Age- and ovarian hormone-dependent regulation of mRNA expression of estrogen receptors in the rat frontal cortex. We measured age- and hormone-dependent changes by TaqMan-based quantitative real-time PCR in mRNA expression of Esr1 (A) and Esr2 (B), encoding ERα and ERβ, respectively. Error bars show SD of six independent measurements. Asterisks indicate changes with statistical significance: *corresponds to 0.01<P < 0.05, ** to 0.001<P < 0.01 and *** to P < 0.001. Y, young rat; M, middle-aged female rat; M/OVX, middle-aged ovariectomized (OVX) rat; M/OVX+E2, middle-aged OVX rat with 17β-estradiol (E2) replacement.