Mechanism of action of atypical antipsychotic drugs and the neurobiology of schizophrenia

A case series of aripiprazole augmentation of selective serotonin reuptake inhibitors in treatment-refractory obsessive compulsive disorder

OBJECTIVE

For the obsessive compulsive disorder (OCD) patients refractory to selective serotonin reuptake inhibitors (SSRIs), atypical antipsychotics, such as risperidone, or olanzapine have been found effective in the augmentation of SSRIs. However these atypical antipsychotics may cause a number of safety concerns associated with body weight or metabolic changes. We sought to investigate the efficacy and safety of a novel atypical neuroleptic aripiprazole as an augmenting agent for the treatment-resistant OCD.

METHODS

Eleven patients who had previously been assessed as poorer responders (<10% reduction of Y-BOCS) to both adequate SSRI monotherapy such as fluvoxamine or paroxetine and the subsequent atypical antipsychotic augmentation of SSRIs were included in this study. The addition of aripiprazole to ongoing SSRIs was continued for at least 12 weeks in the subjects except for one who dropped out during the period.

RESULTS

The mean maximum daily dosage of aripiprazole in the completers was 10.9 ± 3.4 mg/day. Seven of 10 completers exhibited significant reduction of Y-BOCS (>35%) accompanying a few adverse events.

CONCLUSIONS

This preliminary study supports the notion that adding aripiprazole to SSRIs could be a valid and effective strategy for treatment-resistant OCD patients. Thus it points towards the need of further controlled and longitudinal studies.

Quetiapine improves response inhibition in alcohol dependent patients: a placebo-controlled pilot study

RATIONALE

Quetiapine has been shown to be a promising medication for the treatment of alcoholism. As an atypical antipsychotic medication with antagonist activity at D1 and D2, 5-HT(1A) and 5-HT(2A), H(1) and α1 and α2 receptors, quetiapine has been found to decrease impulsivity in other psychiatric disorders but its effects on impulsivity have not been studied in alcohol dependent patients.

OBJECTIVE

This study seeks to test the effects of quetiapine on a specific dimension of impulsivity, namely response inhibition. This pilot study seeks to further elucidate the mechanisms of action of quetiapine for alcohol use disorders.

METHOD

A total of 20 non-treatment seeking alcohol dependent individuals were randomized to one of the following conditions in a double-blind, placebo-controlled design: (1) quetiapine (400 mg/day); or (2) matched placebo. Participants completed two counterbalanced intravenous placebo-alcohol administration sessions as well as behavioral measure of response inhibition (i.e. stop signal task) pre and post placebo-alcohol administration sessions.

RESULTS

Analyses revealed a significant effect of quetiapine in improving response inhibition as measured by the stop signal task. These results provide preliminary evidence suggesting that quetiapine improves response inhibition in alcohol dependent patients, as compared to placebo.

CONCLUSION

This pilot study contributes a novel putative mechanism of action of quetiapine in alcoholism, namely an improvement in response inhibition.

A human laboratory study of the effects of quetiapine on subjective intoxication and alcohol craving

RATIONALE

The available treatments for alcoholism are only modestly effective, and patients vary widely in their treatment response. Quetiapine, an atypical antipsychotic medication with antagonist activity at D1 and D2, 5-HT(1A) and 5-HT(2A), H(1), and α1 and α2 receptors was shown to promote abstinence, reduce drinking days, and reduce heavy drinking days in a 12-week double-blind placebo-controlled trial.

OBJECTIVE

Although quetiapine represents one of the promising pharmacotherapies for the treatment of alcoholism, its mechanisms of action are poorly understood. The objective of this study is to elucidate the biobehavioral mechanisms of action of quetiapine for alcoholism, by examining its effects on subjective intoxication and craving.

METHOD

A total of 20 non-treatment-seeking alcohol-dependent individuals were randomized to one of the following conditions in a double-blind, placebo-controlled design: (1) quetiapine (400 mg/day); or (2) matched placebo. Participants were on the target medication dose (or matched placebo) for 4 weeks during which they completed weekly assessments of drinking, sleep, mood, and anxiety. Participants completed two counterbalanced intravenous placebo-alcohol administration sessions as well as cue-reactivity assessments.

RESULTS

Analyses revealed a significant effect of quetiapine in reducing craving during the alcohol administration, the alcohol cue-exposure, and the weekly reports of alcohol craving. Quetiapine was also found to reduce subjective intoxication and alcohol-induced sedation during the alcohol administration paradigm.

CONCLUSIONS

This study contributes critical new information about mechanisms of response to quetiapine for alcoholism, which, in turn, can inform larger-scale studies and ultimately, clinical practice.

Electroencephalographic spectral and coherence analysis of ketamine in rats: correlation with behavioral effects and pharmacokinetics

AIMS

This study was designed to evaluate the changes in EEG power spectra and EEG coherence in a ketamine model of psychosis in rats. Analyses of behavioral measurements--locomotion and sensorimotor gating--and the pharmacokinetics of ketamine and norketamine were also conducted.

METHODS

Ketamine and norketamine levels in rat sera and brains were analyzed by gas chromatography-mass spectrometry after ketamine 30 mg/kg (i.p.). Ketamine 9 and 30 mg/kg (i.p.) were used in the behavioral and EEG experiments. Locomotor effects in an open field test and deficits in prepulse inhibition of acoustic startle reaction (PPI ASR) were evaluated in the behavioral experiments. EEG signals were simultaneously recorded from 12 implanted active electrodes; subsequently, an EEG power spectral and coherence analysis was performed.

RESULTS

Ketamine had a rapid penetration into the brain; the peak concentrations of the drug were reached within 15 min after administration. Ketamine induced marked hyperlocomotion and deficits in the PPI ASR. EEG spectral analysis mainly showed increases in EEG power as well as coherence. These were most robust at 10-15 min after the administration and influenced all parts of the spectrum with ketamine 30 mg/kg.

CONCLUSIONS

Ketamine at behaviorally active doses induces a robust increase in EEG power spectra and coherence. The maximum levels of change correlated with the kinetics of ketamine.

