THE ENHANCEMENT OF RETENTION PERFORMANCE INDUCED BY PICROTOXIN IN MICE MAY BE MEDIATED THROUGH A RELEASE OF ENDOGENOUS VASOPRESSIN

Male Swiss mice were tested 48 h after training in a one-trial step-th rough inhibitory avoidance task. Immediately posttraining i.p. injecti on of the GABA antagonist picrotoxin (0.33.0 mg/kg), at nonconvulsive doses, induced a dose-dependent modification of retention performance. The lower doses of picrotoxin (0.1-1.0 mg/kg) enhanced retention, whe reas the highest dose (3.0 mg/kg) impaired retention. Picrotoxin did n ot affect response latencies In mice not given the footshock on the tr aining trial, indicating that the actions of picrotoxin on retention p erformance were not due to nonspecific proactive effects on response l atencies. The enhancing effects of picrotoxin (1.0 mg/kg) on retention were time-dependent, which suggests that picrotoxin enhanced storage of recently acquired information. The enhancement of retention induced by picrotoxin (1.0 mg/ kg) was prevented by the vasopressin receptor antagonist, AAVP (0.01 mu g/kg, s.c.) administered immediately after t raining, but prior to picrotoxin treatment This dose of AAVP did not a ffect retention by itself, either under the standard experimental cond itions, or in mice trained with a high footshock. Low subeffective dos es of picrotoxin (0.1 mg/kg, s.c.) administered immediately after trai ning, and hypertonic saline (1 ml of 0.5 M NaCl, i,p.), given 10 min a fter training, interacted to improve retention. Considered together, t hese findings suggest that the better retention performance induced by post-training administration of picrotoxin could result, at least in part, from an endogenous release of vasopressin.