With respect to GnRH neurons, our results clearly show that in these vitellogenic females, a large majority (at least 70%) of the sGnRH-producing neurons in the ventro-caudal telencephalon and anterior preoptic region express rtGR. Results in rats have already shown that, in the homologous regions, medial septum-lateral band of Broca and preoptic area, a subset of GnRH neurons colocalized nuclear GR, providing evidence that GR could directly regulate GnRH gene expression and thus modulate the hypothalamic-pituitary-gonadal axis. More recently, it has been shown in immortalized GnRH-secreting cell lines, which express a functional GR, that dexamethasone represses both the endogenous GnRH gene, decreasing the levels of GnRH mRNA, and the transcriptional activity of transfected rat GnRH promoter-reporter gene vectors. Buy Advair Diskus Online
Further studies on the mouse GnRH promoter have identified negative glucocorticoid-responsive elements (GRE) that bind a multi-proteic complex involving the GR and are required for the repressive effects of glucocorticoids on GnRH expression. In addition to altering GnRH expression, it has also been shown that dexamethasone affects GnRH secretion from GT1-7 cells. Our morphological results, together with the fact that the promoter of GnRH has been shown to contain putative GRE in the Atlantic salmon, Masu salmon, and the stripped bass, indicate that the conditions exist for a potential regulation of GnRH expression by glucocorticoids in teleosts.