GONADOTROPIN-RELEASING HORMONES IN MICRODISSECTED BRAIN-REGIONS OF AN AMPHIBIAN - CONCENTRATION AND ANATOMICAL DISTRIBUTION OF IMMUNOREACTIVE MAMMALIAN GNRH AND CHICKEN GNRH-II

Mammalian and chicken II gonadotropin-releasing hormones (mGnRH, cGnRH II) were extracted from 350 mu m diameter punches from brains of a urodele amphibian, Taricha granulosa, and measured by means of radioimmunoassay (RIA) with specific antisera. Measureable quantitites of both peptides were found in the lateral pallium, the subpallium (along the course of the nervus terminalis), the preoptic area, habenula, optic tectum, infundibulum, paraventricular organ/posterior tubercle of the caudal diencephalon, medulla, and cerebrospinal fluid. Highest concentrations of both peptides were in the preoptic area and infundibulum, suggesting a role in gonadotropin release. In most extrahypothalamic regions, cGnRH II concentrations exceeded those of mGnRH, suggesting that cGnRH II may function as a neurotransmitter in many sites, perhaps to control reproductive behaviors. Results are largely consistent with immunocytochemical (ICC) analyses, except that RIA revealed small amounts of both peptides not found by ICC in some areas of the brain. Results from this microdissection/RIA study and prior ICC studies in amphibians support the conclusions that GnRH cell bodies in the terminal nerve and preoptic area, which project mainly to the median eminence and habenula, express mGnRH, and that GnRH cell bodies in the caudal diencephalon, which project widely throughout the CNS, express cGnRH II. Comparative data support the view that cGnRH II, and the neural systems in which it is expressed, evolved early in vertebrate phylogeny and have been highly conserved.