Effects of GABA A receptor modulation on the expression of GnRH gene and GnRH receptor ( GnRH-R) gene in the hypothalamus and GnRH-R gene in the anterior pituitary gland of follicular-phase ewes

Abstract

The effect of prolonged, intermittent infusion of GABA A receptor agonist (muscimol) or GABA A receptor antagonist (bicuculline) into the third cerebral ventricle on the expression of GnRH gene and GnRH-R gene in the hypothalamus and GnRH-R gene in the anterior pituitary gland was examined in follicular-phase ewes by real-time PCR. The activation or inhibition of GABA A receptors in the hypothalamus decreased or increased the expression of GnRH and GnRH-R genes and LH secretion, respectively. The present results indicate that the GABAergic system in the hypothalamus of follicular-phase ewes may suppress, via hypothalamic GABA A receptors, the expression of GnRH and GnRH-R genes in this structure. The decrease or increase of GnRH-R mRNA in the anterior pituitary gland and LH secretion in the muscimol- or bicuculline-treated ewes, respectively, is probably a consequence of parallel changes in the release of GnRH from the hypothalamus activating GnRH-R gene expression. It is suggested that GABA acting through the GABA A receptor mechanism on the expression of GnRH gene and GnRH-R gene in the hypothalamus may be involved in two processes: the biosynthesis of GnRH and the release of this neurohormone in the hypothalamus.