Hormonal influences during the ontogeny of maternal behavior in female rats.

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Abstract
During the pubertal transition period, the number of days of continuous pup exposure needed to induce maternal behavior in nonpregnant white rats (i.e., the sensitization latency) decreases in females and increases in males. The influence of ovarian hormones on sensitization latencies at different periods in ontogeny and the olfactory inhibition of maternal behavior, maternal nest building and pup retrievals from a T-maze extension of the home cage were studied. Females ovariectomized before puberty failed to show a decline in sensitization latencies when tested 3.5 wk postoperatively. Females ovariectomized during and after puberty had significantly longer latencies than sham operates when tested 8 or more weeks later. Advancing puberty by injecting pregnant mare''s serum on day 21 did not reliably shorten latencies, but modified the effects of prior handling on latencies. Interrupting olfaction by intranasal ZnSO4 reduced latencies of ovariectomized females, males and intact females. Ovariectomized females, after becoming maternal, build less compact maternal nests, and fewer retrieved pups from a T-maze than did sham operates. Estradiol benzoate prior to pup exposure significantly reduced sensitization latencies of both pre- and postpubertally ovariectomized females, increased the proportion retrieving pups from the T-maze, and tended to increase maternal nest ratings. Ovarian hormones, primarily estrogen, exert a tonic facilitatory influence upon maternal responsiveness, beginning at puberty.