Measuring and Modeling the Cochlear Organ-of-Corti Motions Responsible for Inner-and Outer-Hair-Cell Drives and Amplification

项目总结/摘要 我们对耳蜗Corti器官（OoC）力学的认识正在进行重大反思。最近的调查结果 结果表明，网状板（RL）的运动远大于基底膜（BM），且运动时相不同 比以前认为的。我们的高分辨率光学相干断层扫描（OCT）成像和振动测量 在沙鼠高频基底区的测量显示，外毛细胞（OHC）第3行（RL 3）的RL 移动显著大于OHC行1（RL 1）。这一新发现表明RL的镶嵌结构， 由基底倾斜的OHC和顶部倾斜的指骨突（PhPs）的表皮板组成， 不是僵硬的，而是弯曲和/或拉伸。我们的中心假设是Deiters细胞的PhP延伸 (DCs)影响RL马赛克的径向和纵向运动以提供运动相位和/或幅度 在耳蜗放大和灵敏听力所需的每个OHC行。这一假设将由以下人员进行检验： 测量和模型，以确定是否：（1）RL 3运动具有更大的径向分量， 驱动到OHC 3静纤毛;（2）RL嵌合体下方的细胞结构差异（例如，径向和 纵向PhP角）导致径向和纵向运动在三个OHC行上不同;（3） 外隧道（OT）流体空间是对RL径向运动具有实质性影响的谐振系统的一部分;以及 (4)OoC区域改变中阶的压力以产生放大，以及（5）这些运动如何 影响对内毛细胞（IHC）静纤毛束的驱动。一种高分辨率、高帧频的OCT系统， （约2.3-µm轴向分辨率）将用于成像和测量沙鼠和小鼠OoC的运动。我们 将测量BM、OHC-DC的横向和径向运动和/或径向和纵向运动 连接、RL、OT和顶盖膜（TM）响应于多个声级的声刺激;以及 将在大约对应于0.5-kHz（顶端）、2-kHz（中间）和45-kHz的耳蜗位置处这样做 在沙鼠中的10-kHz（基底）位置，以及在小鼠中的10-kHz（顶端）、20-kHz（中间）和60-kHz（基底）位置， 决定我们假设的适用性。从这两个中弯和顶弯的测量结果 这些物种将跨越人类听觉的0.02-20 kHz频率范围的大部分。转换测量的OoC 为了详细了解OHC和IHC刺激的机制，我们将使用 我们的OCT图像和测量，以建立和测试被动和主动3D有限元模型的沙鼠和 小鼠耳蜗。这些模型将在粘性流体环境中结合详细的OoC显微解剖， 包括跨越三行、柱细胞、IHC和TM的径向和纵向PhP角。模型 将允许在耳蜗功能与结构和材料之间建立明确的关系 OoC的特性。这项工作将结合联合收割机实验和建模的努力，以加深我们的理解 耳蜗内产生放大和声音传导的复杂机械相互作用。

Project Summary/Abstract Our knowledge of cochlear organ-of-Corti (OoC) mechanics is undergoing major rethinking. Recent findings show that the reticular lamina (RL) moves much more than the basilar membrane (BM) and with a different phase than previously thought. Our high-resolution optical-coherence-tomography (OCT) imaging and vibrometry measurements in the gerbil high-frequency basal region reveal that the RL at outer-hair-cell (OHC) row 3 (RL3) moves significantly more than at OHC row 1 (RL1). This new discovery suggests that the RL’s mosaic structure, comprised of the cuticular plates of the basally tilted OHCs and apically tilted phalangeal processes (PhPs) is not stiff, but rather bends and/or stretches. Our central hypothesis is that the PhP extensions of the Deiters’ cells (DCs) influence radial and longitudinal motion of the RL mosaic to provide the motion phase and/or magnitude at each OHC row required for cochlear amplification, and sensitive hearing. This hypothesis will be tested by measurements and models to determine if: (1) RL3 motion has a bigger radial component that increases the drive to the OHC3 stereocilia; (2) cytoarchitectural differences below the RL mosaic (e.g., the radial and longitudinal PhP angles) cause the radial and longitudinal motions to differ across the three OHC rows; (3) the outer-tunnel (OT) fluid space is part of a resonant system that has a substantial effect on RL radial motion; and (4) the OoC area changes the pressure in the scala media to produce amplification, and (5) how these motions influence the drive to inner-hair-cell (IHC) stereocilium bundles. A high-resolution, high-framerate OCT system (approx. 2.3-µm axial resolution) will be used to image and measure motions of the OoC in gerbils and mice. We will measure the transverse and radial motions and/or the radial and longitudinal motions of the BM, OHC–DC junctions, RL, OT, and tectorial membrane (TM) in response to acoustic stimulation at multiple sound levels; and will do so at cochlear locations corresponding approximately to 0.5-kHz (apical), 2-kHz (middle), and 45-kHz (basal) locations in gerbil, and 10-kHz (apical), 20-kHz (middle), and 60-kHz (basal) locations in mouse, to determine the applicability of our hypotheses. The measurements from the middle and apical turns in these two species will span much of the 0.02–20 kHz frequency range of human hearing. To translate the measured OoC motions into a detailed understanding of the mechanisms responsible for OHC and IHC stimulation, we will use our OCT images and measurements to build and test passive and active 3D finite-element models of gerbil and mouse cochleae. The models will incorporate, in a viscous-fluid environment, the detailed OoC microanatomy, including the radial and longitudinal PhP angles across the three rows, pillar cells, IHCs, and TM. The models will allow clear relationships to be established between cochlear function and the structure and material properties of the OoC. This work will combine experimental and modeling efforts to deepen our understanding of the complex mechanical interactions within the cochlea that produce amplification and sound transduction.