Neuregulin links dopaminergic and glutamatergic neurotransmission to control hippocampal synaptic plasticity

Neuregulin-1 (NRG-1) and its receptor ErbB4 are genetically associated with schizophrenia, a complex developmental disorder of high heritability but unknown etiology that has been proposed to result from deficits in functional connectivity and synaptic plasticity. Based on pharmacological evidence, imbalances in dopaminergic and glutamatergic transmission systems are believed to contribute to its pathophysiology, but genetic data supporting a causative role for either are sparse. Stimulation of NRG-1/ErbB4 signaling inhibits or reverts hippocampal long-term potentiation (LTP) at glutamatergic synapses between Schaeffer collateral afferents and CA1 pyramidal neurons (SC-->CA1). We have recently demonstrated that NRG-1 regulates glutamatergic plasticity by rapidly increasing extracellular hippocampal dopamine levels and activation of D4 dopamine receptors.7 These new findings position the NRG-1/ErbB4 signaling pathway at the crossroads between dopaminergic and glutamatergic neurotransmission and offer novel ways to consolidate genetic, functional and pharmacological data toward a better understanding of the etiological processes underlying schizophrenia, and the role of NRG-1 for normal synaptic function and plasticity. The currently available data suggest that hippocampal interneurons might play a crucial role in mediating NRG-1 induced depotentiation. This interpretation is in line with other evidence pointing towards an involvement of GABAergic cells in the etiology of schizophrenia.

The role of dopaminergic signalling during larval zebrafish brain development: a tool for investigating the developmental basis of neuropsychiatric disorders

Neurodevelopment depends on intrinsic and extrinsic factors that influence the overall pattern of neurogenesis and neural circuit formation, which has a direct impact on behaviour. Defects in dopamine signalling and brain morphology at a relatively early age, and mutations in neurodevelopmental genes are strongly correlated with several neuropsychiatric disorders. This evidence supports the hypothesis of a neurodevelopmental origin of at least some forms of mental illness. Zebrafish (Danio rerio) has emerged as an important vertebrate model system in biomedical research. The ease with which intrinsic and extrinsic factors can be altered during early development, the relatively conserved dopaminergic circuit organisation in the larval brain, and the emergence of simple sensorimotor behaviours very early in development are some of the appealing features that make this organism advantageous for developmental brain and behaviour research. Thus, examining the impact of altered dopamine signalling and disease related genetic aberrations during zebrafish development presents a unique opportunity to holistically analyse the in vivo biochemical, morphological and behavioural significance of altered dopamine signalling during a crucial period of development using a highly tractable vertebrate model organism. Ultimately, this information will shed new light on potential therapeutic targets for the treatment of schizophrenia and perhaps serve as a paradigm for investigating the neurodevelopmental origin of other psychiatric disorders.

P-glycoprotein influence on the brain uptake of a 5-HT(2A) ligand: [(18)F]MH.MZ

BACKGROUND/AIMS

The serotonergic system, especially the 5-HT(2A) receptor, is involved in various diseases and conditions. We have recently developed a new [(18)F]-5-HT(2A) receptor ligand using an analogue, MDL 100907, as a basis for molecular imaging with positron emission tomography. This tracer, [(18)F]MH.MZ, has been shown to be an adequate tool to visualize the 5-HT(2A) receptors in vivo. However, [(18)F]altanserin, similar in chemical structure, is a substrate of efflux transporters, such as P-glycoprotein (P-gp), of the blood-brain barrier, thus limiting its availability in the central nervous system. The aim of this study was to determine whether transport by P-gp influences the distribution ratio of [(18)F]MH.MZ in the frontal cortex.

METHODS

The approach was based on P-gp knockout mice which were compared with wild-type mice under several conditions. In vivo pharmacokinetic and microPET investigations were carried out.

RESULTS

All analyses showed that [(18)F]MH.MZ entered the brain and was sensitive to P-gp transport. In P-gp knockout mice, brain concentrations of MH.MZ were about 5-fold higher than in wild-type animals which is reflected by a 2-fold increase in standardized uptake values of [(18)F]MH.MZ in the frontal cortex of P-gp knockout mice.

CONCLUSION

Our results give evidence for a functional role of transport mechanisms at the blood-brain barrier, specifically of P-gp, and its subregional distribution. Investigation of these mechanisms will benefit the development of more efficient radioligands and drugs for molecular imaging and pharmacotherapy of the mentally ill.

Metabonomic studies of schizophrenia and psychotropic medications: focus on alterations in CNS energy homeostasis

Schizophrenia is a severe neuropsychiatric disorder with a poorly understood etiology and progression. We and other research groups have found that energy metabolic pathways in the CNS are perturbed in many subjects with this disorder. Antipsychotic drugs that generally target neurotransmission are currently used for clinical management of the disorder, although these can also have marked effects on energy metabolism in the CNS and periphery. Recent proteomic and metabonomic studies have shown that molecular pathways associated with brain energy metabolism are altered in both the disorder and by antipsychotic treatments. This review focuses on discussion of these molecular alterations. Increased knowledge in this area could facilitate biomarker identification and drug discovery based on improving brain energy metabolism in this debilitating disorder.

The role of serotonin receptors in the action of atypical antipsychotic drugs

The main class of atypical antipsychotic drugs (APDs) in current use includes the protypical atypical APD, clozapine, as well as aripiprazole, asenapine, iloperidone, lurasidone, olanzapine, quetiapine, risperidone, and ziprasidone. At clinically effective doses, these agents produce extensive blockade of serotonin (5-HT)(2A) receptors, direct or indirect stimulation of 5-HT(1A) receptors, and to a lesser extent, reduction in dopamine (DA) D(2) receptor-mediated neurotransmission. This contrasts with typical APDs, for example haloperidol and perphenazine, which are mainly DA D(2/)D(3) receptor antagonists and have weaker, if any, potency as 5-HT(2A) receptor antagonists. Some, but not all, atypical APDs are also effective 5-HT(2C) receptor inverse agonists or neutral antagonists, 5-HT(6) or 5-HT(7) receptor antagonists. This diverse action on 5-HT receptors may contribute to significant differences in efficacy and tolerability among the atypical APDs. There is considerable preclinical and some clinical evidence that effects on 5-HT receptors contribute to the low risk of producing extrapyramidal side effects, which is the defining characteristic of an atypical APD, the lack of elevation in plasma prolactin levels (with risperidone and 9-hydroxyrisperidone being exceptions), antipsychotic action, and ability to improve some domains of cognition in patients with schizophrenia. The serotonergic actions of the atypical APDs, especially 5-HT(2A) receptor antagonism, are particularly important to the differential effects of typical and atypical APDs to overcome the effects of acute or subchronic administration of N-methyl-d-aspartate (NMDA) receptor antagonists, such as phencyclidine, ketamine, and dizocipline (MK-801). 5-HT(1A) receptor stimulation and 5-HT(6) and 5-HT(7) receptor antagonism may contribute to beneficial effects of these agents on cognition. In particular, 5-HT(7) receptor antagonism may be the basis for the pro-cognitive effects of the atypical APD, amisulpride, a D(2)/D(3) receptor antagonist, which has no effect on other 5-HT receptor. 5-HT(2C) receptor antagonism appears to contribute to the weight gain produced by some atypical APDs and may also affect cognition and psychosis via its influence on cortical and limbic dopaminergic activity.

