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PubMed1998

Phenotypic characterization of neuroleptic-sensitive neurons in the forebrain: contrasting targets of haloperidol and clozapine.

The prototypical neuroleptic haloperidol and the atypical antipsychotic clozapine induce distinctly different patterns of c-fos expression in the forebrain. While haloperidol appears to increase c-fos expression via its D2 dopamine receptor antagonist properties, the receptor mechanisms by which clozapine produces its unique pattern of c-fos expression are not known. The present experiments sought to address this question by determining the phenotypes of neurons in which clozapine increases Fos-like immunoreactivity (FLI). Fos immunostaining combined with in situ hybridization histochemistry using a cDNA oligonucleotide probe for D3 receptor mRNA indicated that the great majority (95%) of clozapine-induced FLI neurons in the major island of Calleja (ICjM) express D3 receptors. Similarly, in the nucleus accumbens (NAc) and lateral septal nucleus (LSN), the majority of clozapine-induced FLI neurons express D3 receptor mRNA (NAc 69%; LS 73%). In marked contrast, haloperidol-induced FLI neurons failed to express D3 receptors in any brain region. Studies with oligonucleotide probes for enkephalin (ENK) and dynorphin (DYN) indicated that clozapine increases c-fos expression in both ENK and DYN containing neurons in the NAc (ENK 40%, DYN 53%) and LSN (ENK 32%, DYN 59%). Haloperidol also increases c-fos expression in ENK and DYN containing neurons, albeit in a different pattern (striatum: ENK 93%, DYN 20%; nucleus accumbens: ENK 46%, DYN 36%; lateral septum: ENK 29%, DYN 18%). The present results demonstrate that haloperidol and clozapine target different populations of neurons even in regions such as the NAc and LSN, where they both increase c-fos expression. In addition, the fact that the majority of clozapine-sensitive neurons in NAc, LSN, and ICjM express D3 receptors suggests that activity at these receptors may contribute to the unique clinical profile of this antipsychotic agent. These data indicate that D3 receptors may represent novel targets in the pharmacotherapy of schizophrenia.

Animals↗
PubMed2003

Comparative analysis of acute and chronic administration of haloperidol and clozapine using [3H] 2-deoxyglucose metabolic mapping.

In an effort to compare and contrast the mechanisms of action of typical and atypical antipsychotic drugs, [3H] 2-deoxyglucose metabolic mapping was employed following acute and chronic administration of haloperidol (1 mg/kg i.p. acute and 0.5 mg/kg i.p. chronic) and clozapine (20 mg/kg i.p., both acute and chronic). Optical density ratios (ODR) were measured in 62 brain structures. An overall decrease in ODR was observed in many of the regions analyzed. Acute haloperidol elicited significant decreases, particularly in the thalamus and hippocampus. Acute clozapine decreased glucose uptake in the caudate putamen, hippocampus, central gray, locus coreleus, and the thalamus. In both chronically treated haloperidol and clozapine animals, significant decreases in ODR were seen in the thalamus and hippocampal areas most dramatically, with other changes in the superior colliculus, retrospenial cortex, and the cerebellum. Clozapine caused significant effects in 32 nuclei acutely and only 19 nuclei chronically. Haloperidol caused significant effects in 23 nuclei acutely and 15 nuclei chronically. The pattern of change induced by haloperidol and clozapine were remarkably similar when considering their pharmacology is somewhat different. Both antipsychotics elicited fewer significant changes upon chronic administration.

Animals↗
PubMed2003

Weight gain in patients with schizophrenia treated with risperidone, olanzapine, quetiapine or haloperidol: results of the EIRE study.

