Abstract
In terms of reproductive and social functions, vasoactive intestinal polypeptide (VIP) is best known as a major regulator of prolactin secretion in vertebrates and hence, as an essential contributor to parental care. However, VIP and its cognate VPAC receptors are distributed throughout the social behavior network in the brain, suggesting that VIP circuits may play important roles in a variety of behaviors. With the exception of VIP neuronal populations in the suprachiasmatic nucleus and tuberal hypothalamus (which regulate circadian rhythms and prolactin secretion, respectively), we have known very little about the functional properties of VIP circuits until recently. The present review highlights new roles for VIP signaling in avian social behaviors such as affiliation, gregariousness, pair bonding and aggression, and discusses recent advances in VIP's role as a regulator of biological rhythms, including the potential timing of ovulation, photoperiodic response and seasonal migration.