Maternal behavior stimulates c-fos activity within estrogen receptor alpha-containing neurons in lactating rats

Estradiol and other hormones are thought to be critical for the onset, but not maintenance, of maternal behavior in rats. Maternal behavior is instead maintained postpartum by tactile stimulation that darns receive during int eractions with pups, and many neural sites implicated in the control of mat ernal behavior show elevated c-fos activity in response to this stimulation . Many of these sites also contain neurons that express the alpha subtype o f the estrogen receptor (ER alpha). Because of possible interactions betwee n tactile stimulation from pups, c-fos, and ER alpha in the lactating rat b rain, we determined if populations of cells that show increased c-fos activ ity after maternal behavior in lactating rats also contain ER alpha. Dams w ere separated from their pups for 48 h beginning on day 5 postpartum. On da y 7 postpartum, experimental dams were reunited with pups and mother-litter interactions were observed for 60 min. Control darns received no pup stimu lation. Subjects were sacrificed 60 min later and brain sections were doubl e immunolabeled for the Fos and ER alpha proteins. As expected, the number of ER alpha-immunoreactive (ER alpha-ir) neurons did not differ between the two groups in the eight areas analyzed (lateral region of the lateral sept um, posterodorsal medial amygdala, dorsal and ventral medial preoptic area, dorsal and ventral bed nucleus of the stria terminalis, lateral habenula, and ventrolateral caudal periaqueductal gray). Consistent with previous rep orts, maternal dams had 2- to 7-fold more Fos-immunoreactive (Fos-ir) neuro ns in these sites compared with nonstimulated controls. Maternal darns had significantly more Fos-ir neurons that also contained ER alpha-ir in all si tes, with the greatest increases in the ventral medial preoptic area, later al habenula, and ventral bed nucleus of the stria terminalis. Between simil ar to 25 and 45% of the Fos-ir cells in the sites examined also expressed E R alpha. Thus, a substantial number of neurons that are genomically activat ed during maternal behavior contain ER alpha, raising the possibility that the postpartum display of maternal behavior can be influenced by ERa activi ty. Copyright (C) 2000 S. Karger AG.