Chronic ethanol ingestion selectively affects memory modulation in rats

Post-training treatment alters memory by different mechanisms. Naloxone enhances memory by antagonism of endogenous ß-endorphin-induced state dependency. Epinephrine facilitates consolidation at low doses and generates state dependency at high doses. Exposure to a session of tones causes retroactive interference through a cognitive effect. The present data show that chronic ethanol ingestion, in rats, inhibited the post-training effect of naloxone and of a high dose of epinephrine on the retention of an inhibitory avoidance task but did not inhibit retrograde interference by a session of tones or retrograde facilitation by a low dose of epinephrine. Therefore, ethanol appers to selectively affect post-training influences related to state dependency

Gamma-endorphin affects retrieval of an inhibitory avoidance task

Rats were trained in a step-down inhibitory avoidance task and retrieval was measured during a test session conducted 24 h after training. The ip administration of a low dose of gamma-endorphin (0.2 microng/kg) immediately after training reduced retrieval time from 40.6 to 13.5 s (N = 15). Higher doses of gamma-endorphin given 5 min before testing (1.0 microng/kg) or immediately after training (5 microng/kg) enhanced retrieval time from 38.6 to 300 s (N = 15) and from 40.6 to 104.4 s (N = 15). All of these effects were either after training or before testing had no effect on retrieval. Since at least the amnestic effect of gamma-endorphin is similar to that of beta-endorphin, and gamma-endorphin is a possible metabolite of beta-endorphin by limited proteolysis of the carboxyl-terminal amino acid, it is suggested that at least some effects of beta-endorphin on memory may be mediated by its proteolysis product, gamma-endorphin