Dayger Catherine A, Lutterschmidt Deborah I
Portland State University, Department of Biology, 1719 SW 10th Ave., Portland, OR 97201, United States.
Gen Comp Endocrinol. 2017 May 15;246:29-36. doi: 10.1016/j.ygcen.2017.03.008. Epub 2017 Mar 18.
Glucocorticoids often rise and fall with a variety of external and internal cues and frequently vary among life-history stages. This suggests that changing glucocorticoids may coordinate life-history transitions. To explore this hypothesis, we asked if the time-course of stress-induced glucocorticoid levels differ between two life-history transitions (i.e., spring and fall migration) in female red-sided garter snakes (Thamnophis sirtalis parietalis). We collected non-migratory females from a communal den and migratory females from a road along the migration route and treated them with 4h of capture stress; plasma corticosterone was measured before, during and after capture stress. During the spring, den-collected females exhibited a stress-induced peak in corticosterone at an earlier sampling time than migrating, road-collected females. Because the pattern of corticosterone responses varied with migratory state, negative feedback on and/or sensitivity of the hypothalamus-pituitaryadrenal (HPA) axis may be linked to spring migration. During the fall, capture stress elicited an increase in corticosterone in den-collected females but not in migrating, road-collected females. Baseline corticosterone was higher and both maximal and integrated corticosterone responses were lower during the fall compared to spring, indicating that stress responses are smaller when baseline corticosterone is elevated, perhaps due to a "ceiling effect". These data suggest that HPA axis regulation changes during seasonal migration, possibly via altering negative feedback, HPA axis sensitivity, or some other mechanism. This study supports the hypothesis that glucocorticoids coordinate life-history events and suggests that examining a suite of stress response characteristics is most informative for understanding the function of HPA modulation.
糖皮质激素常常随着各种外部和内部线索而起伏，并且在不同的生活史阶段频繁变化。这表明，不断变化的糖皮质激素可能协调着生活史的转变。为了探究这一假设，我们研究了处于两个生活史转变阶段（即春季和秋季迁徙）的雌性红侧带蛇（Thamnophis sirtalis parietalis）应激诱导的糖皮质激素水平的时间进程是否存在差异。我们从一个公共巢穴收集了非迁徙期的雌性蛇，从迁徙路线上的一条道路收集了迁徙期的雌性蛇，并对它们施加了4小时的捕捉应激；在捕捉应激前、应激期间和应激后测量血浆皮质酮水平。在春季，从巢穴收集的雌性蛇在比从道路上收集的迁徙雌性蛇更早的采样时间出现了应激诱导的皮质酮峰值。由于皮质酮反应模式随迁徙状态而变化，下丘脑 - 垂体 - 肾上腺（HPA）轴的负反馈和/或敏感性可能与春季迁徙有关。在秋季，捕捉应激使从巢穴收集的雌性蛇的皮质酮增加，但对从道路上收集的迁徙雌性蛇没有影响。与春季相比，秋季的基础皮质酮水平更高，而皮质酮的最大反应和综合反应更低，这表明当基础皮质酮升高时应激反应较小，可能是由于“天花板效应”。这些数据表明，在季节性迁徙过程中，HPA轴调节发生了变化，可能是通过改变负反馈、HPA轴敏感性或其他一些机制。这项研究支持了糖皮质激素协调生活史事件的假设，并表明检查一系列应激反应特征对于理解HPA调节的功能最具信息价值。