OBJECTIVES: The aim of this cross-sectional study, the EIRE study, was to assess the frequency of several side effects with antipsychotics in the clinical setting. This paper addresses the adverse effect of weight gain. METHOD: Outpatients diagnosed of schizophrenia according to DSM-IV criteria and receiving a single antipsychotic (risperidone, olanzapine, quetiapine or haloperidol) for at least 4 weeks were consecutively recruited. Data were collected in a single visit, including data on demographic, clinical and treatment characteristics. Mean weight change was evaluated retrospectively by means of clinical charts and the weight at the time of the visit; in addition, the corresponding item of a modified version of the UKU, a Scandinavian side-effect rating scale, was used. Chi-squared test and logistic regression methods were used to analyze frequency of weight gain between treatments. RESULTS: Out of 669 recruited, 636 evaluable patients were assessed. The treatment with the highest number of patients with weight gain as an adverse reaction on the UKU scale was olanzapine (74.5%), followed by risperidone (53.4%) and haloperidol (40.0%). The proportion of patients with clinically relevant weight gain (>or=7% increase versus initial weight) was also higher with olanzapine (45.7%) than with risperidone (30.6%) and haloperidol (22.4%). Five patients (13.5%) treated with quetiapine had some degree of weight gain according to the UKU scale, although no patient showed a clinically relevant weight gain (>or=7%). Treatment with olanzapine and risperidone were identified as risk factors of weight gain versus haloperidol. The risk of weight gain was higher in women (OR: 4.4), overweight patients (OR: 3.0) and in patients with <or=1 year of treatment (OR: 6.3) in the olanzapine group. A higher risk of weight gain in women (OR: 2.6) was also seen with risperidone. CONCLUSION: Clinically relevant weight gain is clearly associated with olanzapine, and to lesser extent, with haloperidol and risperidone. Data for quetiapine were not conclusive because of the short duration of treatment.

Adult↗
PubMed2000

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.

Adolescent↗
PubMed2001

Double-blind olanzapine vs. haloperidol D2 dopamine receptor blockade in schizophrenic patients: a baseline-endpoint.

The aim of this study was to compare in vivo striatal D2 dopamine receptor occupancy induced by olanzapine and haloperidol in schizophrenic patients using a baseline-endpoint [(123)I]IBZM single photon computed emission tomography (SPECT) design. The relationships of striatal D2 receptor occupancy with clinical efficacy and extrapyramidal symptoms (EPS) were also assessed. Twenty-seven inpatients with schizophrenia or schizophreniform disorder were included in a 4-week prospective, randomized, double-blind, parallel and comparative clinical trial. Thirteen patients were treated with haloperidol (10 mg/day) and 14 with olanzapine (10 mg/day). Ratings of clinical status and EPS were obtained weekly. The percentage of D2 receptor occupancy was estimated by using basal ganglia (striatum)/frontal cortex IBZM uptake ratios obtained from each patient before and after 4 weeks of maintained antipsychotic treatment. Olanzapine led to a mean striatal D2 receptor occupancy of 49% (range 28-69%), which was significantly lower than that induced by haloperidol (mean 64%, range 46-90%). The baseline-endpoint SPECT design used in this study revealed lower antipsychotic D2 occupancy percentage values than those reported in the literature, using other approaches. The degree of striatal D2 receptor occupancy correlated to the EPS, which predominantly appeared in patients on haloperidol. No relationship was found between the striatal D2 receptor occupancy and clinical improvement. Olanzapine induced a lower striatal D2 occupancy than haloperidol. This low striatal D2 occupancy, together with the lower incidence of EPS in olanzapine-treated patients, contributed to confirm the atypical behavior of this new antipsychotic drug. Nevertheless, conclusions based on SPECT-estimated percentages of antipsychotic D2 occupancy should be cautious, since the SPECT design could influence the results. In this regard, SPECT studies including baseline and endpoint examinations should be encouraged.

Adult↗
PubMed2004

A randomized, controlled comparison of the efficacy and tolerability of low and high doses of haloperidol in the treatment of first-episode psychosis.

While haloperidol is still widely used in the treatment of psychoses, the optimal daily dose remains a topic of controversy, particularly in first-episode psychosis. Previous studies have suggested that doses as low as 2 mg/d may be effective, whereas others have indicated superiority for higher over lower doses. This double-blinded, randomized controlled study compared the efficacy and tolerability of 2 vs. 8 mg/d of haloperidol over 6 wk in 40 subjects with first-episode psychosis. Both treatments were equally effective in reducing the PANSS Total and subscale scores. The low dose of haloperidol was better tolerated, with fewer extrapyramidal side-effects, less frequent use of anticholinergic medication and smaller elevations in prolactin levels. Using a low dose of haloperidol is at least as effective as, and better tolerated than a high dose of haloperidol in the treatment of first-episode psychosis.

Adolescent↗
PubMed2005

Activation of noradrenergic locus coeruleus neurons by clozapine and haloperidol: involvement of glutamatergic mechanisms.

