Intraspecific aggression in male hamsters is inhibited by intrahypothalamic vasopressin‐receptor antagonist

Abstract The present study examines the effect of the arginine vasopressin (AVP) receptor antagonist, d(CH 2 ) 5 Tyr(Me)AVP, on intraspecific aggression between pairs of male Golden hamsters in a neutral territory. Subjects drawn from a group of 24 animals were paired once each with novel partners from the group under each of three experimental conditions: 1) both members of a pair were microinjected into the anterior hypothalamus with saline (S/S), 2) one member of a pair was microinjected with AVP‐receptor antagonist and its partner with saline (A/S), and 3) both members of a pair were microinjected with AVP‐receptor antagonist (A/A). There were significantly (P < .01) fewer attacks during encounters between pairs of hamsters in the A/A condition compared to pairs in the A/S condition. Similarly, pairs in the A/S condition attacked significantly (P < .025) less often than pairs of hamsters in the S/S condition. These results confirm our earlier work showing that AVP‐receptor antagonist reduces intraspecific aggression. In addition, saline‐treated hamsters initiated significantly (P < .001) fewer attacks toward antagonist treated hamsters than would have been predicted if their opponent was not drug treated. These latter results suggest that hamsters microinjected into the anterior hypothalamus with an AVP‐receptor antagonist also elicit less aggression from conspecifics.