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Zhu Z, Reid W, George SS, Ou V, Ó Maoiléidigh D. 3D morphology of an outer-hair-cell hair bundle increases its displacement and dynamic range. Biophys J 2024; 123:3433-3451. [PMID: 39161094 DOI: 10.1016/j.bpj.2024.08.009] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2023] [Revised: 05/22/2024] [Accepted: 08/13/2024] [Indexed: 08/21/2024] Open
Abstract
In mammals, outer-hair-cell hair bundles (OHBs) transduce sound-induced forces into receptor currents and are required for the wide dynamic range and high sensitivity of hearing. OHBs differ conspicuously in morphology from other types of bundles. Here, we show that the 3D morphology of an OHB greatly impacts its mechanics and transduction. An OHB comprises rod-like stereocilia, which pivot on the surface of its sensory outer hair cell. Stereocilium pivot positions are arranged in columns and form a V shape. We measure the pivot positions and determine that OHB columns are far from parallel. To calculate the consequences of an OHB's V shape and far-from-parallel columns, we develop a mathematical model of an OHB that relates its pivot positions, 3D morphology, mechanics, and receptor current. We find that the 3D morphology of the OHB can halve its stiffness, can double its damping coefficient, and causes stereocilium displacements driven by stimulus forces to differ substantially across the OHB. Stereocilium displacements drive the opening and closing of ion channels through which the receptor current flows. Owing to the stereocilium-displacement differences, the currents passing through the ion channels can peak versus the stimulus frequency and vary considerably across the OHB. Consequently, the receptor current peaks versus the stimulus frequency. Ultimately, the OHB's 3D morphology can increase its receptor-current dynamic range more than twofold. Our findings imply that potential pivot-position changes owing to development, mutations, or location within the mammalian auditory organ might greatly alter OHB function.
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Affiliation(s)
- Zenghao Zhu
- Department of Otolaryngology-Head and Neck Surgery, Stanford University, Stanford, California
| | - Wisam Reid
- Department of Otolaryngology-Head and Neck Surgery, Stanford University, Stanford, California; Harvard Medical School, Boston, Massachusetts
| | - Shefin Sam George
- Department of Otolaryngology-Head and Neck Surgery, Stanford University, Stanford, California
| | - Victoria Ou
- Department of Otolaryngology-Head and Neck Surgery, Stanford University, Stanford, California
| | - Dáibhid Ó Maoiléidigh
- Department of Otolaryngology-Head and Neck Surgery, Stanford University, Stanford, California.
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2
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Lukashkin AN, Russell IJ, Rybdylova O. Local cochlear mechanical responses revealed through outer hair cell receptor potential measurements. Biophys J 2024; 123:3163-3175. [PMID: 39014895 PMCID: PMC11427782 DOI: 10.1016/j.bpj.2024.07.015] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2023] [Revised: 03/26/2024] [Accepted: 07/12/2024] [Indexed: 07/18/2024] Open
Abstract
Sensory hair cells, including the sensorimotor outer hair cells, which enable the sensitive, sharply tuned responses of the mammalian cochlea, are excited by radial shear between the organ of Corti and the overlying tectorial membrane. It is not currently possible to measure directly in vivo mechanical responses in the narrow cleft between the tectorial membrane and organ of Corti over a wide range of stimulus frequencies and intensities. The mechanical responses can, however, be derived by measuring hair cell receptor potentials. We demonstrate that the seemingly complex frequency- and intensity-dependent behavior of outer hair cell receptor potentials could be qualitatively explained by a two degrees of freedom system with local cochlear partition and tectorial membrane resonances strongly coupled by the outer hair cell stereocilia. A local minimum in the receptor potential below the characteristic frequency should always be observed at a frequency where the tectorial membrane mechanical impedance is minimal, i.e., at the presumed tectorial membrane resonance frequency. The tectorial membrane resonance frequency might, however, shift with stimulus intensity in accordance with a shift in the maximum of the tectorial membrane radial mechanical responses to lower frequencies, as observed in experiments.
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Affiliation(s)
- Andrei N Lukashkin
- Sensory Neuroscience Research Group, School of Applied Science, University of Brighton, Brighton, United Kingdom.
| | - Ian J Russell
- Sensory Neuroscience Research Group, School of Applied Science, University of Brighton, Brighton, United Kingdom
| | - Oyuna Rybdylova
- Advanced Engineering Centre, School of Architecture, Technology and Engineering, University of Brighton, Brighton, United Kingdom.
