Clarification of the mechanisms involved in circadian body temperature rhythm and its physiological significance

本研究的目的是阐明昼夜体温节律产生的机制。在研究中，我们假设1)视交叉上核（SCN），即昼夜节律中枢，在中枢和外周水平上调节热敏性；2)体温节律在同步中枢和外周节律中起重要作用。在实验中，我们将小鼠置于20℃的低温下，在自由饲养或禁食48 h后，我们测量了棕色脂肪组织的代谢产热和UCP1 mRNA。此外，还估计了下丘脑神经活动反映的cFos表达。在缺乏正常昼夜节律的Clock突变小鼠上重复了相同的实验方案。在自由饲喂期间，低温条件下的体温调节反应和cFos表达没有差异。然而，在禁食期间，产热反应仅在暗期明显，而SCN中的cFos表达在光期增加。在Clock突变小鼠的反应中没有相位差异。我们还发现了与交感神经活动相关的一个抑制网络，来自SCN和室旁核。SCN受环境温度和摄食条件的影响，涉及体温调节的时间依赖性。

The goal of present study was to clarify the mechanism involved in generation of circadian body temperature rhythm. In the research, we hypothesized that 1) the suprachiasmatic nucleus (SCN), i. e. the central for circadian rhythms modulates thermosensitiveity at the levels of the central and periphery, and 2) the body temperature rhythm is important in synchronizing the rhythms of the central and periphery. In experiments, mice were exposed to the cold at 20℃ after ad-lib feeding or 48-h fasting, then we estimated metabolic heat production and UCP1 mRNA in the brown adipose tissue. In addition, cFos expression reflected by neural activity in the hypothalamus was also estimated. The same experimental protocol was repeated on Clock mutant mice, which lacks normal circadian rhythmicity. During ad-lib feeding, there were no differences in thermoregulatory responses and cFos expression in the cold. However, during fasting, heat production response was apparent only in the dark phase, and cFos expression in the SCN was augmented in the light phase. There were no phase-differences in the responses in Clock mutant mice. We also found an inhibitory network from the SCN and paraventricular nucleus associated with the sympathetic nerve activity. The SCN was influenced by environmental temperature and feeding condition, which is involved in time-dependency of body temperature regulation.