Intracerebroventricular administration of oxytocin and maternal behavior in rats after prolonged and acute steroid pretreatment.

The role of oxytocin in the initiation of maternal responsiveness in rats was reexamined. Oxytocin (400 ng in 4 microliters saline) or saline alone was infused into the cerebral ventricular system of ovariectomized steroid-primed virgin females. Subjects received 2 weeks of exposure to ovarian steroids via subcutaneously implanted Silastic capsules (Experiment 1) filled with 17 beta-estradiol (1 mm; from Day 1) and progesterone (15 mm; Days 3-13), or they received a single injection of estradiol benzoate (100 micrograms/kg) 48 hr before intracerebral infusion (Experiment 2). Behavioral testing began immediately after oxytocin or saline administration. Latencies to retrieve, group, and crouch over foster young were scored. Contrary to previous reports, oxytocin did not stimulate a rapid onset of maternal responsiveness. The mean latencies to exhibit pup-oriented behaviors ranged from 2.8 to 5.1 days in all groups, regardless of treatment.