1
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Frost BL, Janjušević NP, Strimbu CE, Hendon CP. Compressed sensing on displacement signals measured with optical coherence tomography. BIOMEDICAL OPTICS EXPRESS 2023; 14:5539-5554. [PMID: 38021133 PMCID: PMC10659783 DOI: 10.1364/boe.503168] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/11/2023] [Revised: 09/21/2023] [Accepted: 09/22/2023] [Indexed: 12/01/2023]
Abstract
Optical coherence tomography (OCT) is capable of angstrom-scale vibrometry of particular interest to researchers of auditory mechanics. We develop a method for compressed sensing vibrometry using OCT that significantly reduces acquisition time for dense motion maps. Our method, based on total generalized variation with uniform subsampling, can reduce the number of samples needed to measure motion maps by a factor of ten with less than 5% normalized mean square error when tested on a diverse set of in vivo measurements from the gerbil cochlea. This opens up the possibility for more complex in vivo experiments for cochlear mechanics.
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Affiliation(s)
- Brian L. Frost
- Department of Electrical Engineering, Columbia University, 500 W. 120th St., Mudd 1310, New York, NY 10027,
USA
| | - Nikola P. Janjušević
- New York University, Tandon School of
Engineering, Electrical and Computer
Engineering, 370 Jay St, Brooklyn, NY 11201, USA
| | - C. Elliott Strimbu
- Columbia
University, Department of Otolaryngology, 630 West 168th
Street, New York, NY 10032, USA
| | - Christine P. Hendon
- Department of Electrical Engineering, Columbia University, 500 W. 120th St., Mudd 1310, New York, NY 10027,
USA
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2
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Oghalai JS. Linear mixed-effect modeling of organ of Corti vibratory tuning curves. Hear Res 2023; 435:108820. [PMID: 37276685 PMCID: PMC10330841 DOI: 10.1016/j.heares.2023.108820] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/29/2023] [Revised: 05/09/2023] [Accepted: 05/30/2023] [Indexed: 06/07/2023]
Abstract
Optical coherence tomography has become the most popular approach to experimental measures of sound-induced vibrations within the mammalian cochlea. Because it is relatively easy to use and works in the unopened cochlea, the measurement of vibratory tuning curves has become highly reliable, and averaging data from multiple animals in different experimental cohorts is now possible. Here I tested a modern statistical approach to compare cohorts for differences in the magnitude and phase of vibration. A linear mixed-effect approach with first, second, third, and fourth-order models to fit the data was tested. The third-order model best fit both the magnitude and phase data without having terms that did not contribute substantively to improving the R2 or the p-value for the independent variables. It identified a difference between cohorts of mice that were different and no difference between cohorts that should not be different. Thus, this approach provides a way to simply compare a full set of tuning curves between cohorts. While further analyses by the investigator will always be needed to study specific details related to the study hypothesis, this statistical technique provides a simple way for the cochlear physiologist to perform an initial assessment of whether the cohorts are same or different.
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Affiliation(s)
- John S Oghalai
- Caruso Department of Otolaryngology - Head and Neck Surgery, University of Southern California.
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3
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Recio-Spinoso A, Dong W, Oghalai JS. On the Tonotopy of the Low-Frequency Region of the Cochlea. J Neurosci 2023; 43:5172-5179. [PMID: 37225436 PMCID: PMC10342220 DOI: 10.1523/jneurosci.0249-23.2023] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2023] [Revised: 04/11/2023] [Accepted: 04/29/2023] [Indexed: 05/26/2023] Open
Abstract
It is generally assumed that frequency selectivity varies along the cochlea. For example, at the base of the cochlea, which is a region sensitive to high-frequency sounds, the best frequency of a cochlear location increases toward the most basal end, that is, near the stapes. Response phases also vary along cochlear locations. At any given frequency, there is a decrease in phase lag toward the stapes. This tonotopic arrangement in the cochlea was originally described by Georg von Békésy in a seminal series of experiments on human cadavers and has been confirmed in more recent works on live laboratory animals. Nonetheless, our knowledge of tonotopy at the apex of the cochlea remains incomplete in animals with low-frequency hearing, which is relevant to human speech. The results of our experiments on guinea pig, gerbil, and chinchilla cochleas, regardless of the sex of the animal, show that responses to sound differ at locations across the apex in a pattern consistent with previous studies of the base of the cochlea.SIGNIFICANCE STATEMENT Tonotopy is an important property of the auditory system that has been shown to exist in many auditory centers. In fact, most auditory implants work on the assumption of its existence by assigning different frequencies to different stimulating electrodes based on their location. At the level of the basilar membrane in the cochlea, a tonotopic arrangement implies that high-frequency stimuli evoke largest displacements at the base, near the ossicles, and low-frequency sounds have their greatest effects at the apex. Although tonotopy has been confirmed at the base of the cochlea on live animals at the apex of the cochlea, however, it has been less studied. Here, we show that a tonotopic arrangement does exist at the apex of the cochlea.
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Affiliation(s)
- Alberto Recio-Spinoso
- Instituto de Investigación en Discapacidades Neurológicas, Universidad de Castilla-La Mancha, 02006 Albacete, Spain
| | - Wei Dong
- Veterans Affairs Loma Linda Healthcare System, Department of Otolaryngology-Head & Neck Surgery, Loma Linda University Health, Loma Linda, California 92374
| | - John S Oghalai
- Caruso Department of Otolaryngology-Head and Neck Surgery, University of Southern California, Los Angeles, Los Angeles, California 90033
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4
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Ashmore JF, Oghalai JS, Dewey JB, Olson ES, Strimbu CE, Wang Y, Shera CA, Altoè A, Abdala C, Elgoyhen AB, Eatock RA, Raphael RM. The Remarkable Outer Hair Cell: Proceedings of a Symposium in Honour of W. E. Brownell. J Assoc Res Otolaryngol 2023; 24:117-127. [PMID: 36648734 PMCID: PMC10121982 DOI: 10.1007/s10162-022-00852-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2021] [Accepted: 05/02/2022] [Indexed: 01/18/2023] Open
Abstract
In 1985, Bill Brownell and colleagues published the remarkable observation that cochlear outer hair cells (OHCs) express voltage-driven mechanical motion: electromotility. They proposed OHC electromotility as the mechanism for the elusive "cochlear amplifier" required to explain the sensitivity of mammalian hearing. The finding and hypothesis stimulated an explosion of experiments that have transformed our understanding of cochlear mechanics and physiology, the evolution of hair cell structure and function, and audiology. Here, we bring together examples of current research that illustrate the continuing impact of the discovery of OHC electromotility.
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Affiliation(s)
| | - John S Oghalai
- Department of Otolaryngology-Head and Neck Surgery, University of Southern California, Los Angeles, USA
| | - James B Dewey
- Department of Otolaryngology-Head and Neck Surgery, University of Southern California, Los Angeles, USA
| | - Elizabeth S Olson
- Department of Otolaryngology Head and Neck Surgery, Vagelos College of Physicians and Surgeons, Columbia University, New York City, USA
| | - Clark E Strimbu
- Department of Otolaryngology Head and Neck Surgery, Vagelos College of Physicians and Surgeons, Columbia University, New York City, USA
| | - Yi Wang
- Department of Otolaryngology Head and Neck Surgery, Vagelos College of Physicians and Surgeons, Columbia University, New York City, USA
| | - Christopher A Shera
- Caruso Department of Otolaryngology and Department of Physics and Astronomy, University of Southern California, Los Angeles, USA
| | - Alessandro Altoè
- Caruso Department of Otolaryngology and Department of Physics and Astronomy, University of Southern California, Los Angeles, USA
| | - Carolina Abdala
- Caruso Department of Otolaryngology, University of Southern California, Los Angeles, USA
| | - Ana B Elgoyhen
- Instituto de Investigaciones en Ingeniería Genética y Biología Molecular "Dr. Héctor N. Torres" (INGEBI), Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Buenos Aires, Argentina
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5
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Charaziak KK, Altoè A. Estimating cochlear impulse responses using frequency sweeps. THE JOURNAL OF THE ACOUSTICAL SOCIETY OF AMERICA 2023; 153:2251. [PMID: 37092917 PMCID: PMC10104686 DOI: 10.1121/10.0017547] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/08/2022] [Revised: 02/10/2023] [Accepted: 02/23/2023] [Indexed: 05/03/2023]
Abstract
Cochlear mechanics tends to be studied using single-location measurements of intracochlear vibrations in response to acoustical stimuli. Such measurements, due to their invasiveness and often the instability of the animal preparation, are difficult to accomplish and, thus, ideally require stimulus paradigms that are time efficient, flexible, and result in high resolution transfer functions. Here, a swept-sine method is adapted for recordings of basilar membrane impulse responses in mice. The frequency of the stimulus was exponentially swept from low to high (upward) or high to low (downward) at varying rates (from slow to fast) and intensities. The cochlear response to the swept-sine was then convolved with the time-reversed stimulus waveform to obtain first and higher order impulse responses. Slow sweeps of either direction produce cochlear first to third order transfer functions equivalent to those measured with pure tones. Fast upward sweeps, on the other hand, generate impulse responses that typically ring longer, as observed in responses obtained using clicks. The ringing of impulse response in mice was of relatively small amplitude and did not affect the magnitude spectra. It is concluded that swept-sine methods offer flexible and time-efficient alternatives to other approaches for recording cochlear impulse responses.
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Affiliation(s)
- Karolina K Charaziak
- Caruso Department of Otolaryngology, Keck School of Medicine, University of Southern California, Los Angeles, California 90033, USA
| | - Alessandro Altoè
- Caruso Department of Otolaryngology, Keck School of Medicine, University of Southern California, Los Angeles, California 90033, USA
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6
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Frost BL, Strimbu CE, Olson ES. Reconstruction of transverse-longitudinal vibrations in the organ of Corti complex via optical coherence tomography. THE JOURNAL OF THE ACOUSTICAL SOCIETY OF AMERICA 2023; 153:1347. [PMID: 36859114 PMCID: PMC9957605 DOI: 10.1121/10.0017345] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/14/2022] [Revised: 01/27/2023] [Accepted: 02/03/2023] [Indexed: 05/06/2023]
Abstract
Optical coherence tomography (OCT) is a common modality for measuring vibrations within the organ of Corti complex (OCC) in vivo. OCT's uniaxial nature leads to limitations that complicate the interpretation of data from cochlear mechanics experiments. The relationship between the optical axis (axis of motion measurement) and anatomically relevant axes in the cochlea varies across experiments, and generally is not known. This leads to characteristically different motion measurements taken from the same structure at different orientations. We present a method that can reconstruct two-dimensional (2-D) motion of intra-OCC structures in the cochlea's longitudinal-transverse plane. The method requires only a single, unmodified OCT system, and does not require any prior knowledge of precise structural locations or measurement angles. It uses the cochlea's traveling wave to register points between measurements taken at multiple viewing angles. We use this method to reconstruct 2-D motion at the outer hair cell/Deiters cell junction in the gerbil base, and show that reconstructed transverse motion resembles directly measured transverse motion, thus validating the method. The technique clarifies the interpretation of OCT measurements, enhancing their utility in probing the micromechanics of the cochlea.
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Affiliation(s)
- Brian L Frost
- Department of Electrical Engineering, Columbia University, 500 West 120th Street, Mudd 1310, New York, New York 10027, USA
| | - Clark Elliott Strimbu
- Department of Otolaryngology Head and Neck Surgery, Vagelos College of Physicians and Surgeons, Columbia University, 630 West 168th Street, New York, New York 10032, USA
| | - Elizabeth S Olson
- Department of Otolaryngology Head and Neck Surgery, Vagelos College of Physicians and Surgeons, Columbia University, 630 West 168th Street, New York, New York 10032, USA
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7
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Kim KS, Koo HY, Bok J. Alternative splicing in shaping the molecular landscape of the cochlea. Front Cell Dev Biol 2023; 11:1143428. [PMID: 36936679 PMCID: PMC10018040 DOI: 10.3389/fcell.2023.1143428] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2023] [Accepted: 02/16/2023] [Indexed: 03/06/2023] Open
Abstract
The cochlea is a complex organ comprising diverse cell types with highly specialized morphology and function. Until now, the molecular underpinnings of its specializations have mostly been studied from a transcriptional perspective, but accumulating evidence points to post-transcriptional regulation as a major source of molecular diversity. Alternative splicing is one of the most prevalent and well-characterized post-transcriptional regulatory mechanisms. Many molecules important for hearing, such as cadherin 23 or harmonin, undergo alternative splicing to produce functionally distinct isoforms. Some isoforms are expressed specifically in the cochlea, while some show differential expression across the various cochlear cell types and anatomical regions. Clinical phenotypes that arise from mutations affecting specific splice variants testify to the functional relevance of these isoforms. All these clues point to an essential role for alternative splicing in shaping the unique molecular landscape of the cochlea. Although the regulatory mechanisms controlling alternative splicing in the cochlea are poorly characterized, there are animal models with defective splicing regulators that demonstrate the importance of RNA-binding proteins in maintaining cochlear function and cell survival. Recent technological breakthroughs offer exciting prospects for overcoming some of the long-standing hurdles that have complicated the analysis of alternative splicing in the cochlea. Efforts toward this end will help clarify how the remarkable diversity of the cochlear transcriptome is both established and maintained.
