Differential effects of acute and subchronic clozapine and haloperidol on phencyclidine-induced decreases in voluntary sucrose consumption in rats.

Prior exposure to the psychotomimetic drug phencyclidine (PCP) decreases voluntary sucrose consumption in rats. This may be indicative of reduced reward function, a phenomenon associated with negative schizophrenic symptomatology. Given that atypical antipsychotics have been shown to ameliorate negative symptoms of schizophrenia more effectively than typical neuroleptics, this effect should be reversed by clozapine but not haloperidol. PCP (15 mg/kg) or saline was administered 20 h prior to testing for voluntary sucrose consumption in non-deprived rats. In the acute experiments, rats were treated with clozapine (5 mg/kg), haloperidol (0.2 mg/kg), or vehicle 45 min prior to testing. In the subchronic experiments, rats were treated with clozapine (3 mg/kg, bid), haloperidol (0.5 mg/kg, bid), or vehicle for 10 days prior to PCP administration. Acute clozapine exacerbated the PCP-induced decrease in sucrose consumption without altering water consumption. Acute haloperidol produced an overall decrease in sucrose consumption in both PCP-pretreated and control groups. Subchronic treatment with clozapine, but not haloperidol, reversed PCP-induced decreases in sucrose consumption. The synergistic effect of acute clozapine and PCP may reflect a PCP-induced increase in the reward-reducing properties of CLZ, normally seen only at higher doses. The observation that subchronic clozapine, but not haloperidol, reversed PCP-induced decreases in sucrose consumption supports the hypothesis that this effect of PCP represents a plausible animal model for negative schizophrenic symptomatology.