Involvement of ACTH and MSH in active and passive avoidance behavior

Intracerebroventricular injection of antiserum to alpha--MSH induces a weak reduction of passive avoidance latencies after administration prior to retention testing. Administration of antiserum to ACTH 1--24 induces a more marked effect in this respect, whereas injection of a combination of these antisera results in the strongest reduction of passive avoidance retention. No effect of this treatment is observed when these antisera are injected immediately after the learning trial. In active avoidance behavior a facilitation of extinction of the response is observed after intracerebroventricular administration of the antisera prior to each extinction session. This effect is comparable with the one observed in passive avoidance behavior. From these data it is suggested that ACTH and alpha-MSH play an important role in processes related to the retrieval of information stored in the brain.