Center for Molecular and Comparative Endocrinology, University of New Hampshire, Durham, NH 03824, USA.
Gen Comp Endocrinol. 2011 Jan 15;170(2):276-82. doi: 10.1016/j.ygcen.2010.08.005. Epub 2010 Aug 13.
Sea lampreys are anadromous and semelparous, i.e., they spawn only once in their lifetime, after which they die. Sexual maturation is thus a synchronized process coordinated with the life stages of the lamprey. Recently, a novel gonadotropin-releasing hormone, lamprey GnRH-II (lGnRH-II), was identified in lampreys and suggested to have a hypothalamic role in reproduction (Kavanaugh et al., 2008). To further understand the role of lGnRH-II, changes in ovarian morphology, brain gonadotropin-releasing hormone (lGnRH-I, -II, and -III), and plasma estradiol were examined during the final two months of the reproductive season of adult male and female sea lamprey. The results showed significant correlations between water temperature, fluctuation of brain GnRHs, plasma estradiol and reproductive stages during this time. In males, lGnRH-I concentration increased early in the season, peaked, then declined with a subsequent increase with the final maturational stages. In comparison, lGnRH-II and -III concentrations were also elevated early in the season in males, dropped and then peaked in mid-season with a subsequent decline of lGnRH-II or increase of lGnRH-III at spermiation. In females, lGnRH-III concentration peaked in mid-season with a drop at ovulation while lGnRH-I remained unchanged during the season. In contrast, lGnRH-II concentrations in females were elevated at the beginning of the season and then dropped and remained low during the rest of the season. In summary, these data provide evidence that there are seasonal and differential changes of the three GnRHs during this final reproductive period suggesting specific roles for each of the GnRHs in male and female reproduction.
海七鳃鳗是溯河洄游性和一次性产卵的，也就是说，它们一生中只产卵一次，之后就会死亡。因此，性成熟是一个与七鳃鳗生命阶段同步的过程。最近，一种新的促性腺激素释放激素，海七鳃鳗 GnRH-II（lGnRH-II），在七鳃鳗中被鉴定出来，并被认为在生殖方面具有下丘脑作用（Kavanaugh 等人，2008 年）。为了进一步了解 lGnRH-II 的作用，在成年雌雄海七鳃鳗生殖季节的最后两个月，研究了卵巢形态、脑促性腺激素释放激素（lGnRH-I、-II 和 -III）和血浆雌二醇的变化。结果表明，在此期间，水温、脑 GnRH 波动、血浆雌二醇与生殖阶段之间存在显著相关性。在雄性中，lGnRH-I 浓度在季节早期升高，达到峰值，然后随着最终成熟阶段的到来而下降。相比之下，lGnRH-II 和 -III 浓度在雄性中也在季节早期升高，在季节中期下降，然后在中期达到峰值，随后在精子发生时 lGnRH-II 下降或 lGnRH-III 增加。在雌性中，lGnRH-III 浓度在季节中期达到峰值，在排卵时下降，而 lGnRH-I 在整个季节保持不变。相比之下，雌性 lGnRH-II 浓度在季节早期升高，然后下降并在季节剩余时间保持低水平。总之，这些数据提供了证据，表明在这个最后的生殖期，三种 GnRH 存在季节性和差异变化，表明每种 GnRH 在雄性和雌性生殖中都有特定的作用。
