The dopamine hypothesis of schizophrenia: limbic interactions with serotonin and norepinephrine

Organization of the Catecholaminergic System in the Short-Lived Fish Nothobranchius furzeri

The catecholaminergic system has received much attention based on its regulatory role in a wide range of brain functions and its relevance in aging and neurodegenerative diseases. In the present study, we analyzed the neuroanatomical distribution of catecholaminergic neurons based on tyrosine hydroxylase (TH) immunoreactivity in the brain of adult Nothobranchius furzeri. In the telencephalon, numerous TH+ neurons were observed in the olfactory bulbs and the ventral telencephalic area, arranged as strips extending through the rostrocaudal axis. We found the largest TH+ groups in the diencephalon at the preoptic region level, the ventral thalamus, the pretectal region, the posterior tuberculum, and the caudal hypothalamus. In the dorsal mesencephalic tegmentum, we identified a particular catecholaminergic group. The rostral rhombencephalon housed TH+ cells in the locus coeruleus and the medulla oblongata, distributing in a region dorsal to the inferior reticular formation, the vagal lobe, and the area postrema. Finally, scattered TH+ neurons were present in the ventral spinal cord and the retina. From a comparative perspective, the overall organization of catecholaminergic neurons is consistent with the general pattern reported for other teleosts. However, N. furzeri shows some particular features, including the presence of catecholaminergic cells in the midbrain. This work provides a detailed neuroanatomical map of the catecholaminergic system of N. furzeri, a powerful aging model, also contributing to the phylogenetic understanding of one of the most ancient neurochemical systems.

Repetitive transcranial magnetic stimulation for depression after basal ganglia ischaemic stroke: protocol for a multicentre randomised double-blind placebo-controlled trial

INTRODUCTION

Studies suggest that repetitive transcranial magnetic stimulation (rTMS) is effective for the treatment of depression and promotes the repair of white matter. This study aims to assess the effectiveness of rTMS in treating depression after basal ganglia ischaemic stroke and to examine whether such effects are related to restoration of white matter integrity.

METHODS AND ANALYSIS

Sixty-six participants will be recruited from Zhujiang Hospital, Nanfang Hospital and Sichuan Bayi Rehabilitation Hospital and randomised in a 1:1 ratio to receive active rTMS treatment or sham rTMS treatment in addition to routine supportive treatments. The data will be collected at 0, 2 and 4 weeks after the commencement of treatment. The primary outcome is the measurement of 24-item Hamilton Depression Rating Scale scores, and the secondary outcomes include diffusion tensor imaging results and the results of neuropsychological tests including the National Institutes of Health Stroke Scale, Activities of Daily Living Scale, Montreal Cognitive Assessment, Clinical Global Impressions scales, Aphasia Battery in Chinese, Social Support Revalued Scale and Medical Coping Modes Questionnaire.

ETHICS AND DISSEMINATION

This study has been approved by the Ethics Committee of Zhujiang Hospital of Southern Medical University. The findings will be disseminated by publication in a peer-reviewed journal and by presentation at international conferences.

TRIAL REGISTRATION NUMBER

NCT03159351.

Neural activity changes in unaffected children of patients with schizophrenia: A resting-state fMRI study

Previous neuroimaging studies have suggested that individuals at risk for schizophrenia exhibit structural and functional brain abnormalities. However, few studies focus on resting state baseline activity in individuals with genetic high-risk for schizophrenia (HR). We examined cerebral spontaneous neural activity in HR by measuring the amplitude of low frequency fluctuations (ALFF) in the blood oxygen level-dependent (BOLD) functional magnetic resonance signal during resting state. Using a 3T MRI scanner, 28 non-psychotic young adult participants with at least one parent with schizophrenia and 44 matched unrelated healthy comparison subjects (HC) were scanned during the resting-state. The ALFF of the BOLD signal for each participant was calculated, and these values were then compared between-groups using voxel-based analysis of the ALFF maps. The HR group showed significantly increased ALFF compared to the HC group in the striatum, including the left caudate nucleus extending to the putamen and the right caudate nucleus. There was also increased ALFF in HR relative to controls in the left medial temporal region including hippocampus, parahippocampal gyrus and the fusiform gyrus, as well as regions including the left lateral thalamus, bilateral ventral and dorsal anterior cingulate cortex, bilateral calcarine sulcus and precuneus. There was significantly decreased ALFF in the HR group relative to controls in the left inferior parietal lobule/postcentral gyrus. Our findings suggest that altered intrinsic neuronal activity in cortico-striato-thalamic networks may represent genetic vulnerability for the development of schizophrenia.

Effect of psilocin on extracellular dopamine and serotonin levels in the mesoaccumbens and mesocortical pathway in awake rats

Psilocin (3-[2-(dimethylamino)ethyl]-1H-indol-4-ol) is a hallucinogenic component of the Mexican mushroom Psilocybe mexicana and a skeletal serotonin (5-HT) analogue. Psilocin is the active metabolite of psilocybin (3-[2-(dimethylamino)ethyl]-1H-indol-4-yl dihydrogen phosphate). In the present study, we examined the effects of systemically administered psilocin on extracellular dopamine and 5-HT concentrations in the ventral tegmental area (VTA), nucleus accumbens, and medial prefrontal cortex of the dopaminergic pathway in awake rats using in vivo microdialysis. Intraperitoneal administration of psilocin (5, 10 mg/kg) significantly increased extracellular dopamine levels in the nucleus accumbens. Psilocin did not affect the extracellular 5-HT level in the nucleus accumbens. Conversely, systemic administration of psilocin (10 mg/kg) significantly increased extracellular 5-HT levels in the medial prefrontal cortex of rats, but dopamine was decreased in this region. However, neither extracellular dopamine nor 5-HT levels in the VTA were altered by administration of psilocin. Behaviorally, psilocin significantly increased the number of head twitches. Thus, psilocin affects the dopaminergic system in the nucleus accumbens. In the serotonergic system, psilocin contribute to a crucial effect in the medial prefrontal cortex. The present data suggest that psilocin increased both the extracellular dopamine and 5-HT concentrations in the mesoaccumbens and/or mesocortical pathway.

Elucidating the role of neurotensin in the pathophysiology and management of major mental disorders

Neurotensin (NT) is a neuropeptide that is closely associated with, and is thought to modulate, dopaminergic and other neurotransmitter systems involved in the pathophysiology of various mental disorders. This review outlines data implicating NT in the pathophysiology and management of major mental disorders such as schizophrenia, drug addiction, and autism. The data suggest that NT receptor analogs have the potential to be used as novel therapeutic agents acting through modulation of neurotransmitter systems dys-regulated in these disorders.

Deep brain stimulation of the medial septum or nucleus accumbens alleviates psychosis-relevant behavior in ketamine-treated rats

Deep brain stimulation (DBS) has been shown to be effective for relief of Parkinson's disease, depression and obsessive-compulsive disorder in humans, but the effect of DBS on psychosis is largely unknown. In previous studies, we showed that inactivation of the medial septum or nucleus accumbens normalized the hyperactive and psychosis-related behaviors induced by psychoactive drugs. We hypothesized that DBS of the medial septum or nucleus accumbens normalizes the ketamine-induced abnormal behaviors and brain activity in freely moving rats. Male Long-Evans rats were subcutaneously injected with ketamine (3 mg/kg) alone, or given ketamine and DBS, or injected with saline alone. Subcutaneous injection of ketamine resulted in loss of gating of hippocampal auditory evoked potentials (AEPs), deficit in prepulse inhibition (PPI) and hyperlocomotion, accompanied by increased hippocampal gamma oscillations of 70-100 Hz. Continuous 130-Hz stimulation of the nucleus accumbens, or 100-Hz burst stimulation of the medial septum (1s on and 5s off) significantly attenuated ketamine-induced PPI deficit and hyperlocomotion. Medial septal stimulation also prevented the loss of gating of hippocampal AEPs and the increase in hippocampal gamma waves induced by ketamine. Neither septal or accumbens DBS alone without ketamine injection affected spontaneous locomotion or PPI. The results suggest that DBS of the medial septum or nucleus accumbens may be an effective method to alleviate psychiatric symptoms of schizophrenia. The effect of medial septal DBS in suppressing both hippocampal gamma oscillations and abnormal behaviors induced by ketamine suggests that hippocampal gamma oscillations are a correlate of disrupted behaviors.

