The atypical neuroleptics clozapine and olanzapine differ regarding their antinociceptive mechanisms and potency

Using the mouse tail-flick assay, we evaluated the antinociceptive effect and the interaction with the opioid, adrenergic, and serotonergic systems of the two "atypical" neuroleptic agents clozapine and olanzapine. Clozapine induced a potent antinociceptive effect in a dose-dependent manner with ED50 of 8.7 mg/kg. This effect was antagonized by the nonselective opioid antagonist naloxone (p < 0.05), implying an opioid mechanism of action involved in clozapine-induced antinociception. Further evaluation demonstrated the involvement of micro1-, micro2-, kappa1- opioid receptor subtypes and of alpha2-adrenoreceptors in clozapine antinociception but not the serotonin receptors. Olanzapine induced a weak antinociceptive effect. The highest effect found was a 50% antinociception following an injection of 10 mg/kg. As the olanzapine dose increased beyond 10 mg/kg, latencies declined almost back to baseline. Yohimbine (an alpha2-adrenoreceptor antagonist) significantly reduced olanzapine's antinociceptive effect almost completely (to 10%; p < 0.05), while both naloxone and metergoline (a nonselective 5-HT receptor antagonist) reduced it only partially. These results indicate the possible involvement of the alpha2-adrenoreceptors in olanzapine antinociception and to a less extent the involvement of opioid and serotonergic receptors. Although both clozapine and olanzapine are dibenzodiazepines with similar "atypical" antipsychotic properties, it seems that they differ notably not only regarding their hematological side effects, but regarding their interaction with the opioid system as well.

Human leukocyte antigen typing, response to neuroleptics, and clozapine-induced agranulocytosis in jewish Israeli schizophrenic patients

The atypical antipsychotic agent clozapine is known to be effective in schizophrenic patients refractory to other medications; however, it induces agranulocytosis in approximately 1-2%. In Jews, this complication is associated with the haplotype HLA B38,DR4,DQ3. The aim of the present study was to determine which human leukocyte antigen (HLA) antigens are involved in clozapine-induced agranulocytosis. We performed HLA typing in 88 Jewish Israeli schizophrenic patients and in 127 ethnically matched healthy individuals. Thirty-eight patients responsive to standard antipsychotic medications were treated with haloperidol, and 50 refractory patients received clozapine. A trend was noted for elevated rates of HLA B38 among control individuals and clozapine-treated patients of Ashkenazi origin compared to individuals of non-Ashkenazi origin, but the findings failed to reach statistical significance. No association was found between HLA class I antigens and the response to haloperidol or clozapine. Neutropenia developed in two clozapine-treated patients and agranulocytosis in one. Two of these three patients were of Ashkenazi origin, and both demonstrated the HLA B38 phenotype. Although the findings did not reach a statistical significance because of the small number of patients, they may support an association between clozapine-induced neutropenia/agranulocytosis and Ashkenazi origin and the HLA B38 phenotype. The rate of agranulocytosis in our sample (2%) is similar to the usual cumulative risk of agranulocytosis but in contrast to its high frequency among Jewish American patients. One possible explanation for this difference is the high rate of Ashkenazi patients in the American sample and the preponderance of non-Ashkenazi patients in our population.

Pentadecapeptide BPC 157 attenuates disturbances induced by neuroleptics: the effect on catalepsy and gastric ulcers in mice and rats

