Subcortical dopamine and serotonin turnover during acute and subchronic administration of typical and atypical neuroleptics

Depression and impulsivity as pathways to violence: implications for antiaggressive treatment

BACKGROUND

Difficulties with affect regulation and impulse control have a strong influence on violence. The objective of this study was to determine whether baseline depression and impulsivity predict aggression and whether they predict differential response to antiaggressive treatment. This is important, as we lack knowledge as to the selection of antipsychotics for the treatment of aggression.

METHODS

Physically aggressive inpatients with schizophrenia who received an evaluation of depression and impulsivity at baseline were randomly assigned in a double-blind, parallel group, 12-week trial to clozapine, olanzapine, or haloperidol. Trait impulsivity was measured by the Barratt Impulsiveness Scale; depression by the Positive and Negative Syndrome Scale Depression factor. The number and severity of aggressive events, as measured by the Modified Overt Aggression Scale (MOAS), were the outcome measures.

RESULTS

Baseline depression and impulsivity predicted higher levels of aggression, as measured by the MOAS total score, over the 12-week treatment period across all 3 medication groups. In addition, there was a strong interaction effect between baseline depression/impulsivity and medication grouping in predicting MOAS score. In particular, when higher depression and impulsivity were present at baseline, patients on haloperidol presented with more aggression than patients on the other 3 medications.

CONCLUSIONS

Depression and impulsivity are important predictors of aggression and of differential response to antiaggressive treatment. This is most likely due to the medications' dissimilar neurotransmitter profiles. By identifying patients who will respond better to a given medication, we will be able to develop individualized strategies for the treatment of violent behavior.

Differential effects of antipsychotics on lateral bias and social attention in female rats

RATIONALE

Prior research has demonstrated that individuals with schizophrenia may exhibit lateral biases in attention and deficits in social behavior. The use of a noninvasive animal model of attentional impairments in schizophrenia and antipsychotic drugs can help elucidate the biological underpinnings of attentional processes and facilitate the study of novel therapeutics.

OBJECTIVES

The purpose of this study was to compare the effects of three antipsychotic drugs on measures of lateral bias and social attention in healthy, unoperated female rats.

MATERIALS AND METHODS

Female Long-Evans rats selected for a preexisting lateral bias in attention, a right behavioral orientation preference (BOP), were administered clozapine, haloperidol, sulpiride, or vehicle. Lateral bias in attention was assessed by determining which forelimb rats removed a nuisance stimulus from first. Social attention was examined by comparing the latency to remove nuisance stimuli in the presence of a social (inaccessible female rat) versus non-social (blinking clock) distractor.

RESULTS

All antipsychotic drugs eliminated right lateral bias in attention, while control animals retained their initial bias. Clozapine eliminated right lateral bias more rapidly than the other drugs. Animals receiving clozapine also selectively displayed increased attention to another rat.

CONCLUSIONS

The results suggest that the antipsychotic medication clozapine rapidly alters attentional bias and uniquely influences attention to a social stimulus. The right BOP paradigm is a useful animal model for comparing antipsychotic drug effects on lateralized attentional bias and attention to social stimuli.

Mapping brain regions in which deep brain stimulation affects schizophrenia-like behavior in two rat models of schizophrenia

BACKGROUND AND OBJECTIVES

The development of more efficient treatment remains a major unmet need in the realm of schizophrenia disease. Using the maternal immune stimulation and the pubertal cannabinoid administration rat model of schizophrenia, the present study aimed at testing the hypothesis that deep brain stimulation (DBS) serves as a novel therapeutic technique for this disorder.

METHODS

Adult offspring of dams, treated with the immune activating agent poly I:C (4 mg/kg, n = 50) or saline (n = 50), underwent bilateral stereotactic electrode implantation into one of the following brain regions: subthalamic nucleus (STN, n = 12/10), entopeduncularis nucleus (EP, n = 10/11), globus pallidus (GP, n = 10/10), medial prefrontal cortex (mPFC, n = 8/8), or dorsomedial thalamus (DM, n = 10/11). Adult rats treated with the CB1 receptor agonist WIN 55,212-2 (WIN, n = 16) or saline (n = 12) during puberty were bilaterally implanted with electrodes into either the mPFC (n = 8/6) or the DM (n = 8/6). After a post-operative recovery period of one week, all rats were tested on a well-established cross-species phenomenon that is disrupted in schizophrenia, the pre-pulse inhibition (PPI) of the acoustic startle reflex (ASR) under different DBS conditions.

