Age- and hormone-dependent alteration in the mRNA expression of widely used microglia marker genes in the frontal cortex of middle-aged female rats. Real-time PCR demonstrated age- and ovarian hormone-related increase in the transcription of Cd11b (A), Cd18 (B), Cd45 (D) and Cd86 (F). 17β-estradiol (E2) replacement attenuated these changes. Cd40 (C) and Cd74 (E) expression did not change after ovariectomy. Error bars show SD of six samples for each group. Statistical significance of the alterations in different groups compared to middle-aged female rats (M) was analyzed by analysis of variance (ANOVA) with Newman-Keuls post hoc test, and considered significant at P < 0.05. Asterisks indicate significant changes: *corresponds to 0.01<P <0.05, ** to 0.001<P <0.01 and *** to P < 0.001. Y, young rat; M/OVX, middle-aged ovariectomized (OVX) rat; M/OVX+E2, middle-aged OVX rat treated chronically with E2.