AMINEPTINE, RESPONSE TIMING, AND TIME DISCRIMINATION IN THE ALBINO-RAT

Experiment 1 recorded the effects of single (doses of 1, 5, 10, and 20 mg/kg) and repeated intraperitoneal injections (10 mg/kg) of aminepti ne (a tricyclic antidepressant drug) on the performance of albino rats in differential reinforcement of low rate (DRL) of 30 s, fixed-interv al (FI) of 60 s, and signalled continuous reinforcement (CRF-S-D) sche dules. In the second experiment, the effects of repeated (10 mg/kg) an d single injections (20 mg/kg) were assessed on the discrimination of the duration of auditory stimuli (2 and 8 s). A dose-related increase in response rates was observed in FI and DRL, correlating with a dose- related impairment in the temporal regulation of performance. However, the drug remained without effect on duration discrimination. In other respects, decreases in response latency in CRF-S-D or duration discri mination tended to indicate that the drug improved vigilance and react ivity to extraneous significant stimuli. Interpretations in terms of s ensitization, tolerance, or dependency could be discarded. Our data su pport the hypothesis that drug effects on temporal regulation in FI an d DRL are secondary to a nonspecific activation of motor activity. The y question the plausibility of an antidepressant effect of the drug in humans via modulation of a timing mechanism.