Brainstem mechanism underlying recurrent laryngospasm in Rett syndrome

清醒时反复呼吸暂停是Rett综合征的一种主要且可能危及生命的症状 (RTT)。最近的一项临床试验显示，RTT患者中的许多此类呼吸暂停事件是由行为- 诱导性非自愿屏气(停止呼气)代替化学反射介导的中枢性呼吸暂停 (停止吸气)，这种呼吸障碍可以通过IGF-1药物治疗来改善 恢复这些患者的脑源性神经营养因子信号。RTT突变小鼠模型的新证据表明 这种病理性屏息很可能代表了一种复发性喉痉挛(发作性喉咙) 脑桥Kölliker-Fuse核(KFN)神经元敏感化引起的内收肌多动 在吸气后(后吸气)时，在控制喉内收肌活动中起着重要作用的核。 I)呼吸节律的阶段，以及在发声和屏气等行为任务期间。一个 KFN中I后驱动神经元的特征是它们对NMDA受体活性的严重依赖，这是一种特性 这将这些神经元与许多其他主要由AMPA受体兴奋的中枢神经元区分开来- 中介电流。在这项提议中要检验的一个中心假设是，KFN后I驱动神经元是 来自喉上神经(SLN)的上行输入介导喉内收肌反射和 经中脑导水管周围灰质(PAG)下行输入介导声门关闭的行为控制 在系统水平上整合，这些KFN神经元的过度活动是由于某种形式的 NMDA和BDNF受体依赖的突触可塑性可能是行为诱发的喉痉挛的基础 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 RTT突变小鼠模型清醒时的屏息表型。目标1将调查这一角色 KFN后I驱动神经元在上行SLN传入引起的喉内收肌反射调制中的作用 接受或不接受IGF-1治疗的突变和野生型小鼠。在目标2中，我们将调查这些KFN作用 在这些动物中，神经元在调节PAG下行输入引起的喉内收肌反应中起作用。 这些多感官整合数据将接受一种新的多尺度指纹分析，该分析验证 PAG-KFN-喉后I区上下游神经元的功能连接 通过匹配一组时间、反应和细胞特异性标记来实现运动神经元通路 神经元。在目标3中，我们将采用细胞旁标记/单单元记录的多重标记技术 结合顺行轴突追踪将PAG和KFN的汇聚输入映射到喉内收肌 延髓中的运动神经元。通过比较突变小鼠和野生型小鼠的这些结构功能数据，我们的 目的是定位参与声门闭合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果指标。

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.