Background: Usual fluctuations of sex hormones during the estrous cycle in female mice affect the hippocampal neurogenesis. The hippocampus also comprises many steroid receptors suggesting the modulatory effects of gonadal hormones on the hippocampal plasticity. Sex differences at the level of structure and function of the hippocampus are mostly due to the fluctuations of steroid hormones during the estrous cycle. The purpose of this study was to investigate the morphological changes in hippocampal astrocytes and also the expression of glial fibrillary acidic protein (GFAP) at different phases of the estrous cycle.

Materials and Methods: In this study, different stages of the estrous cycle were determined in 6-8 week NMRI female mice by methylene blue-stained vaginal smears. The morphological changes of astrocytes in the hippocampus were investigated using GFAP immunohistochemistry. In addition to the morphological study, the expression of astrocytic marker was quantitatively evaluated.

Results: GFAP immunostaining showed the changes in the morphology of astrocytes and also in the serum level of estrogen during the estrous cycle. The highest concentrations of estrogen and GFAP reactivity were observed in the proestrus stage.

Conclusion: Different stages of the estrous cycle in female mice were associated with morphological changes of hippocampal astrocytes and the alternation in the serum level of estrogen.