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3
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Strimbu CE, Chiriboga LA, Frost BL, Olson ES. Regional differences in cochlear nonlinearity across the basal organ of Corti of gerbil: Regional differences in cochlear nonlinearity. Hear Res 2024; 443:108951. [PMID: 38277880 PMCID: PMC10922790 DOI: 10.1016/j.heares.2024.108951] [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: 07/14/2023] [Revised: 01/07/2024] [Accepted: 01/11/2024] [Indexed: 01/28/2024]
Abstract
Auditory sensation is based in nanoscale vibration of the sensory tissue of the cochlea, the organ of Corti complex (OCC). Motion within the OCC is now observable due to optical coherence tomography. In a previous study (Cooper et al., 2018), the region that includes the electro-motile outer hair cells (OHC) and Deiters cells (DC) was observed to move with larger amplitude than the basilar membrane (BM) and surrounding regions and was termed the "hotspot." In addition to this quantitative distinction, the hotspot moved qualitatively differently than the BM, in that its motion scaled nonlinearly with stimulus level at all frequencies, evincing sub-BF activity. Sub-BF activity enhances non-BF motion; thus the frequency tuning of the OHC/DC region was reduced relative to the BM. In this work we further explore the motion of the gerbil basal OCC and find that regions that lack significant sub-BF activity include the BM, the medial and lateral OCC, and the reticular lamina (RL) region. The observation that the RL region does not move actively sub-BF (already observed in Cho and Puria 2022), suggests that hair cell stereocilia are not exposed to sub-BF activity in the cochlear base. The observation that the lateral and RL regions move approximately linearly sub-BF indicates that linear forces dominate non-linear OHC-based forces on these components at sub-BF frequencies. A complex difference analysis was performed to reveal the internal motion of the OHC/DC region and showed that amplitude structure and phase shifts in the directly measured OHC/DC motion emerge due to the internal OHC/DC motion destructively interfering with BM motion.
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Affiliation(s)
- C Elliott Strimbu
- Department of Otolaryngology, Head and Neck Surgery, Columbia University Vagelos College of Physicians and Surgeons, 630 West 168th Street, New York City, NY 10032, USA
| | - Lauren A Chiriboga
- Department of Biomedical Engineering, Columbia University, 1210 Amsterdam Avenue, New York City, NY 10027, USA
| | - Brian L Frost
- Department of Electrical Engineering, Columbia University, 500 West 120th Street, New York City, NY 10027, USA
| | - Elizabeth S Olson
- Department of Otolaryngology, Head and Neck Surgery, Columbia University Vagelos College of Physicians and Surgeons, 630 West 168th Street, New York City, NY 10032, USA; Department of Biomedical Engineering, Columbia University, 1210 Amsterdam Avenue, New York City, NY 10027, USA.
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4
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Strimbu CE, Chiriboga LA, Frost BL, Olson ES. A frame and a hotspot in cochlear mechanics. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.06.29.547111. [PMID: 37873430 PMCID: PMC10592637 DOI: 10.1101/2023.06.29.547111] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/25/2023]
Abstract
Auditory sensation is based in nanoscale vibration of the sensory tissue of the cochlea, the organ of Corti complex (OCC). Motion within the OCC is now observable due to optical coherence tomography. In the cochlear base, in response to sound stimulation, the region that includes the electro-motile outer hair cells (OHC) was observed to move with larger amplitude than the basilar membrane (BM) and surrounding regions. The intense motion is based in active cell mechanics, and the region was termed the "hotspot" (Cooper et al., 2018, Nature comm). In addition to this quantitative distinction, the hotspot moved qualitatively differently than the BM, in that its motion scaled nonlinearly with stimulus level at all frequencies, evincing sub-BF activity. Sub-BF activity enhances non-BF motion; thus the frequency tuning of the hotspot was reduced relative to the BM. Regions that did not exhibit sub-BF activity are here defined as the OCC "frame". By this definition the frame includes the BM, the medial and lateral OCC, and most significantly, the reticular lamina (RL). The frame concept groups the majority OCC as a structure that is largely shielded from sub-BF activity. This shielding, and how it is achieved, are key to the active frequency tuning of the cochlea. The observation that the RL does not move actively sub-BF indicates that hair cell stereocilia are not exposed to sub-BF activity. A complex difference analysis reveals the motion of the hotspot relative to the frame.
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Zhang Y, Lin G, Xue N, Wang Y, Du T, Liu H, Xiong W, Shang W, Wu H, Song L. Differential outcomes of high-fat diet on age-related rescaling of cochlear frequency place coding. FASEB J 2023; 37:e23167. [PMID: 37651093 DOI: 10.1096/fj.202300457rr] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2023] [Revised: 08/01/2023] [Accepted: 08/14/2023] [Indexed: 09/01/2023]
Abstract
Auditory frequency coding is place-specific, which depends on the mechanical coupling of the basilar membrane-outer hair cell (OHC)-tectorial membrane network. Prestin-based OHC electromotility improves cochlear frequency selectivity and sensitivity. Cochlear amplification determines the frequency coding wherein discrete sound frequencies find a 'best' place along the cochlear length. Loss of OHC is the leading cause of age-related hearing loss (ARHL) and is the most common cause of sensorineural hearing loss and compromised speech perception. Lipid interaction with Prestin impacts OHC function. It has been established that high-fat diet (HFD) is associated with ARHL. To determine whether genetic background and metabolism preserve cochlear frequency place coding, we examined the effect of HFD in C57BL/6J (B6) and CBA/CaJ (CBA) on ARHL.We found a significant rescuing effect on ARHL in aged B6 HFD cohort. Prestin levels and cell sizes were better maintained in the experimental B6-HFD group. We also found that distortion product otoacoustic emission (DPOAE) group delay measurement was preserved, which suggested stable frequency place coding. In contrast, the response to HFD in the CBA cohort was modest with no appreciable benefit to hearing threshold. Notably, group delay was shortened with age along with the control. In addition, the frequency dependent OHC nonlinear capacitance gradient was most pronounced at young age but decreased with age. Cochlear RNA-seq analysis revealed differential TRPV1 expression and lipid homeostasis. Activation of TRPV1 and downregulation of arachidonic acid led to downregulation of inflammatory response in B6 HFD, which protects the cochlea from ARHL. The genetic background and metabolic state-derived changes in OHC morphology and function collectively contribute to a redefined cochlear frequency place coding and improved age-related pitch perception.
