Oxytocin administration during early pair formation delays communal nursing in female house mice

Oxytocin manipulation has been implicated in the facilitation of social and cooperative behaviours, either through increasing positive and cooperative social interactions, or facilitating bond formation. Here we aimed to determine whether peripheral administration of oxytocin would affect the propensity of unrelated female house mice, Mus musculus domesticus, to cooperate. To investigate this, we used female house mice, with their cooperative ability to communally nurse offspring. Pairs of unfamiliar females received intraperitoneal injections of oxytocin over a 3-day cohabitation period. Following this initial phase, a male was introduced and allowed to mate with the females. We monitored how long it took females to establish and successfully cooperate in the raising of a communal litter. Oxytocin did not affect the females' ability to reproduce. However, oxytocin-treated females took significantly longer to establish a successful communal litter (with pups of both partners being weaned) than saline-treated control females. This delay in communal nursing was due to higher pup mortality and loss of first-born litters in the oxytocin group during their first reproductive event. We conclude that administration of exogenous oxytocin during the early stages of the female relationship delayed the tendency of female house mice to affiliate and cooperate in rearing a communal litter. Our findings contribute to the growing field of oxytocin-based studies and sheds light on the potential long-term effects of oxytocin during early pairwise social interactions.