 5-HT transporters (5-HTT) was measured throughout the brain in all four groups. All three high fatty acid diets influenced serotonin receptor binding, however the most pronounced effects were that compared with the low fat control group, i) 5-HT(2A) receptor binding was increased in the caudate putamen, but reduced in the mammillary nucleus in high saturated fat and high omega-6 polyunsaturated fatty acid diet groups; ii) 5-HT(2C) receptor binding was reduced in the mamillary nucleus of saturated fat group and reduced in prefrontal cortex of the omega-6 polyunsaturated fatty acid and omega-3 polyunsaturated fatty acid groups; and iii) 5-HTT binding was reduced in the hippocampus in the omega-6 polyunsaturated fatty acid group. Overall, the omega-6 polyunsaturated fatty acid diet exerted the most influence on serotonin receptor and transporter binding. These results may be of importance in relation to neuropsychiatric diseases such as schizophrenia, where associations between altered fatty acid levels and the serotonergic system have been made.

Membrane phospholipid composition, alterations in neurotransmitter systems and schizophrenia

This review addresses the relationship between modifications in membrane phospholipid composition (MPC) and alterations in dopaminergic, serotonergic and cholinergic neurotransmitter systems in schizophrenia. The main evidence in support of the MPC hypothesis of schizophrenia comes from post-mortem and platelet studies, which show that in schizophrenia, certain omega-3 and omega-6 polyunsaturated fatty acid (PUFA) levels are reduced. Furthermore, examination of several biochemical markers suggests abnormal fatty acid metabolism may be present in schizophrenia. Dietary manipulation of MPC with polyunsaturated fatty acid diets has been shown to affect densities of dopamine, serotonin and muscarinic receptors in rats. Also, supplementation with omega-3 fatty acids has been shown to improve mental health rating scores, and there is evidence that the mechanism behind this involves the serotonin receptor complex. This suggests that a tight relationship exists between essential fatty acid status and normal neurotransmission, and that altered PUFA levels may contribute to the abnormalities in neurotransmission seen in schizophrenia.

Serotonin transporter availability in patients with schizophrenia: a positron emission tomography imaging study with [11C]DASB

BACKGROUND

Postmortem studies have reported several alterations in serotonin transporter (SERT) binding parameters in patients with schizophrenia. The aim of this study was to compare SERT availability in vivo in patients with schizophrenia and matched control subjects.

METHODS

Ten medication-free patients with schizophrenia and 10 healthy subjects underwent positron emission tomography (PET) scans for 90 min after 11C-3-amino-4-(2-dimethylaminomethylphenylthio)benzonitrile ([11C]DASB) injection. Metabolite-corrected arterial input function was measured. Regional distribution volumes (mL/g) were derived with a two tissue compartment kinetic model. Outcome measures for SERT availability included binding potential (BP) and the specific-to-nonspecific equilibrium partition coefficient (V3''). Ten brain regions with high density of SERT and where SERT availability can be reliably quantified with [11C]DASB were included in the analysis.

RESULTS

No significant differences were observed in regional BP or V3'' between patients and control subjects. No significant relationships were observed between regional SERT availability and severity of positive, negative, and depressive symptoms.

CONCLUSIONS

This study failed to detect alterations of SERT availability in patients with schizophrenia; however, this study does not rule out the possibility that schizophrenia might be associated with alterations of SERT density in the cortical regions, where the [11C]DASB-specific binding signal is too low for reliable quantification of SERT.

The dorsal raphe nucleus in schizophrenia: a post mortem study of 5-hydroxytryptamine neurones

The 5-hydroxytryptamine (5-HT, serotonin) system has been implicated in the pathophysiology and treatment of schizophrenia. In this study, we addressed the hypothesis that a deficit of 5-HT neurones, either inherited or acquired, is central to the developmental pathology of the disorder. We examined putative 5-HT neurones of the dorsal raphe nucleus (DRN) in post mortem, formalin-fixed tissue from 15 schizophrenic patients and 20 control subjects matched for age and gender. No significant difference was detected between these groups in the number or size (cross-sectional area or diameter) of tryptophan-hydroxylase-immunoreactive cell profiles viewed in transverse sections collected from the level of the trochlear decussation to the emergence of the trigeminal nerve. Profile number was not affected by age, gender, side of the brainstem (left or right) or post mortem interval; however, time in formalin correlated negatively with the number of neurones counted. Moreover, a significant negative correlation was detected between time in formalin and the levels of immunoreaction product (optical density), which in turn correlated positively with our profile counts. A positive correlation was found between the age of subjects and our estimates of cell size. Our results do not support the proposal that an abnormality in the number and/or size of DRN 5-HT neurones is central to the aetiopathology of schizophrenia.