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Affiliation(s)
- Yu Zhang
- 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
| | - Guotong Lin
- 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
| | - Na Xue
- 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
| | - Yi Wang
- School of Life Sciences, Tsinghua University, Beijing, China
| | - Tingting Du
- 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
| | - Huihui Liu
- 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
| | - Wei Xiong
- Chinese Institute for Brain Research, Beijing, China
| | - Wei Shang
- Navy Clinical Medical School, Anhui Medical University, Hefei, China
- In Vitro Fertility (IVF) Center Department of Obstetrics and Gynecology, the Sixth Medical Center of PLA General Hospital, Beijing, China
- Department of Obstetrics and Gynecology, Chinese PLA General Hospital, Beijing, 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
| | - Lei Song
- 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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6
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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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7
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Dewey JB, Shera CA. Bandpass Shape of Distortion-Product Otoacoustic Emission Ratio Functions Reflects Cochlear Frequency Tuning in Normal-Hearing Mice. J Assoc Res Otolaryngol 2023:10.1007/s10162-023-00892-4. [PMID: 37072566 DOI: 10.1007/s10162-023-00892-4] [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: 09/19/2022] [Accepted: 02/02/2023] [Indexed: 04/20/2023] Open
Abstract
The frequency selectivity of the mammalian auditory system is critical for discriminating complex sounds like speech. This selectivity derives from the sharp tuning of the cochlea's mechanical response to sound, which is largely attributed to the amplification of cochlear vibrations by outer hair cells (OHCs). Due to its nonlinearity, the amplification process also leads to the generation of distortion products (DPs), some of which propagate out to the ear canal as DP otoacoustic emissions (DPOAEs). However, the insight that these signals provide about the tuned micro- and macro-mechanics underlying their generation remains unclear. Using optical coherence tomography to measure cochlear vibrations in mice, we show that the cochlea's frequency tuning is reflected in the bandpass shape that is observed in DPOAE amplitudes when the ratio of the two evoking stimulus frequencies is varied (here termed DPOAE "ratio functions"). The tuning sharpness of DPOAE ratio functions and cochlear vibrations co-varied with stimulus level, with a similar quantitative agreement in tuning sharpness observed for both apical and mid-cochlear locations. Measurement of intracochlear DPs revealed that the tuning of the DPOAE ratio functions was not caused by mechanisms that shape DPs locally near where they are generated. Instead, simple model simulations indicate that the bandpass shape is due to a more global wave interference phenomenon. It appears that the filtering of DPOAEs by wave interactions over an extended spatial region allows them to provide a window onto the frequency tuning of single cochlear locations.
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Affiliation(s)
- James B Dewey
- Caruso Department of Otolaryngology - Head and Neck Surgery, University of Southern California, Los Angeles, 90033, CA, USA.
| | - Christopher A Shera
- Caruso Department of Otolaryngology - Head and Neck Surgery, University of Southern California, Los Angeles, 90033, CA, USA
- Department of Physics and Astronomy, University of Southern California, Los Angeles, CA, 90089, USA
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8
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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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9
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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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Levic S, Lukashkina VA, Simões P, Lukashkin AN, Russell IJ. A Gap-Junction Mutation Reveals That Outer Hair Cell Extracellular Receptor Potentials Drive High-Frequency Cochlear Amplification. J Neurosci 2022; 42:7875-7884. [PMID: 36261265 PMCID: PMC9617611 DOI: 10.1523/jneurosci.2241-21.2022] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2021] [Revised: 08/02/2022] [Accepted: 09/02/2022] [Indexed: 11/21/2022] Open
Abstract
