Distribution of three GnRHs in the brain and pituitary of the wild Japanese flounder Paralichthys olivaceus

Abstract

Wild adult maturing and immature female Japanese flounder Paralichthys olivaceus were collected in June 2004 and January 2005, respectively, to clarify a possible role of gonadotropinreleasing hormones (GnRHs) in reproduction. Levels of salmon GnRH (sGnRH), chicken GnRH-II (cGnRH-II) and sea bream GnRH (sbGnRH) in the brain and pituitary were examined by time-resolved fluoroimmunoassay. Three forms of GnRHs were detected in the discrete brain at various levels. In the pituitary of both maturing and immature fish, sbGnRH was abundant together with a pronounced amount of sGnRH, whereas cGnRH-II was almost below the detectable limit. In maturing fish, levels of sbGnRH were high in the telencephalon, hypothalamus and pituitary, while levels of sbGnRH of immature fish were very low in these regions. These results indicate that sbGnRH is mainly responsible for gonadotropin secretion, and that sbGnRH in the anterior part of the brain is associated with gonadal maturation in the Japanese flounder.

Brain morphology and immunohistochemical localization of the gonadotropin-releasing hormone in the bluefin tuna, Thunnus thynnus

“…Surprisingly no immunoreactive structures were found with anti sbGnRH serum although sbGnRH is thought to be the most important regulator of gonadal function (Lethimonier et al, 2004;Pham et al, 2006), and sbGnRH-producing cell bodies project their axons mainly to the pituitary gland (White et al, 1995;Gonzalez-Martinez et al, 2001).This negative result is of difficult interpretation despite the fact that different dilutions and incubation times were used in the experiments carried out here. The lack of anti sbGnRH immunostaining likely depends on technical reasons, including the non-specificity of the primary antibody used, as well as likely antigen damage during the fixation and paraffin wax embedding.…”

“…In teleost fish, 8 GnRH variants have been identified, although two or three of the GnRH forms co-exist in the brain albeit distributed differently (Pham et al, 2006). Among the Pleuronectiforms and Perciformes, sea bream (sb)GnRH-producing cell bodies in the preoptic area project their axons mainly to the pituitary, whereas salmon sGnRHand chicken cGnRH-producing cells connect different areas of the brain through their axons, which, however, do not project to the pituitary (White et al, 1995;Gonzalez-Martínez et al, 2001;Amano et al, 2002).…”

“…Fourteen forms of GnRH have so far been identified in different vertebrate species (Pham et al, 2006). In teleost fish, 8 GnRH variants have been identified, although two or three of the GnRH forms co-exist in the brain albeit distributed differently (Pham et al, 2006).…”

Induction of final oocyte maturation in Cyprinidae fish by hypothalamic factors: a review

“…Into the GnRH1 line belong types such as mGnRH (Matsuo et al, 1971), seabream GnRH (Powell et al, 1994), catfish GnRH (Bogerd et al, 1992). They fulfil hypophysiotropic functions (Pham et al, 2006) and are found in the ventral telencephalon, the preooptic area, the basal hypothalamus and the pituitary gland (Dubois et al, 2002). Despite great effort, the occurrence of the GnRH1 line has not been detected in the cyprinids.…”

Clonagem e avaliação da expressão gênica do sbGnRH em machos juvenis e adultos de linguado, Paralichthys orbignyanus

“…Três principais isoformas do GnRH foram identificadas em pleuronectiformes: sGnRH (salmon GnRH), cGnRH-II (chicken GnRH-II) e sbGnRH (sea bream GnRH) (Amano et al, 2002;Pham et al, 2007), e a isoforma sbGnRH foi identificada como a provável responsável pela maturação gonadal (puberdade) nesses peixes (Amano et al, 2008). Além disso, a expressão desse gene parece não estar restrita ao sistema nervoso central dos peixes.…”