Hippocampal 5-hydroxytryptamine receptors: abnormalities in postmortem brain from schizophrenic subjects

There is strong evidence that hippocampal 5-hydroxytryptamine (5-HT) systems are affected in schizophrenia and hence we have studied a number of markers of the 5-HT system in hippocampi from subjects with schizophrenia. Using in situ radioligand binding with autoradiography we measured [(3)H]proplyamino-8-hydroxy-1,2,3,4-tetrahydronapthalene, [(3)H]ketanserin and [(3)H]sumatriptan binding in hippocampi from 20 schizophrenic and 20 control subjects. There were significant decreases in the density of [(3)H]ketanserin binding to the 5-HT(2A) receptor (5-HT(2A)R) in the Cornu Ammonis (CA) 3 (p=0.006), CA 1 (stratum radiatum p=0.02; pyramidal layer p=0.0008) and subiculum (pyramidal layer p=0.0004), as well as methiothepin-insensitive [(3)H]sumatriptan binding to the 5-HT(1F)R in the CA 1 (p=0.016), stratum radiatum/lacunosum moleculare (p=0.04) and subiculum (p=0.015) from subjects with schizophrenia. There were no differences in the densities of 5-HT(1A)R, 5-HT(1D)R or 5-HT(4)R in hippocampi from subjects with schizophrenia. These data support the hypothesis that regionally specific reductions in the density of the 5-HT(2A)R and 5-HT(1F)R are a component of the pathological processes underlying schizophrenia.

The neurobiology of bipolar disorder: findings using human postmortem central nervous system tissue

OBJECTIVE

Postmortem brain studies have been undertaken to understand changes in the molecular architecture of the central nervous system (CNS) of subjects with bipolar disorder. These studies, along with a limited number of functional neuroimaging studies, have been reviewed to provide information on the neurobiology underlying the disorder.

METHOD

Findings from the study of postmortem brain tissue and neuroimaging were reviewed if their focus was on the molecular architecture of the human CNS to identify future lines of research required to understand the underlying pathology of bipolar disorder.

RESULTS

There is considerable evidence to implicate the serotonergic system of the CNS and abnormalities in signal transduction pathways in the pathology of bipolar disorder. In addition, preliminary findings suggest that changes in the benzodiazepine binding site on the gamma aminobutyric acidA receptor may be affected in bipolar disorder.

CONCLUSIONS

Further systematic studies on the serotonergic systems of the CNS, as well as the interaction between neurotransmitter receptors, G-proteins and signal transduction pathways are required to better understand the pathology of bipolar disorder. In addition, findings on the serotonin transporter indicate that changes in presynaptic function may be a critical component of the pathology of bipolar disorder.

Studies on serotonergic markers in the human hippocampus: changes in subjects with bipolar disorder

BACKGROUND

Various studies suggest the hippocampus and serotonergic systems are important in the pathology of bipolar disorder (BD). We therefore measured hippocampal serotonergic markers in post-mortem tissue from BD and control subjects.

METHODS

The density and affinity of [3H]citalopram binding to the serotonin transporter (SERT), as well as the density of the 5HT(2A), 5HT(1A), 5HT(1D) and 5HT(1F) receptors were measured.

RESULTS

The density of SERT and 5HT receptors was no different in BD. There was a significant decrease in the affinity of [3H]citalopram binding to SERT in the stratum lacunosum-moleculare (S(lac)) in BD (K(d) mean+/-S.E.M.=4.3+/-0.8 vs. 1.9+/-0.3 nM).

LIMITATIONS

This study was completed using relatively small cohorts.

CONCLUSIONS

There are no generalised changes in hippocampal serotonergic markers in the hippocampus from subjects with BD. There is a decreased affinity of radioligand binding to S(lac) SERT in subjects with BD.

