Brain distribution of Gonadotropin inhibitory hormone (GnIH) in an ancient fish, Atractosteus tropicus (Lepisosteiforme)

BERIOTTO, AGUSTINA CARLA; PÉREZ SIRKIN, DANIELA IRINA; VISSIO, PAULA GABRIELA; BATTISTA, ARIADNA; ÁLVAREZ-GONZÁLEZ, CARLOS ALFONSO; DI YORIO, MARÍA PAULA; TSUTSUI, KAZUYOSHI

Buenos Aires

Congreso; XX Jornadas Anuales de la Sociedad Argentina de Biología; 2018

Sociedad Argentina de Biología

Since the discovery of gonadotropin inhibitory hormone (GnIH) in 2000, its function and regulation has been widely studied in birds and mammals. In these groups, GnIH, a RFamide dodecapeptide, downregulates reproductive function; however, 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 the phylogenetic position of holeostean as the sister group of teleost, little is known about the brain distribution of important neuropeptides. Thus, from the viewpoint of comparative neuroanatomy and to infer possible conserved functions, the present study was conducted to elucidate GnIH distribution in the brain of Atractosteus tropicus. Juveniles 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. Three GnIH-ir somata groups were found: a few number of neurons in the intersection of the olfactory bulb (OB) and the telencephalon (Tel); other group was detected in the preoptic area, and the last one surrounding the third ventricle in the hypothalamus (Hpt). The last group, consisted of a high number of GnIH-ir neurons, could be divided into two populations: the more crowded one in a more anterior and dorsal position, and other detected in a ventral position. This hypothalamic GnIH-ir cell group seems to be the most conserved characteristic of GnIH system in vertebrates. 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. Particularly, at Hpt level, a high density of labeled fibers was detected in the median eminence and at the pituitary level, providing morphological evidence of possible indirect and/or direct action of GnIH over pituitary function. GnIH-ir fibers were detected in the pineal gland and saccus vasculosus, indicating its involvement in the transduction of environmental effects in reproduction. Moreover, the detection of GnIH-ir fibers in the optic nerve and the optic tectum (in the periventricular zone) suggests that GnIH acts as a neuromodulator integrating different sensory modalities as it was proposed in other teleost fish. The present study described for the first time the neuroanatomical distribution of GnIH in a holostean fish, where a conserved pattern of distribution of fibers and somata was observed.