The temporal course of expression of c-Fos and Fos B within the medial preoptic area and other brain regions of postpartum female rats during prolonged mother--young interactions.

Maternal behavior is associated with an increase in the expression of c-Fos and Fos B within neurons of the medial preoptic area (MPOA) and ventral bed nucleus of the stria terminalis (vBST). Whether this increase wanes as the duration of mother-young interaction increases is unknown. By varying the length of mother-young interactions in postpartum rats, the authors found that within the MPOA/vBST, the levels of both c-Fos and Fos B, once elevated, remained significantly above control levels through 47 hr of pup exposure. The persistence of c-Fos and Fos B within the MPOA/vBST of females that remained with pups was almost unique in that only one other neural area, the anterior magnocellular part of the paraventricular hypothalamic nucleus, showed such a response. Because MPOA/vBST neurons are essential for maternal behavior, the results suggest that c-Fos and Fos B expression within these regions may be necessary to maintain their normal functional activity.