Comparative evaluation in nonhuman primates of five PET radiotracers for imaging the serotonin transporters: [11C]McN 5652, [11C]ADAM, [11C]DASB, [11C]DAPA, and [11C]AFM

The recent introduction of a number of new radiotracers suitable for imaging the serotonin transporters (SERT) has radically changed the field of SERT imaging. Whereas, until recently, only one selective SERT radiotracer was available ([11C]McN 5652) for SERT imaging with positron emission tomography (PET), several new C-11-labeled radiotracers of the -dimethyl-2-(arylthio)benzylamine class have been described as appropriate imaging agents for the SERT. The aim of this study was to conduct a comparative evaluation of four of the most promising agents in this class ([11C]ADAM, [11C]DASB, [11C]DAPA, and [11C]AFM) with the reference tracer [11C]McN 5652 under standardized experimental conditions. This evaluation included in vitro measurements of affinity and lipophilicity, and in vivo PET imaging experiments in baboons. In vitro, DASB displayed significantly lower affinity for SERT than the other four tracers. In the blood, [11C]DASB and [11C]AFM display faster clearance and higher free fractions. Brain uptake was analyzed with kinetic modeling using a one-tissue compartment model and the metabolite-corrected arterial input function. The kinetic uptake of [11C]DASB was significantly faster compared with the other compounds, and the scan duration required to derive time-independent estimates of regional distribution volumes was shorter. [11C]DAPA exhibited the slowest brain kinetic. Regional-specific-to-nonspecific equilibrium partition coefficient (V3") was the highest for [11C]AFM, followed by [11C]DASB and [11C]DAPA, which in turn provided higher V3" values than [11C]ADAM and [11C]McN 5652. From these experiments, two ligands emerged as superior radiotracers that provide a significant improvement over [11C]McN 5652 for PET imaging of SERT: [11C]DASB, because it enables the measurement of SERT availability in a shorter scanning time, and [11C]AFM, because its higher signal-to-noise ratios provide a more reliable measurement of SERT availability in brain regions with relatively low density of SERT, such as in the limbic system.

A change in the density of [(3)H]flumazenil, but not [(3)H]muscimol binding, in Brodmann's Area 9 from subjects with bipolar disorder

BACKGROUND

This study examines the hypothesis that there are changes in cortical serotonergic, GABAergic and glutamatergic systems in bipolar disorder and schizophrenia.

METHODS

In situ radioligand binding and autoradiography were used to measure neurochemical markers in Brodmann's Area (BA) 9 from control subjects and subjects with bipolar disorder or schizophrenia (n=8 per group).

RESULTS

Compared to tissue from schizophrenic (mean+/-S.E.M, 385+/-44 fmol/mg ETE) and control (383+/-44 fmol/mg ETE) subjects, there was an increase in the density of [(3)H]flumazenil binding to the benzodiazepine binding site on the GABA(A) receptor in subjects with bipolar disorder (451+/-17 fmol/mg ETE; P<0.05). There was no difference in the density of [(3)H]muscimol binding to the GABA(A) receptor or in the density of the serotonin(1A) receptor, serotonin(2A) receptor, ionotropic glutamate receptors or the serotonin transporter between the three cohorts. There was an age-related decrease in NMDA receptor density in control subjects that was absent in schizophrenia and bipolar disorder. An age-related increase in [(3)H]flumazenil binding in schizophrenia was absent in control and bipolar disorder subjects.

LIMITATIONS

This study involved a relatively small number of individuals.

CONCLUSIONS

An increase in the gamma2-receptor sub-unit in the GABA(A) receptor has been shown to increase benzodiazepine but not [(3)H]muscimol binding, this is the mismatch in binding we have shown in BA 9 from subjects with bipolar disorder. Thus, a change in the assembly of receptor subunits into GABA(A) receptors may be involved in the neuropathology of bipolar disorder. There may also be differences in age-related changes in cortical receptor density between bipolar disorder and schizophrenia.

Compensatory responses in the aging hippocampal serotonergic system following neurodegenerative injury with 5,7-dihydroxytryptamine