Dopamine D2 occupancy as a biomarker for antipsychotics: quantifying the relationship with efficacy and extrapyramidal symptoms

For currently available antipsychotic drugs, blockade of dopamine D(2) receptors is a critical component for achieving antipsychotic efficacy, but it is also a driving factor in the development of extrapyramidal symptoms (EPS). To inform the clinical development of asenapine, generic mathematical models have been developed for predicting antipsychotic efficacy and EPS tolerability based on D(2) receptor occupancy. Clinical data on pharmacokinetics, D(2) receptor occupancy, efficacy, and EPS for several antipsychotics were collected from the public domain. Asenapine data were obtained from in-house trials. D(2) receptor occupancy data were restricted to published positron emission tomography studies that included blood sampling for pharmacokinetics. Clinical efficacy data were restricted to group mean endpoint data from short-term placebo-controlled trials, whereas EPS evaluation also included some non-placebo-controlled trials. A generally applicable model connecting antipsychotic dose, pharmacokinetics, D(2) receptor occupancy, Positive and Negative Syndrome Scale (PANSS) response, and effect on Simpson-Angus Scale (SAS) was then developed. The empirical models describing the D(2)-PANSS and D(2)-SAS relationships were used successfully to aid dose selection for asenapine phase II and III trials. A broader use can be envisaged as a dose selection tool for new antipsychotics with D(2) antagonist properties in the treatment of schizophrenia.

Weight gain, schizophrenia and antipsychotics: new findings from animal model and pharmacogenomic studies

Excess body weight is one of the most common physical health problems among patients with schizophrenia that increases the risk for many medical problems, including type 2 diabetes mellitus, coronary heart disease, osteoarthritis, and hypertension, and accounts in part for 20% shorter life expectancy than in general population. Among patients with severe mental illness, obesity can be attributed to an unhealthy lifestyle, personal genetic profile, as well as the effects of psychotropic medications, above all antipsychotic drugs. Novel "atypical" antipsychotic drugs represent a substantial improvement on older "typical" drugs. However, clinical experience has shown that some, but not all, of these drugs can induce substantial weight gain. Animal models of antipsychotic-related weight gain and animal transgenic models of knockout or overexpressed genes of antipsychotic receptors have been largely evaluated by scientific community for changes in obesity-related gene expression or phenotypes. Moreover, pharmacogenomic approaches have allowed to detect more than 300 possible candidate genes for antipsychotics-induced body weight gain. In this paper, we summarize current thinking on: (1) the role of polymorphisms in several candidate genes, (2) the possible roles of various neurotransmitters and neuropeptides in this adverse drug reaction, and (3) the state of development of animal models in this matter. We also outline major areas for future research.

Therapeutic role of 5-HT1A receptors in the treatment of schizophrenia and Parkinson's disease

5-HT(1A) receptors have long been implicated in the pathogenesis and treatment of anxiety and depressive disorders. Recently, several lines of studies have revealed new insights into the therapeutic role of 5-HT(1A) receptors in treating schizophrenia and Parkinson's disease. Specifically, 5-HT(1A) receptors seem to be a promising target for alleviating antipsychotic-induced extrapyramidal side effects (EPS) and cognitive/affective disorders in schizophrenia. In the treatment of patients with Parkinson's disease, 5-HT(1A) agonists are expected to improve not only affective symptoms (e.g., anxiety and depression), but also the core parkinsonian symptoms as well as antiparkinsonian agents-induced side effects (e.g., L-DOPA-induced dyskinesia). Here, the therapeutic mechanisms mediated by 5-HT(1A) receptors in schizophrenia and Parkinson's disease are reviewed. This evidence should encourage discovery of new 5-HT(1A) ligands, which can resolve the unmet clinical needs in the current therapy.

The alpha2 adrenergic receptor antagonist idazoxan, but not the serotonin-2A receptor antagonist M100907, partially attenuated reward deficits associated with nicotine, but not amphetamine, withdrawal in rats

Based on phenomenological similarities between anhedonia (reward deficits) associated with drug withdrawal and the negative symptoms of schizophrenia, we showed previously that the atypical antipsychotic clozapine attenuated reward deficits associated with psychostimulant withdrawal. Antagonism of alpha(2) adrenergic and 5-HT(2A) receptors may contribute to these effects of clozapine. We investigated here whether blockade of alpha(2) or 5-HT(2A) receptors by idazoxan and M100907, respectively, would reverse anhedonic aspects of psychostimulant withdrawal. Idazoxan treatment facilitated recovery from spontaneous nicotine, but not amphetamine, withdrawal by attenuating reward deficits and increase the number of somatic signs. Thus, alpha(2) adrenoceptor blockade may have beneficial effects against nicotine withdrawal and may be involved in the effects of clozapine previously observed. M100907 worsened the anhedonia associated with nicotine and amphetamine withdrawal, suggesting that monotherapy with M100907 may exacerbate the expression of the negative symptoms of schizophrenia or nicotine withdrawal symptoms in people, including schizophrenia patients, attempting to quit smoking.

Emerging role of aripiprazole for treatment of irritability associated with autistic disorder in children and adolescents

Autistic disorder is a largely misunderstood and difficult to treat neurodevelopmental disorder. Three core domains of functioning are affected by autistic disorder, ie, socialization, communication, and behavior. Signs of autistic disorder may be present early, but are frequently overlooked, resulting in a delay in its diagnosis and a subsequent delay in treatment. No one definitive therapy is available, and treatment consists of early educational and behavioral interventions, as well as drug therapy. Atypical antipsychotics have often been used in the treatment of autistic disorder to target irritability, aggression, and self-injurious behavior, all of which can interfere with other aspects of treatment. One atypical antipsychotic, aripiprazole, has recently been approved for treatment of irritability associated with autistic disorder. Based on the results from two randomized, controlled trials, with efficacy data from nearly 300 patients, treatment with aripiprazole was associated with reductions in irritability, global improvements in behavior, and improvements in quality of life from both the patient and caregiver perspectives. Dosage of aripiprazole ranged from 5 mg to 15 mg per day. Aripiprazole was well tolerated during clinical trials, with most adverse events considered mild or moderate. Clinically relevant weight gain occurred in about 30% of patients given aripiprazole, although when compared with other atypical antipsychotics, aripiprazole appears to have fewer metabolic effects and a lower risk of weight gain. However, pediatric patients taking any atypical antipsychotic should be carefully monitored for potential adverse events, because the long-term effects of antipsychotic therapy in this population are not well known. When used appropriately, aripiprazole has the potential to be an effective treatment for children with autistic disorder to improve irritability and aggressive behavior and improve quality of life.

