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Rabbitt RD, Bidone TC. A parametric blueprint for optimum cochlear outer hair cell design. J R Soc Interface 2023; 20:20220762. [PMID: 36789510 PMCID: PMC9929500 DOI: 10.1098/rsif.2022.0762] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/16/2023] Open
Abstract
The present work examines the hypothesis that cochlear outer hair cell (OHC) properties vary in precise proportions along the tonotopic map to optimize electromechanical power conversion. We tested this hypothesis using a very simple model of a single isolated OHC driving a mechanical load. Results identify three non-dimensional ratios that are predicted to optimize power conversion: the ratio of the resistive-capacitive (RC) corner to the characteristic frequency (CF), the ratio of nonlinear to linear capacitance and the ratio of OHC stiffness to cochlear load stiffness. Optimum efficiency requires all three ratios to be universal constants, independent of CF and species. The same ratios are cardinal control parameters that maximize power output by positioning the OHC operating point on the edge of a dynamic instability. Results support the hypothesis that OHC properties evolved to optimize electro-mechanical power conversion. Identification of the RC corner frequency as a control parameter reveals a powerful mechanism used by medial olivocochlear efferent system to control OHC power output. Results indicate the upper-frequency limit of OHC power output is not constrained by the speed of the motor itself but instead is probably limited by the size of the nucleus and membrane surface area available for ion-channel expression.
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Affiliation(s)
- Richard D. Rabbitt
- Biomedical Engineering, University of Utah, 36 S Wasatch Drive, Salt Lake City, UT 84112, USA,Otolaryngology, University of Utah, 36 S Wasatch Drive, Salt Lake City, UT 84112, USA,Neuroscience Program, University of Utah, 36 S Wasatch Drive, Salt Lake City, UT 84112, USA
| | - Tamara C. Bidone
- Biomedical Engineering, University of Utah, 36 S Wasatch Drive, Salt Lake City, UT 84112, USA,Molecular Pharmaceutics, University of Utah, 36 S Wasatch Drive, Salt Lake City, UT 84112, USA,Department of Biochemistry, University of Utah, 36 S Wasatch Drive, Salt Lake City, UT 84112, USA,Scientific Computing & Imaging Institute, University of Utah, 36 S Wasatch Drive, Salt Lake City, UT 84112, USA
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Homma K, Takahashi S, Cheatham MA. How much prestin motor activity is required for normal hearing? Hear Res 2022; 423:108376. [PMID: 34848118 PMCID: PMC9091054 DOI: 10.1016/j.heares.2021.108376] [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: 06/30/2021] [Revised: 10/07/2021] [Accepted: 10/13/2021] [Indexed: 12/20/2022]
Abstract
Prestin (SLC26A5) is a membrane-based voltage-dependent motor protein responsible for outer hair cell (OHC) somatic electromotility. Its importance for mammalian cochlear amplification has been demonstrated using mouse models lacking prestin (prestin-KO) and expressing dysfunctional prestin, prestinV499G/Y501H (499-prestin-KI). However, it is still not elucidated how prestin contributes to the mechanical amplification process in the cochlea. In this study, we characterized several prestin mouse models in which prestin activity in OHCs was variously manipulated. We found that near-normal cochlear function can be maintained even when prestin activity is significantly reduced, suggesting that the relationship between OHC electromotility and the peripheral sensitivity to sound may not be linear. This result is counterintuitive given the large threshold shifts in prestin-KO and 499-prestin-KI mice, as reported in previous studies. To reconcile these apparently opposing observations, we entertain a voltage- and turgor pressure-based cochlear amplification mechanism that requires prestin but is insensitive to significant reductions in prestin protein expression. 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)
- Kazuaki Homma
- Department of Otolaryngology - Head and Neck Surgery, Feinberg School of Medicine, Northwestern University, Chicago, IL 60611, USA; The Hugh Knowles Center for Clinical and Basic Science in Hearing and Its Disorders, Northwestern University, Evanston, IL 60208, USA.
| | - Satoe Takahashi
- Department of Otolaryngology - Head and Neck Surgery, Feinberg School of Medicine, Northwestern University, Chicago, IL 60611, USA
| | - Mary Ann Cheatham
- The Hugh Knowles Center for Clinical and Basic Science in Hearing and Its Disorders, Northwestern University, Evanston, IL 60208, USA; Department of Communication Sciences and Disorders, Northwestern University, Evanston, IL 60208, USA.
