Brainstem mechanism underlying recurrent laryngospasm in Rett syndrome

在清醒状态下反复呼吸暂停是雷特综合征的一个主要的和潜在的危及生命的症状 （RTT）。最近的一项临床试验表明，RTT患者中的许多呼吸暂停事件是由行为- 诱导不自主屏气（呼气停止），而不是化学反射介导的中枢性呼吸暂停 （停止吸气），并且这种呼吸障碍通过IGF-1药物治疗改善， 恢复这些患者的BDNF信号。RTT突变小鼠模型的新证据表明， 这种病理性屏气可能代表一种形式的复发性喉痉挛（阵发性喉痉挛 内收肌活动过度），由Köliker-Nerve核（KFN）神经元的敏化引起， 在吸气后（后）控制喉内收肌活动中起重要作用的核， I）呼吸节律的阶段和行为任务期间，例如发声和屏气。一 KFN中I后驱动神经元的标志是它们对NMDA受体活性的关键依赖，这是一种性质， 这使这些神经元区别于许多其他主要由AMPA受体兴奋的中枢神经元， 介导电流。在该提议中要测试的中心假设是KFN后I驱动神经元是KFN后I驱动神经元。 来自上级喉神经（SLN）的上行输入介导喉内收肌反射的部位， 下行输入通过中脑导水管周围灰质（PAG）介导的声门闭合的行为控制 整合在系统水平，这些KFN神经元的过度活跃，由于一种形式的损伤， NMDA和BDNF受体依赖的突触可塑性可能是行为诱发喉痉挛的基础 在细胞水平上的RTT。作为基线（目标0），我们将检查IGF-1治疗是否改善了 RTT突变小鼠模型中觉醒期间的屏气表型。目标1将研究 KFN后I驱动神经元在调节由SLN上行输入诱导的喉内收肌反射中的作用 用或不用IGF-1治疗的突变型和野生型小鼠。在目标2中，我们将研究这些KFN的作用 神经元在调节喉内收肌反应引起的下行PAG输入在这些动物。 这些多感觉整合数据将受到一种新的多尺度指纹分析， PAG-KFN-喉后I区上游和下游神经元的功能连接 运动神经元通路通过匹配一组时间，反应和细胞特异性标记共享这些 神经元在目标3中，我们将采用多标记技术，包括单细胞标记/单单位记录 结合顺行轴突追踪，将PAG和KFN的会聚性输入映射到喉内收肌 延髓运动神经元。通过比较突变小鼠和野生型小鼠的这些结构-功能数据， 目的是绘制涉及声门闭合的反射和意志控制协调的中枢回路， 健康和RTT。该项目的结果将为正在进行的和未来的临床试验提供信息，以评估 屏气与中枢性呼吸暂停作为评估RTT患者药物治疗的可能结局指标。

Repetitive apnea during wakefulness is a cardinal and potentially life-threatening symptom of Rett syndrome (RTT). A recent clinical trial reveals that many of these apneic events in RTT patients result from behaviorally- induced involuntary breathholding (cessation of expiration) instead of chemoreflex-mediated central apnea (cessation of inspiration), and that such breathing disturbances are ameliorated by IGF-1 drug treatment to restore BDNF signaling in these patients. Emerging evidence from mutant mouse models of RTT suggests that such pathologic breathholding likely represents a form of recurrent laryngospasm (paroxysmal laryngeal adductor hyperactivity) caused by sensitization of neurons in the Kölliker-Fuse nucleus (KFN), a pontine nucleus which plays an important role in controlling laryngeal adductor activity during the post-inspiratory (post- I) phase of the respiratory rhythm and during behavioral tasks such as vocalization and breathholding. A hallmark of the post-I driver neurons in KFN is their critical dependence on NMDA receptor activity, a property which distinguishes these neurons from many other central neurons that are excited mainly by AMPA receptor- mediated currents. A central hypothesis to be tested in this proposal is that KFN post-I driver neurons are the site where ascending input from superior laryngeal nerve (SLN) mediating the laryngeal adductor reflex and descending input via midbrain periaqueductal gray (PAG) mediating behavioral control of glottic closure are integrated at the systems level, and that hyperactivity of these KFN neurons due to impairment of a form of NMDA and BDNF receptors-dependent synaptic plasticity may underlie the behaviorally-evoked laryngospasm in RTT at the cellular level. As a baseline (Aim 0), we will examine whether IGF-1 treatment ameliorates the breathholding phenotype during wakefulness in a mutant mouse model of RTT. Aim 1 will investigate the role of KFN post-I driver neurons in modulating the laryngeal adductor reflex induced by ascending SLN input in mutant and wild-type mice with or without IGF-1 treatment. In Aim 2, we will investigate the role of these KFN neurons in modulating the laryngeal adductor response induced by descending PAG input in these animals. These multisensory integration data will be subjected to a novel multiscale fingerprinting assay which verifies functional connectivity of the neurons that are upstream and downstream of the PAG-KFN-laryngeal post-I motoneuron pathway by matching a set of timing-, response- and cellular-specific markers shared by these neurons. In Aim 3, we will employ a multi-labeling technique with juxtacellular labeling/single unit recording combined with anterograde axonal tracing to map convergent inputs from PAG and KFN to laryngeal adductor motoneurons in medulla. By comparing these structure-function data from mutant mice and wild-type mice, our goal is to map the central circuits involved in coordination of reflex and volitional control of glottic closure in health and in RTT. Results of this project will inform ongoing and future clinical trials to evaluate the validity of breathholding vs. central apnea as possible outcome measures for assessing drug treatments of RTT patients.