Retention of passive avoidance behavior in rats following alpha- and gamma-endorphin administration: effects of post-learning treatments.

Neuropeptides related to beta-endorphin (beta-LPH61-91) profoundly affect avoidance behavior. That gamma- and alpha-endorphin (beta-LPH61-77 and beta-LPH61-76, respectively) influence memory processes, has been investigated on rats. Using a one-trial learning, step-through passive avoidance paradigm, it was found that gamma-endorphin attenuates later retention of passive avoidance behavior when administered immediately or 3 h after learning; alpha-endorphin facilitates this response when given immediately after learning. Neither gamma- nor alpha-endorphin influence retention when the treatment is postponed for 6 h after learning. These data are interpreted as suggesting an opposite effect of gamma- and alpha-endorphin on consolidation processes.