Modulation of memory retrieval by pre-testing vasopressin: involvement of a central cholinergic nicotinic mechanism.

Lysine vasopressin (LVP, 0.003-1.0 mcg/kg, s.c.) and the central acting nicotinic cholinergic agonist nicotine (N, 1.0-30.0 mcg/kg, s.c.) enhanced, whereas the vasopressin receptor antagonist 1-beta-mercapto-beta, beta-cyclopentamethylenepropionic acid-2-(O-methyl)tyrosine, arginine vasopressin (AAVP, 0.01-0.3 mcg/kg, s.c.) impaired retention test performance on a one-trial step-through inhibitory avoidance task when injected into male Swiss mice 20 min before the retention test. Tests were done 48 h following training. In all cases, the effects on retention test performance were dose-dependent. Neither LVP, N nor AAVP when given prior to testing modified latencies to step-through of mice that had not received a footshock during training. These findings suggest that LVP, N and AAVP influence memory retrieval processes. The effect of LVP on memory retrieval was antagonized by the simultaneous administration of AAVP (0.01 mcg/kg, s.c.) or mecamilamine (5 mg/kg, s.c.), but not by hexamethonium (5 mg/kg, s.c.), atropine (0.5 mg/kg, s.c.) or methylatropine (0.5 mg/kq, s.c.). On the contrary, the effect of N was only prevented by mecamilamine (5 mg/kg, s.c.). These results suggest a modulatory role of vasopressin on the activity of central cholinergic nicotinic mechanisms which are critical for memory retrieval.