CAN THE DRL 72S SCHEDULE SELECTIVELY REVEAL ANTIDEPRESSANT DRUG ACTIVITY

The effects of three antidepressants, desipramine (2.5-20 mg/kg) trany lcypromine (0.63-2.5 mg/kg) mianserin (1.25-10 mg/kg) and three non-an tidepressants, chlordiazepoxide (CDP; 1.25-10 mg/kg) haloperidol (0.02 -0.16 mg/kg) d-amphetamine (0.31-1.25 mg/kg) were evaluated in rats re sponding for water reinforcement under a DRL 72s schedule. The antidep ressants all produced dose-related decreases in overall response rates : but no significant changes in reinforcement frequency. In contrast, the anxiolytic CDP did increase the number of reinforcers obtained. Ha loperidol decreased both reinforcers and responses whilst d-amphetamin e stimulated responding, thereby decreasing reinforcement frequency. A n analysis of the modes of inter-response times (IRTs) revealed no sig nificant shifts in the peaks of the IRT distributions for most of the drugs tested. Amphetamine, however, (0.31 and 0.63 mg/kg) decreased th e modal values in correspondence with the shift to the left of the pea k of responding caused by this compound. These results are discussed i n the context of the use of the DRL 72s procedure as a screening test for antidepressant drugs.