Differential effects of repeated administration of novel antipsychotic drugs on the activity of midbrain dopamine neurons in the rat

A greater tendency for representation mediated learning in a ketamine mouse model of schizophrenia

Representation mediated learning is a behavioral paradigm that could be used to potentially capture psychotic symptoms including hallucinations and delusions in schizophrenia. In studies of mediated learning, representations of prior experience can enter into current associations. Using a ketamine model of schizophrenia, we investigated whether mice exposed to ketamine during late adolescence subsequently showed an increased tendency to use a representation of a prior gustatory experience to form associations in learning. Mice were given prior experience of an odor and a taste presented together. The odor was subsequently presented alone with gastrointestinal illness induced by a lithium chloride injection. A consumption test was then given to assess whether the taste, despite its absence during conditioning, entered into an association with the induced illness. Such learning would be mediated via a representation of the taste activated by the odor. Our results showed that control mice displayed no aversion to the taste following the procedures just described, but mice that had been treated developmentally with ketamine exhibited a significant taste aversion, suggesting a greater propensity for mediated learning. Complementary to that finding, ketamine-exposed mice also showed a greater susceptibility to mediated extinction. Chronic treatment with the antipsychotic drug, risperidone, in ketamine-exposed mice attenuated mediated learning, a finding that may be related to its known efficacy in reducing the positive symptoms of schizophrenia. These data provide a setting with potential relevance to preclinical research on schizophrenia, to study the neural mechanisms underlying a propensity for aberrant associations and assessment of therapeutics. (PsycINFO Database Record

Divergent effects of acute and repeated quetiapine treatment on dopamine neuron activity in normal vs. chronic mild stress induced hypodopaminergic states

Clinical evidence supports the use of second-generation dopamine D2 receptor antagonists (D2RAs) as adjunctive therapy or in some cases monotherapy in patients with depression. However, the mechanism for the clinical antidepressant effect of D2RAs remains unclear. Specifically, given accumulating evidence for decreased ventral tegmental area (VTA) dopamine system function in depression, an antidepressant effect of a medication that is expected to further reduce dopamine system activity seems paradoxical. In the present paper we used electrophysiological single unit recordings of identified VTA dopamine neurons to characterize the impact of acute and repeated administration of the D2RA quetiapine at antidepressant doses in non-stressed rats and those exposed to the chronic mild stress (CMS) rodent depression model, the latter modeling the hypodopaminergic state observed in patients with depression. We found that acute quetiapine increased dopamine neuron population activity in non-stressed rats, but not in CMS-exposed rats. Conversely, repeated quetiapine increased VTA dopamine neuron population activity to normal levels in CMS-exposed rats, but had no persisting effects in non-stressed rats. These data suggest that D2RAs may exert their antidepressant actions via differential effects on the dopamine system in a normal vs. hypoactive state. This explanation is supported by prior studies showing that D2RAs differentially impact the dopamine system in animal models of schizophrenia and normal rats; the present results extend this phenomenon to an animal model of depression. These data highlight the importance of studying medications in the context of animal models of psychiatric disorders as well as normal conditions.

Brexpiprazole Alters Monoaminergic Systems following Repeated Administration: an in Vivo Electrophysiological Study

BACKGROUND

Brexpiprazole was recently approved as adjunctive therapy for depression and treatment of schizophrenia in adults. To complement results from a previous study in which its acute effects were characterized, the present study assessed the effect of repeated brexpiprazole administration on monoaminergic systems.

METHODS

Brexpiprazole (1mg/kg, subcutaneous) or vehicle was administered once daily for 2 and 14 days. Single-unit electrophysiological recordings from noradrenaline neurons in the locus coeruleus, serotonin neurons in the dorsal raphe nucleus, dopaminergic neurons in the ventral tegmental area, and pyramidal neurons in the hippocampus CA3 region were obtained in adult male Sprague-Dawley rats under chloral hydrate anesthesia within 4 hours after final dosing.

RESULTS

Brexpiprazole blunted D2 autoreceptor responsiveness, while firing activity of ventral tegmental area dopaminergic neurons remained unaltered. Brexpiprazole increased the firing rate of locus coeruleus noradrenaline neurons and increased noradrenaline tone on α2-adrenergic receptors in the hippocampus. Administration of brexpiprazole for 2 but not 14 days increased the firing rate of serotonin neurons in the dorsal raphe nucleus. In the hippocampus, serotonin1A receptor blockade significantly disinhibited pyramidal neurons after 2- and 14-day brexpiprazole administration. In contrast, no significant disinhibition occurred after 24-hour washout or acute brexpiprazole.

CONCLUSIONS

Repeated brexpiprazole administration resulted in a marked occupancy of D2 autoreceptors, while discharge activity of ventral tegmental area dopaminergic neurons remained unaltered. Brexpiprazole enhanced serotonergic and noradrenergic tone in the hippocampus, effects common to antidepressant agents. Together, these results provide further insight in the neural mechanisms by which brexpiprazole exerts antidepressant and antipsychotic effects.

Asenapine alters the activity of monoaminergic systems following its subacute and long-term administration: an in vivo electrophysiological characterization

Asenapine is a tetracyclic atypical antipsychotic used for treatment of schizophrenia and mania. Previous in vivo electrophysiological studies demonstrated antagonistic action of asenapine at dopamine D2, serotonin (5-HT)2A, and α2-adrenergic receptors. Here, we assessed monoamine system activities after two-day and 21-day asenapine administration at a dosage (0.1mg/kg/day) resulting in clinically relevant plasma levels. In the ventral tegmental area (VTA), asenapine increased the number of spontaneously active dopamine neurons, while firing parameters remained unchanged. Asenapine partially prevented the D2 autoreceptor-mediated inhibitory response to apomorphine after two days of administration. This effect was lost after 21 days of administration, suggesting adaptive changes leading to D2 receptor sensitization. Asenapine increased the firing activity of noradrenergic neurons in the locus coeruleus (LC) after 21, but not two days of administration. Furthermore, it potently blocked 5-HT2A receptors while α2-adrenergic receptors were unaffected by this drug regimen. Both acute and long-term asenapine administration partially blocked α2-adrenergic receptors in the CA3 region of the hippocampus, and noradrenergic tone on α1- and α2-adrenoceptors remained unchanged. In the dorsal raphe nucleus, asenapine increased the firing rate of 5-HT neurons after two, but not 21 days of administration. In addition, responsiveness of 5-HT1A autoreceptors was unaltered by asenapine. In the hippocampus, 21-day asenapine administration increased serotonergic tone by partial agonistic action on postsynaptic 5-HT1A and terminal 5-HT1B receptors. Taken together, asenapine had profound effects on both catecholamine systems, potently blocked 5-HT2A receptors, and enhanced 5-HT tone, effects that could be important in treatment of mood disorders and schizophrenia.

