Jansen Heiko T, Leise Tanya, Stenhouse Gordon, Pigeon Karine, Kasworm Wayne, Teisberg Justin, Radandt Thomas, Dallmann Robert, Brown Steven, Robbins Charles T
Department of Integrative Physiology and Neuroscience, College of Veterinary Medicine, Washington State University, Mailstop 7620, Veterinary and Biomedical Research Bldg., Room 205, Pullman, WA 99164-7620 USA.
Department of Mathematics and Statistics, Amherst College, Amherst, MA 01002 USA.
Front Zool. 2016 Sep 17;13:42. doi: 10.1186/s12983-016-0173-x. eCollection 2016.
Most biological functions are synchronized to the environmental light:dark cycle via a circadian timekeeping system. Bears exhibit shallow torpor combined with metabolic suppression during winter dormancy. We sought to confirm that free-running circadian rhythms of body temperature (Tb) and activity were expressed in torpid grizzly (brown) bears and that they were functionally responsive to environmental light. We also measured activity and ambient light exposures in denning wild bears to determine if rhythms were evident and what the photic conditions of their natural dens were. Lastly, we used cultured skin fibroblasts obtained from captive torpid bears to assess molecular clock operation in peripheral tissues. Circadian parameters were estimated using robust wavelet transforms and maximum entropy spectral analyses.
Captive grizzly bears housed in constant darkness during winter dormancy expressed circadian rhythms of activity and Tb. The rhythm period of juvenile bears was significantly shorter than that of adult bears. However, the period of activity rhythms in adult captive bears was virtually identical to that of adult wild denning bears as was the strength of the activity rhythms. Similar to what has been found in other mammals, a single light exposure during the bear's active period delayed subsequent activity onsets whereas these were advanced when light was applied during the bear's inactive period. Lastly, in vitro studies confirmed the expression of molecular circadian rhythms with a period comparable to the bear's own behavioral rhythms.
Based on these findings we conclude that the circadian system is functional in torpid bears and their peripheral tissues even when housed in constant darkness, is responsive to phase-shifting effects of light, and therefore, is a normal facet of torpid bear physiology.
大多数生物功能通过昼夜节律计时系统与环境的光暗循环同步。熊在冬季休眠期间表现出伴有代谢抑制的浅蛰伏状态。我们试图确认体温（Tb）和活动的自由运行昼夜节律是否在蛰伏的灰熊（棕熊）中表现出来，以及它们是否对环境光有功能反应。我们还测量了在洞穴中野生熊的活动和环境光照暴露情况，以确定节律是否明显以及它们自然洞穴的光照条件如何。最后，我们使用从圈养的蛰伏熊身上获取的培养皮肤成纤维细胞来评估外周组织中的分子时钟运作情况。使用稳健小波变换和最大熵谱分析来估计昼夜节律参数。
冬季休眠期间饲养在持续黑暗环境中的圈养灰熊表现出活动和体温的昼夜节律。幼年熊的节律周期明显短于成年熊。然而，成年圈养熊的活动节律周期与成年野生洞穴熊的活动节律周期几乎相同，活动节律的强度也相同。与在其他哺乳动物中发现的情况类似，在熊的活跃期单次光照会延迟随后的活动开始时间，而在熊的不活跃期光照则会提前活动开始时间。最后，体外研究证实了分子昼夜节律的表达，其周期与熊自身的行为节律相当。
基于这些发现，我们得出结论，即使饲养在持续黑暗环境中，昼夜节律系统在蛰伏的熊及其外周组织中仍起作用，对光的相位转移效应有反应，因此，是蛰伏熊生理学的一个正常方面。
