Oxytocin (OT) is a neuropeptide well known for its role in the periphery, particularly in contraction of the uterus during labour and in ejection of milk during lactation. More recently OT has also been acknowledged for its influences on a wide range of social behaviors including social motivation and approach behavior (6, 7). In many species OT is also important for the formation and expression of social memory as well as for the regulation of aggression, sexual behavior and maternal care (8). In addition, similar to the role of the closely related peptide vasopressin for pair-bonding behavior in male voles, OT has a central role in the formation and regulation of pair-bonding behavior in female voles (9). In the socially monogamous and highly social prairie vole (Microtus ochrogaster) central infusions of OT facilitate (10), whereas a selective oxytocin receptor (OTR) antagonist inhibits, pair-bond formation in female individuals of this species (11). Moreover, there are notable differences in OTR distribution patterns among prairie voles and the non-monogamous montane voles (Microtus montanus), mainly in the brain region nucleus accumbens (12), and an