The major brain noradrenergic nucleus locus coeruleus (LC) has long been thought to be involved in states of alertness and cognitive processes. These functional characteristics make this nucleus interesting with regard to the signs of schizophrenia, especially the negative symptoms of the disease. In the present in-vivo electrophysiological study we analyse a putative interaction between endogenous kynurenic acid (KYNA) and the antipsychotic drugs clozapine and haloperidol on noradrenergic LC neurons. Previous studies have shown that systemically administered antipsychotic drugs increase the neuronal activity of LC noradrenaline (NA) neurons. In line with these findings, our results show that clozapine (1.25-10 mg/kg i.v.) and haloperidol (0.05-0.08 mg/kg i.v.) increased the firing rate of LC NA neurons in anaesthetized rats. Pretreatment with PNU 156561A (40 mg/kg i.v., 3 h), a potent inhibitor of kynurenine 3-hydroxylase, produced a 2-fold increase in rat brain KYNA levels. This treatment prevented the increase in firing rate of LC NA neurons induced by haloperidol (0.05-0.08 mg/kg i.v.) and clozapine in high doses (2.5-10 mg/kg i.v.). However, the excitatory action of the lowest dose of clozapine (1.25 mg/kg i.v.) was not abolished by elevated levels of brain KYNA. Furthermore, pretreatment with L-701,324 (4 mg/kg i.v.) a selective antagonist at the glycine site of the NMDA receptor prevented the excitatory effects of both clozapine and haloperidol. The present results suggest that the excitation of LC NA neurons by haloperidol and clozapine involves a glutamatergic component.

Action Potentials↗
PubMed2001

Differential effects of the antipsychotics haloperidol and clozapine on G protein measures in mononuclear leukocytes of patients with schizophrenia.

AIMS: Heterotrimeric G proteins play a pivotal role in postreceptor information transduction. These proteins were previously implicated in the pathophysiology and treatment of mood and other neuropsychiatric disorders. Recently we showed that untreated patients with schizophrenia have a significantly elevated dopamine-induced Gs protein function which is correlated with the severity of the psychotic symptoms. In contrast, an inverse picture with reduction in the function and the immunoreactivity of Gs protein was detected in patients with Parkinson's disease. The present study aims at investigating the effect of antipsychotic medications on dopamine-induced Gs protein hyperfunction in schizophrenia comparing the classical antipsychotic haloperidol and the newer antipsychotic clozapine, which is devoid of extrapyramidal side effects, on G protein measures. METHODS: G protein functional measurements coupled to beta-adrenergic, muscarinic, and dopamine receptors were undertaken through bacterial toxin sensitive, agonist enhanced [3H]-Gpp(NH)p binding capacity, substantiated by quantitative measures of Gs alpha, Gi alpha, and G beta subunit proteins through immunoblot analysis in mononuclear leukocytes obtained from patients with schizophrenia under haloperidol, or clozapine treatments in comparison with untreated patients with schizophrenia and healthy volunteers. RESULTS: Dopamine-induced Gs hyperfunction characteristic of untreated patients with schizophrenia was not detected under antipsychotic treatment with either haloperidol or clozapine. Haloperidol caused a significant decrease in Gs function and immunoreactivity below normal levels. The extend of reduction in Gs function was found to be correlated with the intensity of extrapyramidal side effects. The pattern of G protein subunits levels in patients with schizophrenia under haloperidol treatment resembles the one obtained in patients with Parkinson's disease. CONCLUSIONS: In the present study it is shown that G protein measurements in patients with schizophrenia under antipsychotic treatments can be used to biochemically monitor effects of antipsychotic medications in living patients. Moreover, these measurements may be used also for monitoring parkinsonian side effects induced by antipsychotic medications.

Adult↗
PubMed1990

A new rodent model for neuroleptic-induced pseudo-parkinsonism: low doses of haloperidol increase forelimb tremor in the rat.

Rats were trained to use the right forelimb to exert continuous downward pressure on a force transducer and simultaneously to drink sweetened milk from a dipper controlled by the emitted force. Oscillations in forelimb force during this performance were spectrally analyzed to describe the tremorogenic effects of haloperidol (0.04, 0.08, or 0.16 mg/kg). Haloperidol reduced time-on-task and increased the variance of force oscillations in the 10.0-25.0-Hz frequency band. When atropine sulfate (5 mg/kg) was given along with haloperidol, time-on-task was partially restored, and the effects of haloperidol on the 10.0-25.0-Hz band were diminished. These data suggest that the behavioral deficits produced by relatively low doses of haloperidol in rats are analogous (and possibly homologous) to neuroleptic-induced Parkinsonian symptoms in humans.