A gastric pentadecapeptide, BPC 157, with the amino acid sequence, Gly-Glu-Pro-Pro-Pro-Gly-Lys-Pro-Ala-Asp-Asp-Ala-Gly-Leu-Val, MW 1419, known to have a variety of protective effects in gastrointestinal tract and other organs, was recently shown to particularly affect dopamine systems. For instance, it blocks the stereotypy produced acutely by amphetamine in rats, and the development of haloperidol-induced supersensitivity to amphetamine in mice. Consequently, whether pentadecapeptide BPC 157, that by itself has no cataleptogenic effect in normal animals, may attenuate the immediate effects of neuroleptics application, particularly catalepsy, was the focus of the present report. Prominent catalepsy, otherwise consistently seen in the mice treated with haloperidol (0.625, 1.25, 2.5, 5.0 and 10.0 mg/kg b.w., i.p.) and fluphenazine (0.3125, 0.625, 1.25, 2.5 and 5.0 mg/kg b.w., i.p.) after 1.5, 3, 4.5, 6 and 7.5 h following administration, was markedly attenuated when pentadecapeptide BPC 157 (10 microg or 10 ng/kg b.w., i.p.) was coadministered with the neuroleptic. The number of cataleptic mice was markedly lower throughout most of the experimental period. Moreover, on challenge with lower doses of neuroleptics, catalepsy appearance was postponed and the mice, otherwise cataleptic since the earliest period, became cataleptic later, not before 3 or 4.5 h after neuroleptic administration, especially if protected with higher pentadecapeptide dose. Besides catalepsy, coadministration of the pentadecapeptide BPC 157, given in the above mentioned doses, reduced not only catalepsy but somatosensory disorientation (for 7.5 h after administration of a neuroleptic, assessed at intervals of 1.5 h, by a simple scoring system [0-5]) in haloperidol- or fluphenazine-challenged mice as it did in mice treated with sulpiride (20, 40, 80 and 160 mg/kg b.w., i.p.) or with clozapine (25, 50 and 100 mg/kg b.w., i.p.), in which case catalepsy was absent. In other experiments, considering the gastric origin of this pentadecapeptide, the focus was shifted to the evidence that a dose of haloperidol, cataleptogenic due to dopamine receptors blockade, induces gastric ulcers in rats. Coadministration of pentadecapeptide BPC 157 (10 microg, 10 ng, 1.0 ng, 100 pg/kg b.w., i.p.) to rats completely inhibited the lesions otherwise regularly evident 24 h after haloperidol (5.0 mg/kg b.w., i.p.) in control rats (18 of 20 rats had gastric lesions). This activity accompanied the antagonism of the haloperidol catalepsy in rats (assessed at 60-min intervals from I to 5 h after haloperidol), when 10-microg- or 10-ng regimens were given (lower doses could not influence catalepsy). Together, these findings indicate that pentadecapeptide BPC 157 fully interacts with the dopamine system, both centrally and peripherally, or at least, that BPC 157 interferes with some steps involved in catalepsy and/or ulcer formation.

Disruption of prepulse inhibition following N-methyl-D-aspartate infusion into the ventral hippocampus is antagonized by clozapine but not by haloperidol: a possible model for the screening of atypical antipsychotics

The present study tested the effects of the typical neuroleptic haloperidol and an atypical neuroleptic clozapine on ventral hippocampus stimulation-induced disruption of prepulse inhibition (PPI). Bilateral infusions of 0.7 microg NMDA into the ventral hippocampus disrupted PPI. The impairment of PPI following the infusion was completely normalized 24 h after the infusion. This disruption of PPI was antagonized by clozapine (5.0 mg/kg), but not by haloperidol (0.2 mg/kg). Since disruption of PPI is considered to constitute an animal model of schizophrenia that is related to the deficit of sensorimotor gating observed in schizophrenic patients, these results suggest that PPI disruption induced by intra-ventral hippocampal infusions of NMDA may serve as an animal model for the selective detection of atypical antipsychotics.

Mice with reduced NMDA receptor expression display behaviors related to schizophrenia

N-methyl-D-aspartate receptors (NMDARs) represent a subclass of glutamate receptors that play a critical role in neuronal development and physiology. We report here the generation of mice expressing only 5% of normal levels of the essential NMDAR1 (NR1) subunit. Unlike NR1 null mice, these mice survive to adulthood and display behavioral abnormalities, including increased motor activity and stereotypy and deficits in social and sexual interactions. These behavioral alterations are similar to those observed in pharmacologically induced animal models of schizophrenia and can be ameliorated by treatment with haloperidol or clozapine, antipsychotic drugs that antagonize dopaminergic and serotonergic receptors. These findings support a model in which reduced NMDA receptor activity results in schizophrenic-like behavior and reveals how pharmacological manipulation of monoaminergic pathways can affect this phenotype.

