Identification and neuroanatomical distribution of immunoreactivity for mammalian gonadotropin-releasing hormone (mGnRH) in the brain and neural hypophyseal lobe of the toad Bufo arenarum

The presence and distribution of gonadotropin-releasing hormone (GnRH) in sexually mature specimens of Bufo arenarum was studied by reverse phase/high performance liquid chromatography (RP-HPLC) combined with radioimmunoassay and immunocytochemistry. The analysis of brain extracts with RP-HPLC followed by radioimmunoassay with PBL#45 antiserum showed the presence of only one peak with immunoreactivity for GnRH (ir-GnRH) having the chromatographic and immunological characteristics of mammalian GnRH (mGnRH). This peak was further analyzed with two mGnRH-specific antisera, EL-15 and m1076, yielding serial dilution displacement curves parallel to those obtained with the mGnRH synthetic standard. Immunocytochemical results with the monoclonal antibody LRH13 showed the presence of a terminal nerve-septo-preoptic system with neurons and fibers distributed from the olfactory bulb, septal area, and anterior preoptic area toward the hypothalamus and hypophyseal neural lobe. The main group of ir-GnRH fibers and neurons was identified in the anterior preoptic area. These neurons appear to be the origin of fibers that, after surrounding the preoptic recess, border the dorsal surface of the optic chiasma, extend through the infundibulum, traverse the external layer of the median eminence, and end in the pars nervosa.