Antipsychotic drug-induced increases in ventral tegmental area dopamine neuron population activity via activation of the nucleus accumbens-ventral pallidum pathway

Acute administration of antipsychotic drugs increases dopamine (DA) neuron activity and DA release via D2 receptor blockade. However, it is unclear whether the DA neuron activation produced by antipsychotic drugs is due to feedback from post-synaptic blockade or is due to an action on DA neuron autoreceptors. This was evaluated using two drugs: the first-generation antipsychotic drug haloperidol that has potent D2 blocking properties, and the second-generation drug sertindole, which is unique in that it is reported to fail to reverse the apomorphine-induced decrease in firing rate typically associated with DA neuron autoreceptor stimulation. Using single-unit extracellular recordings from ventral tegmental area (VTA) DA neurons in anaesthetized rats, both drugs were found to significantly increase the number of spontaneously active DA neurons (population activity). Apomorphine administered within 10 min either before or after sertindole reversed the sertindole-induced increase in population activity, but had no effect when administered 1 h after sertindole. Moreover, both sertindole- and haloperidol-induced increase in population activity was prevented when nucleus accumbens feedback was interrupted by local infusion of the GABAA antagonist bicuculline into the ventral pallidum. Taken together, these data suggest that antipsychotics increase DA neuron population activity via a common action on the nucleus accumbens-ventral pallidum-VTA feedback pathway and thus provide further elucidation on the mechanism by which antipsychotic drugs affect DA neuron activity. This provides an important insight into the relationship between altered DA neuron activity and potential antipsychotic efficacy.

Antipsychotic drugs: comparison in animal models of efficacy, neurotransmitter regulation, and neuroprotection

Various lines of evidence indicate the presence of progressive pathophysiological processes occurring within the brains of patients with schizophrenia. By modulating chemical neurotransmission, antipsychotic drugs may influence a variety of functions regulating neuronal resilience and viability and have the potential for neuroprotection. This article reviews the current literature describing preclinical and clinical studies that evaluate the efficacy of antipsychotic drugs, their mechanism of action and the potential of first- and second-generation antipsychotic drugs to exert effects on cellular processes that may be neuroprotective in schizophrenia. The evidence to date suggests that although all antipsychotic drugs have the ability to reduce psychotic symptoms via D(2) receptor antagonism, some antipsychotics may differ in other pharmacological properties and their capacities to mitigate and possibly reverse cellular processes that may underlie the pathophysiology of schizophrenia.

Effects of antipsychotic treatments and D-serine supplementation on the electrophysiological activation of midbrain dopamine neurons induced by the noncompetitive NMDA antagonist MK 801

The acute administration of the noncompetitive glutamate N-methyl-D-aspartate (NMDA) receptor antagonist dizocilpine (MK 801) is known to increase central dopaminergic activity in rats and to elicit schizophreniform behavior in human. The current study was undertaken to compare the effects of different acute or chronic neuroleptic treatments, on the response of ventral tegmental area dopamine (DA) neurons to MK 801, using the in vivo electrophysiological paradigm in anesthetized preparations. Sprague Dawley male rats were treated, acutely or chronically during 3 weeks, with saline, olanzapine (10 mg/kg), haloperidol (1 mg/kg) or the combination of haloperidol with D-serine (1 mg/kg/300 mg/kg), a gliotransmitter coagonist of the NMDA receptor that has been shown to improve the efficacy of typical neuroleptics. In control animals, the acute administration of MK 801 (0.5 mg/kg, i.v.) increased significantly both the firing and burst activity of DA neurons by 20 and 26%, respectively, the latter effect being partially reversed by the selective 5-HT2A antagonist M 100,907 (0.4 mg/kg, i.v.). The acute preadministration of haloperidol (1 mg/kg, i.p.) and olanzapine (10 mg/kg, i.p.) failed to prevent or reverse the activatory effect of MK 801 on firing activity. On the other hand, MK 801-induced burst activity, was partially prevented by olanzapine, but not by haloperidol pretreatment. All antipsychotic treatments, when administered chronically, prevent the activatory effect of MK 801 on both firing and burst activity, and occasionally convert the response to MK 801 on burst activity to an inhibitory response, the latter occurring more predominantly in rats treated with the combination haloperidol/D-serine. These results suggest that a chronic antipsychotic regime alters the function of the NMDA receptors that tonically control the firing activity of midbrain dopaminergic neurons.

Basal ganglia volumes in drug-naive first-episode schizophrenia patients before and after short-term treatment with either a typical or an atypical antipsychotic drug

The present study examined basal ganglia volumes in drug-naive first-episode schizophrenic patients before and after treatment with either a specific typical or atypical antipsychotic compound. Sixteen antipsychotic drug-naive and three minimally medicated first-episode schizophrenic patients and 19 matched controls participated. Patients were randomly assigned to treatment with either low doses of the typical antipsychotic drug, zuclopenthixol, or the atypical compound, risperidone. High-resolution magnetic resonance imaging (MRI) scans were obtained in patients before and after 12 weeks of exposure to medication and in controls at baseline. Caudate nucleus, nucleus accumbens, and putamen volumes were measured. Compared with controls, absolute volumes of interest (VOIs) were smaller in patients at baseline and increased after treatment. However, with controls for age, gender and whole brain or intracranial volume, the only significant difference between patients and controls was a Hemisphere x Group interaction for the caudate nucleus at baseline, with controls having larger left than right caudate nuclei and patients having marginally larger right than left caudate volumes. Within patients, the two medication groups did not differ significantly with respect to volume changes after 3 months of low dose treatment in any of the VOIs. Nevertheless, when medication groups were examined separately, a significant volume increase in the putamen was evidenced in the risperidone group. The altered asymmetry in caudate volume in patients suggests intrinsic basal ganglia pathology in schizophrenia, most likely of neurodevelopmental origin.

