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Exp Clin Endocrinol Diabetes 2003; 111(6): 335-340
DOI: 10.1055/s-2003-42723
Article

J. A. Barth Verlag in Georg Thieme Verlag Stuttgart · New York

The Role of GabaA Receptors in the Neural Systems of the Ventromedial Hypothalamus-Nucleus Infundibular Region in the Control of GnRH Release in Ewes during Follicular Phase

D. Tomaszewska-Zaremba 1 , K. Mateusiak 1 , F. Przekop 1
  • 1The Kielanowski Institute of Animal Physiology and Nutrition, Polish Academy of Sciences, Jabłonna, Poland
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Publikationsverlauf

Received: July 17, 2002 First decision: November 24, 2002

Accepted: March 3, 2003

Publikationsdatum:
01. Oktober 2003 (online)

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Abstract

To examine the role of the GABAA receptor mediating systems in the control of gonadotropin releasing hormone (GnRH) release from the ventromedial-infundibular region (VEN/NI) of the hypothalamus of ewes during the follicular phase of the estrous cycle, the extracellular concentrations of GnRH, β-endorphin (B-END), noradrenaline (NE), dopamine (DA), and their metabolites MHPG, DOPAC and concentration of luteinizing hormone (LH) in blood plasma were quantified during local stimulation or blockade of GABAA receptors with muscimol and bicuculline, respectively. Stimulation of GABAA receptors attenuated GnRH and LH release, increased β-endorphin outflow and dopaminergic activity but had no evident effect on noradrenergic activity. Blockade of GABAA receptors decreased β-endorphin release but had no evident effect on the extracellular concentration of GnRH, LH levels in the blood and catecholaminergic activity. It is suggested that suppression of GnRH/LH release under muscimol treatment may result from activation of GABAA receptors on GnRH nerve terminals and through GABAA receptor mechanism activated β-endorphinergic and dopaminergic neurons in the VEN/NI. Lack of changes in NE and MHPG concentration during stimulation or blockade of GABAA receptors suggests, that during the follicular phase of the estrous cycle the noradrenergic system in the VEN/NI is not involved in the control of GnRH/LH release by GABA.

Key words

Hypothalamus - GABA - GnRH - B-END - catecholamines

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Ph. D. D. Tomaszewska-Zaremba

Polish Academy of Sciences
The Kielanowski Institute of Animal Physiology and Nutrition

05-110 Jabłonna

Poland

Telefon: + 48227824422

Fax: + 48 2 27 74 20 38

eMail: d_tomaszewska@poczta.onet.pl