Vasopressin and memory .2. Lesions to the hippocampus block the memory enhancing effects of AVP(4-9) in the radial maze

Previous work has shown that the arginine vasopressin fragment AVP(4-9) enhanced overall performance in the radial arm maze. This enhancement effect was due to improved working memory as well as to improved reference memory. The present study uses a behavioral approach to investigate whether these effects of vasopressin on memory are mediated by the hippocampus. Animals received either NMDA lesions to the hippocampus or sham operations and were then treated with AVP(4-9) or saline. The testing was performed in an eight-arm radial maze for 60 sessions; and all injections were given s.c. 30 min prior to testing. The hippocampal lesioned animals showed a marked deficit in working memory that was not ameliorated by AVP(4-9); however, the Improvement in reference memory produced by the compound was as large as in healthy animals. Since the AVP treatment did not differentiate between the two hippocampal groups, the memory enhancing effects of AVP(4-9) were blocked by hippocampal lesions. It is concluded that vasopressin has a more general effect on memory and that its site of action includes but is not limited to the hippocampus. (C) 1997 Elsevier Science B.V.