Cochlear amplification enables the enormous dynamic range of hearing through amplifying cochlear responses to low- to moderate-level sounds and compressing them to loud sounds. Amplification is attributed to voltage-dependent electromotility of mechanosensory outer hair cells (OHCs) driven by changing voltages developed across their cell membranes. At low frequencies, these voltage changes are dominated by intracellular receptor potentials (RPs). However, OHC membranes have electrical low-pass filter properties that attenuate high-frequency RPs, which should potentially attenuate amplification of high-frequency cochlear responses and impede high-frequency hearing. We made in vivo intracellular and extracellular electrophysiological measurements from the organ of Corti of male and female mice of the CBA/J strain, with excellent high-frequency hearing, and from the CD-1 mouse strain, which has sensitive hearing below 12 kHz but loses high-frequency hearing within a few weeks postpartum. The CD-1 mouse strain was transfected with an A88V mutation of the connexin 30 gap-junction protein. By blocking the action of the GJ protein to reduce input resistance, the mutation increased the OHC extracellular RP (ERP) magnitude and rescued high-frequency hearing. However, by increasing the organ of Corti resistance, the mutation rescued high-frequency hearing through preserving the OHC extracellular RP (ERP) magnitude. We measured the voltage developed across the basolateral membranes of OHCs, which controls their electromotility, for low- to high-frequency sounds in male and female mice of the CD-1 strain that expressed the A88V mutation. We demonstrate that ERPs, not RPs, drive OHC motility and cochlear amplification at high frequencies because at high frequencies, ERPs are not frequency attenuated, exceed RPs in magnitude, and are appropriately timed to provide cochlear amplification.SIGNIFICANCE STATEMENT Cochlear amplification, which enables the enormous dynamic range of hearing, is attributed to voltage-dependent electromotility of the mechanosensory outer hair cells (OHCs) driven by sound-induced voltage changes across their membranes. OHC intracellular receptor potentials are electrically low-pass filtered, which should hinder high-frequency hearing. We measured the intracellular and extracellular voltages that control OHC electromotility in vivo in a mouse strain with impaired high-frequency hearing. A gap-junction mutation of the strain rescued high-frequency hearing, increased organ of Corti resistance, and preserved large OHC extracellular receptor potentials but reduced OHC intracellular receptor potentials and impaired low-frequency hearing. We concluded intracellular potentials drive OHC motility at low frequencies and extracellular receptor potentials drive OHC motility and cochlear amplification at high frequencies.
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Affiliation(s)
- Snezana Levic
- Sensory Neuroscience Research Group, School of Pharmacy and Biomolecular Sciences, University of Brighton, Brighton BN2 4GJ, United Kingdom
- Brighton and Sussex Medical School, University of Sussex, Brighton BN1 9PX, United Kingdom
| | - Victoria A Lukashkina
- Sensory Neuroscience Research Group, School of Pharmacy and Biomolecular Sciences, University of Brighton, Brighton BN2 4GJ, United Kingdom
| | - Patricio Simões
- Sensory Neuroscience Research Group, School of Pharmacy and Biomolecular Sciences, University of Brighton, Brighton BN2 4GJ, United Kingdom
| | - Andrei N Lukashkin
- Sensory Neuroscience Research Group, School of Pharmacy and Biomolecular Sciences, University of Brighton, Brighton BN2 4GJ, United Kingdom
| | - Ian J Russell
- Sensory Neuroscience Research Group, School of Pharmacy and Biomolecular Sciences, University of Brighton, Brighton BN2 4GJ, United Kingdom
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11
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Burwood G, He WX, Fridberger A, Ren TY, Nuttall AL. Outer hair cell driven reticular lamina mechanical distortion in living cochleae. Hear Res 2022; 423:108405. [PMID: 34916081 PMCID: PMC9170269 DOI: 10.1016/j.heares.2021.108405] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/16/2021] [Revised: 10/25/2021] [Accepted: 11/25/2021] [Indexed: 11/17/2022]
Abstract
Cochlear distortions afford researchers and clinicians a glimpse into the conditions and properties of inner ear signal processing mechanisms. Until recently, our examination of these distortions has been limited to measuring the vibration of the basilar membrane or recording acoustic distortion output in the ear canal. Despite its importance, the generation mechanism of cochlear distortion remains a substantial task to understand. The ability to measure the vibration of the reticular lamina in rodent models is a recent experimental advance. Surprising mechanical properties have been revealed. These properties merit both discussion in context with our current understanding of distortion, and appraisal of the significance of new interpretations of cochlear mechanics. This review focusses on some of the recent data from our research groups and discusses the implications of these data on our understanding of vocalization processing in the periphery, and their influence upon future experimental directions. 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)
- G Burwood
- Department of Otolaryngology, Head and Neck Surgery, Oregon Health & Science University, Portland OR, United States
| | - W X He
- Department of Otolaryngology, Head and Neck Surgery, Oregon Health & Science University, Portland OR, United States
| | - A Fridberger
- Department of Biomedical and Clinical Sciences, Linköping University, Linköping, Sweden
| | - T Y Ren
- Department of Otolaryngology, Head and Neck Surgery, Oregon Health & Science University, Portland OR, United States
| | - A L Nuttall
- Department of Otolaryngology, Head and Neck Surgery, Oregon Health & Science University, Portland OR, United States.
