Williams Cory T, Radonich Maya, Barnes Brian M, Buck C Loren
Center for Bioengineering Innovation and Department of Biological Sciences, Northern Arizona University, Flagstaff, AZ, USA.
University of Alaska Anchorage, Anchorage, AK, USA.
J Comp Physiol B. 2017 Jul;187(5-6):693-703. doi: 10.1007/s00360-017-1069-6. Epub 2017 Mar 22.
Circadian clocks are near universal among organisms and play a key role in coordinating physiological and metabolic functions to anticipate or coincide with predictable daily changes in the physical and social environment. However, whether circadian rhythms persist and are functionally important during hibernation in all mammals is currently unclear. We examined whether circadian rhythms of body temperature (T ) persist during multi-day, steady-state torpor and investigated the association between timing of animal emergence, exposure to light, and resumption of activity and T rhythms in free-living and captive male arctic ground squirrels. High-resolution (0.02 °C) temperature loggers revealed that circadian rhythms of T were not present during deep torpor in free-living arctic ground squirrels. Significant circadian rhythms of T resumed, however, following the resumption of euthermia, but prior to emergence, though rhythms became much more robust coincident with aboveground emergence. Additionally, squirrels maintained in captivity under conditions of constant darkness spontaneously developed significant circadian rhythms of T and activity soon after ending torpor. Exposing animals to a 5-s pulse of light within a week when they ended torpor increased the strength of rhythms. Our results are consistent with the hypothesis that circadian clock function is inhibited during hibernation in arctic ground squirrels, and we postulate that exposure to external stimuli, such as light in free-living animals, and meals or acute disturbance for captive squirrels, may enhance T rhythmicity by synchronizing loosely coupled circadian oscillators within the suprachiasmatic nucleus.
昼夜节律钟在生物界几乎普遍存在，在协调生理和代谢功能以预测或与物理和社会环境中可预测的每日变化同步方面发挥着关键作用。然而，目前尚不清楚在所有哺乳动物的冬眠过程中，昼夜节律是否持续存在以及是否具有重要功能。我们研究了自由生活和圈养的雄性北极地松鼠在多日稳态蛰伏期间体温（T）的昼夜节律是否持续，并调查了动物出蛰时间、光照暴露以及活动恢复与T节律之间的关联。高分辨率（0.02°C）温度记录器显示，自由生活的北极地松鼠在深度蛰伏期间不存在T的昼夜节律。然而，在恢复正常体温后但出蛰前，T的显著昼夜节律恢复了，尽管节律在与地面出蛰同时出现时变得更为强劲。此外，在持续黑暗条件下圈养的松鼠在结束蛰伏后不久会自发形成显著的T和活动的昼夜节律。在动物结束蛰伏后的一周内，给予它们5秒的光脉冲会增强节律的强度。我们的结果与北极地松鼠在冬眠期间昼夜节律钟功能受到抑制的假设一致，并且我们推测，暴露于外部刺激，如自由生活动物中的光照，以及圈养松鼠的进食或急性干扰，可能通过使视交叉上核内松散耦合的昼夜振荡器同步来增强T的节律性。
