Failure of vasopressin to enhance memory in a passive avoidance task in rats.

Several authors have suggested that the neurohypophysial hormone arginine-8-vasopressin (AVP) facilitates both the consolidation and the retrieval of memory. This conclusion has relied mainly on the finding that AVP increases the latency of re-entry into a box where shock has previously been encountered, that is, in a passive avoidance task. Our results do not support this interpretation. On the contrary, we found that post-trial, intraventricular (i.t.) administration of AVP (1 ng in 1 microliter) produced relatively short as well as long latencies (a bimodal effect), suggesting that the peptide acts on motivational processes, for example by increasing arousal.