Molecular Neuroanatomical Bases of Control of Salmonid Spawning Migration

促性腺激素释放激素（GnRH）调节促性腺激素（GTHs）和其他垂体激素（如生长激素（GH）、催乳素（PRL）、生长肌动素（SL））的合成和释放，具有不同的季节性。在鲑鱼（Oncorhynchus masou）中，编码鲑鱼GnRH （sGnRH）前体的两个基因的表达在青春期前增加，并在性成熟过程中随季节变化。最近，我们在马苏鲑鱼中证明了五种GnRH受体（GnRH- r）基因在大脑、垂体和其他外周组织中以不同的模式表达。在本研究中，我们检测了生长和性成熟期间大脑和垂体中sGnRH和GnRH- r基因的季节性表达模式，以阐明多种GnRH- r在GnRH作用中的作用。此外，通过GnRH类似物（GnRHa）植入实验，检测了GnRH- r基因对GnRH响应的季节性变化。用GnRHa治疗鱼一周，取出脑和垂体。从未成熟期到产卵期，每个月重复一次植入试验。采用实时荧光定量PCR法测定两种sGnRHs和五种GnRH-Rs mrna的绝对含量。在大脑中，两种sGnRH mrna的数量在冬季和春季趋于高，在夏季趋于低，从夏末到产卵又再次增加。5种类型的GnRH-R mRNA的量变化与sGnRHs相似。在垂体中，5种GnRH-R mrna的数量在未成熟和成熟阶段表现出不同的变化，但在产卵前阶段有所增加，其中GnRHa处理使雌性数量增加，而雄性数量减少。sGnRH、GnRH- r和GTH亚基基因在产卵前的同时表达升高，可能对GnRH调控GTH亚基基因表达，进而控制上游迁移具有重要意义。

Gonadotropin-releasing hormone (GnRH) regulates synthesis and release of gonadotropins (GTHs) and other pituitary hormones, such as growth hormone (GH), prolactin (PRL), and somatolactin (SL) in a seasonally different manner. In masu salmon (Oncorhynchus masou), expression of two genes encoding salmon GnRH (sGnRH) precursors increases at prepubertal stages and changes with seasons during sexual maturation. Recently, we demonstrated in masu salmon that five types of GnRH receptor (GnRH-R) genes are expressed in the brain, pituitary and other peripheral tissues in different patterns. In the present study, we examined seasonal expression patterns of sGnRH and GnRH-R genes, in the brain and pituitary during growth and sexual maturation, to elucidate roles of the multiple GnRH-Rs in GnRH action. Moreover, seasonal changes in response to GnRH of GnRH-R genes _were examined by a GnRH analog (GnRHa) implantation experiment. The fish were treated with GnRHa for one week and the brains and pituitaries were taken out. This implantation experiment was repeated every month from immature to spawning periods. The absolute amounts of mRNAs for two sGnRHs and five GnRH-Rs were determined by a quantitative real-time PCR method. In the brain, the amounts of two sGnRH mRNAs tended to be high in winter and spring, and decreased toward summer, and again increased from late summer to spawning. The changes in the amounts of five types of GnRH-R mRNA were similar to that of sGnRHs. In the pituitary, the amounts of five GnRH-R mRNAs showed different changes during immature and maturing stages but increased in pre-spawning periods, in which GnRHa treatment increased the amounts in the females, whereas decreased in the males. The coincidental elevation of expression of sGnRH, GnRH-R and GTH subunit genes in the pre-spawning stage may be important in the regulation of GTH subunit gene expression by GnRH, and further control of upstream migration.