Onuma Takeshi A, Sato Shunpei, Katsumata Hiroshi, Makino Keita, Hu Weiwei, Jodo Aya, Davis Nancy D, Dickey Jon T, Ban Masatoshi, Ando Hironori, Fukuwaka Masa-Aki, Azumaya Tomonori, Swanson Penny, Urano Akihisa
Graduate School of Bioresource and Bioenvironmental Sciences, Kyushu University, Fukuoka 812-8581, Japan.
J Exp Biol. 2009 Jan;212(Pt 1):56-70. doi: 10.1242/jeb.021352.
The activity of the pituitary-gonadal axis (PG axis) in pre-migratory and homing chum salmon was examined because endocrine mechanisms underlying the onset of spawning migration remain unknown. Pre-migratory fish were caught in the central Bering Sea in June, July and September 2001, 2002 and 2003, and in the Gulf of Alaska in February 2006. They were classified into immature and maturing adults on the basis of gonadal development. The maturing adults commenced spawning migration to coastal areas by the end of summer, because almost all fish in the Bering Sea were immature in September. In the pituitaries of maturing adults, the copy numbers of FSHbeta mRNA and the FSH content were 2.5- to 100-fold those of the immature fish. Similarly, the amounts of LHbeta mRNA and LH content in the maturing adults were 100- to 1000-fold those of immature fish. The plasma levels of testosterone, 11-ketotestosterone and estradiol were higher than 10 nmol l(-1) in maturing adults, but lower than 1.0 nmol l(-1) in immature fish. The increase in the activity of the PG-axis components had already initiated in the maturing adults while they were still in the Gulf of Alaska in winter. In the homing adults, the pituitary contents and the plasma levels of gonadotropins and plasma sex steroid hormones peaked during upstream migration from the coast to the natal hatchery. The present results thus indicate that the seasonal increase in the activity of the PG axis is an important endocrine event that is inseparable from initiation of spawning migration of chum salmon.
由于产卵洄游开始的内分泌机制尚不清楚，因此对洄游前和洄游归巢的大麻哈鱼的垂体-性腺轴（PG轴）活性进行了研究。2001年、2002年和2003年的6月、7月和9月以及2006年2月在白令海中部捕获洄游前的鱼，以及在阿拉斯加湾捕获。根据性腺发育情况将它们分为未成熟和成熟的成年鱼。成熟的成年鱼在夏末开始向沿海地区进行产卵洄游，因为9月白令海中几乎所有的鱼都是未成熟的。在成熟成年鱼的垂体中，FSHβmRNA的拷贝数和FSH含量是未成熟鱼的2.5至100倍。同样，成熟成年鱼中LHβmRNA的量和LH含量是未成熟鱼的100至1000倍。成熟成年鱼中睾酮、11-酮睾酮和雌二醇的血浆水平高于10 nmol l(-1)，而未成熟鱼中低于1.0 nmol l(-1)。PG轴成分活性的增加在成熟成年鱼冬季仍在阿拉斯加湾时就已经开始。在洄游归巢的成年鱼中，促性腺激素的垂体含量和血浆水平以及血浆性类固醇激素在上游从海岸向出生孵化场洄游期间达到峰值。因此，目前的结果表明，PG轴活性的季节性增加是一个重要内分泌事件，与大麻哈鱼产卵洄游的开始密不可分。
