GONADOTROPIN INHIBITORY HORMONE (GNIH) DISTRIBUTION IN THE BRAIN OF THE ANCIENT FISH, ATRACTOSTEUS TROPICUS (LEPISOSTEIFORMES: LEPISOSTEIDAE)

BATTISTA, ARIADNA; VISSIO, PAULA G.; PEREZ SIRKIN, DANIELA; TSUTSUI K; DI YORIO, MARÍA PAULA; ÁLVAREZ-GONZÁLEZ CA

Manaos

Congreso; 11 th International Symposium on Reproductive Physiology of Fish; 2018

IntroductionGnIH is a dodecapeptide that belongs to the RFamide family. This peptide downregulates reproductive function in avians and mammals, but its role in other vertebrates? groups is not clearly established. Immunohistochemical studies have provided data of the distribution of GnIH immunoreactive (GnIH-ir) neurons and fibers in the brain of major teleost fish models. Despite of lepisosteis? phylogenetic position, little is known about the brain distribution of important neuropeptides. Thus, we considered worth it to start investigating GnIH system in the brain of lepisosteids from the viewpoint of comparative neuroanatomy and thus, to infer possible conserved functions. The present study was conducted to elucidate GnIH distribution in the brain of Atractosteus tropicus. MethodsJuveniles were obtained from the aquaculture facility of La Universidad Juárez Autónoma de Tabasco in Villahermosa, México. Brains with pituitary attached, fixed in Bouin?s solution, were processed for immunohistochemistry. An antiserum raised against a bullfrog peptide closely related to GnIH and previously tested in teleost species, was used. Results and DiscussionThree GnIH-ir cell groups were found: a few number of neurons observed in the intersection of the telencephalon (Tel) and the olfactory bulb (OB), other group detected in the preoptic area, and the last one, with high number of GnIH-ir somata, surrounding the third ventricle in the hypothalamus (Hpt). In this last group, two somata populations were shown: the more crowded one in a more anterior and dorsal position, and other detected in a ventral position. The Hpt GnIH-ir cell population seems to be the most conserved characteristic of GnIH system vertebrate?s species. GnIH-ir fibers showed a wide spread distribution over all brain regions, except the cerebellum which has the lowest density. Fibers were detected in a ventral position in the olfactory nerve. The central region of the OB-Tel, and the Hpt showed the highest density of fibers, with the thickest fibers in a more ventral position. At Hpt level, a high density of labeled fibers was detected in the median eminence and less number of fibers were observed at pituitary level, providing morphological evidence of possible indirect and/or direct action of GnIH over pituitary function. GnIH-ir fibers were shown in the optic nerve and the optic tectum, innervating the periventricular zone, suggesting that GnIH act as a neuromodulator integrating different sensory modalities as it was proposed in other teleost fish.ConclusionThe present study described for the first time the neuroanatomical distribution of GnIH in a non teleost actinopterigian fish, where a conserved pattern of distribution of fibers and somata was observed.