Emerging treatments in the management of schizophrenia - focus on sertindole

The antipsychotic treatment of schizophrenia is still marked by poor compliance, and drug discontinuation; the development of more effective and safer drugs still remains a challenge. Sertindole is a second-generation antipsychotic with high affinity for dopamine D₂, serotonin 5-HT_2A, 5-HT_2C, and α₁-adrenergic receptors, and low affinity for other receptors. Sertindole undergoes extensive hepatic metabolism by the cytochrome P450 isoenzymes CYP2D6 and CYP3A4 and has an elimination half-life of approximately three days. In controlled clinical trials sertindole was more effective than placebo in reducing positive and negative symptoms, whereas it was as effective as haloperidol and risperidone against the positive symptoms of schizophrenia. The effective dose-range of sertindole is 12–20 mg, administered orally once daily. The most common adverse events are headhache, insomnia, rhinitis/nasal congestion, male sexual dysfunction, and moderate weight gain, with few extrapyramidal symptoms and metabolic changes. Sertindole is associated with corrected QT interval prolongation, with subsequent risk of serious arrythmias. Due to cardiovascular safety concerns, sertindole is available as a second-line choice for patients intolerant to at least one other antipsychotic agent. Further clinical studies, mainly direct “head-to-head” comparisons with other second-generation antipsychotic agents, are needed to define the role of sertindole in the treatment of schizophrenia.

Iloperidone—A Second-Generation Antipsychotic for the Treatment of Acute Schizophrenia

Objective:

To review the pharmacology, efficacy, and tolerability of iloperidone, a second-generation antipsychotic, in the treatment of acute schizophrenia in adults.

Data Sources:

English-language articles were obtained via MEDLINE (1966-March 2010) and International Pharmaceutical Abstracts (1970-March 2010) searches using the key words iloperidone, acute schizophrenia, atypical antipsychotics, second-generation antipsychotics, HP 873, P88–8991, P95–12113, and Fanapt. Bibliographies of selected articles were used to identify additional sources.

Study Selection and Data Extraction:

Available published articles reporting the results of human studies of iloperidone were reviewed for inclusion in this article. Additional information regarding pharmacology, adverse events, contraindications, and precautions was obtained from the manufacturer's prescribing information.

Data Synthesis:

Iloperidone is a second-generation antipsychotic approved for the treatment of acute schizophrenia in adults. Iloperidone is well absorbed upon oral administration, highly protein bound, and metabolized primarily by CYP3A4 and 2D6. Phase 3 clinical trials evaluating the efficacy of iloperidone demonstrated significantly higher response rates with iloperidone compared with placebo in the treatment of positive, negative, and cognitive symptoms associated with acute schizophrenia when the drug was given in doses up to 24 mg daily. Dizziness, dry mouth, and nausea were the most commonly reported adverse events and appear to be dose related. Additional adverse events occurring in 5% or more of patients include orthostatic hypotension, somnolence, tachycardia, fatigue, nasal congestion, and weight increase. Iloperidone should be titrated slowly over a 7-day interval to avoid the potential for orthostatic hypotension. Product labeling includes a black box warning against the use of iloperidone in dementia-related psychosis and precautions regarding QT interval prolongation.

Conclusions:

Iloperidone is an effective treatment for the symptoms of acute schizophrenia in adults. Additional studies are needed to assess comparative effectiveness with other pharmacologic treatments of schizophrenia, long-term efficacy, and long-term safety.

Contrasting effects of increased and decreased dopamine transmission on latent inhibition in ovariectomized rats and their modulation by 17beta-estradiol: an animal model of menopausal psychosis?

Women with schizophrenia have later onset and better response to antipsychotic drugs (APDs) than men during reproductive years, but the menopausal period is associated with increased symptom severity and reduced treatment response. Estrogen replacement therapy has been suggested as beneficial but clinical data are inconsistent. Latent inhibition (LI), the capacity to ignore irrelevant stimuli, is a measure of selective attention that is disrupted in acute schizophrenia patients and in rats and humans treated with the psychosis-inducing drug amphetamine and can be reversed by typical and atypical APDs. Here we used amphetamine (1 mg/kg)-induced disrupted LI in ovariectomized rats to model low levels of estrogen along with hyperfunction of the dopaminergic system that may be occurring in menopausal psychosis, and tested the efficacy of APDs and estrogen in reversing disrupted LI. 17beta-Estradiol (50, 150 microg/kg), clozapine (atypical APD; 5, 10 mg/kg), and haloperidol (typical APD; 0.1, 0.3 mg/kg) effectively reversed amphetamine-induced LI disruption in sham rats, but were much less effective in ovariectomized rats; 17beta-estradiol and clozapine were effective only at high doses (150 microg/kg and 10 mg/kg, respectively), whereas haloperidol failed at both doses. Haloperidol and clozapine regained efficacy if coadministered with 17beta-estradiol (50 microg/kg, an ineffective dose). Reduced sensitivity to dopamine (DA) blockade coupled with spared/potentiated sensitivity to DA stimulation after ovariectomy may provide a novel model recapitulating the combination of increased vulnerability to psychosis with reduced response to APD treatment in female patients during menopause. In addition, our data show that 17beta-estradiol exerts antipsychotic activity.

Do atypical antipsychotic drugs reduce the risk of ischemic heart disease and mortality? Possible role of 5-HT2A receptor blockade

A recent Finnish study reported that long-term cumulative exposure to any antipsychotic treatment was related to lower mortality than was no drug exposure. We hypothesize that the antipsychotic 5-HT2A receptor blockade might protect from ischemic heart disease and buffer the deleterious metabolic effects of antipsychotics. The 5-HT2A receptor may be involved in vascular smooth muscle contraction, coronary artery spasms, platelet aggregation and thrombus formation. 5-HT2A receptor blockade might protect from ischemic heart disease by decreasing platelet aggregation and myocardium hypertrophy. Long-term follow-up studies are needed to clearly establish the long-term contribution of the various antipsychotic drugs to ischemic heart disease, and to explore our hypothesis that 5-HT2A receptor blockade may be protective for cardiovascular disease.

Two four-marker haplotypes on 7q36.1 region indicate that the potassium channel gene HERG1 (KCNH2, Kv11.1) is related to schizophrenia: a case control study

Background

The pathobiology of schizophrenia is still unclear. Its current treatment mainly depends on antipsychotic drugs. A leading adverse effect of these medications is the acquired long QT syndrome, which results from the blockade of cardiac HERG1 channels (human ether-a-go-go-related gene potassium channels 1) by antipsychotic agents. The HERG1 channel is encoded by HERG1 (KCNH2, Kv11.1) gene and is most highly expressed in heart and brain. Genetic variations in HERG1 predispose to acquired long QT syndrome. We hypothesized that the blockade of HERG1 channels by antipsychotics might also be significant for their therapeutic mode of action, indicating a novel mechanism in the pathogenesis of schizophrenia.