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Affiliation(s)
- Kwan Soo Kim
- Department of Anatomy, Yonsei University College of Medicine, Seoul, Republic of Korea
- Brain Korea 21 Project for Medical Science, Yonsei University College of Medicine, Seoul, Republic of Korea
| | - Hei Yeun Koo
- Department of Anatomy, Yonsei University College of Medicine, Seoul, Republic of Korea
| | - Jinwoong Bok
- Department of Anatomy, Yonsei University College of Medicine, Seoul, Republic of Korea
- Brain Korea 21 Project for Medical Science, Yonsei University College of Medicine, Seoul, Republic of Korea
- Department of Otorhinolaryngology, Yonsei University College of Medicine, Seoul, Republic of Korea
- *Correspondence: Jinwoong Bok,
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8
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Robillard KN, de Vrieze E, van Wijk E, Lentz JJ. Altering gene expression using antisense oligonucleotide therapy for hearing loss. Hear Res 2022; 426:108523. [PMID: 35649738 DOI: 10.1016/j.heares.2022.108523] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/04/2021] [Revised: 04/20/2022] [Accepted: 05/14/2022] [Indexed: 12/12/2022]
Abstract
Hearing loss affects more than 430 million people, worldwide, and is the third most common chronic physical condition in the United States and Europe (GBD Hearing Loss Collaborators, 2021; NIOSH, 2021; WHO, 2021). The loss of hearing significantly impacts motor and cognitive development, communication, education, employment, and overall quality of life. The inner ear houses the sensory organs for both hearing and balance and provides an accessible target for therapeutic delivery. Antisense oligonucleotides (ASOs) use various mechanisms to manipulate gene expression and can be tailor-made to treat disorders with defined genetic targets. In this review, we discuss the preclinical advancements within the field of the highly promising ASO-based therapies for hereditary hearing loss disorders. Particular focus is on ASO mechanisms of action, preclinical studies on ASO treatments of hearing loss, timing of therapeutic intervention, and delivery routes to the inner ear.
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Affiliation(s)
| | - Erik de Vrieze
- Department of Otorhinolaryngology, RUMC, Geert Grooteplein 10, Route 855, GA, Nijmegen 6525, the Netherlands; Donders Institute for Brain, Cognition, and Behavior, RUMC, Nijmegen, NL
| | - Erwin van Wijk
- Department of Otorhinolaryngology, RUMC, Geert Grooteplein 10, Route 855, GA, Nijmegen 6525, the Netherlands; Donders Institute for Brain, Cognition, and Behavior, RUMC, Nijmegen, NL.
| | - Jennifer J Lentz
- Neuroscience Center of Excellence, LSUHSC, New Orleans, LA, USA; Department of Otorhinolaryngology, LSUHSC, 2020 Gravier Street, Lions Building, Room 795, New Orleans, LA, USA.
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9
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Guinan JJ. Cochlear amplification in the short-wave region by outer hair cells changing organ-of-Corti area to amplify the fluid traveling wave. Hear Res 2022. [DOI: 10.1016/j.heares.2022.108641] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/04/2022]
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10
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The reticular lamina and basilar membrane vibrations in the transverse direction in the basal turn of the living gerbil cochlea. Sci Rep 2022; 12:19810. [PMID: 36396720 PMCID: PMC9671912 DOI: 10.1038/s41598-022-24394-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2022] [Accepted: 11/15/2022] [Indexed: 11/18/2022] Open
Abstract
The prevailing theory of cochlear function states that outer hair cells amplify sound-induced vibration to improve hearing sensitivity and frequency specificity. Recent micromechanical measurements in the basal turn of gerbil cochleae through the round window have demonstrated that the reticular lamina vibration lags the basilar membrane vibration, and it is physiologically vulnerable not only at the best frequency but also at the low frequencies. These results suggest that outer hair cells from a broad cochlear region enhance hearing sensitivity through a global hydromechanical mechanism. However, the time difference between the reticular lamina and basilar membrane vibration has been thought to result from a systematic measurement error caused by the optical axis non-perpendicular to the cochlear partition. To address this concern, we measured the reticular lamina and basilar membrane vibrations in the transverse direction through an opening in the cochlear lateral wall in this study. Present results show that the phase difference between the reticular lamina and basilar membrane vibration decreases with frequency by ~ 180 degrees from low frequencies to the best frequency, consistent with those measured through the round window. Together with the round-window measurement, the low-coherence interferometry through the cochlear lateral wall demonstrates that the time difference between the reticular lamina and basilar membrane vibration results from the cochlear active processing rather than a measurement error.
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11
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Xia A, Udagawa T, Quiñones PM, Atkinson PJ, Applegate BE, Cheng AG, Oghalai JS. The impact of targeted ablation of one row of outer hair cells and Deiters' cells on cochlear amplification. J Neurophysiol 2022; 128:1365-1373. [PMID: 36259670 PMCID: PMC9678430 DOI: 10.1152/jn.00501.2021] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2021] [Revised: 10/13/2022] [Accepted: 10/17/2022] [Indexed: 11/22/2022] Open
Abstract
The mammalian cochlea contains three rows of outer hair cells (OHCs) that amplify the basilar membrane traveling wave with high gain and exquisite tuning. The pattern of OHC loss caused by typical methods of producing hearing loss in animal models (noise, ototoxic exposure, or aging) is variable and not consistent along the length of the cochlea. Thus, it is difficult to use these approaches to understand how forces from multiple OHCs summate to create normal cochlear amplification. Here, we selectively removed the third row of OHCs and Deiters' cells in adult mice and measured cochlear amplification. In the mature cochlear epithelia, expression of the Wnt target gene Lgr5 is restricted to the third row of Deiters' cells, the supporting cells directly underneath the OHCs. Diphtheria toxin administration to Lgr5DTR-EGFP/+ mice selectively ablated the third row of Deiters' cells and the third row of OHCs. Basilar membrane vibration in vivo demonstrated disproportionately lower reduction in cochlear amplification by about 13.5 dB. On a linear scale, this means that the 33% reduction in OHC number led to a 79% reduction in gain. Thus, these experimental data describe the impact of reducing the force of cochlear amplification by a specific amount. Furthermore, these data argue that because OHC forces progressively and sequentially amplify the traveling wave as it travels to its peak, the loss of even a relatively small number of OHCs, when evenly distributed longitudinally, will cause a substantial reduction in cochlear amplification.NEW & NOTEWORTHY Normal cochlear physiology involves force production from three rows of outer hair cells to amplify and tune the traveling wave. Here, we used a genetic approach to target and ablate the third row of outer hair cells in the mouse cochlea and found it reduced cochlear amplification by 79%. This means that the loss of even a relatively small number of OHCs, when evenly distributed, causes a substantial reduction in cochlear amplification.
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Affiliation(s)
- Anping Xia
- Department of Otolaryngology-Head and Neck Surgery, Stanford University School of Medicine, Stanford, California
| | - Tomokatsu Udagawa
- Department of Otolaryngology-Head and Neck Surgery, Stanford University School of Medicine, Stanford, California
- Department of Otorhinolaryngology, The Jikei University School of Medicine, Tokyo, Japan
| | - Patricia M Quiñones
- Caruso Department of Otolaryngology-Head & Neck Surgery, University of Southern California, Los Angeles, California
| | - Patrick J Atkinson
- Department of Otolaryngology-Head and Neck Surgery, Stanford University School of Medicine, Stanford, California
| | - Brian E Applegate
- Caruso Department of Otolaryngology-Head & Neck Surgery, University of Southern California, Los Angeles, California
- Department of Biomedical Engineering, Denney Research Center (DRB) 140, University of Southern California, Los Angeles, California
| | - Alan G Cheng
- Department of Otolaryngology-Head and Neck Surgery, Stanford University School of Medicine, Stanford, California
| | - John S Oghalai
- Caruso Department of Otolaryngology-Head & Neck Surgery, University of Southern California, Los Angeles, California
- Department of Biomedical Engineering, Denney Research Center (DRB) 140, University of Southern California, Los Angeles, California
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12
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Emerging Roles of RNA-Binding Proteins in Inner Ear Hair Cell Development and Regeneration. Int J Mol Sci 2022; 23:ijms232012393. [PMID: 36293251 PMCID: PMC9604452 DOI: 10.3390/ijms232012393] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2022] [Revised: 10/07/2022] [Accepted: 10/14/2022] [Indexed: 11/05/2022] Open
Abstract
RNA-binding proteins (RBPs) regulate gene expression at the post-transcriptional level. They play major roles in the tissue- and stage-specific expression of protein isoforms as well as in the maintenance of protein homeostasis. The inner ear is a bi-functional organ, with the cochlea and the vestibular system required for hearing and for maintaining balance, respectively. It is relatively well documented that transcription factors and signaling pathways are critically involved in the formation of inner ear structures and in the development of hair cells. Accumulating evidence highlights emerging functions of RBPs in the post-transcriptional regulation of inner ear development and hair cell function. Importantly, mutations of splicing factors of the RBP family and defective alternative splicing, which result in inappropriate expression of protein isoforms, lead to deafness in both animal models and humans. Because RBPs are critical regulators of cell proliferation and differentiation, they present the potential to promote hair cell regeneration following noise- or ototoxin-induced damage through mitotic and non-mitotic mechanisms. Therefore, deciphering RBP-regulated events during inner ear development and hair cell regeneration can help define therapeutic strategies for treatment of hearing loss. In this review, we outline our evolving understanding of the implications of RBPs in hair cell formation and hearing disease with the aim of promoting future research in this field.
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13
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Altoè A, Dewey JB, Charaziak KK, Oghalai JS, Shera CA. Overturning the mechanisms of cochlear amplification via area deformations of the organ of Corti. THE JOURNAL OF THE ACOUSTICAL SOCIETY OF AMERICA 2022; 152:2227. [PMID: 36319240 PMCID: PMC9578757 DOI: 10.1121/10.0014794] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/28/2022] [Revised: 08/17/2022] [Accepted: 09/23/2022] [Indexed: 06/16/2023]
Abstract
The mammalian ear embeds a cellular amplifier that boosts sound-induced hydromechanical waves as they propagate along the cochlea. The operation of this amplifier is not fully understood and is difficult to disentangle experimentally. In the prevailing view, cochlear waves are amplified by the piezo-electric action of the outer hair cells (OHCs), whose cycle-by-cycle elongations and contractions inject power into the local motion of the basilar membrane (BM). Concomitant deformations of the opposing (or "top") side of the organ of Corti are assumed to play a minor role and are generally neglected. However, analysis of intracochlear motions obtained using optical coherence tomography calls this prevailing view into question. In particular, the analysis suggests that (i) the net local power transfer from the OHCs to the BM is either negative or highly inefficient; and (ii) vibration of the top side of the organ of Corti plays a primary role in traveling-wave amplification. A phenomenological model derived from these observations manifests realistic cochlear responses and suggests that amplification arises almost entirely from OHC-induced deformations of the top side of the organ of Corti. In effect, the model turns classic assumptions about spatial impedance relations and power-flow direction within the sensory epithelium upside down.
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Affiliation(s)
- Alessandro Altoè
- Caruso Department of Otolaryngology, University of Southern California, Los Angeles, California 90033, USA
| | - James B Dewey
- Caruso Department of Otolaryngology, University of Southern California, Los Angeles, California 90033, USA
| | - Karolina K Charaziak
- Caruso Department of Otolaryngology, University of Southern California, Los Angeles, California 90033, USA
| | - John S Oghalai
- Caruso Department of Otolaryngology, University of Southern California, Los Angeles, California 90033, USA
| | - Christopher A Shera
- Caruso Department of Otolaryngology, University of Southern California, Los Angeles, California 90033, USA
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14
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Quiñones PM, Meenderink SWF, Applegate BE, Oghalai JS. Unloading outer hair cell bundles in vivo does not yield evidence of spontaneous oscillations in the mouse cochlea. Hear Res 2022; 423:108473. [PMID: 35287989 PMCID: PMC9339463 DOI: 10.1016/j.heares.2022.108473] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/01/2021] [Revised: 02/11/2022] [Accepted: 02/28/2022] [Indexed: 12/21/2022]
Abstract
Along with outer hair cell (OHC) somatic electromotility as the actuator of cochlear amplification, active hair bundle motility may be a complementary mechanism in the mammalian auditory system. Here, we searched the mouse cochlea for the presence of spontaneous bundle oscillations that have been observed in non-mammalian ears. In those systems, removal of the overlying membrane is necessary for spontaneous bundle oscillations to manifest. Thus, we used a genetic mouse model with a C1509G (cysteine-to-glycine) point mutation in the Tecta gene where the tectorial (TM) is lifted away from the OHC bundles, allowing us to explore whether unloaded bundles spontaneously oscillate. We used VOCTV in vivo to detect OHC length changes due to electromotility as a proxy for the spontaneous opening and closing of the mechanoelectrical transduction (MET) channels associated with bundle oscillation. In wild type mice with the TM attached to OHC bundles, we did find peaks in vibratory magnitude spectra. Such peaks were not observed in the mutants where the TM is detached from the OHC bundles. Statistical analysis of the time signals indicates that these peaks do not signify active oscillations. Rather, they are filtered responses of the sensitive wild type cochlea to weak background noise. We therefore conclude that, to the limits of our system (∼30 pm), there is no spontaneous mechanical activity that manifests as oscillations in OHC electromotility within the mouse cochlea, arguing that unloaded OHC bundles do not oscillate in vivo. This article is part of the Special Issue Outer hair cell Edited by Joseph Santos-Sacchi and Kumar Navaratnam.