This study utilized a multidisciplinary approach to examine injury-induced compensatory responses in the aging hippocampal serotonin transporter (5-HTT), a membrane protein implicated in a variety of neurodegenerative disorders. Age-dependent cellular, anatomical, and physiological changes of the 5-HTT were evaluated in female Fischer 344 rats (2 and 17 months) following denervation of the serotonergic afferents (fimbria-fornix and cingulum bundle) to the dorsal hippocampus using the neurotoxicant 5,7-dihydroxytryptamine (5,7-DHT). Seven days following 5,7-DHT administration, a uniform loss of the hippocampal 5-HTT immunoreactivity was observed in both age groups. However, at 21 days 5-HTT immunoreactivity in young 5,7-DHT-treated animals was similar to control levels, indicative of recovery, while older animals exposed to 5,7-DHT did not show recovery of hippocampal 5-HTT expression. 5-HTT binding site density, as determined by quantitative autoradiography ([3H]citalopram), supported the immunohistochemical results by demonstrating a recovery of 5-HTT binding sites in young, but not old animals, at 21 days following the lesion (P < 0.001). Furthermore, cellular electrophysiological function of hippocampal CA1 pyramidal neurons in 3- and 18-month-old F344 rats at 21 days following 5,7-DHT or vehicle treatment were assessed using in vivo microiontophoretic application of serotonin (5-HT). Independent of changes in sensitivity to the inhibitory effects of 5-HT application, the time to recovery of cell firing following application of 5-HT was significantly increased in the 18-month 5,7-DHT group compared to the 18-month vehicle and 3-month 5,7-DHT groups (60 and 59% increases, respectively; P < 0.05). Overall, these series of studies comprise a model which can be used to identify cellular events underlying both the formation of injury-induced compensatory processes in younger animals and the lack thereof with advancing age.

A proposed pathological model in the hippocampus of subjects with schizophrenia

1. The hippocampal formation plays an important role in the normal functioning of the brain, being implicated in cognition and sensory gating, both of which are affected in schizophrenia. The hippocampal formation receives information from the association cortices, which is processed by glutamatergic transmission within the hippocampus. Dopamine, noradrenaline, 5-hydroxytryptamine (5-HT), acetylcholine and GABA, all of which have been proposed to play a role in the neurobiology of schizophrenia, can affect this transmission. 2. The advent of the 'atypical' antipsychotics, with their broad pharmacological spectra and improved therapeutic outcome, has revitalized research into neurotransmitter dysfunction other than that of dopamine. In particular, there has been interest in the serotonergic and cholinergic systems within the hippocampal formation because these are two of the transmitter systems targeted by clozapine and olanzapine. 3. From the study of these systems, using tissue obtained postmortem from subjects with schizophrenia, we propose that there is a hyperserotonergic state in the hippocampal formation of some subjects with schizophrenia caused by a conformational change in the 5-HT transporter. The model we propose allows us to construct further studies that will test the consequences of such a hyperserotonergic state in the hippocampal formation. This model has the potential to open new avenues in schizophrenia research.

Increased protein levels of serotonin transporter in frontal cortex of patients with Down syndrome

Serotonin transporters (SERTs) are presynaptic proteins specialized for the clearance of serotonin from the synaptic cleft. A large body of evidence exists on altered platelet serotonin uptake and metabolism in Down syndrome (DS). Besides, dysregulation of SERTs expression have been reported in various complex behavioural traits and disorders including, neurodegenerative disorders. This prompted us to investigate SERT protein levels in adult brain specimens. Western blot analyses were performed in frontal cortex and cerebellum of aged controls and patients with DS and Alzheimer's disease (AD). The result revealed that frontal cortex SERT was significantly increased (P<0.05) in DS, whereas in AD it was comparable to controls. In cerebellum, no significant difference was observed among the study populations. A remarkable difference was noted when SERT was normalized vs. neuron specific enolase (NSE), a neuronal marker. The increase in SERT/NSE was highly significant (P<0.01) in DS frontal cortex compared to controls. Neither AD frontal cortex nor DS and AD cerebellum did show any significant difference. These findings indicate that a region specific alteration in SERT expression may exist in DS with AD-like pathology. As little is known about the status of serotenergic synaptic markers in DS brain, the findings may contribute to an effort made to delineate the underlying causes of serotonergic dysfunction in DS and the quest for therapeutic strategies. The study also suggest caution should be taken in applying data obtained from DS to model AD biochemical defects.

Neural models of schizophrenia

Hallucinations and delusions - two diagnostic features of psychosis shared across the spectrum of heterogeneous schizophrenia constructs - can be described in terms of the pathophysiology of sensory information processing: hallucination is the impaired ability to classify representations as internally or externally generated, while delusion is the immutable linking of representations with each other in the absence of external dependency. The key anatomical systems in higher-order information processing are the cortex, thalamus, basal ganglia, and medial temporal lobe, each of which is modulated by neurotransmitter projection systems. Preliminary evidence, concentrating to date on the dorsolateral prefontal cortex, thalamus, and hippocampal region of the medial temporal lobe, points to neural circuitry dysfunction within and between each system in psychosis. This may account for specific symptoms and associated cognitive deficits such as memory impairment, attention deficit, and language disturbance.

