Sports Sciences for the Promotion of Active Life, Waseda University, Saitama, Japan.
Chronobiol Int. 2012 Jul;29(6):736-46. doi: 10.3109/07420528.2012.678452.
Fasted mice show torpor-like hypothermia in the cold in their inactive phase. The aim of the present study was to elucidate whether leptin and/or ghrelin are involved in this reaction and to identify its neurophysiological mechanisms. In ob/ob mice, which lack leptin, metabolic heat production (oxygen consumption, Vo(2)) was suppressed in 20°C cold in both the light and dark phases, resulting in hypothermia. When wild-type mice received a systemic injection of 8 µg ghrelin in the early light phase, followed by a 2-h cold exposure to 10°C, their core body temperature (T(b)) decreased by 1.7°C, and they displayed a less marked increase in Vo(2) compared with vehicle-injected mice. However, ghrelin injection in the early dark phase resulted in the maintenance of T(b) and increased Vo(2) in the mice, which was similar to the result observed in the vehicle-injected mice. The number of doubly labeled neurons with cFos and neuropeptide Y (NPY) in the suprachiasmatic nucleus was greater in the light phase in the ghrelin-injected mice, which may suggest that ghrelin activates NPY neurons. On the contrary, in the paraventricular nucleus, the counts became greater only when they were exposed to the cold in the dark phase. These results indicate that ghrelin plays an important role in inducing time-dependent changes in thermoregulation in the cold via hypothalamic pathways.
禁食的小鼠在不活动期的寒冷环境中表现出类似冬眠的低温。本研究旨在阐明瘦素和/或胃饥饿素是否参与这种反应，并确定其神经生理机制。在缺乏瘦素的 ob/ob 小鼠中，代谢产热（耗氧量，Vo(2)) 在光照和黑暗两个阶段的 20°C 低温下均受到抑制，导致体温过低。当野生型小鼠在光照早期接受 8 µg 全身性胃饥饿素注射，随后在 10°C 的寒冷环境中暴露 2 小时时，其核心体温（T(b)) 下降 1.7°C，与接受载体注射的小鼠相比，Vo(2)的增加幅度较小。然而，在光照早期给予胃饥饿素注射会导致小鼠的 T(b)保持稳定，并增加 Vo(2)，这与接受载体注射的小鼠的结果相似。在接受胃饥饿素注射的小鼠的视交叉上核中，与 cFos 和神经肽 Y (NPY) 双重标记的神经元数量在光照相时更多，这可能表明胃饥饿素激活了 NPY 神经元。相反，在室旁核中，只有在黑暗中暴露于寒冷时，计数才会增加。这些结果表明，胃饥饿素通过下丘脑途径在寒冷中发挥重要作用，诱导与时间相关的体温调节变化。
