Stimulus processing in mammalian vestibular organs

描述(申请人提供)：前庭传入神经纤维将头部位置和运动信号从内耳传递到大脑，在那里它们驱动控制凝视、姿势和平衡的反射，并有助于感知方向和自我运动。我们建议研究电信号是如何在初级前庭传入中产生的，重点是内在离子通道和钙结合蛋白的作用。我们将研究前庭传入中特定活动模式(动作电位的放电模式，也称为棘波)的起源。在活体记录中，前庭传入在棘波间期的规律性上有很大的变化；这种变化是高度系统化的，与许多形态和生理特性一起变化。因此，高度规则的传入神经倾向于携带紧张性信号，具有较小的直径和延伸的树突分支，并支配感觉上皮的外周区。相反，高度不规则的传入细胞往往有时相信号，具有大直径和致密的树突，具有大的帽状传入终末，支配中央区域并表达特定的钙结合蛋白(CBPS)。高规律性可增强对~20 Hz以下头部运动频率的信息量和时间编码；高规律性可反映对突触电流的高敏感性。二十多年前，研究人员探索了设定放电模式的可能因素，表明传入纤维中的本征离子通道可能是重要的。我们现在知道，像许多脑神经元一样，前庭神经节神经元(VGNs)中的离子通道补体比之前想象的要复杂得多，我们有更好的工具来研究这个问题。我们建议使用全细胞膜片钳方法对啮齿类动物的室旁核进行放电模式以及电压和钙门控离子通道的研究。VGNs将在体外作为分离的体细胞进行研究，也将在包括感觉上皮和神经节的半完整制剂中进行研究。这两种准备方法有不同的优点：分离的VGNs提供优越的电压钳制，而半完整准备的VGNs接受毛细胞的突触输入。初步数据表明，VGNs表达离子通道的特定补体，对注入电流产生不同的内源性放电模式。我们将测试内源性离子通道有助于在体内建立不同的尖峰规律性模式的假设，以及特定离子通道参与设定放电模式的假设。我们将使用RT-PCR来筛选候选离子通道，并使用免疫细胞化学根据传入类型、感觉上皮内的区域和细胞位置(胞体与传入终末)来定位通道。我们将研究特定的CBPS是否通过调节钙依赖的钾通道来帮助设定放电模式。我们将开发计算模型来测试我们对离子通道如何影响激发模式的全面理解。内耳的五个前庭器官向大脑传递关于头部位置和头部运动的信息，在那里它驱动反射，稳定凝视、姿势和平衡，并提供自我运动和定向感。这项拟议的研究将调查前庭传入神经元如何使用离子通道来产生电活动模式，用来编码头部的运动和位置。对前庭传入电信号的详细了解对于了解内耳损伤是如何导致平衡不良和定向障碍至关重要的。内耳损伤在人群中普遍存在。这些知识还将帮助我们设计假体，以电刺激前庭系统，以恢复功能。

DESCRIPTION (provided by applicant): Vestibular afferent nerve fibers convey head position and motion signals from the inner ear to the brain, where they drive reflexes controlling gaze, posture and balance and contribute to perceptions of orientation and self-motion. We propose to study how electrical signals are generated in primary vestibular afferents, focusing on the contributions of intrinsic ion channels and calcium binding proteins. We will examine the origins of specific patterns of activity (firing patterns of action potentials, also called spikes) in vestibular afferents. In recordings made in vivo, vestibular afferents vary greatly in the regularity of inter-spike intervals; this variation is highly systematic, co-varying with many morphological and physiological properties. Thus, highly regular afferents tend to carry tonic signals, to have small diameters and extended dendritic arbors, and to innervate peripheral zones of the sensory epithelia. In contrast, highly irregular afferents tend to have phasic signals, to have large diameters and compact dendritic arbors with large, calyceal afferent terminals, to innervate central zones and to express particular Ca2+ binding proteins (CBPs). High regularity may enhance the information content and temporal encoding for head movement frequencies below ~20 Hz; high irregularity may reflect high sensitivity to synaptic currents. Over two decades ago, investigators exploring possible factors in setting firing patterns suggested that intrinsic ion channels in the afferent fibers were likely to be important. We now know that ion channel complements in vestibular ganglion neurons (VGNs), as in many brain neurons, are much more complex than previously imagined, and we have better tools to study this issue. We propose to use the whole-cell patch clamp method on VGNs from rodents to characterize firing patterns and the underlying voltage- and calcium-gated ion channels. VGNs will be studied in vitro as isolated somata and also within a semi-intact preparation that includes sensory epithelia and the ganglion. The two preparations have different advantages: isolated VGNs provide superior voltage clamp, while VGNs in the semi-intact preparation receive synaptic input from hair cells. Preliminary data suggest that VGNs express specific complements of ion channels, giving rise to distinct endogenous firing patterns in response to injected currents. We will test the hypothesis that the endogenous ion channels help establish different patterns of spike regularity in vivo, and the involvement of specific ion channels in setting firing patterns. We will use RT-PCR to screen for candidate ion channels and immunocytochemistry to localize channels according to afferent type, zone within the sensory epithelium, and cellular location (soma vs. afferent terminal). We will investigate whether specific CBPs help set firing patterns by modulating calcium-dependent potassium channels. We will develop computational models to test our comprehensive understanding of how ion channels contribute to firing patterns. A set of five vestibular organs in the inner ear conveys information about head position and head motion to the brain, where it drives reflexes that stabilize gaze, posture and balance, and provide a sense of self-motion and orientation. The proposed research will investigate how vestibular afferent neurons use ion channels to generate patterns of electrical activity with which they encode head motion and position. Detailed knowledge of electrical signaling by vestibular afferents is essential to understand how inner ear damage, which is widespread in the population, causes poor balance and disorientation. Such knowledge will also help us design prosthetics to electrically stimulate the vestibular system in order to restore function.