Association study of a functional serotonin transporter gene polymorphism with schizophrenia, psychopathology and clozapine response

Serotonin is implicated in the pathogenesis of schizophrenia. Following serotonin release, the serotonin transporter (5-HTT) is the major determinant of serotonin inactivation. The present study tested the hypothesis that a biallelic polymorphism in the 5' regulatory region of the 5-HTT gene (5-HTTLPR) confers susceptibility to schizophrenia, association with the clinical manifestations of schizophrenia or clozapine response. 90 treatment-resistant schizophrenic patients were assessed using the Brief Psychiatric Rating Scale before and after clozapine treatment. The results demonstrated that the 5-HTTLPR variants did not play a major role in the susceptibility, clinical manifestations or clozapine response in schizophrenia.

Signal transmission, rather than reception, is the underlying neurochemical abnormality in schizophrenia

OBJECTIVE

This review aims to summarise the outcome of studies on changes in the molecular architecture of the brain of subjects with schizophrenia and formulate a hypothesis on mechanisms involved in the pathology of the illness.

METHOD

The outcomes from key studies using neuroimaging techniques and tissue obtained post-mortem that have been directed toward identifying abnormalities in the molecular architecture of the brain in subjects with schizophrenia were summarised. Using the results from these studies hypotheses were formulated on the underlying pathological process that precipitate schizophrenia.

RESULTS

Studies using neuroimaging techniques or tissue obtained post-mortem have revealed changes in the dopaminergic, serotoninergic, glutamatergic, GABAergic and cholinergic systems of the brain in schizophrenia. Some of these studies have identified abnormalities in presynaptic proteins or functioning that may be central to the pathology of schizophrenia.

CONCLUSIONS

There appears to be diverse changes in the molecular cytoarchitecture of the brains from subjects with schizophrenia. It could be that it is by affecting these multiple systems that the atypical antipsychotic drugs produce their improved clinical outcomes. Abnormal functioning of presynaptic processes could be central to the pathology of schizophrenia. If the 'presynaptic' hypothesis is proven, future antipsychotic drug design should be directed away from post-synaptic receptor antagonism toward the modulating the functions of presynaptic neurones.

Olanzapine, quetiapine, and risperidone: long-term effects on monoamine transporters in rat forebrain

Long-term effects of novel atypical antipsychotic drugs on monoamine transporters are unknown. We compared labeling of dopamine (DAT) and serotonin (SERT) transporter proteins in subregions of rat corpus striatum by quantitative autoradiography with [(3)H]2-beta-carbomethoxy-3-beta-[4'-iodophenyl]tropane ([(3)H]beta-CIT) and [(3)H]paroxetine after 28 days of continuous subcutaneous infusion of olanzapine, quetiapine, risperidone, or vehicle controls. Drug treatment did not significantly alter the abundance of either transporter type in caudate-putamen or nucleus accumbens, indicating that transporter proteins required to inactivate synaptically released dopamine and serotonin resist adaptations to long-term treatment with novel antipsychotics that affect neurotransmission by these amines.

Dopamine and serotonin transporters in patients with schizophrenia: an imaging study with [(123)I]beta-CIT

BACKGROUND

Several lines of evidence derived from imaging and postmortem studies suggest that schizophrenia is associated with hyperactivity of dopamine function and deficiency in serotonin (5-HT) function. The aim of this study was to investigate potential alterations of striatal dopamine transporters (DAT) and brainstem serotonin transporters (SERT) density in schizophrenia.

METHODS

Striatal DAT and brainstem SERT were measured in 24 patients with schizophrenia and 22 matched healthy control subjects using single photon emission computed tomography and [(123)I]beta-CIT. In this cohort of subjects, we previously reported an increase in striatal amphetamine-induced dopamine release, measured as the displacement of the D(2) receptor radiotracer [(123)I]IBZM.

