Functional and Structural Diversity in Hypoglossal Motoneurons

项目总结/摘要 舌下神经运动神经元（XIIMNs）支配的舌肌对于生存至关重要， 哺乳、吞咽、咀嚼、呼吸和更高级的功能，如人类的语言。的 舌下神经运动核是由7个独立的运动神经元池组成的双侧集合体， 每个池支配七种不同舌肌中的一种。我们最近发现， 新生大鼠舌上级肌和颏舌肌的静息状态有显著差异 膜电位、动作电位激发阈值和f-I曲线，即，作为函数的发射率的变化 注入电流。这些发现提出了三个非常重要的问题：（1） 个体XIIMN池内和池间的表型多样性？2)什么是解剖和离子 这种表型多样性背后的机制3)XIIMN之间的结构和功能差异是否 每个池映射到独特的基因表达谱？我们提出了一个合理和强大的方法来解决这些问题 问题：具体地说，描述形态，内在膜特性，和转录组， 肌肉特异性XIIMN。我们最初的目标是支配颏舌肌、舌骨舌肌和上级肌的XIIMNs 尿道肌肉，因为每块肌肉对舌头运动有不同的影响。肌肉特异性XIIMN将 通过向每块肌肉注射与荧光报告分子偶联的逆行示踪剂来鉴定。所有 实验使用来自5 - 12天龄的新生大鼠的脑组织。关键技术包括神经解剖追踪 定义神经元形态学、免疫组织化学、全细胞膜片钳电生理学，然后- RNA测序。这些基础科学研究将确定与以下疾病相关的独特分子靶点： 运动神经元池之间的功能和/或结构差异。如果没有这些基本信息， 旨在刺激或抑制特定舌肌活动的干预是不精确的 导致意外的结果。相比之下，独特分子靶点的具体知识将集中在 开发旨在刺激和/或抑制特定舌肌的治疗方法。 初步数据显示，运动神经元功能和基因表达的几个池特异性差异，强烈 这表明，拟议的工作将提供真正的解剖，生理和分子的新数据， 肌肉特异性舌下运动神经元池内和之间表型多样性的基础。这个， 反过来，将导致我们对舌头肌肉如何执行复杂，协调， 行为，如吮吸，吞咽，和睡眠期间上呼吸道的防御，并将奠定基础 用于开发旨在控制特定舌肌活动的疗法。

PROJECT SUMMARY/ABSTRACT Tongue muscles, which are innervated by hypoglossal motoneurons (XIIMNs), are critical for survival given their role in suckling, swallowing, mastication, breathing and more advanced functions such as human speech. The hypoglossal motor nucleus is a bilateral collection of seven separate motoneuron pools, with motoneurons in each pool innervating one of the seven different tongue muscles. We recently showed that XIIMNs innervating the superior longitudinalis and genioglossus tongue muscles of neonatal rats have significantly different resting membrane potentials, action potential firing thresholds, and f-I curves, i.e., the change in firing rate as a function of injected current. These findings raise three very important questions: 1) what is the extent and nature of phenotypic diversity both within and between individual XIIMN pools? 2) what are the anatomic and ionic mechanisms that underlie this phenotypic diversity? 3) do structural and functional differences among XIIMNs in each pool map to unique gene expression profiles? We propose a rational and robust approach to address these questions: specifically, to describe the morphology, intrinsic membrane properties, and the transcriptome of muscle specific XIIMNs. Our initial targets are XIIMNs innervating the genioglossus, hyoglossus and superior longitudinalis muscles, as each muscle has different effects on tongue movement. Muscle-specific XIIMNs will be identified by injecting each of the muscles with a retrograde tracer conjugated to a fluorescent reporter. All experiments use brain tissue from neonatal rats 5-12 days of age. Key techniques include neuroanatomic tracing to define neuron morphology, immunohistochemistry, whole cell patch clamp electrophysiology and next- generation RNA sequencing. These basic science studies will identify unique molecular targets associated with functional and/or structural differences between the motoneuron pools. Without this fundamental information, interventions aimed at stimulating or inhibiting the activity of specific tongue muscles will be imprecise and may result in unintended outcomes. In contrast, specific knowledge of unique molecular targets will focus the development of therapeutic approaches aimed at stimulation and/or inhibition of specific tongue muscles. Preliminary data show several pool-specific differences in motoneuron function and gene expression, strongly suggesting that the proposed work will provide truly novel data on the anatomic, physiologic, and molecular underpinnings of phenotypic diversity within and between muscle-specific hypoglossal motoneuron pools. This, in turn, will lead to a major leap in our understanding of how the tongue muscles perform complex, coordinated behaviors such as suckling, swallowing, and defense of the upper airway during sleep, and will lay the foundation for the development of therapies aimed at controlling the activity of specific tongue muscles.