Long Term Effect of Vasopressin on the Maintenance of a Conditioned Avoidance Response in Rats

Abstract

RATS subjected to posterior lobectomy are unable to maintain a shuttle-box avoidance response without reinforcement¹, but normal behaviour can be restored to that of sham-operated controls by treatment with pitressin tannate in oil, a relatively crude extract of posterior and intermediate pituitary lobes. Long acting preparations of ACTH and α-MSH can also restore the normal rate of extinction of an avoidance response in posterior lobectomized rats². Pitressin as well as ACTH analogues, including α-MSH, delay the extinction of an avoidance response also in intact rats^3,4. Treatment with pitressin tannate in oil, however, preserves a conditioned avoidance response whether the treatment is given during acquisition or extinction, while ACTH or ACTH analogues inhibit extinction most markedly during the treatment period³. These observations suggest that the mechanisms by which pitressin and analogues of ACTH affect conditioned avoidance behaviour are basically different. The fact that rats treated with pitressin retain the avoidance response for a considerable time after treatment suggests that this preparation contains peptides which interfere with long term memory storage, but that peptides with a configuration like that of ACTH participate in short term (trial to trial) memory processes³.