Regional Differences in the Action of Antipsychotic Drugs: Implications for Cognitive Effects in Schizophrenic Patients

Dopamine guides competition for cognitive control: Common effects of haloperidol on working memory and response conflict

Several lines of evidence suggest that dopamine modulates working memory (the ability to faithfully maintain and efficiently manipulate information over time) but its specific role has not been fully defined. Nor is it clear whether any effects of dopamine are specific to memory processes or whether they reflect more general cognitive mechanisms that extend beyond the working memory domain. Here, we examine the effect of haloperidol, principally a dopamine D₂ receptor antagonist, on the ability of humans to ignore distracting information or update working memory contents. We compare these effects to performance on an independent measure of cognitive control (response conflict) which has minimal memory requirements. Haloperidol did not selectively affect the ability to ignore or update, but instead reduced the overall quality of recall. In addition, it impaired the ability to overcome response conflict. The deleterious effect of haloperidol on response conflict was selectively associated with the negative effect of the drug on ignoring - but not updating - suggesting that dopamine affects protection of working memory contents and inhibition in response conflict through a common mechanism. These findings provide new insights into the role of dopamine D₂ receptors on human cognition. They suggest that D₂ receptor effects on protecting the memory contents from distraction might be related to a more general process that supports inhibitory control in contexts that do not require working memory.

Differential effects of clozapine, metoclopramide, haloperidol and risperidone on acquisition and performance of operant responding in rats

RATIONALE

Prior research has not systematically investigated the effects of systemic antipsychotic drugs on operant response acquisition, specifically their behavioural microstructure, reinforcement blunting and relative potency in acquisition compared to performance once operant responding has stabilized.

OBJECTIVES

This study aims to systematically investigate the effects of systemically administered clozapine, metoclopramide, haloperidol and risperidone during free operant response acquisition and performance.

METHODS

Following magazine training, food-restricted male Wistar rats lever pressed for food reward in 15 min daily operant conditioning sessions.

RESULTS

All drugs suppressed operant response acquisition and performance. Risperidone and metoclopramide, but not clozapine or haloperidol, suppressed operant responding more potently during acquisition than performance. The dopamine D2-like receptor antagonists haloperidol and metoclopramide that affect the ventral and dorsal striatum blunted reinforcement and decreased inactive lever presses in acquisition. In contrast, the atypical antipsychotics clozapine and risperidone that affect the ventral striatum and prefrontal cortex failed to decrease inactive lever presses during acquisition, suggesting a possible decision-making deficit. Haloperidol decreased active lever pressing over performance days. The drugs did not appear to affect rats' sensitivity to active lever press outcome, even though they suppressed active lever pressing.

CONCLUSIONS

Results suggest that reinforcement impact during operant acquisition is dependent on dopamine D2 receptors while drugs affecting, among other areas, the prefrontal cortex produce a deficit in ability to suppress inactive lever press responses.

Comprehensive family therapy: an effective approach for cognitive rehabilitation in schizophrenia

BACKGROUND

Antipsychotic medication has limited abilities to improve the cognitive impairments that accompany schizophrenia. Adding psychosocial treatment may result in marked improvements in cognitive function, as compared to antipsychotic treatment alone. We hypothesized that a combination of individual and family interventions may be a useful cognitive rehabilitation paradigm for schizophrenia.

MATERIALS AND METHODS

An 18-month follow-up clinical trial of 256 stabilized patients with schizophrenia at six communities in Shanghai, People's Republic of China were randomly assigned to into either a comprehensive family therapy (CFT) group or a usual daily care (UDC) group. The Repeatable Battery for the Assessment of Neuropsychological Status (RBANS) and the Positive and Negative Syndrome Scale (PANSS) were the primary outcome instruments for this study.

