Oxytocin and the molecular basis of monogamy

Previous studies in rats have implicated central oxytocin (OT) pathways in the onset of maternal behavior, female sexual receptivity, and the response of the pups to social separation. However, the rat is not ideal for studying effects of OT on attachment as rats fail to form selective, enduring social bonds. To study male-female pair bonds, our laboratory has focused on a microtine rodent, the prairie vole, which is monogamous and highly affiliative. Adult prairie voles form pair bonds after mating (with prolonged, repeated bouts of copulation). As mating releases OT in several species of mammals, we hypothesized that this release was important for pair bond formation in the prairie vole. Central administration of an OT antagonist (but not a V1 antagonist) prevents pair bonding without interfering with the mating behavior. Moreover, central infusion of OT (but not vasopressin, AVP) facilitates pair bonding n the absence of mating. In males, it is AVP (not OT) that appears necessary for pair bond formation. The pattern of OT (and AVP) receptor distribution in the prairie vole brain is entirely distinct from the pattern observed in the closely related non-monogamous montane vole. OT receptors (OTR) in these two species show virtually identical kinetics, specificities, and cDNA sequences (RNA from parturient uterus). In current studies, we are screening genomic libraries from prairie and montane voles to determine if species differences in OTR promoters account for the strikingly different patterns of regional expression in brain. These studies should ultimately provide insight into a neuroendocrine mechanism for pair bond formation.