Vasopressin and memory .1. The vasopressin analogue AVP(4-9) enhances working memory as well as reference memory in the radial arm maze

The present study examined the effects of vasopressin on memory. Healthy rats were injected with the arginine vasopressin fragment AVP(4-9) and the AVP antagonist [beta-mercapto-beta,beta-cyclopentamethylenepropionl(1),O-Et-Pyr(2),Val(4),Arg(8)] and were tested in an eight-arm radial maze for 60 sessions. All injections were given s.c. 30 min prior to testing. AVP(4-9) enhanced radial arm maze performance. AVP(4-9) treated animals showed enhancement in performance as well as increases in the rate of learning, indicating that they learned the task faster. Furthermore, the overall memory enhancement was due to improved working memory as well as to improved reference memory. These results cannot be explained in terms of changes in locomotor activity because an open field test revealed no differences between groups for both of these compounds. The AVP antagonist did not impair performance in the radial maze. It is concluded that AVP(4-9) has a more general effect on memory, one that is not limited to a specific type of memory. (C) 1997 Elsevier Science B.V.