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Affiliation(s)
- Patricia M Quiñones
- Caruso Department of Otolaryngology - Head and Neck Surgery, University of Southern California, Los Angeles, CA, USA
| | | | - Brian E Applegate
- Caruso Department of Otolaryngology - Head and Neck Surgery, University of Southern California, Los Angeles, CA, USA; Department of Biomedical Engineering, University of Southern California, Los Angeles, CA, USA
| | - John S Oghalai
- Caruso Department of Otolaryngology - Head and Neck Surgery, University of Southern California, Los Angeles, CA, USA.
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15
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Cho NH, Wang H, Puria S. Cochlear Fluid Spaces and Structures of the Gerbil High-Frequency Region Measured Using Optical Coherence Tomography (OCT). J Assoc Res Otolaryngol 2022; 23:195-211. [PMID: 35194695 PMCID: PMC8964889 DOI: 10.1007/s10162-022-00836-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2021] [Accepted: 01/04/2022] [Indexed: 10/19/2022] Open
Abstract
Since it has been difficult to directly observe the morphology of the living cochlea, our ability to infer the mechanical functioning of the living ear has been limited. Nearly all our knowledge about cochlear morphology comes from postmortem tissue that was fixed and processed using procedures that possibly distort the structures and fluid spaces of the organ of Corti. In this study, optical coherence tomography was employed to obtain volumetric images of the high-frequency hook region of the gerbil cochlea, as viewed through the round window, with far better resolution capability than had been possible before. The anatomical structures and fluid spaces of the organ of Corti were segmented and quantified in vivo and over a 90-min postmortem period. We find that the arcuate-zone and pectinate-zone widths change very little postmortem. The volume of the scala tympani between the round-window membrane and basilar membrane and the volume of the inner spiral sulcus decrease in the first 60-min postmortem. While textbook drawings of the mammalian organ of Corti and cortilymph prominently depict the tunnel of Corti, the outer tunnel is typically missing. This is likely because textbook drawings are typically made from images obtained by histological methods. Here, we show that the outer tunnel is nearly twice as big as the tunnel of Corti or the space of Nuel. This larger outer tunnel fluid space could have a substantial, little-appreciated effect on cochlear micromechanics. We speculate that the outer tunnel forms a resonant structure that may affect reticular-lamina motion.
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Affiliation(s)
- Nam Hyun Cho
- Department of Otolaryngology-Head and Neck Surgery, Harvard Medical School, Boston, MA, 02114, USA
- Eaton-Peabody Laboratories, Massachusetts Eye and Ear, Boston, MA, 02114, USA
| | - Haobing Wang
- Department of Otolaryngology-Head and Neck Surgery, Harvard Medical School, Boston, MA, 02114, USA
- Eaton-Peabody Laboratories, Massachusetts Eye and Ear, Boston, MA, 02114, USA
| | - Sunil Puria
- Department of Otolaryngology-Head and Neck Surgery, Harvard Medical School, Boston, MA, 02114, USA.
- Eaton-Peabody Laboratories, Massachusetts Eye and Ear, Boston, MA, 02114, USA.
- Speech and Hearing Bioscience and Technology Program, Harvard University, Cambridge, MA, 02138, USA.
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16
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Kim W, Liu D, Kim S, Ratnayake K, Macias-Escriva F, Mattison S, Oghalai JS, Applegate BE. Vector of motion measurements in the living cochlea using a 3D OCT vibrometry system. BIOMEDICAL OPTICS EXPRESS 2022; 13:2542-2553. [PMID: 35519276 PMCID: PMC9045890 DOI: 10.1364/boe.451537] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/16/2021] [Revised: 03/11/2022] [Accepted: 03/11/2022] [Indexed: 05/22/2023]
Abstract
Optical coherence tomography (OCT) has become an important tool for measuring the vibratory response of the living cochlea. It stands alone in its capacity to measure the intricate motion of the hearing organ through the surrounding otic capsule bone. Nevertheless, as an extension of phase-sensitive OCT, it is only capable of measuring motion along the optical axis. Hence, measurements are 1-D. To overcome this limitation and provide a measure of the 3-D vector of motion in the cochlea, we developed an OCT system with three sample arms in a single interferometer. Taking advantage of the long coherence length of our swept laser, we depth (frequency) encode the three channels. An algorithm to depth decode and coregister the three channels is followed by a coordinate transformation that takes the vibrational data from the experimental coordinate system to Cartesian or spherical polar coordinates. The system was validated using a piezo as a known vibrating element that could be positioned at various angles. The angular measurement on the piezo was shown to have an RMSE of ≤ 0.30° (5.2 mrad) with a standard deviation of the amplitude of ≤ 120 pm. Finally, we demonstrate the system for in vivo imaging by measuring the vector of motion over a volume image in the apex of the mouse cochlea.
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Affiliation(s)
- Wihan Kim
- Caruso Department of Otolaryngology - Head and Neck Surgery, University of Southern California, Los Angeles, CA 90033, USA
- Contributed equally
| | - Derek Liu
- Caruso Department of Otolaryngology - Head and Neck Surgery, University of Southern California, Los Angeles, CA 90033, USA
- Contributed equally
| | - Sangmin Kim
- Department of Biomedical Engineering, Texas A&M University, College Station, TX 77843, USA
| | - Kumara Ratnayake
- Caruso Department of Otolaryngology - Head and Neck Surgery, University of Southern California, Los Angeles, CA 90033, USA
| | - Frank Macias-Escriva
- Caruso Department of Otolaryngology - Head and Neck Surgery, University of Southern California, Los Angeles, CA 90033, USA
| | - Scott Mattison
- Department of Biomedical Engineering, Texas A&M University, College Station, TX 77843, USA
- Current address: Department of Engineering and Physics, University of Central Oklahoma, Edmond, OK 73034, USA
| | - John S. Oghalai
- Caruso Department of Otolaryngology - Head and Neck Surgery, University of Southern California, Los Angeles, CA 90033, USA
| | - Brian E. Applegate
- Caruso Department of Otolaryngology - Head and Neck Surgery, University of Southern California, Los Angeles, CA 90033, USA
- Department of Biomedical Engineering, University of Southern California, Los Angeles, CA. 90089, USA
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17
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Frost BL, Strimbu CE, Olson ES. Using volumetric optical coherence tomography to achieve spatially resolved organ of Corti vibration measurements. THE JOURNAL OF THE ACOUSTICAL SOCIETY OF AMERICA 2022; 151:1115. [PMID: 35232061 PMCID: PMC8853734 DOI: 10.1121/10.0009576] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/23/2021] [Revised: 01/03/2022] [Accepted: 01/26/2022] [Indexed: 05/22/2023]
Abstract
Optical coherence tomography (OCT) has become a powerful tool for measuring vibrations within the organ of Corti complex (OCC) in cochlear mechanics experiments. However, the one-dimensional nature of OCT measurements, combined with experimental and anatomical constraints, make these data ambiguous: Both the relative positions of measured structures and their orientation relative to the direction of measured vibrations are not known a priori. We present a method by which these measurement features can be determined via the use of a volumetric OCT scan to determine the relationship between the imaging/measurement axes and the canonical anatomical axes. We provide evidence that the method is functional by replicating previously measured radial vibration patterns of the basilar membrane (BM). We used the method to compare outer hair cell and BM vibration phase in the same anatomical cross section (but different optical cross sections), and found that outer hair cell region vibrations lead those of the BM across the entire measured frequency range. In contrast, a phase lead is only present at low frequencies in measurements taken within a single optical cross section. Relative phase is critical to the workings of the cochlea, and these results emphasize the importance of anatomically oriented measurement and analysis.
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Affiliation(s)
- Brian L Frost
- Department of Electrical Engineering, Columbia University, 500 W. 120th St., Mudd 1310, New York, New York 1002, USA
| | - Clark Elliott Strimbu
- Department of Otolaryngology Head and Neck Surgery, Vagelos College of Physicians and Surgeons, Columbia University, 630 W. 168th St., New York, New York 10032, USA
| | - Elizabeth S Olson
- Department of Otolaryngology Head and Neck Surgery, Vagelos College of Physicians and Surgeons, Columbia University, 630 W. 168th St., New York, New York 10032, USA
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18
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Badash I, Quiñones PM, Oghalai KJ, Wang J, Lui CG, Macias-Escriva F, Applegate BE, Oghalai JS. Endolymphatic Hydrops is a Marker of Synaptopathy Following Traumatic Noise Exposure. Front Cell Dev Biol 2021; 9:747870. [PMID: 34805158 PMCID: PMC8602199 DOI: 10.3389/fcell.2021.747870] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2021] [Accepted: 10/20/2021] [Indexed: 12/28/2022] Open
Abstract
After acoustic trauma, there can be loss of synaptic connections between inner hair cells and auditory neurons in the cochlea, which may lead to hearing abnormalities including speech-in-noise difficulties, tinnitus, and hyperacusis. We have previously studied mice with blast-induced cochlear synaptopathy and found that they also developed a build-up of endolymph, termed endolymphatic hydrops. In this study, we used optical coherence tomography to measure endolymph volume in live CBA/CaJ mice exposed to various noise intensities. We quantified the number of synaptic ribbons and postsynaptic densities under the inner hair cells 1 week after noise exposure to determine if they correlated with acute changes in endolymph volume measured in the hours after the noise exposure. After 2 h of noise at an intensity of 95 dB SPL or below, both endolymph volume and synaptic counts remained normal. After exposure to 2 h of 100 dB SPL noise, mice developed endolymphatic hydrops and had reduced synaptic counts in the basal and middle regions of the cochlea. Furthermore, round-window application of hypertonic saline reduced the degree of endolymphatic hydrops that developed after 100 dB SPL noise exposure and partially prevented the reduction in synaptic counts in the cochlear base. Taken together, these results indicate that endolymphatic hydrops correlates with noise-induced cochlear synaptopathy, suggesting that these two pathologic findings have a common mechanistic basis.
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Affiliation(s)
- Ido Badash
- Caruso Department of Otolaryngology-Head and Neck Surgery, Keck School of Medicine of the University of Southern California, Los Angeles, CA, United States
| | - Patricia M Quiñones
- Caruso Department of Otolaryngology-Head and Neck Surgery, Keck School of Medicine of the University of Southern California, Los Angeles, CA, United States
| | - Kevin J Oghalai
- Viterbi School of Engineering, University of Southern California, Los Angeles, CA, United States
| | - Juemei Wang
- Caruso Department of Otolaryngology-Head and Neck Surgery, Keck School of Medicine of the University of Southern California, Los Angeles, CA, United States
| | - Christopher G Lui
- Department of Otolaryngology-Head and Neck Surgery, Northwestern University Feinberg School of Medicine, Chicago, IL, United States
| | - Frank Macias-Escriva
- Caruso Department of Otolaryngology-Head and Neck Surgery, Keck School of Medicine of the University of Southern California, Los Angeles, CA, United States
| | - Brian E Applegate
- Caruso Department of Otolaryngology-Head and Neck Surgery, Keck School of Medicine of the University of Southern California, Los Angeles, CA, United States.,Viterbi School of Engineering, University of Southern California, Los Angeles, CA, United States
| | - John S Oghalai
- Caruso Department of Otolaryngology-Head and Neck Surgery, Keck School of Medicine of the University of Southern California, Los Angeles, CA, United States.,Viterbi School of Engineering, University of Southern California, Los Angeles, CA, United States
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19
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Cochlear outer hair cell electromotility enhances organ of Corti motion on a cycle-by-cycle basis at high frequencies in vivo. Proc Natl Acad Sci U S A 2021; 118:2025206118. [PMID: 34686590 DOI: 10.1073/pnas.2025206118] [Citation(s) in RCA: 35] [Impact Index Per Article: 11.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 09/07/2021] [Indexed: 11/18/2022] Open
Abstract
Mammalian hearing depends on an amplification process involving prestin, a voltage-sensitive motor protein that enables cochlear outer hair cells (OHCs) to change length and generate force. However, it has been questioned whether this prestin-based somatic electromotility can operate fast enough in vivo to amplify cochlear vibrations at the high frequencies that mammals hear. In this study, we measured sound-evoked vibrations from within the living mouse cochlea and found that the top and bottom of the OHCs move in opposite directions at frequencies exceeding 20 kHz, consistent with fast somatic length changes. These motions are physiologically vulnerable, depend on prestin, and dominate the cochlea's vibratory response to high-frequency sound. This dominance was observed despite mechanisms that clearly low-pass filter the in vivo electromotile response. Low-pass filtering therefore does not critically limit the OHC's ability to move the organ of Corti on a cycle-by-cycle basis. Our data argue that electromotility serves as the primary high-frequency amplifying mechanism within the mammalian cochlea.
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20
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Murakami Y. Fast time-domain solution of a nonlinear three-dimensional cochlear model using the fast Fourier transform. THE JOURNAL OF THE ACOUSTICAL SOCIETY OF AMERICA 2021; 150:2589. [PMID: 34717501 DOI: 10.1121/10.0006533] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/07/2021] [Accepted: 09/13/2021] [Indexed: 06/13/2023]
Abstract
A fast numerical time-domain solution of a nonlinear three-dimensional (3D) cochlear model is proposed. In dynamical systems, a time-domain solution can determine nonlinear responses, and the human faculty of hearing depends on nonlinear behaviors of the microscopically structured organs of the cochlea. Thus, time-domain 3D modeling can help explain hearing. The matrix product, an n2 operation, is a central part of the time-domain solution procedure in cochlear models. To solve the cochlear model faster, the fast Fourier transform (FFT), an n log n operation, is used to replace the matrix product. Numerical simulation results verified the similarity of the matrix product and the FFT under coarse grid settings. Furthermore, applying the FFT reduced the computation time by a factor of up to 100 owing to the computational complexity of the proposed approach being reduced from n2 to n log n. Additionally, the proposed method successfully computed 3D models under moderate and fine grid settings that were unsolvable using the matrix product. The 3D cochlear model exhibited nonlinear responses for pure tones and clicks under various gain distributions in a time-domain simulation. Thus, the FFT-based method provides fast numerical solutions and supports the development of 3D models for cochlear mechanics.