Animals↗
PubMed1994

Spatial localization in the Morris water maze in rats: acquisition is affected by intra-accumbens injections of the dopaminergic antagonist haloperidol.

Previous studies (G. E. Ploeger, B. M. Spruijt, & A. R. Cools, 1992) showed that low doses of systemically injected haloperidol affected spatial learning in the Morris water maze. This study investigated effects of intra-accumbens injections of haloperidol on spatial learning. To control for motivation and sensorimotor coordination, the researchers trained the rats to escape onto a visible platform. Low doses (50-100 ng) of haloperidol impaired spatial learning, whereas escaping on a visible platform was undisturbed. The 500-ng dose of haloperidol completely blocked acquisition because of combined learning and motor impairments. Retrieval of an acquired escape response was unaffected by 500 ng haloperidol. The data show that mesolimbic dopaminergic activity is involved in the acquisition of spatial localization. The results are related to studies demonstrating the involvement of the nucleus accumbens in cue-directed behaviors.

Animals↗
PubMed2002

Haloperidol attenuates rewarding and aversively conditioned suppression of saccharin solution intake: reevaluation of the anhedonia hypothesis of dopamine blocking.

The dopamine (DA) antagonist, haloperidol, affected the conditioned suppression of a saccharin solution intake (the conditioned stimulus, CS) induced by amphetamine (AMPH) and lithium chloride (LiCl) unconditioned stimuli (USs). Four experiments showed that (a) haloperidol by itself did not reduce saccharin solution intake. (b) When haloperidol was injected between the CS and the US, the conditioned suppression was attenuated; however, (c) this did not occur when haloperidol was injected after the US, indicating that haloperidol affected the perception of the US. (d) This attenuation was found with both rewarding AMPH and aversive LiCl treatments, indicating that the valence of the US was unimportant. Thus, the so-called "anhedonia response" might be due to weakening of US impact. A general salient-stimulus hypothesis was proposed, with the anhedonia hypothesis of DA blocking as its subset.

Amphetamine↗
PubMed1994

Quantitative analysis of two pyridinium metabolites of haloperidol in patients with schizophrenia.

OBJECTIVE: A pyridinium metabolite (HPP+) of the neuroleptic drug haloperidol has been identified in rats and in the urine of patients. The purpose of this study was to measure the steady-state blood and plasma concentrations and daily urinary excretion of HPP+ in patients treated with haloperidol. METHODS: HPP+ was measured by HPLC with fluorescence detection. The chromatograms also revealed the presence of a previously unknown pyridinium species, which was identified in urine by liquid chromatography/mass spectrometry/mass spectrometry as 4-(4-chlorophenyl)-1-4-(4-fluorophenyl)-4-hydroxybutylpyridinium (RHPP+). Concentrations of RHPP+ were then measured by HPLC. RESULTS: The steady-state concentrations of HPP+ or RHPP+ in blood and plasma from 34 patients were virtually identical. The plasma concentrations of each metabolite were related to the daily dose of haloperidol and to its plasma concentrations. Nonlinearity in the elimination of RHPP+ was suggested by the increase in the ratio between RHPP+ and HPP+ plasma concentrations with dose or steady-state concentrations of haloperidol. The concentrations of RHPP+ in plasma and urine generally exceeded those of HPP+; the ratio between them in plasma ranged from 0.9 to 14.1. The daily urinary excretion of HPP+ and RHPP+ accounted for 0.40% +/- 0.18% and 2.3% +/- 1.4% of the haloperidol dose, respectively. The renal clearance of each species was 4.5 +/- 2.5 and 11.3 +/- 5.3 L/hr, respectively. CONCLUSIONS: The presence of these pyridinium species in humans raises the concern that they may be neurotoxic in a manner similar to the dopaminergic pro-neurotoxin, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine.

Adult↗
PubMed2004

A pilot study of risperidone, olanzapine, and haloperidol in psychotic youth: a double-blind, randomized, 8-week trial.