Regulation of ionotropic glutamate receptors in the rat brain in response to the atypical antipsychotic seroquel (quetiapine fumarate)

The interplay between dopamine and glutamate appears to be relevant in the etiopathology of schizophrenia. Although currently used antipsychotics do not interact with glutamatergic receptors, previous results have demonstrated that the expression profile of ionotropic glutamate receptors can be regulated by drugs such as haloperidol or clozapine. In the present investigation, the mRNA levels for NMDA and AMPA receptor subunits were measured after chronic treatment with the novel antipsychotic agent Seroquel (quetiapine fumarate, quetiapine) as compared to haloperidol and clozapine. Similarly to the prototype atypical clozapine, quetiapine reduced the mRNA expression for NR-1 and NR-2C, two NMDA forming subunits, in the nucleus accumbens. Furthermore, quetiapine, but not haloperidol or clozapine, increased the hippocampal expression for the AMPA subunits GluR-B and GluR-C. The differences between classical and atypical antipsychotics, as well as among the novel agents, might be relevant for specific aspects of their therapeutic activity and could provide valuable information for the role of glutamate in specific symptoms of schizophrenia.

In vivo receptor occupancy of NRA0045, a putative atypical antipsychotic, in rats

We have previously reported that (R)-(+)-2-amino-4-(4-fluorophenyl)-5-[1-[4-(4-fluorophenyl)-4-oxobutyl]+ ++pyrrolidin-3-yl]thiazole (NRA0045) is a novel antipsychotic agent with affinities for dopamine D4, 5-hydroxytryptamine 2A (5-HT2A) and alpha1 receptors. In the present study, in vivo receptor occupancy of 5-HT2A, alpha1, dopamine D2 and D3 receptors by NRA0045 was assessed, based on in vivo and ex vivo receptor binding, and findings were compared to reference antipsychotic drugs (haloperidol, risperidone, clozapine). Intraperitoneal administration of haloperidol highly occupied the dopamine D2 receptor in the striatum and nucleus accumbens, and alpha1 adrenoceptors in the frontal cortex. Occupation of the 5-HT2A receptor in the frontal cortex and the dopamine D3 receptor in the nucleus accumbens and islands of Cajella was moderate. By contrast, atypical antipsychotics such as risperidone and clozapine dose-dependently occupied the 5-HT2A receptor in the frontal cortex, with moderate to negligible occupancy of the D2 receptor in the striatum and the nucleus accumbens. Clozapine and risperidone also occupied the alpha1 adrenoceptor in the frontal cortex, and clozapine did not occupy the dopamine D3 receptor. As seen with other atypical antipsychotics, intraperitoneal administration of NRA0045 dose-dependently occupied the 5-HT2A receptor and the alpha1 adrenoceptor in the frontal cortex, while it was without effect on dopamine D2 and D3 receptors in the striatum, nucleus accumbens and islands of Cajella. Thus, the strong occupancy of 5-HT2A and alpha1 receptors is involved in the pharmacological action of NRA0045.

Effects of clozapine and haloperidol on 5-HT6 receptor mRNA levels in rat brain

The high affinity of 5-HT6 receptors for atypical antipsychotic drugs, and their localization in limbic and cortical regions of the brain, suggest that they might play a role in the pathophysiology of schizophrenia. To determine if this receptor is regulated by antipsychotics, rats were injected with clozapine (20 mg/kg/day), haloperidol (2 mg/kg/day), or vehicle daily for 2 weeks, and 5-HT6 receptor mRNA levels were measured by in situ hybridization. Clozapine but not haloperidol significantly decreased 5-HT6 expression in all subfields of the hippocampus. No drug effects were observed in cortical or forebrain structures. These results suggest that downregulation of this receptor in the hippocampus might be a characteristic of atypical antipsychotic drugs, although this hypothesis will require testing with other atypical antipsychotics.

Clozapine pre-treatment enhances raclopride catalepsy

The clinical replacement of clozapine by another antipsychotic sometimes causes extrapyramidal signs, including dystonia, to appear suddenly. The present study was done, therefore, to test whether clozapine pre-treatment of rats could affect raclopride-induced catalepsy. Clozapine, at 5 mg/kg, given 2 h before a catalepsy-threshold dose of 0.1 mg/kg raclopride, markedly enhanced raclopride-induced catalepsy in the rats. The results are compatible with earlier in vitro data where pre-exposure of human cloned dopamine D2 receptors to clozapine resulted in an increased potency of raclopride in inhibiting the binding of [3H]clozapine to the receptors. The mechanism of clozapine potentiation of raclopride action may contribute to the clinically observed post-clozapine dystonia.

