Afferent Innervation in the Mouse Cochlea

描述（由申请人提供）：我的研究的长期目标是了解陆生哺乳动物耳蜗的基本结构-功能关系。在听力受损的耳蜗区域可以发现毛细胞损失和静纤毛病理学，但并不总是如此。然而，内毛细胞（IHC）上的传入终末在对噪声的反应中经历了急性结构变化，但对神经支配密度和突触形态的长期影响及其对听力的影响尚不清楚。本研究将首先建立C57 BL/6 J小鼠耳蜗的频率-位置图，这将使我们能够在后续的实验中进行结构-功能相关。目前还没有任何小鼠品系的结论性图谱。使用逆行示踪剂注射到耳蜗核的限定频率区域，我们将绘制进入Corti器官的听觉神经传入投射。一旦频率图可用，我们将使用连续切片的电子显微镜分析来表征特定频率位置（例如16 kHz）处IHC上神经末梢的形态、密度和组织。我们将结合联合收割机这种分析与一个公正的体视学协议开发，使用只有一小部分的部分，在几种动物的突触形态学的准确和有效的研究。最后，我们将测试的假设，噪声损伤有一个有害的长期影响的结构上的传入终端和他们的突触与IHC，这些变化与永久性听力损失。本目标将使用第二个目标中开发的体视学技术，研究噪声在对应于永久性阈值偏移的频率位置处对IHC-传入接口结构的影响。小鼠是听觉神经解剖学的有用模型，因为它的小尺寸使得有效的显微镜分析，其基因组是转基因和突变体创造不可或缺的。更好地了解IHC的正常和异常突触结构可能会为听力损失的机制提供新的见解，并将增加发现和开发新疗法的机会。

DESCRIPTION (provided by applicant): The long-term goal of my research is to understand fundamental structure-function relationships in the cochlea of terrestrial mammals. Hair cell loss and stereocilia pathology can be found in cochlear regions where hearing is impaired, but not always. Afferent terminals on inner hair cells (IHC), however, undergo acute structural changes in response to noise, but the long-term effects on innervation density and synaptic morphology, and their implications for hearing are unknown. This study will first establish a frequency-place map for the C57BL/6J mouse cochlea, which will enable us to make structure-function correlations in the subsequent experiments. At present there is no conclusive map for any mouse strain. Using retrograde tracer injections into defined frequency regions of the cochlear nucleus, we will plot auditory nerve afferent projections into the organ of Corti. Once a frequency map is available, we will characterize the morphology, density, and organization of nerve terminals on IHCs at specific frequency locations (e.g. 16kHz) using electron microscopic analyses of serial sections. We will combine this analysis with an unbiased stereological protocol developed to use only a fraction of the sections for accurate and efficient study of synaptic morphology in several animals. Lastly, we will test the hypothesis that noise damage has a detrimental long term effect on the structure of afferent terminals and their synapses with IHCs, and that these changes are associated with permanent hearing loss. This aim will study the effects of noise on structure of the IHC-afferent interface at frequency locations corresponding to permanent threshold shift, using stereological techniques developed in the 2nd aim. The mouse is a useful model for auditory neuroanatomy because its small size makes for efficient microscopic analysis, and its genome is indispensable for transgenic and mutant creations. A better understanding of normal and abnormal synaptic structure at IHCs may provide new insights into the mechanisms of hearing loss and will increase opportunities for discovery and for the development of new therapies.