This pilot study was undertaken to estimate the acute antipsychotic effect size and side effect propensity of risperidone and olanzapine in the pediatric population, in comparison to haloperidol, a conventional antipsychotic with established efficacy. Risperidone and olanzapine are widely used as first-line treatments to ameliorate psychotic symptoms in youth, but their abilities to specifically treat children and adolescents presenting due to psychotic symptoms have not been rigorously studied. Subjects, selected because of prominent positive psychotic symptoms, were randomly assigned to double-blind, parallel treatment with risperidone, olanzapine, or haloperidol for 8 weeks. The primary outcome was reduction in the Brief Psychiatric Rating Scale for Children total score from baseline to termination. An exploratory, descriptive analysis was done to compare the three treatments. A total of 50 patients, 8-19 years, participated. All treatments reduced symptoms significantly with p-values (corrected for multiple comparisons) of 0.0018 for each of the atypical agents and 0.012 for haloperidol. In all, 88% of subjects treated with olanzapine, 74% treated with risperidone, and 53% treated with haloperidol met response criteria. The primary side effects observed in all patients were mild to moderate sedation, extrapyramidal symptoms, and weight gain. Risperidone and olanzapine acutely reduced psychotic symptoms in this pediatric sample. Exploratory comparisons indicate the magnitude of the antipsychotic response with these atypical agents is comparable to that observed with haloperidol. However, youth treated with risperidone and olanzapine experienced weight gain and extrapyramidal effects that appear more prevalent and severe than reported in adults.

Adolescent↗
PubMed1998

Widespread expression of Fos protein induced by acute haloperidol administration in the rat brain.

The effect of acute haloperidol administration on Fos protein expression was examined immunohistochemically in discrete regions of the rat brain. Male Wistar rats were injected subcutaneously (s.c.) with 0.1, 0.25, or 1.0 mg/kg of haloperidol. Two h after the injection, the rats were perfused, and the numbers of Fos immunoreactive neurons were counted in 24 brain regions. In contrast to the limited changes in Fos immunoreactivity at the low dose of haloperidol (0.1 mg/kg), the moderate dose (0.25 mg/kg) induced widespread increases in Fos-positive neurons in the rat brain. Large increases were produced in the caudate-putamen, nucleus accumbens, central amygdaloid nucleus, dorsomedial hypothalamic nucleus, hippocampus CA1 and substantia nigra pars compacta. Moderate increases were observed in the entorhinal cortex, lateral septum, lateral habenula, lateral amygdaloid nucleus, dentate gyrus, and mesencephalic central grey. Mild increases were induced in the anterior cingulate, temporal, occipital and perirhinal cortex, and central medial thalamic nucleus. The distribution of changes in Fos immunoreactivity at the high dose of haloperidol (1.0 mg/kg) were comparable to their distribution at the moderate dose. These findings indicate that the effect of acute haloperidol on Fos expression is widely distributed in the rat brain beyond the previously known dopamine-rich areas at the dose which produces plasma levels equivalent to those within the therapeutic range used clinically in humans. Further studies on the effects of chronic antipsychotic treatment are needed in order to identify the sites of the therapeutic action of antipsychotic drugs.

Animals↗
PubMed2001

Olanzapine versus haloperidol in the treatment of patients with chronic schizophrenia: results of the Japan multicenter, double-blind olanzapine trial.

This randomized double-blind trial was conducted to test the efficacy and safety of olanzapine in Japanese patients with schizophrenia. Importantly, this study also represents the first large clinical trial of olanzapine conducted in an Asian population. Patients (n = 182) were randomly assigned to treatment with olanzapine or haloperidol over a period of 8 weeks. The primary analyses included: (i) a test of non-inferiority of olanzapine compared with haloperidol in efficacy using the Final Global Improvement Rating (FGIR); and (ii) comparison between the treatment groups in extrapyramidal symptom severity using the Drug-Induced Extrapyramidal Symptoms Scale (DIEPSS). Olanzapine was comparable to haloperidol in efficacy in treating positive symptoms and significantly superior in treating negative symptoms. Extrapyramidal symptom severity was significantly improved for olanzapine-treated patients versus haloperidol-treated patients. Olanzapine was shown to be more effective and better tolerated than haloperidol in the treatment of Japanese patients suffering from chronic schizophrenia.