RESULTS

There was no significant difference between the CFT and UDC for all demographic characteristics at the baseline assessment. During the 18-month follow-up observation, changes in RBANS total score indicated that patients undergoing CFT showed greater improvement from baseline to the follow-up assessments in cognitive function than those in the UDC group (F=9.77, P=0.002). Post hoc analysis showed that the CFT group presented with significant differences in the RBANS total score, immediate memory, visuospatial skill, language, attention, and delayed memory sections compared with the UDC after 18 months of follow-up (all P<0.01).

CONCLUSION

Our findings suggest that CFT can be easily adapted and may prove to be an effective approach for improving cognitive function in patients with schizophrenia. Our program provides a potential paradigm for cognitive rehabilitation for schizophrenia patients in the community.

The effect of quetiapine (Seroquel™) on conditioned place preference and elevated plus maze tests in rats when administered alone and in combination with (+)-amphetamine

RATIONALE

Recent case reports describe recreational use of quetiapine and drug-seeking behaviour to obtain quetiapine, an atypical antipsychotic.

OBJECTIVE

We examined the hypothesis that quetiapine (10, 20 or 40 mg/kg) alone or co-administered with (+)-amphetamine (0.25, 0.5, 0.75 or 2.0 mg/kg) will affect reward and/or decrease anxiety in rats, as measured by conditioned place preference (CPP) and elevated plus maze (EPM) test, respectively.

RESULTS

Quetiapine (20 mg/kg) produced greater open arm time and entries in the EPM test compared to 10 and 40 mg/kg, and quetiapine (10 mg/kg) significantly increased open arm entries and time when co-administered with (+)-amphetamine (0.5 mg/kg) compared to (+)-amphetamine (0.5 mg/kg) alone, suggesting decreased anxiety. Quetiapine (10, 20 or 40 mg/kg) produced no CPP when administered alone; the lowest dose of quetiapine (10 mg/kg) reduced CPP produced by a low dose of (+)-amphetamine (0.25 mg/kg), but had no significant effect on CPP produced by a higher dose (0.5 mg/kg).

DISCUSSION

The quetiapine-induced anxiolytic effect in the EPM might explain why humans are misusing quetiapine and combining it with (+)-amphetamine. It is possible that humans experience an anxiolytic effect of the combined drugs and relatively unaltered rewarding effects of (+)-amphetamine. The results shed some light on the question of why humans are abusing and misusing quetiapine, despite its dopamine (DA) D2 receptor antagonism; it will be the task of future studies to identify the pharmacological mechanism mediating this behaviour.

Neuropsychological correlates of P50 sensory gating in patients with schizophrenia

Impaired inhibition of P50 cerebral evoked response is one of the best validated endophenotypes in schizophrenia. There are controversial data on the relationship between P50 evoked potential deficit and measures of cognitive function in schizophrenia. A comprehensive clinical and neurocognitive assessment plus an evaluation of P50 sensory gating was performed in 160 schizophrenia patients and 64 controls. Neurocognitive scores from each cognitive domain were converted to demographically-adjusted T-scores (age, gender, and years of education) for all study participants. The relationship between P50 and neurocognitive variables was assessed via parametric and nonparametric correlations and categorical strategies: we compared neuropsychological test scores in patients and controls in the lowest P50 quartile vs. the highest. Controls had better performance than schizophrenia patients in all cognitive domains. Schizophrenia patients had significantly higher P50 ratios than controls, and no significant correlation was found between P50 gating measures and neuropsychological test scores in schizophrenia patients or healthy controls. Moreover, no differences in neurocognitive performance were found between subjects in the lowest P50 ratio quartile vs. the highest in healthy controls or patients with schizophrenia. We concluded that there is no evidence of an association between P50 ratio and cognitive measures in schizophrenia patients, and this seems to be also the case in healthy controls.