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3
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Lin X, Li G, Zhang Y, Zhao J, Lu J, Gao Y, Liu H, Li GL, Yang T, Song L, Wu H. Hearing consequences in Gjb2 knock-in mice: implications for human p.V37I mutation. Aging (Albany NY) 2019; 11:7416-7441. [PMID: 31562289 PMCID: PMC6782001 DOI: 10.18632/aging.102246] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2019] [Accepted: 08/22/2019] [Indexed: 01/09/2023]
Abstract
Human p.V37I mutation of GJB2 gene was strongly correlated with late-onset progressive hearing loss, especially among East Asia populations. We generated a knock-in mouse model based on human p.V37I variant (c.109G>A) that recapitulated the human phenotype. Cochlear pathology revealed no significant hair cell loss, stria vascularis atrophy or spiral ganglion neuron loss, but a significant change in the length of gap junction plaques, which may have contributed to the observed mild endocochlear potential (EP) drop in homozygous mice lasting lifetime. The cochlear amplification in homozygous mice was compromised, but outer hair cells' function remained unchanged, indicating that the reduced amplification was EP- rather than prestin-generated. In addition to ABR threshold elevation, ABR wave I latencies were also prolonged in aged homozygous animals. We found in homozygous IHCs a significant increase in ICa but no change in Ca2+ efficiency in triggering exocytosis. Environmental insults such as noise exposure, middle ear injection of KCl solution and systemic application of furosemide all exacerbated the pathological phenotype in homozygous mice. We conclude that this Gjb2 mutation-induced hearing loss results from 1) reduced cochlear amplifier caused by lowered EP, 2) IHCs excitotoxicity associated with potassium accumulation around hair cells, and 3) progression induced by environmental insults.
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Affiliation(s)
- Xin Lin
- Department of Otolaryngology-Head and Neck Surgery, Shanghai Ninth People's Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai 200011, China.,Ear Institute, Shanghai Jiao Tong University School of Medicine, Shanghai 200125, China.,Shanghai Key Laboratory of Translational Medicine on Ear and Nose diseases, Shanghai 200125, China
| | - Gen Li
- Department of Otolaryngology-Head and Neck Surgery, Shanghai Ninth People's Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai 200011, China.,Ear Institute, Shanghai Jiao Tong University School of Medicine, Shanghai 200125, China.,Shanghai Key Laboratory of Translational Medicine on Ear and Nose diseases, Shanghai 200125, China
| | - Yu Zhang
- Department of Otolaryngology-Head and Neck Surgery, Shanghai Ninth People's Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai 200011, China.,Ear Institute, Shanghai Jiao Tong University School of Medicine, Shanghai 200125, China.,Shanghai Key Laboratory of Translational Medicine on Ear and Nose diseases, Shanghai 200125, China
| | - Jingjing Zhao
- Department of Otolaryngology-Head and Neck Surgery, Shanghai Ninth People's Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai 200011, China.,Ear Institute, Shanghai Jiao Tong University School of Medicine, Shanghai 200125, China.,Shanghai Key Laboratory of Translational Medicine on Ear and Nose diseases, Shanghai 200125, China
| | - Jiawen Lu
- Department of Otolaryngology-Head and Neck Surgery, Shanghai Ninth People's Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai 200011, China.,Ear Institute, Shanghai Jiao Tong University School of Medicine, Shanghai 200125, China.,Shanghai Key Laboratory of Translational Medicine on Ear and Nose diseases, Shanghai 200125, China
| | - Yunge Gao
- Department of Otolaryngology-Head and Neck Surgery, Shanghai Ninth People's Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai 200011, China.,Ear Institute, Shanghai Jiao Tong University School of Medicine, Shanghai 200125, China.,Shanghai Key Laboratory of Translational Medicine on Ear and Nose diseases, Shanghai 200125, China
| | - Huihui Liu
- Department of Otolaryngology-Head and Neck Surgery, Shanghai Ninth People's Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai 200011, China.,Ear Institute, Shanghai Jiao Tong University School of Medicine, Shanghai 200125, China.,Shanghai Key Laboratory of Translational Medicine on Ear and Nose diseases, Shanghai 200125, China
| | - Geng-Lin Li
