MORPHOLOGICAL RELATIONSHIP BETWEEN GNIH AND GNRH NEURONS IN THE BRAIN OF THE NEOTROPICAL CICHLID FISH CICHLASOMA DIMERUS

PAULA G. VISSIO; JUAN ANTONIO MUÑOZ-CUETO; DANIELA I. PÉREZ SIRKIN; TSUTSUI, K.; GUSTAVO M. SOMOZA; SALLEMI, JULIETA EMILSE; TOMÁS H. DELGADIN; DI YORIO, MARÍA PAULA

Manaos

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

IntroductionThe first neuropeptide identified that regulates reproduction was the gonadotropin-releasing hormone (GnRH). After 30 years, a new peptide that inhibits gonadotropin synthesis and secretion was discovered, the gonadotropin-inhibitory hormone (GnIH). Its role in reproduction has been widely studied as well as the interaction between GnRH and GnIH neurons, especially in adults of avians and mammals. In other vertebrate groups, there is little information about the relationship between both systems. In previous works, we characterized the three GnRH variants and GnIH peptide, and demonstrated that GnIH inhibited gonadotropins release in adults of Cichlasoma dimerus. Because no innervation was detected at pituitary level in adults, we analyzed the anatomical relationship between neurons expressing GnIH and the three GnRH variants in adults and in addition, we started studying that relationship during the development of C. dimerus. MethodsReproductive adult?s brain with pituitary attached and larvae were fixed in Bouin?s solution and processed for immunohistochemistry or double labelling confocal immunofluorescence using heterologous antibodies. Larvae were obtained from 4 independent spawning and samples taken from hatching to 85 days post-hatching (dph). Neurons of both nuclei were quantified and measured. Results and DiscussionIn adults, it was shown no apparent contacts between GnIH and GnRH1, so whether GnIH regulates the expression or secretion of GnRH1, an indirect modulation seems more plausible. There were fiber to fiber contacts between GnIH and GnRH2 in the midbrain and in the nucleus lateralis tuberis, suggesting an interaction between both systems. Finally, it was observed co-localization of GnIH and GnRH3 variant only in the nucleus olfacto-retinalis (NOR) neurons, and fibers that co-expressed both peptides while others that expressed only one of them, in all brain regions studied. During the development, the two GnIH-immunoreactive (GnIH-ir) nuclei with spatial and temporal differences were detected: one was observed by 3 dph in the NOR and the other by 14 dph in the nucleus posterioris periventricularis; as described in adults. Moreover, we showed that only NOR neurons co-expressed GnIH and GnRH3 in larvae, result that is in correspondence with the obtained in adults. Surprisingly, there were GnIH-ir fibers at pituitary level from 14 dph, but the density of these fibers diminished by 37 dph; suggesting a change in the regulation of GnIH over pituitary function from larvae to adult.ConclusionThe present study provide new clues to investigate the role of NOR cells, possible GnIH and GnRH3 interactions in the modulation of the reproductive network of teleost fish, and also new functions of GnIH during the development.