Effects of parturition on immediate early gene protein expression within the brains of female rats

The mother–infant interaction that occurs immediately postpartum period has important consequences including changes in protein expression in the astrocytes within cingulate cortex area 2 (Cg2). Because increased expression of basic fibroblast growth factor (bFGF) and glial fibrillary acidic protein (GFAP) has been associated with increased neuronal activity we used immediate early gene expression to evaluate the effects of parturition plus interaction with pups during and immediately after delivery to investigate patterns of neural activation in a number of brain areas including Cg2. In the first experiment, we compared levels of immunoreactivity of two immediate early genes: c-Fos and egr-1, among three groups of animals: Cycling, Late Pregnant, and rats perfused 1.5 h postpartum. The average number of Fos and egr-1-ir cells/section were calculated for the Parietal Cortex (ParCx), nucleus accumbens (NAc), medial amygdala (MEA), medial preoptic area (MPOA), supraoptic area (SON) and Cg2. In a second experiment, Fos-ir induction was compared between cycling rats and rats at hour 3 postpartum. Contrary to our hypothesis no changes in expression of either immediate early gene were observed in Cg2. In Experiment 1 however, an upregulation in both early genes was seen in the ParCx, and, of Fos-ir only in the MPOA of postpartum animals. A decrease in Fos-ir was seen in the NAc of late pregnant animals and no significant differences were seen in either immediate early gene expression within the MEA. Interestingly, areas that showed a significant increase in neuronal activation project to Cg2. The possibility of an interaction between these changes and glial cells in Cg2 is discussed.