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 r adioimmunoassay and immunocytochemistry. The analysis of brain extract s with RP-HPLC followed by radioimmunoassay with PBL#45 antiserum show ed the presence of only one peak with immunoreactivity for GnRH (ir-Gn RH) having the chromatographic and immunological characteristics of ma mmalian GnRH (mGnRH). This peak was further analyzed with two mGnRH-sp ecific antisera, EL-15 and m1076, yielding serial dilution displacemen t 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 an d fibers distributed from the olfactory bulb, septal area, and anterio r preoptic area toward the hypothalamus and hypophyseal neural lobe. T he main group of ir-GnRH fibers and neurons was identified in the ante rior preoptic area. These neurons appear to be the origin of fibers th at, after surrounding the preoptic recess, border the dorsal surface o f the optic chiasma, extend through the infundibulum, traverse the ext ernal layer of the median eminence, and end in the pars nervosa.