Effects of arginine 8-vasopressin administered at different times in the learning of an appetitive visual discriminative task in mice

Abstract

A visual discrimination task was used to investigate the effect of the intra-hippocampal injection of arginine 8-vasopressin (AVP) in male Balb/c mice at different stages of the learning processes. The peptide was bilaterally microinjected at a dose of 25 pg per animal, i.e. 833 pg/kg, into the ventral hippocampus, in a volume of 0.3 μl 10 min before either the first or the second learning session, or immediately after the first or second learning session. Following pre-session administration of AVP, no effect of the peptide was observed on the session prior to which it was administered. On the other hand, 48 h after the pre-first session treatment, it seems that AVP animals had trouble learning the task. Following post-session injection of AVP, no effect was observed when the treatment was given after the first learning session and a tendency to improve performance was noted when the treatment was given after the second learning session. Thus, whatever time AVP was injected during learning, little or no effect was observed. These results and previous work on the same behavioral task showing a clear enhancing effect of the peptide on retrieval processes, suggest that prior experience or mnemonic context before AVP treatment is as important a factor in understanding the effects of AVP on memory processes as the administration route or the doses used.