Neural Versus Gonadal GnIH: Are they Independent Systems? A Mini-Review

Abstract

Based on research in protochordates and basal vertebrates, we know that communication across the first endocrine axes likely relied on diffusion. Because diffusion is relatively slow, rapid responses to some cues, including stress-related cues, may have required further local control of axis outputs (e.g., steroid hormone production by the gonads). Despite the evolution of much more efficient circulatory systems and complex nervous systems in vertebrates, production of many "neuro"transmitters has been identified outside of the hypothalamus across the vertebrate phylogeny and these neurotransmitters are known to locally regulate endocrine function. Our understanding of tissue-specific neuropeptide expression and their role coordinating physiological/behavioral responses of the whole organism remains limited, in part, due to nomenclature and historic dogma that ignores local regulation of axis output. Here, we review regulation of gonadotropin-inhibitory hormone (GnIH) across the reproductive axis in birds and mammals to bring further attention to context-dependent disparities and similarities in neuropeptide production by the brain and gonads. We find that GnIH responsiveness to cues of stress appears conserved across species, but that the response of specific tissues and the direction of GnIH regulation varies. The implications of differential regulation across tissues remain unclear in most studies, but further work that manipulates and contrasts function in different tissues has the potential to inform us about both organism-specific function and endocrine axis evolution.

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

“…Additionally, in vitro, melatonin administration dose‐dependently increases Gnih mRNA and decreases testosterone release from gonadotrophin‐stimulated testes . Taken together, these results suggest that sex steroid secretion is regulated seasonally in starling testes by direct actions of melatonin on gonadal GnIH production …”

“…86 Taken together, these results suggest that sex steroid secretion is regulated seasonally in starling testes by direct actions of melatonin on gonadal GnIH production. [86][87][88]…”

Role of RFRP-3 in the development of cold stress-induced polycystic ovary phenotype in rats

“…RFamide-related peptide (also known as gonadotropininhibitory hormone, GnIH) is a neuropeptide that is present in human brain and gonads and is known to act on human ovary (Tsutsui et al 2007, Tsutsui 2009, Ubuka et al 2009b, Singh et al 2011a, Oishi et al 2012. Functional evidence from humans and other species suggests that the peptide could be involved in pathologies that affect ovulation, follicular development and steroid secretion by the ovary (Ubuka et al 2009b, Oishi et al 2012, Bentley et al 2017. One of these pathologies, polycystic ovary syndrome (PCOS), is the most common ovarian disease in reproductive age women (Lara et al 1993).…”

Changes in brain peptides associated with reproduction and energy homeostasis: Putative roles of gonadotrophin‐releasing hormone‐II and tyrosine hydroxylase in determining reproductive performance in response to daily food availability times in diurnal zebra finches

“…The primary antibodies that we used are specific and have been used for IHC in passerine birds, including zebra finches . Because GnRH antiserum recognises both GnRH‐I and GnRH‐II isoforms, we identified them based on immunoreactions with reference to their location in the brain (POA: GnRH‐I; midbrain: GnRH‐II) …”

“…18,20,21 Briefly, birds were deeply anaesthetised with ketamine-xylazine solution (0.003 mL g -1 body weight) and transcardially perfused successively with 50 mL saline The primary antibodies that we used are specific and have been used for IHC in passerine birds, including zebra finches. 18,20,21,48 Because GnRH antiserum recognises both GnRH-I and GnRH-II isoforms, we identified them based on immunoreactions with reference to their location in the brain (POA: GnRH-I; midbrain:…”