Abnormal plasma monoamine metabolism in schizophrenia and its correlation with clinical responses to risperidone treatment

Abnormalities in plasma monoamine metabolism reflect partly the illness of schizophrenia and sometimes the symptoms. Such studies have been repeatedly reported but have rarely taken both metabolites and parent amines or inter-amine activity ratios into account. In this study, the monoamines, their metabolites, turnovers and between-metabolite ratios in plasma were measured longitudinally in 32 schizophrenic patients treated with risperidone for 6 weeks, to examine possible biochemical alterations in schizophrenia, and to examine the association between treatment responses and psychopathology assessed according to the Positive and Negative Syndrome Scale (PANSS). The results showed lower level of plasma 3,4-dihydroxyphenylacetic acid (DOPAC) in relapsed versus first-episode schizophrenic patients, higher norepinephrine (NE) turnover rate (TR) in undifferentiated in comparison to paranoid schizophrenic patients and relatively higher metabolic activity of dopamine (DA) to serotonin (5-HT) in first-episode versus relapsed schizophrenic patients. Risperidone treatment induced a decrement of plasma DA levels and increments of plasma DOPAC and DA TR in the total group of schizophrenic patients. The turnover rate of 5-HT was was reduced in undifferentiated and relapsed subgroups of schizophrenic patients. The linkages between 5-HT TR, DA/NE relative activity and clinical symptomatology were also identified. These findings are consistent with an involvement of these systems in the pathogenesis of schizophrenia as well as in the responses to treatment, and the usefulness of certain biochemical indices as markers for subgrouping.

Functional crosstalk and heteromerization of serotonin 5-HT2A and dopamine D2 receptors

The serotonin 5-HT(2A) receptor (5-HT(2A)R) and dopamine D(2) receptor (D(2)R) are high-affinity G protein-coupled receptor targets for two different classes of antipsychotic drugs used to treat schizophrenia. Interestingly, the antipsychotic effects are not based on the regulation of same signaling mediators since activation of the 5-HT(2A)R and of the D(2)R regulate G(q/11) protein and G(i/o) protein, respectively. Here we use radioligand binding and second messenger production assays to provide evidence for a functional crosstalk between 5-HT(2A)R and D(2)R in brain and in HEK293 cells. D(2)R activation increases the hallucinogenic agonist affinity for 5-HT(2A)R and decreases the 5-HT(2A)R induced inositol phosphate production. In vivo, 5-HT(2A)R expression is necessary for the full effects of D(2)R antagonist on MK-801-induced locomotor activity. Co-immunoprecipitation studies show that the two receptors can physically interact in HEK293 cells and raise the possibility that a receptor heterocomplex mediates the crosstalk observed. The existence of this 5-HT(2A)R-D(2)R heteromer and crosstalk may have implications for diseases involving alterations of serotonin and dopamine systems and for the development of new classes of therapeutic drugs.

The habenula: from stress evasion to value-based decision-making

Surviving in a world with hidden rewards and dangers requires choosing the appropriate behaviours. Recent discoveries indicate that the habenula plays a prominent part in such behavioural choice through its effects on neuromodulator systems, in particular the dopamine and serotonin systems. By inhibiting dopamine-releasing neurons, habenula activation leads to the suppression of motor behaviour when an animal fails to obtain a reward or anticipates an aversive outcome. Moreover, the habenula is involved in behavioural responses to pain, stress, anxiety, sleep and reward, and its dysfunction is associated with depression, schizophrenia and drug-induced psychosis. As a highly conserved structure in the brain, the habenula provides a fundamental mechanism for both survival and decision-making.

Profiles of serotonin receptors in the developing human thalamus

The critical importance of the thalamus and its serotonergic innervation with respect to neuropsychiatric syndromes is increasingly recognized. This study investigates the localization of serotonin (5-hydroxytryptamine; 5-HT) receptors by immunohistochemistry in the thalamic nuclei of human fetuses aged 21 to 32 weeks of gestation. Results indicate that, already at 21 weeks of gestation, two 5-HT receptors are present in the dorsomedial nucleus of the developing thalamus: 5-HT2A receptors are localized in neurons and 5-HT2C receptors in fibers. By 31 and 32 weeks of gestation, 5-HT1A and 5-HT4 receptors are also detected in neuronal fibers of the same nucleus. At this later developmental stage, the percentage of 5-HT2A labeled neurons has significantly increased in the dorsomedial nucleus, and 5-HT2C positive neurons are observed in the centromedian and lateroventral thalamic nuclei as well. In contrast, neither neuronal cells nor fibers display any immunoreactivity for 5-HT3 or 5-HT6 receptors at any of the ages examined. Our observation that 5-HT1A, 5-HT2A, 5-HT2C and 5-HT4 receptors are present in the human thalamus prenatally indicates that 5-HT may play a role during fetal development. Disrupted development of the thalamic serotonergic system during this gestational period may contribute to the pathophysiology of neuropsychiatric disorders.

Persistent downregulation of hippocampal CREB mRNA parallels a Y-maze deficit in adolescent rats following semi-chronic amphetamine administration

BACKGROUND AND PURPOSE

We investigated possible differences in the impact of chronic amphetamine administration during adolescence and adulthood on aspects of behaviour and brain chemistry.

EXPERIMENTAL APPROACH

Adult (n=32) and adolescent (n=32) male Sprague-Dawley rats were given either D-amphetamine sulphate (10 mg kg(-1) daily, i.p.) or saline (1 mL kg(-1), i.p.) for 10 days. Rats were subsequently tested for anxiety-like behaviour, learning and memory, and sensorimotor gating. Nine weeks later, rats received saline (1 mL kg(-1)) or acute amphetamine challenge (1.5 mg kg(-1)) and the expression levels of mRNA for tyrosine kinase B (TrkB) or cAMP response element-binding protein (CREB) were measured in the hippocampus.

KEY RESULTS

The adolescent amphetamine pretreated group revealed a deficit in exploration on the Y-maze during a 6 h retention test. The frequency of visits to the novel arm was 35% lower for the amphetamine group compared with controls. In parallel, a 43% decrease in hippocampal CREB mRNA, but not TrkB mRNA, was observed in periadolescent rats treated chronically with amphetamine 9 weeks earlier. None of the effects were detected in the adult treated cohort.

CONCLUSIONS AND IMPLICATIONS

Chronic amphetamine treatment during periadolescence resulted in altered behaviour on the Y-maze and persistent downregulation of hippocampal CREB mRNA expression. Given that this group had intact spatial learning and reference memory, it would appear that the deficits observed on the Y-maze reflect a dysfunction in response to novelty. Because no effects of amphetamine treatment were observed in the adult cohort, these data suggest idiosyncratic sensitivity of periadolescence to the long-term effects of psychostimulants.

A single application of MK801 causes symptoms of acute psychosis, deficits in spatial memory, and impairment of synaptic plasticity in rats

Schizophrenia is mostly a progressive psychiatric illness. Although cognitive changes in chronic schizophrenia have been investigated, little is known about the consequences of a single psychotic episode on memory mechanisms and formation. We investigated changes in hippocampal long-term potentiation (LTP) and spatial memory in a rat model of an acute psychotic episode. Application of NMDA receptor antagonists, such as MK801 (dizolcilpine) in rats, have been shown to give rise to an acute and short-lasting behavioral state, which mirrors many symptoms of schizophrenia. Furthermore, NMDA antagonist-intake in humans elicits symptoms of schizophrenia such as hallucinations, delusions, and affective blunting. We therefore treated animals with a single systemic injection of MK801 (5 mg/kg). Increased stereotypy, locomotion, and ataxia were evident immediately after MK801-treatment, with effects disappearing within 24 h. MK801-treatment caused a disruption of prepulse inhibition of the acoustic startle reflex, 1 day but not 7 or 28 days after treatment. These effects were consistent with the occurrence of an acute psychotic episode. LTP was profoundly impaired in freely moving rats 7 days after MK801 application. Four weeks after treatment, a slight recovery of LTP was seen, however marked deficits in long-term spatial memory were evident. These data suggest that treatment with MK801 to generate an acute psychotic episode in rats, gives rise to grave disturbances in synaptic plasticity and is associated with lasting impairments with the ability to form spatial memory.

