Uncovering cerebellar mechanisms of tremor using the efficacy of propranolol to test circuit function

项目总结/摘要 震颤是世界上最常见的神经运动障碍，影响世界上超过1000万人。 美国一个人震颤的特征是身体部位不自主的、无法控制的振荡运动， 使患者衰弱，并且可以在任何年龄出现，在两种性别中，来自遗传或特发性起源。震颤 病理学被认为涉及运动脑中心，如小脑，但特定细胞的身份， 震颤的活动模式和分子机制仍然是一个谜。为了研究这些未知数，我 开发了一种研究震颤的方法，使用处方药普萘洛尔作为机械工具， 小脑通路和电路活动模式，驱动震颤，希望揭示潜在的治疗 目标的普萘洛尔是一种β-肾上腺素能受体阻滞剂（或β-受体阻滞剂）， 作为治疗震颤的一线药物。虽然它减少震颤的神经机制是 目前尚不清楚，普萘洛尔对震颤患者的高疗效率使其成为治疗震颤的理想和独特的工具。 震颤病理学研究。越来越多的文献表明小脑回路 活动异常可能会导致震颤，我给小鼠服用心得安，表现出强大的遗传 的震颤，并发现普萘洛尔不仅是非常有效地消除震颤表型，但 在普萘洛尔主动减少震颤的过程中，小脑的活动发生了显著的改变。在具有遗传基因的小鼠中， 在震颤中，已知浦肯野细胞更不规则地并且以高得多的放电速率放电。使用体内电- 在生理学上，我发现普萘洛尔显著降低了遗传性震颤小鼠的浦肯野细胞放电率。 此外，这种放电率降低的持续时间与震颤严重程度降低的持续时间相关;一旦 经过足够的时间，普萘洛尔从系统中消除，浦肯野速率恢复到震颤性 水平，震颤表型也恢复了。我的数据提出了一个有趣的假设， 小脑回路中的关键细胞的模式，如浦肯野细胞，其活动模式很容易被 普萘洛尔是大脑震颤病理学的核心。为了验证这一假设，我提出了两个目标， 进一步揭示震颤背后的小脑功能，使用心得安作为机械工具来测试 震颤中小脑的分子遗传学特性（目的1），并剖析浦肯野细胞活性的作用 产生和减少震颤（目标2）。为了这两个目标，我将使用基因杂交来创造具有靶向的小鼠。 小脑回路中的基因操作和小脑神经元的体内电生理学记录， 行为动物这些目标的完成将要求重新评估未解决和有争议的理论 试图解释震颤是如何在中枢神经系统中开始的，以及如何提供关键的见解。 最常用的震颤药确实对病人有效关于神经回路的知识的可用性 潜在的震颤病理学将为基于药物和替代药物的巨大进步提供机会。 治疗震颤，如大脑刺激为基础的治疗，并最终带领我们更接近未来的治疗。

PROJECT SUMMARY/ABSTRACT Tremor is the most common neurological movement disorder in the world, affecting over 10 million people in the U.S. alone. Characterized by involuntary, uncontrollable oscillating movements of body parts, tremor is debilitating to patients and can emerge at any age, in both genders, from genetic or idiopathic origins. Tremor pathology is thought to involve motor brain centers such as the cerebellum, but the identities of specific cellular activity patterns and molecular mechanisms underlying tremor remain a mystery. To study these unknowns, I developed a method of studying tremor using the prescription drug propranolol as a mechanistic tool to uncover cerebellar pathways and circuit activity patterns that drive tremor, with hopes of revealing potential therapeutic targets. Propranolol is a β-adrenergic receptor blocker (or beta-blocker) that has been continuously prescribed to patients as a first-line treatment for tremor since 1965. Though its neural mechanisms for tremor reduction are not yet understood, propranolol’s high rate of efficacy in tremor patients makes it an ideal and unique tool for the study of tremor pathology. Motivated by the increasingly extensive literature implicating that cerebellar circuit activity abnormalities may contribute to tremor, I administered propranolol to mice that exhibit a robust genetic form of tremor, and found that not only was propranolol highly effective in eliminating the tremor phenotype, but that cerebellar activity was significantly altered during propranolol’s active tremor reduction. In mice with genetic tremor, Purkinje cells are known to fire more irregularly and at a much higher firing rate. Using in vivo electro- physiology, I found that propranolol dramatically reduces Purkinje cell firing rate in mice with genetic tremor. Moreover, the duration of this reduced firing rate correlated with the duration of decreased tremor severity; once enough time had passed that propranolol was eliminated from the system, Purkinje rates returned to tremorgenic levels, and the tremor phenotype returned as well. My data raise the intriguing hypothesis that abnormal firing patterns of key cells in the cerebellar circuit, such as Purkinje cells whose activity patterns are readily altered by propranolol, are at the heart of tremor pathology in the brain. To test this hypothesis, I generated two aims to further uncover the cerebellar functions underlying tremor, using propranolol as a mechanistic tool to test the molecular genetic properties of the cerebellum in tremor (Aim 1), and to dissect the role of Purkinje cell activity in generating and reducing tremor (Aim 2). For both aims, I will use genetic crosses to create mice with targeted manipulations of genes in the cerebellar circuit and in vivo electrophysiology recordings of cerebellar neurons in behaving animals. The completion of these aims will call for a reevaluation of the unsolved and debated theories that attempt to explain how tremor begins in the central nervous system, as well as give key insights into how the most-prescribed tremor drug truly works in patients. The availability of knowledge about the neural circuitry underlying tremor pathology will provide opportunities for great advancements in both drug-based and alternative treatments for tremor, such as brain stimulation-based treatments, and ultimately lead us closer to a future cure.