Neuroscience Program, Skidmore College, 815 N. Broadway, Saratoga Springs, NY 12866, United States of America.
Biology Department, Swarthmore College, 500 College Avenue, Swarthmore, PA 19081, United States of America.
Physiol Behav. 2019 Jul 1;206:143-156. doi: 10.1016/j.physbeh.2019.03.027. Epub 2019 Mar 29.
Sleep abnormalities have widespread and costly public health consequences, yet we have only a rudimentary understanding of the events occurring at the cellular level in the brain that regulate sleep. Several key signaling molecules that regulate sleep across taxa come from the family of neuropeptide transmitters. For example, in Drosophila melanogaster, the neuropeptide Y (NPY)-related transmitter short neuropeptide F (sNPF) appears to promote sleep. In this study, we utilized optogenetic activation of neuronal populations expressing sNPF to determine the causal effects of precisely timed activity in these cells on sleep behavior. Combining sNPF-GAL4 and UAS-Chrimson transgenes allowed us to activate sNPF neurons using red light. We found that activating sNPF neurons for as little as 3 s at a time of day when most flies were awake caused a rapid transition to sleep that persisted for another 2+ hours following the stimulation. Changing the timing of red light stimulation to times of day when flies were already asleep caused the control flies to wake up (due to the pulse of light), but the flies in which sNPF neurons were activated stayed asleep through the light pulse, and then showed further increases in sleep at later points when they would have normally been waking up. Video recording of individual fly responses to short-term (0.5-20 s) activation of sNPF neurons demonstrated a clear light duration-dependent decrease in movement during the subsequent 4-min period. These results provide supportive evidence that sNPF-producing neurons promote long-lasting increases in sleep, and show for the first time that even brief periods of activation of these neurons can cause changes in behavior that persist after cessation of activation. We have also presented evidence that sNPF neuron activation produces a homeostatic sleep drive that can be dissipated at times long after the neurons were stimulated. Future studies will determine the specific roles of sub-populations of sNPF-producing neurons, and will also assess how sNPF neurons act in concert with other neuronal circuits to control sleep.
睡眠异常具有广泛且代价高昂的公共卫生后果，但我们对调节睡眠的大脑细胞水平上发生的事件只有初步的了解。有几种关键的信号分子，它们来自神经肽递质家族，在不同分类群中调节睡眠。例如，在黑腹果蝇中，神经肽 Y（NPY）相关递质短神经肽 F（sNPF）似乎促进睡眠。在这项研究中，我们利用表达 sNPF 的神经元群体的光遗传学激活来确定这些细胞中精确计时的活动对睡眠行为的因果影响。结合 sNPF-GAL4 和 UAS-Chrimson 转基因，我们可以使用红光激活 sNPF 神经元。我们发现，每天大多数果蝇清醒时，一次激活 sNPF 神经元长达 3 秒，会迅速过渡到睡眠状态，并在刺激后持续 2 小时以上。将红光刺激的时间改为果蝇已经入睡的时间，会使对照果蝇醒来（由于光脉冲），但激活 sNPF 神经元的果蝇会在光脉冲期间保持睡眠状态，然后在稍后的时间点进一步增加睡眠，而这些时间点通常是它们正常醒来的时间。对单个果蝇对 sNPF 神经元短期（0.5-20 秒）激活的反应进行视频记录，结果表明，在随后的 4 分钟内，运动明显随光持续时间的减少而减少。这些结果提供了支持性证据，表明产生 sNPF 的神经元促进了长时间的睡眠增加，并首次表明，即使这些神经元的短暂激活也会导致激活停止后持续的行为变化。我们还提供了证据表明，sNPF 神经元的激活产生了可以在神经元被刺激后很长时间内消散的稳态睡眠驱动。未来的研究将确定产生 sNPF 的神经元亚群的具体作用，并评估 sNPF 神经元如何与其他神经元回路协同作用来控制睡眠。
