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Abstract

Motherhood differentially affects learning and memory performance and this effect depends on reproductive experience. In turn, evidence suggests that the effects of oestradiol on learning and memory are mediated through binding to oestrogen receptors in the hippocampus and this is related to hippocampal neurogenesis. The present study investigated the effect of pregnancy and reproductive experience on ERα expression throughout the hippocampus as well as cell proliferation, cell survival, and cell death (as measured by pyknotic cells) in the granule cell layer of the hippocampus. Three groups of female Sprague-Dawley rats were used; virgin, primigravid and multigravid. All rats were injected with 5-bromo-2-deoxyuridine (BrdU; 200 mg/kg) on the afternoon of impregnation and at matched time-points in virgins. Rats were perfused either during early pregnancy (gestation day 1) or late pregnancy (gestation day 21) after BrdU injection. Results show that during late pregnancy females, whether first or second pregnancy, have fewer ERα-positive cells in the CA3 region of the dorsal hippocampus than virgin females. In addition during early pregnancy, females have significantly fewer pyknotic cells in the granule cell layer than virgin females. There were no other differences between groups in the number of ERα-positive, BrdU–positive or pyknotic cells. Future work aims to investigate the mechanisms and consequences of the alteration in ERα expression in the hippocampus during late pregnancy as well as the possible changes in ERβ expression at this time.