title: 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 preovulatory 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 micrograms 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 +/- 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.
authors.affiliation: Department of Obstetrics-Gynecology, University of Washington, Seattle 98195, USA.
authors.forename: W G
authors.initials: WG
authors.lastname: Rossmanith
authors.forename: D L
authors.initials: DL
authors.lastname: Marks
authors.forename: D K
authors.initials: DK
authors.lastname: Clifton
authors.forename: R A
authors.initials: RA
authors.lastname: Steiner
mesh_terms: D000818:Animals; D001921:Brain / Q000166:cytology; D001923:Brain Chemistry / Q000187:drug effects; D004958:Estradiol / Q000494:pharmacology*; D005260:Female; D019004:Galanin / Q000096:biosynthesis*; D007987:Gonadotropin-Releasing Hormone / Q000502:physiology*; D007091:Image Processing, Computer-Assisted; D017403:In Situ Hybridization; D007986:Luteinizing Hormone / Q000097:blood; D009474:Neurons / Q000187:drug effects / Q000378:metabolism*; D010052:Ovariectomy; D011374:Progesterone / Q000494:pharmacology*; D015347:RNA Probes; D012333:RNA, Messenger / Q000096:biosynthesis*; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D015347:RNA Probes; D012333:RNA, Messenger; D007987:Gonadotropin-Releasing Hormone; D011374:Progesterone; D004958:Estradiol; D019004:Galanin; D007986:Luteinizing Hormone