Clozapine-induced locomotor suppression is mediated by 5-HT2A receptors in the forebrain

The need for safer, more effective therapeutics for the treatment of schizophrenia is widely acknowledged. To optimally target novel pharmacotherapies, in addition to establishing the mechanisms responsible for the beneficial effects of antipsychotics, the pathways underlying the most severe side effects must also be elucidated. Here we investigate the role of serotonin 2A (5-HT(2A)), serotonin 2C (5-HT(2C)), and dopamine 2 receptors (D₂) in mediating adverse effects associated with canonical first- and second-generation antipsychotic drugs in mice. Wild-type (WT) and 5-HT(2A) knockout (KO) mice treated with haloperidol, clozapine, and risperidone were assessed for locomotor activity and catalepsy. WT mice showed a marked reduction in locomotor activity following acute administration of haloperidol and high-dose risperidone, which was most likely secondary to the severe catalepsy caused by these compounds. Clozapine also dramatically reduced locomotor activity, but in the absence of catalepsy. Interestingly, 5-HT(2A) KO mice were cataleptic following haloperidol and risperidone, but did not respond to clozapine's locomotor-suppressing effects. Restoration of 5-HT(2A) expression to cortical glutamatergic neurons re-instated the locomotor-suppressing effects of clozapine in the open field. In sum, we confirm that haloperidol and risperidone caused catalepsy in rodents, driven by strong antagonism of D₂. We also demonstrate that clozapine decreases locomotor activity in a 5-HT(2A)-dependent manner, in the absence of catalepsy. Moreover, we show that it is the cortical population of 5-HT(2A) that mediate the locomotor-suppressing effects of clozapine.

Probabilistic classification and gambling in patients with schizophrenia receiving medication: comparison of risperidone, olanzapine, clozapine and typical antipsychotics

RATIONALE

We have previously shown that patients with schizophrenia treated with typical antipsychotics were impaired on the weather prediction probabilistic classification learning (PCL) task that relies on striatal function, and that similar patients treated with atypical antipsychotics were impaired on the Iowa gambling task (IGT) that depends on medial prefrontocortical function.

OBJECTIVES

We tested the hypothesis that test performance of patients treated with risperidone will be more similar to those treated with typical rather than atypical antipsychotics.

RESULTS

Groups of schizophrenia patients treated with risperidone, olanzapine, clozapine or typical antipsychotics did not differ on the Positive and Negative Syndrome Scale or the Mini Mental State Exam (MMSE) but scored lower than controls on the MMSE. For the PCL task, patients treated with clozapine improved over trials while those treated with typical antipsychotics, olanzapine, or risperidone did not. For the IGT, patients treated with typical antipsychotics or risperidone improved over trials while those treated with clozapine or olanzapine did not.

CONCLUSIONS

Results generally supported the hypothesis that patients treated with risperidone perform more like those treated with typical antipsychotics than those treated with other atypical antipsychotics.

Epigenetics and biomarkers in the staging of neuropsychiatric disorders

Epigenetics, or alterations in the phenotype or gene expression due to mechanisms other than changes in the underlying DNA sequence, reflects the sensitivity and responsiveness of human and animal brains in constantly varying circumstances regulating gene expression profiles that define the biomarkers and present the ultimate phenotypical outcomes, such as cognition and emotion. Epigenetics is associated with functionally relevant alterations to the genome in such a fashion that under the particular conditions of early, adolescent, and adult life, environmental signals may activate intracellular pathways that remodel the "epigenome," triggering changes in gene expression and neural function. Thus, genetic influences in neuropsychiatric disorders that are subject to clinical staging, epigenetics in schizophrenia, epigenetic considerations in the expression of sensorimotor gating resulting from disease conditions, biomarkers of drug use and addiction, current notions on the role of dopamine in schizophrenia spectrum disorders, and the discrete interactions of biomarkers in persistent memory were to greater or lesser extents reflected upon. The relative contributions of endophenotypes and epistasis for mediating epigenetic phenomena and the outcomes as observed in the analysis of biomarkers appear to offer a multitude of interactive combinations to further complicate the labyrinthine machinations of diagnosis, intervention, and prognosis.