- Department of Otolaryngology-Head and Neck Surgery, Shanghai Ninth People's Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai 200011, China.,Ear Institute, Shanghai Jiao Tong University School of Medicine, Shanghai 200125, China.,Shanghai Key Laboratory of Translational Medicine on Ear and Nose diseases, Shanghai 200125, China
| | - Tao Yang
- Department of Otolaryngology-Head and Neck Surgery, Shanghai Ninth People's Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai 200011, China.,Ear Institute, Shanghai Jiao Tong University School of Medicine, Shanghai 200125, China.,Shanghai Key Laboratory of Translational Medicine on Ear and Nose diseases, Shanghai 200125, China
| | - Lei Song
- Department of Otolaryngology-Head and Neck Surgery, Shanghai Ninth People's Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai 200011, China.,Ear Institute, Shanghai Jiao Tong University School of Medicine, Shanghai 200125, China.,Shanghai Key Laboratory of Translational Medicine on Ear and Nose diseases, Shanghai 200125, China
| | - Hao Wu
- Department of Otolaryngology-Head and Neck Surgery, Shanghai Ninth People's Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai 200011, China.,Ear Institute, Shanghai Jiao Tong University School of Medicine, Shanghai 200125, China.,Shanghai Key Laboratory of Translational Medicine on Ear and Nose diseases, Shanghai 200125, China
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Walton JP, Dziorny AC, Vasilyeva ON, Luebke AE. Loss of the Cochlear Amplifier Prestin Reduces Temporal Processing Efficacy in the Central Auditory System. Front Cell Neurosci 2018; 12:291. [PMID: 30297983 PMCID: PMC6160587 DOI: 10.3389/fncel.2018.00291] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/09/2018] [Accepted: 08/14/2018] [Indexed: 11/24/2022] Open
Abstract
Active mechanical amplification of sound occurs in cochlear outer hair cells (OHCs) that change their length with oscillations of their membrane potential. Such length changes are the proposed cellular source of the cochlear amplifier, and prestin is the motor protein responsible for OHC electromotility. Previous findings have shown that mice lacking prestin displayed a loss of OHC electromotility, subsequent loss of distortion-product otoacoustic emissions, and a 40–60 dB increase in hearing thresholds. In this study we were interested in studying the functional consequences of the complete loss of cochlear amplification on neural coding of frequency selectivity, tuning, and temporal processing in the auditory midbrain. We recorded near-field auditory evoked potentials and multi-unit activity from the inferior colliculus (IC) of prestin (−/−) null and prestin (+/+) wild-type control mice and determined frequency response areas (FRAs), tuning sharpness, and gap detection to tone bursts and silent gaps embedded in broadband noise. We were interested in determining if the moderate to severe sensorineural hearing loss associated with the loss of motor protein prestin would also impair auditory midbrain temporal-processing measures, or if compensatory mechanisms within the brainstem could compensate for the loss of prestin. In prestin knockout mice we observed that there are severe impairments in midbrain tuning, thresholds, excitatory drive, and gap detection suggesting that brainstem and midbrain processing could not overcome the auditory processing deficits afforded by the loss of OHC electromotility mediated by the prestin protein.
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Affiliation(s)
- Joseph P Walton
- Department of Communication Sciences and Disorders, University of South Florida, Tampa, FL, United States.,Department of Chemical and Biomedical Engineering, University of South Florida, Tampa, FL, United States.,Global Center for Hearing and Speech Research, University of South Florida, Tampa, FL, United States
| | - Adam C Dziorny
- Department of Biomedical Engineering, University of Rochester, Rochester, NY, United States
| | - Olga N Vasilyeva
- Department of Neuroscience, The Ernest J. Del Monte Institute for Neuroscience, University of Rochester Medical Center, Rochester, NY, United States
| | - Anne E Luebke
- Department of Biomedical Engineering, University of Rochester, Rochester, NY, United States.,Department of Neuroscience, The Ernest J. Del Monte Institute for Neuroscience, University of Rochester Medical Center, Rochester, NY, United States
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5
