Hypocretinergic integration of circadian rhythms and sleep

 描述（由申请人提供）：昼夜节律（~24小时）影响行为和生理的几乎所有方面。昼夜节律的紊乱导致了广泛的人类健康状况，包括睡眠障碍，如轮班工作障碍和情感障碍，如焦虑和抑郁。然而，了解昼夜节律如何控制或影响行为仍然是神经科学中的一个基本问题。虽然大脑中的大多数神经元都包含一个“分子钟”，但明显的昼夜节律是由主起搏器-视交叉上核（SCN）协调的。SCN的神经元有节奏地激发动作电位，并作为一个网络，将昼夜信息传递给负责复杂行为的其他回路，其中最明显的可能是睡眠。理论研究表明，睡眠的昼夜节律驱动（过程C）和稳态睡眠压力（过程S）遵循不同的，尽管相互关联的振荡。下丘脑分泌素/食欲素（hypocretin/orexin，Hcrt）系统是下丘脑外侧的一组神经元，对唤醒的稳定性至关重要。Hcrt或其受体的丧失与发作性睡病相关，发作性睡病的特征在于睡眠侵入觉醒，并且Hcrt神经元的光遗传学刺激直接促进睡眠-觉醒转换。重要的是，Hcrt神经元活动（由c-Fos读出）、Hcrt转录水平和脑脊液中Hcrt水平表现出昼夜节律性。由于生物钟基因在整个大脑中无处不在，并且已被证明会影响SCN以外的神经活动和行为，因此一个有趣的可能性是，SCN内的分子钟可能是一种生物钟。 Hcrt神经元独立于SCN的输入或与SCN的输入同时调节它们的活动。因此，我假设SCN神经活动和Hcrt神经元内的分子钟协同地对Hcrt神经活动和睡眠/觉醒行为施加昼夜节律控制。为了验证这一假设，我将研究昼夜节律，Hcrt神经活动和睡眠之间的联系，使用一种独特的策略，该策略结合了SCN活动的光遗传学操纵，Hcrt神经元特异性分子时钟中断，Hcrt活动的体内钙成像和睡眠状态的多导睡眠图记录。这一提议不仅将为昼夜节律和唤醒之间的基本关系提供新的见解，而且还将为定义复杂行为的神经机制提供一般的神经科学问题，当这些行为被破坏时，可能会导致精神疾病。要了解昼夜节律失调如何导致睡眠和情感障碍等疾病，首先需要了解它们在健康大脑中的工作原理。因此，这项研究计划将最终提高我们对重要昼夜节律和睡眠回路相互作用的理解，这些回路的功能障碍可能对人类健康产生负面影响。

 DESCRIPTION (provided by applicant): Circadian (~24 hr) rhythms influence nearly all aspects of behavior and physiology. Disrupted circadian rhythms contribute to a wide range of human health conditions including sleep disorders such as shift work disorder and affective disorders such as anxiety and depression. However, understanding how circadian rhythms control or influence behavior remains a fundamental problem in neuroscience. While most neurons in the brain contain a "molecular clock", overt circadian rhythms are orchestrated by the master pacemaker, the suprachiasmatic nucleus (SCN). Neurons of the SCN rhythmically fire action potentials and, together as a network, communicate circadian information to other circuits responsible for complex behaviors, perhaps the most obvious of which is sleep. Theoretical work has suggested that circadian drive for sleep (Process C) and homeostatic sleep pressure (Process S) follow distinct, albeit interconnected oscillations. A proposed mechanistic link between these processes lies in the hypocretin/orexin (Hcrt) system, a collection of neurons in the lateral hypothalamus that is essential for the stability of arousal. The loss of Hcrt or its receptors is associated with the disorder narcolepsy, which is characterized by the intrusion of sleep into wakefulness, and the optogenetic stimulation of Hcrt neurons directly promotes sleep-to-wake transitions. Importantly, Hcrt neuron activity (as read out by c-Fos), Hcrt transcript levels, and levels of Hcrt in the cerebrospinal fluid exhibit circadian rhythmicity. As circadian clock genes are ubiquitous throughout the brain and have been shown to influence neural activity and behavior outside the SCN, an intriguing possibility is that the molecular clock within Hcrt neurons regulates their activity independent of, or in concurrence with, input from the SCN. Thus, I hypothesize that SCN neural activity and the molecular clock within Hcrt neurons synergistically exert circadian control over Hcrt neural activity and sleep/wake behavior. To test this hypothesis, I will investigate the link between circadian rhythms, Hcrt neural activity, and sleep using a unique strategy that combines optogenetic manipulation of SCN activity, Hcrt neuron-specific molecular clock disruption, in vivo calcium imaging of Hcrt activity, and polysomnographic recording of sleep state. This proposal will provide novel insight into not only the essential relationship between circadian rhythms and arousal, but also the general neuroscience question of defining the neural mechanisms of complex behaviors that, when disrupted, can cause mental disease. To understand how the dysregulation of circadian rhythms may lead to illnesses such as sleep and affective disorders, it is first necessary to understand how they work in a healthy brain. Thus, this research plan will ultimately improve our understanding of the interplay of vital circadian and sleep circuits whose dysfunction can negatively impact human health.