Gonadotropin-inhibitory hormone in the flatfish: molecular cloning, brain localization and physiological effects

Abstract

In our study, we focused on the gonadotropin-inhibitory hormone (GnIH) system in the Senegalese sole (Solea senegalensis), aiming to clarify its role in neuroendocrine and environmental control of reproduction. We successfully cloned the full-length Gnih precursor sequence, coding for three putative GnIH peptides (ssGnIH), and generated specific antibodies against these peptides. Using these antibodies, we localized GnIH cells and their projections in the brain and pituitary. We observed significant gnih expression in the diencephalon, as well as in the olfactory bulbs/cerebral hemispheres, optic tectum/tegmentum, retina, and pituitary. The antibodies consistently revealed ssGnIH-immunoreactive perikarya in the olfactory bulbs, ventral telencephalon, caudal preoptic area, dorsal tegmentum, and rostral rhombencephalon, with fibers innervating the brain and pituitary extensively. Functionally, intramuscular injection of ssGnIH-3 significantly reduced gnrh-3 and lh expression, while ssGnIH-2 had no effect on the main reproductive genes. These results indicate the presence of a functional GnIH system in the sole, with widespread innervation of brain areas and the pituitary gland. This system likely plays a crucial role in the neuroendocrine regulation of flatfish reproduction, providing new insights into the broader functions of GnIH in teleosts.