Induction of Galanin mRNA in GnRH Neurons by Estradiol and its Facilitation by Progesterone

Abstract

On the day of proestrus in the rat, rising plasma levels of estradiol (E) act in concert with progesterone (P) to trigger a preovulator y release of gonadotropins. Cellular levels of galanin mRNA in GnRH neurons are increased in association with the proestrous surge of gonadotropin secretion; however, the relative contribution made by E and P to the induction of galanin mRNA expression in GnRH neurons is unknown. We investigated the role of E and P in the induction of galanin gene expression in GnRH neurons by examining the effects of different combinations of E (estradiol benzoate; 50 mg and P (5 mg)) on the LH surge and the concomitant induction of galanin mRNA in GnRH neurons. We sacrificed ovariectomized adult rats after 1 of 4 treatments: Group 1: vehicle control (n=6); Group 2: P alone (n= 7) Group 3: E alone (n=7); Group 4: combined E/P (n=6); the animals were killed at 18.00 h at the time of the LH surge. The brains from these animals were processed by double-label in situ hybridization to allow measurement of galanin mRNA levels in GnRH neurons. GnRH neurons were identified with a digoxigenin-labeled cRNA probe for GnRH mRNA, and galanin mRNA was detected and measured simultaneously with an 35S-labeled cRNA probe coupled with computerized grain counting. Estimation of cellular levels of GnRH mRNA was accomplished with single-label in situ hybridization, an 35S-labeled GnRH cRNA probe and computerized grain counting. We observed a 3-fold induction of galanin mRNA in the GnRH neurons of animals treated with E alone compared with those treated with the vehicle alone (vehicle: 13±2 vs E: 42±4 grains/cell (g/c); P<0.01); LH levels in the E-treated animals were elevated, albeit moderately, with respect to the vehicle controls. Compared with vehicle-treated animals, those treated with the combination of E and P showed a 5-fold induction of galanin mRNA in GnRH neurons (68±9 g/c), which was significantly (P<0.01) greater than that observed in the animals treated with E alone; in addition, the magnitude of the LH surge was much greater (P<0.05) in the E/P-treated group compared with the E alone group. In contrast, compared to the vehicle controls, animals treated with P alone (15±2 g/c) showed no discernable effect on galanin mRNA levels; moreover, no LH surge occurred in the P alone group. Neither the number of identified GnRH cells nor their content of GnRH mRNA differed significantly among the experimental groups (GnRH mRNA signal: vehicle controls: 153±6 vs E: 159±6 vs E/P: 153±3 vs P: 148±8 g/c). We conclude that while E is the primary ovarian signal inducing galanin mRNA expression in GnRH neurons and the LH surge itself, P plays a facilitatory role in both of these processes.In the rat, beginning on the day of diestrus and continuing pin secretion (3, 4 ). While the basic endocrine aspects of this so-called positive feedback event have been carefully defined over through proestrus, a rising tide of estradiol (E ) serves as the proximate signal eliciting the preovulatory surge of LH (see ( 1) the p...

The regulative effect of galanin family members on link of energy metabolism and reproduction

“…As the rats were treated with estradiol alone or both estradiol and progesterone, the galanin mRNA expression in the GnRH cells was increased about 3-fold or 5-fold respectively compared with vehicle-treated animals [146]. Last, on the day of proestrus progesterone facilitated galanin mRNA expression in GnRH cells and the LH surge triggered by estradiol-induced positive feedback signals [146]. In turn, galanin may markedly stimulate progesterone release from cultured granulosa cells.…”

Effects of cycle stage on regionalised galanin, galanin receptors 1–3, GNRH and GNRH receptor mRNA expression in the ovine hypothalamus

“…Previous work has reported that hypothalamic galaninergic gene expression varies with oestrus cycle stage (Brann et al 1993, Rossmanith et al 1996, Finn et al 1998, Tourlet et al 2005) and/or is affected by steroids (Tourlet et al 2005). Using a targeted approach, the results of this study suggest that galanin mRNA expression changes over the oestrous cycle, in a region-specific manner (mPOA/OVLT, PVN, ARC but not mPOA), conducive with localised actions.…”

“…That study, however, used immunocytochemistry and it is possible that more localised transitory changes in expression could have been missed. Elevated galanin expression during the follicular phase has previously been reported in rodents (Brann et al 1993, Rossmanith et al 1996, Finn et al 1998) and in one study on sheep in which galanin expression was assessed as the number of detectable immunoreactive cells (Tourlet et al 2005). While Tourlet et al (2005) reported changes in ovine galanin expression within the POA but not in the BNST or infundibular nucleus in response to an E 2 signal, comparison of the anatomical data indicates that the stimulatory effects on galanin immunoreactive cells corresponds with the increase in mRNA expression seen in the mPOA/OVLT in the current study, with little effect in the more rostral regions of the POA.…”

Developmental changes in galanin in lumbosacral sympathetic ganglionic neurons innervating the avian uterine oviduct and galanin induction by sex steroids

“…A similar effect of ovarian sex steroids on the induction of galanin mRNA has been reported in the rat central nervous system (Rossmanith et al 1996). According to Rossmanith et al, was the primary ovarian signal inducing galanin mRNA expression in gonadotrophin-releasing hormone (GnRH) neurons.…”

“…According to Rossmanith et al, was the primary ovarian signal inducing galanin mRNA expression in gonadotrophin-releasing hormone (GnRH) neurons. In addition, progesterone facilitated the action of oestradiol-17 on galanin gene expression in GnRH neurons (Merchenthaler et al 1991, Rossmanith et al 1996. It has also been reported that galanin neurons exhibit oestrogen receptors in the rat hypothalamus (Horvath et al 1995).…”