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Affiliation(s)
- Yasuki Murakami
- Faculty of Design, Kyushu University, 4-9-1 Shiobaru, Minamiku, Fukuoka 815-8540, Japan
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21
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Tuned vibration modes in a miniature hearing organ: Insights from the bushcricket. Proc Natl Acad Sci U S A 2021; 118:2105234118. [PMID: 34551976 PMCID: PMC8488673 DOI: 10.1073/pnas.2105234118] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 08/17/2021] [Indexed: 12/04/2022] Open
Abstract
Most hearing organs contain an array of sensory cells that act as miniature microphones, each tuned to its own frequency like piano strings. Acoustically communicating insects like bushcrickets have evolved miniscule hearing organs, typically smaller than 1 mm, in their forelegs. It is still unknown how the sensory structures inside the leg vibrate in response to sound. Using advanced imaging techniques, we meticulously mapped the nanovibrations in the bushcricket ear. We discovered a complex motion pattern in which structures separated by only 1/50 mm showed systematic tuning differences. Despite the insect ear’s tiny dimensions, its mode of operation strikingly resembled that of vertebrate ears. Apparently, evolution has provided similar solutions to the spectral processing of sounds. Bushcrickets (katydids) rely on only 20 to 120 sensory units located in their forelegs to sense sound. Situated in tiny hearing organs less than 1 mm long (40× shorter than the human cochlea), they cover a wide frequency range from 1 kHz up to ultrasounds, in tonotopic order. The underlying mechanisms of this miniaturized frequency-place map are unknown. Sensory dendrites in the hearing organ (crista acustica [CA]) are hypothesized to stretch, thereby driving mechanostransduction and frequency tuning. However, this has not been experimentally confirmed. Using optical coherence tomography (OCT) vibrometry, we measured the relative motion of structures within and adjacent to the CA of the bushcricket Mecopoda elongata. We found different modes of nanovibration in the CA that have not been previously described. The two tympana and the adjacent septum of the foreleg that enclose the CA were recorded simultaneously, revealing an antiphasic lever motion strikingly reminiscent of vertebrate middle ears. Over the entire length of the CA, we were able to separate and compare vibrations of the top (cap cells) and base (dorsal wall) of the sensory tissue. The tuning of these two structures, only 15 to 60 μm (micrometer) apart, differed systematically in sharpness and best frequency, revealing a tuned periodic deformation of the CA. The relative motion of the two structures, a potential drive of transduction, demonstrated sharper tuning than either of them. The micromechanical complexity indicates that the bushcricket ear invokes multiple degrees of freedom to achieve frequency separation with a limited number of sensory cells.
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22
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Choi S, Ota T, Nin F, Shioda T, Suzuki T, Hibino H. Rapid optical tomographic vibrometry using a swept multi-gigahertz comb. OPTICS EXPRESS 2021; 29:16749-16768. [PMID: 34154231 DOI: 10.1364/oe.425972] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/25/2021] [Accepted: 05/10/2021] [Indexed: 06/13/2023]
Abstract
We propose a rapid tomographic vibrometer technique using an optical comb to measure internal vibrations, transient phenomena, and tomographic distributions in biological tissue and microelectromechanical system devices at high frequencies. This method allows phase-sensitive tomographic measurement in the depth direction at a multi-MHz scan rate using a frequency-modulated broadband electrooptic multi-GHz supercontinuum comb. The frequency spacing was swept instantaneously in time and axisymmetrically about the center wavelength via a dual-drive Mach-Zehnder modulator driven by a variable radio frequency signal. This unique sweeping method permits direct measurement of fringe-free interferometric amplitude and phase with arbitrarily changeable measurement range and scan rate. Therefore, a compressive measurement can be made in only the depth region where the vibration exists, reducing the number of measurement points. In a proof-of-principle experiment, the interferometric amplitude and phase were investigated for in-phase and quadrature phase-shifted interferograms obtained by a polarization demodulator. Tomographic transient displacement measurements were performed using a 0.12 mm thick glass film and piezo-electric transducer oscillating at 10-100 kHz with scan rates in the range 1-20 MHz. The depth resolution and precision of the vibrometer were estimated to be approximately 25 µm and 1.0 nm, respectively.
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23
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Chen T, Rohacek AM, Caporizzo M, Nankali A, Smits JJ, Oostrik J, Lanting CP, Kücük E, Gilissen C, van de Kamp JM, Pennings RJE, Rakowiecki SM, Kaestner KH, Ohlemiller KK, Oghalai JS, Kremer H, Prosser BL, Epstein DJ. Cochlear supporting cells require GAS2 for cytoskeletal architecture and hearing. Dev Cell 2021; 56:1526-1540.e7. [PMID: 33964205 PMCID: PMC8137675 DOI: 10.1016/j.devcel.2021.04.017] [Citation(s) in RCA: 15] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2020] [Revised: 02/01/2021] [Accepted: 04/16/2021] [Indexed: 11/16/2022]
Abstract
In mammals, sound is detected by mechanosensory hair cells that are activated in response to vibrations at frequency-dependent positions along the cochlear duct. We demonstrate that inner ear supporting cells provide a structural framework for transmitting sound energy through the cochlear partition. Humans and mice with mutations in GAS2, encoding a cytoskeletal regulatory protein, exhibit hearing loss due to disorganization and destabilization of microtubule bundles in pillar and Deiters' cells, two types of inner ear supporting cells with unique cytoskeletal specializations. Failure to maintain microtubule bundle integrity reduced supporting cell stiffness, which in turn altered cochlear micromechanics in Gas2 mutants. Vibratory responses to sound were measured in cochleae from live mice, revealing defects in the propagation and amplification of the traveling wave in Gas2 mutants. We propose that the microtubule bundling activity of GAS2 imparts supporting cells with mechanical properties for transmitting sound energy through the cochlea.
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Affiliation(s)
- Tingfang Chen
- Department of Genetics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA
| | - Alex M Rohacek
- Department of Genetics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA
| | - Matthew Caporizzo
- Department of Physiology, Pennsylvania Muscle Institute, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA
| | - Amir Nankali
- The Caruso Department of Otolaryngology-Head and Neck Surgery, University of Southern California, Los Angeles, CA, USA
| | - Jeroen J Smits
- Department of Otorhinolaryngology, Radboud University Medical Center, Nijmegen, the Netherlands
| | - Jaap Oostrik
- Department of Otorhinolaryngology, Radboud University Medical Center, Nijmegen, the Netherlands
| | - Cornelis P Lanting
- Department of Otorhinolaryngology, Radboud University Medical Center, Nijmegen, the Netherlands
| | - Erdi Kücük
- Department of Human Genetics, Radboud University Medical Center, Nijmegen, the Netherlands
| | - Christian Gilissen
- Department of Human Genetics, Radboud University Medical Center, Nijmegen, the Netherlands
| | - Jiddeke M van de Kamp
- Department of Clinical Genetics, Amsterdam UMC, Vrije Universiteit Amsterdam, Amsterdam, the Netherlands
| | - Ronald J E Pennings
- Department of Otorhinolaryngology, Radboud University Medical Center, Nijmegen, the Netherlands
| | - Staci M Rakowiecki
- Department of Genetics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA
| | - Klaus H Kaestner
- Department of Genetics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA
| | - Kevin K Ohlemiller
- Department of Otolaryngology-Head and Neck Surgery, Washington University School of Medicine, St. Louis, MO, USA
| | - John S Oghalai
- The Caruso Department of Otolaryngology-Head and Neck Surgery, University of Southern California, Los Angeles, CA, USA
| | - Hannie Kremer
- Department of Otorhinolaryngology, Radboud University Medical Center, Nijmegen, the Netherlands; Department of Human Genetics, Radboud University Medical Center, Nijmegen, the Netherlands
| | - Benjamin L Prosser
- Department of Physiology, Pennsylvania Muscle Institute, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA
| | - Douglas J Epstein
- Department of Genetics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA.
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24
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Wang Z, Ma Q, Lu J, Cui X, Chen H, Wu H, Huang Z. Functional Parameters of Prestin Are Not Correlated With the Best Hearing Frequency. Front Cell Dev Biol 2021; 9:638530. [PMID: 34046403 PMCID: PMC8144510 DOI: 10.3389/fcell.2021.638530] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2020] [Accepted: 03/23/2021] [Indexed: 11/29/2022] Open
Abstract
Among the vertebrate lineages with different hearing frequency ranges, humans lie between the low-frequency hearing (1 kHz) of fish and amphibians and the high-frequency hearing (100 kHz) of bats and dolphins. Little is known about the mechanism underlying such a striking difference in the limits of hearing frequency. Prestin, responsible for cochlear amplification and frequency selectivity in mammals, seems to be the only candidate to date. Mammalian prestin is densely expressed in the lateral plasma membrane of the outer hair cells (OHCs) and functions as a voltage-dependent motor protein. To explore the molecular basis for the contribution of prestin in hearing frequency detection, we collected audiogram data from humans, dogs, gerbils, bats, and dolphins because their average hearing frequency rises in steps. We generated stable cell lines transfected with human, dog, gerbil, bat, and dolphin prestins (hPres, dPres, gPres, bPres, and nPres, respectively). The non-linear capacitance (NLC) of different prestins was measured using a whole-cell patch clamp. We found that the Qmax/Clin of bPres and nPres was significantly higher than that of humans. The V1/2 of hPres was more hyperpolarized than that of nPres. The z values of hPres and bPres were higher than that of nPres. We further analyzed the relationship between the high-frequency hearing limit (Fmax) and the functional parameters (V1/2, z, and Qmax/Clin) of NLC among five prestins. Interestingly, no significant correlation was found between the functional parameters and Fmax. Additionally, a comparative study showed that the amino acid sequences and tertiary structures of five prestins were quite similar. There might be a common fundamental mechanism driving the function of prestins. These findings call for a reconsideration of the leading role of prestin in hearing frequency perception. Other intriguing kinetics underlying the hearing frequency response of auditory organs might exist.
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Affiliation(s)
- Zhongying Wang
- Department of Otolaryngology-Head and Neck Surgery, Shanghai Ninth People's Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, China.,Ear Institute, Shanghai Jiao Tong University School of Medicine, Shanghai, China.,Shanghai Key Laboratory of Translational Medicine on Ear and Nose Diseases, Shanghai, China
| | - Qingping Ma
- Department of Otolaryngology-Head and Neck Surgery, Shanghai Ninth People's Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, China.,Ear Institute, Shanghai Jiao Tong University School of Medicine, Shanghai, China.,Shanghai Key Laboratory of Translational Medicine on Ear and Nose Diseases, Shanghai, China
| | - Jiawen Lu
- Department of Otolaryngology-Head and Neck Surgery, Shanghai Ninth People's Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, China.,Ear Institute, Shanghai Jiao Tong University School of Medicine, Shanghai, China.,Shanghai Key Laboratory of Translational Medicine on Ear and Nose Diseases, Shanghai, China
| | - Xiaochen Cui
- State Key Laboratory of Microbial Metabolism, Joint International Research Laboratory of Metabolic and Developmental Sciences, Department of Bioinformatics and Biostatistics, National Experimental Teaching Center for Life Sciences and Biotechnology, School of Life Sciences and Biotechnology, Shanghai Jiao Tong University, Shanghai, China
| | - Haifeng Chen
- State Key Laboratory of Microbial Metabolism, Joint International Research Laboratory of Metabolic and Developmental Sciences, Department of Bioinformatics and Biostatistics, National Experimental Teaching Center for Life Sciences and Biotechnology, School of Life Sciences and Biotechnology, Shanghai Jiao Tong University, Shanghai, China.,Shanghai Center for Bioinformation Technology, Shanghai, China
| | - Hao Wu
- Department of Otolaryngology-Head and Neck Surgery, Shanghai Ninth People's Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, China.,Ear Institute, Shanghai Jiao Tong University School of Medicine, Shanghai, China.,Shanghai Key Laboratory of Translational Medicine on Ear and Nose Diseases, Shanghai, China
| | - Zhiwu Huang
- Department of Otolaryngology-Head and Neck Surgery, Shanghai Ninth People's Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, China.,Ear Institute, Shanghai Jiao Tong University School of Medicine, Shanghai, China.,Shanghai Key Laboratory of Translational Medicine on Ear and Nose Diseases, Shanghai, China
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25
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Iwasa KH. Kinetic Membrane Model of Outer Hair Cells. Biophys J 2020; 120:122-132. [PMID: 33248133 PMCID: PMC7820742 DOI: 10.1016/j.bpj.2020.11.017] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2020] [Revised: 10/12/2020] [Accepted: 11/17/2020] [Indexed: 12/02/2022] Open
Abstract
The effectiveness of outer hair cells (OHCs) in amplifying the motion of the organ of Corti, and thereby contributing to the sensitivity of mammalian hearing, depends on the mechanical power output of these cells. Electromechanical coupling in OHCs, which enables these cells to convert electrical energy into mechanical energy, has been analyzed in detail using isolated cells using primarily static membrane models. The mechanical output of OHCs was previously evaluated by developing a kinetic theory based on a simplified one-dimensional model for OHCs. Here, a kinetic description of OHCs is extended by using the membrane model, which was used for analyzing in vitro experiments. This theory predicts, for systems without inertial load, that elastic load enhances positive shift of voltage dependence of the membrane capacitance because of turgor pressure. The effect of turgor pressure increases with increasing elastic load. For systems with inertia, the magnitude of mechanical power output could be ∼5% higher than the value predicted by the one-dimensional model at the optimal turgor pressure.