RESULTS

Poly I:C induced deficits in PPI of the ASR were normalized upon DBS. DBS effects depended on both stimulation target and stimulation parameters. Most prominent effects were found under DBS at high frequencies in the mPFC and DM. These effects were replicated in the pubertal WIN administration rat model of schizophrenia.

CONCLUSIONS

Brain regions, in which DBS normalized PPI deficits, might be of therapeutic relevance to the treatment of schizophrenia. Results imply that DBS could be considered a plausible therapeutic technique in the realm of schizophrenia disease.

Transient inactivation of the neonatal ventral hippocampus impairs attentional set-shifting behavior: reversal with an α7 nicotinic agonist

Cognitive deficits represent a core symptom cluster in schizophrenia that are thought to reflect developmental dysregulations within a neural system involving the ventral hippocampus (VH), nucleus accumbens (NAC), and prefrontal cortex (PFC). The present experiments determined the cognitive effects of transiently inactivating VH in rats during a sensitive period of development. Neonatal (postnatal day 7, PD7) and adolescent (PD32) male rats received a single bilateral infusion of saline or tetrodotoxin (TTX) within the VH to transiently inactivate local circuitry and efferent outflow. Rats were tested as adults on an attentional set-shifting task. Performance in this task depends upon the integrity of the PFC and NAC. TTX infusions did not affect the initial acquisition or ability to learn an intra-dimensional shift. However, TTX rats required a greater number of trials than did controls to acquire the first reversal and extra-dimensional shift (ED) stages. These impairments were age and region-specific as rats infused with TTX into the VH at PD32, or into the dorsal hippocampus at PD7, exhibited performance in the task similar to that of controls. Finally, acute systemic administration of the partial α7 nicotinic acetylcholine receptor (nAChR) agonist SSR 180711 (3.0 mg/kg) eliminated the TTX-induced performance deficits. Given that patients with schizophrenia exhibit hippocampal pathophysiology and deficits in the ED stages of set-shifting tasks, our results support the significance of transient hippocampal inactivation as an animal model for studying the cognitive impairments in schizophrenia as well as the pro-cognitive therapeutic potential of α7 nAChR agonists.

Transient inactivation of the neonatal ventral hippocampus permanently disrupts the mesolimbic regulation of prefrontal cholinergic transmission: implications for schizophrenia

These experiments determined the mesolimbic modulation of cortical cholinergic transmission in a neurodevelopmental model of schizophrenia. Mesolimbic-cholinergic abnormalities are hypothesized to contribute to the cognitive deficits seen in schizophrenia. Stimulation of NMDA receptors in nucleus accumbens (NAC) increases acetylcholine (ACh) release in the prefrontal cortex (PFC), a mechanism recently demonstrated to contribute to the control of attentional performance. We determined the ability of intra-NAC administration of NMDA to increase prefrontal ACh levels in adult rats that had received bilateral infusions of tetrodotoxin (TTX) to transiently interrupt impulse flow in the ventral hippocampus (VH) during development. Rats received infusions of TTX or saline on postnatal day 7 (PD7) or day 32 (PD32), and the effects of NAC NMDA receptor stimulation on prefrontal cholinergic neurotransmission were assessed in adulthood. In animals treated as controls on PD7, NMDA increased prefrontal ACh levels by 121% above baseline. In contrast, PD7 infusions of TTX into the VH abolished the ability of NAC NMDA to activate prefrontal cholinergic neurotransmission (7% increase). In animals that received TTX infusions on PD32, NMDA-evoked cholinergic activity did not differ from controls, indicating a restricted, neonatal critical period during which VH TTX impacts the organization of mesolimbic-basal forebrain-cortical circuitry. Importantly, the failure of NAC NMDA to evoke cholinergic activity in rats treated with TTX on PD7 did not reflect a reduced excitability of corticopetal cholinergic neurons because administration of amphetamine produced similar elevations of prefrontal ACh levels in PD7 TTX and PD7 control animals. A third series of experiments demonstrated that the effects of PD7 TTX are a specific consequence of transient disruption of impulse flow in the VH. Intra-NAC NMDA evoked prefrontal ACh release in rats receiving TTX, on PD7, into the dorsal hippocampus (DH), basolateral amygdala, or NAC. Thus, impulse flow specifically within the VH, during a sensitive period of development, is necessary for the functional organization of a mesolimbic-cortical circuit known to mediate attentional control processes. Therefore, neonatal inactivation of VH represents an effective animal model for studying the basis of certain cognitive symptoms of schizophrenia.

