Plasticity in the maternal circuit: Effects of pup exposure and retention interval on astrocyte numbers in primiparous and multiparous animals

Experience with pups postpartum enhances the expression of maternal behavior up to a month later. These long-term behavioral changes are accompanied by long-term changes in immunohistochemical expression of neuronal and glial proteins, specifically Fos, Protein Kinase C (PKC), and Glial Fibrillary Acidic Protein (GFAP) in the medial preoptic area.; The goal of the present study was to examine astrocytic changes (as assessed by Glial Fibrillary Acidic Protein) following varying amounts of maternal experience and over a longer time-frame. Primiparous and multiparous animals (2x pregnant), were given a brief exposure (either 2 or 24 hours) to 1-3 day old rat pups the day following parturition, or were given a similar control manipulation. Animals were then sacrificed and subjected to immunohistochemistry either 1 day, 5 days or 10 days following postpartum pup exposure.; A main effect for parity in favor of multiparous animals was seen in the MPOA. An opposite effect for parity was found in the medial and lateral habenula, as well as the medial amygdala (MEA), with primiparous animals having higher numbers of astrocytes than multiparous animals. Parity differences in the MPOA were slight at one day after exposure/manipulation, but were significantly different at day five. At day ten, parity differences were seen, but were dependent upon pup exposure. In contrast, in the MEA and habenula nuclei, parity differences were most substantial at day one.; The results suggest that primiparous and multiparous animals differ not only in what they learn, as evidenced from the dissociation between MPOA and MEA/habenula brain regions, but also differ in terms of when learning takes place.