Time-related memory effects of vasopressin analogues in rats

The present study was designed to investigate critical time periods for the memory modulating effect of vasopressin and several analogues in rats using a passive avoidance test as the behavioral paradigm. AVP, AVP-(4-8) and AVP-(5-8) were more effective when given immediately after the learning trial (consolidation), while AVP-(1-8) (DGAVP) and AVP-(5-9) were more active when administered one hour prior to the retention test (retrieval). DDAVP and AVP-(4-9) were highly active both when given immediately after the learning trial or 1 hour before the retention test. The period between 12 and 18 hr after the learning trial appeared to be another sensitive period. Administration, in particular of DGAVP, and AVP-(5-9) at 12, 15, and 18 hr after the learning trial induced marked retention of the avoidance response at the 24 hr retention test. Injection at 6 and 21 hr after the learning trial was the least effective in facilitating passive avoidance latencies. The more stable analogue DDAVP facilitated avoidance latencies irrespective of the time of administration. Vasopressin and related peptides exert a long term effect on avoidance behavior. However, DGAVP and AVP-(5-9) facilitated passive avoidance behavior at the 24, 48, and 72 hr retention test if administered immediately after the learning trial. If injection was postponed till 15 hr after the learning trial, passive avoidance behavior was facilitated at the 24 hr retention test only.(ABSTRACT TRUNCATED AT 250 WORDS)