Frontal dopamine D(2/3) receptor binding in drug-naive first-episode schizophrenic patients correlates with positive psychotic symptoms and gender

BACKGROUND

The aim of the study was to examine extrastriatal dopamine D(2/3) receptor binding and psychopathology in schizophrenic patients, and to relate binding potential (BP) values to psychopathology.

METHODS

Twenty-five drug-naive schizophrenic patients and 20 healthy controls were examined with single-photon emission computerized tomography (SPECT) using the D(2/3)-receptor ligand [123I]epidepride.

RESULTS

In the hitherto largest study on extrastriatal D(2/3) receptors we detected a significant correlation between frontal D(2/3) BP values and positive schizophrenic symptoms in the larger group of male schizophrenic patients, higher frontal BP values in male (n = 17) compared to female (n = 8) patients, and - in accordance with this - significantly fewer positive schizophrenic symptoms in the female patients. No significant differences in BP values were observed between patients and controls; the patients, however, had significantly higher BP in the right compared to the left thalamus, whereas no significant hemispheric imbalances were observed in the healthy subjects.

CONCLUSIONS

The present data are the first to confirm a significant correlation between frontal D(2/3) receptor BP values and positive symptoms in male schizophrenic patients. They are in agreement with the hypothesis that frontal D(2/3) receptor activity is significant for positive psychotic symptoms. Additionally, the data support a thalamic hemispheric imbalance in schizophrenia.

Effects of (-)stepholidine in animal models for schizophrenia

AIM

(-)Stepholidine (SPD) is an active ingredient of the Chinese herb Stephania intermedia, which binds to the dopamine D(1) and D(2) like receptors. Biochemical, electrophysiological and behavioural experiments have provided strong evidence that SPD is both a D(1) and a D(2) antagonist, which could make SPD a unique antipsychotic drug. The present study aimed to investigate the antipsychotic properties of SPD in two animal models for schizophrenia.

METHODS

The effects of SPD, clozapine and haloperidol in increasing forelimb and hindlimb retraction time in the paw test and in reversing the apomorphine and MK801-induced disruption of prepulse inhibition was investigated.

RESULTS

In the paw test, clozapine and SPD increased the hindlimb retraction time, with only a marginal effect on the forelimb retraction time, whereas haloperidol potently increased both. In the prepulse inhibition paradigm, all three drugs reverse the apomorphine-induced disruption in prepulse inhibition, while none of the drugs could reverse the MK801-induced disruption. SPD even slightly, but significantly, potentiated the effects of MK801.

CONCLUSION

The data show that SPD showed antipsychotic-like effects in both the prepulse inhibition paradigm and in the paw test. Moreover, the results of the paw test suggest that SPD has an atypical character with a relatively small potency to induce extrapyramidal side effects.

How antipsychotics work-from receptors to reality

How does a small molecule blocking a few receptors change a patients' passionately held paranoid belief that the FBI is out to get him? To address this central puzzle of antipsychotic action, we review a framework linking dopamine neurochemistry to psychosis, and then link this framework to the mechanism of action of antipsychotics. Normal dopamine transmission has a role in predicting novel rewards and in marking and responding to motivationally salient stimuli. Abnormal dopamine transmission alters these processes and results in an aberrant sense of novelty and inappropriate assignment of salience leading to the experience of psychosis. Antipsychotics improve psychosis by diminishing this abnormal transmission by blocking the dopamine D2/3 receptor (not D1 or D4), and although several brain regions may be involved, it is suggested that the ventral striatal regions (analog of the nucleus accumbens in animals) may have a particularly critical role. Contrary to popular belief, the antipsychotic effect is not delayed in its onset, but starts within the first few days. There is more improvement in the first 2 weeks, than in any subsequent 2-week period thereafter. However, a simple organic molecule cannot target the complex phenomenology of the individual psychotic experience. Antipsychotics diminish dopamine transmission and thereby dampen the salience of the pre-occupying symptoms. Therefore, in the initial stage of an antipsychotic response, the patients experience a detachment from symptoms, a relegation of the delusions and hallucinations to the back of their minds, rather than a complete erasure of the symptoms. Only with time, and only in some, via the mediation of new learning and plasticity, is there a complete resolution of symptoms. The implications of these findings for clinical care, animal models, future target discovery and drug development are discussed.

Effect of the acute and chronic administration of the putative atypical antipsychotic drug Y-931 (8-fluoro-12- (4-methylpiperazin-1-yl)-6H-[1]benzothieno[2,3b][1,5] benzodiazepine maleate) on spontaneously active rat midbrain dopamine neurons: an in vivo electrophysiological study

This study examined the effect of the p.o. administration of the putative atypical antipsychotic drug Y-931 (8-fluoro-12-(4-methylpiperazin-1-yl)-6H-[1]benzothieno[2,3b][1,5] benzodiazepine maleate) on the activity of spontaneously active dopamine (DA) neurons in the ventral tegmental area (VTA) and substantia nigra pars compacta (SNC) in anesthetized male Sprague-Dawley rats. This was accomplished using in vivo electrophysiology. The acute p.o. administration of Y-931 did not significantly alter the number of spontaneously active SNC DA neurons compared to vehicle-treated animals. A single p.o. administration of 3 and 10 mg/kg of Y-931 significantly increased and decreased, respectively, the number of spontaneously active VTA DA neurons compared to vehicle-treated animals. The acute administration of 3 mg/kg of Y-931 significantly altered the firing pattern parameters for all spontaneously active SNC DA. The 3 and 10 mg/kg doses of Y-931 significantly increased the degree of bursting and irregular activity of spontaneously active VTA and SNC DA neurons firing in a bursting pattern. The repeated p.o. administration (21 days) of 1, 3, or 10 mg/kg of Y-931 significantly decreased the number of spontaneously active VTA DA neurons but had no significant effect on SNC DA neurons compared to vehicle-treated animals. The repeated administration of Y-931 did not significantly alter the firing pattern of all spontaneously active SNC or VTA DA neurons. Our findings indicate that the acute and chronic administration of Y-931 significantly alters the activity of midbrain DA neurons in rats and the electrophysiological profile of chronic Y-931 resembles that of atypical antipsychotic agents.

