Department of Psychology, Center for Studies in Behavioral Neurobiology/Groupe de Recherche en Neurobiologie Comportementale, Concordia University, Montréal, QC, Canada.
Eur J Neurosci. 2009 Jun;29(11):2217-22. doi: 10.1111/j.1460-9568.2009.06766.x. Epub 2009 May 21.
When food availability is restricted to a single time of day, circadian rhythms of behavior and physiology in rodents shift to anticipate the predictable time of food arrival. It has been hypothesized that certain food-anticipatory rhythms are linked to the induction and entrainment of rhythms in clock gene expression in the dorsomedial hypothalamic nucleus (DMH), a putative food-entrained circadian oscillator. To study this concept further, we made food availability unpredictable by presenting the meal at a random time each day (variable restricted feeding, VRF), either during the day, night or throughout the 24-h cycle. Wheel running activity and the expression of the clock protein, Period1 (PER1), in the DMH and the suprachiasmatic nucleus (SCN) were assessed. Rats exhibited increased levels of activity during the portion of the day when food was randomly presented but, as expected, failed to entrain anticipatory wheel running activity to a single time of day. PER1 expression in the SCN was unchanged by VRF schedules. In the DMH, PER1 expression became rhythmic, peaking at opposite times of day in rats fed only during the day or during the night. In rats fed randomly throughout the entire 24-h cycle, PER1 expression in the DMH remained arrhythmic, but was elevated. These results demonstrate that VRF schedules confined to the day or night can induce circadian rhythms of clock gene expression in the DMH. Such feeding schedules cannot entrain behavioral rhythms, thereby showing that food-entrainment of behavior and circadian rhythms of clock gene expression in the DMH are dissociable.
当食物供应仅限于一天中的单一时间时，啮齿动物的行为和生理节律会发生变化，以预测食物到达的可预测时间。有人假设，某些与食物相关的节律与时钟基因表达在背内侧下丘脑核（DMH）中的诱导和同步有关，DMH 是一个假定的食物同步生物钟振荡器。为了进一步研究这个概念，我们通过每天在随机时间（可变限制进食，VRF）提供膳食来使食物供应变得不可预测，无论是在白天、晚上还是整个 24 小时周期内。评估了轮跑活动和时钟蛋白 Period1（PER1）在 DMH 和视交叉上核（SCN）中的表达。当食物随机出现时，大鼠表现出更高水平的活动，但正如预期的那样，未能将预期的轮跑活动同步到一天中的单一时间。VRF 方案对 SCN 中的 PER1 表达没有影响。在 DMH 中，PER1 表达变得有节律，仅在白天或晚上进食的大鼠在一天中的相反时间达到峰值。在整个 24 小时周期内随机进食的大鼠中，DMH 中的 PER1 表达仍然没有节律，但升高了。这些结果表明，仅限于白天或晚上的 VRF 方案可以诱导 DMH 中时钟基因表达的昼夜节律。这种喂养方案不能使行为节律同步，从而表明 DMH 中行为和时钟基因表达的昼夜节律与食物同步是可分离的。
