Mishra Ila, Singh Devraj, Kumar Vinod
IndoUS Center for Biological Timing, Department of Zoology, University of Delhi, Delhi 110 007, India.
IndoUS Center for Biological Timing, Department of Zoology, University of Delhi, Delhi 110 007, India.
Horm Behav. 2017 Aug;94:114-123. doi: 10.1016/j.yhbeh.2017.07.004. Epub 2017 Jul 25.
The circadian rhythms are involved in the photostimulation of seasonal responses in migratory blackheaded buntings. Here, we investigated whether changes in daily levels and rhythm in corticosterone (cort) and insulin secretions were associated with transitions in the photoperiodic seasonal states. Buntings were exposed to short days to maintain the winter (photosensitive) non-migratory state, and to long days for varying durations to induce the premigratory, migratory (shown by migratory restlessness at night, Zugunruhe) and summer non-migratory (photorefractory) states. We monitored activity patterns, and measured plasma cort and insulin levels at six and four times, respectively, over 24h in each seasonal state. Buntings were fattened and weighed heavier, and exhibited intense nighttime activity in the migratory state. The daytime activity patterns also showed seasonal differences, with a bimodal pattern with morning and evening activity bouts only in the summer non-migratory state. Further, the average baseline hormone levels were significantly higher in premigratory and migratory than in the winter non-migratory state. Both cort and insulin levels showed a significant daily rhythm, but with seasonal differences. Whereas, cort rhythm acrophases (estimated time of peak secretion over 24h) were at night in the winter non-migratory, premigratory and migratory states, the insulin rhythm acrophases were found early in the day and night in winter and summer non-migratory states, respectively. These results suggest that changes in daily levels and rhythm in cort and insulin mediate changes in the physiology and behavior with photostimulated transition in seasonal states in migratory blackheaded buntings.
昼夜节律参与了迁徙黑头鹀季节性反应的光刺激过程。在此，我们研究了皮质酮（cort）和胰岛素分泌的日水平及节律变化是否与光周期季节性状态的转变相关。将鹀暴露于短日照下以维持冬季（光敏）非迁徙状态，暴露于长日照下不同时长以诱导迁徙前期、迁徙期（以夜间迁徙不安，即 Zugunruhe 表现）和夏季非迁徙（光不应性）状态。我们监测了活动模式，并在每个季节性状态下的 24 小时内分别于六个时间点和四个时间点测量了血浆皮质酮和胰岛素水平。鹀在迁徙状态下会育肥且体重增加，并表现出强烈的夜间活动。白天的活动模式也呈现出季节性差异，仅在夏季非迁徙状态下呈现出包含早晚活动高峰的双峰模式。此外，迁徙前期和迁徙期的平均基础激素水平显著高于冬季非迁徙状态。皮质酮和胰岛素水平均呈现出显著的日节律，但存在季节性差异。在冬季非迁徙、迁徙前期和迁徙期，皮质酮节律的高峰相位（24 小时内估计的分泌高峰时间）在夜间，而胰岛素节律的高峰相位在冬季非迁徙状态下出现在白天早些时候，在夏季非迁徙状态下出现在白天和夜间。这些结果表明，皮质酮和胰岛素的日水平及节律变化介导了迁徙黑头鹀在光刺激诱导的季节性状态转变过程中的生理和行为变化。
