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 receptor 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 ovariectomized and then given silastic capsules containing 5% 17beta-estradiol. or empty implants, and killed 4 days after implantation. By means of in situ 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 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 ER alpha mRNA in the VMH and ARC was significantly impaired with age, but not in the POA.

Hypothalamic pro-opiomelanocortin mRNA is reduced by fasting and [corrected] in ob/ob and db/db mice, but is stimulated by leptin.

Reduction in the activity of the alpha-melanocyte-stimulating hormone (alpha-MSH) system causes obesity, and infusions of alpha-MSH can produce satiety, raising the possibility that alpha-MSH may mediate physiological satiety signals. Since alpha-MSH is coded for by the pro-opiomelanocortin (POMC) gene, we examined if POMC gene expression would be inhibited by fasting in normal mice or in models of obesity characterized by leptin insufficiency (ob/ob) or leptin insensitivity (db/db). In wild-type mice, hypothalamic POMC mRNA was decreased > 60% after a 2-day fast and was positively correlated with leptin mRNA. Similarly, compared with controls, POMC mRNA was decreased by at least 60% in both db/db and ob/ob mice. POMC mRNA was negatively correlated with both neuropeptide Y (NPY) and melanin-concentrating hormone (MCH) mRNA. Finally, treatment of both male and female ob/ob mice with leptin stimulated hypothalamic POMC mRNA by about threefold. These results suggest that impairment in production, processing, or responsiveness to alpha-MSH may be a common feature of obesity and that hypothalamic POMC neurons, stimulated by leptin, may constitute a link between leptin and the melanocortin system.

Changes in preproenkephalin messenger RNA level in the rat ventromedial hypothalamus during the estrous cycle.

To gain a better understanding of the relationship between the female rat reproductive system and preproenkephalin (PPE) expressing neurons under physiological conditions, we examined changes in PPE mRNA levels in the mediobasal hypothalamus during the rat estrous cycle by means of northern blotting and in situ hybridization histochemistry (ISHH). In the Northern blot studies, we found that PPE mRNA levels in the mediobasal hypothalamus were significantly increased by noon of proestrus compared to those in the morning and stayed high until diestrus day 1, and returned toward low levels on diestrous day 2. In contrast, measured as controls, glyceraldehyde-3-phosphate-dehydrogenase mRNA levels were significantly higher on proestrus regardless of time of day compared to diestrus day 2, and levels of calcineurin mRNA on proestrous and estrous were significantly lower than diestrous day 1 and day 2. ISHH studies revealed that these changes in PPE mRNA levels were specific in the ventromedial hypothalamic nucleus pars ventrolateralis (VMHVL), since we could not see any significant changes in signal in other parts including ventromedial hypothalamic nucleus pars dorsomedialis and arcuate hypothalamic nucleus. In the VMHVL, PPE mRNA levels in the afternoon of proestrous were significantly higher than those in the afternoon of diestrous day 2 whereas no significant change in PPE mRNA was observed in the caudate-putamen. The present study provides additional information relevant to possible implications of PPE gene expression in female reproductive systems, since changes in PPE mRNA levels may be associated with estrogen as well as progesterone or other hormonal concentrations during the estrous cycle.(ABSTRACT TRUNCATED AT 250 WORDS)

Estrogen increases HIP-70/PLC-alpha messenger ribonucleic acid in the rat uterus and hypothalamus.

In the ventromedial hypothalamus (VMH) of female rats, estrogen induces a protein isoform, HIP-70, whose sequence is identical to a protein reported to be phosphoinositol-specific phospholipase-C-alpha (PLC-alpha). Since previous studies explored induction only at the protein level, we examined both the distribution of HIP-70/PLC-alpha mRNA in various tissues and the effects of estrogen on HIP-70/PLC-alpha mRNA. Using slot blot analysis, we found that HIP-70/PLC-alpha mRNA is most abundant in pituitary, uterus, and VMH of female rats compared with other brain regions and tissues. Since these are target tissues for estrogen action, we examined the effects of estrogen on the abundance of HIP-70/PLC-alpha mRNA in these areas. Levels of HIP-70/PLC-alpha mRNA increased greater than 3-fold in the uterus 18 h after estrogen treatment. HIP-70/PLC-alpha mRNA in the VMH also increased about 35% 3 h after estrogen treatment. In situ hybridization corroborated the induction in the ventrolateral ventromedial hypothalamus. No effect of estrogen was observed on pituitary PLC-alpha mRNA. These results indicate that estrogen does increase HIP-70/PLC-alpha mRNA levels in certain tissues. Since the induction of HIP-70/PLC-alpha mRNA in VMH is relatively modest compared to the much larger induction of the HIP-70 protein isoform, regulation of HIP-70/PLC-alpha may entail both pre- and posttranslational mechanisms. Because members of the PLC family catalyze the hydrolysis of phosphatidyl inositol, potentially activating several secondary mediators (intracellular Ca2+, protein kinase-C, and eicanosoids), this second messenger pathway may mediate some effects of estrogen.