Atypical antipsychotics, neurocognitive deficits, and aggression in schizophrenic patients

The purpose of this study was to compare the effects of olanzapine, clozapine, and haloperidol on neurocognitive function in schizophrenic patients who present with documented episodes of physical aggression and to determine whether change in cognitive function is related to aggression. One hundred physically aggressive schizophrenic inpatients were assigned to a randomized, double-blind, parallel-group, 12-week treatment, and received cognitive evaluations at baseline. There were 33, 34, and 33 subjects in the clozapine, olanzapine, and haloperidol groups, respectively. They were administered a battery of tests assessing psychomotor function, general executive function, visual and verbal memory, and visuospatial ability. A general cognitive index was derived from the above battery. The overall score on the Modified Overt Aggression Scale was used to measure the number and severity of the aggressive events. Psychiatric symptoms and side effects were also assessed. The improvement in the general cognitive index differed significantly among the 3 treatment groups, with olanzapine being superior to both haloperidol and clozapine. Further analyses revealed significantly greater improvement with olanzapine in several cognitive domains. Furthermore, improvement in the general cognitive index was significantly associated with a decrease in aggression in the olanzapine group but not in the other 2 medication groups. In violent schizophrenic patients, olanzapine treatment is associated with better cognitive functioning relative to haloperidol and clozapine. This improvement in neurocognitive function is associated with a decrease in aggressive behavior. As clozapine markedly reduced aggression, there may be different pathways for the antiaggressive effect of olanzapine and that of clozapine.

EFFECTS OF ARIPIPRAZOLE ON ALCOHOL INTAKE IN AN ANIMAL MODEL OF HIGH-ALCOHOL DRINKING

AIMS

This study examined the effects of aripiprazole, a novel atypical antipsychotic drug with partial agonist properties at dopamine D2 receptors, on the voluntary limited access alcohol drinking of alcohol-preferring AA (Alko, Alcohol) rats.

METHODS

AA rats were taught to drink 10% alcohol in a 4 h limited access paradigm. Effects of acute aripiprazole (0, 0.3, 1.0, and 3.0 mg/kg) on the limited access alcohol drinking were studied. In repeated treatment experiment, aripiprazole (0, 1.0, and 6.0 mg/kg) was administered once daily over five successive days. To reveal any effect by aripiprazole not selective for alcohol drinking, 0.025% saccharin solution was substituted for alcohol during the 4 h limited access, and acute treatments were repeated. The effects of aripiprazole on ambulatory locomotor activity were tested with doses that were used in the acute experiments.

RESULTS

Acute aripiprazole at the doses of 0.3, 1.0, and 3.0 mg/kg had no effect on alcohol drinking. Repeated treatment with the aripiprazole dose of 6.0 mg/kg significantly diminished alcohol drinking at the 1 h time point. This dose had no effect on saccharin drinking when given acutely. Acute aripiprazole at the doses of 1.0, 3.0, and 6.0 mg/kg significantly suppressed locomotor activity.

CONCLUSIONS

Aripiprazole decreased limited access alcohol drinking in AA rats, but only at a high dose that also strongly suppressed locomotor activity.

Poor evidence for depolarization block but uncoupling of nigral from striatal dopamine metabolism after chronic haloperidol treatment in the rat

Chronic haloperidol treatment induces depolarization block in midbrain dopamine neuronal systems. We studied the effect of this treatment on nigrostriatal dopamine catabolism using microwave fixation in situ of the brain to prevent post-mortem changes. Male Sprague-Dawley rats were given haloperidol (0.4 mg/kg/day, i.p.) or vehicle for 21 days. On day 22, some rats in each group received a haloperidol challenge (0.4 mg/kg, i.p.), and the remaining rats were given the vehicle. Dopamine metabolite levels 60 min after the challenge were assayed by combined gas chromatography-mass fragmentography. Haloperidol pretreatment significantly modified haloperidol challenge effect on regional dopamine metabolite contents. The challenge elevated all striatal metabolites studied similarly in the chronic vehicle- or chronic haloperidol-pretreated rats. In contrast, it did not significantly affect nigral dopamine metabolites except it elevated 3,4-dihydroxyphenylacetic acid in the haloperidol-pretreated rats. A linear correlation between the nigral and striatal contents of 3-methoxytyramine (R = 0.72, p = 0.03), and a trend for correlation (R = 0.65, p = 0.06) between the respective 3,4-dihydroxyphenylacetic acid contents were found after the haloperidol challenge in the vehicle-pretreated rats only. These results suggest that chronic haloperidol treatment uncouples somatodendritic dopamine turnover and release from those in the axon terminals of nigrostriatal dopamine neurons.