Clozapine interaction with the M2 and M4 subtypes of muscarinic receptors

Available evidence indicates that the antipsychotic drug clozapine acts as a partial agonist at the muscarinic M4 and as an antagonist at the M2 receptors. We wondered whether there is indeed a fundamental difference between its action on these two receptor subtypes, and whether it interacts with their classical or allosteric binding sites. In experiments on Chinese hamster ovary cells stably expressing the M2 or M4 receptors, clozapine inhibited the binding of the specific muscarinic ligand [3H]N-methylscopolamine to either receptor subtype. The affinity of the high-affinity sites for clozapine was diminished by GTP in the way expected for agonists on both the M2 and the M4 receptor subtypes. Arunlakshana-Schild plots of data obtained in saturation binding experiments with [3H]N-methylscopolamine at different concentrations of clozapine were linear with a slope of unity. Clozapine did not alter the time course of [3H]N-methylscopolamine dissociation from muscarinic M2 or M4 receptors. It inhibited the synthesis of cyclic AMP in cells expressing the M4 receptor subtype, but did not measurably inhibit the synthesis of cyclic AMP in cells expressing the M2 receptor subtype. We conclude that clozapine has a high affinity for muscarinic M2 and M4 receptor subtypes, that it associates with the classical and not with the allosteric binding site, and that it acts as a partial agonist on both the M2 and the M4 receptor subtype.

Differential induction of Fos-like-immunoreactivity in the extended amygdala after haloperidol and clozapine

The extended amygdala is composed of the central and medial amygdaloid nucleus which through the sublenticular extended amygdala (SLEA) and the interstitial nucleus of the posterior limb of the anterior commissure (IPAC) merge into the bed nucleus of stria terminals (BST). Based on anatomical connections with limbic areas, the extended amygdala has been proposed to play an important role in cognitive and affective processes. This study examines the effect of the atypical antipsychotic clozapine and the classical antipsychotic haloperidol on Fos-like-immunoreactivity (FLI) induction in areas belonging to the extended amygdala. Acute administration of clozapine (10-20 mg/kg) induced FLI in the central amygdaloid nucleus, IPAC, SLEA, and BST lateral division and, as previously described, in areas connected to the extended amygdala, such as the prefrontal cortex and nucleus accumbens shell. In contrast, acute administration of haloperidol (0.1-1 mg/kg) failed to induce FLI in the BST lateral division and SLEA but increased FLI in the IPAC. A small increase in FLI was observed in the central amygdaloid nucleus after 0.1 but not after 1 mg/kg of haloperidol. The present results, showing a preferential influence of clozapine, as compared to haloperidol, in the extended amygdala propose a new brain structure involved in the pharmacological effects of atypical antipsychotics.

Clozapine reduces severe self-mutilation and aggression in psychotic patients with borderline personality disorder

BACKGROUND

Clozapine has been reported to be effective in diminishing violence toward others in psychotic patients. This article describes the impact of clozapine on severe self-mutilation among patients with the dual diagnoses of borderline personality disorder and persistent psychoses.

METHOD

Seven subjects known to the authors were selected for careful chart audits. These subjects had been admitted to 2 state psychiatric hospitals owing to severe self-mutilation and/or violence and subsequently treated with clozapine. A mirror-image design anchored to the start date of clozapine treatment and extending in either direction to a maximum of 1 year was used to extract data. Data extracted included incidents of self-mutilation (restraint), seclusion, the as and when needed (p.r.n.) use of medications, injuries to staff and peers, hospital privileges, and Global Assessment of Functioning (GAF) scores.

RESULTS

The subjects were all white women with a mean age of 37 years. All subjects carried DSM-III-R or DSM-IV borderline personality disorder diagnoses and an Axis I disorder diagnosis. They had received trials of several psychotropic agents, often in combination and mostly without benefit. After clozapine treatment, there were statistically significant reductions in incidents of self-mutilation (restraint), seclusion, the use of p.r.n. antianxiety medications, and injuries to staff and peers. These subjects received higher levels of hospital privileges, and their GAF scores nearly doubled following clozapine treatment. Four subjects were subsequently discharged from hospital.

CONCLUSION

These preliminary but nonetheless favorable results suggest that clozapine deserves careful consideration for a controlled study in patients with borderline personality disorder and psychoses, especially if the clinical issues include severe self-mutilation, aggression, and violence. Until such studies are done, the risk-to-benefit ratio of clozapine treatment needs to be carefully evaluated on an individualized basis in such subjects.

