Retention of rapid onset of maternal behavior during pregnancy in primiparous rats

Possible inhibitory effects of pregnancy upon the retention of maternal responsiveness in primiparous rats were examined by measuring behavioral latencies to respond to foster young in pregnant primiparous, nonpregnant primiparous, and virgin female rats. While high serum titers of progesterone associated with pregnancy are reported to inhibit rapid onset of maternal behavior in primigravid rats, findings in the present study demonstrate that the physiological state associated with a second pregnancy did not disrupt rapid reestablishment of maternal behavior. Specifically, 30–36 days after last exposure to their own young the median latencies to respond maternally to foster young ranged from 0.43 to 1.25 days for pregnant and nonpregnant primiparous rats. In contrast, virgin female rats with no prior maternal experience responded maternally significantly slower (median latencies: 4.33–4.75 days) than did primiparous females. These data suggest that after hormonal activation maternal responsiveness is retained independent of hormonal state.