Changes in estrogenic regulation of estrogen receptor α mRNA and progesterone receptor mRNA in the female rat hypothalamus during aging: an in situ hybridization study

Abstract We examined two molecular responses to estrogen, reduction in estrogen receptor α (ERα) mRNA and increase in progesterone receptor (PR) mRNA, in the hypothalamus of 3- (young) and 10-month-old (middle-aged) cycling, and 15-month-old (old) acyclic, Fischer 344 female rats. The rats were ovariectomized and then given silastic capsules containing 5% 17β-estradiol, or empty implants, and killed 4 days after implantation. By means of in situ hybridization, we found that, in young rats, estrogen reduced ERα mRNA in both the ventromedial hypothalamus (VMH) and arcuate nucleus (ARC) but not in the preoptic area (POA). In contrast, the effect of estrogen on ERα mRNA in the VMH and ARC of middle-aged and old rats was not statistically significant. On the other hand in all regions the induction of PR mRNA by estrogen was at least as strong in middle-aged and old as in young rats. The present study revealed that the induction of PR mRNA by estrogen in the hypothalamus was not impaired with age but ERα mRNA in the VMH and ARC was significantly impaired with age, but not in the POA.