Methods

We genotyped four single nucleotide polymorphisms (SNPs) in 7q36.1 region (two SNPs, rs1805123 and rs3800779, located on HERG1, and two SNPs, rs885684 and rs956642, at the 3'-downstream intergenic region) and then performed single SNP and haplotype association analyses in 84 patients with schizophrenia and 74 healthy controls after the exclusion of individuals having prolonged or shortened QT interval on electrocardiogram.

Results

Our analyses revealed that both genotype and allele frequencies of rs3800779 (c.307+585G>T) were significantly different between populations (P = 0.023 and P = 0.018, respectively). We also identified that two previously undescribed four-marker haplotypes which are nearly allelic opposite of each other and located in chr7:150225599-150302147bp position encompassing HERG1 were either overrepresented (A-A-A-T, the at-risk haplotype, P = 0.0007) or underrepresented (C-A-C-G, the protective haplotype, P = 0.005) in patients compared to controls.

Conclusions

Our results indicate that the potassium channel gene HERG1 is related to schizophrenia. Our findings may also implicate the whole family of HERG channels (HERG1, HERG2 and HERG3) in the pathogenesis of psychosis and its treatment.

Anxiolytic-like property of risperidone and olanzapine as examined in multiple measures of fear in rats

Atypical antipsychotics are also used in the treatment of anxiety-related disorders. Clinical and preclinical evidence regarding their intrinsic anxiolytic efficacy has been mixed. In this study, we examined the potential anxiolytic-like effects of risperidone and olanzapine, and compared them with haloperidol, chlordiazepoxide (a prototype of sedative-anxiolytic drug) or citalopram (a selective serotonin reuptake inhibitor). We used a composite of two-way avoidance conditioning and acoustic startle reflex model and examined the effects of drug treatments during the acquisition phase (Experiment 1) or extinction phase (Experiments 2 and 3) on multiple measures of conditioned and unconditioned fear/anxiety-like responses. In Experiment 4, we further compared risperidone, olanzapine, haloperidol, citalopram and chlordiazepoxide in a standard elevated plus maze test. Results revealed three distinct anxiolytic-like profiles associated with risperidone, olanzapine and chlordiazepoxide. Risperidone, especially at 1.0mg/kg, significantly decreased the number of avoidance responses, 22kHz ultrasonic vocalization, avoidance conditioning-induced hyperthermia and startle reactivity, but did not affect defecations or time spent on the open arms. Olanzapine (2.0mg/kg, sc) significantly decreased the number of avoidance responses, 22kHz vocalization and amount of defecations, but it did not inhibit startle reactivity and time spent on the open arms. Chlordiazepoxide (10mg/kg, ip) significantly decreased the number of 22kHz vocalization, avoidance conditioning-induced hyperthermia and amount of defecations, and increased time spent on the open arms, but did not decrease avoidance responses or startle reactivity. Haloperidol and citalopram did not display any anxiolytic-like property in these tests. The results highlight the importance of using multiple measures of fear-related responses to delineate behavioral profiles of psychotherapeutic drugs.

Effects of a positive allosteric modulator of mGluR5 ADX47273 on conditioned avoidance response and PCP-induced hyperlocomotion in the rat as models for schizophrenia

Metabotropic glutamate receptors of the subtype 5 (mGluR(5)) are located in brain regions implicated in schizophrenia such as the cerebral cortex or the nucleus accumbens. They may therefore provide an interesting target for the treatment of psychoses. Currently available agonists of mGluR(5) are not selective, do not penetrate the brain and induce a tonic activation resulting in a rapid desensitization. Therefore, the research focus was shifted to positive allosteric modulators (PAMs). Subsequently several mGluR(5) PAMs have been discovered, e.g. ADX47273 (S-(4-fluoro-phenyl)-{3-[3-(4-fluoro-phenyl)-[1,2,4]oxadiazol-5-yl]-piperidin-1-yl}-methanone). In the present study, effects of ADX47273 (1-100mg/kg) were evaluated in rat models used for detecting antipsychotic-like activity: the conditioned avoidance response (CAR) and the phencyclidine (PCP)-induced hyperlocomotion models. Furthermore, the cataleptogenic potential of ADX47273 was compared to that of haloperidol. ADX47273 (100mg/kg) and various clinically used neuroleptics (haloperidol, olanzapine, and aripiprazole) attenuated CAR behaviour in rats. However, ADX47273 and aripiprazole failed to reduce the PCP-induced hyperlocomotion, whereas olanzapine and haloperidol diminished it. In contrast to haloperidol, ADX47273 (100mg/kg) failed to induce consistent catalepsy in rats. In conclusion, ADX47273 shows promising antipsychotic activity in some tests which require future investigation.

Disruption of latent inhibition induced by ovariectomy can be reversed by estradiol and clozapine as well as by co-administration of haloperidol with estradiol but not by haloperidol alone

INTRODUCTION

Epidemiological and clinical life cycle studies have indicated that the more favorable illness course and the better response to antipsychotic drugs (APDs) in women with schizophrenia correlate with high levels of estrogen, whereas increased vulnerability to exacerbation and relapse and reduced sensitivity to treatment are associated with low estrogen levels. Accordingly, the estrogen hypothesis of schizophrenia proposes that estrogen has a neuroprotective effect in women vulnerable to schizophrenia.

MATERIALS AND METHODS

Latent inhibition (LI), the capacity to ignore stimuli that received nonreinforced preexposure prior to conditioning, is disrupted in acute schizophrenia patients and in rats and humans treated with the psychosis inducing drug amphetamine. Disruption of LI is reversible by typical and atypical APDs. The present study tested whether low levels of estrogen induced by ovariectomy (OVX) would lead to disruption of LI in female rats and whether such disruption would be normalized by estrogen replacement treatment and/or APDs.

RESULTS

Results showed that OVX led to LI disruption, which was reversed by 17beta-estradiol (150 microg/kg) and the atypical APD clozapine (5 mg/kg), but not by the typical APD haloperidol (0.1, 0.2, 0.3 mg/kg). Haloperidol regained efficacy when administered with 17beta-estradiol (50 microg/kg).

DISCUSSION

These results provide the first demonstration in rats that low levels of hormones can induce a pro-psychotic state that is resistant to at least typical antipsychotic treatment. This constellation may mimic states seen in schizophrenic women during periods associated with low levels of hormones such as the menopause.

A naturalistic study of grey matter volume increase after early treatment in anti-psychotic naïve, newly diagnosed schizophrenia

BACKGROUND

Anti-psychotic treatment appears to be associated with striatal volume increase, but how early this change occurs is still unknown.

METHODS

A single prospective cohort of 20 anti-psychotic-naïve patients, newly diagnosed with schizophrenia, underwent magnetic resonance imaging brain scan at baseline. This was repeated following up to 8 weeks of anti-psychotic treatment. Ten patients had repeat scan within only 3 weeks. The choice of anti-psychotic medication was naturalistic, i.e., clinician-led. Well-matched healthy individuals were also scanned to control for non-specific changes over a 3-week period.

