Chapter 3 The GnRH System and the Neuroendocrine Regulation of Reproduction

Publisher This chapter discusses the neuroendocrine pathways that regulate the synthesis and release of the pituitary gonadotropins, follicle-stimulating hormone (FSH) and luteinizing hormone (LH), in teleost fish with a primary focus on the multiple forms of both gonadotropinreleasing hormone (GnRH) and its receptors in relation to their actions within the brain and pituitary. Recent studies have demonstrated that a vast number of neurotransmitters, neuropeptides and other factors exert inhibitory and/or stimulatory control over the GnRH–FSH/LH system. The identity and roles of these factors at the various stages of gonadal development are also discussed in the chapter together with an examination of the manner in which the actions of sex steroids and the inhibitory neurotransmitter dopamine coordinate the activation of the GnRH–FSH/LH system during puberty and in relation to sexual maturation and spawning. Gonadal steroids and changes in steroid feedback regulation appear to play a role in mediating the seasonal/maturational differences in the availability of LH and FSH for release.