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

We examined two molecular responses to estrogen: reduction in estrogen rece ptor alpha (ER alpha) 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 ovar iectomized and then given silastic capsules containing 5% 17 beta-estradiol : or empty implants. and killed 4 days after implantation. By means of in s itu hybridization, we found that. in young rats, estrogen reduced ER alpha 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 ER alpha mRNA in the VMH and ARC of middle-aged and old rats was not statis tically significant. On the other hand in all regions the induction of PR m RNA by estrogen was at least as strong in middle-aged and old as in young r ats. The present study revealed that the induction of PR mRNA by estrogen i n the hypothalamus was not impaired with age but ER alpha mRNA in the VMH a nd ARC was significantly impaired with age: but not in the POA. (C) 2000 El sevier Science Ireland Ltd and the Japan Neuroscience Society. All rights r eserved.