RESULTS

No differences were observed between patients and control subjects in the equilibrium uptake ratio (V(3)") of [(123)I]beta-CIT in the striatum, indicating that schizophrenia is not generally associated with an alteration of striatal DAT density; however, a trend level association (p =.07) was observed in patients with schizophrenia between low striatal [(123)I]beta-CIT V(3)" and severity of negative symptoms. After controlling for age, striatal [(123)I]beta-CIT V(3)" in patients was not associated with duration of illness, suggesting that this relative deficit was not secondary to a neurodegenerative process. No correlation was observed between DAT density and amphetamine-induced dopamine release, either in the patients or in the controls. Brainstem [(123)I]beta-CIT V(3)" was unaffected in patients with schizophrenia, and was unrelated to symptomatology.

CONCLUSIONS

Schizophrenia is generally not associated with alterations of DAT in the striatum or SERT in the brainstem. In some patients, a relative deficit in dopamine nerve terminals might play a role in the pathophysiology of negative symptoms.

No change in the density of the serotonin1A receptor, the serotonin4 receptor or the serotonin transporter in the dorsolateral prefrontal cortex from subjects with schizophrenia

Changes in serotonin receptors and the serotonin transporter have been reported in the dorsolateral prefrontal cortex from subjects with schizophrenia, an area of the brain thought to be important in the pathology of the illness. To further our understanding on how such changes could play a role in the pathology of the illness, in situ radioligand binding with autoradiography was used to measure the density of the serotonin1A receptor, the serotonin4 receptor and the serotonin transporter in the dorsolateral prefrontal cortex, obtained at autopsy, from 10 schizophrenic and 10 control subjects. The binding of [3H]8-OH-DPAT to serotonin1A receptor, [3H]GR113808 to the 5HT4 receptor and [3H]citalopram to serotonin transporter was not altered in subjects with schizophrenia. significantly, only in tissue from the control subjects was there a relationship between age and the density of the serotonin4 receptor in Brodmann's areas 8 (r = 0.71, P = 0.02) and 10 (r = -0.67, P = 0.03). Importantly, this confounding factor did not influence the comparison of the density of serotonin4 receptor in the tissue from the schizophrenic and control subjects. This study has failed to show a difference in the density of serotonin1A receptor, the serotonin4 receptor or the serotonin transporter in the dorsolateral prefrontal cortex (Brodmann's areas 8, 9 and 10) from subjects with schizophrenia. These data suggest that not all serotonergic markers are altered in the dorsolateral prefrontal cortex from schizophrenic subjects.

Serotonin transporter gene is not associated with symptomatology of schizophrenia

The serotonin transporter gene is a primary candidate for involvement in major psychoses. A functional polymorphism in the upstream regulatory region of the serotonin transporter gene (5-HTTLPR) has recently been reported to be associated with a variety of psychopathological conditions. In the present study, we investigated the potential influence of the 5-HTTLPR on the psychopathology of schizophrenia. One hundred and sixty-one inpatients affected by schizophrenia (DSMIII-R) were assessed by the Operational Criteria checklist for psychotic illness (OPCRIT) and were typed for their 5-HTTLPR variants by PCR techniques. Mania, Depression, Delusion and Disorganization were the four symptomatologic factors used to define phenotype. 5-HTTLPR variants were not associated with these symptomatologic factors, and consideration of possible stratification effects such as sex, and age of onset did not reveal any association either. The serotonin transporter gene is not a liability factor for the symptomatology of schizophrenia.

Changes in protein kinase C and adenylate cyclase in the temporal lobe from subjects with schizophrenia

Changes in G-protein linked neurotransmitter receptors have been reported in a number of regions of the brain of schizophrenic subjects. These changes, if functional, could cause a change in proteins such as protein kinase C (PKC) and adenylate cyclase (AC) which are important components of the G-protein linked second messenger cascades. We therefore used autoradiography to measure the distribution and density of [3H]phorbol ester binding to PKC and [3H]forskolin binding to AC in tissue obtained at autopsy from schizophrenic and non-schizophrenic subjects (Controls). There were significant decreases in the density of PKC in the parahippocampal gyrus (687 +/- 60 vs. 885 +/- 51 fmol/mg TE; mean +/- SEM; p < 0.01) and in AC in the dentate gyrus (75 +/- 4.9 vs. 92 +/- 6.5, p < 0.05) from the schizophrenic subjects. These data could indicate that changes in neurotransmitter receptors in the hippocampus from subjects with schizophrenia could have resulted in a change in their associated second messenger systems.

