Detection of estrogen receptor-beta messenger ribonucleic acid and I-125-estrogen binding sites in luteinizing hormone-releasing hormone neurons of the rat brain

Luteinizing hormone-releasing hormone (LHRH) neurons of the forebrain play a pivotal role in the neuroendocrine control of reproduction. Although seru m estrogen levels influence many aspects of LHRH neuronal activity in the f emale, earlier studies were unable to detect estrogen receptors (ERs) withi n LHRH neurons, thus shaping a consensus view that the effects of estradiol an the LHRH neuronal system are mediated by interneurons and/or the glial matrix. The present studies used dual-label in situ hybridization histochem istry (ISHH) and combined LHRH-immunocytochemistry/I-125-estrogen binding t o readdress the estrogen-receptivity of LHRH neurons in the female rat. in ISHH experiments we found that the majority of LHRH neurons exhibited hybri dization signal for the "beta" form of ER (ER-beta). The degree of colocali zation was similar in topographically distinct populations of LHRH neurons and was not significantly altered by estradiol (67.2+/-1.8% in ovariectomiz ed and 73.8+/-4.2% in ovariectomized and estradiol-treated rats). in contra st, the mRNA encoding the classical ER-alpha could not be detected within L HRH neurons. In addition in vivo binding studies using I-125-estrogen revea led a subset of LHRH-immunoreactive neurons (8.8%) which accumulated the ra dioligand thus providing evidence for the translation of ER protein(s) with in these cells. The findings that most LHRH neurons in the female rat expre ss ER-beta mRNA and at least some are capable of binding I-125-estrogen cha llenge the current opinion that estrogen does not exert direct effects upon the LHRH neuronal system.