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12
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Strimbu CE, Olson ES. Salicylate-induced changes in organ of Corti vibrations. Hear Res 2022; 423:108389. [PMID: 34774368 PMCID: PMC9058039 DOI: 10.1016/j.heares.2021.108389] [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: 07/08/2021] [Revised: 10/19/2021] [Accepted: 10/26/2021] [Indexed: 11/04/2022]
Abstract
Intra organ of Corti (OC) vibrations differ from those measured at the basilar membrane (BM), with higher amplitudes and a wide-band nonlinearity extending well below a region's best frequency. The vibrations are boosted by the cochlear amplifier, the active processes within the mammalian hearing organ, and are thus sensitive to metabolic or pharmacological manipulation. We introduced salicylate, a known blocker of outer hair cell (OHC) based electromotility, into the perilymphatic space by applying sodium salicylate onto the round window membrane. Vibration patterns of an area of the OC were mapped with phase sensitive optical coherence tomography before and after treatment; distortion product otoacoustic emissions (DPOAEs) were measured at similar times to assess the cochlear condition. Following treatment, all regions showed a loss of vibration amplitude and tuning while OHC-region vibrations retained their wide-band nonlinearity. OC vibrations, which had been relatively confined in a region including OHCs and extending to the BM at the outer pillar foot, became less confined with structures lateral to the OHCs sometimes exhibiting the highest amplitudes. Vibrations and DPOAEs could recover to baseline levels over approximately three hours post treatment. 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)
- C. Elliott Strimbu
- Columbia University, Department of Otolaryngology, 630 West 168th Street, New York, NY 10032, USA
| | - Elizabeth S. Olson
- Columbia University, Department of Otolaryngology, 630 West 168th Street, New York, NY 10032, USA
- Columbia University, Department of Biomedical Engineering, 1210 Amsterdam Avenue, New York, NY 10027 USA
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13
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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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14
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Nankali A, Shera CA, Applegate BE, Oghalai JS. Interplay between traveling wave propagation and amplification at the apex of the mouse cochlea. Biophys J 2022; 121:2940-2951. [PMID: 35778839 PMCID: PMC9388393 DOI: 10.1016/j.bpj.2022.06.029] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2021] [Revised: 03/08/2022] [Accepted: 06/27/2022] [Indexed: 11/18/2022] Open
Abstract
Sounds entering the mammalian ear produce waves that travel from the base to the apex of the cochlea. An electromechanical active process amplifies traveling wave motions and enables sound processing over a broad range of frequencies and intensities. The cochlear amplifier requires combining the global traveling wave with the local cellular processes that change along the length of the cochlea given the gradual changes in hair cell and supporting cell anatomy and physiology. Thus, we measured basilar membrane (BM) traveling waves in vivo along the apical turn of the mouse cochlea using volumetric optical coherence tomography and vibrometry. We found that there was a gradual reduction in key features of the active process toward the apex. For example, the gain decreased from 23 to 19 dB and tuning sharpness decreased from 2.5 to 1.4. Furthermore, we measured the frequency and intensity dependence of traveling wave properties. The phase velocity was larger than the group velocity, and both quantities gradually decrease from the base to the apex denoting a strong dispersion characteristic near the helicotrema. Moreover, we found that the spatial wavelength along the BM was highly level dependent in vivo, such that increasing the sound intensity from 30 to 90 dB sound pressure level increased the wavelength from 504 to 874 μm, a factor of 1.73. We hypothesize that this wavelength variation with sound intensity gives rise to an increase of the fluid-loaded mass on the BM and tunes its local resonance frequency. Together, these data demonstrate a strong interplay between the traveling wave propagation and amplification along the length of the cochlea.
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Affiliation(s)
- Amir Nankali
- Caruso Department of Otolaryngology-Head and Neck Surgery, University of Southern California, Los Angeles, California
| | - Christopher A Shera
- Caruso Department of Otolaryngology-Head and Neck Surgery, University of Southern California, Los Angeles, California; Department of Physics and Astronomy, University of Southern California, Los Angeles, California
| | - Brian E Applegate
- Caruso Department of Otolaryngology-Head and Neck Surgery, University of Southern California, Los Angeles, California
| | - John S Oghalai
- Caruso Department of Otolaryngology-Head and Neck Surgery, University of Southern California, Los Angeles, California.
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15
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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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16
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Zosuls A, Rupprecht LC, Mountain DC. Inner hair cell stereocilia displacement in response to focal stimulation of the basilar membrane in the ex vivo gerbil cochlea. Hear Res 2021; 412:108372. [PMID: 34775267 PMCID: PMC8756456 DOI: 10.1016/j.heares.2021.108372] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/05/2020] [Revised: 10/03/2021] [Accepted: 10/13/2021] [Indexed: 12/01/2022]
Abstract
The inner hair cells in the mammalian cochlea transduce mechanical signals to electrical signals that provide input to the auditory nerve. The spatial-temporal displacement of the inner hair cell stereocilia (IHCsc) relative to basilar membrane (BM) displacement is central to characterizing the transduction process. This study specifically focuses on measuring displacement of the stereocilia hair bundles in the radial dimensions where they are most sensitive. To simplify the mechanical response of the cochlear partition, a mechanical probe was used to drive the BM. Optical imaging was used to measure radial displacement of the inner hair cell stereocilia local to the probe in ex vivo gerbil cochleae. The mechanical probe displaced the BM in the transverse direction using sinusoidal stimuli with frequencies ranging from 10 Hz to 42.5 kHz. IHCsc displacement measurements were made in the radial dimension as a function of their longitudinal location along the length of the BM. The results were used to quantify the frequency response, longitudinal space coupling, traveling wave velocity, and wavelength of the radial displacement of the stereocilia. The measurements were centered at two best frequency locations along the BM: Proximal to the round window (first turn), and in the second turn. At both locations, frequency tuning was seen that was consistent with published place maps. At both locations, traveling waves were observed simultaneously propagating basal and apical from the probe. The velocity of the traveling waves at the center frequency (CF) of the location was higher in the first turn than in the second. As the stimulus frequency increased and approached CF for a location, the traveling wavelength decreased. Differential motion of the BM and IHCsc was observed in the second turn as the stimulus frequency increased toward CF. The longitudinal coupling measured in this study was longer than observed in previous studies. In summary the results suggest that the shape of the wave patterns present on the BM are not sufficient to characterize the displacement of the IHCsc.