RESULTS

After 3 weeks of anti-psychotic treatment, significant grey matter volume increase in the right caudate, superior and inferior frontal gyrus, precentral gyrus, and left inferior parietal lobule was noted. However, after 8 weeks of anti-psychotic treatment, volume increase in the right thalamus and bilateral cerebellum was observed. Significant grey matter reduction was detected in the left medial frontal gyrus at both 3- and 8-week intervals.

CONCLUSIONS

Early increase in striatal volume change occurs as early as 3 weeks after anti-psychotic treatment, whilst thalamic volume increase is apparent later, by 8 weeks of treatment. We speculate that drug-mediated neuroplasticity may provide a biomarker for clinical recovery.

Iloperidone: in schizophrenia

Iloperidone is an atypical antipsychotic that is approved for the treatment of adult patients with schizophrenia. In several large (n > 570 per trial), 4- or 6-week, double-blind, multinational, multicentre trials in adult patients with schizophrenia, recommended target dosages of oral iloperidone (6-12 mg twice daily) generally showed better efficacy than placebo, in terms of improvements in Positive and Negative Syndrome Scale (PANSS) total scores or Brief Psychiatric Rating Scale (BPRS) scores (primary endpoints) and also for most secondary endpoints, including PANSS subscale scores. In addition, pharmacogenomic studies identified single nucleotide polymorphisms (SNPs) that were associated with an enhanced response to iloperidone during acute treatment of schizophrenia. More limited data also support the role of these SNPs in enhancing responses to iloperidone during longer-term treatment. In a pooled analysis of three 52-week, double-blind, multinational, multicentre trials (n = 473), iloperidone treatment was shown to be equivalent to that with haloperidol, based on Kaplan-Meier estimates of the time to relapse (primary endpoint). Iloperidone was generally well tolerated and was associated with few extrapyramidal symptoms or changes in metabolic parameters in short- and longer-term clinical trials in adult patients with schizophrenia.

Analyzing the effects of psychotropic drugs on metabolite profiles in rat brain using 1H NMR spectroscopy

The mechanism of action of standard drug treatments for psychiatric disorders remains fundamentally unknown, despite intensive investigation in academia and the pharmaceutical industry. So far, little is known about the effects of psychotropic medications on brain metabolism in either humans or animals. In this study, we investigated the effects of a range of psychotropic drugs on rat brain metabolites. The drugs investigated were haloperidol, clozapine, olanzapine, risperidone, aripiprazole (antipsychotics); valproate, carbamazapine (mood stabilizers) and phenytoin (antiepileptic drug). The relative concentrations of endogenous metabolites were determined using high-resolution proton nuclear magnetic resonance (1H NMR) spectroscopy. The results revealed that different classes of psychotropic drugs modulated a range of metabolites, where each drug induced a distinct neurometabolic profile. Some common responses across several drugs or within a class of drug were also observed. Antipsychotic drugs and mood stabilizers, with the exception of olanzapine, consistently increased N-acetylaspartate (NAA) levels in at least one brain area, suggesting a common therapeutic response on increased neuronal viability. Most drugs also altered the levels of several metabolites associated with glucose metabolism, neurotransmission (including glutamate and aspartate) and inositols. The heterogenic pharmacological response reflects the functional and physiological diversity of the therapeutic interventions, including side effects. Further study of these metabolites in preclinical models should facilitate the development of novel drug treatments for psychiatric disorders with improved efficacy and side effect profiles.

Comparison of the mGlu(5) receptor positive allosteric modulator ADX47273 and the mGlu(2/3) receptor agonist LY354740 in tests for antipsychotic-like activity

Recently, it has been proposed that activation of either metabotropic glutamate receptors e.g. mGlu(5) by positive allosteric modulators or stimulation of mGluR(2/3) receptors by agonists may offer new strategy in schizophrenia treatment. The aim of the present study was to compare the effect of mGlu(5) receptor positive allosteric modulator, ADX47273 (S-(4-Fluoro-phenyl)-{3-[3-(4-fluoro-phenyl)-[1,2,4]oxadiazol-5-yl]-piperidin-1-yl}-methanone), mGluR(2/3) agonist, LY354740 ((1S,2S,5R,6S)-2-aminobicyclo[3.1.0]hexane-2,6-dicarboxylate monohydrate) and selected neuroleptics in animal models for positive schizophrenia symptoms. ADX47273 (3 and 10mg/kgi.p.), the typical antipsychotic haloperidol (0.1 and 0.2mg/kgi.p.), the atypical antipsychotics aripiprazole (1.25-5mg/kgi.p.) and olanzapine (2.5 and 5mg/kgi.p.) all reduced amphetamine-induced hyperlocomotion in Sprague-Dawley rats, unlike the mGlu(2/3) receptor agonist LY354740 (1-10mg/kgi.p.). Interestingly, haloperidol (0.1 and 0.2mg/kgi.p.), aripiprazole (1.25-5mg/kgi.p.) and olanzapine (1.25-5mg/kgi.p.), but not ADX47273 (1-10mg/kgi.p.), all reduced spontaneous locomotion and rearings at doses effective against amphetamine-induced hyperlocomotion. This indicates that the effect of ADX47273 in combination with amphetamine may be specific, and also suggests a lack of sedative side effects. Moreover, ADX47273 (30mg/kgi.p.), haloperidol (0.1 and 0.2mg/kgi.p.) and aripiprazole (5 and 10mg/kgi.p.) reversed apomorphine (0.5mg/kgs.c.)-induced deficits of prepulse inhibition, whereas neither LY354740 (1-10mg/kgi.p.) nor olanzapine (1.25-5mg/kgi.p.) produced this effect. Lack of effect of olanzapine was unexpected and at present no convincing explanation can be provided. In conclusion, in selected rodent models for positive schizophrenia symptoms, ADX47273 showed better efficacy than LY354740.

Asenapine

Asenapine is a novel psychopharmacological agent that binds with high affinity and specificity to numerous dopamine, serotonin, noradrenaline (norepinephrine) and histamine receptor subtypes. It is being developed for the treatment of schizophrenia and bipolar mania. In two randomized, controlled trials of asenapine monotherapy and in one randomized, controlled trial of adjunctive asenapine therapy in adult patients with bipolar I disorder, sublingual asenapine produced significantly greater reductions from baseline than placebo in clinician-assessed Young Mania Rating Scale (YMRS) total score at 3 weeks. In two randomized, controlled trials in adult patients with acute schizophrenia, treatment with asenapine reduced from baseline the clinician-assessed Positive and Negative Syndrome Scale (PANSS) total score to a significantly greater extent than placebo at 6 weeks. In schizophrenic patients with predominant, persistent, negative symptoms, asenapine at 26 weeks reduced the Negative Symptom Assessment (NSA-16) total score from baseline to an extent similar to that observed with olanzapine. Sublingual asenapine was generally well tolerated in clinical trials, with most treatment-emergent adverse events being of mild to moderate severity. Incidence rates of clinically significant weight gain, extrapyramidal symptoms, hyperprolactinaemia and alterations in glucose or lipid metabolism were generally low.

