Age and gender effects on microglia and astrocyte numbers in brains of mice.

The morphological changes that occur during normal brain aging are not well understood. This study used modern stereology to assess the effects of age and gender on total numbers of astrocytes and microglia in the hippocampal formation in C57Bl/6NNIA (B6) mice. Astrocytes and microglia were visualized using immunocytochemistry for glial fibrillary acidic protein (GFAP) and complement receptor 3 (Mac-1), respectively, and numbers of each cell type in dentate gyrus (DG) and CA1 regions were estimated using the optical fractionator method. The results reveal significantly greater ( approximately 20%) numbers of microglia and astrocytes in aged females compared to young female B6 mice. We also report that on average female B6 mice have 25-40% more astrocytes and microglia in DG and CA1 regions than age-matched male C57Bl/6J mice. Since astrocytes and microglia are thought to be targets of gonadal hormones, the effects of sex hormones and reproductive aging may be responsible for these findings.