Clinical advantages of amisulpride in the treatment of acute schizophrenia

Five studies have been conducted with the atypical anti-psychotic amisulpride (100-1200 mg/day) involving 1358 patients with acute exacerbations of schizophrenia; four studies were short-term (4-8 weeks), double-blind studies and one was a 12-month, open, randomized comparison. Amisulpride improved positive symptoms consistently, and changes were more pronounced than with haloperidol, flupenthixol and risperidone; amisulpride showed a more rapid onset of action compared to haloperidol, and improvement in negative symptoms was more effective than with any comparator. An optimum response was obtained with amisulpride doses 400-800 mg/day. The long-term study confirmed the usefulness of amisulpride for maintenance treatment in schizophrenia, with a clear advantage over haloperidol, leading to better functioning and quality of life. Amisulpride caused fewer neurological side-effects than conventional anti-psychotics and less weight gain than risperidone, both of which are crucial factors for long-term compliance.

Amisulpride has a superior benefit/risk profile to haloperidol in schizophrenia: results of a multicentre, double-blind study (the Amisulpride Study Group)

In a multicentre, double-blind, flexible-dose study, 199 patients with paranoid schizophrenia or schizophreniform disorders received haloperidol (10-30 mg/d) or amisulpride (400-1200 mg/d) for four months. More patients in the haloperidol group withdrew prematurely (44% vs 26%; P = 0.0077) due to a higher incidence of adverse events. Amisulpride was at least as effective as haloperidol in reducing the Brief Psychiatric Rating Scale (BPRS) total score (-27.3 vs -21.9) (non-inferiority test; P < 0.001). The PANSS positive score improved to a similar extent in both groups whilst improvement in the PANSS negative score was significantly greater with amisulpride (-10.5 vs -7.2; P = 0.01). The percentage of responders on the Clinical Global Impression scale was also significantly greater with amisulpride (71% vs 47%; P < 0.001). Both the Quality of Life Scale (QLS) and the Functional Status Questionnaire (FSQ) improved to a significantly greater extent under amisulpride. Haloperidol was associated with a greater incidence in extrapyramidal symptoms and with a greater increase in the Simpson-Angus score than was seen with amisulpride (0.32 vs 0.02; P < 0.001). In conclusion, amisulpride is globally superior to haloperidol in the treatment of acute exacerbations of schizophrenia and significantly improves patients' quality of life and social adjustment.

Intravenous and oral clozapine pharmacokinetics, pharmacodynamics, and concentration-effect relations: acute tolerance

We examined the pharmacokinetics and pharmacodynamics of intravenous (1-5 mg/kg) and oral clozapine (2.5-10 mg/kg) in rats (terminal half-life=81.8 min; oral bioavailability=5.32%). Both dose- and concentration-effect relations of clozapine were characterized. Clozapine's effects were similar to those of benzodiazepines because of the similarity in effect-time profiles between the two classes of drugs. The IC(50) value increased as a function of dose; consequently, clozapine's relative potency decreased linearly with the logarithm of AUC((0-infinity)), or bioavailable dose regardless of route of administration. The IC(50) is an index for the sensitivity of behavioral performance to clozapine; relative potency provides an index for estimating the extent of acute tolerance. As IC(50) increases, relative potency decreases, and consequently, acute tolerance increases. Our results demonstrated that greater acute tolerance was observed for i.v. clozapine than for p.o. clozapine; however, clozapine exhibited a single concentration-effect relation across dose and route of administration after correcting for relative potencies.

Serotonergic function and negative and depressive symptomatology in schizophrenia and major depression

BACKGROUND

Serotonergic abnormalities are found in both major depressive disorder (MDD) and schizophrenia. Depressive symptoms commonly occur alongside the negative or defect symptoms in schizophrenia and antiserotonergic drugs may be particularly effective in their treatment. We wished to explore whether these symptoms could be distinguished biologically by directly comparing serotonergic function in these two illnesses.

