Abstract
Male Wistar rats were trained to hold down a lever for reinforcement with food pellets. No external stimulus signalled the end of the required duration. The minimum duration required was gradually raised to, and fixed at, 2 seconds. This was achieved in about 1-2 months. At the end of pre-drug training, the average response duration was 2.06±0.03 seconds in a daily 10-minute session. Daily injections of pyrithiamine, a thiamine analog which causes a rapid depletion of the brain vitamin, were given after the daily experimental sessions. The average response duration increased significantly by the 8th day of pyrithiamine treatment (2mg/kg/day), without altering any other parameters examined. This pyrithiamine-induced change in duration, which was gradually diminished after the 14-day drug period, could be reversed with thiamine (2 doses of 5mg/kg). On the other hand, oxythiamine did not cause an increase in duration over the 14 days of daily injections. The results obtained suggest that pyrithiamine exerted significant effects on discrimination of duration or internal timing mechanism in rats at the doses used, perhaps because of the depletion of the brain vitamin.
