Effect of pretraining administration of NC-1900, a vasopressin fragment analog, on memory performance in non- or CO2-amnesic mice.

In the present study, we investigated the facilitative effect of NC-1900, a new arginine vasopressin (AVP(1-9)) fragment analog, on memory performance in eight-arm radial maze or passive avoidance (PA) tasks in nonamnesic and amnesic (PA tasks only) mice. In the radial maze, all injections (subcutaneous) were given daily 60 min before each trail. NC-1900 (1 ng/kg)-treated animals showed enhancement of performance, and AVP(4-9) (1 microg/kg), an AVP(1-9) fragment, had similar effects, although the effective dose was 1000-fold higher. In the PA task, all drugs were administrated subcutaneously 60 min before the acquisition trial (Acq.), and the amnesic mice were exposed to CO(2) just after the Acq. NC-1900 (1 ng/kg) enhanced the memory performance of nonamnesic mice and ameliorated CO(2)-induced amnesia. AVP(4-9) (1 microg/kg) had a similar effect, although only at higher doses, while AVP(1-9) (0.1-1 microg/kg) had no effect. The facilitating effect of NC-1900 on nonamnesic mice was inhibited by coinjection [Pmp(1)-Tyr(Me)(2)]-AVP (Pmp,Tyr-AVP; 1 microg/kg), a V(1A) antagonist, but not by OPC-31260, a vasopressin(2) (V(2)) antagonist. The effect of NC-1900 on CO(2)-induced amnesia was also decreased by coinjection of Pmp,Tyr-AVP or [deamino-Pen(1), Me-Tyr(2)]-AVP (10 microg/kg), both of which are V(1) antagonists. These results suggested that NC-1900 has a more potent effect on facilitation of memory via the V(1A) receptor than AVP(4-9) in non- and CO(2)-amnesic conditions.