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Xia A, Song Y, Wang R, Gao SS, Clifton W, Raphael P, Chao SI, Pereira FA, Groves AK, Oghalai JS. Prestin regulation and function in residual outer hair cells after noise-induced hearing loss. PLoS One 2013; 8:e82602. [PMID: 24376553 PMCID: PMC3869702 DOI: 10.1371/journal.pone.0082602] [Citation(s) in RCA: 55] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2013] [Accepted: 10/25/2013] [Indexed: 12/27/2022] Open
Abstract
The outer hair cell (OHC) motor protein prestin is necessary for electromotility, which drives cochlear amplification and produces exquisitely sharp frequency tuning. TectaC1509G transgenic mice have hearing loss, and surprisingly have increased OHC prestin levels. We hypothesized, therefore, that prestin up-regulation may represent a generalized response to compensate for a state of hearing loss. In the present study, we sought to determine the effects of noise-induced hearing loss on prestin expression. After noise exposure, we performed cytocochleograms and observed OHC loss only in the basal region of the cochlea. Next, we patch clamped OHCs from the apical turn (9–12 kHz region), where no OHCs were lost, in noise-exposed and age-matched control mice. The non-linear capacitance was significantly higher in noise-exposed mice, consistent with higher functional prestin levels. We then measured prestin protein and mRNA levels in whole-cochlea specimens. Both Western blot and qPCR studies demonstrated increased prestin expression after noise exposure. Finally, we examined the effect of the prestin increase in vivo following noise damage. Immediately after noise exposure, ABR and DPOAE thresholds were elevated by 30–40 dB. While most of the temporary threshold shifts recovered within 3 days, there were additional improvements over the next month. However, DPOAE magnitudes, basilar membrane vibration, and CAP tuning curve measurements from the 9–12 kHz cochlear region demonstrated no differences between noise-exposed mice and control mice. Taken together, these data indicate that prestin is up-regulated by 32–58% in residual OHCs after noise exposure and that the prestin is functional. These findings are consistent with the notion that prestin increases in an attempt to partially compensate for reduced force production because of missing OHCs. However, in regions where there is no OHC loss, the cochlea is able to compensate for the excess prestin in order to maintain stable auditory thresholds and frequency discrimination.
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MESH Headings
- Animals
- Cochlear Microphonic Potentials
- Evoked Potentials, Auditory, Brain Stem
- Gene Expression Regulation
- Hair Cells, Auditory, Outer/metabolism
- Hair Cells, Auditory, Outer/pathology
- Hearing Loss, Noise-Induced/metabolism
- Hearing Loss, Noise-Induced/pathology
- Hearing Loss, Noise-Induced/physiopathology
- Mice
- Models, Biological
- Molecular Motor Proteins/genetics
- Molecular Motor Proteins/metabolism
- Noise
- Otoacoustic Emissions, Spontaneous
- Patch-Clamp Techniques
- RNA, Messenger/genetics
- RNA, Messenger/metabolism
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Affiliation(s)
- Anping Xia
- Department of Otolaryngology–Head and Neck Surgery, Stanford University, Stanford, California, United States of America
| | - Yohan Song
- Department of Otolaryngology–Head and Neck Surgery, Stanford University, Stanford, California, United States of America
| | - Rosalie Wang
- Department of Otolaryngology–Head and Neck Surgery, Stanford University, Stanford, California, United States of America
| | - Simon S. Gao
- Department of Otolaryngology–Head and Neck Surgery, Stanford University, Stanford, California, United States of America
- Department of Bioengineering, Rice University, Houston, Texas, United States of America
| | - Will Clifton
- Bobby R. Alford Department of Otolaryngology – Head and Neck Surgery, Baylor College of Medicine, Houston, Texas, United States of America
| | - Patrick Raphael
- Department of Otolaryngology–Head and Neck Surgery, Stanford University, Stanford, California, United States of America
| | - Sung-il Chao
- Department of Otolaryngology–Head and Neck Surgery, Stanford University, Stanford, California, United States of America
- Department of Otolaryngology–Head and Neck Surgery, Chosun University, Gwangju, South Korea
| | - Fred A. Pereira
