The role of the vasopressin 1b receptor in aggression and other social behaviours.

While the importance of vasopressin (Avp) in the neuroendocrine regulation of behaviour is clear, most of Avp's effects on behaviour have been linked to its action via its 1a receptor (Avpr1a) subtype. There is, however, emerging evidence and cross-species consensus that the vasopressin 1b receptor (Avpr1b) is also important in mediating the effects of Avp on behaviour. The Avpr1b is highly expressed in the anterior pituitary where it is thought to play a role in the neuroendocrine response to stress. The Avpr1b is also prominently expressed in the pyramidal cells of the CA2 hippocampal area. Interestingly, in mice, Avpr1b mRNA within the pyramidal neurons of the CA2 field is unaffected by restraint stress or adrenalectomy. Avpr1b knockout mice (--) have provided strong, consistent evidence that the Avpr1b plays a critical role in the regulation of social behaviour. Avpr1b(-/-) mice display reduced levels of social forms of aggression, reduced social motivation and impaired social memory (including the Bruce effect). Avpr1b(-/-) mice, however, have normal main olfactory ability, spatial memory and defensive and predatory behaviours. Mice lacking a functional accessory olfactory system display many of these same behavioural deficits, suggesting that Avpr1b(-/-) mice may have a deficit in the processing, perception and/or integration of olfactory stimuli detected by the accessory olfactory system. We suggest that the role of the Avpr1b is to couple socially relevant accessory olfactory cues with the appropriate behavioural response. Furthermore, given its prominence in the CA2 field of the hippocampus, we hypothesize that Avpr1b may be important for the formation or recall of memories that have an olfactory-based social component.