Metabolic correlates of antidepressant and antipsychotic response in patients with psychotic depression undergoing electroconvulsive therapy

OBJECTIVES

Although electroconvulsive therapy (ECT) is a very effective treatment of depression and psychosis, the mechanisms by which this occurs are not fully delineated. The objective of this study was to investigate the functional alterations in brain metabolism in response to ECT through the use of positron emission tomography assessment of cerebral glucose metabolism before and after a course of ECT.

METHODS

Ten subjects with psychotic depression were studied with positron emission tomography using [F]fluorodeoxyglucose before and between 2 and 3 weeks after a course of ECT. Statistical parametric mapping and region of interest analyses of the anterior cingulate cortex (ACC) subregions (dorsal, rostral, subcallosal, and subgenual) and hippocampus were used to determine glucose metabolic changes from ECT. The Hamilton Depression Rating Scale and the Scale for Assessing Positive Symptoms were the primary measures used for assessing clinical changes from ECT.

RESULTS

Electroconvulsive therapy led to significant increases in the left subgenual ACC and hippocampal metabolism, which were directly correlated with each other and to a reduction in depression as measured by total Hamilton Depression Rating Scale scores. Better antidepressant responders had increased, whereas poorer responders had a decreased left subgenual ACC and hippocampal metabolism. The decrease in positive symptoms was also correlated with increased left hippocampal metabolism.

CONCLUSIONS

The antidepressant effect of ECT was correlated with increased metabolism in the left subgenual ACC and hippocampus, whereas the antipsychotic effect of ECT was only correlated with increased left hippocampal metabolism. This finding has implications to better understand the mechanism of antidepressant and antipsychotic effects of ECT.

Neurotensin agonists: potential in the treatment of schizophrenia

Neurotensin (NT) is a neuropeptide that, for decades, has been implicated in the biology of schizophrenia. It is closely associated with, and is thought to modulate, dopaminergic and other neurotransmitter systems involved in the pathophysiology of various neuropsychiatric diseases, including schizophrenia. This review outlines the neurochemistry and function of the NT system and the data implicating its role in schizophrenia. The data suggest that NT receptor agonists have the potential to be used as novel therapeutic agents for the treatment of schizophrenia, with the added benefits of (i) not causing weight gain, an adverse effect that is problematic with some of the currently used atypical antipsychotic drugs; and (ii) helping patients to stop smoking, a behaviour that is highly prevalent in those with schizophrenia.

Chronic nicotine exposure affects the normal operation of hippocampal circuits

Evidence suggests that dopamine hyperfunction in schizophrenia blocks direct sensory information flow to CA1 pyramidal cells via the temporoammonic path. Owing to the high prevalence of smoking in schizophrenics, we examined whether nicotine modulates synaptic transmission in the temporoammonic path. Application of nicotine suppressed temporoammonic synaptic transmission as in the case of dopamine application. The suppressive effect of nicotine, however, disappeared in chronic nicotine-exposed hippocampi, suggesting the loss of nicotinic modulation of transmission in the temporoammonic path. In addition, the dopaminergic modulation of temporoammonic synaptic transmission decreased after chronic nicotine treatment. These observations suggest that chronic nicotine exposure affects the normal operation of hippocampal circuits.

Analysis of plasma biopterin levels in psychiatric disorders suggests a common BH4 deficit in schizophrenia and schizoaffective disorder

Tetrahydrobiopterin (BH4) is an essential cofactor for amine neurotransmitter synthesis. BH4 also stimulates and modulates the glutamatergic system, and regulates the synthesis of nitric oxide by nitric oxide synthases. A connection between BH4 deficiencies and psychiatric disorders has been previously reported; major depression and obsessive-compulsive disorder have been found in subjects with a BH4 deficiency disorder and more recently we have observed a robust plasma deficit of biopterin (a measure of BH4), in a large group of schizophrenic patients compared to control subjects. To extend our previous finding in schizophrenia, we analyzed plasma biopterin levels from patients with schizoaffective and bipolar disorders. A significant difference in biopterin was seen among the diagnostic groups (P < 0.0001). Post hoc analyses indicated significant biopterin deficits relative to the normal control group for the schizoaffective group, who had biopterin levels comparable to the schizophrenic group. Bipolar disorder subjects had plasma biopterin levels that were higher that the schizoaffective disorder group and significantly higher than the schizophrenic group. The demonstrated significant biopterin deficit in both schizophrenia and schizoaffective disorder, may suggest an etiological role of a BH4 deficit in these two disorders, via dysregulation of neurotransmitter systems.

SCH 23390 in the prefrontal cortex enhances the effect of apomorphine on prepulse inhibition of rats

The aim of this study was to investigate the role of dopaminergic activity in the prefrontal cortex in the regulation of prepulse inhibition (PPI) of acoustic startle. Rats were instrumented with permanent indwelling cannulas into the prefrontal cortex region and tested at least one week after surgery using a randomized sequence, repeated-measures protocol. Doses of apomorphine (0.1 mg/kg subcutaneously, s.c.) and MK-801 (0.03 mg/kg s.c.) were obtained from preliminary dose-response studies. Intracerebral injection of 0.5 microg/side of the dopamine D1 receptor antagonist, SCH 23390, significantly enhanced the disruptive effect of apomorphine on PPI, but had no effect on its own or on startle amplitude or habituation. Furthermore, the effect of SCH 23390 on PPI was not seen with a lower dose (0.2 microg/side) or in combination with the NMDA receptor antagonist, MK-801. These data confirm and extend previous reports on the importance of dopaminergic innervation of the prefrontal cortex in the regulation of PPI. It is suggested that apomorphine treatment directly or indirectly activates dopamine D1 receptors in the prefrontal cortex to inhibit its own action on PPI elsewhere in the brain, presumably in the nucleus accumbens. Antagonism of this inhibitory component by SCH 23390 therefore leads to a larger disruption of PPI.

The role of the extrapersonal brain systems in religious activity

The neuropsychology of religious activity in normal and selected clinical populations is reviewed. Religious activity includes beliefs, experiences, and practice. Neuropsychological and functional imaging findings, many of which have derived from studies of experienced meditators, point to a ventral cortical axis for religious behavior, involving primarily the ventromedial temporal and frontal regions. Neuropharmacological studies generally point to dopaminergic activation as the leading neurochemical feature associated with religious activity. The ventral dopaminergic pathways involved in religious behavior most closely align with the action-extrapersonal system in the model of 3-D perceptual-motor interactions proposed by . These pathways are biased toward distant (especially upper) space and also mediate related extrapersonally dominated brain functions such as dreaming and hallucinations. Hyperreligiosity is a major feature of mania, obsessive-compulsive disorder, schizophrenia, temporal-lobe epilepsy and related disorders, in which the ventromedial dopaminergic systems are highly activated and exaggerated attentional or goal-directed behavior toward extrapersonal space occurs. The evolution of religion is linked to an expansion of dopaminergic systems in humans, brought about by changes in diet and other physiological influences.

Evidence for a tetrahydrobiopterin deficit in schizophrenia

Tetrahydrobiopterin (BH(4)) is a vital cofactor maintaining availability of the amine neurotransmitters [dopamine (DA), noradrenaline (NA), and serotonin (5-HT)], regulating the synthesis of nitric oxide (NO) by nitric oxide synthase (NOS), and stimulating and modulating the glutamatergic system (directly and indirectly). These BH(4) properties and their potential relevance to schizophrenia led us to investigate the hypothesis of a study group (healthy controls, n=37; schizophrenics, n=154) effect on fasting plasma total biopterin levels (a measure of BH(4)). Study analysis showed a highly significant deficit of total biopterins for the schizophrenic sample after partialling out the effects of potential confounds of gender, age, ethnicity, neuroleptic use history and dose of current use, 24-hour dietary phenylalanine/protein ratio (a dietary variable relevant to BH(4) synthesis), and plasma phenylalanine (which stimulates BH(4) synthesis). A mean decrement of 34% in plasma total biopterins for schizophrenics from control values supports clinical relevance for the finding. In a subsample (21 controls and 23 schizophrenics), sequence analysis was done of the GTP cyclohydrolase I feedback regulatory gene and no mutations were found in the coding region of the gene. A deficiency of BH(4) could lead to hypofunction of the systems of DA, NA, 5-HT, NOS/NO, and glutamate, all of which have been independently implicated in schizophrenia psychopathology. Further, evidence has been accumulating which implicates the critical interdependence of these neurotransmitter systems in schizophrenia; this concept, along with the present study finding of a biopterin deficit, suggests that further study of the BH(4) system in schizophrenia is warranted and desirable.