Raclopride and chlorpromazine, but not clozapine, increase muscle rigidity in the rat: relationship with D2 dopamine receptor occupancy

The aim of the present study was to investigate the relationship between effects on muscle tone and D2 receptor occupancy of two typical antipsychotic drugs, raclopride and chlorpromazine, and the atypical drug, clozapine. Increased muscle tone (i.e., muscle rigidity), was measured as increases in tonic electromyographic (EMG) activity of the antagonistic muscles of the rat hind limb. D2 dopamine receptor occupancy was assessed in the striatum and substantia nigra, areas involved in the regulation of muscle tone. Raclopride and chlorpromazine produced dose-dependent increases in EMG activity associated with D2 occupancy of 68%-80% in the striatum and 67%-76% in the nigra. No significant increases in EMG were observed with clozapine which showed low D2 occupancy. The results are consistent with those from human studies showing extrapyramidal side effects were associated with striatal D2 occupancy of > 70%.

Normalization of information processing deficits in schizophrenia with clozapine

OBJECTIVE

The authors tested the hypothesis that the use of an atypical drug, clozapine, for patients with schizophrenia is related to less impairment in information processing deficits (assessed by prepulse inhibition of the startle response) than is the use of typical antipsychotics.

METHOD

Two groups of schizophrenic patients--receiving either clozapine or a range of typical antipsychotics--were tested for prepulse inhibition (a reduction in response to a starting stimulus, if preceded briefly by a weak, nonstartling stimulus; measured at prepulse-to-pulse intervals of 30 msec, 60 msec, and 120 msec) of the acoustic startle response and compared with a group of healthy volunteers.

RESULTS

Patients receiving typical antipsychotics showed less prepulse inhibition with 30-msec and 60-msec prepulse trials than did comparison subjects. Clozapine-treated patients showed normal levels of prepulse inhibition.

CONCLUSIONS

Clozapine is superior to typical antipsychotics in normalizing prepulse inhibition, presumably because of its pharmacological effects on prefrontal regions of the brain or its effects on a broader range of neuroreceptors.

Selective modulation of fibroblast growth factor-2 expression in the rat brain by the atypical antipsychotic clozapine

In the present paper we investigated, in the rat brain, the expression of basic fibroblast growth factor (FGF-2) in response to the atypical antipsychotic clozapine. We found that acute or chronic administration of this compound produced a selective increase of FGF-2 mRNA and protein in the striatum. Although acute injection of clozapine did increase FGF-2 expression in parietal cortex and nucleus accumbens we found that, following repeated administration, the induction of the trophic molecule was taking place only at striatal level. The analysis of other antipsychotic drugs did not provide conclusive evidence for the molecular mechanisms involved in clozapine-induced elevation of FGF-2. In fact, chronic administration of classical neuroleptics, haloperidol and chlorpromazine, did not alter the expression of FGF-2. Furthermore the novel drugs quetiapine and olanzapine, despite some similarities in their receptor profiles, were similarly ineffective. Hence these data suggest that, among antipsychotic drugs, the induction of FGF-2 is unique to clozapine. On the basis of the neuroprotective activity of this trophic molecule, our data might be relevant for the potential use of clozapine in tardive dyskinesia and parkinsonism, which develop during long term administration of classical neuroleptic drugs.

The effects of atypical antipsychotics and phencyclidine (PCP) on rotorod performance

A series of six experiments were conducted to determine the effects of haloperidol, clozapine, olanzapine, and phencyclidine (PCP) on rotorod performance. Rodents were trained to walk on a rotorod to avoid a mild shock to a criterion of 20 rpm for 3 min. None of the vehicles of any of these drugs disrupted rotorod performance. Haloperidol disrupted rotorod performance at doses of 0.03, 0.1, and 0.3 mg/kg, and olanzapine disrupted rotorod performance at doses of 3.0 and 10.0 mg/kg. Clozapine produced a much milder disruption across all three doses (3.0, 10.0, and 30.0 mg/kg). PCP produced a consistent and severe disruption of rotorod performance at doses of 4.0 and 6.0 mg/kg, but not at a dose of 2.0 mg/kg. Twenty-four hours postinjection there were no residual PCP effects on rotorod performance. Coadministration of either haloperidol or olanzapine with PCP did not reverse PCP-induced disruption in rotorod performance, while clozapine produced a partial reversal at only one dose. These findings indicate that olanzapine functions similarly to classic antipsychotics with respect to their effects on locomotion and balance.