SSR181507, a dopamine D(2) receptor antagonist and 5-HT(1A) receptor agonist. I: Neurochemical and electrophysiological profile

SSR181507 ((3-exo)-8-benzoyl-N-[[(2S)7-chloro-2,3-dihydro-1,4-benzodioxin-1-yl]methyl]-8-azabicyclo[3.2.1]octane-3-methanamine monohydrochloride) is a novel tropanemethanamine benzodioxane derivative that possesses high and selective affinities for D2-like and 5-HT(1A) receptors (K(I)=0.8, 0.2, and 0.2 nM for human D(2), D(3), and 5-HT(1A), respectively). In vivo, SSR181507 inhibited [(3)H]raclopride binding to D(2) receptors in the rat (ID(50)=0.9 and 1 mg/kg, i.p. in limbic system and striatum, respectively). It displayed D(2) antagonist and 5-HT(1A) agonist properties in the same concentration range in vitro (IC(50)=5.3 nM and EC(50)=2.3 nM, respectively, in the GTPgammaS model) and in the same dose range in vivo (ED(50)=1.6 and 0.7 mg/kg, i.p. on striatal DA and 5-HT synthesis, respectively, and 0.03-0.3 mg/kg, i.v. on dorsal raphe nucleus firing rate). It selectively enhanced Fos immunoreactivity in mesocorticolimbic areas as compared to the striatum. This regional selectivity was confirmed in electrophysiological studies where SSR181507, given acutely (0.1-3 mg/kg, i.p.) or chronically (3 mg/kg, i.p., o.d., 22 days), increased or decreased, respectively, the number of spontaneous active DA cells in the ventral tegmental area, but not in the substantia nigra. Moreover, SSR181507 increased both basal and phasic DA efflux (as assessed by microdialysis and electrochemistry) in the medial prefrontal cortex and nucleus accumbens, but not in the striatum. This study shows that the combination of D(2) receptor antagonism and 5-HT(1A) agonism, in the same dose range, confers on SSR181507 a unique neurochemical and electrophysiological profile and suggests the potential of this compound for the treatment of the main dimensions of schizophrenia.

Clozapine, quetiapine and olanzapine among addicted schizophrenic patients: towards testable hypotheses

Although life prevalence of substance use disorders among patients with schizophrenia is close to 50%, few studies have been carried out to date to identify an integrated pharmacological treatment for this comorbidity. So far, the most promising results, that we report here, have been obtained with clozapine. To a lesser extent, quetiapine and olanzapine, both clozapine analogues, have also shown promising results. Further to these observations, the present paper critically reviews the advantages associated with clozapine, quetiapine and olanzapine, and their relevance to the treatment of addiction among schizophrenic patients. Six characteristics seem to distinguish clozapine, quetiapine and olanzapine from the first-generation antipsychotics: (1) acting preferentially on the reward system, these second-generation antipsychotics (mainly clozapine and quetiapine) induce almost no extrapyramidal symptoms; (2) quickly dissociating from D(2), theses drugs (mainly clozapine and quetiapine) seem not to induce dysphoria, unlike conventional antipsychotics like haloperidol;(3) these drugs (mainly clozapine) seem more effective in the treatment of negative symptoms than conventional antipsychotics; (4) because of a diversified activity on several serotoninergic and noradrenergic receptors, these drugs positively alter mood, which does not seem to be the case with conventional antipsychotics, except for flupenthixol; (5) these drugs have a positive impact on cognition, which is not the case with the first-generation antipsychotics; (6) unlike conventional antipsychotics, these drugs seem to have a moderate affinity for 5-HT(3), the receptor on which ondansetron, an anti-craving medication, acts.

Treatment with the atypical antipsychotic, olanzapine, prevents the expression of amphetamine-induced place conditioning in the rat

Place conditioning (PC) experiments were conducted as a means to further elaborate the treatment potential of the atypical antipsychotic, olanzapine (OLZ), for stimulant abuse. The resulting preference/aversion provides an indirect measure of the incentive salience (i.e., euphoria/dysphoria) produced by a drug. Male Sprague-Dawley rats (n=48) were conditioned in two unique environments (i.e., vertical vs. horizontal stripped walls, large vs. small grid flooring) using injections (1.0 mg/kg ip) of either amphetamine (AMPH) or saline (SAL). On average, animals displayed a significant preference for the AMPH-paired location after 2.5 weeks of conditioning (five pairings each of AMPH and SAL). Once the preference was established, animals were pretreated (60 min) with a single dose of OLZ (0.0, 0.56, 1.0 or 1.5 mg/kg sc) given on the test (AMPH-free) day. For the following week's test, animals were injected with SAL (1.0 mg/kg ip) in an attempt to recapture the side preference exhibited before OLZ treatment. OLZ treatment prevented the expression of the AMPH-conditioned preference and reduced locomotor activity. Inhibition of preference resulted from the highest dose of OLZ (1.5 mg/kg), while the inhibition of locomotor activity occurred across all three doses. Additionally, while the effects on preference were no longer apparent by the SAL test the following week (reversible), the activity was still depressed during the SAL tests in animals that had experienced the highest dose of OLZ (1.5 mg/kg). Control experiments, in which OLZ was used as the conditioning drug, suggest that OLZ itself possesses no aversive effects in the PC paradigm, and may even produce a preference for the drug-paired chamber. Because the AMPH preference is dependent on dopamine (DA) release in the nucleus accumbens (NAcc), these experiments suggest that OLZ pretreatment interferes with the rewarding, as well as the subjective effects of AMPH.

Peripheral injection of risperidone, an atypical antipsychotic, alters the bodyweight gain of rats

