Organization of the gonadotropin-inhibitory hormone (Lpxrfa) system in the brain of zebrafish (Danio rerio)

• Published in: General and comparative endocrinology Vol. 304; p. 113722
• Main Authors: Song, Yanlong, Peng, Wei, Luo, Junzhi, Zhu, Zuoyan, Hu, Wei
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01.04.2021
• Subjects: Animals; Animals, Genetically Modified; Brain - metabolism; GnIH; GnRH3; Gonadotropin-Releasing Hormone - genetics; Gonadotropin-Releasing Hormone - metabolism; Hypothalamic Hormones - genetics; Hypothalamic Hormones - metabolism; Lpxrfa; Luteinizing Hormone, beta Subunit; Neuron; Neurons - metabolism; Npffr; Pituitary Gland - metabolism; Zebrafish; Zebrafish - genetics; Zebrafish - metabolism; Zebrafish; Neuron; Lpxrfa; GnRH3; GnIH; Npffr
• ISSN: 0016-6480; 1095-6840
• DOI: 10.1016/j.ygcen.2021.113722

•Tg(gnih:mCherry) zebrafish shows GnIH cells restricted in the NPPv regions.•GnIH processes project to the hypothalamus, telencephalon, and olfactory bulb.•GnIH processes are in contact with the TN-GnRH3 cell somata in the olfactory bulb.•Hypothalamic GnIH processes make a close apposition with the GnRH3 fibers.•GnIH-3 peptide injection stimulates gnrh3 expression in the zebrafish brain. Gonadotropin-inhibitory hormone (GnIH) is a hypothalamic neuropeptide that inhibits gonadotropin secretion in birds and mammals. However, the role of GnIH (Lpxrfa) in teleosts is unknown. In this study, a transgenic zebrafish (Danio rerio) line Tg(gnih:mCherry) was developed to determine the organization of GnIH neurons in the brain. Another transgenic line, Tg(gnih:mCherry; gnrh3:eGFP), was established to determine the positional relationships between GnIH and GnRH3 neurons. In these transgenic lines, the mCherry protein was specifically expressed in GnIH neurons, and eGFP was expressed exclusively in GnRH3 neurons. We found that GnIH cell somata were restricted to the posterior periventricular nucleus (NPPv). Most GnIH neuronal processes projected to the hypothalamus, but a few extended to the posterior tuberculum, telencephalon, and olfactory bulb. GnIH neuronal processes were in close apposition with GnRH3 cell somata and processes in the preoptic-hypothalamic area but were seldom in direct contact. However, in the olfactory bulb, GnIH neuronal processes were in proximity to the terminal nerve GnRH3 cell somata. Neither GnIH cell soma nor neuronal processes were detected in the pituitary, although GnIH receptor mRNAs (npffr1l1, npffr1l2, and npffr1l3) were detected. Intraperitoneal administration of GnIH-3 peptides promoted the transcription of brain gnrh3 as well as pituitary fshβ but not lhβ. Thus, GnIH cell somata were specifically distributed in the NPPv, and their fibers extended to the hypothalamus and advanced to the telencephalon and olfactory bulb. We conclude that GnIH may directly stimulate terminal nerve GnRH3 neurons in the zebrafish brain.