Molecular biology of cochlear efferent receptors

描述（由申请人提供）：所有毛细胞系统，包括侧线器官、前庭器官和耳蜗，都含有传出神经支配，起源于脑干并投射到感觉上皮中的毛细胞和/或神经元件。在哺乳动物耳蜗中，该传出系统起源于上级橄榄复合体，并且被称为橄榄耳蜗（OC）通路，并且由内侧（MOC）和外侧（OOC）成分组成。耳蜗传出神经可能有两个功能：保护听觉免受过度刺激和在背景噪声存在下增强声音识别。在上一个项目期间，我们确定MOC传出可以通过新发现的α 9/10 nACh受体复合物保护耳蜗免受声学过度刺激。在下一个项目期间，我们将重点关注含有降钙素基因相关肽（CGRP）的前传出纤维。我们确定，基因敲除小鼠中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减小。然而，在毛细胞器官中有几个CGRP能神经元系统：传出以及支配血管的通路，这可能有助于听觉表型。我们的目标是确定传出纤维释放CGRP影响神经元传入的分子机制。在这些目标中，我们将（1）确定CGRP受体信号传导对声音诱发活动的影响;（2）确定CGRP受体信号传导的生化时程;（3）确定CGRP受体信号传导的生理靶细胞。我们将使用腺病毒基因转移、DPOAE、ABR和CAP听觉功能测试、荧光化学、免疫共沉淀、生物射弹转染和FRET成像来实现这些目标。从这些研究中获得的信息将提供直接评估的CGRP传出反馈通路，以增强耳蜗神经的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.