title: Long-term exposure to continuous light inhibits precocity in European male sea bass (Dicentrarchus labrax, L.): hormonal aspects.
abstract: The effect of long-term exposure to continuous light on the hormonal aspects of the reproductive axis was investigated in juvenile male sea bass (Dicentrarchus labrax, L.) during the first annual cycle. Four-month-old fish were exposed to a simulated natural photoperiod (NP) and a continuous light (24 h) regime (LL) under natural conditions of temperature (13.3-25.8 degrees C). A dot-blot technique was used to analyse gonadotropin (the common glycoprotein alpha, GPalpha; the follicle stimulating hormone beta, FSHbeta; and the luteinizing hormone beta, LHbeta, subunits) mRNA levels in the pituitary during the experiment. A homologous ELISA was used to determine pituitary sea bream gonadotropin-releasing hormone (sbGnRH) and LH and plasma LH levels; gonadal and plasma sex steroids concentrations were determined by specific immunoassays. LL significantly inhibited the expression of all three gonadotropins subunits in the pituitary. However, no significant differences on plasma LH levels were observed between NP and LL groups throughout the period of the experience. Long-term exposure to LL regime was extremely effective in inhibiting gonadal growth and hence precocious maturation as well as the accumulation of Testosterone (T) and 11-ketotestosterone (11-KT) in the gonads compared to the control group. 11-KT plasma levels remained low and unchanged in the LL group during the study. This work describe important alterations of the endocrine system, particularly at the pituitary-gonad axis provoked by exposure to continuous illumination and discusses the mechanism by which precocity in male sea bass is generated.
authors.affiliation: Consejo Superior de Investigaciones Científicas (CSIC), Instituto de Acuicultura de Torre la Sal, Ribera de Cabanes, 12595 Torre de la Sal, Castellón, Spain.
authors.forename: Lucinda
authors.initials: L
authors.lastname: Rodríguez
authors.forename: Ideal
authors.initials: I
authors.lastname: Begtashi
authors.forename: Silvia
authors.initials: S
authors.lastname: Zanuy
authors.forename: Manuel
authors.initials: M
authors.lastname: Carrillo
mesh_terms: D000818:Animals; D001492:Bass / Q000254:growth & development*; D004797:Enzyme-Linked Immunosorbent Assay; D007987:Gonadotropin-Releasing Hormone / Q000378:metabolism / Q000494:pharmacology; D008027:Light; D007986:Luteinizing Hormone / Q000096:biosynthesis / Q000097:blood; D008297:Male; D010902:Pituitary Gland / Q000502:physiology; D013696:Temperature; D013737:Testis / Q000254:growth & development* / Q000502:physiology; D013739:Testosterone / Q000096:biosynthesis / Q000097:blood
chemical_list: D007987:Gonadotropin-Releasing Hormone; D013739:Testosterone; D007986:Luteinizing Hormone