- Bobby R. Alford Department of Otolaryngology – Head and Neck Surgery, Baylor College of Medicine, Houston, Texas, United States of America
| | - Andrew K. Groves
- Department of Neuroscience, Baylor College of Medicine, Houston, Texas, United States of America
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas, United States of America
- Program in Developmental Biology, Baylor College of Medicine, Houston, Texas, United States of America
| | - John S. Oghalai
- Department of Otolaryngology–Head and Neck Surgery, Stanford University, Stanford, California, United States of America
- * E-mail:
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Selective ablation of pillar and deiters' cells severely affects cochlear postnatal development and hearing in mice. J Neurosci 2013; 33:1564-76. [PMID: 23345230 DOI: 10.1523/jneurosci.3088-12.2013] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023] Open
Abstract
Mammalian auditory hair cells (HCs) are inserted into a well structured environment of supporting cells (SCs) and acellular matrices. It has been proposed that when HCs are irreversibly damaged by noise or ototoxic drugs, surrounding SCs seal the epithelial surface and likely extend the survival of auditory neurons. Because SCs are more resistant to damage than HCs, the effects of primary SC loss on HC survival and hearing have received little attention. We used the Cre/loxP system in mice to specifically ablate pillar cells (PCs) and Deiters' cells (DCs). In Prox1CreER(T2)+/-;Rosa26(DTA/+) (Prox1DTA) mice, Cre-estrogen receptor (CreER) expression is driven by the endogenous Prox1 promoter and, in presence of tamoxifen, removes a stop codon in the Rosa26(DTA/+) allele and induces diphtheria toxin fragment A (DTA) expression. DTA produces cell-autonomous apoptosis. Prox1DTA mice injected with tamoxifen at postnatal days 0 (P0) and P1 show significant DC and outer PC loss at P2-P4, that reaches ∼70% by 1 month. Outer HC loss follows at P14 and is almost complete at 1 month, while inner HCs remain intact. Neural innervation to the outer HCs is disrupted in Prox1DTA mice and auditory brainstem response thresholds in adults are 40-50 dB higher than in controls. The hearing deficit correlates with loss of cochlear amplification. Remarkably, in Prox1DTA mice, the auditory epithelium preserves the ability to seal the reticular lamina and spiral ganglion neuron counts are normal, a key requirement for cochlear implant success. In addition, our results show that cochlear SC pools should be appropriately replenished during HC regeneration strategies.
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Yamashita T, Fang J, Gao J, Yu Y, Lagarde MM, Zuo J. Normal hearing sensitivity at low-to-middle frequencies with 34% prestin-charge density. PLoS One 2012; 7:e45453. [PMID: 23029017 PMCID: PMC3448665 DOI: 10.1371/journal.pone.0045453] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2012] [Accepted: 08/22/2012] [Indexed: 11/24/2022] Open
Abstract
The mammalian outer hair cells (OHCs) provide a positive mechanical feedback to enhance the cochlea's hearing sensitivity and frequency selectivity. Although the OHC-specific, somatic motor protein prestin is required for cochlear amplification, it remains unclear whether prestin can provide sufficient cycle-by-cycle feedback. In cochlear mechanical modeling, varying amounts of OHC motor activity should provide varying degrees of feedback efficiency to adjust the gain of cochlear amplifier at resonant frequencies. Here we created and characterized two new prestin-hypomorphic mouse models with reduced levels of wild-type prestin. OHCs from these mice exhibited length, total elementary charge movement (Qmax), charge density, and electromotility intermediate between those of wild-type and prestin-null mice. Remarkably, measurements of auditory brainstem responses and distortion product otoacoustic emissions from these mice displayed wild-type like hearing sensitivities at 4–22 kHz. These results indicate that as low as 26.7% Qmax, 34.0% charge density and 44.0% electromotility in OHCs were sufficient for wild-type-like hearing sensitivity in mice at 4–22 kHz, and that these in vitro parameters of OHCs did not correlate linearly with the feedback efficiency for in vivo gain of the cochlear amplifier. Our results thus provide valuable data for modeling cochlear mechanics and will stimulate further mechanistic analysis of the cochlear amplifier.
