Clozapine attenuates disruptions in response inhibition and task efficiency induced by repeated phencyclidine administration in the intracranial self-stimulation procedure

Abstract

Currently available antipsychotic medications lack satisfactory effectiveness against several symptom clusters of schizophrenia, including affective symptoms (e.g., anhedonia) and cognitive deficits (e.g., impulsivity). Translational animal models analogous to these symptoms are necessary to provide insights into the neurobiological events underlying these impairments and allow the development of improved schizophrenia treatments. We investigated the effects of repeated administration of the psychotomimetic phencyclidine (PCP), a noncompetitive N-methyl-D-aspartate receptor antagonist, on performance in the intracranial self-stimulation (ICSS) procedure, a test of reward function. We also explored how chronic treatment with clozapine, an atypical antipsychotic with limited effectiveness on affective and cognitive schizophrenia symptoms, would affect PCP-induced disruptions of ICSS performance. A single injection of 2 mg/kg PCP elevated ICSS thresholds, suggesting a reward deficit. Repeated PCP administration (2 mg/kg once daily for 2 consecutive days followed by a 10-day drug free period, and then 5 consecutive days of 2 mg/kg PCP daily, s.c., 30 min pretreatment) resulted in a small, but significant, lowering of ICSS reward thresholds, indicating increased reward function. Chronic clozapine did not alter the effects of repeated PCP on ICSS thresholds. Repeated PCP also increased the number of extra and timeout responses performed during the ICSS procedure, reflecting disinhibition of inappropriate responding and decreased task efficiency. Chronic clozapine attenuated the increase in extra responses induced by repeated PCP and tended to reduce the PCP-induced increase in timeout responses. These results suggest that repeated PCP administration does not produce an anhedonia-like state resembling that seen in schizophrenia. However, the increased impulsivity and reduced task efficiency seen with repeated PCP administration, and the sensitivity of these effects to attenuation with an atypical antipsychotic, suggest that repeated PCP administration may be a useful inducing condition for eliciting cognitive deficits with relevance to schizophrenia.