Regulation of Sleep by Environmental Light

我们一生中约有三分之一的时间在睡觉，睡眠中断是导致健康问题的主要因素，包括警觉性和记忆力差、反应时间缩短、动力减弱、抑郁、代谢异常、肥胖、免疫力下降以及患癌症和冠心病的风险增加。睡眠是一个复杂的过程，涉及大脑的多个区域和大量的神经递质。它是由熟悉的过程调节的，在这种过程中，随着长时间清醒的睡眠需求增加(睡眠稳态)，以及身体内部24小时时钟(生物钟)产生的对清醒的驱动力。此外，环境光在调节睡眠/清醒周期的时间以及睡眠和觉醒状态的急剧变化方面发挥着关键作用。光环境的变化是由眼睛通过许多不同的感光细胞来检测的。其中包括调节成像视觉的视杆细胞和视锥细胞。然而，在过去的十年里，人们在眼睛中发现了一种新的光敏感细胞。由于感光蛋白黑素的存在，形成投射到大脑的视神经的一小部分视网膜神经节细胞被发现是直接光敏的(PRGC)。这些细胞不是让我们能够创建外部世界的精确图像，而是简单地检测环境光的亮度(辐照度)，在许多非成像反应中发挥关键作用，例如将生物钟设置为昼夜周期和调节睡眠。因此，眼睛执行两项非常不同的感官任务--第一，生成我们周围世界的图像，第二，对光环境进行采样，以调节一系列非成像反应，包括睡眠。最近的研究表明，缺乏黑色素的小鼠在夜间暴露在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，在其他时间暴露在光下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，虽然黑色素对光的反应有助于睡眠调节，但其他光感受器也起到了作用。光环境提供了复杂的刺激，除了照度，光的波长和变化率预计将决定哪些光感受器参与其中。人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，我们对容纳实验室小鼠的最佳光环境知之甚少。本研究旨在确定视杆细胞、视锥细胞和黑素蛋白pRGCs在不同光照条件下对睡眠的调节作用。在小鼠中，睡眠通常是通过脑电(EEG)来测量的，EEG涉及到植入电极来测量大脑的电活动。在老鼠身上，这是侵入性的，而且耗时和昂贵。我们最近开发了一种方法，使用放置在动物笼子上方的微型夜视摄像头来测量小鼠的睡眠。使用计算机软件跟踪动物的运动，并将睡眠定义为延长不动的时间段，与同时进行的脑电测量相比，我们能够以惊人的精度测量睡眠。我们将使用这种非侵入性的高通量方法来研究一系列小鼠模型对光的反应，在这些小鼠模型中，视杆细胞、视锥细胞和黑素蛋白发生了基因改变。我们还将筛选MRC Harwell产生的突变小鼠的睡眠反应，以确定参与调节睡眠对光的反应的新基因。这项工作将使我们更好地理解视杆细胞、视锥细胞和黑素蛋白pRGCs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.