Molecular biology of cochlear efferent receptors

描述(申请人提供)：所有毛细胞系统，包括侧线器官、前庭器官和耳蜗，都含有传出神经，起源于脑干，投射到感觉上皮中的毛细胞和/或神经元件。在哺乳动物的耳蜗中，这个传出系统起源于上橄榄复合体，被称为橄榄耳蜗(OC)通路，由内侧(MOC)和外侧(LOC)组成。耳蜗传出信号可能具有两种功能：防止声学过度刺激和在存在背景噪声的情况下增强声音识别。在上一个项目期间，我们确定了MOC的传出可以通过新发现的α9/10 NACH受体复合体来保护耳蜗免受声过度刺激的影响。在接下来的项目期间，我们将重点介绍含有降钙素基因相关肽(CGRP)的LOC传出纤维。我们确定，在基因敲除的小鼠中，CGRP的缺失降低了耳蜗神经的声音诱发活动，这将导致声音感知的动态范围缩小。然而，毛细胞器官中有几个CGRP能神经元系统：支配血管系统的传出和通路，这可能与听觉表型有关。我们的目标是确定从传出纤维释放的CGRP影响神经元传入的分子机制。为此，我们将(1)确定CGRP受体信号对声诱发活动的影响；(2)确定CGRP受体信号的生化时程；(3)确定CGRP受体信号的生理靶细胞。我们将使用腺病毒基因转移、DPOAE、ABR和CAP检测听觉功能、免疫组化、免疫共沉淀、生物转染法和FRET成像来实现这些目标。从这些研究中获得的信息将直接评估CGRP传出反馈通路用于增强耳蜗神经中声音诱发活动的分子机制。

DESCRIPTION (provided by applicant): All hair cell systems, including lateral-line organs, vestibular organs and the cochlea, contain an efferent innervations, originating in the brainstem and projecting to the hair cells and/or neural elements in the sensory epithelium. In the mammalian cochlea, this efferent system originates in the superior olivary complex and has been called the olivocochlear (OC) pathway and consists of a medial (MOC) and lateral (LOC) component. Cochlear efferent is likely to serve two functions: protection from acoustic over stimulation and enhancement of sound recognition in the presence of background noises. In the last project period, we determined that the MOC efferent could protect the cochlea from acoustic over stimulation working through the newly discovered alpha 9/10 nACh receptor complex. In this next project period, we will focus on the LOC efferent fibers that contain calcitonin gene-related peptide (CGRP). We determined that the loss of CGRP in knockout mice reduced sound-evoked activity of the cochlear nerve, which would then cause a reduction in the dynamic range of sound perception. However there are several CGRP-ergic neuronal systems in hair cell organs: the efferent as well as pathways innervating the vasculature, which could have contributed to the auditory phenotype. Our goal is to determine the molecular mechanism by which CGRP released from efferent fibers influences neuronal afferents. In these aims we will (1) determine effect of CGRP receptor signaling on sound-evoked activity; (2) determine biochemical time course for CGRP receptor signaling; (3) determine physiological target cells for CGRP receptor signaling. We will use adenoviral gene transfer, DPOAE, ABR, and CAP testing for auditory function, immunohistochemisty, coimmunoprecipitation, biolistic transfection, and FRET imaging to carry out these aims. Information gained from these studies will provide direct assessment of the molecular mechanisms used by the CGRP efferent feedback pathway to enhance sound-evoked activity in the cochlear nerve.