Synaptic Processing in the Vestibular System

项目摘要/摘要 前庭内耳向大脑提供有关头部运动和位置的信息，驱动力强大 在头部运动时稳定凝视和姿势的反射，有助于我们的头晕感和 我们在世界上行走时的方位。虽然我们通常不知道这些功能，但它们的损失 严重影响行动能力，导致视力不稳定和眩晕。前庭功能的丧失通常源于 损害毛细胞及其与投射到大脑的前庭传入神经纤维的突触。 这些毛细胞、突触和传入纤维具有令人惊叹的特性，但人们对这些特性还知之甚少。这个 这项研究计划的长期目标是建立对前庭如何 信息在内耳中产生和编码。目前的提案主要集中在突触转移上 从毛细胞到初级前庭神经元的头部运动信号(目标1)和随后的启动 小鼠椭圆囊的动作电位(棘波)(AIM 2)，一个关于遗传、发育和 生理学研究。主要方法是毛细胞和传入神经元的全细胞膜片钳； 电压门控离子通道、泵和突触标志物的免疫定位和计算模型 毛细胞，突触和传入神经纤维，结合了离子通道，泵， 和形态。 前庭传入神经元使II型毛细胞上的常规突触终末独一无二 I型毛细胞上的花蕾接触。毛细胞在毛囊和花萼上都会释放谷氨酸小泡。 (“量子”突触传递)进入突触间隙，激活脑内谷氨酸受体通道。 突触后膜产生兴奋性突触后电位并启动棘波。在肾盏接触处， 一种额外的“非量子”传递机制不依赖于囊泡释放或缝隙连接，而是 而是取决于离子从毛细胞流经离子通道进入突触间隙并通过 不同的离子通道。突触后对单个发束的控制刺激反应表明 量子和非量子传输模式可以发生在同一盏突触上，而非量子传输模式可以发生在同一盏突触上 MODE提供了一个快速信号，这可能对高速前庭反射很重要。建议的实验 建模将研究关键毛细胞离子通道对非量子传输和 描述量子和非量子传递如何在单个肾盏和传入神经中整合 纤维。其他实验将测试特定的电压门控钾离子通道和钠离子通道 突触形成突触后电压反应和轴突起始段的尖峰。免疫定位 揭示了花萼末端和附近棘突的微域中离子通道的显著浓度 起爆区。实验重点放在可能形成显著反应差异的通道上 不同连接性(毛细胞输入)的传入和不同脑区之间的动力学和棘波时序 感觉上皮细胞。

Project Summary/Abstract The vestibular inner ear supplies information about head motion and position to the brain, driving powerful reflexes that stabilize gaze and posture during head motions, and contributing to our sense of heading and orientation as we move through the world. Although we are not normally aware of these functions, their loss severely affects mobility by destabilizes vision and causes vertigo. Loss of vestibular function often originates in damage to hair cells and their synapses with the afferent vestibular nerve fibers that project to the brain. These hair cells, synapses, and afferent fibers have striking properties that are only partly understood. The longterm goal of this program of research is to build a comprehensive understanding of how vestibular information is generated and encoded in the inner ear. The current proposal focuses on the synaptic transfer of head motion signals from hair cells to primary vestibular neurons (Aim 1) and the subsequent initiation of action potentials (spikes) (Aim 2) in the mouse utricle, a model preparation for genetic, developmental and physiological studies. Principal methods are whole-cell patch clamping of hair cells and afferent neurons; immunolocalization of voltage-gated ion channels, pumps and synaptic markers; and computational modeling of the hair cells, synapses and afferent nerve fibers, incorporating current information on ion channels, pumps, and morphology. Vestibular afferent neurons make conventional bouton synaptic terminals on type II hair cells and unique calyceal contacts on type I hair cells. At both boutons and calyces, hair cells release vesicles of glutamate (“quantal” synaptic transmission) into the synaptic cleft, activating glutamate receptor-channels in the postsynaptic membrane to produce excitatory postsynaptic potentials and initiate spikes. At calyceal contacts, an additional “non-quantal” transmission mechanism depends not on vesicular release or gap junctions, but rather on flow of ions from the hair cell through ion channels into the synaptic cleft and into the calyx through different ion channels. Postsynaptic responses to controlled stimulation of individual hair bundles show that quantal and non-quantal transmission modes can occur at the same calyceal synapse and that the non-quantal mode provides a fast signal that may be important for high-speed vestibular reflexes. Proposed experiments and modeling will investigate the impact of key hair cell ion channels on non-quantal transmission and delineate how quantal and non-quantal transmission are integrated in individual calyces and afferent nerve fibers. Other experiments will test how specific voltage-gated potassium and sodium channels in calyces and boutons shape the postsynaptic voltage response and spikes in the axonal initial segment. Immunolocalization has revealed remarkable concentrations of ion channels in microdomains of the calyx ending and nearby spike initiation zone. Experiments focus on channels with the potential to shape salient differences in response dynamics and spike timing between afferents of different connectivity (hair cell inputs) and different zones of the sensory epithelium.