Enhancement of long-term potentiation at CA1-subiculum synapses in MK-801-treated rats

The subiculum plays a key role in processing neuronal information from the hippocampus to different cortical and subcortical brain regions. The subicular projections to the nucleus accumbens and the prefrontal cortex have received increasing attention, as alterations of their activity seem to be involved in schizophrenia. Phencyclidine and other non-competitive antagonists of NMDA receptors (such as ketamine and MK-801) induce psychotic effects in humans that closely resemble the positive, negative and cognitive symptoms of schizophrenia. Using the MK-801 model of psychosis, we investigated the time course of alterations of synaptic transmission and plasticity at CA1-subiculum synapses of hippocampal brain slices 4 h, 24 h and 4 weeks after MK-801 treatment. We report here that systemic application of MK-801 causes a facilitation of LTP at CA1-subiculum synapses 24 h after treatment as compared with control LTP. Four weeks after MK-801 treatment, the magnitude of LTP reversed to control values. The priming of LTP 24 h after systemic application of MK-801 suggest a new form of metaplasticity that sheds light on the delayed facilitating effect of this drug on synaptic efficacy.

5-HT2A and muscarinic receptors in schizophrenia: a postmortem study

Although evidence suggests that 5-HT(2A) and muscarinic M1/M4 receptors are implicated in the pathology of schizophrenia, the results are not conclusive. In the present study we tested the hypothesis that binding of 5-HT(2A) and M1/M4 receptors is altered in the postmortem brain of schizophrenia subjects. Quantitative autoradiography was employed to measure [(3)H]ketanserin binding to 5-HT(2A) receptors and [(3)H]pirenzepine binding to both M1 and M4 receptors in Brodmann's area 9 (BA9), caudate/putamen, and the hippocampal formation from six schizophrenic and six control subjects. A significant reduction in the density of 5HT(2A) receptors in BA 9 of schizophrenic subjects was observed (p=0.036). No significant difference was observed in the density of 5HT(2A) receptors in the hippocampus or caudate/putamen between the two groups. No significant changes in the density of M1/M4 receptors was observed in these three regions between the two groups. These findings support a possible involvement of the serotonergic system in the pathology of schizophrenia.

Tonic modulation of inhibition by dopamine D4 receptors in the rat hippocampus

Dopaminergic pathways have been recognized to play a critical role in cognition and emotion. Dopamine D2 and D4 receptors are the target for most common antipsychotics and their activation, particularly those in the medial temporal lobe structures, has been associated with their beneficial actions. The entorhinal cortex, which is the cortical area most consistently and severely affected in schizophrenia constitutes the main input to the hippocampus. Since the D4 receptor is highly concentrated in the hippocampus, and the effects of the selective activation of D4 receptors on the input/output function of the hippocampal formation are poorly understood, we sought to investigate the role of these receptors in the synaptic transmission and paired-pulse inhibition from the perforant path to area CA1 and the dentate gyrus. The D4 receptor antagonist, clozapine, translated paired-pulse inhibition into paired-pulse potentiation in both perforant path targets. By contrast, the D2/D3 antagonist quinpirole had no effect. The blockade of the D2/3 receptors with sulpiride, and of D1/5 receptors with SCH-23390, has no effect on paired-pulse inhibition, suggesting that these receptors are not involved in feedforward inhibition in these hippocampal areas. Interestingly, the perfusion of the D4 selective antagonist, L-745,870 (Patel et al., 1997: J Pharmacol Exp Ther 283:636-647) during the blockade of D2/3 and D1/5 receptors produces a reversible decrease in paired-pulse inhibition in CA1, but not in the DG. Our results show that endogenous DA tonically modulates feedforward inhibition in area CA1 and the dentate gyrus through the activation of D4 receptors located in the interneuronal population of these hippocampal regions. Since activation of the D4 receptor inhibits GABA release and GABAergic synaptic transmission, we suggest that the perforant path stimulates interneurons that have the D4 receptor and that, in turn, contact other interneurons that synapse onto pyramidal cells. (c) 2004 Wiley-Liss, Inc.

Adulthood nicotine treatment alleviates behavioural impairments in rats neonatally treated with quinpirole: possible roles of acetylcholine function and neurotrophic factor expression

Increases in dopamine D(2) receptor sensitivity are known to be common in drug abuse and neurological disorders. Past data from this laboratory have shown that long-term increases in D(2) sensitivity can be produced by quinpirole treatment (a D(2)/D(3) agonist) during early development. The present investigation was designed to test the hypothesis that nicotine administration in adulthood would reduce both cognitive and skilled reaching impairments produced by increases in D(2) sensitivity. Female Sprague-Dawley rats were treated with quinpirole (1 mg/kg) or saline from postnatal day 1 (PD 1) to PD 21. Beginning in adulthood (PD 61), rats were treated with nicotine (0.3 mg/kg free base) or saline twice daily for 14 consecutive days before behavioural testing commenced. Animals neonatally treated with quinpirole demonstrated performance deficits on the Morris water task and a skilled reaching task compared to controls. Deficits on both tasks were completely alleviated by adulthood nicotine treatment. Animals neonatally treated with quinpirole demonstrated a significant 36% decrease of ChAT in the hippocampus compared to saline controls that was partially eliminated by nicotine. Additionally, neonatal quinpirole produced a significant decrease in hippocampal NGF content compared to controls, however, nicotine failed to alleviate this decrease in NGF. The results of this investigation demonstrate that long-term increases in dopamine D(2) receptor sensitivity produce significant decreases in hippocampal cholinergic and NGF expression that may result in cognitive impairment. Nicotine alleviates both cognitive and skilled reaching impairments caused by increases in D(2) sensitivity, but the mechanism through which nicotine is acting is currently unknown.

Nonparametric linkage analysis between schizophrenia and candidate genes of dopaminergic and serotonergic systems

BACKGROUND

Alterations in dopaminergic and serotonergic systems have been implicated in the pathophysiology of schizophrenia for many years. This study was performed to assess the possible involvement of the dopamine receptor genes D2 (DRD2), D3, D4, serotonin receptor genes 1Da, 1Db, and 2A in the etiology of schizophrenia.

METHODS

We examined 33 multiplex schizophrenic families from Portugal.

RESULTS

Linkage analysis performed by GENEHUNTER showed nonsignificant linkage for these genes. A maximum nonparametric linkage score of 1.635 (P=.032) at DRD2 gene was observed, and this finding suggests DRD2 gene for further studies.

CONCLUSION

the polymorphisms studied at dopamine receptor genes D3, D4, serotonin receptor genes 1Da, 1Db, and 2A do not have a major effect in susceptibility to schizophrenia in a Portuguese population.

Juvenile emotional experience alters synaptic composition in the rodent cortex, hippocampus, and lateral amygdala

A quantitative anatomical study in the rodent anterior cingulate and somatosensory cortex, hippocampus, and lateral amygdala revealed region-, cell-, and dendrite-specific changes of spine densities in 3-week-old Octodon degus after repeated parental separation. In parentally separated animals significantly higher spine densities were found on the apical and basal dendrites of the cingulate cortex (up to 143% on apical and 138% on basal dendrite). Branching order analysis revealed that this effect is seen on all segments of the apical dendrite, whereas on the basal dendrites significantly higher spine densities were seen only on the outer branches (third to fifth dendritic segments). Increased spine densities were also observed on the hippocampal CA1 pyramidal neurons (up to 109% on the distal apical segments and up to 106% on the basal segment) compared with the control group. In contrast, significantly reduced spine densities were observed on the granule cell dendrites in the dentate gyrus (down to 92%) and on the apical dendrites in the medial nucleus of the amygdala (down to 95%). No significant changes of spine densities were seen in the somatosensory cortex (except for an increase in the proximal apical segments) and in the lateral nucleus of the dorsal amygdala (except for an increase in the proximal basal dendritic segments). These results demonstrate that repeated stressful emotional experience alters the balance of presumably excitatory synaptic inputs of pyramidal neurons in the limbic system. Such experience-induced modulations of limbic circuits may determine psychosocial and cognitive capacities during later life.

