Table 1.

Summary of estrogen receptor expression changes during aging. OVX ovariectomized, E2 estradiol, SON supraoptic nucleus

ER subtype, location	Experimental group	Methods	Main finding(s)	Reference
ERα and ERβ, brain	Female Sprague-Dawley rats; intact vs. OVX E2-treated; young (3–4 months), middle-aged (11–12 months), old (19–24 months)	In situ hybridization for ERα and ERβ, quantify mRNA levels	ERα: mRNA in periventricular preoptic, medial preoptic, ventromedial, and arcuate nuclei with levels decreased in only periventricular preoptic nucleus of old rats ERβ: mRNA in various brain regions with a decrease in level only observed in the cerebral cortex and SON of OVX E2-treated middle-aged and old rats	[39]
ERα, brain	Female Sprague-Dawley rats; young (3–4 months, n = 11) vs. aged (22–23 months, n = 10); OVX and E2 replacement implant	Postembedding immunogold and quantification	Subcellular distribution of ERα in the hippocampus and corresponding decreased responsiveness to E2 in female aged rats	[40]
ERα, cerebral blood vessels	Fischer 344 female rats; 3 months intact vs. OVX vs. OVX E2-treated	Immunohistochemistry, immunoblot/Western blot analyses	Multiple forms of ERα identified and localized in both smooth muscle and endothelial cells of cerebral blood vessels in female rats All forms of cerebral blood vessel ERα decreased after OVX but increased after chronic E2 treatment	[41]