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Affiliation(s)
- Aleksandrs Zosuls
- Hearing Research Center, Department of Biomedical Engineering, Boston University, 44 Cummington Mall, Boston, 02215, MA, United States.
| | - Laura C Rupprecht
- Hearing Research Center, Department of Biomedical Engineering, Boston University, 44 Cummington Mall, Boston, 02215, MA, United States.
| | - David C Mountain
- Hearing Research Center, Department of Biomedical Engineering, Boston University, 44 Cummington Mall, Boston, 02215, MA, United States
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17
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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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18
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He W, Ren T. The origin of mechanical harmonic distortion within the organ of Corti in living gerbil cochleae. Commun Biol 2021; 4:1008. [PMID: 34433876 PMCID: PMC8387486 DOI: 10.1038/s42003-021-02540-0] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2021] [Accepted: 08/11/2021] [Indexed: 11/09/2022] Open
Abstract
Although auditory harmonic distortion has been demonstrated psychophysically in humans and electrophysiologically in experimental animals, the cellular origin of the mechanical harmonic distortion remains unclear. To demonstrate the outer hair cell-generated harmonics within the organ of Corti, we measured sub-nanometer vibrations of the reticular lamina from the apical ends of the outer hair cells in living gerbil cochleae using a custom-built heterodyne low-coherence interferometer. The harmonics in the reticular lamina vibration are significantly larger and have broader spectra and shorter latencies than those in the basilar membrane vibration. The latency of the second harmonic is significantly greater than that of the fundamental at low stimulus frequencies. These data indicate that the mechanical harmonics are generated by the outer hair cells over a broad cochlear region and propagate from the generation sites to their own best-frequency locations.
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Affiliation(s)
- Wenxuan He
- Oregon Hearing Research Center, Department of Otolaryngology, Oregon Health & Science University, Portland, OR, USA
| | - Tianying Ren
- Oregon Hearing Research Center, Department of Otolaryngology, Oregon Health & Science University, Portland, OR, USA.
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19
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Wang Y, Steele CR, Puria S, Ricci AJ. In situ motions of individual inner-hair-cell stereocilia from stapes stimulation in adult mice. Commun Biol 2021; 4:958. [PMID: 34381157 PMCID: PMC8357788 DOI: 10.1038/s42003-021-02459-6] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2020] [Accepted: 07/12/2021] [Indexed: 11/09/2022] Open
Abstract
In vertebrate hearing organs, mechanical vibrations are converted to ionic currents through mechanoelectrical-transduction (MET) channels. Concerted stereocilia motion produces an ensemble MET current driving the hair-cell receptor potential. Mammalian cochleae are unique in that the tuning of sensory cells is determined by their mechanical environment and the mode of hair-bundle stimulation that their environment creates. However, little is known about the in situ intra-hair-bundle motions of stereocilia relative to one another, or to their environment. In this study, high-speed imaging allowed the stereocilium and cell-body motions of inner hair cells to be monitored in an ex vivo organ of Corti (OoC) mouse preparation. We have found that the OoC rotates about the base of the inner pillar cell, the hair bundle rotates about its base and lags behind the motion of the apical surface of the cell, and the individual stereocilia move semi-independently within a given hair bundle.
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Affiliation(s)
- Yanli Wang
- Otolaryngology-HNS, Stanford University, Stanford, CA, USA
- Mechanical Engineering, Stanford University, Stanford, CA, USA
- Massachusetts Eye and Ear, Harvard Medical School, Boston, MA, USA
| | | | - Sunil Puria
- Massachusetts Eye and Ear, Harvard Medical School, Boston, MA, USA
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20
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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: 18] [Impact Index Per Article: 6.0] [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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21
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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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22
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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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23
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McGowen MR, Tsagkogeorga G, Williamson J, Morin PA, Rossiter ASJ. Positive Selection and Inactivation in the Vision and Hearing Genes of Cetaceans. Mol Biol Evol 2020; 37:2069-2083. [DOI: 10.1093/molbev/msaa070] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Abstract
The transition to an aquatic lifestyle in cetaceans (whales and dolphins) resulted in a radical transformation in their sensory systems. Toothed whales acquired specialized high-frequency hearing tied to the evolution of echolocation, whereas baleen whales evolved low-frequency hearing. More generally, all cetaceans show adaptations for hearing and seeing underwater. To determine the extent to which these phenotypic changes have been driven by molecular adaptation, we performed large-scale targeted sequence capture of 179 sensory genes across the Cetacea, incorporating up to 54 cetacean species from all major clades as well as their closest relatives, the hippopotamuses. We screened for positive selection in 167 loci related to vision and hearing and found that the diversification of cetaceans has been accompanied by pervasive molecular adaptations in both sets of genes, including several loci implicated in nonsyndromic hearing loss. Despite these findings, however, we found no direct evidence of positive selection at the base of odontocetes coinciding with the origin of echolocation, as found in studies examining fewer taxa. By using contingency tables incorporating taxon- and gene-based controls, we show that, although numbers of positively selected hearing and nonsyndromic hearing loss genes are disproportionately high in cetaceans, counts of vision genes do not differ significantly from expected values. Alongside these adaptive changes, we find increased evidence of pseudogenization of genes involved in cone-mediated vision in mysticetes and deep-diving odontocetes.