Repeated antidepressant drug treatment, time of death and frequency of handling do not affect [3H]paroxetine binding in rat cortex

[3H]Paroxetine binding to the serotonin transporter has been shown to be altered in brain tissue from schizophrenic subjects. Some schizophrenic subjects are treated with antidepressant drugs, some of which bind to the serotonin transporter and their time of death is variable. To determine if these confounding factors could affect [3H]paroxetine binding, [3H]paroxetine binding to cortical membrane from rats treated with the antidepressant drugs for 10 or 28 days and in non-treated rats that were killed at different times of the day was measured. Drug treatment, when compared to injection with 0.9% saline and time of death, did not affect [3H]paroxetine binding. Treatment with imipramine [10 days: mean +/- S.D.: 590 +/- 59 fmol/mg protein (P < 0.05); 28 days: 653 +/- 59 fmol/mg protein (P < 0.01)] or mianserin [10 days: 600 +/- 43 (P < 0.05)] caused a significant decrease in the density of [3H]paroxetine binding compared to that in fluoxetine-treated rats (10 days: 820 +/- 211 fmol/mg protein; 28 days: 764 +/- 100 fmol/mg protein). Thus, overall, these data do not suggest changes in [3H]paroxetine binding reported in the human brain tissue would be due to antidepressant drug treatment or time of death.

Alterations in the cortical serotonergic system in schizophrenia: a postmortem study

Previous studies have suggested a disturbance in the cortical serotonergic (5-HT) system in schizophrenia; however, these studies have been confounded by suicide in the patients groups, which in itself is associated with alterations in the 5-HT system. In this study we characterized various components of the 5-HT system in 14 areas of the frontal and parietal cortex in tissue obtained at postmortem from aged chronically hospitalized nonsuicidal schizophrenics compared to age-matched controls. We found no differences between control and schizophrenic subjects in the density of 5-HT uptake sites or other markers of 5-HT innervation. In Brodmann areas 24 and 6 the concentration of 5-HT2A,C receptors was decreased in all schizophrenics regardless of their antipsychotic treatment history. In all other areas examined 5-HT2A,C receptor concentrations were dramatically decreased in schizophrenics patients on drugs at time of death, whereas those off drugs at death showed the same values as control subjects. The density of 5-HT1A receptors was increased in areas 24, 9a (caudal part of area 9), 44, and 6 in subjects with schizophrenia. Antipsychotic treatment did not appear to have a significant effect. Thus, the specific pattern of alterations in the 5-HT system in schizophrenia may depend on the patient population and on antemortem antipsychotic treatment. These data also provide evidence that regulation of the 5-HT2 receptor may be involved in antipsychotic action.

Differences between males and females in rates of serotonin synthesis in human brain

Rates of serotonin synthesis were measured in the human brain using positron emission tomography. The sensitivity of the method is indicated by the fact that measurements are possible even after a substantial lowering of synthesis induced by acute tryptophan depletion. Unlike serotonin levels in human brain, which vary greatly in different brain areas, rates of synthesis of the indolamine are rather uniform throughout the brain. The mean rate of synthesis in normal males was found to be 52% higher than in normal females; this marked difference may be a factor relevant to the lower incidence of major unipolar depression in males.

Levels of the growth-associated protein GAP-43 are selectively increased in association cortices in schizophrenia

The pathophysiology of schizophrenia may involve perturbations of synaptic organization during development. The presence of cytoarchitectural abnormalities that may reflect such perturbations in the brains of patients with this disorder has been well-documented. Yet the mechanistic basis for these features of the disorder is still unknown. We hypothesized that altered regulation of the neuronal growth-associated protein GAP-43, a membrane phosphoprotein found at high levels in the developing brain, may play a role in the alterations in brain structure and function observed in schizophrenia. In the mature human brain, GAP-43 remains enriched primarily in association cortices and in the hippocampus, and it has been suggested that this protein marks circuits involved in the acquisition, processing, and/or storage of new information. Because these processes are known to be altered in schizophrenia, we proposed that GAP-43 levels might be altered in this disorder. Quantitative immunoblots revealed that the expression of GAP-43 is increased preferentially in the visual association and frontal cortices of schizophrenic patients, and that these changes are not present in other neuropsychiatric conditions requiring similar treatments. Examination of the levels of additional markers in the brain revealed that the levels of the synaptic vesicle protein synaptophysin are reduced in the same areas, but that the abundance of the astrocytic marker of neurodegeneration, the glial fibrillary acidic protein, is unchanged. In situ hybridization histochemistry was used to show that the laminar pattern of GAP-43 expression appears unaltered in schizophrenia. We propose that schizophrenia is associated with a perturbed organization of synaptic connections in distinct cortical associative areas of the human brain, and that increased levels of GAP-43 are one manifestation of this dysfunctional organization.

