Differential distribution of gonadotropin-releasing hormone variants in the brain of Hydrochaeris hydrochaeris (Mammalia, Rodentia)

1. In a previous paper we reported evidence for the presence of mGnRH- and sGnRH-like peptides in the preoptic-hypothalamic region of the: capybara Hy drochaeris hydrochaeris (Montaner er al, 1998). In that study, the presence of a cGnRH-II like molecule in olfactory bulb extracts was suggested. 2. The capybara, the largest living rodent in the world, belongs to the ord er Hystricomorpha, which is considered to be one of the oldest groups of ro dents. Some authors consider that this group is the ancestor of all remaini ng rodents. 3. In this study we have characterized GnRH molecular variants found in ext racts from the olfactory bulbs and the mesencephalic region of capybara. Th ese regions represent the two GnRH neuronal systems: the terminal nerve-sep topreoptic and the midbrain systems. 4. An indirect method combining reverse-phase high-performance liquid chrom atography (RP-HPLC) and radioimmunoassay (RIA) was used to characterize GnR H variants. The analysis of both extracts with two different RIA systems re vealed three immunoreactive GnRH peaks, coeluting with mGnRH, cIIGnRH, and sGnRH synthetic standards. These results were additionally supported by ser ial dilution studies with specific antisera. 5. To our knowledge this the first report on the presence of three GnRH var iants in the brain of an eutherian mammal. These results suggest that, simi larly to other vertebrates, the expression of multiple GnRH variants may al so be a common pattern in mammals.