Improvement of memory by a vasopressin fragment: importance of individual differences in mnemonic function

Three studies examined the effect of AVP4-9 on memory in an appetitively motivated task (the radial maze) to ascertain the generality of the mnemonic effects seen with vasopressin analogues in avoidance paradigms. Both pre- and posttrial administration of this vasopressin fragment significantly alleviated the forgetting seen in the control condition. However, a significant relation was observed between the proficiency of the rats and the degree to which their performance was improved by the posttrial AVP4-9 treatment. The more proficient subjects did not benefit from this treatment despite the fact that their performance provided evidence of significant forgetting. This pattern of results suggests that physiological differences of animals varying in mnemonic ability may account for their disparate response to the peptide treatment. The present findings support vasopressin's putative mnemonic role but indicate that exogenous administration of vasopressinlike peptides may improve memory only in certain subgroups, and possibly only under particular testing conditions.