Afferent Innervation in the Mouse Cochlea

描述(申请人提供)：我研究的长期目标是了解陆生哺乳动物耳蜗内的基本结构-功能关系。在听力受损的耳蜗区，可以发现毛细胞丢失和立体纤毛病理，但并非总是如此。然而，内毛细胞(IHC)上的传入终末在噪声的响应下经历了急剧的结构变化，但对神经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C57BL/6J小鼠耳蜗的频率-位置图，这将使我们能够在随后的实验中建立结构-功能相关性。目前还没有关于任何老鼠品系的确凿图谱。使用逆行示踪剂注射到耳蜗核的特定频率区域，我们将绘制听觉神经传入到Corti器官的投射图。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IHC上特定频率位置(例如16 kHz)的神经末梢的形态、密度和组织。我们将把这一分析与一种无偏见的体视学方案结合起来，该方案只使用一小部分切片来准确和有效地研究几种动物的突触形态。最后，我们将检验这样一种假设，即噪声损伤对传入终末及其与IHC的突触的结构具有有害的长期影响，并且这些变化与永久性听力损失有关。这个目标将利用在第二个目标中开发的体视学技术，在对应于永久阈值漂移的频率位置上研究噪声对IHC-传入界面结构的影响。小鼠是听觉神经解剖学的有用模型，因为它的体积小有助于进行有效的显微分析，而且它的基因组对于转基因和突变的创造是必不可少的。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.