title: The role of GABA(A) receptors in the neural systems of the ventromedial-infundibular region of the hypothalamus in the control of gonadotropin release during the luteal phase in ewes.
abstract: To examine the role of GABA(A) receptor mediating systems in the control of gonadotropin-releasing hormone (GnRH) release from the ventromedial-infundibular region (VEN/NI) in ewes during luteal phase, the extracellular concentrations of GnRH, beta-endorphin, noradrenaline (NE), dopamine (DA), and their metabolites: MHPG and DOPAC were quantified by local stimulation or blockade of GABA(A) receptors with muscimol or bicuculline, respectively. Stimulation of GABA(A) receptors in the VEN/NI did not affect GnRH, beta-endorphin release or catecholaminergic system activity. Blockade of GABA(A) receptors decreased beta-endorphinergic and dopaminergic activity, and lowered the extracellular concentration of MHPG. It did not affect GnRH release or luteinizing hormone (LH) secretion. It is suggested that progesterone-induced GABAergic activity during the luteal phase may desensitize GABA(A) receptors to muscimol. Lack of changes in GnRH/LH secretion with concomitant depressed beta-endorphinergic activity corroborated the conclusion that beta-endorphin does not inhibit GnRH release from the VEN/NI during the luteal phase. The physiological significance of changes in the catecholaminergic system activity under GABA(A) receptor blockade in the control of GnRH secretion awaits to be established.
authors.affiliation: Polish Academy of Sciences, The Kielanowski Institute of Animal Physiology and Nutrition, 05-110 Jabłonna, Poland. d_tomaszewska@poczta.onet.pl
authors.forename: D
authors.initials: D
authors.lastname: Tomaszewska-Zaremba
authors.forename: K
authors.initials: K
authors.lastname: Mateusiak
authors.forename: F
authors.initials: F
authors.lastname: Przekop
mesh_terms: D015102:3,4-Dihydroxyphenylacetic Acid / Q000378:metabolism; D000818:Animals; D001640:Bicuculline / Q000494:pharmacology; D004298:Dopamine / Q000378:metabolism; D005260:Female; D018755:GABA Agonists / Q000494:pharmacology; D018756:GABA Antagonists / Q000494:pharmacology; D007987:Gonadotropin-Releasing Hormone / Q000378:metabolism; D006062:Gonadotropins / Q000378:metabolism*; D008183:Luteal Phase / Q000502:physiology; D007986:Luteinizing Hormone / Q000378:metabolism; D008734:Methoxyhydroxyphenylglycol / Q000378:metabolism; D009118:Muscimol / Q000494:pharmacology; D009638:Norepinephrine / Q000378:metabolism; D010904:Pituitary Gland, Posterior / Q000378:metabolism*; D011963:Receptors, GABA-A / Q000378:metabolism*; D012756:Sheep; D001615:beta-Endorphin / Q000378:metabolism
chemical_list: D018755:GABA Agonists; D018756:GABA Antagonists; D006062:Gonadotropins; D011963:Receptors, GABA-A; D015102:3,4-Dihydroxyphenylacetic Acid; D009118:Muscimol; D007987:Gonadotropin-Releasing Hormone; D008734:Methoxyhydroxyphenylglycol; D001615:beta-Endorphin; D007986:Luteinizing Hormone; D004298:Dopamine; D009638:Norepinephrine; D001640:Bicuculline