Experimental study of the cochlear amplifier

描述（由申请人提供）：哺乳动物耳蜗通过称为“耳蜗放大器”的主动放大机制实现其显著的灵敏度、精确的频率选择性和巨大的动态范围，该主动放大机制使用代谢能量来增强基底膜（BM）振动。虽然外毛细胞（OHC）可以通过体细胞和毛束运动产生力，但耳蜗放大的机械机制仍不清楚。本申请是研究体细胞和毛束运动在耳蜗放大中的作用，通过使用我们最近开发的扫描低相干外差干涉仪在正常和遗传修饰耳蜗中进行一组新的实验。具体目标一是测量敏感小鼠和沙鼠耳蜗BM、网状板（RL）和覆膜（TM）的振动。假设是，在敏感的小鼠耳蜗中，基于OHC的耳蜗放大器在RL处比在BM处产生更大且更非线性的振动。小鼠的BM和RL振动是高度敏感的，并且与用于耳蜗力学研究的其他常用动物（例如沙鼠）一样显示出尖锐的调谐和非线性。本实验的数据将是研究小鼠和沙鼠耳蜗微观力学的基础。具体目标二将通过测量没有体细胞运动的小鼠耳蜗中的BM、RL和TM振动来确定OHC体细胞运动的作用。假设是，在普雷斯廷499敲入小鼠中，体细胞运动的缺乏导致BM、RL和TM振动的灵敏度降低和急剧调谐和非线性的损失。由于普雷斯廷499基因敲入小鼠中OHC的机械电转导、刚度和形态是正常的，因此预期的变化将归因于体细胞运动的缺乏。具体目标三将通过测量具有无效毛束运动的小鼠耳蜗中的BM、RL和TM振动来确定OHC毛束运动的作用。假设是，缩短和分离TM与独立的毛束妥协TectaC 1509 G/C1509 G小鼠的毛束运动，机电转导和耳蜗放大，降低灵敏度，尖锐的调谐，和非线性的声学诱发BM，RL和TM振动。然而，电刺激激活躯体和发束运动性，并导致BM，RL和TM振动和电诱发耳声发射。水杨酸抑制体细胞运动后，可以在野生型小鼠中测量毛束运动介导的反应，但在TectaC 1509 G/C1509 G小鼠中不能测量。将通过测量和比较TectaC 1509 G/C1509 G和野生型小鼠在水杨酸盐应用后的电诱发反应来确定毛束运动性对耳蜗放大的贡献。这项研究的新数据将提供关键的信息，OHC体细胞和毛束运动在耳蜗放大中的重要作用，并了解人类听觉障碍的机制。

DESCRIPTION (provided by applicant): The mammalian cochlea achieves its remarkable sensitivity, exquisite frequency selectivity, and enormous dynamic range through an active amplification mechanism called the "cochlear amplifier", which uses metabolic energy to boost basilar membrane (BM) vibration. Although it is well established that outer hair cells (OHCs) can generate forces through somatic and hair-bundle motility, the mechanical mechanism of cochlear amplification remains unclear. This application is to study the role of somatic and hair-bundle motility in cochlear amplification by conducting a set of novel experiments in normal and genetically modified cochleae using our recently developed scanning low-coherence heterodyne interferometer. Specific aim one will measure the BM, reticular lamina (RL), and tectorial membrane (TM) vibration in sensitive mouse and gerbil cochleae. The hypothesis is that, in sensitive mouse cochleae, the OHC-based cochlear amplifier produces a larger and more nonlinear vibration at the RL than that at the BM. BM and RL vibrations in mice are highly sensitive, and show sharp tuning and nonlinearity as in other commonly used animals for cochlear mechanics study, such as gerbils. The data from this experiment will be essential for studying cochlear micromechanics in mice and gerbils. Specific aim two will determine the role of the OHC somatic motility by measuring the BM, RL, and TM vibration in mouse cochleae without somatic motility. The hypothesis is that, in prestin 499 knockin mice, the lack of somatic motility results in decreased sensitivity and loss of sharp tuning and nonlinearity of the BM, RL, and TM vibration. Because the mechanoelectrical transduction, stiffness, and morphology of OHCs in prestin 499 knockin mice are normal, the expected changes will be attributed to the absence of somatic motility. Specific aim three will determine the role of the OHC hair-bundle motility by measuring the BM, RL, and TM vibration in mouse cochleae with ineffective hair-bundle motility. The hypothesis is that shortened and detached TM with free-standing hair bundles compromises hair-bundle motility, mechanoelectrical transduction, and cochlear amplification in TectaC1509G/C1509G mice, decreasing sensitivity, sharp tuning, and nonlinearity of acoustically evoked BM, RL, and TM vibration. However, electrical stimulation activates both somatic and hair-bundle motility and results in BM, RL, and TM vibration and electrically evoked otoacoustic emissions. After somatic motility is suppressed by salicylate, hair-bundle motility-mediated responses can be measured in wild-type but not in TectaC1509G /C1509G mice. The contribution of hair-bundle motility to cochlear amplification will be determined by measuring and comparing electrically evoked responses in TectaC1509G /C1509G and wild-type mice after salicylate application. The new data from this study will provide critical information on the essential role of OHC somatic and hair-bundle motility in cochlear amplification and for understanding mechanisms of auditory disorders in humans.