Effects of maternal hormones on 'timidity' and attraction to pup-related odors in female rats.

The present study was designed to determine whether changes in 'emotionality' and responses to odorants that occur in the postpartum rat are due to the same configuration of hormones that facilitate the expression of maternal behavior. Ovariectomized females were implanted with silastic capsules containing progesterone and estradiol or cholesterol for a 19-21 day period and were tested 1 or 7 days later for emergence behavior, ambulation in the open-field and responses to nesting-material containing different odorants. All females were given two tests in which clean nest-material was presented and two with lactating nest material. In comparison to cholesterol animals hormonally primed animals emerged more rapidly into the open-field, crossed more squares while in the field and spent more time around the odor stimulus. Moreover, hormonally primed animals crossed more squares in the region around the odor source when lactating nest odor was present than when it was not and, under the lactating nest odor condition, crossed more squares in the stimulus region than did any other group. This study suggests that the Bridges' regimen of progesterone and estradiol reduces general 'timidity,' reflected in open-field performance, and increases attraction to pup-related odors. These hormone-induced behavioral changes may well contribute to the heightened maternal responsiveness also produced by these hormones.