PERIPHERAL POST-TRAINING ADMINISTRATION OF 4-OH AMPHETAMINE ENHANCES RETENTION OF A REDUCTION IN REWARD MAGNITUDE

This experiment examined the effect of post-training systemic (sc) inj ections of 4-OH amphetamine on memory for a reduction in reward. Rats were trained to run in a straight alley (six trials per day, 30-s inte rtrial interval) and received either 1 or 10 45-mg sucrose pellets on each trial. On Day 8, rats receiving 10 pellets were shifted to the 1- pellet reward. Shifted rats displayed a characteristic increase in res ponse latencies typically attributed to an aversive emotional response to reward reduction. Immediately after the reward shift, all rats rec eived an injection of either 2 mg/kg of 4-OH amphetamine or the equiva lent volume of physiological saline. The rats were then returned to th eir home cages for 6 days without further training. On Day 15 the rats were returned to training, all with 1 sucrose pellet as reward. The p erformance of unshifted rats was comparable to that on Day 8 and the f irst trial performance of shifted rats given post-training saline was not significantly different from that of unshifted rats. Further, the shifted saline group's mean latencies for the entire training block on Day 15 were comparable to their mean latencies on Day 8. These findin gs suggest that the shifted saline rats did not remember the prior rew ard reduction on Day 8. In contrast, the shifted rats given post-train ing 4-OH amphetamine displayed first trial latencies that were longer than those of all other groups on Day 15. Additionally, on the entire training block on Day 15 the latencies of the shifted 4-OH amphetamine group were longer than those recorded on Day 8, indicating that shift ed 4-OH amphetamine rats retained memory of the prior reward reduction . These findings suggest that post-training activation of peripheral a drenergic systems by 4-OH amphetamine enhances the retention for avers ive emotional consequences elicited by reward reduction. (C) 1996 Acad emic Press, Inc.