Effects of estrogen and progesterone on luteinizing hormone-releasing hormone messenger ribonucleic acid levels: consideration of temporal and neuroanatomical variables.

Abstract

We examined temporal effects of estradiol (E2) and progesterone on cellular levels of LHRH messenger RNA (mRNA) in several brain regions. Female rats were ovariectomized and implanted with SILASTIC brand capsules of oil or E2 1 week later (day 0). Progesterone capsules were implanted on the morning of day 2. Using in situ hybridization histochemistry, we found that on day 2, E2 induced a complex temporal pattern of changes in LHRH mRNA levels. Levels in ovariectomized E2-treated animals were lower than control values in the morning, then increased before the LH surge and declined again as the surge waned. The magnitude of these changes was greatest in neurons of the rostral preoptic area/organum vasculosum of the lamina terminalis, but a similar pattern was detected in neurons of the medial preoptic area. No changes were seen in neurons of the diagonal band of Broca. Our finding that the effect of E2 on LHRH mRNA levels depends on the time of day and brain region examined largely reconciles discrepancies among previous studies. Progesterone triggered events that advanced the onset of and augmented the LH surge, but had no effect on LHRH mRNA levels. These findings support the hypothesis that the mechanism by which E2 induces region-specific changes in LHRH mRNA levels before the surge is separate from the progesterone-amplified mechanism that induces LHRH release.

Effect of Estrogen on Hypothalamic Transforming Growth Factor Alpha and Gonadotropin-Releasing Hormone Gene Expression in the Female Rhesus Monkey

“…Using in situ hybridization to quantitate gene expression, several groups [22, 23, 24] have also demonstrated that estradiol replacement decreases GnRH gene expression in the ovariectomized rat during the morning hours when the negative feedback action of estradiol on gonadotropin secretion is manifest [25]. An inhibitory action of estradiol on GnRH gene expression at this phase of the light-dark cycles, however, has not always been a universal finding in the rat [26].…”

Suppression of Vasoactive Intestinal Polypeptide in the Suprachiasmatic Nucleus Leads to Aging-Like Alterations in cAMP Rhythms and Activation of Gonadotropin-Releasing Hormone Neurons

“…Using modified stainless steel needles, the rMPN (17 gauge), SCN (21 gauge), and cortex (17 gauge) were microdissected and stored at Ϫ80°C until processed. The organun vasculosum of the lamina terminalisrMPN contains the subpopulation of GnRH neurons that regulate LH secretion (Swanson, 1987;Petersen et al, 1995). We chose to examine these areas based on previous work showing that VIP predominately innervates the GnRH neurons in this region and that GnRH neurons that are lateral to these regions were not included (van der Beek et al, 1997;Krajnak et al, 2001) Stereotaxic surgery.…”

A Role for Hypothalamic Astrocytes in Dehydroepiandrosterone and Estradiol Regulation of Gonadotropin-Releasing Hormone (GnRH) Release by GnRH Neurons

“…However, steroids have not been shown to affect secretion of GnRH from GT1–7 cells and E2 caused a slight but significant inhibition of GnRH gene expression [55]. This is in contrast to the stimulatory effect of E2 on GnRH gene expression [56, 57, 58, 59, 60, 61]and secretion [8]in vivo supporting our proposal that E2 acts to induce GnRH through actions on astrocytes found in vivo but not present in the GT1–7 cultures.…”