title: Neuroanatomical organization of gonadotropin-releasing hormone neurons during the oestrus cycle in the ewe.
abstract: BACKGROUND
  During the preovulatory surge of gonadotropin-releasing hormone (GnRH), a very large amount of the peptide is released in the hypothalamo-hypophyseal portal blood for 24-36H00. To study whether this release is linked to a modification of the morphological organization of the GnRH-containing neurons, i.e. morphological plasticity, we conducted experiments in intact ewes at 4 different times of the oestrous cycle (before the expected LH surge, during the LH surge, and on day 8 and day 15 of the subsequent luteal phase). The cycle stage was verified by determination of progesterone and LH concentrations in the peripheral blood samples collected prior to euthanasia.
  
  
  RESULTS
  The distribution of GnRH-containing neurons throughout the preoptic area around the vascular organ of the lamina terminalis was studied following visualisation using immunohistochemistry. No difference was observed in the staining intensity for GnRH between the different groups. Clusters of GnRH-containing neurons (defined as 2 or more neurons being observed in close contact) were more numerous during the late follicular phase (43 +/- 7) than during the luteal phase (25 +/- 6), and the percentage of clusters was higher during the beginning of the follicular phase than during the luteal phase. There was no difference in the number of labelled neurons in each group.
  
  
  CONCLUSIONS
  These results indicate that the morphological organization of the GnRH-containing neurons in ewes is modified during the follicular phase. This transitory re-organization may contribute to the putative synchronization of these neurons during the surge. The molecular signal inducing this plasticity has not yet been identified, but oestradiol might play an important role, since in sheep it is the only signal which initiates the GnRH preovulatory surge.
authors.affiliation: Neurobiologie et Maîtrise des Fonctions Saisonnières, UMR 6175 INRA-CNRS-Université de Tours-Haras Nationaux, IFR 135, INRA Centre de Tours, 37380 Nouzilly, France. martine.batailler@tours.inra.fr <martine.batailler@tours.inra.fr>
authors.forename: Martine
authors.initials: M
authors.lastname: Batailler
authors.forename: Alain
authors.initials: A
authors.lastname: Caraty
authors.forename: Benoît
authors.initials: B
authors.lastname: Malpaux
authors.forename: Yves
authors.initials: Y
authors.lastname: Tillet
mesh_terms: D000818:Animals; D030762:Estrous Cycle; D005260:Female; D007987:Gonadotropin-Releasing Hormone / Q000032:analysis*; D007150:Immunohistochemistry; D007986:Luteinizing Hormone / Q000097:blood; D009474:Neurons / Q000737:chemistry / Q000166:cytology*; D011301:Preoptic Area / Q000166:cytology*; D011374:Progesterone / Q000097:blood; D012756:Sheep
chemical_list: D007987:Gonadotropin-Releasing Hormone; D011374:Progesterone; D007986:Luteinizing Hormone