1. Risperidone is an atypical antipsychotic drug that possesses 5-hydroxytryptamine 5-HT2 receptor antagonism combined with milder dopamine D2 receptor antagonism. 2. Excessive bodyweight gain is one of the side-effects of antipsychotics. Risperidone treatment causes a greater increase in the body mass of patients than treatment with conventional antipsychotics, such as haloperidol. Therefore, the present study was undertaken in order to address the aetiology of the risperidone-induced bodyweight change in rats by examining the expression of leptin, an appetite-regulating hormone produced in white adipose tissue (WAT), and uncoupling protein (UCP)-1, a substance promoting energy expenditure in the brown adipose tissues (BAT). 3. Eight-week-old male rats were injected subcutaneously with risperidone (0.005, 0.05 or 0.5 mg/kg) twice daily for 21 days. Both bodyweight and food intake were monitored daily. On day 21, rats were decapitated and their serum leptin and prolactin concentrations were measured. Expression levels of leptin, Ucp1 and beta3-adrenoceptor (beta3-AR) genes in WAT and BAT were quantified using real-time polymerase chain reaction amplification. 4. Injection of 0.005 mg/kg risperidone into rats increased food intake and the rate of bodyweight gain, as well as the augmentation of leptin gene expression in WAT. Injection of 0.05 mg/kg risperidone increased food intake and leptin gene expression in WAT, but the rate of bodyweight gain was not affected. Injection of 0.5 mg/kg risperidone caused a reduction in bodyweight gain, as well as enhanced Ucp1 gene expression in BAT and serum prolactin concentrations. The serum leptin concentration and beta3-AR gene expression in WAT and BAT were not affected by injection of 0.5 mg/kg risperidone. 5. Although the changes in food intake observed in risperidone-injected rats were rationalized neither by serum leptin nor prolactin concentrations, the reduction in the rate of bodyweight gain following injection of 0.5 mg/kg can be explained, in part, by increased energy expenditure, as revealed by the remarkable increase in the UCP-1 mRNA expression level in BAT. The role of leptin in risperidone-induced alterations in bodyweight gain remain to be clarified.

Olanzapine for the treatment of chronic refractory schizophrenia: a 12-month follow-up naturalistic study

OBJECTIVE

The aim of this study is to provide long-term data on the effectiveness and safety of olanzapine in a group of patients with severe refractory schizophrenia.

GENERAL METHODS

Twenty patients who had previously received treatment with typical antipsychotic agents and who met the DSM-IV criteria of schizophrenia and refractoriness to treatment were evaluated in a 1-year prospective study after switching to olanzapine. The Positive and Negative Symptoms Scale (PANSS) and the Brief Psychiatric Rating Scale (BPRS) were used to measure effectiveness. The extrapyramidal symptoms were also recorded. Serial laboratory tests, electrocardiograms and body weight measurements were also performed. Longitudinal statistical analyses were performed on the global changes in the scores of the scales by means of a repeated measures analysis of variance.

RESULTS

Significant reductions in the global scores from baseline in the PANSS, as well as in the BPRS, were observed. Furthermore, these reductions were also significant when considered only from Week 12. Olanzapine was, in general, well tolerated; a weight gain was observed between baseline and Month 4.5, but, interestingly, it decreased again from this time point to Month 12.

CONCLUSION

Olanzapine was shown to be a suitable treatment for refractory schizophrenia in this series of seriously ill patients. Although most of the effects were observed before Week 12, improvement persisted after 1 year. Weight gain stopped or even regressed when the treatment was prolonged. Large controlled clinical trials to define the role of atypical antipsychotics for the management of treatment-refractory schizophrenia are necessary.

Treatments for chronic psychosis

Psychosis is a mental condition characterized by hallucinations, delusions, and thought disorder; it spans diagnostic entities that respond to similar therapeutic approaches. Psychosis has no fully described tissue pathology, as vet, but is still identified and assessed symptomatically. The first generation of antipsychotic drugs was developed in the middle of the 20th century. The second generation of drugs arrived in the 1990s. This new group of antipsychotic drugs has potent therapeutic actions on the positive symptoms of psychosis with far fewer side effects, especially motor effects. However, each of the new drugs has its own characteristic clinical and pharmacological features that affect individual patient response. Understanding these individual drug characteristics can promote optimal drug choice and use in conditions of chronic psychosis.

A current review of olanzapine's safety in the geriatric patient: from pre-clinical pharmacology to clinical data

OBJECTIVE

Olanzapine (OLZ) is unique among currently available antipsychotic medications in its antagonism of a range of receptor systems including dopamine, norepinephrine, serotonin, acetylcholine, and histamine. Olanzapine's mechanistic complexity provides a broad efficacy profile in patients with schizophrenia and acute, pure or mixed mania. Patients experience symptomatic relief of mania, anxiety, hallucinations, delusions, and agitation/aggression and reduced depressive, negative, and some cognitive symptoms. This paper will review the safety profile of OLZ, focusing on the elderly, where data are available.

METHOD

Preclinical and clinical studies of OLZ are reviewed, with emphasis on its possible effects on the cholinergic system and the histamine H(1) receptor. Weight change and related metabolic considerations, cardiac and cardiovascular safety, and motor function during treatment with OLZ are also reviewed.

RESULTS AND CONCLUSION

In vitro receptor characterization methods, when done using physiologically relevant conditions allow accurate prediction of the relatively low rate of anticholinergic-like adverse events, extrapyramidal symptoms, and cardiovascular adverse events during treatment with OLZ. Currently available clinical data suggest olanzapine is predictably safe in treating adult patients of any age with schizophrenia and acute bipolar mania, as well as in treatment of patients with some types of neurodegenerative disorders.

In vitro modulation of the firing rate of dopamine neurons in the rat substantia nigra pars compacta and the ventral tegmental area by antipsychotic drugs

An in vitro experimental midbrain slice preparation is described which allows simultaneous extracellular recordings of the (spontaneous) electrical activity of dopamine neurons in the rat substantia nigra (SN) and the ventral tegmental area (VTA). Under identical in vitro circumstances the mean firing frequency of the SN dopamine neurons was higher than that of the VTA dopamine neurons (2.1 vs. 1.4Hz). With this slice preparation, modulation of the electrical activity of SN and VTA dopamine neurons by (new) drugs can be quickly determined. Experiments with the selective D2 receptor agonist quinpirole and the selective D2 receptor antagonist (-)-sulpiride indicated that dopamine neurons in the SN and VTA hardly differ in their pharmacological properties for the D2-like (auto)receptor. (-)-Sulpiride and to a lesser extent risperidone induced a small increase in firing rate in SN and VTA neurons, which was reversible upon wash-out. Olanzapine-induced increase in firing rate was persistent in SN and VTA neurons, whereas the clozapine-induced increase in firing rate was only completely recovered upon wash-out in SN neurons. The difference in firing rates of SN and VTA dopamine neurons could have consequences for the effectiveness of dopaminergic drugs acting at the D2-like dopamine (auto)receptor on these neurons.

