Further evidence for a dissociation of peripheral and central effects of vasopressin

The influence of AVP on open field behavior was studied at 15 and 60 min after s.c. injection. AVP injected 15 min before the session modified all patterns of behavior in the open field. Locomotion and rearing along the wall were significantly decreased, while locomotion in the center was increased. AVP also reduced grooming and defecation. Injection 60 min prior to the session did not affect the open field behavior. AVP increased resistance to extinction of pole-jumping avoidance behavior independent of whether the first acquisition session was given at 20 min after injection at the height of the behavioral depression or at 65 min when these effects had disappeared. However, the rats trained at 20 min after AVP administration made significantly more avoidances on the second day of acquisition training than did the controls. The vasopressin fragment DGAVP, which exhibits almost no peripheral effects, did not cause gross behavioral changes in the open field as did AVP, but it did increase resistance to extinction of the avoidance response comparable to that of AVP. These findings indicate that, although peripheral effects may contribute to the effects of AVP on modulation of memory processes, such effects are not essential.