The function of the cochlea is to transduce complex sound pressure waves into electrical signals. Organ of Corti vibration is based upon a complex interplay between passive mechanical structures and active OHC- based processes. While laser Doppler vibrometry has added tremendously to our understanding of cochlear physiology, this technique is limited. Only motion from one point on the basilar membrane can be measured, and this provides only a surrogate measure for what is actually responsible for the sense of hearing: deflection of the IHC stereociliary bundle. Thus, these measurements alone cannot explain how the cells and tissues within the organ of Corti work collaboratively to develop cochlear amplification. Vibratory measurements of all of the structures within the intact organ of Corti are needed to understand this process. We have developed a novel technique, volumetric optical coherence tomography vibrometry (VOCTV, pronounced voctive) that overcomes these limitations because it can image directly through the mouse otic capsule bone and simultaneously resolve vibrations at every voxel. Thus, we are at the cusp of understanding how the active and passive mechanics of the cochlea drive IHC stimulation, i.e. the input received by the brain. Our preliminary data demonstrate that frequency-dependent differential motion within the organ of Corti exists. We hypothesize that these movements are mechanically coupled to tilting of the OHC-Deiter cell junction, that the tilting varies with the passive stiffness of the HC, and that the tilting is enhanced by OHC electromotility. This hypothesis is important because, if true, it means that OHC electromotility improves hearing not by increasing vertical displacements of the organ of Corti, but by converting vertical displacement of the basilar membrane into radial fluid movement that can stimulate IHCs. Our studies will explicitly measure the role of the OHC by comparing the in vivo vibratory patterns of wild-type mice (normal OHC stiffness, normal electromotility), prestin 499 mice (normal OHC stiffness, no electromotility), and prestin null mice (decreased OHC stiffness, no electromotility).
Aim 1 is to use our existing 1D-VOCTV system to study mice positioned at two different angles to measure both vertical and radial displacements throughout the organ of Corti.
Aim 2 is to develop the optical technology and software to perform simultaneous 3D vibratory measurements for every voxel (3D-VOCTV).
Aim 3 is use 3D-VOCTV in living mice to measure transverse, radial, and longitudinal motion. If our hypothesis is true, wild- type mice will demonstrate significantly largr radial and/or longitudinal displacements of the OHC-Deiter cell junction compared to dead wild-type, live prestin 499, and live prestin null mice. In addition, the frequency tuning of these displacements should be less sharp in prestin null mice compared to prestin 499 mice. The data obtained with this grant will likely explain the basis for the unique and highly structured anatomy of cells within the organ of Corti. The state-of-the-art technology developed with this grant is likely to become the new standard for making in vivo vibratory measurements.

Public Health Relevance

Mammals hear when the highly-organized organ of Corti vibrates in response to sound pressure waves and stimulates hair cells. Herein, we propose to develop the technology to image these vibrations non-invasively in 3-D. We will then determine the impact of outer hair cell passive stiffness and active force generation on the vibratory patterns using transgenic mouse strains.

Agency
National Institute of Health (NIH)
Institute
National Institute on Deafness and Other Communication Disorders (NIDCD)
Type
Research Project (R01)
Project #
7R01DC013774-04
Application #
9545142
Study Section
Special Emphasis Panel (ZRG1)
Program Officer
Cyr, Janet
Project Start
2015-04-10
Project End
2020-03-31
Budget Start
2017-08-01
Budget End
2018-03-31
Support Year
4
Fiscal Year
2017
Total Cost
Indirect Cost
Name
University of Southern California
Department
Otolaryngology
Type
Schools of Medicine
DUNS #
072933393
City
Los Angeles
State
CA
Country
United States
Zip Code
90033
Dewey, James B; Xia, Anping; Müller, Ulrich et al. (2018) Mammalian Auditory Hair Cell Bundle Stiffness Affects Frequency Tuning by Increasing Coupling along the Length of the Cochlea. Cell Rep 23:2915-2927
Kim, Jinkyung; Xia, Anping; Grillet, Nicolas et al. (2018) Osmotic stabilization prevents cochlear synaptopathy after blast trauma. Proc Natl Acad Sci U S A 115:E4853-E4860
Jawadi, Zina; Applegate, Brian E; Oghalai, John S (2016) Optical Coherence Tomography to Measure Sound-Induced Motions Within the Mouse Organ of Corti In Vivo. Methods Mol Biol 1427:449-62
Xia, Anping; Liu, Xiaofang; Raphael, Patrick D et al. (2016) Hair cell force generation does not amplify or tune vibrations within the chicken basilar papilla. Nat Commun 7:13133
Lee, Hee Yoon; Raphael, Patrick D; Xia, Anping et al. (2016) Two-Dimensional Cochlear Micromechanics Measured In Vivo Demonstrate Radial Tuning within the Mouse Organ of Corti. J Neurosci 36:8160-73
Kim, Sangmin; Raphael, Patrick D; Oghalai, John S et al. (2016) High-speed spectral calibration by complex FIR filter in phase-sensitive optical coherence tomography. Biomed Opt Express 7:1430-44
Zeng, Wei-Zheng; Grillet, Nicolas; Dewey, James B et al. (2016) Neuroplastin Isoform Np55 Is Expressed in the Stereocilia of Outer Hair Cells and Required for Normal Outer Hair Cell Function. J Neurosci 36:9201-16
Lee, Hee Yoon; Raphael, Patrick D; Park, Jesung et al. (2015) Noninvasive in vivo imaging reveals differences between tectorial membrane and basilar membrane traveling waves in the mouse cochlea. Proc Natl Acad Sci U S A 112:3128-33
Song, Yohan; Xia, Anping; Lee, Hee Yoon et al. (2015) Activity-dependent regulation of prestin expression in mouse outer hair cells. J Neurophysiol 113:3531-42