METHOD

Fifteen patients with MDD and 13 patients with schizophrenia underwent testing with the specific serotonin releasing agent D-fenfluramine (D-FEN). Prolactin and cortisol responses were measured to ascertain central serotonergic function. Individual patient results were compared with their own carefully matched control to correct for the effect of age, sex, weight and menstrual cycle, before the two patient groups were then compared.

RESULTS

Prolactin responses differed significantly between the two patient groups, being lower in MDD patients and higher in schizophrenia patients than their individually matched controls. Cortisol responses did not differ. Within the schizophrenia group, increased serotonergic function correlated positively with depressive symptoms, but there was no such correlation with defect symptoms. Depressive scores were negatively correlated with the presence of negative symptoms in the schizophrenic group.

CONCLUSIONS

Schizophrenia and MDD have distinct and opposite neuroendocrine responses to D-FEN. There is no evidence that depressive symptoms in these two conditions have a common serotonergic basis. Moreover, these responses distinguished between negative and depressive symptoms in our schizophrenic group.

Correlated reductions in cerebrospinal fluid 5-HIAA and MHPG concentrations after treatment with selective serotonin reuptake inhibitors

We sought to determine whether fluvoxamine and fluoxetine, two different antidepressants with in vitro selectivity for the serotonin uptake transporter also demonstrated similar selectivity in vivo. To accomplish this, we measured cerebrospinal fluid (CSF) concentrations of 5-hydroxyindoleacetic acid (5-HIAA), 3-methoxy-4-hydroxyphenylglycol (MHPG), and homovanillic acid (HVA) before and after 6 weeks of treatment with these two drugs. Twenty-four subjects who had major depression according to DSM-III-R criteria gave written, informed consent for the collection of CSF during a double-blind comparative treatment trial of fluvoxamine (50-150 mg/day) and fluoxetine (20-80 mg/day). The symptoms of subjects were assessed clinically on a weekly basis throughout the treatment trial. CSF samples were obtained after a 7- to 14-day washout period before treatment and again at the end of treatment. CSF samples were analyzed for 5-HIAA, HVA, and MHPG using high-pressure liquid chromatography coupled to electrochemical detection. Fluvoxamine- and fluoxetine-treated patients did not differ in clinical outcome or in the CSF concentrations of monoamine metabolite levels before or after treatment. Therefore, the CSF data were pooled. Drug treatment, overall, was associated with significant decreases in 5-HIAA and MHPG and a trend toward a reduction in HVA levels. Levels of 5-HIAA, MHPG, and HVA were reduced by 57%, 48%, and 17%, respectively. In addition, the magnitude of the decreases in 5-HIAA and MHPG appeared to be correlated (r = 0.83) across the subjects, although a Spearman rank correlation indicated that outlying values had an undue effect on this relationship. These results suggest that treatment with selective serotonin reuptake inhibitors, which are selective for serotonin uptake in vitro, does not show a similarly selective effect on serotonin in vivo during treatment of patients.

The effects of clozapine and haloperidol on serotonin-1A, -2A and -2C receptor gene expression and serotonin metabolism in the rat forebrain

The therapeutic and side-effect profiles of clozapine differ from those of typical antipsychotic drugs such as haloperidol. Effects on the serotonin system, especially serotonin-2 receptors, may contribute to clozapine's atypicality. We injected rats for 14 days with clozapine (25 mg/kg/day) or haloperidol (2 mg/kg/day), and measured three aspects of the serotonin system in forebrain regions: abundance of serotonin-2A, -2C and -1A receptor messenger RNAs by in situ hybridization histochemistry; serotonin-2A and -1A binding sites using receptor autoradiography, and levels of serotonin and 5-hydroxyindoleacetic acid with high-performance liquid chromatography. Clozapine administration decreased serotonin-2A receptor messenger RNA and the density of [3H]ketanserin binding in cingulate and frontal cortex, but not in piriform cortex. Serotonin-1A receptor expression and serotonin-2C receptor messenger RNA were unchanged in all areas. The treatment markedly decreased serotonin and 5-hydroxyindoleacetic acid concentrations in striatum with similar trends in cortex and hippocampus. Haloperidol administration did not affect the expression of the three serotonin receptors, but was associated with a modest reduction of striatal and hippocampal 5-hydroxyindoleacetic acid. The selective reduction of serotonin-2A receptors confirms earlier findings and supports the view that this receptor may have relevance for the actions of clozapine. The fact that the encoding messenger RNA is decreased shows that the the effect is mediated at the level of gene expression. In contrast, the unchanged serotonin-2C receptor messenger RNA level indicates that the reported loss of serotonin-2C receptors after clozapine treatment is due to translational or post-translational events. The relationship between the reduction in serotonin-2A receptor expression and the altered serotonin metabolism remains unclear.