Traditional and new antipsychotic drugs differentially alter neurotransmission markers in basal ganglia-thalamocortical neural pathways

The effects of three chronically administered antipsychotic drugs on selected neurochemical markers of dopaminergic and GABAergic transmission were compared within the cerebral regions making up the basal ganglia-thalamocortical parallel processing neuronal pathways. All three drugs reduce psychosis in humans, whereas only haloperidol, but not olanzapine or sertindole, induce purposeless oral chewing movements (CMs) in rats or cause high rates of parkinsonism or tardive dyskinesia in humans. Male Sprague Dawley rats were treated with haloperidol, sertindole, or olanzapine delivered in drinking water for 6 months at doses which produce drug plasma levels in rat in the human therapeutic range. Results show the expected dopamine D2 receptor upregulation in striatum predominantly with haloperidol, although mild D2 upregulation was apparent in striatum after olanzapine. GAD67 mRNA was increased in striatum and decreased in globus pallidus by haloperidol and sertindole, but not by olanzapine. In the substantia nigra pars reticulata (SNR), both olanzapine and sertindole failed to induce GABA(A) receptor upregulation or D1 receptor downregulation, but haloperidol did both, confirming a previous report. In thalamus, all three drugs increased GAD expression in the reticular nucleus, whereas only haloperidol decreased GABA(A) binding in the mediodorsal nucleus, actions consistent with a reduction in nigrothalamic, GABA-mediated neural transmission. These results are consistent with the idea that the two new antipsychotics tested have mild and regionally restricted actions within the basal ganglia nuclei and a common action on increasing GAD expression in the reticular nucleus of the thalamus (RtN). Haloperidol, in contrast, has a broad and potent action in basal ganglia, causing changes in SNR and in the mediodorsal nucleus, while also altering GAD mRNA in RtN, potentially reflective of its dyskinetic and antipsychotic actions.

Effect of chronic olanzapine treatment on striatal synaptic organization

Our previous work has shown that chronic haloperidol treatment decreases striatal symmetric synapses preferentially in rats which develop oral dyskinesias (vacuous chewing movements (VCMs)). The present experiment tests the hypothesis that olanzapine, which does not cause dyskinesia in humans or rats, would not cause the ultrastructural changes produced by haloperidol. After 6 months of treatment, VCM scores for the olanzapine group (5.1 +/- 4.5) were similar to those of controls (5.2 +/- 3.9), whereas rats in the haloperidol group were either nondyskinetic (4.3 +/- 2.2) or dyskinetic (16.9 +/- 6.7). The volume of the striatum (mm(3)), did not differ among the groups: control, 37.5 +/- 4.7; olanzapine, 36.4 +/- 4.3; haloperidol, nondyskinetic, 40.5 +/- 6.3; haloperidol, dyskinetic, 36.6 +/- 5.9. Synaptic density (per 1 microm(3)), obtained from the central region of the striatum, did not differ between the olanzapine (0.699 +/- 0.146) and control groups (0.652 +/- 0.108). The number of asymmetric synapses in the olanzapine group (0.624 +/- 0.136) was also similar to that of controls (0.550 +/- 0.090). The number of symmetric synapses in the olanzapine group (0.074 +/- 0.032) was not significantly different from that of controls (0.096 +/- 0.043). Thus, olanzapine, in contrast to haloperidol, did not produce dyskinesias or synapse loss. These results strengthen the correlation between the expression of VCMs and striatal synaptic changes and indicate that olanzapine has fewer behavioral and anatomical side effects than does haloperidol.

Definition, psychopharmacological basis and clinical evaluation of novel/atypical neuroleptics: methodological issues and clinical consequences

High expectations have been put into new/atypical neuroleptics for the treatment of schizophrenia: the higher extrapyramidal-motor tolerability and better efficacy in treating negative symptoms supposedly result in a more favourable influencing of the overall course of the disease and in a higher quality of life for the patients. This article will report about the state of evaluation and therapeutic advantages of new/atypical neuroleptics, and thereby deal with problems of definition and methodology. It also describes differences in the unwanted adverse events profile of the different new/atypical antipsychotics.

Region-specific induction of deltaFosB by repeated administration of typical versus atypical antipsychotic drugs

Whereas acute administration of many types of stimuli induces c-Fos and related proteins in brain, recent work has shown that chronic perturbations cause the region-specific accumulation of novel Fos-like proteins of 35-37 kD. These proteins, termed chronic FRAs (Fos-related antigens), have recently been shown to be isoforms of DeltaFosB, which accumulate in brain due to their enhanced stability. In the present study, we sought to extend earlier findings that documented the effects of acute administration of antipsychotic drugs (APDs) on induction of Fos-like proteins by investigating the ability of typical and aytpical APDs, after chronic administration, to induce these DeltaFosB isoforms in several brain regions implicated in the clinical actions of these agents. By Western blotting we found that chronic administration of the typical APD, haloperidol, dramatically induces DeltaFosB in caudate-putamen (CP), a brain region associated with the extrapyramidal side effects of this drug. A smaller induction was seen in the nucleus accumbens (NAc) and prefrontal cortex (PFC), brain regions associated with the antipsychotic effects of the drug. In contrast, chronic administration of the prototype atypical APD clozapine failed to significantly increase levels of DeltaFosB in any of the three brain regions, and even tended to reduce DeltaFosB levels in the NAc. Two putative atypical APDs, risperidone and olanzapine, produced small but still significant increases in the levels of DeltaFosB in CP, but not NAc or PFC. Studies with selective receptor antagonists suggested that induction of DeltaFosB in CP and NAc is most dependent on antagonism of D2-D3 dopamine receptors, with antagonism of D1-like receptors most involved in the PFC. Immunohistochemical analysis confirmed the greater induction of DeltaFosB in CP by typical versus atypical APDs, with no significant induction seen in PFC with either class of APD. Together, these findings demonstrate that repeated administration of APDs results in the induction of long-lasting Fos-like transcription factors that could mediate some of the persistent and region-specific changes in brain function associated with chronic drug exposure. Synapse 33:118-128, 1999.

A comparative review of new antipsychotics

OBJECTIVE

To review the preclinical and clinical properties of various established and putative antipsychotic medications, namely clozapine, risperidone, amisulpride, olanzapine, quetiapine, sertindole, and ziprasidone.

METHODS

This paper proposes a decision algorithm for comparing drugs used for psychotic disorders, based on biochemical profile, experimental pharmacology, postiron emission tomography (PET) scan results, and clinical efficacy on positive, negative, anxious, depressive, and cognitive symptoms. This "quotient" aims to compare the different available drugs, regardless of their development and registration status.

