Regulation of Sleep by Environmental Light

我们一生中大约有三分之一的时间都在睡觉，睡眠中断是导致健康问题的主要因素，这些问题包括警惕性和记忆力差，反应时间缩短，动力减少，抑郁，代谢异常，肥胖，免疫力下降以及癌症和冠心病风险增加。睡眠是一个复杂的过程，涉及大脑的多个区域和许多神经递质。它是由熟悉的过程，即有一个增加的睡眠需求与延长清醒（睡眠稳态）以及驱动器的觉醒产生的身体内部24小时时钟（昼夜节律钟）。此外，环境光在调节睡眠/觉醒周期的时间以及睡眠和觉醒状态的急剧变化方面起着关键作用。光环境的变化是由眼睛通过许多不同的光感受细胞来检测的。这些包括调节图像形成视觉的杆和锥。然而，在过去的十年中，人们在眼睛中发现了一类新的光敏细胞。已经发现形成投射到大脑的视神经的视网膜神经节细胞的一小部分是直接光敏的（pRGC），这是由于存在感光蛋白黑视素。这些细胞并不能让我们对外部世界产生精确的图像，而是简单地检测环境光的亮度（辐照度），在许多非图像形成反应中起着关键作用，例如将生物钟设置为昼夜周期和调节睡眠。因此，眼睛执行两个非常不同的感官任务-首先，生成我们周围世界的图像，其次，对光环境进行采样以调节一系列非图像形成反应，包括睡眠。最近的研究表明，缺乏黑视素的小鼠在夜间暴露于光线下时会表现出睡眠减少。然而，在这些动物中，相对于光/暗周期的睡眠时间是正常的，并且在其他时间暴露于光仍然可以产生正常的睡眠反应。我们最近未发表的数据表明，虽然黑视蛋白有助于睡眠调节对光的反应，但其他光感受器也有贡献。光环境提供了复杂的刺激，以及辐照度，光的波长和变化率预计将确定涉及哪些光感受器。我们对这些光感受器在不同光照条件下的贡献知之甚少，因此我们对实验室小鼠的最佳光照环境只有很差的了解。该提议旨在确定视杆细胞、视锥细胞和黑视素pRGC在不同光照条件下对睡眠调节的贡献。在小鼠中，睡眠通常通过脑电图（EEG）来测量，EEG包括植入电极来测量大脑的电活动。在小鼠中，这是侵入性的，并且耗时和昂贵。我们最近开发了一种测量小鼠睡眠的方法，使用放置在动物笼子上方的微型夜视摄像机。使用计算机软件来跟踪动物的运动，并将睡眠定义为一段时间的延长不动，我们能够测量睡眠与同步脑电图测量相比具有显着的精度。我们将使用这种非侵入性，高通量的方法来研究一系列小鼠模型中的光反应，其中杆，锥和黑视蛋白被遗传改变。我们还将筛选MRC Harwell生产的突变小鼠的睡眠反应，以确定参与调节睡眠对光反应的新基因。这项工作将使我们更好地理解视杆细胞、视锥细胞和黑视素pRGC在睡眠调节中的作用，并有望提高我们对视网膜疾病如何导致睡眠中断的理解。

We spend around a third of our lives asleep and sleep disruption is a major contributing factor to a health problems ranging from poor vigilance and memory, reduced reaction times, reduced motivation, depression, metabolic abnormalities, obestity, reduced immunity and elevated risks of cancer and coronary heart disease. Sleep is a complex process, involving multiple areas of the brain and numerous neurotransmitters. It is regulated by the familiar process whereby there is a increased requirement for sleep with prolonged waking (the sleep homeostat) as well as a drive for wakefulness produced by the body's internal 24h clock (circadian clock). In addition, environmental light plays a critical role in regulating the timing of the sleep/wake cycle as well as acute changes in sleep and arousal states. Changes in the light environment are detected by eye via a number of different photoreceptive cells. These include the rods and cones which mediate image-forming vision. However, the last decade has witnessed the remarkable discovery of a new class of light sensitive cell in the eye. A small subset of the retinal ganglion cells that form the optic nerve that projects to the brain have been found to be directly photosensitive (pRGCs) due to the presence of the light-sensing protein melanopsin. Rather than enabling us to create precise images of the external world, these cells simply detect the brightness of environmental light (irradiance), playing a critical role in many non-image forming responses such as setting the body clock to the day-night cycle and regulating sleep. As such, the eye performs two very different sensory tasks - firstly, to generate images of the world around us and secondly, to sample the light environment to regulate a range of non-image forming responses, including sleep. Recent studies have shown that mice lacking melanopsin show reduced sleep when exposed to light during the night. However, the sleep timing with respect to the light/dark cycle is normal in these animals, and exposure to light at other times can still produce normal sleep responses. Our recent unpublished data show that whilst melanopsin contributes to sleep regulation in response to light, other photoreceptors also contribute. The light environment provides a complex stimulus, and as well as the irradiance, the wavelength and rate of change of the light are expected to determine which photoreceptors are involved. Little is known about the contribution of these photoreceptors under different lighting conditions, and as a result we have only a poor understanding of the optimum light environment for housing laboratory mice. This proposal aims to determine the contribution of rods, cones and melanopsin pRGCs to the regulation of sleep under different lighting conditions. In mice, sleep is normally measured by electroencephalography (EEG) which involves implanting electrodes to measure electrical activity of the brain. In mice, this is invasive as well as time-consuming and expensive. We have recently developed a method of measuring sleep in mice using miniature night-vision cameras placed above the animal's cage. Using computer software to track the animal's movement, and defining sleep as a period of extended immobility we are able to measure sleep with remarkable precision compared to simultaneous EEG measures. We will use this non-invasive, high-throughput approach to study responses to light in a range of mouse models in which rods, cones and melanopsin are genetically altered. We will also screen sleep responses in mutant mice produced by MRC Harwell to identify novel genes which are involved in the regulation of sleep in response to light. This work will lead to a greater understanding of the role of rods, cones and melanopsin pRGCs in the regulation of sleep and is expected to improve our understanding of how retinal disease may give rise to sleep disruption.