Malan André
Institute of Cellular and Integrative Neurosciences, CNRS (National Center for Scientific Research) and University of Strasbourg, France.
J Biol Rhythms. 2010 Jun;25(3):166-75. doi: 10.1177/0748730410368621.
During the hibernation season, mammalian hibernators alternate between prolonged bouts of torpor with a reduced body temperature (Tb) and short arousals with a return to euthermy. Evidence is presented here to show that this metabolic-and also physiological and neuroanatomical-rhythm is controlled by a clock, the torpor-arousal (TA) clock. The temperature dependence of torpor bout duration in 3 species of Spermophilus (published data) may be described by assuming that the TA clock is a circadian clock (probably not the suprachiasmatic clock) that has lost its temperature compensation. This loss might result either from a permanent deletion, or more likely from a seasonal epigenetic control at the level of the clock gene machinery. This hypothesis was verified over the full Tb range on published data from 5 other species (a monotreme, a marsupial, and 3 placental mammals). In a hibernation season, instantaneous subjective time of the putative TA clock was summated over each torpor bout. For each animal, torpor bout length (TBL) was accurately predicted as a constant fraction of a subjective day, for actual durations in astronomical time varying between 4 and 13 to 20 days. The resulting temperature dependence of the interval between arousals predicts that energy expenditure over the hibernation season will be minimal when Tb is as low as possible without eliciting cold thermogenesis.
在冬眠季节，哺乳类冬眠动物在体温（Tb）降低的长时间蛰伏期和恢复正常体温的短暂觉醒期之间交替。本文提供的证据表明，这种代谢以及生理和神经解剖学节律受一个时钟——蛰伏-觉醒（TA）时钟控制。通过假设TA时钟是一个已失去温度补偿的昼夜节律时钟（可能不是视交叉上核时钟），可以描述3种黄鼠属动物（已发表数据）蛰伏期持续时间的温度依赖性。这种丧失可能是由于永久缺失，或者更有可能是由于时钟基因机制水平上的季节性表观遗传控制。这一假设在来自其他5个物种（一种单孔目动物、一种有袋动物和3种胎盘哺乳动物）的已发表数据的整个Tb范围内得到了验证。在一个冬眠季节，假定的TA时钟的瞬时主观时间在每个蛰伏期进行累加。对于每只动物，蛰伏期长度（TBL）被准确预测为一个主观日的恒定比例，实际持续时间在天文时间上为4至13至20天不等。由此产生的觉醒间隔的温度依赖性预测，当Tb尽可能低而不引发冷产热时，整个冬眠季节的能量消耗将最小。