RESULTS

Antipsychotic drugs have been classified in many ways, mainly according to their chemical structure, clinical effects, receptor affinity, or side effects. Preclinical data have indicated that these drugs might be effective antipsychotic agents, causing fewer extrapyramidal side effects than most of the previously marketed drugs. However, the biological basis for the putative superiority of these drugs in treating psychosis has yet to be ascertained.

CONCLUSIONS

Although most antipsychotics have been shown to be at least equivalent to haloperidol on positive symptoms, they must be studied further to establish their absolute and relative efficacy on positive symptoms, negative and primary negative symptoms, cognition, psychotic anxiety, psychotic depression, suicidality, and quality of life. These drugs should be valuable in treating schizophrenia, but their merit in the long-term management of patients with schizophrenia still needs to be confirmed.

Clozapine in bipolar disorder: treatment implications for other atypical antipsychotics

Traditional neuroleptics are often utilized clinically for the management of bipolar disorder. Although effective as antimanic agents, their mood stabilizing properties are less clear. Additionally, their acute clinical side effect profile and long term risk of tardive dyskinesia, particularly in mood disorder patients, portend significant liability. This review focuses on the use of atypical antipsychotics in the treatment of bipolar disorder focusing on clozapine as the prototypical agent. Although, preclinical research and clinical experience suggest that the atypical antipsychotics are distinctly different from typical antipsychotics, they themselves are heterogeneous in profiles of neuropharmacology, clinical efficacy, and tolerability. The early clinical experience of clozapine as a potential mood stabilizer suggests greater antimanic than antidepressant properties. Conversely, very preliminary clinical experience with risperidone suggests greater antidepressant than antimanic properties and some liability for triggering or exacerbating mania. Olanzapine and sertindole are under investigation in psychotic mood disorders. The foregoing agents and future drugs with atypical neuroleptic properties should come to play an increasingly important role, compared to the older classical neuroleptics, in the acute and long term management of bipolar disorder.

Emerging roles for novel antipsychotic medications in the treatment of schizophrenia

Antipsychotic medications are the mainstay of treatment for schizophrenia. The recent advent of atypical antipsychotics has provided new clinical options and set higher expectations for the treatment of schizophrenia. It is not yet clear how each different drug will fit within the therapeutic armamentarium and this lack is most evident with considering patients with treatment refractory schizophrenia. On the other hand, the expectation of superior efficacy, more benign side effect profile and potential to impact the longitudinal course of schizophrenia provide a rationale for the use of novel antipsychotics as a first-line treatment of schizophrenia.

Double-blind comparison of olanzapine versus risperidone in the treatment of schizophrenia and other psychotic disorders

Olanzapine and risperidone, both second-generation antipsychotic agents, represent two different pharmacologic strategies. Although they share some in vitro properties, they differ by virtue of their chemical structure, spectrum of receptor binding affinities, animal neuropharmacology, pharmacokinetics, and in vivo neuroimaging profile. Based on such differences, it was hypothesized that the two compounds would show distinct safety and/or efficacy characteristics. To test this hypothesis, an international, multicenter, double-blind, parallel-group, 28-week prospective study was conducted with 339 patients who met DSM-IV criteria for schizophrenia, schizophreniform disorder, or schizoaffective disorder. Results of the study indicated that both olanzapine and risperidone were safe and effective in the management of psychotic symptoms. However, olanzapine demonstrated significantly greater efficacy in negative symptoms (Scale for Assessment of Negative Symptoms summary score), as well as overall response rate (> or = 40% decrease in the Positive and Negative Syndrome Scale total score). Furthermore, a statistically significantly greater proportion of the olanzapine-treated than risperidone-treated patients maintained their response at 28 weeks based on Kaplan-Meier survival curves. The incidence of extrapyramidal side effects, hyperprolactinemia, and sexual dysfunction was statistically significantly lower in olanzapine-treated than risperidone-treated patients. In addition, statistically significantly fewer adverse events were reported by olanzapine-treated patients than by their risperidone-treated counterparts. Thus, the differential preclinical profiles of these two drugs were also evident in a controlled, clinical investigation. Olanzapine seemed to have a risk-versus-benefit advantage.

Two rapid-dose titrations of sertindole in patients with schizophrenia

The novel antipsychotic sertindole has demonstrated efficacy in psychosis with an extrapyramidal syndrome profile indistinguishable from placebo. Prior trials of sertindole have increased the dose by 4 mg every third day, whereas the present study evaluated the safety and tolerability of two, previously untested, more rapid dose escalation regimens. Sixteen schizophrenic inpatients entered a 4-day, single-blind placebo washout period in two consecutive groups. All patients received sertindole in 4-mg dose increments up to a maximum dose of 24 mg, which was maintained for 5 days. Dose increases were every other day for group 1 (N = 8) and daily for group 2 (N = 8). Adverse events, electrocardiograms, routine laboratory tests, and plasma sertindole concentrations were recorded. No patient was discontinued because of adverse events. The most frequent adverse events were tachycardia upon orthostatic challenge, nasal congestion, dry mouth, and headache; except for dry mouth, the incidence of these was greater in group 2. All cases of tachycardia were asymptomatic. No clinically significant laboratory abnormalities were detected in either group. In conclusion, 4-mg increases of sertindole every other day seems to be safe. Daily titration was, in general, not well tolerated.

The promise of new drugs for schizophrenia treatment

OBJECTIVE

To present aspects of preclinical and clinical pharmacology of new antipsychotic drugs and to emphasize those preclinical drug characteristics which might predict desirable clinical actions.

METHOD

Review of the relevant literature and publicly presented data.

RESULTS

Traditional neuroleptics have considerable effectiveness in treating positive symptoms of psychosis but can cause serious motor side effects. Clozapine produces no motor side effects and delivers a unique antipsychotic action. Risperidone also produces low motor side effects, but only at relatively low doses. Olanzapine and sertindole are newly introduced. Both have potent antipsychotic actions, with greatly reduced motor side effects. Both drugs also have possible advantages in negative symptoms.

CONCLUSIONS

These data support the conclusion that several new antipsychotics are becoming available for general use which are safe and effective in the treatment of psychosis and have several advantages over traditional neuroleptics.