Pharmacological characterization of senktide-induced tail whips

The tachykinin NK(3) receptor shows promise as a novel target for antipsychotics, but knowledge of downstream activity following tachykinin NK(3) receptor activation is lacking. To determine the practical utility of senktide-induced tail whips in mice as a tool for determining and characterizing downstream activity following tachykinin NK(3) receptor activation, mice were injected with 0.05 nmol of senktide i.c.v. and the number of tail whip bouts was counted for 20 min. Strain differences were observed, with NMRI mice showing a stronger tail whip response than C57Bl/6J mice. Tachykinin NK(3) receptor specificity was confirmed by the absence of the senktide-induced tail whip response in tachykinin NK(3) receptor knockout mice. Effects of tachykinin receptor pharmacological agents were tested by pretreatment with tachykinin NK(3) receptor antagonists (SB222200, talnetant and osanetant), which attenuated senktide-induced tail whips, and the tachykinin NK(1) receptor antagonist MK869, which had no effect on senktide-induced tail whips. Pharmacological interactions with other neurotransmitter systems were determined by pretreatment with dopamine D(1), D(2), and D(3) receptor antagonists, atypical antipsychotics, serotonin 5HT(1a) receptor antagonists, serotonin 5HT(2a/c) receptor antagonists, benzodiazepine and putative anxiolytics, antidepressants, and an anticholinergic. Senktide-induced tail whips were attenuated by dopamine D(2) receptor antagonists, atypical antipsychotics, serotonin 5HT(2a/c) antagonists, and benzodiazepine anxiolytics, but unaffected by drugs from other classes. Thus, the senktide-induced tail whip response is easily quantifiable, specific to the tachykinin NK(3) receptor, and provides valuable information on the downstream pharmacology of tachykinin NK(3) receptor activation.

In thrombin stimulated human platelets Citalopram, Promethazine, Risperidone, and Ziprasidone, but not Diazepam, may exert their pharmacological effects also through intercalation in membrane phospholipids in a receptor-independent manner

Intercalation of drugs in the platelet membrane affects phospholipid-requiring enzymatic processes according to the drugs' intercalation capability. We investigated effects of Promethazine, Citalopram, Ziprasidone, Risperidone, and Diazepam on phospholipase A(2) (PLA(2)) and polyphosphoinositide (PPI) metabolism in thrombin-stimulated human platelets. We also examined effects of the drugs on monolayers of glycerophospholipids using the Langmuir technique. Diazepam did not influence PLA( 2 ) activity, had no effects on PPI cycle, and caused no change in mean molecular area of phospholipid monolayers. The remaining psychotropic drugs affected these parameters in different ways and levels of potency suggesting that they act by being intercalated between the molecules of adjacent membrane phospholipids, thus causing changes in substrate availability for phospholipid-hydrolyzing enzymes (PLA(2) and Phospholipase C). We show that several psychotropic drugs can also have other cellular effects than receptor antagonism. These effects may be implicated in the psychotropic effects of the drugs and/or their side effects.

Enhanced latent inhibition in dopamine receptor-deficient mice is sex-specific for the D1 but not D2 receptor subtype: implications for antipsychotic drug action

Latent inhibition (LI) is reduced learning to a stimulus that has previously been experienced without consequence. It is an important model of abnormal allocation of salience to irrelevant information in patients with schizophrenia. In rodents LI is abolished by psychotomimetic drugs and in experimental conditions where LI is low in controls, its expression is enhanced by antipsychotic drugs with activity at dopamine (DA) receptors. It is however unclear what the independent contributions of DA receptor subtypes are to these effects. This study therefore examined LI in congenic DA D1 and D2 receptor knockout (D1 KO and D2 KO) mice. Conditioned suppression of drinking was used as the measure of learning in the LI procedure. Both male and female DA D2 KO mice showed clear enhancement of LI reproducing antipsychotic drug effects in the model. Unexpectedly, enhancement was also seen in D1 KO female mice but not in D1 KO male mice. This sex-specific pattern was not replicated in locomotor or motor coordination tasks nor in the effect of DA KOs on baseline learning in control groups indicating some specificity of the effect to LI. These data suggest that the dopaminergic mechanism underlying LI potentiation and possibly antipsychotic action may differ between the sexes, being mediated by D2 receptors in males but by both D1 and D2 receptors in females. These data suggest that the DA D1 receptor may prove an important target for understanding sex differences in the mechanisms of action of antipsychotic drugs and in the aetiology of aberrant salience allocation in schizophrenia.

The leukocytes expressing DARPP-32 are reduced in patients with schizophrenia and bipolar disorder

Bipolar disorder (BPD) and schizophrenia (SCZ) are severe disorders representing an enormous social, familiar and individual burden, being SCZ the most disabling psychiatric disorder characterized by psychosis and cognitive impairment. It is well known that SCZ and BPD are associated with abnormalities in dopamine signaling pathway. Recent data in the literature have demonstrated altered expression levels of some proteins involved in the modulation of this pathway in both brain and peripheral tissues. It was shown that protein and mRNA levels of dopamine and cAMP regulated phosphoprotein (DARPP-32) were downregulated in dorsolateral prefrontal cortex (DLPFC) of patients with SCZ or BPD when compared to controls. Due to the difficulty to access brain tissue and the absence of objective laboratory tests for bio-markers, we measured DARPP-32 expression in blood cell sub-populations (CD4+ T lymphocytes, CD56+ NK cells, CD19+ B lymphocytes and CD14+ monocytes) taking advantage of the close relation of nervous and immune systems. Using flow cytometry as the analytical method, our results have shown that the DARPP-32 expression was diminished in CD4+ T lymphocytes, CD19+ B lymphocytes and CD14+ monocytes of BPD patients and was also decreased in CD4+ T lymphocytes and CD56+ NK cells of SCZ patients. These results showed that DARPP-32 expression in immune cells agrees with reports of reduced DARPP-32 protein in the DLPFC of BPD or SCZ patients. Our data suggest that DARPP-32 expression in PBMC could be used as a source of bio-markers to help in the treatment response of neuropsychiatry disorders as a window to the changes in the brain of those patients.

