Sleep, proprioception, and forebrain activity in infant mutant mice

描述（由申请人提供）：睡眠占据了我们成人生活的三分之一，但我们仍然不知道它的功能。在婴儿中，睡眠更为突出，自发的肌阵挛性抽搐是活跃（或REM）睡眠的一个定义特征。在幼鼠中，抽搐每天产生数万次，抽搐的感觉反馈对初级体感皮层产生实质性的刺激。事实上，每天在大脑皮层中，与睡眠相关的抽搐会触发数千个皮层振荡事件——称为纺锤波爆发。这种与睡眠相关的新皮层的激活随后被引导到海马体，海马体在婴儿早期的活动似乎主要是在睡眠期间被驱动的。因此，有人提出，自发的、与睡眠相关的运动活动有助于新皮层和海马体内部和之间神经回路的发育，就像视网膜波被认为有助于视觉皮层和相关结构的发育一样。有趣的是，我们实验室的工作表明，肢体抽搐的本体感觉反馈可能会特异性地触发纺锤体爆发；四肢的触觉刺激似乎不足以产生纺锤体爆裂。因此，本R21探索性/发展性应用旨在研究抽搐本体感觉反馈对新皮层和海马活动和发育的具体贡献。由于破坏本体感觉的手术和药理学方法对这种模式没有足够的特异性，而且可能也会破坏运动流出，从而破坏抽搐本身，我们建议在这里测试经过基因工程改造的突变幼鼠，这样它们就不能发育肌肉纺锤体，而肌肉纺锤体是本体感觉所必需的感觉器官。这些突变体发育神经肌肉连接和从肌肉到脊髓的传入连接。重要的是，我们还证实了这些突变幼鼠中抽搐的存在及其与野生型的相似性。使用我们实验室开发的方法来记录未麻醉的幼鼠在睡眠和清醒之间自发循环的神经生理活动，并对实验者控制的外周触觉和本体感觉刺激做出反应，我们将记录突变型和野生型幼鼠在早期发育过程中的睡眠-觉醒活动、新皮层和海马活动。该应用的创新之处在于在条件敲除小鼠中使用最先进的记录技术来测试有关体感觉发育中睡眠相关运动活动的现象学和功能的特定机制假设。此外，该应用程序将为未来小鼠神经生理和睡眠-觉醒活动的发育研究提供基础，这些研究可以充分利用该物种中现成的分子工具。最后，该应用程序与IH神经科学蓝图兼容，该蓝图强调需要更多的基础研究来了解神经发育，神经变性和神经可塑性。

DESCRIPTION (provided by applicant): Sleep occupies one-third of our adult lives and yet its function is still not known. In infants, sleep is even more prominent, as are the spontaneous myoclonic twitches that are a defining feature of active (or REM) sleep. In infant rats, twitches are produced tens of thousands of times each day, and sensory feedback from twitching produces substantial stimulation to the primary somatosensory cortex. In fact, each day in neocortex, sleep- related twitches trigger thousands of cortical oscillatory events - called spindl bursts. This sleep-related activation of neocortex is channeled subsequently to the hippocampus, whose activity in early infancy appears to be driven primarily during sleep. Accordingly, it has been suggested that spontaneous, sleep-related motor activity contributes to the development of neural circuits within and between neocortex and hippocampus, just as retinal waves are thought to contribute to the development of visual cortex and related structures. Interestingly, work in our laboratory suggests that it may be the proprioceptive feedback from limb twitches that specifically trigger spindle bursts; tactile stimulation of the limbs appears insufficient for producing a spindle burst. Thus, this R21 exploratory/developmental application aims to investigate the specific contributions of proprioceptive feedback from twitching to neocortical and hippocampal activity and development. Because surgical and pharmacological methods of disrupting proprioception are not sufficiently specific to that modality - and may also disrupt motor outflow and thus disrupt twitching itself - we propose here to test infant mutant mice that are genetically engineered such that they fail to develop muscle spindles, the sensory organs essential for proprioception. These mutants develop neuromuscular junctions and Ia afferent connections from muscle to spinal cord. Importantly, we have also confirmed the presence of twitching in these infant mutant mice and its similarity to that in wild-types. Using methods that were developed in our laboratory for recording neurophysiological activity in unanesthetized infant rats as they cycle spontaneously between sleep and wakefulness and respond to experimenter-controlled delivery of peripheral tactile and proprioceptive stimuli, we will record sleep-wake activity and neocortical and hippocampal activity in infant mutant and wild-type mice across early development. The innovation of this application lies in the use of state-of-the-art recording techniques in conditional knockout mice to test specific, mechanistic hypotheses concerning the phenomenology and function of sleep-related motor activity in somatosensory development. Also, this application will provide a foundation for future developmental studies of neurophysiological and sleep-wake activity in mice that can take full advantage of the molecular tools that are readily available in that species. Finally, this application is compatible with the IH Blueprint for Neuroscience, which emphasized the need for more basic research to understand neurodevelopment, neurodegeneration, and neuroplasticity. PUBLIC HEALTH RELEVANCE: The NIH Blueprint for Neuroscience emphasized the need for interdisciplinary basic research that addresses critical issues concerning neurodegeneration, neurodevelopment, and neuroplasticity. The current application fits well with the Blueprint by focusing on the role of sensory feedback from sleep-related "twitch" movements - which are especially prominent during the prenatal and early postnatal period - in the construction of the nervous system, including the cerebral cortex and hippocampus. By understanding how the brain interprets these twitch movements and how interrupting sensory feedback from twitches alters the course of development, we will begin to shed light on how early somatosensory experiences during sleep and wakefulness help to shape both normal and pathological outcomes.