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Effects of GABA B Receptor Modulation on Gonadotropin‐Releasing Hormone and β‐Endorphin Release, and on Catecholaminergic Activity in the Ventromedial Hypothalamus‐Infundibular Nucleus Region of Anoestrous Ewes
Author(s) -
TomaszewskaZaremba D.,
Przekop F.
Publication year - 2005
Publication title -
journal of neuroendocrinology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.062
H-Index - 116
eISSN - 1365-2826
pISSN - 0953-8194
DOI - 10.1111/j.1365-2826.2005.01276.x
Subject(s) - medicine , endocrinology , catecholaminergic , hypothalamus , nucleus , gonadotropin releasing hormone , receptor , gonadotropin , hormone , chemistry , biology , catecholamine , luteinizing hormone , neuroscience
To examine the role of γ‐aminobutyric acid (GABA) B receptor mediating systems in the ventromedial hypothalamus‐infundibular nucleus region (VMH/NI) of anoestrous ewes in controlling gonadotropin‐releasing hormone (GnRH) release, the extracellular concentrations of GnRH, β‐endorphin, norepinephrine, dopamine, 4‐hydroxy‐3‐methoxy‐glycol and 3,4‐dihydroxy‐phenylacetic acid were quantified during infusion of baclofen or phaclofen (agonist and antagonist of GABA B receptors, respectively) in this structure. The stimulation of GABA B receptors activates GnRH/luteinising hormone (LH) release, attenuates noradrenergic and β‐endorphinergic tone but has no evident effect on the dopaminergic system. Blockade of GABA B receptors in this structure increases the extracellular β‐endorphin concentration but has no significant influence on GnRH release or catecholaminergic activity. It is suggested that activation of GnRH/LH release in the VMH/NI of anoestrous ewes may result from a decrease of norepinephrine output and hence its inhibitory effect on GnRH secretion. Activation of GABA B receptors, as well as their blockade, did not change dopaminergic system activity, indicating that GABA B does not affect GnRH release indirectly by a GABA B receptor mechanism acting on dopaminergic neurones in the VMH/NI. Increased activity of the β‐endorphinergic system during blockade of GABA B receptors does not change GnRH release, suggesting that β‐endorphin does not play a significant role in the control of GnRH secretion in anoestrous ewes.