The output of the hippocampus is inhibited during social behavior in the male rat.

During sexual behavior in the male rat, peptidergic cells in the medial amygdaloid nucleus become active and release a vasopressin-like peptide. The present experiments were designed to examine hippocampal changes as a result of this peptide's action during sexual behaviors. Chronic field-potential recordings from the hippocampus of male rats were acquired in a wide variety of social and nonsocial circumstances. Hippocampal responses that resemble the known action of the vasopressin-like peptide were seen only with social stimuli such as sexual stimuli and stimuli that led to aggressive behavior between males. The results show that the occasions of peptide action in the hippocampus correlate with the occasions of peptide release as determined by recording from the peptidergic cell bodies. The results are interpreted to indicate that the amygdala projection to the hippocampus has a special role to play in social behavior.