Expression of neuronal calcium sensor-1 (NCS-1) is decreased in leukocytes of schizophrenia and bipolar disorder patients

Schizophrenia (SCZ) and bipolar disorder (BPD) are severe illnesses representing an enormous social, familiar and individual burden that affect 1% of the population world-wide. Several evidences indicate abnormalities of the dopamine system in both SCZ and BPD. Neuronal calcium sensor-1 (NCS-1) is a protein that has many functions in neurotransmission such as inhibition of dopamine D(2) receptor desensitization, regulation of ionic channels and enhancement of exocytosis of neurotransmitters. In addition, NCS-1 protein expression and mRNA levels were found increased in pre-frontal cortex (PFC) of SCZ and BPD patients. NCS-1 expression in neural and neuroendocrine cells is well documented and, recently, it was shown that NCS-1 is also expressed in mast cells and neutrophils. NCS-1 has important functions in mast cells since it stimulates Fc epsilon RI-triggered exocytosis and the release of arachidonic acid metabolites. Then, due to the known close relation between the nervous and immune systems, we sought to investigate the NCS-1 expression in lymphocytes and monocytes (CD4+ T lymphocytes, CD56+ NK cells, CD19+ B lymphocytes and CD14+ monocytes) of SCZ and BPD patients. Using flow cytometry, our results have shown that NCS-1 expression was diminished in CD4+T lymphocytes, CD19+ B lymphocytes and CD14+ monocytes of BPD patients and also decreased in CD4+ T lymphocytes and CD56+ NK cells of SCZ patients. Results suggest that immune cells might be a cellular model for studies with SCZ and BPD patients considering NCS-1 functions. Efforts need to be done to investigate the motive of the decreased percentage of immune cells expressing NCS-1 in patients with SCZ and BPD.

Effects of a metabotropic glutamate receptor group II agonist LY354740 in animal models of positive schizophrenia symptoms and cognition

It has been proposed that activation of metabotropic glutamate receptor subtype 2/3 (mGluR2/3) may induce both antipsychotic and anxiolytic effects. The aim of this study was to evaluate further the effect of the mGluR2/3 agonist, LY354740 [(+)-2-aminobicyclo(3.1.0)hexane-2,6-dicarboxylate monohydrate] in animal models relevant to both psychotic and cognitive impairment in schizophrenia. The elevated plus maze was used to select the doses for further experiments, LY354740 induced anxiolytic-like effects at doses of 3 and 10 mg/kg but not 1 mg/kg. At a dose of 10 mg/kg. LY354740 attenuated phencyclidine (PCP)-induced locomotor activity. Administered alone, it had no effect on horizontal activity, but at doses of 3 and 10 mg/kg, slightly decreased vertical activity (rearings). LY354740 (1-10 mg/kg intraperitoneally) affected neither prepulse inhibition in normal rats nor reversed the disruption of prepulse inhibition produced by PCP (2 mg/kg subcutaneously). Moreover, LY354740 (3-10 mg/kg) did not modify PCP-induced working memory deficits assessed in a spontaneous alternation task and had no effect on PCP-evoked amnesia in the passive avoidance test. LY354740 alone (3 and 10 mg/kg) induced working memory deficits, but had no effect on acquisition of passive avoidance. In conclusion, LY354740 was effective in models for anxiety and positive symptoms of schizophrenia but not in models for sensorimotor gating and cognitive impairment.

Risperidone alters food intake, core body temperature, and locomotor activity in mice

Risperidone induces significant weight gain in female mice; however, the underlying mechanisms related to this effect are unknown. We investigated the effects of risperidone on locomotor activity, core body temperature, and uncoupling protein (UCP) and hypothalamic orexin mRNA expression. Female C57BL/6J mice were acclimated to individual housing and randomly assigned to either risperidone (4 mg/kg BW day) or placebo (PLA). Activity and body temperature were measured over 48-hour periods twice a week for 3 weeks. Food intake and body weights were measured weekly. UCP1 (BAT), UCP3 (gastrocnemius), and orexin (hypothalamus) mRNA expressions were measured using RT-PCR. Risperidone-treated mice consumed more food (p=0.050) and gained more weight (p=0.0001) than PLA-treated mice after 3 weeks. During the initial 2 days of treatment, there was an acute effect of treatment on activity (p=0.046), but not body temperature (p=0.290). During 3 weeks of treatment, average core body temperatures were higher in risperidone-treated mice compared to controls during the light phase (p=0.0001), and tended to be higher during the dark phase (p=0.057). Risperidone-treated mice exhibited lower activity levels than controls during the dark phase (p=0.006); there were no differences in activity during the light phase (p=0.47). UCP1 (p<0.01) and UCP3 (p<0.05) mRNA expressions were greater in risperidone-treated mice compared to controls, whereas, orexin mRNA expression was lower in risperidone-treated mice (p<0.01). These results suggest that risperidone-induced weight gain in mice is a consequence of increased energy intake and reduced activity, while the elevation in body temperature may be a result of thermogenic effect of food intake and elevated UCP1, UCP3, and a reduced hypothalamic orexin expression.

Pharmacological modulation of the neural basis underlying inhibition of return (IOR) in the human 5-HT2A agonist and NMDA antagonist model of psychosis

RATIONALE

Attentional deficits are common symptoms in schizophrenia. Recent evidence suggests that schizophrenic patients show abnormalities in spatial orienting of attention, particularly a deficit of inhibition of return (IOR). IOR is mostly thought to reflect an automatic, inhibitory mechanism protecting the organism from redirecting attention to previously scanned, insignificant locations. Pharmacologic challenges with hallucinogens have been used as models for psychosis.

OBJECTIVES

The aim of this study was to investigate the neural correlates underlying orienting of attention in the human N-methyl-D-aspartic acid antagonist and 5-HT2A agonist models of psychosis.

MATERIALS AND METHODS

Fourteen healthy volunteers participated in a randomized, double-blind, cross-over event-related functional magnetic resonance imaging (fMRI) study with dimethyltryptamine (DMT) and S-ketamine. We administered a covert orienting of attention task with nonpredictive peripheral cues, and we scanned the subjects on two separate days at least 14 days apart with a placebo and a verum condition on each day.

RESULTS

DMT, but not S-ketamine, slowed down reaction times significantly. IOR was blunted after DMT, but not after S-ketamine. Relative to placebo, S-ketamine increased activation in the IOR condition in the right superior frontal gyrus, left superior temporal gyrus, and right midfrontal frontal gyrus.

CONCLUSIONS

The discrepancy between the behavioral and functional imaging outcome indicates that pharmacological fMRI might be a sensitive tool to detect drug-modulated blood oxygenation level-dependent signal changes in the absence of behavioral abnormalities. Our findings might help to further clarify the contradictory findings of IOR in schizophrenic patients and might, thus, shed more light on possible differential pathomechanisms of schizophrenic symptoms.