Mechanisms of action of atypical antipsychotic drugs: a critical analysis

Various criteria used to define atypical antipsychotic drugs include: 1) decrease, or absence, of the capacity to cause acute extrapyramidal motor side effects (acute EPSE) and tardive dyskinesia (TD); 2) increased therapeutic efficacy reflected by improvement in positive, negative, or cognitive symptoms; 3) and a decrease, or absence, of the capacity to increase prolactin levels. The pharmacologic basis of atypical antipsychotic drug activity has been the target of intensive study since the significance of clozapine was first appreciated. Three notions have been utilized conceptually to explain the distinction between atypical versus typical antipsychotic drugs: 1) dose-response separation between particular pharmacologic functions; 2) anatomic specificity of particular pharmacologic activities; 3) neurotransmitter receptor interactions and pharmacodynamics. These conceptual bases are not mutually exclusive, and the demonstration of limbic versus extrapyramidal motor functional selectivity is apparent within each arbitrary theoretical base. This review discusses salient distinctions predominantly between prototypic atypical and typical antipsychotic drugs such as clozapine and haloperidol, respectively. In addition, areas of common function between atypical and typical antipsychotic drug action may also be crucial to our identification of pathophysiological foci of the different dimensions of schizophrenia, including positive symptoms, negative symptoms, and neurocognitive deficits.

Male reproductive systems under chronic fluoxetine or trimipramine treatment

Adult male Long-Evans rats (n = 9 per group) received daily exposure for 4 weeks to fluoxetine (0.75 mg FLUOX/kg body weight) or trimipramine (1.6 mg TRIMI/kg body weight). Separate tests of copulation, sexual motivation, and intermale aggressive behaviors were used to evaluate functional changes during chronic exposure to either typical or atypical antidepressant drugs with more or less serotonin specificity. Circulating hormones, primary and secondary sex structures, and concentrations of dopamine (DA) and serotonin (5-HT) from mesolimbic tissue were assessed at necropsy. Results of tests with estrous females and untreated males revealed progressive disruption to sexual performance and aggressive responsiveness over time of treatment with TRIMI and, to a lesser extent, with FLUOX. By contrast, motivation, testosterone, and all measures of reproductive physiology were indistinguishable from controls. Ratios of transmitter metabolites relative to the parent compounds indicated similar reductions of 5-HT turnover with FLUOX and TRIMI. However, influences on DA turnover were significantly less with FLUOX than with TRIMI. Conclusions are that long-term intervention with antidepressant drugs may disrupt sociosexual exchanges without compromising male rats' interest in sexual contact or integrity of their reproductive physiology. Lessened disruption of sociosexual behaviors with this regimen of chronic FLUOX treatment may be related to the greater selectivity on serotonin relative to dopamine turnover.

Enhancement of the prolactin response to d-fenfluramine in drug-naive schizophrenic patients

BACKGROUND

We wished to investigate central serotonergic function in untreated schizophrenia.

METHOD

Thirteen drug-naive, DSM-III-R schizophrenic patients were compared with sex, race, age, weight and menstrual phase matched controls. Plasma prolactin and cortisol responses to a specific serotonergic probe, d-fenfluramine, were measured along with BPRS ratings.

RESULTS

Prolactin responses were enhanced in schizophrenic patients compared to controls (P < 0.05) and were correlated positively with BPRS items for depression, anxiety and guilt. Baseline cortisol was also raised in those with schizophrenia (P < 0.001).

CONCLUSIONS

Central serotonergic tone may be raised in acute, drug-naive schizophrenia and may be associated with the presence of affective symptomatology.