Olanzapine. A review of its pharmacological properties and therapeutic efficacy in the management of schizophrenia and related psychoses

Olanzapine is a thienobenzodiazepine derivative which displays efficacy in patients with schizophrenia and related psychoses. It has structural and pharmacological properties resembling those of the atypical antipsychotic clozapine and an improved tolerability profile compared with the classical antipsychotic haloperidol. In several large, well controlled trials in patients with schizophrenia or related psychoses, olanzapine generally 5 to 20 mg/day was at least as effective as haloperidol (5 to 20mg) and more so than placebo, as assessed by overall rating scales for psychoses. Olanzapine improved negative symptoms to a greater extent than haloperidol in 2 of 3 comparative trials, including the largest trial. Efficacy of olanzapine has a rapid onset (within 1 to 2 weeks). Its clinical benefits appear to be maintained for treatment periods of up to 1 year, as shown by analysis of the extension phase of several trials demonstrating decreased probability of hospitalisation over this period compared with haloperidol. Preliminary data suggest the drug may also improve quality of life. Olanzapine was associated with significantly fewer adverse movement disorders (e.g. akathisia, dystonia, hypertonia, extrapyramidal symptoms) than haloperidol. There have been no reports of agranulocytosis (as occurs with clozapine) or any other haemotoxicity attributed to olanzapine, and the drug has shown minimal effect on prolactin levels. Transient increases in levels of hepatic transaminases seem to be clinically important. The only events recorded more frequently during olanzapine than during haloperidol therapy were weight gain, dry mouth and increased appetite. Although the antipsychotic activity of olanzapine has been well demonstrated. Its efficacy in refractory schizophrenia and its place relative to other atypical antipsychotics remain to be determined. Nevertheless, if the long term tolerability profile of olanzapine is confirmed, the drug should provide a valuable therapeutic alternative in the management of schizophrenia and related psychoses.

Role of 5-HT1A receptors in the ability of mixed 5-HT1A receptor agonist/dopamine D2 receptor antagonists to inhibit methylphenidate-induced behaviors in rats

Behavioral effects produced by the indirect-acting dopamine receptor agonist, methylphenidate (40 mg/kg i.p.) were examined in rats after administration of the 5-HT1A receptor agonists (+/-)-8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) and flesinoxan, the mixed 5-HT1A receptor agonist/dopamine D2 receptor antagonists buspirone and 1-[-4-fluorobenzoylamino)ethyl]-ethyl]-4-(7-methoxynaphthyl) piperazine (S 14506), the neuroleptics haloperidol and clozapine, and the sigma receptor ligand/partial 5-HT1A receptor agonist alpha-(4-fluorophenyl)-4-(5-fluoro-2-pyrimidinyl)-1-piperazine-butanol (BMY 14802). All of the compounds produced dose-related decreases in methylphenidate-induced stereotyped gnawing, and, as gnawing was inhibited, other methylphenidate-induced responses (i.e. sniffing, rearing and locomotion) appeared. Higher doses of haloperidol and buspirone, but none of the remaining compounds, inhibited these other responses, so that the behavior of the methyphenidate-treated animals became similar to that of normal controls. Pretreatment with the 5-HT1A receptor antagonist N-[2-4-(2-methoxyphenyl)-1-piperazinyl]-ethyl]-N-(2-pyridinyl)- cyclohexanecarboxamide (WAY-100635; 0.63 mg/kg s.c.) blocked the ability of 8-OH-DPAT, S 14506 and flesinoxan to inhibit methylphenidate-induced gnawing, demonstrating the involvement of 5-HT1A receptors in their ability to inhibit methylphenidate-induced behaviors. In contrast, pretreatment with WAY-100635 did not alter the ability of haloperidol, clozapine, buspirone, or BMY 14802 to inhibit methylphenidate-induced gnawing, or in the case of haloperidol and buspirone, to normalize behavior. The results indicate that mixed compounds with 5-HT1A receptor agonist and dopamine receptor antagonist properties can be differentiated on the basis of the ability of WAY-100635 to reverse their effects on methylphenidate-induced behaviors.

Inhibitory effects on the discriminative stimulus properties of D-amphetamine by classical and newer antipsychotics do not correlate with antipsychotic activity. Relation to effects on the reward system?

Classical antipsychotics exemplified by haloperidol (0.30), fluphenazine (0.070) and cis(Z)-flupentixol (0.088; ED50 values in mumol/kg are given in parentheses for all compounds) potently block the discriminative stimulus properties of D-amphetamine (1.0 mg/kg, IP) in rats. Newer antipsychotics have very different profiles: clozapine (7.2) and olanzapine (5.9) induce dose-dependent inhibition, while risperidone (> 6.1) and remoxipride (> 47) show weak inhibitory effects and sertindole (> 23), seroquel (> 20), amperozide (> 2.9) and the putative antipsychotic MDL 100151 (> 13; racemate with MDL 100907 as the active enantiomer) are ineffective. Antagonists of alpha 1-adrenoceptors (prazosin; > 6.0), 5-HT2A/2C (ritanserin; > 2.6) and histamine H1 receptors (mepyramine; > 50) are ineffective. Sertindole (0.076), risperidone (0.23), clozapine (0.39), olanzapine (0.088), MDL 100151 (0.0082), fluphenazine (0.13) and ritanserin (0.12) are potent inhibitors of the discriminative stimulus induced by the 5-HT2A/2C agonist DOI (0.63 mg/kg, IP), while haloperidol (approximately 0.4), cis(Z)-flupentixol (approximately 0.04), amperozide (approximately 0.5) and prazosin (> 12) show partial inhibition and remoxipride (> 23) and mepyramine (> 25) are ineffective. The results indicate that inhibition of D-amphetamine discrimination does not correlate with antipsychotic activity of newer antipsychotics, as has previously been suggested in the literature. Furthermore, the inhibitory potencies against D-amphetamine-induced discrimination (present study) and hypermotility (previous study in the same strain of rats) do not correlate either for several of the newer antipsychotics (e.g. for sertindole, risperidone, seroquel and remoxipride). The discrepancies cannot solely be explained by additional pharmacological effects of these compounds, e.g. 5-HT2 receptor blockade. The D-amphetamine discrimination is documented to depend on increased limbic dopamine function which in humans is associated with increased euphoria. Based on these results, it is hypothesized that D-amphetamine discrimination rather than a model for antipsychotic activity may reflect dysphoric or anhedonic activity.