Adult↗
PubMed1994

Regulation of mu-opioid receptor mRNA in rat globus pallidus: effects of enkephalin increases induced by short- and long-term haloperidol administration.

The mRNA encoding mu-opioid receptors is expressed in neurons of the globus pallidus, a region of the basal ganglia that receives a dense enkephalinergic innervation from the striatum. The regulation of the mRNAs encoding the opioid peptide enkephalin in the striatum and the mu-opioid receptor in the globus pallidus was examined with in situ hybridization histochemistry following short- or long-term haloperidol treatments, which alter striatal enkephalin mRNA levels. Animals were administered haloperidol daily for 3 or 7 days (1 mg/kg, s.c.) or continuously for 8 months (1 mg/kg, depot followed by oral). Enkephalin and mu-opioid receptor mRNA levels were unchanged after 3 days of haloperidol treatment. In contrast, the enkephalin mRNA level was increased in the striatum, and mu-opioid receptor mRNA levels were markedly decreased in the globus pallidus after 7 days of haloperidol administration. Similar effects were observed in rats treated with haloperidol for 8 months. The results provide the first evidence of regulation of mu-opioid receptor mRNA in vivo.

Animals↗
PubMed2003

Time-dependent changes in gene expression profiles of midbrain dopamine neurons following haloperidol administration.

Antipsychotic drugs require a treatment regimen of several weeks before clinical efficacy is achieved in patient populations. While the biochemical mechanisms underlying the delayed temporal profile remain unclear, molecular adaptations in specific neuroanatomical loci are likely involved. Haloperidol-induced changes in gene expression in various brain regions have been observed; however, alterations in distinct neuronal populations have remained elusive. The present study examined changes in gene expression profiles of ventral tegmental area (VTA) and substantia nigra (SN) tyrosine hydroxylase immunopositive neurons following 1, 10 or 21 days of haloperidol administration (0.5 mg/kg/day). Macroarrays were used to study the expression of receptors, signaling proteins, transcription factors and pre- and post-synaptic proteins. Data were analyzed using conventional statistical procedures as well as self-organizing maps (SOM) to elucidate conserved patterns of expression changes. Results show statistically significant haloperidol-induced and time-dependent alterations in 17 genes in the VTA and 25 genes in the SN, including glutamate and GABA receptor subunits, signaling proteins and transcription factors. SOMs revealed distinct patterns of gene expression changes in response to haloperidol. Understanding how gene expression is altered over a clinically relevant time course of haloperidol administration may provide insight into the development of antipsychotic efficacy as well as the underlying pathology of schizophrenia.

Analysis of Variance↗
PubMed1992

Differential expression of c-fos and zif268 in rat striatum after haloperidol, clozapine, and amphetamine.

Antipsychotic drugs are monoamine receptor antagonists. However, the mechanisms by which these direct actions are translated into therapeutic effects are unknown. Candidate mechanisms include receptor-mediated regulation of gene expression in target neurons. Inducible transcription factors, including certain immediate early genes (IEGs), may mediate between receptor-activated second messenger systems and expression of genes involved in the differentiated functions of neurons. We examined the specificity of induction of the IEGs c-fos and zif268 after acute administration of several antipsychotic drugs and, for comparison, the stimulant amphetamine, which has pharmacologic effects relatively opposite to those of antipsychotics. Antipsychotic drugs with potent dopamine D2 receptor antagonist properties, such as haloperidol, induced both c-fos and zif268 mRNA in the caudate-putamen; however, the atypical antipsychotic drug clozapine induced zif268 but not c-fos mRNA in that region. Similarly, haloperidol, but not clozapine, induced c-Fos-like immunoreactivity in the caudate-putamen. In contrast, both drugs induced c-Fos-like immunoreactivity in the nucleus accumbens. Like haloperidol, amphetamine induced both c-fos and zif268 mRNA in the caudate-putamen, but the anatomic patterns of induction of c-Fos-like immunoreactivity by the two drugs were dramatically different. Haloperidol and amphetamine induced AP-1 binding activity in cell extracts from the caudate-putamen, indicating that drug-induced IEG expression results in protein products that may function in the regulation of target gene expression. Thus these data demonstrate that inductions of IEG expression by haloperidol, clozapine, and amphetamine are specific, may be biologically relevant, and suggest avenues for further investigation.

Amino Acid Isomerases↗