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Changes in levels of GnRH in the brain and pituitary and GTH in the pituitary in male masu salmon, Oncorhynchus masou, from hatching to maturation.

Abstract：

:Levels of two types of gonadotropin-releasing hormone (salmon GnRH and chicken GnRH-II) in the brain and pituitary, and content of gonadotropin (GTHIβ and IIβ) in the pituitary were measured in male masu salmon from hatching to gonadal maturation for three years in order to clarify the involvement of GnRHs in precocious maturation.Underyearling precocious males were distinguishable in summer of year 1 and were marked by an increased GSI. Spermiation was observed among these individuals thereafter every autumn. Pituitary GTHIβ content in both precocious and immature males, and GTHIIβ content in precocious males showed seasonal fluctuations - high in autumn and low in winter. Pituitary GTHIIβ content was low in immature males.Pituitary sGnRH content in precocious males increased from spring to autumn during the three-year period. sGnRH concentrations in discrete brain areas showed seasonal changes - high during autumn to winter and low in summer. Concentrations in the olfactory bulbs and hypothalamus increased significantly in association with testicular maturation during year 3. sGnRH concentrations in the hypothalamus were significantly higher in precocious males than in immature males; this was possibly due to positive feedback of steroid hormones. cGnRH-II was undetectable in the pituitary and no distinct changes were observed in its concentration in the brain in relation to maturation.The phenomenon of underyearling precocious maturation is considered to be triggered before the onset of early summer. It is suggested that males which mature precociously are larger in size and contain much sGnRH in the pituitary before the outward signs of precocity appear; sGnRH may stimulate GTH II synthesis and induce precocious maturation.

journal_name

Fish Physiol Biochem

journal_title

Fish physiology and biochemistry

authors

Amano M,Aida K,Okumoto N,Hasegawa Y

doi

10.1007/BF00004570

subject

Has Abstract

pub_date

1993-07-01 00:00:00

pages

233-40

issue

1-6

eissn

0920-1742

issn

1573-5168

journal_volume

pub_type

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Changes in levels of GnRH in the brain and pituitary and GTH in the pituitary in male masu salmon, Oncorhynchus masou, from hatching to maturation.