Dopamine and serotonin function in untreated schizophrenia: clinical correlates of the apomorphine and d-fenfluramine tests

This study examined the prolactin (PRL), adrenocorticotropin (ACTH) and cortisol responses to the direct DA receptor agonist apomorphine (APO) and the selective 5HT-releasing agent d-fenfluramine (d-FEN) in 20 untreated inpatients with DSM-IV schizophrenia and without a history of suicide attempt, compared to 23 hospitalized healthy controls. We hypothesized that different patterns of responsiveness of the DA and 5-HT systems might be associated with specific schizophrenic symptom clusters. A positive correlation was observed between pituitary-adrenal response to APO and d-FEN tests (i.e. deltaACTH and deltacortisol) in the overall population and in schizophrenic patients. Pituitary-adrenal response to APO was lower in patients than in normal controls. Moreover, lower pituitary-adrenal response to APO and d-FEN was associated with increased severity of BPRS thought disturbance score. Lower pituitary-adrenal responses to APO (and to a lesser degree to d-FEN) differentiated paranoid from disorganized schizophrenic patients. Neither PRL suppression to APO, nor PRL stimulation to d-FEN were altered in schizophrenic patients. Our results suggest that decreased hypothalamic DA receptor activity (possibly secondary to increased presynaptic DA release) together with relatively decreased 5-HT tone characterize paranoid SCH, while normal hypothalamic DA receptor activity together with relatively increased 5-HT tone characterize the disorganized SCH subtype.

Phenylalanine hydroxylase gene in psychiatric patients: screening and functional assay of mutations

BACKGROUND

Reports relating phenylalanine kinetics and metabolism to psychiatric disorders led us to undertake the comprehensive screening of the phenylalanine hydroxylase (PAH) coding region and functional testing of discovered mutations in a sample of psychiatric patients and healthy control subjects.

METHODS

Genomic DNA from psychiatric patients and control subjects was assayed for sequence variants in all PAH coding regions and splice junctions. In vivo functional analysis of mutations was conducted by assessing the kinetics and conversion to tyrosine of a standardized phenylalanine dose and by measuring fasting pterin levels.

RESULTS

A known missense mutation was observed in a schizoaffective subject, and a novel missense mutation was discovered in four subjects with schizophrenia and one normal subject. The schizoaffective patient heterozygous for the known A403V mutation showed the lowest rate of phenylalanine kinetics and lowest conversion to tyrosine in the patient sample. The four schizophrenic patients heterozygous for the novel K274E mutation showed significantly decreased phenylalanine kinetics, reduced conversion to tyrosine, and increased synthesis of the PAH cofactor tetrahydrobiopterin compared with schizophrenic subjects without the mutation.

CONCLUSIONS

The study findings suggest that larger scale studies are warranted to test the relationship of the PAH genotype with a psychiatric phenotype.

Influence of postweaning social isolation in the rat on brain development, conditioned behavior, and neurotransmission

There is substantial evidence that early life events influence brain development and subsequent adult behavior and play an important role in the causation of certain psychiatric disorders including schizophrenia and depression. The underlying mechanism of the effects of these early environmental factors is still not understood. It is a challenge to attempt to model early environmental factors in animals to gain understanding of the basic mechanisms that underlie the long-term effects. This paper reviews the effects of rearing rats from weaning in social isolation and reports some recent results indicating hippocampal dysfunction. Isolation rearing in rats from weaning produces a range of persistent behavioral changes in the young adult, including hyperactivity in response to novelty and amphetamine and altered responses to conditioning. These are associated with alterations in the central aminergic neurotransmitter functions in the mesolimbic areas and other brain regions. Isolation-reared rats have enhanced presynaptic dopamine (DA) and 5-HT function in the nucleus accumbens (NAC) associated with decreased presynaptic 5-HT function in the frontal cortex and hippocampus. Isolation-reared rats have reduced presynaptic noradrenergic function in the hippocampus, but have enhanced presynaptic DA function in the amygdala. These neurochemical imbalances may contribute to the exaggerated response of the isolated rat to a novel stimulus or to stimuli predictive of danger, and isolation-induced behavioral changes. These changes have neuroanatomical correlates, changes which seem to parallel to a certain degree those seen in human schizophrenia. A greater understanding of the processes that underlie these changes should improve our knowledge of how environmental events may alter brain development and function, and play a role in the development of neuropsychiatric disorders.

Serotonergic effects of clozapine and its metabolites in hippocampal HT22 cells

In the hippocampal neuronal in vitro system of HT22 cells, we studied the effects of clozapine (Cloz) and its metabolites clozapine-N-oxide (Cloz-N-oxide) and norclozapine (Norcloz) on 5-HT transporter affinity (K(M)) and uptake (V(max)), MAO-B affinity (K(M)) and maximal velocity (V(max)), as well as on 5-HT(2) receptor affinity and density. Clinically relevant concentrations of Cloz (200 and 400 ng/ml) and its metabolites (100 and 200 ng/ml) were used for the examination of the effects after short-term (4 h) and long-term (24 h) incubation. Statistical evaluation revealed that a significantly lowered 5-HT transporter affinity (higher K(M)) was related to higher concentrations of Cloz and its metabolites. A significantly higher 5-HT transporter uptake was dependent on both high concentrations of drugs and an increased time of incubation. No significant influence of the investigated independent variables on MAO-B affinity could be demonstrated, whereas a significant drug-related increase of MAO-B velocity was detectable. Additionally, low and high concentrations of Cloz and its metabolites induced a higher 5-HT(2) receptor affinity (lower K(D)). No significant influences of the investigated independent variables on 5-HT(2) receptor density were detectable. The results of the present study show that Cloz and its metabolites induce significant alterations in serotoninergic parameters of hippocampal HT22 cells, validating the system of hippocampal HT22 cells for further examinations of the mechanisms of action of atypical neuroleptics.

The pharmacology of psilocybin

Psilocybin (4-phosphoryloxy-N,N-dimethyltryptamine) is the major psychoactive alkaloid of some species of mushrooms distributed worldwide. These mushrooms represent a growing problem regarding hallucinogenic drug abuse. Despite its experimental medical use in the 1960s, only very few pharmacological data about psilocybin were known until recently. Because of its still growing capacity for abuse and the widely dispersed data this review presents all the available pharmacological data about psilocybin.

A model of prefrontal cortex dopaminergic modulation during the delayed alternation task

Working memory performance is modulated by the level of dopamine (DA) D1 receptors stimulation in the prefrontal cortex (PFC). This modulation is exerted at different time scales. Injection of D1 agonists/antagonists exerts a long-lasting influence (several minutes or hours) on PFC pyramidal neurons. In contrast, during performance of a cognitive task, the duration of the postsynaptic effect of phasic DA release is short lasting. The functional relationships of these two time scales of DA modulation remain poorly understood. Here we propose a model that combines these two time scales of DA modulation on a prefrontal neural network. The model links the cellular and behavioral levels during performance of the delayed alternation task. The network, which represents the activity of deep-layer pyramidal neurons with intrinsic neuronal properties, exhibits two stable states of activity that can be switched on and off by excitatory inputs from long-distance cortical areas arriving in superficial layers. These stable states allow PFC neurons to maintain representations during the delay period. The role of an increase of DA receptors stimulation is to restrict inputs arriving on the prefrontal network. The model explains how the level of working memory performance follows an inverted U-shape with an increased stimulation of DA D1 receptors. The model predicts that (1) D1 receptor agonists increase perseverations, (2) D1 antagonists increase distractability, and (3) the duration of the postsynaptic effect of phasic DA release in the PFC is adjusted to the delay period of the task. These results show how the precise duration of the postsynaptic effect of phasic DA release influences behavioral performance during a simple cognitive task.