Effects of clozapine on awareness of illness and cognition in schizophrenia

Awareness of illness is a crucial factor in schizophrenia, both for clinical management and psychopathological modeling. To date, there has been relatively little investigation of the influence of treatment with conventional versus atypical neuroleptics in relation to awareness and cognitive functions. The effect of clozapine treatment, compared with conventional neuroleptics, was studied in 22 schizophrenic patients in a crossover study. The P300 component of the event-related potential and scores on the Scale for Unawareness of Mental Disorder (SUMD), the Extrapyramidal Side Effects Scale (EPS), and Andreasen's Scales for the Assessment of Positive (SAPS) and Negative Symptoms (SANS) were studied at time 1 (conventional neuroleptic treatment) and time 2 (after 6 months of treatment with clozapine, in patients who interrupted the previous conventional regimen). Significantly increased P300 amplitudes were associated with clozapine treatment, together with heightened insight and reduced involuntary movements. The results confirm the effectiveness of clozapine not only in enhancing neurocognitive function, but also in increasing awareness of illness in schizophrenic patients.

Voluntary consumption of amphetamine, cocaine, ethanol and morphine by rats as influenced by a preceding period of forced drug intake and clozapine

Forced nicotine intake was previously found to decrease a subsequent free choice selection, whereas clozapine (CL) caused a marked increase in its consumption. Here these findings are extended to ethanol, cocaine, morphine and amphetamine. Forced intake of ethanol, cocaine, morphine and amphetamine had no major effect on a subsequent voluntary intake. CL, a dopamine D4 antagonist, increased the voluntary consumption of amphetamine and morphine with no effects on ethanol or cocaine intake. Only for cocaine was it found that low-consuming rats increased but high-consuming rats decreased their voluntary cocaine intake by CL. Thus, forced drug exposure per se does not lead to subsequent enhancement of voluntary intake; CL exerts differential effects on intake of these drugs, and a specific dopaminergic set point may govern the voluntary intake of cocaine by individual rats.

The effects of clozapine on cognitive functioning in schizophrenia

Cognitive function may be markedly impaired in patients with schizophrenia; however, it has only recently been recognized as an important factor in determining patient outcome. Research has shown that improvements in cognitive functioning occur independently of improvements in positive or negative clinical symptoms, and whereas typical antipsychotics may improve clinical symptoms, they have little or no efficacy in improving cognitive dysfunction. However, there is evidence that the atypical antipsychotic clozapine may improve this core deficit of schizophrenia. This review summarizes 12 published studies that assessed the effect of clozapine on cognitive functioning. As a group, these studies suggest that psychomotor speed, verbal fluency, and verbal learning and memory may be improved by treatment with clozapine. Such cognitive improvements with clozapine treatment may offer an advantage to patients with schizophrenia by enhancing the possibility of better vocational functioning and quality of life.

The effects of clozapine on aggression and substance abuse in schizophrenic patients

Aggressive behavior in schizophrenic patients, although infrequent, is a serious problem. It is, however, a relatively common reason for psychiatric admission and poses an increasing threat as more patients are cared for in the community. There is a strong association between substance abuse and violent behavior, and comorbid substance abuse in schizophrenia is also a major problem. The recent introduction of the atypical antipsychotics has brought hope for the pharmacologic management of this group of patients. These newer agents are thought to have antiaggressive effects and perhaps decrease cravings for illicit substances and alcohol. Data from a number of studies have demonstrated that clozapine has antiaggressive effects. A retrospective analysis of 331 schizophrenic patients assessed the effects of clozapine on hostility and aggression. At baseline, 31.4% of patients showed overt physical aggression, and after an average of 47 weeks of treatment with clozapine, this rate had fallen to 1.1%. The antiaggressive effects of clozapine were relatively specific and could not be explained by sedation or general antipsychotic effects. These effects were more pronounced than the effects on other symptoms and were also present in those patients who showed the highest pretreatment levels of hostility and aggression. Clozapine may also be of benefit in the treatment of schizophrenic patients with comorbid substance abuse. After 6 months of treatment with clozapine, substance abusers and nonabusers with schizophrenia or schizoaffective disorder showed similar improvements on measures of psychopathology and psychosocial functioning.

