Oxytocin activates the postpartum onset of rat maternal behavior in the ventral tegmental and medial preoptic areas.

Oxytocin binding (Bmax) was found to be higher in the ventral tegmental area (VTA) and the medial preoptic area (MPOA) at midparturition compared with Pregnancy Days 15-17 or Postpartum Days 5-7 in rat dams. Pup retrieval and assuming a nursing posture over pups were blocked in parturient dams by infusions of an oxytocin antagonist into the VTA or MPOA and by infusions of a vasopressin (V1) antagonist into the MPOA. These results implicate oxytocin in the VTA and MPOA and vasopressin in the MPOA, as well as a parturition-associated rise in oxytocin binding in these sites in the postpartum activation of maternal behavior.