Endocrine Abstracts

The gonadotropin-releasing hormone (GnRH) neurosecretory system represents the final common hypothalamic pathway in the neuroendocrine control of reproduction. Changing levels of the ovarian sex steroid hormone 17β-estradiol (E₂) tightly regulate the activity of GnRH cells via feedback actions. Recently, our group has localized the second isoform of estrogen receptors (ER-β) within GnRH neurons of the rat brain, indicating that GnRH cells are capable of directly sensing circulating estrogens. To address the issue of whether GnRH neurons of the human hypothalamus also contain ER-β, we have carried out dual-label immunocytochemical studies on autopsy samples. Research protocols to obtain and handle tissues were reviewed and approved by the Regional Committee of Science and Research Ethics (TUKEB 49/1999). Combined technical efforts that minimized post-mortem interval (<24 h), optimized fixation conditions (use of a mixture of 2% paraformaldehyde and 4% acrolein) and sensitized the immunocytochemical detection (application of silver-intensified nickel-diaminobenzidine chromogen) allowed the visualization of nuclear ER-β immunoreactivity in 10.8–28.0% of GnRH neurons in the preoptic/hypothalamic area of male human individuals. The demonstration of ER-β in human GnRH cells, which lack the classical ER-α receptor isoform, indicate that estrogens may exert direct actions upon GnRH cells selectively through ER-β. In the light of the differing ligand binding characteristics of ER-β from those of ER-α, this discovery offers a potential novel approach to influence estrogen feed-back mechanisms to GnRH neurons through the recently available ER-β-selective ligands.