Synaptic Mechanisms of Vestibular Efferent Responses

描述(申请人提供)：前庭器官，通过它们的毛细胞和传入神经，传递有关头部和身体运动的方向、速度和幅度的信息，这对保持我们的姿势和稳定我们的凝视至关重要。几乎所有脊椎动物的前庭器官也接受显著的传出神经支配，开始时在脑干内有数百个神经元，在外周广泛分布，最后在毛细胞和传入细胞上都有数千个神经末梢。这种传出神经在外周前庭通路中处于如此早期的阶段，这表明它准备调节前庭线索的初始处理。对传出神经元的电刺激导致一系列深刻而明显的兴奋性和抑制性传入反应，其中激活和持续时间的动力学可以从毫秒到分钟不等。到目前为止，三种药理上不同的尼古丁型ACh受体、一种毒鼠型ACh受体、至少两类钾通道以及毛细胞内库(例如突触下池)释放的钙被认为是不同传出反应的基础。然而，关于这些不同的传出成分如何以及何时影响前庭传入神经对其自然刺激的反应，我们的知识存在明显的差距。为了便于了解前庭生理学中的传出功能，将在甲鱼半规管中进行三项主要研究，其中一些传出功能的药理学基础已经建立，毛细胞和传入的形态生理学也得到了充分的描述。其具体目的是：(1)确定电刺激传出纤维的传入反应的突触机制；(2)确定电刺激传出纤维是如何改变前庭输出的；(3)表征传出神经元的形态生理学特性。为了完成特定的目标1和2，在传出和机械刺激过程中，将对初级传入、传入终末和毛细胞进行尖电极和膜片钳记录。将应用药理学试剂来识别受体和下游效应器，以及确定每个传出突触机制如何影响前庭刺激。平行的免疫组织化学研究将被用来定位我们的生理和药理学实验所涉及的不同成分。对于特定的目的3，将使用尖尖电极来记录去大脑准备中的传出活动并标记单个传出纤维。光学显微镜和电子显微镜将用于重建终末树，并检查传出终末的分布和突触结构。这些研究将提供对传出系统招募来调节传入放电的机制的洞察，以及识别可能以药物为靶点的突触过程，以治疗疾病和外周前庭装置的功能缺陷。鉴于其在解剖学上从无颌鱼到人类的普遍存在，外周前庭装置的传出神经支配对于正常的前庭功能是必要的。破译前庭传出系统如何以及何时改变前庭加工的初始阶段，对于理解它在前庭生理学中的作用至关重要。

DESCRIPTION (provided by applicant): Vestibular organs, via their hair cells and afferent innervation, transmit information about the direction, speed, and magnitude of head and body movements, which are critical for maintaining our posture and stabilizing our gaze. The vestibular organs of nearly every vertebrate also receive a prominent efferent innervation which begins as a few hundred neurons within the brainstem and extensively collateralizes in the periphery to end as several thousands of bouton terminals on both hair cells and afferents. That this efferent innervation is positioned at such an early stage in the peripheral vestibular pathway suggests it is poised to modulate the initial processing of vestibular cues. Electrical stimulation of efferent neurons results in a diverse panel of profound, yet distinct, excitatory and inhibitory afferent responses where the kinetics of both activation and duration can vary from milliseconds to minutes. To date, three pharmacologically-distinct nicotinic ACh receptors, a muscarinic ACh receptor, at least two classes of potassium channels, and the release of calcium from hair cell internal stores (e.g., subsynaptic cisterns) are thought to underlie the different efferent responses. However, there is a clear gap in our knowledge in relating how and when these different efferent-mediated components impact the responses of vestibular afferents to their natural stimulus. To facilitate an understanding of efferent function in vestibular physiology, three major studies will be performed in the turtle semicircular canal where a strong pharmacological basis for some of the efferent actions has been established, and both hair cell and afferent morphophysiology have been adequately described. The specific aims are: (1) Identify the synaptic mechanisms underlying afferent responses to electrical activation of efferent fibers, (2) Establish how vestibular output is modified by electrical activation of efferent fibers, and (3) Characterize the morphophysiological properties of efferent neurons. To complete specific aims 1 and 2, sharp-electrode and patch clamp recordings will be made from primary afferents, afferent terminals, and hair cells during efferent and mechanical stimulation. Pharmacological agents will be applied to identify the receptors and downstream effectors as well as defining how each efferent synaptic mechanism impacts vestibular stimulation. Parallel immunohistochemical studies will be used to localize the different components implicated by our physiological and pharmacological experiments. For specific aim 3, sharp-electrodes will be used to record efferent activity and label single efferent fibers in a decerebrate preparation. Light and EM microscopy will be used to reconstruct terminal trees and to examine the distribution and synaptic structure of efferent terminals. These studies will provide insights into the mechanisms that the efferent system recruits to modulate afferent discharge as well as identifying synaptic processes that may be targeted pharmacologically for the treatment of diseases and functional defects of the peripheral vestibular apparatus. Given its anatomical prevalence from jawless fish to humans, an efferent innervation of the peripheral vestibular apparatus is necessary for normal vestibular function. Deciphering how and when the vestibular efferent system modifies the initial stages of vestibular processing are crucial to understanding its role in vestibular physiology.