The role of limbic vasopressin and oxytocin in social recognition.
Young male rats were exposed two times for 5 min, to older male rats with an interval of 30 min in the anti-vasopressin serum experiments and with an interval of 120 min in the anti-oxytocin serum experiments. The time spent by the older rats with social investigation of the younger animal was scored during the two encounters. In placebo-treated animals the time spent on social investigation of the younger animal during the second encounter at 30 min is significantly shorter than during the first one (social recognition). However, intracerebroventricular or local application of anti-vasopressin serum in the dorsal or ventral hippocampus or in the dorsal septal area, but not in the n. olfactorius, results in similar periods of time spent for social investigation during the two encounters. Thus, endogenous vasopressin in the dorsal and ventral hippocampus and in the dorsal septal region plays a physiological role in social recognition/memory. In placebo-treated rats the time spent on social investigation of the younger animal during the second encounter at 120 min is similar to that during the first encounter. However, local administration of anti-oxytocin serum in the ventral hippocampus, but not in the dorsal hippocampus, nor in the n. olfactorius or the septal area, results in shorter investigation times during the second encounter. Thus, taken together the presence or local release of vasopressin and oxytocin in the ventral hippocampus and that of vasopressin (but not oxytocin) in the dorsal hippocampus and dorsal septal area are of physiological importance for social recognition.