The effects of antipsychotic drugs on Fos protein expression in the prefrontal cortex: cellular localization and pharmacological characterization

The assessment of immediate-early gene induction has proven to be a useful method for delineating the neural systems that subserve antipsychotic drug actions. In order to differentiate the sites and mechanisms of action of typical and atypical antipsychotic drugs, we examined the effects of antipsychotic drugs on Fos protein expression in the medial prefrontal cortex. The atypical antipsychotic drug clozapine selectively increased the number of neurons that expressed Fos-like immunoreactivity in the prefrontal cortex, targeting the deep layers of the infralimbic and prelimbic cortices. Pyramidal cells were the major cell type in which Fos was expressed. A small number of calbindin-like immunoreactive, but not parvalbumin- or reduced nicotinamide adenine dinucleotide phosphate diaphorase-containing, interneurons also expressed Fos after clozapine challenge. Immunoblot studies revealed that clozapine induced Fos protein in the infralimbic and prelimbic cortices. Other antipsychotic drugs that are D2 receptor antagonists, including haloperidol, raclopride, sulpiride, remoxipride and loxapine, did not alter Fos expression. The clozapine-induced increase in Fos expression was also not attributable to actions at the D1 dopamine receptor, nor to serotonin type 2a/2c receptor antagonism or combined serotonin type 2-D2 dopamine receptor antagonism. The ability of clozapine to block alpha 1-adrenergic or muscarinic cholinergic receptors did not contribute to the unique actions of clozapine. Despite the inability of dopamine receptor antagonists other than clozapine to elicit an increase in Fos expression, both the mixed D1-D2 dopamine agonist apomorphine and the D2-like agonist quinpirole increased Fos protein levels in the prefrontal cortex. However, neither pretreatment with sulpiride to block D2/3/4 dopamine receptors or SCH 23390 to block D1/5 dopamine receptors modified the Fos response to clozapine. Since dopamine receptor antagonist pretreatments did not attenuate the clozapine-elicited Fos expression, but D2 agonists increased cortical Fos expression, clozapine may act in the prefrontal cortex on an as yet undefined dopamine receptor. In contrast to the nucleus accumbens shell, where all antipsychotic drugs increase Fos expression, only clozapine induced Fos in the medial prefrontal cortex. These observations suggest that the ability of clozapine to treat schizophrenic patients who are resistant to the therapeutic benefits of conventional antipsychotic drugs may occur through actions in the prefrontal cortex.

Kainic acid decreases hippocampal neuronal number and increases dopamine receptor binding in the nucleus accumbens: an animal model of schizophrenia

Intracerebroventricular (i.c.v.) administration of kainic acid (KA) produces graded neuronal loss in the hippocampus and other regions of the medial temporal lobe. Many of these brain regions send excitatory projections to the nucleus accumbens, a dopaminergic brain area implicated in psychotomimetic and antipsychotic drug action. In the present study, neurochemical function in the nucleus accumbens and anterior caudate-putamen was examined one week after i.c.v. administration of 1.5, 4.5, or 6.6 nmol of KA. As expected, i.c.v. KA produced dose-dependent neuronal loss in the dorsal and ventral hippocampus. Extrahippocampal neuronal loss was also observed in the thalamus and piriform cortex in some of the KA-treated rats. While ambient levels of dopamine turnover and excitatory amino acids in the nucleus accumbens were unaltered by KA, administration of the highest KA dose elevated [3H]spiperone binding exclusively in the accumbens. Finally, behavioral hyperactivity was observed in KA-treated rats over a five-week period following i.c.v. administration. The pattern of neuronal loss, receptor upregulation, and behavioral hyperactivity found after i.c.v. KA administration may provide a useful animal model of the limbic neuropathology and neurochemical dysfunction associated with schizophrenia.

Cortical maldevelopment, anti-psychotic drugs, and schizophrenia: a search for common ground

Two of the favorite hypotheses of schizophrenia research-maldevelopment of cerebral cortex and malfunction of brain dopamine systems-have often seemed difficult to reconcile. This article reviews recent research that suggests a heuristically useful reconciliation centered on the functional neuroanatomical concept of prefrontal-temporolimbic cortical connectivity. Anatomical findings from postmortem studies and neuropsychological and neuroimaging studies of brain function in patients with schizophrenia have implicated a developmental 'dysconnection' of temporolimbic-prefrontal cortices. The possibility that such dysconnection can account for the principal phenomenology of the illness, including its delayed onset and its treatment, is suggested by neurologic disease analogies such as metachromatic leukodystrophy and by recent studies in animals with developmental cortical lesions. Studies mapping neuronal gene expression indicate that all antipsychotic drugs modulate DNA transcription in a region of the nucleus accumbens that receives converging inputs from prefrontal and temporolimbic cortices, suggesting that indirect compensation for dysfunctional communication between prefrontal and temporolimbic cortices is a therapeutic mechanism of these drugs. Treatments aimed at direct cortical compensation may be more effective.