Aromatic amino acid hydroxylase genes and schizophrenia

Phenylalanine hydroxylase (PAH), which catalyzes the conversion of phenylalanine to tyrosine, shares physical, structural and catalytic properties with tyrosine hydroxylase (TH) and tryptophan hydroxylase (TPH) that catalyze the rate-limiting steps in the biosynthesis of the neurotransmitters dopamine, noradrenaline, and serotonin. Because these neurotransmitter systems have all been implicated in the pathophysiology of schizophrenia, the aromatic amino acid hydroxylases are among the likely candidates for genes associated with schizophrenia. A mutation in the functionally critical tetrahydrobiopterin cofactor binding domain of the PAH gene had been identified in African-American patients with the diagnosis of schizophrenia, and biochemical analyses suggested that this mutation has physiological consequences related to amine neurotransmitter function. DNA sequencing of the highly conserved cofactor binding domain of the PAH, TH, and TPH genes in African-American subjects with schizophrenia and unrelated, never mentally ill subjects from the NIMH Schizophrenia Genetics Initiative, was undertaken to assess the concordance of mutant genotype with psychiatric phenotype. The K274E mutation was observed in the PAH gene cofactor binding domain, and several polymorphisms were identified in adjacent intronic regions of the PAH, TH, and TPH genes. All of the genetic variants observed were represented in the schizophrenia group and in the never mentally ill group. Genetic evaluation of the family members of subjects with the PAH K274E mutation showed that all individuals with the K274E mutation also exhibited the PAH L321L polymorphism in the catalytic domain of the PAH enzyme.

An integrative theory of the phasic and tonic modes of dopamine modulation in the prefrontal cortex

This paper presents a model of both tonic and phasic dopamine (DA) effects on maintenance of working memory representations in the prefrontal cortex (PFC). The central hypothesis is that DA modulates the efficacy of inputs to prefrontal pyramidal neurons to prevent interferences for active maintenance. Phasic DA release, due to DA neurons discharges, acts at a short time-scale (a few seconds), while the tonic mode of DA release, independent of DA neurons firing, acts at a long time-scale (a few minutes). The overall effect of DA modulation is modeled as a threshold restricting incoming inputs arriving on PFC neurons. Phasic DA release temporary increases this threshold while tonic DA release progressively increases the basal level of this threshold. Thus, unlike the previous gating theory of phasic DA release, proposing that it facilitates incoming inputs at the time of their arrival, the effect of phasic DA release is supposed to restrict incoming inputs during a period of time after DA neuron discharges. The model links the cellular and behavioral levels during performance of a working memory task. It allows us to understand why a critical range of DA D1 receptors stimulation is required for optimal working memory performance and how D1 receptor agonists (respectively antagonists) increase perseverations (respectively distractability). Finally, the model leads to several testable predictions, including that the PFC regulates DA neurons firing rate to adapt to the delay of the task and that increase in tonic DA release may either improve or decrease performance, depending on the level of DA receptors stimulation at the beginning of the task.

Storage, recall, and novelty detection of sequences by the hippocampus: elaborating on the SOCRATIC model to account for normal and aberrant effects of dopamine

In order to understand how the molecular or cellular defects that underlie a disease of the nervous system lead to the observable symptoms, it is necessary to develop a large-scale neural model. Such a model must specify how specific molecular processes contribute to neuronal function, how neurons contribute to network function, and how networks interact to produce behavior. This is a challenging undertaking, but some limited progress has been made in understanding the memory functions of the hippocampus with this degree of detail. There is increasing evidence that the hippocampus has a special role in the learning of sequences and the linkage of specific memories to context. In the first part of this paper, we review a model (the SOCRATIC model) that describes how the dentate and CA3 hippocampal regions could store and recall memory sequences in context. A major line of evidence for sequence recall is the "phase precession" of hippocampal place cells. In the second part of the paper, we review the evidence for theta-gamma phase coding. According to a framework that incorporates this form of coding, the phase precession is interpreted as cued recall of a discrete sequence of items from long-term memory. The third part of the paper deals with the issue of how the hippocampus could learn memory sequences. We show that if multiple items can be active within a theta cycle through the action of a short-term "buffer," NMDA-dependent plasticity can lead to the learning of sequences presented at realistic item separation intervals. The evidence for such a buffer function is reviewed. An important underlying issue is whether the hippocampal circuitry is configured differently for learning and recall. We argue that there are indeed separate states for learning and recall, but that both involve theta oscillations, albeit in possibly different forms. This raises the question of how neuromodulatory input might switch the hippocampus between learning and recall states and more generally how different neuromodulatory inputs reconfigure the hippocampus for different functions. In the fifth part of this paper we review our studies of dopamine and dopamine/NMDA interactions in the control of synaptic function. Our results show that dopamine dramatically reduces the direct cortical input to CA1 (the perforant path input), while having little effect on the input from CA3. In order to interpret the functional consequences of this pathway-specific modulation, it is necessary to understand the function of CA1 and the role of dopaminergic input from the ventral tegmental area (VTA). In the sixth part of this paper we consider several possibilities and address the issue of how dopamine hyperfunction or NMDA hypofunction, abnormalities that may underlie schizophrenia, might lead to the symptoms of the disease. Relevant to this issue is the demonstrated role of the hippocampus in novelty detection, a function that is likely to depend on sequence recall by the hippocampus. Novelty signals are generated when reality does not match the expectations generated by sequence recall. One possible site for computing mismatch is CA1, since it receives predictions from CA3 and sensory "reality" via the perforant path. Our data suggest that disruption of this comparison would be expected under conditions of dopamine hyperfunction or NMDA hypofunction. Also relevant is the fact that the VTA, which fires in response to novelty, may both depend on hippocampal-dependent novelty detection processes and, in turn, affect hippocampal function. Through large-scale modeling that considers both the processes performed by the hippocampus and the neuromodulatory loops in which the hippocampus is embedded, it is becoming possible to generate working hypotheses that relate synaptic function and malfunction to behavior.

The discovery of PD 89211 and related compounds: selective dopamine D4 receptor antagonists

The dopamine (DA) D2 family of receptors consists of the D2, D3, and D4 receptors. The DA D4 receptor is of interest as a target for drugs to treat schizophrenia based upon its high affinity for the atypical antipsychotic clozapine and its localization to the limbic and cortical regions of the brain. As part of a program to identify novel DA D4 receptor antagonists, a high-volume screen using the Parke-Davis compound library was initiated. This led to the discovery of PD 89211 (benzenemethanol, 2-chloro-4-[4-[(1H-benzimidazol-2-yl)methyl]-1-piperzinyl]) that displaced [3H]spiperone binding to hD4.2 with an affinity (Ki) of 3.7 nM. PD 89211 exhibited high selectivity for the DA D4.2 receptor (> 800-fold) as compared to other hDA receptor subtypes, rat brain serotonin, and adrenergic receptors. In vitro, PD 89211 had D4 receptor antagonist activity reversing quinpirole-induced [3H]thymidine uptake in CHOpro5 cells (IC50 = 2.1 nM). Limited structure-activity relationship (SAR) studies indicated that compounds with a 4-chloro-, 4-methyl-, and 3-chloro- substituents on the phenyl ring retained high affinity for D4 receptors, while those with a 4-methoxy- and no substituent had less affinity. While all clinically effective antipsychotics increase DA synthesis (DOPA accumulation) in rodents, PD 89211 did not increase DA synthesis in the DA-enriched striatum, indicating no effect on DA turnover and low propensity for exhibiting motor side effects. However, it did increase catecholamine synthesis in rat hippocampus, as did clozapine. Moreover, PD 89211 selectivity increased catecholamine synthesis in the hippocampus of wild type but not in mice lacking D4 receptors, suggesting that one function of D4 receptors may be to modulate DA/norepinephrine (NE) turnover in this brain area known to possess D4 receptors. The discovery of compounds like PD 89211 provides a tool to help in understanding the function of DA D4 receptors in the CNS.

