Neuroanatomical Organization of the Brain Gonadotropin-Inhibitory Hormone and Gonadotropin-Releasing Hormone Systems in the Frog <b><i>Pelophylax esculentus</i></b>

Abstract

Growing evidence suggests that gonadotropin-inhibitory hormone (GnIH) may play a key role in mediating vertebrate reproduction. GnIH inhibits gonadotropin synthesis and release by decreasing the activity of gonadotropin-releasing hormone (GnRH) neurons as well as by directly regulating gonadotropin secretion from the pituitary. Whereas the presence of GnIH has been widely investigated in various classes of vertebrates, there are very few immunohistochemical reports focusing on GnIH in amphibians. The aim of this study was to assess the presence and neuroanatomical distribution of GnIH-like immunoreactivity in the brain of the anuran amphibian Pelophylax (Rana) esculentus (esculenta) and to explore any potential anatomical relationship with mammalian GnRH-immunoreactive (mGnRH-ir) elements. The GnIH-like immunoreactive (GnIH-ir) system constitutes two distinct subpopulations in the telencephalon and diencephalon, with the highest number of immunoreactive cells located in the preoptic and suprachiasmatic areas. GnIH-ir neurons were also observed in the medial septum, the anterior commissure, the dorsal hypothalamus, the periventricular nucleus of the hypothalamus, and the posterior tuberculum. Scattered GnIH-ir fibers were present in all major subdivisions of the brain but only occasionally in the median eminence. mGnRH-ir neurons were distributed in the mediobasal telencephalon, the medial septal area, and the anterior preoptic area. Double-label immunohistochemistry revealed that the GnRH and GnIH systems coexist and have overlapping distributions at the level of the anterior preoptic area. Some GnIH-ir fibers were in close proximity to mGnRH-ir cell bodies. Our results suggest that both the neuroanatomy and the functional regulation of GnRH release are conserved properties of the hypothalamic GnIH-ir system among vertebrate species.

Gonadotrophin‐inhibitory hormone and its mammalian orthologue RFamide‐related peptide‐3: Discovery and functional implications for reproduction and stress

“…As indicated previously, the first evidence of a direct interaction of GnIH and GnRH in the brain came from a neuroanatomical study on birds . Putative contacts by GnIH/RFRP‐3 cells onto GnRH cells in the hypothalamus have subsqeuently been demonstrated in all vertebrates studied, including fish, frogs, hamsters, mice, rats, sheep, monkeys, naked mole‐rats and humans . Although there is putative contact between GnIH/RFRP‐3 and GnRH cells in all vertebrates studied, a functional interaction remains to be demonstrated in some cases.…”

“…15 Putative contacts by GnIH/RFRP-3 cells onto GnRH cells in the hypothalamus have subsqeuently been demonstrated in all vertebrates studied, including fish, frogs, hamsters, mice, rats, sheep, monkeys, naked mole-rats and humans. 30,36,44,45,[47][48][49] Although there is putative contact between GnIH/RFRP-3 and GnRH cells in all vertebrates studied, a functional interaction remains to be demonstrated in some cases. However, in birds and mammals, GnRH neurones express GPR147.…”

Dual Actions of Mammalian and Piscine Gonadotropin-Inhibitory Hormones, RFamide-Related Peptides and LPXRFamide Peptides, in the Hypothalamic–Pituitary–Gonadal Axis

“…In situ hybridization of GPR147 mRNA combined with GnRH immunocytochemistry shows expression of GPR147 mRNA in GnRH1 neurons in birds ( 11 ). GnIH (RFRP) axons also terminate on the hypophysiotropic type of GnRH neurons in humans ( 5 ), monkey ( 6 ), sheep ( 56 ), hamsters ( 7 , 45 ), rats ( 39 , 57 ), mice ( 58 ), frog ( 59 ), zebrafish ( 60 ), and lamprey ( 20 ). Double-immunohistochemistry using GPR147 and GnRH antibodies shows GPR147 on GnRH neurons in hamsters ( 7 ) (Figure 1 ).…”

Comparative and Evolutionary Aspects of Gonadotropin-Inhibitory Hormone and FMRFamide-Like Peptide Systems

“…GnIH neuronal cell bodies constitute two subpopulations in the telencephalon and diencephalon and the highest number of cell bodies are located in the POA and suprachiasmatic areas of the anuran amphibian Rana esculenta (Pinelli et al, 2015 ). GnIH neuronal cell bodies also exist in the medial septum, anterior commissure, dorsal hypothalamus, PerVN of the hypothalamus, and posterior tuberculum.…”

“…GnIH neuronal fibers are only occasionally present in the median eminence. GnIH neuronal fibers exist in close proximity to GnRH cell bodies (Pinelli et al, 2015 ). GnIH (LPXRFa) neuronal cell bodies are located in the nucleus posterioris periventricularis and the nervus terminalis, and the fibers extend to nucleus lateralis tuberis pars posterioris and pituitary in goldfish and sockeye salmon (Sawada et al, 2002b ; Amano et al, 2006 ).…”