The behavioral effect of vasopressin in the ventral hippocampus is antagonized by an oxytocin receptor antagonist

[Arg(8)]vasopressin improved long-term retrieval processes and relearning i n a go-no go visual discrimination task when bilaterally microinjected at a dose of 25 pg/animal into the ventral hippocampus of mice, 10 min prior to the retention session. We had shown that this enhancing effect is antagoni zed by pretreatment with equal or lower doses (25 pg or 1 ng) of the vasopr essin V-1 receptor antagonist, (d(CH2)(5)Tyr(Me)-vasopressin). The present study was an attempt to determine whether the vasopressin V-2 receptor anta gonist or oxytocin receptor antagonist is as effective as the vasopressin V -1 receptor antagonist to block the behavioral effect of vasopressin in the ventral hippocampus. We tested the effect of 25 pg of [d(CH2)(5)-D-Ile(5), Ile(4),Arg(8)]vasopressin, a vasopressin V-2 receptor antagonist, and [d(CH 2)(5),Tyr(Me)(2),Thr(4),Tyr-NH29]ornithine vasotocin, an oxytocin receptor antagonist, under the same experimental conditions as those used to test th e effect of the vasopressin V-1 receptor antagonist. The results showed tha t the vasopressin V-2 receptor antagonist microinjected into the ventral hi ppocampus did not alter the enhancing effect of vasopressin on retrieval an d relearning. In contrast, the oxytocin receptor antagonist blocked the vas opressin-enhancing effect on retention processes. We can conclude from the data that both vasopressin V-1 receptors and oxytocin receptors seem to be involved in the enhancing effect of vasopressin on memory retention. In con trast, the vasopressin V-2 receptors do not seem to be involved in the effe ct of the peptide. (C) 1998 Elsevier Science B.V. All rights reserved.