Immunohistochemical localization of GABAB receptor in the entorhinal cortex and inferior temporal cortex of schizophrenic brain

Immunocytochemical techniques were employed to examine the changes in immunolabeling of the gamma-aminobutyric acid (GABA)B receptor within the entorhinal cortex and inferior temporal isocortex of the schizophrenic brain. In the entorhinal cortex of the control subjects, an intense immunoreactivity was observed in the soma and processes of stellate cells in Layer II, in pyramidal cells in Layers II, III, and V, and in nonpyramidal interneurons. In subjects with schizophrenia, GABA(B) immunoreactivity was markedly reduced in pyramidal cells throughout the layers. In the inferior temporal cortex of the controls, both pyramidal cells and nonpyramidal interneurons demonstrated an intense immunoreactivity, while in the same region of the schizophrenic brain a marked reduction of the GABA(B) immunolabeling was observed in pyramidal cells in Layer V. These findings suggest that in the entorhinal cortex and the inferior temporal cortex of the schizophrenic brain, the expression of the GABA(B) receptor is reduced, and raise the possibility that GABA(B) receptor dysfunction is involved in the pathophysiology of schizophrenia.

Haloperidol downregulates phospholipase A(2) signaling in rat basal ganglia circuits

Our laboratory has developed an in vivo method to quantitatively evaluate phospholipase A(2) (PLA(2))-mediated signal transduction in brain regions of rodents. In this method, quantitative autoradiography is used to identify brain uptake of intravenously injected, radiolabeled arachidonic acid ([3H]AA). Dopamine D(2) receptors are coupled to G-proteins that activate PLA(2), releasing AA from the stereospecifically numbered (sn) 2 position of phospholipids, and regional [3H]AA uptake is proportional to the rate of release. In the present experiment, the D(2) antagonist haloperidol (1.0 mg/kg i.p.) or the drug vehicle was administered to male adult rats for 21 days. Rats were infused 3 days later with 1.75 mCi/kg [3H]AA (i.v.), anesthetized and decapitated 20 min after infusion onset, and brains were processed for quantitative autoradiography. Chronic haloperidol significantly decreased [3H]AA incorporation in two primary dopaminergic basal ganglia-frontal cortex circuits, the mesocorticolimbic and nigrostriatal systems, while insignificant changes in AA incorporation were noted in other brain regions. These results suggest that one mechanism by which haloperidol exerts its effect is by downregulating D(2)-mediated PLA(2) signaling involving AA release in basal ganglia-frontal cortex circuitry.

Inhibition of nicotinic receptor-mediated catecholamine secretion by Dryobalanops aromatica in bovine adrenal chromaffin cells

Effect of the aqueous extract from a medicinal plant Dryobalanops aromatica(Dipterocarpaceae) on catecholamine secretion was investigated in bovine adrenal chromaffin cells. The aqueous extract inhibited [(3)H]norepinephrine ([(3)H]NE) secretion induced by 1,1-dimethyl-4-phenylpiperazinium iodide (DMPP), a nicotinic acetylcholine receptor (nAChR) agonist, with a half-maximal inhibitory concentration (IC(50)) of 8.4 +/- 1.7 microgml(-1). Increases in cytosolic calcium ([Ca(2+)](i)) and sodium ([Na(+)](i)) induced by DMPP were also inhibited by the extract. However, the binding of [(3)H]nicotine to nAChRs was not affected by the addition of the extract in receptor binding competition analysis, suggesting that active components in the extract and nicotine do not share the binding site in the nAChR. On the other hand, [Ca(2+)](i)increases induced by high K(+), ionomycin, bradykinin, angiotensin II, and thapsigargin were not inhibited by the extract. The data suggest that the extract from D. aromatica specifically inhibits catecholamine secretion by blocking nAChR in a noncompetitive manner.

Monoaminergic synapses and schizophrenia: 45 years of neuroleptics

In 1952 Delay and Deniker introduced the first antipsychotic, chlorpromazine, into the treatment of mental patients. They subsequently defined the word 'neuroleptic' to describe drugs as different as reserpine and chlorpromazine which seemed to have similar effects on the mental life of patients. In the 1960s the hypothesis was developed, mainly due to Carlsson, that the principal mode of action of neuroleptics was to interfere with synaptic transmission mediated by dopamine (DA) in the brain. This concept was given substantial credence with the discovery by Seeman and Snyder in the 1970s that many of the neuroleptics acted as DA receptor blockers. Subsequently two different classes of DA receptor were defined on the basis of their coupling to adenylate cyclase by Kebabian. In the 1980s molecular biology led to the cloning of five different DA receptors, and at the end of this period vanTol and his colleagues cloned the D4 DA receptor, which has been of considerable interest in the 1990s as it is greatly elevated in the brains of schizophrenics. This historical review ends with a consideration of the possibility that in addition to DA receptors, serotonin and perhaps other transmitter receptors are involved in the aetiology of schizophrenia.

Catecholamine systems in the brain of vertebrates: new perspectives through a comparative approach

A comparative analysis of catecholaminergic systems in the brain and spinal cord of vertebrates forces to reconsider several aspects of the organization of catecholamine systems. Evidence has been provided for the existence of extensive, putatively catecholaminergic cell groups in the spinal cord, the pretectum, the habenular region, and cortical and subcortical telencephalic areas. Moreover, putatively dopamine- and noradrenaline-accumulating cells have been demonstrated in the hypothalamic periventricular organ of almost every non-mammalian vertebrate studied. In contrast with the classical idea that the evolution of catecholamine systems is marked by an increase in complexity going from anamniotes to amniotes, it is now evident that the brains of anamniotes contain catecholaminergic cell groups, of which the counterparts in amniotes have lost the capacity to produce catecholamines. Moreover, a segmental approach in studying the organization of catecholaminergic systems is advocated. Such an approach has recently led to the conclusion that the chemoarchitecture and connections of the basal ganglia of anamniote and amniote tetrapods are largely comparable. This review has also brought together data about the distribution of receptors and catecholaminergic fibers as well as data about developmental aspects. From these data it has become clear that there is a good match between catecholaminergic fibers and receptors, but, at many places, volume transmission seems to play an important role. Finally, although the available data are still limited, striking differences are observed in the spatiotemporal sequence of appearance of catecholaminergic cell groups, in particular those in the retina and olfactory bulb.

Clozapine inhibits synaptic transmission at GABAergic synapses established by ventral tegmental area neurones in culture

Elucidation of the mechanism of action of the atypical antipsychotic clozapine is complicated by the finding that this molecule interacts with multiple targets including dopaminergic and serotonergic receptors. Binding studies have suggested that clozapine also antagonises GABA(A) receptors, but physiological evidence for such a block at functional synapses is lacking. In this study, we explored this antagonism by using electrophysiological techniques on GABAergic neurones of the ventral tegmental area in culture. Inhibitory post-synaptic currents (IPSCs) evoked in isolated GABAergic neurones were found to be dose-dependently inhibited by clozapine. Compatible with a post-synaptic mechanism, we found that membrane currents evoked by exogenous applications of GABA were similarly dose-dependently inhibited by clozapine. An analysis of miniature inhibitory post-synaptic currents (mIPSCs) showed that clozapine reduced the amplitude of quantal events in a way similar to SR-95531, a specific GABA(A) receptor antagonist. Both drugs caused a similar leftward shift of the cumulative probability distribution of mIPSC amplitudes. This suggests that clozapine acts on both synaptic and extrasynaptic GABA(A) receptors. In conclusion, our work demonstrates that clozapine produces a functional antagonism of GABA(A) receptors at synapses. Because this effect occurs at concentrations that could be found in the brain of patients treated with clozapine, a reduction in GABAergic synaptic transmission could be implicated in the therapeutic actions and/or side-effects of clozapine.

