Sleep, proprioception, and forebrain activity in infant mutant mice

描述(申请人提供)：睡眠占据了我们成年人生活的三分之一，但它的功能仍不清楚。在婴儿中，睡眠甚至更突出，自发的肌阵挛抽动也是活跃(或快速眼动)睡眠的一个决定性特征。在幼年大鼠中，每天会发生数以万计的抽搐，抽动产生的感觉反馈会对初级躯体感觉皮质产生实质性刺激。事实上，每天在新大脑皮层，与睡眠相关的抽搐都会触发数以千计的皮质振荡事件--称为纺锤波爆发。这种与睡眠有关的新大脑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驱动的。因此，有人认为，与睡眠相关的自发运动活动有助于新皮质和海马区内和之间的神经回路的发展，就像视网膜波被认为有助于视觉皮质和相关结构的发展一样。有趣的是，我们实验室的工作表明，可能是肢体抽动的本体感觉反馈特定地触发了纺锤波；对肢体的触觉刺激似乎不足以产生纺锤波。因此，R21的探索性/发育性应用旨在研究抽动对新皮质和海马区活动和发育的本体感觉反馈的具体贡献。由于干扰本体感觉的外科和药理学方法不够针对这种方式--而且还可能干扰运动外流，从而扰乱抽动本身--我们建议在这里测试通过基因改造而无法发育肌梭的婴儿突变小鼠，肌梭是本体感觉所必需的感觉器官。这些突变体形成神经肌肉连接和从肌肉到脊髓的Ia传入连接。重要的是，我们还证实了这些幼年突变小鼠中抽动的存在，以及它与野生型的相似之处。使用我们实验室开发的方法，记录未麻醉的幼鼠在睡眠和清醒之间自发循环时的神经生理活动，并对实验控制的外周触觉和本体感觉刺激的传递做出反应，我们将记录婴儿突变体和野生型小鼠的睡眠-觉醒活动以及新皮质和海马区的活动。这一应用的创新之处在于在条件性基因敲除小鼠中使用最先进的记录技术来测试关于睡眠相关运动活动在躯体感觉发育中的现象学和功能的特定的、机械性的假设。此外，这一应用将为未来对小鼠的神经生理和睡眠觉醒活动的发展研究提供基础，从而能够充分利用该物种中现成的分子工具。最后，这一应用程序与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。 公共卫生相关性：美国国立卫生研究院神经科学蓝图强调了跨学科基础研究的必要性，以解决与神经退行性变、神经发育和神经可塑性有关的关键问题。目前的应用与蓝图非常契合，因为它侧重于与睡眠相关的“抽动”运动的感官反馈在神经系统(包括大脑皮层和海马体)的构建中的作用--在产前和出生后早期尤为突出。通过了解大脑如何解释这些抽搐运动，以及抽搐产生的干扰感觉反馈如何改变发育过程，我们将开始阐明睡眠和清醒期间的早期体感体验如何有助于塑造正常和病理结果。

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.