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Affiliation(s)
- Kuni H Iwasa
- National Institutes of Health, NIDCD, Bethesda, Maryland.
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26
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The Notch Ligand Jagged1 Is Required for the Formation, Maintenance, and Survival of Hensen's Cells in the Mouse Cochlea. J Neurosci 2020; 40:9401-9413. [PMID: 33127852 DOI: 10.1523/jneurosci.1192-20.2020] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2020] [Revised: 10/16/2020] [Accepted: 10/23/2020] [Indexed: 01/09/2023] Open
Abstract
During cochlear development, the Notch ligand JAGGED 1 (JAG1) plays an important role in the specification of the prosensory region, which gives rise to sound-sensing hair cells and neighboring supporting cells (SCs). While JAG1's expression is maintained in SCs through adulthood, the function of JAG1 in SC development is unknown. Here, we demonstrate that JAG1 is essential for the formation and maintenance of Hensen's cells, a highly specialized SC subtype located at the edge of the auditory epithelium. Using Sox2 CreERT2/+::Jag1loxP/loxP mice of both genders, we show that Jag1 deletion at the onset of differentiation, at embryonic day 14.5, disrupted Hensen's cell formation. Similar loss of Hensen's cells was observed when Jag1 was deleted after Hensen's cell formation at postnatal day (P) 0/P1 and fate-mapping analysis revealed that in the absence of Jag1, some Hensen's cells die, but others convert into neighboring Claudius cells. In support of a role for JAG1 in cell survival, genes involved in mitochondrial function and protein synthesis were downregulated in the sensory epithelium of P0 cochlea lacking Jag1 Finally, using Fgfr3-iCreERT2 ::Jag1loxP/loxP mice to delete Jag1 at P0, we observed a similar loss of Hensen's cells and found that adult Jag1 mutant mice have hearing deficits at the low-frequency range.SIGNIFICANCE STATEMENT Hensen's cells play an essential role in the development and homeostasis of the cochlea. Defects in the biophysical or functional properties of Hensen's cells have been linked to auditory dysfunction and hearing loss. Despite their importance, surprisingly little is known about the molecular mechanisms that guide their development. Morphologic and fate-mapping analyses in our study revealed that, in the absence of the Notch ligand JAGGED1, Hensen's cells died or converted into Claudius cells, which are specialized epithelium-like cells outside the sensory epithelium. Confirming a link between JAGGED1 and cell survival, transcriptional profiling showed that JAGGED1 maintains genes critical for mitochondrial function and tissue homeostasis. Finally, auditory phenotyping revealed that JAGGED1's function in supporting cells is necessary for low-frequency hearing.
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Olson ES, Strimbu CE. Cochlear mechanics: new insights from vibrometry and Optical Coherence Tomography. CURRENT OPINION IN PHYSIOLOGY 2020; 18:56-62. [PMID: 33103018 DOI: 10.1016/j.cophys.2020.08.022] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
Abstract
The cochlea is a complex biological machine that transduces sound-induced mechanical vibrations to neural signals. Hair cells within the sensory tissue of the cochlea transduce vibrations into electrical signals, and exert electromechanical feedback that enhances the passive frequency separation provided by the cochlea's traveling wave mechanics; this enhancement is termed cochlear amplification. The vibration of the sensory tissue has been studied with many techniques, and the current state of the art is optical coherence tomography (OCT). The OCT technique allows for motion of intra-organ structures to be measured in vivo at many layers within the sensory tissue, at several angles and in previously under-explored species. OCT-based observations are already impacting our understanding of hair cell excitation and cochlear amplification.
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Affiliation(s)
- Elizabeth S Olson
- Department of Otolaryngolgy Head and Neck Surgery, Vagelos College of Physicians and Surgeons, Columbia University, 630 W 168th St, New York, NY 10032.,Department Biomedical Engineering, Columbia University, 351 Engineering Terrace, 1210 Amsterdam Avenue,New York, NY 10027
| | - C Elliott Strimbu
- Department of Otolaryngolgy Head and Neck Surgery, Vagelos College of Physicians and Surgeons, Columbia University, 630 W 168th St, New York, NY 10032
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Guinan JJ. The interplay of organ-of-Corti vibrational modes, not tectorial- membrane resonance, sets outer-hair-cell stereocilia phase to produce cochlear amplification. Hear Res 2020; 395:108040. [PMID: 32784038 PMCID: PMC7502208 DOI: 10.1016/j.heares.2020.108040] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/08/2020] [Revised: 07/06/2020] [Accepted: 07/08/2020] [Indexed: 01/27/2023]
Abstract
The mechanical motions that deflect outer-hair-cell (OHC) stereocilia and the resulting effects of OHC motility are reviewed, concentrating on high-frequency cochlear regions. It has been proposed that a tectorial-membrane (TM) resonance makes the phase of OHC stereocilia motion be appropriate to produce cochlear amplification, i.e. so that the OHC force that pushes the basilar membrane (BM) is in the same direction as BM velocity. Evidence for and against the TM-resonance hypothesis are considered, including new cochlear-motion measurements using optical coherence tomography, and it is concluded that there is no such TM resonance. The evidence points to there being an advance in the phase of reticular lamina (RL) radial motion at a frequency approximately ½ octave below the BM characteristic frequency, and that this is the main source of the phase difference between the TM and RL radial motions that produces cochlear amplification. It appears that the change in phase of RL radial motion comes about because of a transition between different organ-of-Corti (OoC) vibrational modes that changes RL motion relative to BM and TM motion. The origins and consequences of the large phase change of RL radial motion relative to BM motion are considered; differences in the reported patterns of these changes may be due to different viewing angles. Detailed motion data and new models are needed to better specify the vibrational patterns of the OoC modes and the role of the various OoC structures in producing the modes and the mode transition.
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Affiliation(s)
- John J Guinan
- Eaton-Peabody Lab, Mass. Eye and Ear, 243 Charles St, Boston, MA, 02114, USA; Harvard Medical School, Dept. of Otolaryngology, Boston, MA, USA.
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Optical coherence tomography: current and future clinical applications in otology. Curr Opin Otolaryngol Head Neck Surg 2020; 28:296-301. [PMID: 32833887 DOI: 10.1097/moo.0000000000000654] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
PURPOSE OF REVIEW This article reviews literature on the use of optical coherence tomography (OCT) in otology and provides the reader with a timely update on its current clinical and research applications. The discussion focuses on the principles of OCT, the use of the technology for the diagnosis of middle ear disease and for the delineation of in-vivo cochlear microarchitecture and function. RECENT FINDINGS Recent advances in OCT include the measurement of structural and vibratory properties of the tympanic membrane, ossicles and inner ear in healthy and diseased states. Accurate, noninvasive diagnosis of middle ear disease, such as otosclerosis and acute otitis media using OCT, has been validated in clinical studies, whereas inner ear OCT imaging remains at the preclinical stage. The development of recent microscopic, otoscopic and endoscopic systems to address clinical and research problems is reviewed. SUMMARY OCT is a real-time, noninvasive, nonionizing, point-of-care imaging modality capable of imaging ear structures in vivo. Although current clinical systems are mainly focused on middle ear imaging, OCT has also been shown to have the ability to identify inner ear disease, an exciting possibility that will become increasingly relevant with the advent of targeted inner ear therapies.
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Perez-Flores MC, Lee JH, Park S, Zhang XD, Sihn CR, Ledford HA, Wang W, Kim HJ, Timofeyev V, Yarov-Yarovoy V, Chiamvimonvat N, Rabbitt RD, Yamoah EN. Cooperativity of K v7.4 channels confers ultrafast electromechanical sensitivity and emergent properties in cochlear outer hair cells. SCIENCE ADVANCES 2020; 6:eaba1104. [PMID: 32285007 PMCID: PMC7141818 DOI: 10.1126/sciadv.aba1104] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/05/2019] [Accepted: 01/14/2020] [Indexed: 05/22/2023]
Abstract
The mammalian cochlea relies on active electromotility of outer hair cells (OHCs) to resolve sound frequencies. OHCs use ionic channels and somatic electromotility to achieve the process. It is unclear, though, how the kinetics of voltage-gated ionic channels operate to overcome extrinsic viscous drag on OHCs at high frequency. Here, we report ultrafast electromechanical gating of clustered Kv7.4 in OHCs. Increases in kinetics and sensitivity resulting from cooperativity among clustered-Kv7.4 were revealed, using optogenetics strategies. Upon clustering, the half-activation voltage shifted negative, and the speed of activation increased relative to solitary channels. Clustering also rendered Kv7.4 channels mechanically sensitive, confirmed in consolidated Kv7.4 channels at the base of OHCs. Kv7.4 clusters provide OHCs with ultrafast electromechanical channel gating, varying in magnitude and speed along the cochlea axis. Ultrafast Kv7.4 gating provides OHCs with a feedback mechanism that enables the cochlea to overcome viscous drag and resolve sounds at auditory frequencies.
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Affiliation(s)
- Maria C. Perez-Flores
- Department of Physiology, School of Medicine, University of Nevada, Reno, Reno, NV 89557, USA
| | - Jeong H. Lee
- Department of Physiology, School of Medicine, University of Nevada, Reno, Reno, NV 89557, USA
| | - Seojin Park
- Department of Physiology, School of Medicine, University of Nevada, Reno, Reno, NV 89557, USA
| | - Xiao-Dong Zhang
- Department of Internal Medicine, Division of Cardiology, University of California, Davis, Davis, CA 95616, USA
- Department of Veterans Affairs, Northern California Health Care System, Mather, CA 95655, USA
| | - Choong-Ryoul Sihn
- Department of Physiology, School of Medicine, University of Nevada, Reno, Reno, NV 89557, USA
| | - Hannah A. Ledford
- Department of Internal Medicine, Division of Cardiology, University of California, Davis, Davis, CA 95616, USA
| | - Wenying Wang
- Department of Physiology, School of Medicine, University of Nevada, Reno, Reno, NV 89557, USA
| | - Hyo Jeong Kim
- Department of Physiology, School of Medicine, University of Nevada, Reno, Reno, NV 89557, USA
| | - Valeriy Timofeyev
- Department of Internal Medicine, Division of Cardiology, University of California, Davis, Davis, CA 95616, USA
- Department of Veterans Affairs, Northern California Health Care System, Mather, CA 95655, USA
| | - Vladimir Yarov-Yarovoy
- Department of Physiology and Membrane Biology, University of California, Davis, Davis, CA 95616, USA
| | - Nipavan Chiamvimonvat
- Department of Internal Medicine, Division of Cardiology, University of California, Davis, Davis, CA 95616, USA
- Department of Veterans Affairs, Northern California Health Care System, Mather, CA 95655, USA
| | - Richard D. Rabbitt
- Departments of Biomedical Engineering, Otolaryngology, and Neuroscience Program, University of Utah, Salt Lake City, UT 84112, USA
- Corresponding author. (E.N.Y.); (R.D.R.)
| | - Ebenezer N. Yamoah
- Department of Physiology, School of Medicine, University of Nevada, Reno, Reno, NV 89557, USA
- Corresponding author. (E.N.Y.); (R.D.R.)
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Goodman SS, Lee C, Guinan JJ, Lichtenhan JT. The Spatial Origins of Cochlear Amplification Assessed by Stimulus-Frequency Otoacoustic Emissions. Biophys J 2020; 118:1183-1195. [PMID: 31968228 DOI: 10.1016/j.bpj.2019.12.031] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2019] [Revised: 12/04/2019] [Accepted: 12/27/2019] [Indexed: 10/25/2022] Open
Abstract
Cochlear amplification of basilar membrane traveling waves is thought to occur between a tone's characteristic frequency (CF) place and within one octave basal of the CF. Evidence for this view comes only from the cochlear base. Stimulus-frequency otoacoustic emissions (SFOAEs) provide a noninvasive alternative to direct measurements of cochlear motion that can be measured across a wide range of CF regions. Coherent reflection theory indicates that SFOAEs arise mostly from the peak region of the traveling wave, but several studies using far-basal suppressor tones claimed that SFOAE components originate many octaves basal of CF. We measured SFOAEs while perfusing guinea pig cochleas from apex to base with salicylate or KCl solutions that reduced outer-hair-cell function and SFOAE amplification. Solution effects on inner hair cells reduced auditory nerve compound action potentials (CAPs) and provided reference times for when solutions reached the SFOAE-frequency CF region. As solution flowed from apex to base, SFOAE reductions generally occurred later than CAP reductions and showed that the effects of cochlear amplification usually peaked ∼1/2 octave basal of the CF region. For tones ≥2 kHz, cochlear amplification typically extended ∼1.5 octaves basal of CF, and the data are consistent with coherent reflection theory. SFOAE amplification did not extend to the basal end of the cochlea, even though reticular lamina motion is amplified in this region, which indicates that reticular lamina motion is not directly coupled to basilar membrane traveling waves. Previous reports of SFOAE-frequency residuals produced by suppressor frequencies far above the SFOAE frequency are most likely due to additional sources created by the suppressor. For some tones <2 kHz, SFOAE amplification extended two octaves apical of CF, which highlights that different vibratory motions produce SFOAEs and CAPs, and that the amplification region depends on the cochlear mode of motion considered. The concept that there is a single "cochlear amplification region" needs to be revised.
