The role of GABA_A receptors in the neural systems of the medial preoptic area in the control of GnRH release during the luteal phase of the oestrous cycle in ewes

Abstract

Recent studies from our laboratory suggested that functional interconnection of the GABAergic system with the GnRHergic, β-endorphinergic and catecholaminergic systems in the medial preoptic area (MPOA) plays an important role in the modulation of gonadoliberin (GnRH) release during the follicular phase of the oestrous cycle in ewes. Since the mode of action of γ-aminobutyric acid (GABA) on GnRH neurons is highly dependent on gonadal steroids, we extended our studies to the role of GABA A receptors in the MPOA on the activity of all of the above-mentioned systems during the luteal phase of the oestrous cycle. Stimulation of GABA A receptors by muscimol did not affect either GnRH/LH, β-endorphin release or catecholaminergic activity, expressed by extracellular concentrations of noradrenaline (NE), dopamine (DA) and their metabolites MHPG and DOPAC. Blockade of GABA A receptors decreased β-endorphin release, dopaminergic and noradrenergic activity but did not change GnRH release or LH secretion. It is suggested that progesterone secretion during the luteal phase may desensitize GABA A receptors to further stimulation.