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The Gonadoliberin(S)-Gonadotropin(S) Axis in the Eel: Expression and Regulation Under Induced Maturation and Sex Steroid Feedbacks

  • Chapter
Spawning Migration of the European Eel

Part of the book series: Fish & Fisheries Series ((FIFI,volume 30))

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At the start of the reproductive migration towards the Sargasso Sea, silver eels are still immature and remain blocked at this prepubertal stage as long as migration is prevented. To date, adult mature eels have never been caught and only experimental treatments of silver eels with gonadotropic hormones have led to the observation of sexually mature animals (Fontaine 1936; Fontaine et al. 1964). The lack of sexual maturation at the silver stage is due to a deficient production of pituitary gonadotro-pins (GtHs) (Dufour et al. 1983a, b). Stimulation of synthesis and release of pituitary gonadotropin in the silver eel can be induced by combined treatments with a GnRH-agonist and a dopamine-antagonist, indicating that a double neuroendocrine block was responsible for the deficient pituitary gonadotropic function: a lack of endogenous stimulation by GnRH due to a deficient production of GnRH and a strong dopaminer-gic inhibition of GnRH action (Dufour et al. 1988, 1991; Vidal et al. 2004).

In vertebrates, it is well known that the gonadotropins (luteinizing hormone, LH and follicle stimulating hormone, FSH) are secreted by the gonadotrophs in the anterior pituitary under the control of the gonadoliberin (GnRH) produced by the brain. The gonadotropins act on the ovaries and testes to promote gametogenesis and reproductive function, and to stimulate the production of sex steroids. In turn, gonadotropin secretion and subunit gene expression are regulated by sex steroids acting either directly on the gonadotrophs or indirectly by alterations of GnRH from the hypothalamus (Gharib et al. 1990). This review will mainly focus on the differential feedbacks exerted by sex steroids on the gonadoliberins/gonadotropins system in teleost fishes (especially the European eel).

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Authors and Affiliations

  1. Department of Biology, Karlstad University, Karlstad, S-651 88, Sweden

    Monika Schmitz

  2. Department of Aquaculture, National Taiwan Ocean University, Keelung 202, Taiwan, ROC

    Ching-Fong Chang

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  1. Salima Aroua
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  2. Karine Rousseau
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  4. Ching-Fong Chang
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  1. Institute of Biology, Leiden University, POB 9516, RA Leiden, 2300, The Netherlands

    Guido van den Thillart

  2. UMR CNRS 5178 “Biology of Marine Organisms and Ecosystems” 7 rue Cuvier, CP 32, Museum National d'Histoire Naturelle DMPA, 75231 Paris cedex 05, France

    Sylvie Dufour

  3. Department of Chemical and Biological Science, University of Huddersfield Queensgate, HD1 3DH, UK

    J. Cliff Rankin

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Aroua, S., Rousseau, K., Schmitz, M., Chang, CF., Dufour, S. (2009). The Gonadoliberin(S)-Gonadotropin(S) Axis in the Eel: Expression and Regulation Under Induced Maturation and Sex Steroid Feedbacks. In: van den Thillart, G., Dufour, S., Rankin, J.C. (eds) Spawning Migration of the European Eel. Fish & Fisheries Series, vol 30. Springer, Dordrecht. https://doi.org/10.1007/978-1-4020-9095-0_11

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