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Affiliation(s)
- Michael R McGowen
- School of Biological and Chemical Sciences, Queen Mary, University of London, London, United Kingdom
- Department of Vertebrate Zoology, Smithsonian National Museum of Natural History, Washington, DC
| | - Georgia Tsagkogeorga
- School of Biological and Chemical Sciences, Queen Mary, University of London, London, United Kingdom
| | - Joseph Williamson
- School of Biological and Chemical Sciences, Queen Mary, University of London, London, United Kingdom
| | - Phillip A Morin
- Southwest Fisheries Science Center, National Marine Fisheries Service, NOAA, La Jolla, CA
| | - and Stephen J Rossiter
- School of Biological and Chemical Sciences, Queen Mary, University of London, London, United Kingdom
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24
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Two-tone distortion in reticular lamina vibration of the living cochlea. Commun Biol 2020; 3:35. [PMID: 31965040 PMCID: PMC6972885 DOI: 10.1038/s42003-020-0762-2] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2019] [Accepted: 01/06/2020] [Indexed: 11/09/2022] Open
Abstract
It has been demonstrated that isolated auditory sensory cells, outer hair cells, can generate distortion products at low frequencies. It remains unknown, however, whether or not motile outer hair cells are able to generate two-tone distortion at high frequencies in living cochleae under the mechanical loads caused by surounding tissues and fluids. By measuring sub-nanometer vibration directly from the apical ends of outer hair cells using a custom-built heterodyne low-coherence interferometer, here we show outer hair cell-generated two-tone distortion in reticular lamina motion in the living cochlea. Reticular-lamina distortion is significantly greater and occurs at a broader frequency range than that of the basilar membrane. Contrary to expectations, our results indicate that motile outer hair cells are capable of generating two-tone distortion in vivo not only at the locations tuned to primary tones but also at a broad region basal to these locations. Ren et al. used an in house heterodyne low-coherence interferometer to measure sub-nanometer vibrations, a proxy for distortion products, in living cochleae of gerbils. They were able to locate the generation source of the outer hair cell in the reticular lamina versus the basilar membrane in vivo.
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25
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Sellon JB, Ghaffari R, Freeman DM. The Tectorial Membrane: Mechanical Properties and Functions. Cold Spring Harb Perspect Med 2019; 9:cshperspect.a033514. [PMID: 30348837 DOI: 10.1101/cshperspect.a033514] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
The tectorial membrane (TM) is widely believed to play a critical role in determining the remarkable sensitivity and frequency selectivity that are hallmarks of mammalian hearing. Recently developed mouse models of human hearing disorders have provided new insights into the molecular, nanomechanical mechanisms that underlie resonance and traveling wave properties of the TM. Herein we review recent experimental and theoretical results detailing TM morphology, local poroelastic and electromechanical interactions, and global spread of excitation via TM traveling waves, with direct implications for cochlear mechanisms.
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Affiliation(s)
- Jonathan B Sellon
- Research Laboratory of Electronics, MIT, Cambridge, Massachusetts 02139
| | - Roozbeh Ghaffari
- Research Laboratory of Electronics, MIT, Cambridge, Massachusetts 02139
| | - Dennis M Freeman
- Research Laboratory of Electronics, MIT, Cambridge, Massachusetts 02139.,Department of Electrical Engineering and Computer Science, MIT, Cambridge, Massachusetts 02139
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26
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Burwood GWS, Fridberger A, Wang RK, Nuttall AL. Revealing the morphology and function of the cochlea and middle ear with optical coherence tomography. Quant Imaging Med Surg 2019; 9:858-881. [PMID: 31281781 PMCID: PMC6571188 DOI: 10.21037/qims.2019.05.10] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2019] [Accepted: 05/09/2019] [Indexed: 01/17/2023]
Abstract
Optical coherence tomography (OCT) has revolutionized physiological studies of the hearing organ, the vibration and morphology of which can now be measured without opening the surrounding bone. In this review, we provide an overview of OCT as used in the otological research, describing advances and different techniques in vibrometry, angiography, and structural imaging.