Dopamine depresses excitatory synaptic transmission onto rat subicular neurons via presynaptic D1-like dopamine receptors

Schizophrenia is considered to be associated with an abnormal functioning of the hippocampal output. The high clinical potency of antipsychotics that act as antagonists at dopamine (DA) receptors indicate a hyperfunction of the dopaminergic system. The subiculum obtains information from area CA1 and the entorhinal cortex and represents the major output region of the hippocampal complex. To clarify whether an enhanced dopaminergic activity alters the hippocampal output, the effect of DA on alveus- and perforant path-evoked excitatory postsynaptic currents (EPSCs) in subicular neurons was examined using conventional intracellular and whole cell voltage-clamp recordings. Dopamine (100 microM) depressed alveus-elicited (S)-alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor-mediated EPSCs to 56 +/- 8% of control while perforant path-evoked EPSCs were attenuated to only 76 +/- 7% of control. Dopamine had no effect on the EPSC kinetics. Dopamine reduced the frequency of spontaneous miniature EPSCs without affecting their amplitudes. The sensitivity of subicular neurons to the glutamate receptor agonist (S)-alpha-amino-3-hydoxy-5-methyl-4-isoxazolepropionic acid was unchanged by DA pretreatment, excluding a postsynaptic mechanism for the observed reduction of excitatory synaptic transmission. The effect of DA on evoked EPSCs was mimicked by the D1 receptor agonist SFK 38393 and partially antagonized by the D1 receptor antagonist SCH 23390. While the D2 receptor agonist quinelorane failed to reduce the EPSCs, the D2 receptor antagonist sulpiride did not block the action of DA. The results indicate that DA strongly depresses the hippocampal and the entorhinal excitatory input onto subicular neurons by decreasing the glutamate release following activation of presynaptic D1-like DA receptors.

Pharmacological and molecular targets in the search for novel antipsychotics

The recent enthusiasm among clinicians for the so-called 'atypical antipsychotics' has both improved treatment for schizophrenic patients and provided a welcome stimulus for basic research on antipsychotic mechanisms. Even the newer drugs have shortcomings, and research is underway aimed at identifying novel agents with greater efficacy and safety. Much of this effort is directed towards compounds which, in addition to blocking dopamine receptors, also act on other neurotransmitter receptors such as 5-HT2, 5-HT1A and alpha2-adrenergic receptors. However, there is also a large amount of scientific activity seeking to discover and develop selective dopamine receptor subtype antagonists (including compounds which specifically block D3 or D4 receptors) or drugs that specifically target the dopamine autoreceptor. Finally, a number of drug development programmes are searching for non-dopaminergic antipsychotics. Drugs that do not have affinity for dopamine receptors but act through neurotensin, sigma or cannabinoid CB1 receptors or glutamatergic mechanisms are currently being evaluated. If any of these agents prove to have clinical efficacy this may lead to a third generation of antipsychotics. It is likely, however, that the mechanisms of action of such drugs will nevertheless imply the intimate involvement of dopaminergic pathways.

Dopamine depresses polysynaptic inhibition in rat subicular neurons

Schizophrenia is considered to be associated with a hyperfunction of the dopaminergic system and with abnormalities in hippocampal information processing. To clarify whether an enhanced dopaminergic activity alters the hippocampal output, the effect of dopamine (DA) on inhibitory postsynaptic responses (IPSPs) in subicular neurons was examined. DA (200 microM) induced a small and inconsistent hyperpolarization that was accompanied by a reduction of membrane resistance. DA decreased polysynaptic IPSPs which was paralleled by a depression of isolated AMPA/kainate and NMDA receptor-mediated excitatory postsynaptic responses (EPSPs). In contrast, DA had no effect on isolated monosynaptic GABA(A) and GABA(B) receptor-mediated IPSP/Cs. We conclude that in addition to membrane effects, DA decreases polysynaptic IPSPs by attenuating the glutamatergic drive onto subicular interneurons.

Borderline personality disorder. Overview of biologic factors

Exploring the biology of neurotransmitters and polymorphic genes that influence behavior most certainly will increase understanding of the complexity of personality disorders and the people who suffer with them. Continuing biologic exploration of the personality disorders will also provide new and valuable information that will inform and direct ever more sophisticated and specific psychiatric treatments. Further, it will supply knowledge that might begin to erode the strong biases and negative labels that have for too long been applied to these patients. These labels may have been applied not because these patients are bad people, but because of ignorance in understanding their complexity and limited ability to improve their condition. Nonetheless, clinicians must refrain from concluding that the answers to all problems in psychiatric treatment can be answered by the molecular geneticist or biologic researcher. As Reiss et al have written when speaking about nonshared environmental effects and its role in the development of psychopathology: "Psychiatry has been forced into the chronically uncomfortable position of straddling biomedicine and the social sciences and seems always to hunger for relief.... [Yet] the data simply do not permit a conception of the future centered on a straightforward biomedical answer to the fundamental question of the pathogenesis of major disorders. Indeed, a balanced image of the future contains a growing and equal partnership of the social sciences and molecular biology."

Personality traits and dopamine receptors (D2 and D4): linkage studies in families of alcoholics

Activation of the mesolimbic dopamine pathway appears to promote drug- and alcohol-seeking behavior in laboratory animals. Results for association and linkage analysis between various alcohol dependence phenotypes and the dopamine receptors have been quite mixed. Similarly, both positive and negative results have been presented concerning dopamine receptor genes and temperament. Cloninger has postulated that the novelty seeking factor from the Tridimensional Personality Questionnaire (TPQ) may be related to the dopamine neurotransmitter system. As novelty seeking is a trait of some importance for substance-dependent individuals, our goal was to test this relationship within a sample of families of alcoholics. No evidence favoring linkage between D2, D4, or DAT1 was found for TPQ novelty seeking. However, the harm-avoidance trait from the TPQ showed evidence for linkage to both the D4 and one of the D2 loci (TaqI A). The Multidimensional Personality Questionnaire (MPQ) was used to provide converging evidence for these results. The TPQ harm-avoidance scale loads heavily on introversion (worry, pessimism, shyness), characteristics that may be especially salient in alcoholic families. Thus, planned comparisons were made between selected MPQ traits measuring the affective dimension (negative affectivity, stress reaction, alienation, and well-being). We find evidence favoring linkage between the D2 and D4 receptor loci and these MPQ traits, with stronger evidence being seen for the D2 polymorphisms. Am. J. Med. Genet. (Neuropsychiatr. Genet.) 88:634-641, 1999.

C5-substituted derivatives of 5-OMe-BPAT: synthesis and interactions with dopamine D2 and serotonin 5-HT1A receptors

Eight new C5-substituted derivatives of the potential atypical antipsychotic agent 5-methoxy-2-[N-(2-benzamidoethyl)-N-n-propylamino]tetralin (5-OMe-BPAT, 1) have been prepared by chemical conversion of the 5-trifluoromethylsulfonyloxy (triflate) analogue 4 via various Stille-type cross-couplings, a Heck reaction, and an amidation in moderate to good yields. The 5-acetyl, 5-cyano, 5-methyl, 5-(2-furyl), 5-phenyl, methyl 5-carboxylate, and the 5-carboxamido analogues 5-11 thus obtained, the previously disclosed 5-methoxy, 5-hydroxy, and 5-unsubstituted analogues 1-3, and the 5-triflate analogue 4 were evaluated for their ability to compete for [3H]-spiperone binding to rat striatal membranes containing dopamine D2 receptors, and their ability to compete for [3H]-8-OH-DPAT binding to rat frontal cortex membranes containing serotonin 5-HT1A receptors in vitro. Compounds 1-11 displayed weak to high affinities for dopamine D2 receptors, with Ki-values ranging from 550 nM for the 5-carboxamido analogue to 4.9 nM for the 5-hydroxy analogue. The relative affinities of the 5-methoxy, 5-hydroxy, and 5-unsubstituted analogues suggested that these compounds may bind to the same site and in a similar way as the 5-oxygenated DPATs, with the 5-methoxy substituent of 1 functioning as a hydrogen bond acceptor. The serotonin 5-HT1A receptor tolerated more structural diversity at the C5-position of 1, as revealed by the higher Ki-values of 1-11, which ranged from 60 nM for the 5-carboxamido analogue to 1.0 nM for the 5-unsubstituted analogue. Partial least-squares (PLS) analysis of a set of 24 molecular descriptors, generated for each analogue, revealed no significant correlation between the dopamine D2 receptor affinities of 1-11 and their molecular properties, supporting the view that they may have different binding modes at this receptor subtype. A PLS model with moderate predictability (Q2 = 0.49) could be derived for the serotonin 5-HT1A receptor affinities of 1-11. According to the model, a relatively lipophilic, nonpolar C5-substituent should be optimal for a high affinity at this receptor subtype.