The Peripheral Vestibular System in Congenital Vestibular Disorders

摘要 在美国，估计有330万儿童经历头晕和平衡问题（19）。儿童 先天性前庭障碍（CVD）表现出运动发育延迟和维持姿势的挑战 和平衡，表明前庭神经回路受到影响。计算机断层扫描（CT）显示， 患有心血管疾病的儿童最常见的是形成囊状内耳，半规管缺失或被截断。 目前尚不清楚他们的前庭连接是如何改变的。我们假设囊状内耳的形成 在妊娠早期导致前庭神经节细胞数量减少，形成较少的初级前庭神经节细胞， 外周毛细胞和前庭核神经元上的突触，导致 前庭系统我们进一步假设囊状内耳病理导致异常会聚 前庭神经核神经元上的神经管和耳石纤维，或异常连接，有助于异常 这些神经元中的信号处理。拟议的工作将建立一个框架， 假设先天性畸形的囊状内耳的形成改变了周围和周围的神经系统， 中枢前庭神经回路为了解决这些问题，我们的实验室已经实施并验证了 一种新的鸡胚模型。通过手术旋转，我们可以在85%的病例中产生可重复的动物模型。 2日龄鸡胚一侧180°的内耳或“耳囊”发育（E2）。由于手术 包括前后轴耳囊旋转产生囊状内耳，该模型被称为 ARO/S小鸡。ARO/s雏鸡的囊状内耳类似于患有CVD的儿童的囊状内耳。 孵化后（H），ARO/s小鸡在保持平衡和行走方面遇到挑战。的第一步 了解囊状内耳对发育中的前庭神经回路的影响， 具体目标1我们将进一步分析前庭上皮和量化前庭神经节细胞， 确定在ARO/s雏鸡中初级前庭传入突触减少的程度。具体目标 2、我们将联合收割机成像和电生理方法相结合，以确定是否存在结构均匀的 前庭神经核中的一类神经元，即切向核（TN）的主要细胞，获得有序的输入 从管和耳石纤维，被动和主动膜的性质，和突触传递发现，在正常 小妞们在具体目标3中，我们将进行行为学测试，以表征H5 ARO/s的姿势和平衡 鸡，然后通过水平前庭眼反射（hVOR）使用地球垂直轴旋转（EVAR）来测试 耳道功能和静态倾斜台试验评价耳石功能。实验结果将 为更好地了解前庭神经回路的病理变化提供了基础。 CVD患者，并修改我们对如何治疗这些疾病的想法。

ABSTRACT In the US, an estimated 3.3 million children experience dizziness and balance problems (19). Children with congenital vestibular disorders (CVDs) show delayed motor development and challenges in maintaining posture and balance, indicating that the vestibular neural circuitry is affected. Computed tomography (CT) shows that children with CVDs most commonly form a sac-like inner ear with the semicircular canals missing or truncated. It is not known how their vestibular connectivity is altered. We hypothesize that formation of a sac-like inner ear during early gestation results in a reduced number of vestibular ganglion cells forming fewer primary vestibular synapses on hair cells peripherally and on vestibular nuclei neurons centrally, leading to underconnectivity in the vestibular system. We further hypothesize that the sac-like inner ear pathology results in abnormal convergence of canal and otolith fibers onto vestibular nuclei neurons, or anomalous connectivity, contributing to abnormal signal processing in these neurons. The proposed work will establish a framework to test the overarching hypothesis that formation of a congenitally-malformed, sac-like inner ear alters the peripheral and central vestibular neural circuitry. To address these questions, our laboratory has implemented and validated a new chick embryo model. We can produce a reproducible animal model in 85% of cases by surgically rotating the developing inner ear or “otocyst” 180° on one side in two-day old chick embryos (E2). Since the procedure involves Anterior-posterior axis Rotation of the Otocyst to produce a Sac-like inner ear, the model is called the ARO/s chick. The sac-like inner ear of ARO/s chicks resembles the sac-like inner ear in children with CVDs. After hatching (H), ARO/s chicks experience challenges in maintaining balance and walking. As a first step in understanding the consequences of the sac-like inner ear on the developing vestibular neural circuitry, in Specific Aim 1 we will further analyze the vestibular epithelium and quantify vestibular ganglion cells to determine to what extent primary vestibular afferent synapses are decreased in ARO/s chicks. In Specific Aim 2, we will combine imaging and electrophysiological approaches to determine whether a structurally-uniform class of vestibular nuclei neurons, the principal cells of the tangential nucleus (TN), acquire the orderly inputs from canal and otolith fibers, passive and active membrane properties, and synaptic transmission found in normal chicks. In Specific Aim 3, we will perform ethological tests to characterize posture and balance in H5 ARO/s chicks, followed by the horizontal vestibuloocular reflex (hVOR) using Earth vertical axis rotation (EVAR) to test canal function and the static tilting platform test to evaluate otolith function. The experimental outcomes will provide a foundation to better understand the pathological changes occurring in the vestibular neural circuitry of CVD patients, and modify our thinking on how to treat these disorders.