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Affiliation(s)
- Shawn S Goodman
- Communication Sciences and Disorders, University of Iowa, Iowa City, Iowa
| | - Choongheon Lee
- Department of Otolaryngology, Washington University School of Medicine in St. Louis, St. Louis, Missouri
| | - John J Guinan
- Department of Otolaryngology, Harvard Medical School, Boston, Massachusetts; Eaton-Peabody Laboratories, Massachusetts Eye and Ear, Boston, Massachusetts
| | - Jeffery T Lichtenhan
- Department of Otolaryngology, Washington University School of Medicine in St. Louis, St. Louis, Missouri.
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Choi S, Nin F, Ota T, Sato K, Muramatsu S, Hibino H. In vivo tomographic visualization of intracochlear vibration using a supercontinuum multifrequency-swept optical coherence microscope. BIOMEDICAL OPTICS EXPRESS 2019; 10:3317-3342. [PMID: 31467780 PMCID: PMC6706039 DOI: 10.1364/boe.10.003317] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/23/2019] [Revised: 06/05/2019] [Accepted: 06/07/2019] [Indexed: 06/10/2023]
Abstract
This study combined a previously developed optical system with two additional key elements: a supercontinuum light source characterized by high output power and an analytical technique that effectively extracts interference signals required for improving the detection limit of vibration amplitude. Our system visualized 3D tomographic images and nanometer scale vibrations in the cochlear sensory epithelium of a live guinea pig. The transverse- and axial-depth resolution was 3.6 and 2.7 µm, respectively. After exposure to acoustic stimuli of 21-25 kHz at a sound pressure level of 70-85 dB, spatial amplitude and phase distributions were quantified on a targeted surface, whose area was 522 × 522 μm2.
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Affiliation(s)
- Samuel Choi
- Niigata University, Department of Electrical and Electronics Engineering, 8050 Ikarashi-2, Niigata 950-2181, Japan
- AMED-CREST, AMED, Japan
| | - Fumiaki Nin
- AMED-CREST, AMED, Japan
- Niigata University, School of Medicine, Department of Molecular Physiology, 757 Ichibancho, Asahimachi, Niigata 951-8510, Japan
- Niigata University, Center for Transdisciplinary Research, 8050 Ikarashi-2, Niigata 950-2181, Japan
| | - Takeru Ota
- AMED-CREST, AMED, Japan
- Niigata University, School of Medicine, Department of Molecular Physiology, 757 Ichibancho, Asahimachi, Niigata 951-8510, Japan
| | - Kouhei Sato
- Niigata University, Department of Electrical and Electronics Engineering, 8050 Ikarashi-2, Niigata 950-2181, Japan
| | - Shogo Muramatsu
- Niigata University, Department of Electrical and Electronics Engineering, 8050 Ikarashi-2, Niigata 950-2181, Japan
- AMED-CREST, AMED, Japan
| | - Hiroshi Hibino
- AMED-CREST, AMED, Japan
- Niigata University, School of Medicine, Department of Molecular Physiology, 757 Ichibancho, Asahimachi, Niigata 951-8510, Japan
- Niigata University, Center for Transdisciplinary Research, 8050 Ikarashi-2, Niigata 950-2181, Japan
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Abstract
The spatial variations of the intricate cytoarchitecture, fluid scalae, and mechano-electric transduction in the mammalian cochlea have long been postulated to provide the organ with the ability to perform a real-time, time-frequency processing of sound. However, the precise manner by which this tripartite coupling enables the exquisite cochlear filtering has yet to be articulated in a base-to-apex mathematical model. Moreover, while sound-evoked tuning curves derived from mechanical gains are excellent surrogates for auditory nerve fiber thresholds at the base of the cochlea, this correlation fails at the apex. The key factors influencing the divergence of both mechanical and neural tuning at the apex, as well as the spatial variation of mechanical tuning, are incompletely understood. We develop a model that shows that the mechanical effects arising from the combination of the taper of the cochlear scalae and the spatial variation of the cytoarchitecture of the cochlea provide robust mechanisms that modulate the outer hair cell-mediated active response and provide the basis for the transition of the mechanical gain spectra along the cochlear spiral. Further, the model predicts that the neural tuning at the base is primarily governed by the mechanical filtering of the cochlear partition. At the apex, microscale fluid dynamics and nanoscale channel dynamics must also be invoked to describe the threshold neural tuning for low frequencies. Overall, the model delineates a physiological basis for the difference between basal and apical gain seen in experiments and provides a coherent description of high- and low-frequency cochlear tuning.
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Amplification and Suppression of Traveling Waves along the Mouse Organ of Corti: Evidence for Spatial Variation in the Longitudinal Coupling of Outer Hair Cell-Generated Forces. J Neurosci 2019; 39:1805-1816. [PMID: 30651330 DOI: 10.1523/jneurosci.2608-18.2019] [Citation(s) in RCA: 50] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2018] [Revised: 01/06/2019] [Accepted: 01/09/2019] [Indexed: 11/21/2022] Open
Abstract
Mammalian hearing sensitivity and frequency selectivity depend on a mechanical amplification process mediated by outer hair cells (OHCs). OHCs are situated within the organ of Corti atop the basilar membrane (BM), which supports sound-evoked traveling waves. It is well established that OHCs generate force to selectively amplify BM traveling waves where they peak, and that amplification accumulates from one location to the next over this narrow cochlear region. However, recent measurements demonstrate that traveling waves along the apical surface of the organ of Corti, the reticular lamina (RL), are amplified over a much broader region. Whether OHC forces accumulate along the length of the RL traveling wave to provide a form of "global" cochlear amplification is unclear. Here we examined the spatial accumulation of RL amplification. In mice of either sex, we used tones to suppress amplification from different cochlear regions and examined the effect on RL vibrations near and far from the traveling-wave peak. We found that although OHC forces amplify the entire RL traveling wave, amplification only accumulates near the peak, over the same region where BM motion is amplified. This contradicts the notion that RL motion is involved in a global amplification mechanism and reveals that the mechanical properties of the BM and organ of Corti tune how OHC forces accumulate spatially. Restricting the spatial buildup of amplification enhances frequency selectivity by sharpening the peaks of cochlear traveling waves and constrains the number of OHCs responsible for mechanical sensitivity at each location.SIGNIFICANCE STATEMENT Outer hair cells generate force to amplify traveling waves within the mammalian cochlea. This force generation is critical to the ability to detect and discriminate sounds. Nevertheless, how these forces couple to the motions of the surrounding structures and integrate along the cochlear length remains poorly understood. Here we demonstrate that outer hair cell-generated forces amplify traveling-wave motion on the organ of Corti throughout the wave's extent, but that these forces only accumulate longitudinally over a region near the wave's peak. The longitudinal coupling of outer hair cell-generated forces is therefore spatially tuned, likely by the mechanical properties of the basilar membrane and organ of Corti. Our findings provide new insight into the mechanical processes that underlie sensitive hearing.
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Dong W, Xia A, Raphael PD, Puria S, Applegate B, Oghalai JS. Organ of Corti vibration within the intact gerbil cochlea measured by volumetric optical coherence tomography and vibrometry. J Neurophysiol 2018; 120:2847-2857. [PMID: 30281386 DOI: 10.1152/jn.00702.2017] [Citation(s) in RCA: 32] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
There is indirect evidence that the mammalian cochlea in the low-frequency apical and the more commonly studied high-frequency basal regions function in fundamentally different ways. Here, we directly tested this hypothesis by measuring sound-induced vibrations of the organ of Corti (OoC) at three turns of the gerbil cochlea using volumetric optical coherence tomography vibrometry (VOCTV), an approach that permits noninvasive imaging through the bone. In the apical turn, there was little frequency selectivity, and the displacement-vs.-frequency curves had low-pass filter characteristics with a corner frequency of ~0.5-0.9 kHz. The vibratory magnitudes increased compressively with increasing stimulus intensity at all frequencies. In the middle turn, responses were similar except for a slight peak in the response at ~2.5 kHz. The gain was ~50 dB at the peak and 30-40 dB at lower frequencies. In the basal turn, responses were sharply tuned and compressively nonlinear, consistent with observations in the literature. These data demonstrated that there is a transition of the mechanical response of the OoC along the length of the cochlea such that frequency tuning is sharper in the base than in the apex. Because the responses are fundamentally different, it is not appropriate to simply frequency shift vibratory data measured at one cochlear location to predict the cochlear responses at other locations. Furthermore, this means that the number of hair cells stimulated by sound is larger for low-frequency stimuli and smaller for high-frequency stimuli for the same intensity level. Thus the mechanisms of central processing of sounds must vary with frequency. NEW & NOTEWORTHY A volumetric optical coherence tomography and vibrometry system was used to probe cochlear mechanics within the intact gerbil cochlea. We found a gradual transition of the mechanical response of the organ of Corti along the length of the cochlea such that tuning at the base is dramatically sharper than that at the apex. These data help to explain discrepancies in the literature regarding how the cochlea processes low-frequency sounds.
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Affiliation(s)
- Wei Dong
- VA Loma Linda Healthcare System, Loma Linda, California.,Department of Otolaryngology - Head and Neck Surgery, Loma Linda University Health , Loma Linda, California
| | - Anping Xia
- Department of Otolaryngology - Head and Neck Surgery, Stanford University , Stanford, California
| | - Patrick D Raphael
- Department of Otolaryngology - Head and Neck Surgery, Stanford University , Stanford, California
| | - Sunil Puria
- Eaton-Peabody Laboratories, Massachusetts Eye and Ear Infirmary and Harvard Medical School , Boston, Massachusetts
| | - Brian Applegate
- Department of Biomedical Engineering, Texas A&M University , College Station, Texas
| | - John S Oghalai
- Caruso Department of Otolaryngology - Head and Neck Surgery, University of Southern California , Los Angeles, California
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He W, Kemp D, Ren T. Timing of the reticular lamina and basilar membrane vibration in living gerbil cochleae. eLife 2018; 7:37625. [PMID: 30183615 PMCID: PMC6125122 DOI: 10.7554/elife.37625] [Citation(s) in RCA: 44] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2018] [Accepted: 08/14/2018] [Indexed: 12/22/2022] Open
Abstract
Auditory sensory outer hair cells are thought to amplify sound-induced basilar membrane vibration through a feedback mechanism to enhance hearing sensitivity. For optimal amplification, the outer hair cell-generated force must act on the basilar membrane at an appropriate time at every cycle. However, the temporal relationship between the outer hair cell-driven reticular lamina vibration and the basilar membrane vibration remains unclear. By measuring sub-nanometer vibrations directly from outer hair cells using a custom-built heterodyne low-coherence interferometer, we demonstrate in living gerbil cochleae that the reticular lamina vibration occurs after, not before, the basilar membrane vibration. Both tone- and click-induced responses indicate that the reticular lamina and basilar membrane vibrate in opposite directions at the cochlear base and they oscillate in phase near the best-frequency location. Our results suggest that outer hair cells enhance hearing sensitivity through a global hydromechanical mechanism, rather than through a local mechanical feedback as commonly supposed. What is the quietest sound the ear can detect? All sounds begin as vibrating air molecules, which enter the ear and cause the eardrum to vibrate. We can detect vibrations that move the eardrum by a distance of less than one picometer. That’s one thousandth of a nanometer, or about 100 times smaller than a hydrogen atom. But how does the ear achieve this level of sensitivity? Vibrations of the eardrum cause three small bones within the middle ear to vibrate. The vibrations then spread to the cochlea, a fluid-filled spiral structure in the inner ear. Tiny hair cells lining the cochlea move as a result of the vibrations. There are two types of hair cells: inner and outer. Outer hair cells amplify the vibrations. It is this amplification that enables us to detect such small movements of the eardrum. Inner hair cells then convert the amplified vibrations into electrical signals, which travel via the auditory nerve to the brain. The bases of outer hair cells are connected to a structure called the basilar membrane, while their tops are anchored to a structure called the reticular lamina. It was generally assumed that outer hair cells amplify vibrations of the basilar membrane via a local positive feedback mechanism that requires the hair cells to vibrate first. But by comparing the timing of reticular lamina and basilar membrane vibrations in gerbils, He et al. show that this is not the case. Outer hair cells vibrate after the basilar membrane, not before. This indicates that outer hair cells use a mechanism other than commonly assumed local feedback to amplify sounds. The results presented by He et al. change our understanding of how the cochlea works, and may help bioengineers to design better hearing aids and cochlea implants. Millions of patients worldwide who suffer from hearing loss may ultimately stand to benefit.
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Affiliation(s)
- Wenxuan He
- Oregon Hearing Research Center, Department of Otolaryngology, Oregon Health & Science University, Portland, United States
| | - David Kemp
- University College London Ear Institute, University College London, London, United Kingdom
| | - Tianying Ren
- Oregon Hearing Research Center, Department of Otolaryngology, Oregon Health & Science University, Portland, United States
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Cooper NP, Vavakou A, van der Heijden M. Vibration hotspots reveal longitudinal funneling of sound-evoked motion in the mammalian cochlea. Nat Commun 2018; 9:3054. [PMID: 30076297 PMCID: PMC6076242 DOI: 10.1038/s41467-018-05483-z] [Citation(s) in RCA: 81] [Impact Index Per Article: 13.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2018] [Accepted: 07/09/2018] [Indexed: 12/03/2022] Open
Abstract
The micromechanical mechanisms that underpin tuning and dynamic range compression in the mammalian inner ear are fundamental to hearing, but poorly understood. Here, we present new, high-resolution optical measurements that directly map sound-evoked vibrations on to anatomical structures in the intact, living gerbil cochlea. The largest vibrations occur in a tightly delineated hotspot centering near the interface between the Deiters' and outer hair cells. Hotspot vibrations are less sharply tuned, but more nonlinear, than basilar membrane vibrations, and behave non-monotonically (exhibiting hyper-compression) near their characteristic frequency. Amplitude and phase differences between hotspot and basilar membrane responses depend on both frequency and measurement angle, and indicate that hotspot vibrations involve longitudinal motion. We hypothesize that structural coupling between the Deiters' and outer hair cells funnels sound-evoked motion into the hotspot region, under the control of the outer hair cells, to optimize cochlear tuning and compression.