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Affiliation(s)
- George W. S. Burwood
- Department of Otolaryngology, Oregon Hearing Research Center/HNS, Oregon Health & Science University, Portland, OR, USA
| | - Anders Fridberger
- Department of Otolaryngology, Oregon Hearing Research Center/HNS, Oregon Health & Science University, Portland, OR, USA
- Department of Clinical and Experimental Medicine, Section for Neurobiology, Linköping University, Linköping, Sweden
| | - Ruikang K. Wang
- Department of Bioengineering and Department of Ophthalmology, University of Washington, Seattle, WA, USA
| | - Alfred L. Nuttall
- Department of Otolaryngology, Oregon Hearing Research Center/HNS, Oregon Health & Science University, Portland, OR, USA
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27
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Sellon JB, Azadi M, Oftadeh R, Nia HT, Ghaffari R, Grodzinsky AJ, Freeman DM. Nanoscale Poroelasticity of the Tectorial Membrane Determines Hair Bundle Deflections. PHYSICAL REVIEW LETTERS 2019; 122:028101. [PMID: 30720330 PMCID: PMC6813812 DOI: 10.1103/physrevlett.122.028101] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/26/2018] [Revised: 10/14/2018] [Indexed: 06/09/2023]
Abstract
Stereociliary imprints in the tectorial membrane (TM) have been taken as evidence that outer hair cells are sensitive to shearing displacements of the TM, which plays a key role in shaping cochlear sensitivity and frequency selectivity via resonance and traveling wave mechanisms. However, the TM is highly hydrated (97% water by weight), suggesting that the TM may be flexible even at the level of single hair cells. Here we show that nanoscale oscillatory displacements of microscale spherical probes in contact with the TM are resisted by frequency-dependent forces that are in phase with TM displacement at low and high frequencies, but are in phase with TM velocity at transition frequencies. The phase lead can be as much as a quarter of a cycle, thereby contributing to frequency selectivity and stability of cochlear amplification.
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Affiliation(s)
- Jonathan B. Sellon
- Research Laboratory of Electronics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
| | - Mojtaba Azadi
- School of Engineering, College of Science and Engineering, San Francisco State University, San Francisco, CA 94132, USA
- Center for Biomedical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139
- Department of Biological Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - Ramin Oftadeh
- Center for Biomedical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139
- Department of Biological Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - Hadi Tavakoli Nia
- Massachusetts General Hospital, Harvard Medical School, Boston, MA 02114, USA
| | - Roozbeh Ghaffari
- Research Laboratory of Electronics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
| | - Alan J. Grodzinsky
- Center for Biomedical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139
- Department of Biological Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
- Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
- Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - Dennis M. Freeman
- Research Laboratory of Electronics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
- Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
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28
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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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29
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Fritzsch B, Elliott KL. Auditory Nomenclature: Combining Name Recognition With Anatomical Description. Front Neuroanat 2018; 12:99. [PMID: 30532697 PMCID: PMC6265345 DOI: 10.3389/fnana.2018.00099] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2018] [Accepted: 11/05/2018] [Indexed: 01/20/2023] Open
Abstract
The inner ear and its two subsystems, the vestibular and the auditory system, exemplify how the identification of distinct cellular or anatomical elements ahead of elucidating their function, leads to a medley of anatomically defined and recognition oriented names that confused generations of students. Past attempts to clarify this unyielding nomenclature had incomplete success, as they could not yet generate an explanatory nomenclature. Building on these past efforts, we propose a somewhat revised nomenclature that keeps most of the past nomenclature as proposed and follows a simple rule: Anatomical and explanatory terms are combined followed, in brackets, by the name of the discoverer (see Table 1). For example, the "organ of Corti" will turn into the spiral auditory organ (of Corti). This revised nomenclature build as much as possible on existing terms that have explanatory value while keeping the recognition of discoverers alive to allow a transition for those used to the eponyms. Once implements, the proposed terminology should help future generations in learning the structure-function correlates of the ear more easily. To facilitate future understanding, leading genetic identifiers for a given structure have been added wherever possible.
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Affiliation(s)
- Bernd Fritzsch
- Department of Biology, The University of Iowa, Iowa City, IA, United States
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30
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Elliott KL, Fritzsch B, Duncan JS. Evolutionary and Developmental Biology Provide Insights Into the Regeneration of Organ of Corti Hair Cells. Front Cell Neurosci 2018; 12:252. [PMID: 30135646 PMCID: PMC6092489 DOI: 10.3389/fncel.2018.00252] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2018] [Accepted: 07/23/2018] [Indexed: 01/19/2023] Open
Abstract
We review the evolution and development of organ of Corti hair cells with a focus on their molecular differences from vestibular hair cells. Such information is needed to therapeutically guide organ of Corti hair cell development in flat epithelia and generate the correct arrangement of different hair cell types, orientation of stereocilia, and the delayed loss of the kinocilium that are all essential for hearing, while avoiding driving hair cells toward a vestibular fate. Highlighting the differences from vestibular organs and defining what is known about the regulation of these differences will help focus future research directions toward successful restoration of an organ of Corti following long-term hair cell loss.
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Affiliation(s)
- Karen L Elliott
- Department of Biology, University of Iowa, Iowa City, IA, United States
| | - Bernd Fritzsch
- Department of Biology, University of Iowa, Iowa City, IA, United States
| | - Jeremy S Duncan
- Department of Biological Sciences, Western Michigan University, Kalamazoo, MI, United States
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