EFFECTS OF ARGININE(8)-VASOPRESSIN ADMINISTERED AT DIFFERENT TIMES INTHE LEARNING OF AN APPETITIVE VISUAL DISCRIMINATIVE TASK IN MICE

A visual discrimination task was used to investigate the effect of the intra-hippocampal injection of arginines-vasopressin (AVP) in male Ba lb/c mice at different stages of the learning processes. The peptide w as bilaterally microinjected at a dose of 25 pg per animal, i.e. 833 p g/kg, into the ventral hippocampus, in a volume of 0.3 mu l 10 min bef ore either the first or the second learning session, or immediately af ter the first or second learning session. Following pre-session admini stration 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 lea rning the task. Following post-session injection of AVP, no effect was observed when the treatment was given after the first learning sessio n and a tendency to improve performance was noted when the treatment w as given after the second learning session. Thus, whatever time AVP wa s injected during learning, little or no effect was observed. These re sults and previous work on the same behavioral task showing a clear en hancing effect of the peptide on retrieval processes, suggest that pri or experience or mnemonic context before AVP treatment is as important a factor in understanding the effects of AVP on memory processes as t he administration route or the doses used. (C) 1997 Elsevier Science B .V.