Localization of [3H]-estradiol and gonadotropin-releasing hormone (GnRH) in the hypothalamus of the fetal guinea-pig.

Guinea-pig fetuses at the end of gestation were injected subcutaneously, "in vivo", with [3H]-estradiol, and 60 min later the autoradiographic localization of radioactivity was studied in the hypothalamus using thin frontal and medial sagittal brain sections. Concentration of radioactivity in cell nuclei was found in the nucleus arcuatus and preoptic area. Autoradiography was combined with an immunohistochemical technique on the same section to detect those neurons which simultaneously contained [3H]-estradiol and gonadotropin releasing hormone (GnRH). [3H]-estradiol and GnRH in the same neurons were found in the nucleus arcuatus and preoptic area; GnRH was also observed in the median eminence, in the ependymal cells bordering the third ventricle and in neuronal perikarya of the preoptic area.