Antipsychotic drug effects on the behavior of squirrel monkeys differentially controlled by noxious stimuli

The effects of several antipsychotic compounds were examined on two types of behavioral performances of squirrel monkeys. Both behaviors occurred simultaneously and were maintained separately by different schedules using noxious stimuli. Steady rates of responding were maintained when a chain pulling response postponed electric shock delivery (avoidance schedule). Concurrently, positively accelerated rates of responding were maintained on a lever where the first response after 3 min produced electric shock (fixed-interval 3-min schedule). The effects of the different drugs depended both upon whether the behavior postponed or presented shock and on the particular drug. Chlorpromazine (0.001-0.03 mg/kg), haloperidol (0.001-0.01 mg/kg), molindone (0.001-0.03 mg/kg) and thiothixene (0.001-0.03 mg/kg) increased slightly or had no effect on responding under the shock-postponement schedule at doses that decreased responding maintained by shock presentation. The effects of clozapine, a clinically effective antipsychotic compound, differed markedly from the other antipsychotic drugs. Clozapine (0.01-1.0 mg/kg) increased responding maintained by the presentation of shock at doses that decreased responding under the shock-postponement schedule. Higher doses of these drugs decreased responding under both schedules and, with the exception of clozapine, resulted in increased frequency of shocks under the postponement schedule.