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 amineptine (a tricyclic antidepressant drug) on the performance of albino rats in differential reinforcement of low rate (DRL) of 30 s, fixed-interval (FI) of 60 s, and signalled continuous reinforcement (CRF-SD) schedules. In the second experiment, the effects of repeated (10 mg/kg) and 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-SD or duration discrimination tended to indicate that the drug improved vigilance and reactivity to extraneous significant stimuli. Interpretations in terms of sensitization, tolerance, or dependency could be discarded. Our data support the hypothesis that drug effects on temporal regulation in FI and DRL are secondary to a nonspecific activation of motor activity. They question the plausibility of an antidepressant effect of the drug in humans via modulation of a timing mechanism.