Different effects of subchronic clozapine and haloperidol on dye-coupling between neurons in the rat striatal complex

Atypical antipsychotic drugs, such as clozapine, are distinguished from classical antipsychotics (e.g. haloperidol) by their lower liability for producing motor side-effects. Although initial studies suggested that the clinical efficacy of antipsychotic drugs is related to their affinity for the D2 dopamine receptor, the delayed onset of both the therapeutic effects and the extrapyramidal symptoms associated with these drugs implicates a more complex mechanism of action. In this study, we found that continuous (but not acute) treatment of rats with either drug caused an increase in dye coupling between neurons in the limbic component of the rat striatal complex (i.e. the shell region of the nucleus accumbens) after withdrawal of the drugs. Furthermore, continuous treatment with haloperidol, but not clozapine, also increased dye coupling in the motor-related part of the striatal complex (i.e. the dorsal striatum). Thus, both therapeutically effective drugs show a delayed effect on dye coupling between neurons in the accumbens shell, whereas only the drug associated with motor side effects altered coupling between cells in the dorsal striatum. Antipsychotic drugs may therefore alleviate the profound disturbances in cognitive function of schizophrenics by producing sustained alterations in the way signals from the cortex are integrated within these brain regions.

Neonatal excitotoxic ventral hippocampal damage alters dopamine response to mild repeated stress and to chronic haloperidol

The effects of neonatal excitotoxic ventral hippocampus (VH) lesions on dopamine release in response to repeated stress (saline injections) and to chronic haloperidol treatment were investigated in Sprague-Dawley rats infused with ibotenic acid or vehicle into the VH on day 7 of postnatal life (PD7). Beginning on PD35, lesioned and sham-operated rats were injected i.p. with saline (INJ) once daily for 3 weeks or were not treated (NO INJ). Another cohort of rats was given haloperidol (HAL, 0.4 mg/kg, i.p.) or vehicle beginning on PD35 and thereafter once daily for 3 weeks. 3-Methoxytyramine (3-MT) was measured by combined gas chromatography/mass spectrometry in the frontal cortex (FC), nucleus accumbens (NAcc), and striatum (STR) at PD56 following MAO inhibition with pargyline. At baseline (NO INJ), 3-MT was reduced in STR of lesioned rats. Repeated saline injections resulted in a further 3-MT reduction in STR, FC, and NAcc of lesioned animals, but had no effect in sham rats. Chronic HAL, compared with vehicle, suppressed locomotor activity, and increased 3-MT accumulation in the FC, NAcc, and STR in sham and lesioned rats. This increase was enhanced in the FC of lesioned rats. These data show that mild repeated stress attenuates dopamine release in FC, NAcc, and STR of lesioned rats, while chronic HAL augments it in FC of lesioned animals versus controls. We conclude that the neonatal excitotoxic lesion of VH alters the functioning of midbrain dopamine systems during environmental and pharmacological challenge.

Subcortical excitatory amino acid levels after acute and subchronic administration of typical and atypical neuroleptics

The effects of three atypical neuroleptic compounds, clozapine, sulpiride, and (-)-3-(3-hydroxyphenyl)-N-n-propyl-piperidine ((-)-3-PPP) were compared to the effects of haloperidol and saline on excitatory amino acid levels in the rodent nucleus accumbens and corpus striatum after acute (1 day) and subchronic (28 days) treatment. Equivalent doses of each drug were determined by assessing their in vivo displacement of [3H]spiperone binding in the nucleus accumbens and corpus striatum. After acute treatment, all three atypical neuroleptics, but not haloperidol, produced a significant decrease in nucleus accumbens glutamate concentrations. Acute haloperidol treatment significantly elevated glutamate concentrations in the corpus striatum when compared to all three atypical drugs. After subchronic treatment, (-)-3-PPP significantly increased glutamate concentrations in the nucleus accumbens when compared to the effects of haloperidol and clozapine. There were no major between-group differences in glutamate levels after subchronic treatment in the corpus striatum. The effects of acute and subchronic neuroleptic administration on aspartate levels in the nucleus accumbens and corpus striatum were highly variable. These findings indicate that atypical and typical neuroleptics may alter subcortical excitatory amino acid levels in a site-specific manner.