Abstract

Circadian rhythms and sleep homeostasis constitute the two-process model for daily sleep regulation. However, evidence for circadian control of sleep-wake cycles has been relatively short since clock-less animals often show sleep behaviors quantitatively comparable to wild-type. Here we examine Drosophila sleep behaviors under different light-dark regimes and demonstrate that circadian clocks gate light-induced arousal. Genetic excitation of tyrosine decarboxylase 2 (TDC2)-expressing neurons suppressed sleep more evidently at night, causing nocturnal activity. The arousal effects were likely mediated in part by glutamate transmission from the octopaminergic neurons and substantially masked by light. Application of T12 cycles (6-h light: 6-h dark) further showed that the light-sensitive effects of TDC2 neurons depended on the time of the day. In particular, light-sensing via visual input pathway led to strong sleep suppression at subjective night, and such an effect disappeared in clock-less mutants. Transgenic mapping revealed that light-induced arousal and free-running behavioral rhythms require distinct groups of circadian pacemaker neurons. These results provide convincing evidence that circadian control of sleep is mediated by the dedicated clock neurons for light-induced arousal.

摘要

昼夜节律和睡眠稳态构成了日常睡眠调节的双过程模型。然而，昼夜节律控制睡眠-觉醒周期的证据相对较短，因为无生物钟的动物通常表现出与野生型动物相当的睡眠行为。在这里我们检查果蝇不同明暗状态下的睡眠行为，并证明生物钟控制光诱导的唤醒。表达酪氨酸脱羧酶 2 (TDC2) 的神经元的基因兴奋在夜间更明显地抑制睡眠，导致夜间活动。唤醒效应可能部分是由章鱼胺能神经元的谷氨酸传输介导的，并且基本上被光掩盖了。T12 周期（6 小时光照：6 小时黑暗）的应用进一步表明，TDC2 神经元的光敏感效应取决于一天中的时间。特别是，通过视觉输入途径的光感应导致主观夜间的强烈睡眠抑制，并且这种效应在无时钟突变体中消失。转基因图谱显示，光诱导的唤醒和自由运行的行为节律需要不同的昼夜节律起搏神经元组。