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Affiliation(s)
- Tetsuji Yamashita
- Department of Developmental Neurobiology, St. Jude Children's Research Hospital, Memphis, Tennessee, United States of America
| | - Jie Fang
- Department of Developmental Neurobiology, St. Jude Children's Research Hospital, Memphis, Tennessee, United States of America
| | - Jiangang Gao
- Department of Developmental Neurobiology, St. Jude Children's Research Hospital, Memphis, Tennessee, United States of America
| | - Yiling Yu
- Department of Developmental Neurobiology, St. Jude Children's Research Hospital, Memphis, Tennessee, United States of America
| | - Marcia Mellado Lagarde
- Department of Developmental Neurobiology, St. Jude Children's Research Hospital, Memphis, Tennessee, United States of America
| | - Jian Zuo
- Department of Developmental Neurobiology, St. Jude Children's Research Hospital, Memphis, Tennessee, United States of America
- * E-mail:
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8
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Progress in cochlear physiology after Békésy. Hear Res 2012; 293:12-20. [PMID: 22633944 DOI: 10.1016/j.heares.2012.05.005] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/18/2012] [Revised: 05/08/2012] [Accepted: 05/10/2012] [Indexed: 11/20/2022]
Abstract
In the fifty years since Békésy was awarded the Nobel Prize, cochlear physiology has blossomed. Many topics that are now current are things Békésy could not have imagined. In this review we start by describing progress in understanding the origin of cochlear gross potentials, particularly the cochlear microphonic, an area in which Békésy had extensive experience. We then review progress in areas of cochlear physiology that were mostly unknown to Békésy, including: (1) stereocilia mechano-electrical transduction, force production, and response amplification, (2) outer hair cell (OHC) somatic motility and its molecular basis in prestin, (3) cochlear amplification and related micromechanics, including the evidence that prestin is the main motor for cochlear amplification, (4) the influence of the tectorial membrane, (5) cochlear micromechanics and the mechanical drives to inner hair cell stereocilia, (6) otoacoustic emissions, and (7) olivocochlear efferents and their influence on cochlear physiology. We then return to a subject that Békésy knew well: cochlear fluids and standing currents, as well as our present understanding of energy dependence on the lateral wall of the cochlea. Finally, we touch on cochlear pathologies including noise damage and aging, with an emphasis on where the field might go in the future.
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10
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Eatock RA, Songer JE. Vestibular hair cells and afferents: two channels for head motion signals. Annu Rev Neurosci 2011; 34:501-34. [PMID: 21469959 DOI: 10.1146/annurev-neuro-061010-113710] [Citation(s) in RCA: 158] [Impact Index Per Article: 12.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Vestibular epithelia of the inner ear detect head motions over a wide range of amplitudes and frequencies. In mammals, afferent nerve fibers from central and peripheral zones of vestibular epithelia form distinct populations with different response dynamics and spike timing. Central-zone afferents are large, fast conduits for phasic signals encoded in irregular spike trains. The finer afferents from peripheral zones conduct more slowly and encode more tonic, linear signals in highly regular spike trains. The hair cells are also of two types, I and II, but the two types do not correspond directly to the two afferent populations. Zonal differences in afferent response dynamics may arise at multiple stages, including mechanoelectrical transduction, voltage-gated channels in hair cells and afferents, afferent transmission at calyceal and bouton synapses, and spike generation in regular and irregular afferents. In contrast, zonal differences in spike timing may depend more simply on the selective expression of low-voltage-activated ion channels by irregular afferents.
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Affiliation(s)
- Ruth Anne Eatock
- Department of Otology and Laryngology, Department of Neurobiology, Harvard Medical School, Boston, Massachusetts 02114, USA.
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Reduced electromotility of outer hair cells associated with connexin-related forms of deafness: an in silico study of a cochlear network mechanism. J Assoc Res Otolaryngol 2010; 11:559-71. [PMID: 20635191 DOI: 10.1007/s10162-010-0226-3] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2009] [Accepted: 06/23/2010] [Indexed: 10/19/2022] Open
Abstract
Mutations in the GJB2 gene encoding for the connexin 26 (Cx26) protein are the most common source of nonsyndromic forms of deafness. Cx26 is a building block of gap junctions (GJs) which establish electrical connectivity in distinct cochlear compartments by allowing intercellular ionic (and metabolic) exchange. Animal models of the Cx26 deficiency in the organ of Corti seem to suggest that the hearing loss and the degeneration of outer hair cells (OHCs) and inner hair cells is due to failed K(+) and metabolite homeostasis. However, OHCs can develop normally in some mutants, suggesting that the hair cells death is not the universal mechanism. In search for alternatives, we have developed an in silico large scale three-dimensional model of electrical current flow in the cochlea in the small signal, linearised, regime. The effect of mutations was analysed by varying the magnitude of resistive components representing the GJ network in the organ of Corti. The simulations indeed show that reduced GJ conductivity increases the attenuation of the OHC transmembrane potential at frequencies above 5 kHz from 6.1 dB/decade in the wild-type to 14.2 dB/decade. As a consequence of increased GJ electrical filtering, the OHC transmembrane potential is reduced by up to 35 dB at frequencies >10 kHz. OHC electromotility, driven by this potential, is crucial for sound amplification, cochlear sensitivity and frequency selectivity. Therefore, we conclude that reduced OHC electromotility may represent an additional mechanism underlying deafness in the presence of Cx26 mutations and may explain lowered OHC functionality in particular reported Cx26 mutants.
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