The capacity to develop maternal behavior is enhanced during aging in rats

Abstract

The induction of maternal behavior (MB) in response to stimulation by pups was studied in aged rats (19–20 months old). We used virgin female rats, neon androgenized female rats and male rats. Both groups of female rats showed a constant estrous vaginal smear. Maternal responsiveness was compared with that of young rats (3–4 months old). Normal and androgenized female aged rats showed a very high percentage of immediate maternal responsiveness and 100% of the rats were fully maternal within 24 hr of testing. The percentage of cyclic and androgenized young rats showing MB were significantly lower. Chronic ovariectomy performed 17 months before testing but not acute ovariectomy abolished MB. Estrogen treatment (5 μg 15 hours before pup presentation) to chronically ovariectomized aged rats was not sufficient to reestablish significantly t capacity of the normal female aged rats to become short-latency maternal. Young and aged male rats showed no difference in maternal responsiveness to the presence of foster pups. The percentage of maternal aged male rats was significantly lower than that of the normal and androgenized aged female rats, whereas young male and female rats showed a similar level of MB, indicating a sex difference in the development of MB with age. In conclusion the high percentage of rats becoming maternal and the short-latency maternal responsiveness in aged female rats appears to be the result of a prolonged estrogen and/or prolactin stimulation.