Effects of ACTH and ACTH 4-10 on aversive memory retrieval in rats.

The aim of the study was to examine whether ACTH and ACTH-fragment 4-10, given before the test would produce a selectively enhanced retrieval of aversive memories, in the same way as preexposure to inescapable footshocks, in rats. For this purpose animals conditioned in a T-maze with appetitive (10% sucrose) and aversive (2.0 mA footshock) events were administered (s.c.) a single dose of 10, 20 or 40 ug/rat of ACTH or 5, 10 or 20 ug/rat of ACTH-fragment 4-10, 20-min before testing. The retention test conducted in the same training apparatus 72-hrs after conditioning showed a dose-dependent increase in latencies to enter the previously shocked goalarm with the absence of such a difference in responding to the nonshocked goalarm, in ACTH and ACTH 4-10 treated groups. This differential response was not observed in saline treated rats. This effect of peptides on memory retrieval was similar to that seen following inescapable footshock in rats. The results suggest the possible involvement of ACTH in the differential enhancement of memory of helplessness condition.