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Affiliation(s)
- Nigel P Cooper
- Department of Neuroscience, Erasmus MC, Room Ee 1285, P.O. Box 2040, 3000 CA, Rotterdam, The Netherlands
| | - Anna Vavakou
- Department of Neuroscience, Erasmus MC, Room Ee 1285, P.O. Box 2040, 3000 CA, Rotterdam, The Netherlands
| | - Marcel van der Heijden
- Department of Neuroscience, Erasmus MC, Room Ee 1285, P.O. Box 2040, 3000 CA, Rotterdam, The Netherlands.
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Santos-Sacchi J, Tan W. The Frequency Response of Outer Hair Cell Voltage-Dependent Motility Is Limited by Kinetics of Prestin. J Neurosci 2018; 38:5495-5506. [PMID: 29899032 PMCID: PMC6001036 DOI: 10.1523/jneurosci.0425-18.2018] [Citation(s) in RCA: 48] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2018] [Revised: 05/14/2018] [Accepted: 05/16/2018] [Indexed: 01/07/2023] Open
Abstract
The voltage-dependent protein SLC26a5 (prestin) underlies outer hair cell electromotility (eM), which is responsible for cochlear amplification in mammals. The electrical signature of eM is a bell-shaped nonlinear capacitance (NLC), deriving from prestin sensor-charge (Qp) movements, which peaks at the membrane voltage, Vh, where charge is distributed equally on either side of the membrane. Voltage dependencies of NLC and eM differ depending on interrogation frequency and intracellular chloride, revealing slow intermediate conformational transitions between anion binding and voltage-driven Qp movements. Consequently, NLC exhibits low-pass characteristics, substantially below prevailing estimates of eM frequency response. Here we study in guinea pig and mouse of either sex synchronous prestin electrical (NLC, Qp) and mechanical (eM) activity across frequencies under voltage clamp (whole cell and microchamber). We find that eM and Qp magnitude and phase correspond, indicating tight piezoelectric coupling. Electromechanical measures (both NLC and eM) show dual-Lorentzian, low-pass behavior, with a limiting (τ2) time constant at Vh of 32.6 and 24.8 μs, respectively. As expected for voltage-dependent kinetics, voltage excitation away from Vh has a faster, flatter frequency response, with our fastest measured τ2 for eM of 18.2 μs. Previous observations of ultrafast eM (τ ≈ 2 μs) were obtained at offsets far removed from Vh We hypothesize that trade-offs in eM gain-bandwith arising from voltage excitation at membrane potentials offset from Vh influence the effectiveness of cochlear amplification across frequencies.SIGNIFICANCE STATEMENT Of two types of hair cells within the organ of Corti, inner hair cells and outer hair cells, the latter evolved to boost sensitivity to sounds. Damage results in hearing loss of 40-60 dB, revealing amplification gains of 100-1000× that arise from voltage-dependent mechanical responses [electromotility (eM)]. eM, driven by the membrane protein prestin, may work beyond 70 kHz. However, this speed exceeds, by over an order of magnitude, kinetics of typical voltage-dependent membrane proteins. We find eM is actually low pass in nature, indicating that prestin bears kinetics typical of other membrane proteins. These observations highlight potential difficulties in providing sufficient amplification beyond a cutoff frequency near 20 kHz. Nevertheless, observed trade-offs in eM gain-bandwith may sustain cochlear amplification across frequency.
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Affiliation(s)
- Joseph Santos-Sacchi
- Department of Surgery (Otolaryngology),
- Department of Neuroscience, and
- Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, Connecticut 06510
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Dewey JB, Xia A, Müller U, Belyantseva IA, Applegate BE, Oghalai JS. Mammalian Auditory Hair Cell Bundle Stiffness Affects Frequency Tuning by Increasing Coupling along the Length of the Cochlea. Cell Rep 2018; 23:2915-2927. [PMID: 29874579 PMCID: PMC6309882 DOI: 10.1016/j.celrep.2018.05.024] [Citation(s) in RCA: 26] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2018] [Revised: 04/24/2018] [Accepted: 05/08/2018] [Indexed: 01/15/2023] Open
Abstract
The stereociliary bundles of cochlear hair cells convert mechanical vibrations into the electrical signals required for auditory sensation. While the stiffness of the bundles strongly influences mechanotransduction, its influence on the vibratory response of the cochlear partition is unclear. To assess this, we measured cochlear vibrations in mutant mice with reduced bundle stiffness or with a tectorial membrane (TM) that is detached from the sensory epithelium. We found that reducing bundle stiffness decreased the high-frequency extent and sharpened the tuning of vibratory responses obtained postmortem. Detaching the TM further reduced the high-frequency extent of the vibrations but also lowered the partition's resonant frequency. Together, these results demonstrate that the bundle's stiffness and attachment to the TM contribute to passive longitudinal coupling in the cochlea. We conclude that the stereociliary bundles and TM interact to facilitate passive-wave propagation to more apical locations, possibly enhancing active-wave amplification in vivo.
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Affiliation(s)
- James B Dewey
- The Caruso Department of Otolaryngology - Head & Neck Surgery, University of Southern California, Los Angeles, CA 90033, USA
| | - Anping Xia
- Department of Otolaryngology - Head & Neck Surgery, Stanford University, Stanford, CA 94305, USA
| | - Ulrich Müller
- The Solomon H. Snyder Department of Neuroscience, School of Medicine, Johns Hopkins University, Baltimore, MD 21205, USA
| | | | - Brian E Applegate
- Department of Biomedical Engineering, Texas A&M University, College Station, TX 77843, USA
| | - John S Oghalai
- The Caruso Department of Otolaryngology - Head & Neck Surgery, University of Southern California, Los Angeles, CA 90033, USA.
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40
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Kim J, Xia A, Grillet N, Applegate BE, Oghalai JS. Osmotic stabilization prevents cochlear synaptopathy after blast trauma. Proc Natl Acad Sci U S A 2018; 115:E4853-E4860. [PMID: 29735658 PMCID: PMC6003510 DOI: 10.1073/pnas.1720121115] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Traumatic noise causes hearing loss by damaging sensory hair cells and their auditory synapses. There are no treatments. Here, we investigated mice exposed to a blast wave approximating a roadside bomb. In vivo cochlear imaging revealed an increase in the volume of endolymph, the fluid within scala media, termed endolymphatic hydrops. Endolymphatic hydrops, hair cell loss, and cochlear synaptopathy were initiated by trauma to the mechanosensitive hair cell stereocilia and were K+-dependent. Increasing the osmolality of the adjacent perilymph treated endolymphatic hydrops and prevented synaptopathy, but did not prevent hair cell loss. Conversely, inducing endolymphatic hydrops in control mice by lowering perilymph osmolality caused cochlear synaptopathy that was glutamate-dependent, but did not cause hair cell loss. Thus, endolymphatic hydrops is a surrogate marker for synaptic bouton swelling after hair cells release excitotoxic levels of glutamate. Because osmotic stabilization prevents neural damage, it is a potential treatment to reduce hearing loss after noise exposure.
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Affiliation(s)
- Jinkyung Kim
- Department of Otolaryngology-Head and Neck Surgery, Stanford University, Stanford, CA 94305
| | - Anping Xia
- Department of Otolaryngology-Head and Neck Surgery, Stanford University, Stanford, CA 94305
| | - Nicolas Grillet
- Department of Otolaryngology-Head and Neck Surgery, Stanford University, Stanford, CA 94305
| | - Brian E Applegate
- Department of Biomedical Engineering, Texas A&M University, College Station, TX 77843
| | - John S Oghalai
- Caruso Department of Otolaryngology-Head and Neck Surgery, University of Southern California, Los Angeles, CA 90033
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KIM WIHAN, KIM SANGMIN, OGHALAI JOHNS, APPLEGATE BRIANE. Endoscopic optical coherence tomography enables morphological and subnanometer vibratory imaging of the porcine cochlea through the round window. OPTICS LETTERS 2018; 43:1966-1969. [PMID: 29714773 PMCID: PMC6731066 DOI: 10.1364/ol.43.001966] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/02/2018] [Accepted: 03/19/2018] [Indexed: 05/21/2023]
Abstract
A highly phase stable hand-held (HH) endoscopic system has been developed for optical coherence tomography and vibrometry. Designed to transit the ear canal to the middle ear space and peer through the round window (RW), it is capable of imaging the vibratory function of the cochlear soft tissues with subnanometer scale sensitivity. A side-looking, 9 cm long rigid endoscope with a distal diameter of 1.2 mm, was able to fit within the RW niche and provide imaging access. The phase stability was achieved in part by fully integrating a Michelson interferometer into the HH device. Ex vivo imaging of a domestic pig demonstrated the system's ability for functional vibratory imaging of the cochlea via the RW.
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Affiliation(s)
- WIHAN KIM
- Department of Biomedical Engineering, Texas A&M University, College Station, TX 77843, USA
| | - SANGMIN KIM
- Department of Biomedical Engineering, Texas A&M University, College Station, TX 77843, USA
| | - JOHN S. OGHALAI
- Caruso Department of Otolaryngology–Head and Neck Surgery, University of Southern California, Los Angeles, CA 90089, USA
| | - BRIAN E. APPLEGATE
- Department of Biomedical Engineering, Texas A&M University, College Station, TX 77843, USA
- Corresponding author:
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Negative membrane capacitance of outer hair cells: electromechanical coupling near resonance. Sci Rep 2017; 7:12118. [PMID: 28935970 PMCID: PMC5608895 DOI: 10.1038/s41598-017-12411-6] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2017] [Accepted: 09/06/2017] [Indexed: 01/30/2023] Open
Abstract
Outer hair cells in the cochlea have a unique motility in their cell body based on mechanoelectric coupling, with which voltage changes generated by stimuli at their hair bundles drive the cell body and, in turn, it has been assumed, amplifies the signal. In vitro experiments show that the movement of the charges of the motile element significantly increases the membrane capacitance, contributing to the attenuation of the driving voltage. That is indeed the case in the absence of mechanical load. Here it is predicted, however, that the movement of motile charges creates negative capacitance near the condition of mechanical resonance, such as those in the cochlea, enhancing energy output.
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Neuroplastin Isoform Np55 Is Expressed in the Stereocilia of Outer Hair Cells and Required for Normal Outer Hair Cell Function. J Neurosci 2017; 36:9201-16. [PMID: 27581460 DOI: 10.1523/jneurosci.0093-16.2016] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2016] [Accepted: 07/14/2016] [Indexed: 11/21/2022] Open
Abstract
UNLABELLED Neuroplastin (Nptn) is a member of the Ig superfamily and is expressed in two isoforms, Np55 and Np65. Np65 regulates synaptic transmission but the function of Np55 is unknown. In an N-ethyl-N-nitrosaurea mutagenesis screen, we have now generated a mouse line with an Nptn mutation that causes deafness. We show that Np55 is expressed in stereocilia of outer hair cells (OHCs) but not inner hair cells and affects interactions of stereocilia with the tectorial membrane. In vivo vibrometry demonstrates that cochlear amplification is absent in Nptn mutant mice, which is consistent with the failure of OHC stereocilia to maintain stable interactions with the tectorial membrane. Hair bundles show morphological defects as the mutant mice age and while mechanotransduction currents can be evoked in early postnatal hair cells, cochlea microphonics recordings indicate that mechanontransduction is affected as the mutant mice age. We thus conclude that differential splicing leads to functional diversification of Nptn, where Np55 is essential for OHC function, while Np65 is implicated in the regulation of synaptic function. SIGNIFICANCE STATEMENT Amplification of input sound signals, which is needed for the auditory sense organ to detect sounds over a wide intensity range, depends on mechanical coupling of outer hair cells to the tectorial membrane. The current study shows that neuroplastin, a member of the Ig superfamily, which has previously been linked to the regulation of synaptic plasticity, is critical to maintain a stable mechanical link of outer hair cells with the tectorial membrane. In vivo recordings demonstrate that neuroplastin is essential for sound amplification and that mutation in neuroplastin leads to auditory impairment in mice.