Clozapine and other 5-hydroxytryptamine-2A receptor antagonists alter the subcellular distribution of 5-hydroxytryptamine-2A receptors in vitro and in vivo

In this study, we demonstrate that clozapine and other atypical antipsychotic drugs induce a paradoxical internalization of 5-hydroxytryptamine-2A receptors in vitro and a redistribution of 5-hydroxytryptamine-2A receptors in vivo. We discovered that clozapine, olanzapine, risperidone and the putative atypical antipsychotic drug MDL 100,907 all induced 5-hydroxytryptamine-2A receptor internalization in fibroblasts stably expressing the 5-hydroxytryptamine-2A receptor in vitro. Two 5-hydroxytryptamine-2A antagonists (mianserin and ritanserin), which have been demonstrated to reduce negative symptoms in schizophrenia, also caused 5-hydroxytryptamine-2A receptor internalization. Four different drugs, each devoid of 5-hydroxytryptamine-2A antagonist activity, had no effect on the subcellular distribution of 5-hydroxytryptamine-2A receptors in vitro. Treatment of rats for seven days with clozapine induced an increase in intracellular 5-hydroxytryptamine-2A receptor-like immunoreactivity in pyramidal neurons, while causing a decrease in labeling of apical dendrites in the medial prefrontal cortex. This redistribution of 5-hydroxytryptamine-2A receptors in pyramidal neurons was also seen when rats were chronically treated with another atypical antipsychotic drug, olanzapine. The typical antipsychotic drug haloperidol, however, did not induce a redistribution of 5-hydroxytryptamine-2A receptors in pyramidal neurons in the medial prefrontal cortex. Taken together, these results demonstrate that several atypical antipsychotic drugs with high 5-hydroxytryptamine-2A receptor affinities induce a redistribution of 5-hydroxytryptamine-2A receptors both in vivo and in vitro. It is conceivable that the loss of 5-hydroxytryptamine-2A receptors from the apical dendrites of pyramidal neurons is important for the beneficial effects of atypical antipsychotic drugs and other 5-hydroxytryptamine-2A antagonists in schizophrenia.

Effects of acute and chronic administration of olanzapine in comparison to clozapine and haloperidol on extracellular recordings of substantia nigra reticulata neurons in the rat brain

RATIONALE

Previously, we have shown that the atypical antipsychotics clozapine and risperidone, unlike haloperidol, decreased the firing rate of substantia nigra reticulata (SNR) neurons. As the SNR receives substantial input from the striatum, an area where motoric side-effects of antipsychotics are thought to be mediated, the SNR might be an interesting brain structure with regard to motor side-effects.

OBJECTIVE

The newly developed atypical antipsychotic olanzapine was studied for its effects on the firing rate of SNR cells. In addition, to gain insight in the implications of our experimental setup for clinical use, responses upon clozapine, olanzapine and haloperidol were studied after chronic treatment.

METHODS

In chloralhydrate-anaesthetized male Wistar rats, extracellular recordings were made from SNR neurons upon intravenously (i.v.) administered cumulative doses of the antipsychotics. Naive rats and rats that were subcutaneously (SC) injected for 21 days with an antipsychotic were used.

RESULTS

Olanzapine (50-1600 mg/kg; i.v.), significantly inhibited the firing rate of the SNR neurons. Upon 21 days of treatment with a daily SC injection of 20 mg/kg clozapine, the challenge on day 22 with cumulative injections of clozapine (200 6400 mg/kg; i.v.) significantly inhibited the firing rate of the SNR neurons. Olanzapine (50-1600 mg/kg; i.v.) also significantly inhibited the SNR activity when pretreated with olanzapine in an SC administered dose of 1 mg/kg, but not 5 mg/kg. Haloperidol (12.5-800 microg/kg; i.v.) did not significantly affect the SNR activity in rats pretreated with SC administered 0.5 mg/kg haloperidol.

CONCLUSIONS

Upon acute and chronic administration of clozapine and olanzapine versus haloperidol, differential effects on SNR neuronal firing could be obtained. The experimental setup seem to be valid for further studies into the mechanism of action of typical versus (relatively low doses of) atypical antipsychotics. The implications of the inhibitory effect of atypical antipsychotics on the SNR firing rate are presently unknown, but could be associated with the lower propensity to induced motoric side-effects. On the other hand, the SNR activity might also reflect non-motoric activity possibly related to negative symptoms.