Memory modulation by the administration of ACTH, adrenaline or beta-endorphin after training or prior to testing in an inhibitory avoidance task in rats.

The ip administration of ACTH1-24 (0.2 microgram/kg) or adrenaline-HCl (5.0 micrograms/kg) immediately after training or 6 min prior to testing facilitated retrieval of a one-trial step-down inhibitory avoidance task in rats, acquired using a low intensity footshock. Post-training administration of beta-endorphin (0.1 micrograms/kg, ip) caused retrograde amnesia, but pre-test administration facilitated retrieval. The amnesia caused by post-training administration of beta-endorphin was prevented by ACTH, adrenaline or beta-endorphin given prior to testing. Memory facilitation was most pronounced when the same drug was administered both after the training session and prior to testing. These findings suggest that ACTH, adrenaline and beta-endorphin have at least two effects on memory processing: 1) during the post-training period on the entry of recently stored information into a system that makes it available for retrieval; and 2) both after training and during the test session, that makes learning dependent on states induced by the drugs.