A comparison of clozapine, chlorpromazine, and thioridazine upon DRL performance in the squirrel monkey.

Clozapine (0.16--10 mg/kg, p. o.), chlorpromazine (0.25--2 mg/kg, p. o.), and thioridazine (0.25--2 mg/kg, p. o.) were administered to squirrel monkeys subjected to a DRL 10 s schedule. The reinforcer consisted of 50% unsweetened orange juice. Chlorpromazine and thioridazine had no effect at the lower doses, but decreased response rate at the highest dose. Clozapine increased response rates at the low doses (0.31--2.5 mg/kg) and decreased rates at the high dose (10 mg/kg). Clozapine appears to show a major difference from other neuroleptic drugs in this test by increasing response rate. Since clozapine produces few extrapyramidal side effects in man, this procedure may be useful in selecting and developing new anti-psychotic drugs with less liability for side effects.