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Two-Dimensional Cochlear Micromechanics Measured In Vivo Demonstrate Radial Tuning within the Mouse Organ of Corti. J Neurosci 2017; 36:8160-73. [PMID: 27488636 DOI: 10.1523/jneurosci.1157-16.2016] [Citation(s) in RCA: 88] [Impact Index Per Article: 12.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2016] [Accepted: 06/07/2016] [Indexed: 12/18/2022] Open
Abstract
UNLABELLED The exquisite sensitivity and frequency discrimination of mammalian hearing underlie the ability to understand complex speech in noise. This requires force generation by cochlear outer hair cells (OHCs) to amplify the basilar membrane traveling wave; however, it is unclear how amplification is achieved with sharp frequency tuning. Here we investigated the origin of tuning by measuring sound-induced 2-D vibrations within the mouse organ of Corti in vivo Our goal was to determine the transfer function relating the radial shear between the structures that deflect the OHC bundle, the tectorial membrane and reticular lamina, to the transverse motion of the basilar membrane. We found that, after normalizing their responses to the vibration of the basilar membrane, the radial vibrations of the tectorial membrane and reticular lamina were tuned. The radial tuning peaked at a higher frequency than transverse basilar membrane tuning in the passive, postmortem condition. The radial tuning was similar in dead mice, indicating that this reflected passive, not active, mechanics. These findings were exaggerated in Tecta(C1509G/C1509G) mice, where the tectorial membrane is detached from OHC stereocilia, arguing that the tuning of radial vibrations within the hair cell epithelium is distinct from tectorial membrane tuning. Together, these results reveal a passive, frequency-dependent contribution to cochlear filtering that is independent of basilar membrane filtering. These data argue that passive mechanics within the organ of Corti sharpen frequency selectivity by defining which OHCs enhance the vibration of the basilar membrane, thereby tuning the gain of cochlear amplification. SIGNIFICANCE STATEMENT Outer hair cells amplify the traveling wave within the mammalian cochlea. The resultant gain and frequency sharpening are necessary for speech discrimination, particularly in the presence of background noise. Here we measured the 2-D motion of the organ of Corti in mice and found that the structures that stimulate the outer hair cell stereocilia, the tectorial membrane and reticular lamina, were sharply tuned in the radial direction. Radial tuning was similar in dead mice and in mice lacking a tectorial membrane. This suggests that radial tuning comes from passive mechanics within the hair cell epithelium, and that these mechanics, at least in part, may tune the gain of cochlear amplification.
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45
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Landry TG, Bance ML, Leadbetter J, Adamson RB, Brown JA. In vivo measurement of basilar membrane vibration in the unopened chinchilla cochlea using high frequency ultrasound. THE JOURNAL OF THE ACOUSTICAL SOCIETY OF AMERICA 2017; 141:4610. [PMID: 28679279 DOI: 10.1121/1.4985622] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
The basilar membrane and organ of Corti in the cochlea are essential for sound detection and frequency discrimination in normal hearing. There are currently no methods used for real-time high resolution clinical imaging or vibrometry of these structures. The ability to perform such imaging could aid in the diagnosis of some pathologies and advance understanding of the causes. It is demonstrated that high frequency ultrasound can be used to measure basilar membrane vibrations through the round window of chinchilla cochleas in vivo. The basic vibration characteristics of the basilar membrane agree with previous studies that used other methods, although as expected, the sensitivity of ultrasound was not as high as optical methods. At the best frequency for the recording location, the average vibration velocity amplitude was about 4 mm/s/Pa with stimulus intensity of 50 dB sound pressure level. The displacement noise floor was about 0.4 nm with 256 trial averages (5.12 ms per trial). Although vibration signals were observed, which likely originated from the organ of Corti, the spatial resolution was not adequate to resolve any of the sub-structures. Improvements to the ultrasound probe design may improve resolution and allow the responses of these different structures to be better discriminated.
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Affiliation(s)
- Thomas G Landry
- Division of Otolaryngology, Nova Scotia Health Authority, Halifax, Nova Scotia, Canada
| | - Manohar L Bance
- Division of Otolaryngology, Department of Surgery, Dalhousie University, Halifax, Nova Scotia, Canada
| | - Jeffrey Leadbetter
- School of Biomedical Engineering, Dalhousie University, Halifax, Nova Scotia, Canada
| | - Robert B Adamson
- School of Biomedical Engineering, Dalhousie University, Halifax, Nova Scotia, Canada
| | - Jeremy A Brown
- School of Biomedical Engineering, Dalhousie University, Halifax, Nova Scotia, Canada
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46
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Bulut E, Öztürk L. Spontaneous otoacoustic emission recordings during contralateral pure-tone activation of medial olivocochlear reflex. Physiol Int 2017. [PMID: 28648121 DOI: 10.1556/2060.104.2017.2.7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
We hypothesized that cochlear frequency discrimination occurs through medial olivocochlear efferent (MOCE)-induced alterations in outer hair cell (OHC) electromotility, which is independent from basilar membrane traveling waves. After obtaining informed consent, volunteers with normal hearing (n = 10; mean age: 20.6 ± 1.2 years) and patients with unilateral deafness (n = 10; mean age: 30.2 ± 17.9 years) or bilateral deafness (n = 8; mean age: 30.7 ± 13.8 years) underwent a complete physical and audiological examination, and audiological tests including transient evoked otoacoustic emission and spontaneous otoacoustic emission (TEOAE and SOAE, respectively). SOAE recordings were performed during contralateral pure-tone stimuli at 1 and 3 kHz. SOAE recordings in the presence of contralateral pure-tone stimuli showed frequency-specific activation out of the initial frequency range of SOAE responses. Basilar membrane motion during pure-tone stimulation results from OHC activation by means of MOCE neurons rather than from a traveling wave. Eventually, frequency-specific responses obtained from SOAEs suggested that OHC electromotility may be responsible for frequency discrimination of the cochlea independently from basilar membrane motion.
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Affiliation(s)
- E Bulut
- 1 Department of Audiology, Trakya University Faculty of Health Sciences , Edirne, Turkey.,2 Department of Physiology, Faculty of Medicine, Trakya University , Edirne, Turkey
| | - L Öztürk
- 2 Department of Physiology, Faculty of Medicine, Trakya University , Edirne, Turkey
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47
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Recio-Spinoso A, Oghalai JS. Mechanical tuning and amplification within the apex of the guinea pig cochlea. J Physiol 2017; 595:4549-4561. [PMID: 28382742 DOI: 10.1113/jp273881] [Citation(s) in RCA: 41] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2016] [Accepted: 03/28/2017] [Indexed: 12/21/2022] Open
Abstract
KEY POINTS A popular conception of mammalian cochlear physiology is that tuned mechanical vibration of the basilar membrane defines the frequency response of the innervating auditory nerve fibres However, the data supporting these concepts come from vibratory measurements at cochlear locations tuned to high frequencies (>7 kHz). Here, we measured the travelling wave in regions of the guinea pig cochlea that respond to low frequencies (<2 kHz) and found that mechanical tuning was broad and did not match auditory nerve tuning characteristics. Non-linear amplification of the travelling wave functioned over a broad frequency range and did not substantially sharpen frequency tuning. Thus, the neural encoding of low-frequency sounds, which includes most of the information conveyed by human speech, is not principally determined by basilar membrane mechanics. ABSTRACT The popular notion of mammalian cochlear function is that auditory nerves are tuned to respond best to different sound frequencies because basilar membrane vibration is mechanically tuned to different frequencies along its length. However, this concept has only been demonstrated in regions of the cochlea tuned to frequencies >7 kHz, not in regions sensitive to lower frequencies where human speech is encoded. Here, we overcame historical technical limitations and non-invasively measured sound-induced vibrations at four locations distributed over the apical two turns of the guinea pig cochlea. In turn 3, the responses demonstrated low-pass filter characteristics. In turn 2, the responses were low-pass-like, in that they occasionally did have a slight peak near the corner frequency. The corner frequencies of the responses were tonotopically tuned and ranged from 384 to 668 Hz. Non-linear gain, or amplification of the vibrations in response to low-intensity stimuli, was found both below and above the corner frequencies. Post mortem, cochlear gain disappeared. The non-linear gain was typically 10-30 dB and was broad-band rather than sharply tuned. However, the gain did reach nearly 50 dB in turn 2 for higher stimulus frequencies, nearly the amount of gain found in basal cochlear regions. Thus, our data prove that mechanical responses do not match neural responses and that cochlear amplification does not appreciably sharpen frequency tuning for cochlear regions that respond to frequencies <2 kHz. These data indicate that the non-linear processing of sound performed by the guinea pig cochlea varies substantially between the cochlear apex and base.
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Affiliation(s)
- Alberto Recio-Spinoso
- Instituto de Investigación en Discapacidades Neurológicas, Universidad de Castilla-La Mancha, Albacete, Spain
| | - John S Oghalai
- Deparment of Otolaryngology-Head and Neck Surgery, Stanford University School of Medicine, Stanford, CA, USA
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48
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Choi S, Sato K, Ota T, Nin F, Muramatsu S, Hibino H. Multifrequency-swept optical coherence microscopy for highspeed full-field tomographic vibrometry in biological tissues. BIOMEDICAL OPTICS EXPRESS 2017; 8:608-621. [PMID: 28270971 PMCID: PMC5330561 DOI: 10.1364/boe.8.000608] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/01/2016] [Revised: 12/27/2016] [Accepted: 12/29/2016] [Indexed: 05/03/2023]
Abstract
Because conventional laser Doppler vibrometry or Doppler optical coherence tomography require mechanical scanning probes that cannot simultaneously measure the wide-range dynamics of bio-tissues, a multifrequency-swept optical coherence microscopy with wide-field heterodyne detection technique was developed. A 1024 × 1024 × 2000 voxel volume was acquired with an axial resolution of ~1.8 μm and an acquisition speed of 2 s. Vibration measurements at 10 kHz were performed over a wide field of view. Wide-field tomographic vibration measurements of a mouse tympanic membrane are demonstrated to illustrate the applicability of this method to live animals.
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Affiliation(s)
- Samuel Choi
- Niigata University, Department of Electrical and Electronics Engineering, 8050 Ikarashi-2, Niigata 950-2181, Japan
- AMED-CTRST, AMED, Japan
| | - Keita Sato
- Niigata University, Department of Electrical and Electronics Engineering, 8050 Ikarashi-2, Niigata 950-2181, Japan
| | - Takeru Ota
- AMED-CTRST, AMED, Japan
- Niigata University, School of Medicine, Department of Molecular Physiology, 757 Ichibancho, Asahimachi, Niigata 951-8510, Japan
| | - Fumiaki Nin
- AMED-CTRST, AMED, Japan
- Niigata University, School of Medicine, Department of Molecular Physiology, 757 Ichibancho, Asahimachi, Niigata 951-8510, Japan
- Niigata University, Center for Transdisciplinary Research, 8050 Ikarashi-2, Niigata 950-2181, Japan
| | - Shogo Muramatsu
- Niigata University, Department of Electrical and Electronics Engineering, 8050 Ikarashi-2, Niigata 950-2181, Japan
- AMED-CTRST, AMED, Japan
| | - Hiroshi Hibino
- AMED-CTRST, AMED, Japan
- Niigata University, School of Medicine, Department of Molecular Physiology, 757 Ichibancho, Asahimachi, Niigata 951-8510, Japan
- Niigata University, Center for Transdisciplinary Research, 8050 Ikarashi-2, Niigata 950-2181, Japan
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Brownell WE. What Is Electromotility? -The History of Its Discovery and Its Relevance to Acoustics. ACOUSTICS TODAY 2017; 13:20-27. [PMID: 29051713 PMCID: PMC5645053] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Experiments on an inner ear sensory cell revealed that it converts electrical energy directly into mechanical energy at acoustic frequencies.
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Affiliation(s)
- William E Brownell
- Department of Otolaryngology-Head and Neck Surgery, Baylor College of Medicine, One Baylor Plaza, Houston, Texas 77030, USA
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50
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Xia A, Liu X, Raphael PD, Applegate BE, Oghalai JS. Hair cell force generation does not amplify or tune vibrations within the chicken basilar papilla. Nat Commun 2016; 7:13133. [PMID: 27796310 PMCID: PMC5095595 DOI: 10.1038/ncomms13133] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/2015] [Accepted: 09/07/2016] [Indexed: 12/22/2022] Open
Abstract
Frequency tuning within the auditory papilla of most non-mammalian species is electrical, deriving from ion-channel resonance within their sensory hair cells. In contrast, tuning within the mammalian cochlea is mechanical, stemming from active mechanisms within outer hair cells that amplify the basilar membrane travelling wave. Interestingly, hair cells in the avian basilar papilla demonstrate both electrical resonance and force-generation, making it unclear which mechanism creates sharp frequency tuning. Here, we measured sound-induced vibrations within the apical half of the chicken basilar papilla in vivo and found broadly-tuned travelling waves that were not amplified. However, distortion products were found in live but not dead chickens. These findings support the idea that avian hair cells do produce force, but that their effects on vibration are small and do not sharpen tuning. Therefore, frequency tuning within the apical avian basilar papilla is not mechanical, and likely derives from hair cell electrical resonance. The avian auditory papilla has many similarities to the mammalian cochlea but whether force generation by hair cells amplifies the travelling wave, as it does in mammals, remains unknown. Here the authors show that the chicken basilar papilla does not have a ‘cochlear amplifier' and that sharp frequency tuning does not derive from mechanical vibrations.
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Affiliation(s)
- Anping Xia
- Department of Otolaryngology-Head and Neck Surgery, Stanford University, 801 Welch Road, Stanford, California 94305, USA
| | - Xiaofang Liu
- Department of Otolaryngology-Head and Neck Surgery, Stanford University, 801 Welch Road, Stanford, California 94305, USA.,Department of Anorectal Surgery, the First Affiliated hospital of China Medical University, 155 NanjingBei Street, ShenYang, LiaoNing Province 110001, China
| | - Patrick D Raphael
- Department of Otolaryngology-Head and Neck Surgery, Stanford University, 801 Welch Road, Stanford, California 94305, USA
| | - Brian E Applegate
- Department of Biomedical Engineering, Texas A&M University, 5059 Emerging Technology Building, 3120 TAMU, College Station, Texas 77843, USA
| | - John S Oghalai
- Department of Otolaryngology-Head and Neck Surgery, Stanford University, 801 Welch Road, Stanford, California 94305, USA
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