Department of Biology, University of Michigan, Ann Arbor, Michigan 48109-1048.
Integr Comp Biol. 2002 Jul;42(3):565-73. doi: 10.1093/icb/42.3.565.
Basal activity of the hypothalamo-pituitary-interrenal (HPI) axis changes over development in larval amphibians, but development of the responsiveness of this axis to an external stressor has not been studied. We compared developmental changes in whole-body corticosterone content of two anuran amphibian species, Rana pipiens (family Ranidae) and Xenopus laevis (family Pipidae). We also examined developmental changes in the responsiveness of the HPI axis by subjecting tadpoles of different developmental stages to a laboratory shaking/confinement stress and to ACTH injection. We measured whole-body corticosterone content as an indicator of the activity of the HPI axis. Whole-body corticosterone content of R. pipiens remained low during premetamorphosis and prometamorphosis but increased dramatically at metamorphic climax and remained elevated in juvenile frogs. By contrast, whole-body corticosterone content of X. laevis was highest during premetamorphosis, declined at the onset of prometamorphosis, increased at metamorphic climax and remained at climax levels in juvenile frogs. Premetamorphic and prometamorphic tadpoles of both species showed strong corticosterone responses to both shaking stress and ACTH injection. The magnitude and pattern of response differed among developmental stages, with premetamorphic tadpoles of both species showing greater responsiveness to stress and ACTH. Our results show that interrenal responsiveness is developed in premetamorphic tadpoles, suggesting that at these stages tadpoles are capable of mounting an increase in stress hormone production in response to changes in the external environment. Our results also highlight the importance of comparative studies in understanding the development of the stress axis.
下丘脑-垂体-肾上腺（HPI）轴的基础活性在幼年两栖动物的发育过程中会发生变化，但该轴对外部应激源的反应性的发育尚未得到研究。我们比较了两种蛙科两栖动物（Ranidae 家族的 Rana pipiens 和 Pipidae 家族的 Xenopus laevis）的全身皮质酮含量的发育变化。我们还通过将处于不同发育阶段的蝌蚪暴露于实验室摇晃/限制应激和 ACTH 注射来检查 HPI 轴反应性的发育变化。我们测量了作为 HPI 轴活性指标的全身皮质酮含量。在变态前期和变态前期，R. pipiens 的全身皮质酮含量保持较低水平，但在变态高峰期急剧增加，并在幼蛙中保持升高。相比之下，X. laevis 的全身皮质酮含量在变态前期最高，在变态前期开始时下降，在变态高峰期增加，并在幼蛙中保持在高峰期水平。两种物种的变态前期和变态前期蝌蚪对摇晃应激和 ACTH 注射均表现出强烈的皮质酮反应。反应的幅度和模式因发育阶段而异，两种物种的变态前期蝌蚪对应激和 ACTH 的反应性更强。我们的结果表明，间肾对皮质酮的反应性是在变态前期的蝌蚪中发展起来的，这表明在这些阶段，蝌蚪能够在外部环境变化时增加应激激素的产生。我们的结果还强调了比较研究在理解应激轴发育中的重要性。