Neonatal insult to the hippocampal region and schizophrenia: a review and a putative animal model

OBJECTIVE

To review the mounting evidence implicating early hippocampal dysfunction in the pathogenesis and the pathophysiology of schizophrenia. An account is made of recent neurodevelopmental hypotheses indicating how an early dysfunction of the hippocampal region disrupts maturational events in brain systems connected to that structure, thus inducing dysfunctional connectional development. Finally, an animal model is presented.

METHOD

Socioemotional behaviour of monkeys (Macaca mulatta) with selective neonatal hippocampal lesions was assessed by analyzing their interactions with their age-matched controls at 2 months, 6 months, and 5 to 8 years of age and by comparing the social interactions at each age with those of normal controls paired together.

RESULTS

At 2 months of age, monkeys with neonatal hippocampal lesions presented minor disturbances in initiation of social interactions. These subtle changes of behaviour were less evident at 6 months, although by that age, the operated monkeys displayed more withdrawals in response to an increase in aggressive responses from their unoperated peers. In adulthood, the amount of time spent by the hippocampectomized monkeys in social contacts with their normal peers decreased markedly. In addition, operated monkeys exhibited more locomotor stereotypies than normal controls.

CONCLUSION

These experimental findings indicate that the time-course and nature of the behavioural disturbances resulting from early trauma to the hippocampal region have some similarities with the clinical symptoms of schizophrenic patients and the typical time-course of the disease.

Immunocytochemical detection of the serotonin transporter in rat brain

The regional distribution of the serotonin uptake system was studied in rat brain using a specific polyclonal antibody raised against the putative extracellular loop between transmembrane domains 7 and 8 of the cloned rat serotonin transporter. Light microscope analysis with fluorescence and avidin-biotin-peroxidase techniques revealed a punctate staining as well as numerous labelled thin fibres, which exhibited accumulation of reaction end-product deposit over varicosities. These immunopositive processes were widely and heterogeneously distributed in the rat brain. High densities of immunoreactivity were seen within the caudate-putamen, amygdaloid complex, cortical areas, substantia nigra, ventral pallidum, Islands of Calleja, septal nuclei, interpeduncular nucleus, trigeminal motor nucleus and olfactory nuclei. We also found strong expression of serotonin transporter in the stratum oriens of area CA3 and, to a lesser extent, in the stratum oriens of CA1 and the stratum lacunosum molecular of CA1-CA3 regions of the hippocampus. Within the raphe nuclei, a moderate to high incidence of stained processes was observed, and immunopositive cell bodies were detected in the dorsal raphe nucleus. In addition, some immunoreactive fibres were present in the molecular and granular layers of the cerebellum as well as in the cochlear and olivary nuclei. In none of the regions analysed was evidence for glial staining obtained. The present immunocytochemical data reveal a widespread and heterogeneous distribution of the serotonin transporter in rat brain and suggest that serotoni transporter is preferentially sorted into axons, where it appears concentrated at varicosities and terminal boutons.

Changes in the serotonin transporter in the hippocampus of subjects with schizophrenia identified using [3H]paroxetine

[3H]paroxetine binding to membrane from hippocampus, obtained at autopsy, from 24 schizophrenic and 24 non-schizophrenic subjects has been measured. The affinity of [3H]paroxetine binding to hippocampal membrane was decreased in subjects with schizophrenia (Kd = 0.50 +/- 0.04 vs. 0.24 +/- 0.02nM; mean +/- S.E.M. p < 0.001) but was not different in schizophrenic subjects who had or had not committed suicide (Kd = 0.50 +/- 0.07 vs. 0.50 +/- 0.04nM). The density of [3H]paroxetine binding sites did not differ between the schizophrenic and non-schizophrenic subjects. For the schizophrenic subjects, there was no relationship between ante-mortem neuroleptic drug treatment and [3H]paroxetine binding to the hippocampal membrane. Finally, this study has shown that neuroleptic drug treatment of rats does not alter [3H]paroxetine binding to the hippocampal membranes. Thus, it would seem that the changes in the affinity of [3H]paroxetine binding to the hippocampus of schizophrenic subjects are not likely to be due to neuroleptic drug treatment but may be involved in the pathology of the illness.