Effects of GnRH and the dual regulatory actions of GnIH in the pituitary explants and brain slices of Astyanax altiparanae males

Abstract

The pituitary gonadotropins, Fsh (follicle-stimulating hormone) and Lh (luteinizing hormone), regulate testicular development and functions in all vertebrates. At the pituitary, different signaling systems regulate the synthesis and secretion of the gonadotropins, such as the hypothalamic neuropeptides GnRH (gonadotropin-releasing hormone) and GnIH (gonadotropin-inhibitory hormone). While GnRH exerts stimulatory roles, the actions of GnIH remain controversial for many teleost species. Therefore, the aim of this study was to evaluate the in vitro effects of chicken GnRH2 (cGnRH2) and zebrafish GnIH-3 (zGnIH-3) on the male gonadotropin and GnRH system expression using pituitary explants and brain slices from a neotropical species with economical and ecological relevance, Astyanax altiparanae. Our results showed that in males, cGnRH2 increased fshb and lhb mRNA levels in the pituitary explants. Interestingly, zGnIH-3 has no effect on basal gonadotropin expression, however zGnIH-3 decreased the cGnRH2-induced fshb and lhb transcripts in male pituitary explants. In the male brain slices, zGnIH-3 showed stimulatory effects, increasing gnrh2 mRNA levels. Overall, our results suggested that GnIH seems to have dual regulatory actions on gonadotropin and GnRH2 expression of A. altiparanae males. This study provided basic information on endocrine regulation of A. altiparanae reproduction, and the obtained results will expand our knowledge, improving the reproductive management of this economically important freshwater species.

The Gonadotropin-Inhibitory Hormone: What We Know and What We Still Have to Learn From Fish

“…Moreover, gGnIH-III differentially affected GnRH2 and GnRH3 actions depending on the sexual stage. Similar effects of GnIH peptides were demonstrated in Amphiprion melanopus (46) and in Astyanax altiparanae (78). This preventive-GnRH-stimulatory effect has been proposed to depend on the action of estradiol or neuroestrogen levels; the abundance of GnIH-R, GnRH and estrogen receptors, and the inhibition of cAMP pathways or the hyperpolarization of gonadotropes by activating K + , both exerted by the activation of GnIH-R. Other possibility is that GnIH-R and GnRH-R could form heterodimers modifying the action of their ligands on gonadotrophs [for review see (79)].…”

Thyroid hormones deficiency impairs male germ cell development: a cross talk between hypothalamic-pituitary-thyroid, and - gonadal axes in zebrafish

“…While transcript levels of gnrh2 and gnrh3 did not change, gnih mRNA levels were significantly elevated in the brain of animals after methimazole exposure. In fish, GnIH orthologs have double mechanism, including stimulatory and inhibitory actions on gonadotropin secretion and growth hormone production, depending on the species studied, mode of treatment, and season (Amano et al, 2006;Zhang et al, 2010;Moussavi et al, 2012;Branco et al, 2018;Fallah et al, 2019;Ma et al, 2020a, b). In addition, Tsutsui and collaborators (2017) showed that hypothyroidism induced by PTU increases GnIH expression and reduces gonadotropins and plasma steroid levels in female mice.…”

Interaction of thyroid hormones and gonadotropin inhibitory hormone in the multifactorial control of zebrafish (Danio rerio) spermatogenesis

“…For the in vitro experiments, the filtered-sterilized Leibovitz’s L-15 Medium (Thermo Fisher Scientific, G ibco®, Canada) was used for dilution and preparing the final concentration of 100 nM of zGnih. Since pharmacological data are not available for zebrafish receptors, zGnih ligand concentration was chosen based on previous studies in different species including zebrafish (Moussavi et al, 2012; Branco et al, 2018; Ma et al, 2020 a, b). In most of these studies, the effects of zGnih have been seen in the range of 10-1000 nM.…”