Effects of oxytocin ablation on pup rescue, nursing behaviors and response to pup separation in early-to-mid postpartum mice.

Oxytocin, a neuropeptide hormone, is indispensable for milk ejection during nursing and is important for uterine contractions during parturition. The exact functions of oxytocin in postpartum maternal behaviors and motivations require further investigation. To this end, we characterized the role of oxytocin in components of maternal motivations during the mid-postpartum period, which has not been previously studied. To maintain suckling stimuli, postpartum oxytocin knockout (Oxt -/- ) and heterozygous (Oxt +/- ) littermates were co-housed with a wild-type lactating mother and its litter, and were examined for their ability to retrieve pups under standard or high-risk conditions, nursing behavior, maternal aggression towards an unfamiliar intruder, and motivation to regain contact with separated pups. One-third of Oxt -/- mothers exhibited prolonged parturition but were otherwise grossly healthy. Despite their inability to eject milk, Oxt -/- mothers displayed nursing behaviors for similar durations to Oxt +/- mothers during the second postpartum week. In addition, Oxt -/- mothers were essentially intact for pup retrieval under standard conditions and were motivated to stay close to pups, although they showed a mild decrease in maternal care under high-risk conditions and increased anxiety-like behaviors in pup-related contexts. The present findings indicate that oxytocin is dispensable for nursing behavior and maternal motivations, yet suggest that oxytocin may be relevant for stress resilience in the postpartum period.