Expression of Fos-like immunoreactivity in the preoptic area of maternally behaving virgin and postpartum rats.

This study uses Fos immunocytochemistry to show that the medial preoptic area and ventral bed nucleus of the stria terminalis are activated in maternally behaving female rats. In Experiment 1, virgin female rats that showed maternal behavior toward pups had more cells in these regions that expressed Fos-like immunoreactivity than did virgin females that were not maternally responsive. In Experiment 2, postpartum rats that were exposed to pups and showed maternal behavior had more Fos-labeled cells in these regions than did postpartum rats exposed to candy. Evidence also indicated that functional modifications in the medial amygdala were related to the changes in Fos expression observed in the preoptic area and ventral bed nucleus of the stria terminalis.