Elevated Fos-like immunoreactivity in the brains of postpartum female prairie voles, Microtus ochrogaster

This study investigated the expression of the protein product of the immedi ate early gene c-fos in the brains of female prairie voles (Microtus ochrog aster) in association with pregnancy and postparturient activities includin g maternal behavior, lactation and postpartum estrus. Fos expression was as sessed in female voles that were late in pregnancy, nonpregnant or at one o f three different rimes postpartum (0-8, 12-24, and 24-48 h, respectively). A significant increase in the number of cells displaying Fos immunoreactiv ity (Fos-ir) was observed during the 0-8 h and 12-24 h postpartum time peri ods in the accessory olfactory bulbs, medial preoptic area, hypothalamus (s pecifically, the supraoptic nucleus, ventromedial hypothalamus, and paraven tricular nucleus), lateral septum, bed nucleus of the stria terminalis, and primary somatosensory area of the brain. The number of Fos-ir cells decrea sed after 24 h postpartum. There were no significant changes in Fos-ir cell numbers in the primary olfactory bulbs, hippocampus, or caudate putamen. T he neural activation of the medial preoptic area, accessory olfactory bulbs , hypothalamus, and bed nucleus is consistent with reports in rats of Fos i nduction associated with the onset of maternal behavior. In voles postpartu m estrous behavior begins and ends 0-12 h after parturition. Maternal behav ior, including lactation, is initiated at the Same time but persists for se veral weeks. The highest Fos-ir cell numbers reported here coincide with th e timing of postpartum estrous behavior in this species.