Aroua Salima, Schmitz Monika, Baloche Sylvie, Vidal Bernadette, Rousseau Karine, Dufour Sylvie
MNHN, Département des Milieux et Peuplements Aquatiques, USM 0401, UMR 5178 CNRS, Paris, France.
Neuroendocrinology. 2005;82(3-4):221-32. doi: 10.1159/000092642. Epub 2006 Apr 10.
Silvering (transition from yellow to silver eel) has been traditionally considered as a metamorphosis in view of the numerous morphological, physiological and behavioral changes preparing the eel for the oceanic migration. However, some changes, such as increases in gonad weight and steroidogenesis, suggest that silvering could also be considered as a pubertal event. In order to assess which endocrine axis may be involved in the induction of silvering, we compared the profiles of pituitary and peripheral hormones during the transition from yellow to silver female eels. A strong activation of the gonadotropic axis was shown during silvering. Follicle-stimulating hormone (FSH) mRNA levels increased during the early stages of silvering, followed by a later increase in luteinizing hormone (protein and mRNA) levels. In addition, plasma levels of sexual steroids (estradiol, E2; testosterone, T, and 11-ketotestosterone) and of vitellogenin significantly increased. In contrast, thyrotropin mRNA levels did not change and no or weak variations in plasma thyroid hormones were observed, indicating no or moderate change of the thyrotropic axis during silvering. Similarly, the somatotropic axis was not activated, as shown by pituitary growth hormone expression (protein and mRNA) and plasma levels. In addition, we studied the effects of chronic treatments of female yellow eels with thyroid hormone (thyroxine, T4) and sex steroids (T and E2) on biometrical parameters characteristics of silvering. T induced an increase in eye size and a reduction of digestive tract, whereas T4 and E2 had no effect. These hormonal profiles and experimental data lead to the conclusion that eel silvering should be considered as an onset of puberty rather than a 'genuine' metamorphosis.
鉴于鳗鱼为进行海洋洄游所发生的众多形态、生理和行为变化，传统上一直将银化（从黄鳗转变为银鳗）视为一种变态。然而，一些变化，如性腺重量增加和类固醇生成，表明银化也可被视为青春期事件。为了评估哪个内分泌轴可能参与银化的诱导过程，我们比较了雌性黄鳗向银鳗转变过程中垂体和外周激素的变化情况。结果显示，银化过程中性腺轴被强烈激活。在银化早期，促卵泡激素（FSH）mRNA水平升高，随后促黄体生成素（蛋白质和mRNA）水平在后期升高。此外，性类固醇（雌二醇、E2；睾酮、T和11 - 酮睾酮）和卵黄蛋白原的血浆水平显著升高。相比之下，促甲状腺激素mRNA水平没有变化，血浆甲状腺激素也未观察到变化或仅有微弱变化，这表明银化过程中促甲状腺轴没有变化或仅有适度变化。同样，生长激素轴也未被激活，垂体生长激素表达（蛋白质和mRNA）及血浆水平均表明了这一点。此外，我们研究了用甲状腺激素（甲状腺素、T4）和性类固醇（T和E2）长期处理雌性黄鳗对银化相关生物测量参数的影响。T导致眼睛大小增加和消化道缩小，而T4和E2没有影响。这些激素变化情况和实验数据得出结论：鳗鱼银化应被视为青春期的开始，而非“真正的”变态。
