Comparison of the effects of ACTH and lysine vasopressin on avoidance-of-attack in mice

Abstract

Single injections of either ACTH or lysine vasopressin (LVP) were administered to mice at one of three times: either (1) prior to training in a passive avoidance situation where the aversive stimulus is attack by a trained fighter mouse, (2) just following acquisition of the passive avoidance response, or (3) just prior to a first retention test at 24 hr after acquisition. Retention of the avoidance response also was assessed at 48 and 240 hr postacquisition. Both ACTH and LVP enhanced retention of the response, although their effects were different in character. ACTH's effects were relatively short-lived: the facilitatory effect of ACTH treatment was evident at the first (24 hr) retention test but had disappeared by the 240 hr test. On the other hand, LVP's effects became apparent later (at 48 hr) but lasted through the 240 hr test. In addition, the critical times for their administration were different: ACTH treatment enhanced avoidance retention no matter when the hormone was administered, whereas LVP only enhanced retention if this hormone had been administered after acquisition or prior to the first retention test; LVP treatment before acquisition did not affect avoidance-of-attack. The effects of ACTH and LVP on avoidance-of-attack are basically similar in form to the effects of these hormones on avoidance-of-shock.