The Medio-Basal Hypothalamus as a Dynamic and Plastic Reproduction-Related Kisspeptin-gnrh-Pituitary Center in Fish

Abstract

Kisspeptin regulates reproductive events, including puberty and ovulation, primarily via GnRH neurons. Prolonged treatment of prepubertal striped bass females with kisspeptin (Kiss) 1 or Kiss2 peptides failed to enhance puberty but suggested a gnrh-independent pituitary control pathway. Kiss2 inhibited, but Kiss1 stimulated, FShβ expression and gonadal development, although hypophysiotropic gnrh1 and gnrh receptor expression remained unchanged. In situ hybridization and immunohistochemistry on brains and pituitaries revealed a differential plasticity between the 2 kisspeptin neurons. The differences were most pronounced at the prespawning phase in 2 regions along the path of gnrh1 axons: the nucleus lateralis tuberis (NLT) and the neurohypophysis. Kiss1 neurons appeared in the NLT and innervated the neurohypophysis of prespawning males and females, reaching Lh gonadotropes in the proximal pars distalis. Males, at all reproductive stages, had Kiss2 innervations in the NLT and the neurohypophysis, forming large axonal bundles in the former and intermingling with gnrh1 axons. Unlike in males, only preovulatory females had massive NLT-neurohypophysis staining of kiss2. Kiss2 neurons showed a distinct appearance in the NLT pars ventralis-equivalent region only in spawning zebrafish, indicating that this phenomenon is widespread. These results underscore the NLT as important nuclei for kisspeptin action in 2 facets: 1) kisspeptin-gnrh interaction, both kisspeptins are involved in the regulation of gnrh release, in a stage- and sex-dependent manner, especially at the prespawning phase; and 2) gnrh-independent effect of Kiss peptides on the pituitary, which together with the plastic nature of their neuronal projections to the pituitary implies that a direct gonadotropic regulation is plausible.

Lack of evidence for a role of olfaction on first maturation in farmed sea bass Dicentrarchus labrax

“…This lack of differential GnRH1 and GnRH3 expression in face of downregulation of gonadotrophin b-subunit gene expression is surprising since it has been shown that neurons projecting from olfactory regions express GnRH1 and GnRH3 gene products (González-Martínez et al, 2001;Kah et al, 2007) and ablation of GnRH3 in zebrafish lead to reduced fecundity (Abraham et al, 2010). Our gene expression results for KISS2 and gonadotrophin b-subunits suggest a direct action of kisspeptin in the pituitary in this species, as had been suggested for rats, goldfish (C. auratus) and striped bass (Morone saxatilis) (Chang et al, 2012;Gutiérrez-Pascual et al, 2007;Zmora et al, 2014). In sea bass kiss2 neurons have been mapped mainly to the hypothalamus with projections to the subpallium and pallium, the preoptic region, the thalamus, the pretectal area, the optic tectum, the torus semicircularis, the mediobasal medial and caudal hypothalamus, and the neurohypophysis (Escobar et al, 2013a,b).…”

Neurokinin B regulates reproduction via inhibition of kisspeptin in a teleost, the striped bass

“…Lh levels in the plasma were measured using ELISA as previously described (Mananos et al 1997). Levels of Fsh were measured using a specific ELISA developed for tilapia Fsh (Aizen et al 2007) and validated for use in STB (Zmora et al 2014). Gnrh decapeptide levels were measured using ELISA (Holland et al 1998, Zmora et al 2014.…”

“…Levels of Fsh were measured using a specific ELISA developed for tilapia Fsh (Aizen et al 2007) and validated for use in STB (Zmora et al 2014). Gnrh decapeptide levels were measured using ELISA (Holland et al 1998, Zmora et al 2014. 11-Ketotestosterone (11-KT) levels in the plasma were measured using 11-KT EIA kit (Cayman Chemicals) according to the manufacturer's protocol.…”

Transcriptome annotation and marker discovery in white bass (Morone chrysops) and striped bass (Morone saxatilis)

“…; Zmora et al . ). Genetic information has been restricted to a single‐tissue (ovary) transcriptome and a microsatellite linkage map from striped bass (Liu et al .…”