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。我们建议研究初级前庭传入信号是如何产生的，重点关注内在离子通道和钙结合蛋白的贡献。我们将研究前庭传入事件中特定活动模式的起源（动作电位的放电模式，也称为尖峰）。在活体记录中，前庭传入事件在峰间间隔的规律性上变化很大；这种变化是高度系统性的，与许多形态和生理特性共同变化。因此，高度规则的传入神经倾向于携带强直信号，具有小直径和延伸的树突状乔木，并支配感觉上皮的外周区。相反，高度不规则的传入神经往往具有相位信号，具有大直径和紧凑的树突状乔木，具有大的花萼传入终端，支配中枢区并表达特定的Ca2+结合蛋白（CBPs）。对于~ 20hz以下的头部运动频率，高的规律性可以增强信息含量和时间编码；高度不规则可能反映了对突触电流的高度敏感性。二十多年前，研究人员探索了设定放电模式的可能因素，认为传入纤维中的内在离子通道可能很重要。我们现在知道，前庭神经节神经元（VGNs）中的离子通道补体，就像许多大脑神经元一样，比以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在啮齿动物VGNs上表征放电模式和潜在的电压和钙门控离子通道。vgn将在体外作为分离体进行研究，也将在包括感觉上皮和神经节的半完整制备中进行研究。这两种制备方法具有不同的优点：分离的VGNs提供优越的电压箝位，而半完整制备的VGNs接受来自毛细胞的突触输入。初步数据表明，VGNs表达特定的离子通道补体，在响应注入电流时产生不同的内源性放电模式。我们将验证内源性离子通道有助于在体内建立不同的尖峰规律模式的假设，以及特定离子通道参与设置放电模式的假设。我们将使用RT-PCR筛选候选离子通道和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（体细胞与传入端）来定位通道。我们将研究特定CBPs是否通过调节钙依赖性钾通道来帮助设置放电模式。我们将开发计算模型来测试我们对离子通道如何促进发射模式的全面理解。内耳的一组五个前庭器官将头部位置和头部运动的信息传递给大脑，在那里它驱动稳定凝视、姿势和平衡的反射，并提供自我运动和方向感。这项拟议的研究将调查前庭传入神经元如何利用离子通道产生电活动模式，并以此编码头部运动和位置。通过前庭传入的电信号的详细知识对于理解在人群中广泛存在的内耳损伤如何导致平衡能力差和定向障碍至关重要。这些知识也将帮助我们设计假肢，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.