Polymodal dose-response curve for oxytocin in the social recognition test.

Available data concerning the effect of oxytocin on memory are often inconsistent. In the present study it was found that oxytocin, intracerebroventricularly injected to adult male rats in a dose range of 1 fg-10 ng/rat immediately after a 5-minute encounter with a juvenile, significantly reduces the social investigation time of the adult rat towards the same juvenile during a second encounter (120 min later) with two peaks of activity, at 10 fg and 1 ng/rat. Larger doses of oxytocin were ineffective. The oxytocin antagonist d(CH2)5Tyr(Me)-Orn8-vasotocin, injected 5 min before oxytocin by the same route and at the same doses, while being ineffective per se, completely abolished the memory-improving effect of a low dose of oxytocin (1 ng/rat) and, on the other hand, turned into memory-improving the effect of a high dose of oxytocin (500 ng/rat).