Responsiveness of pituitary to galanin throughout the reproductive cycle of male European sea bass (Dicentrarchus labrax)

Abstract

The neuropeptide galanin (Gal) is a putative factor regulating puberty onset and reproduction through its actions on the pituitary. The present study investigated the pituitary responsiveness to galanin and the patterns of galanin receptors (Galrs) expression throughout the reproductive cycle of two years old male European sea bass (Dicentrarchus labrax), an important aquaculture species. Quantitative analysis of pituitary and hypothalamus transcript expression of four galr subtypes revealed differential regulation according to the testicular developmental stage, with an overall decrease in expression from the immature stage to the mid-recrudescence stage. Incubation of pituitary cells with mammalian 1-29Gal peptide induced significant changes in cAMP concentration, with sensitivities that varied according to the testicular development stages. Furthermore 1-29Gal was able to stimulate both follicle stimulating hormone (Fsh) and luteinizing hormone (Lh) release from pituitary cell suspensions. The magnitude of the effects and effective concentrations varied according to reproductive stage, with generalized induction of Fsh and Lh release in animals sampled in January (full spermiation). The differential expression of galrs in pituitary and hypothalamus across the reproductive season, together with the differential effects of Gal on gonadotropins release in vitro strongly suggests the involvement of the galaninergic system in the regulation the hypothalamus-pituitary-gonad axis of male sea bass. This is to our knowledge the first clear evidence for the involvement of galanin in the regulation of reproduction in non-mammalian vertebrates.

Spexin and a Novel Cichlid-Specific Spexin Paralog Both Inhibit FSH and LH Through a Specific Galanin Receptor (Galr2b) in Tilapia

“…Recently, a plethora of neuropeptides involved in the control of reproduction were investigated. Most of them are stimulatory neuropeptides, such as neurokinin B (19), neuropeptide Y (20), secretoneurin (21), galanin (22), agouti-related peptide (23), kisspeptin (24), and melanocortin (25). However, the study of neuropeptides that relay their signal through inhibitory pathways is more challenging, and hence are less studied.…”

Spexin in the European sea bass, Dicentrarchus labrax: Characterization, brain distribution, and interaction with Gnrh and Gnih neurons

“…The presence of Galr1a, Galr1b, Galr2a, and Galr2b has been characterized in the pituitary of sea bass, with the first two receptors exhibiting significant changes in expression along the reproductive cycle (Martins et al., 2021 ). Interestingly, Gal stimulates pituitary gonadotropins release in vitro and gonadotropins release induced by Gal varies across the reproductive cycle (Pinto et al., 2017 ), actions that are probably mediated by galanin receptors present in gonadotropic cells. Considering that Spx acts on the same receptors as Gal, and that we did not observe any Spx1 fibers entering into the pituitary of this species, these results suggest that Spx1 produced in the PPD and PI may act on gonadotropic cells of sea bass in a paracrine or autocrine manner rather than in a neuroendocrine way, to modulate Lh and/or Fsh synthesis and secretion.…”