scholarly journals Cochlear amplification and tuning depend on the cellular arrangement within the organ of Corti

2018 ◽  
Vol 115 (22) ◽  
pp. 5762-5767 ◽  
Author(s):  
Hamid Motallebzadeh ◽  
Joris A. M. Soons ◽  
Sunil Puria
Keyword(s):  
Hair Cells ◽  
Outer Hair Cell ◽  
Basilar Membrane ◽  
Measurement Techniques ◽  
Organ Of Corti ◽  
Sensory Epithelium ◽  
Sound Levels ◽  
Cochlear Amplification ◽  
Sound Transduction ◽  
Deiters Cell

The field of cochlear mechanics has been undergoing a revolution due to recent findings made possible by advancements in measurement techniques. While it has long been assumed that basilar-membrane (BM) motion is the most important determinant of sound transduction by the inner hair cells (IHCs), it turns out that other parts of the sensory epithelium closer to the IHCs, such as the reticular lamina (RL), move with significantly greater amplitude for weaker sounds. It has not been established how these findings are related to the complex cytoarchitecture of the organ of Corti between the BM and RL, which is composed of a lattice of asymmetric Y-shaped elements, each consisting of a basally slanted outer hair cell (OHC), an apically slanted phalangeal process (PhP), and a supporting Deiters’ cell (DC). Here, a computational model of the mouse cochlea supports the hypothesis that the OHC micromotors require this Y-shaped geometry for their contribution to the exquisite sensitivity and frequency selectivity of the mammalian cochlea. By varying only the OHC gain parameter, the model can reproduce measurements of BM and RL gain and tuning for a variety of input sound levels. Malformations such as reversing the orientations of the OHCs and PhPs or removing the PhPs altogether greatly reduce the effectiveness of the OHC motors. These results imply that the DCs and PhPs must be properly accounted for in emerging OHC regeneration therapies.

Chlorpromazine Alters Cochlear Mechanics and Amplification: In Vivo Evidence for a Role of Stiffness Modulation in the Organ of Corti

2007 ◽  
Vol 97 (2) ◽  
pp. 994-1004 ◽  
Author(s):  
Jiefu Zheng ◽  
Niranjan Deo ◽  
Yuan Zou ◽  
Karl Grosh ◽  
Alfred L. Nuttall
Keyword(s):  
Outer Hair Cell ◽  
Basilar Membrane ◽  
Organ Of Corti ◽  
Lateral Wall ◽  
Mechanical Force ◽  
Dependent Manner ◽  
Concentration Dependent Manner ◽  
Cochlear Amplification

Although prestin-mediated outer hair cell (OHC) electromotility provides mechanical force for sound amplification in the mammalian cochlea, proper OHC stiffness is required to maintain normal electromotility and to transmit mechanical force to the basilar membrane (BM). To investigate the in vivo role of OHC stiffness in cochlear amplification, chlorpromazine (CPZ), an antipsychotic drug that alters OHC lateral wall biophysics, was infused into the cochleae in living guinea pigs. The effects of CPZ on cochlear amplification and OHC electromotility were observed by measuring the acoustically and electrically evoked BM motions. CPZ significantly reduced cochlear amplification as measured by a decline of the acoustically evoked BM motion near the best frequency (BF) accompanied by a loss of nonlinearity and broadened tuning. It also substantially reduced electrically evoked BM vibration near the BF and at frequencies above BF (≤80 kHz). The high-frequency notch (near 50 kHz) in the electrically evoked BM response shifted toward higher frequency in a CPZ concentration-dependent manner with a corresponding phase change. In contrast, salicylate resulted in a shift in this notch toward lower frequency. These results indicate that CPZ reduces OHC-mediated cochlear amplification probably via its effects on the mechanics of the OHC plasma membrane rather than via a direct effect on the OHC motor, prestin. Through modeling, we propose that with a combined OHC somatic and hair bundle forcing, the upward-shift of the ∼50-kHz notch in the electrically-evoked BM motion may indicate stiffness increase of the OHCs that is responsible for the reduced cochlear amplification.

scholarly journals All Three Rows of Outer Hair Cells Are Required for Cochlear Amplification

2015 ◽  
Vol 2015 ◽  
pp. 1-12 ◽  
Author(s):  
Michio Murakoshi ◽  
Sho Suzuki ◽  
Hiroshi Wada
Keyword(s):  
Hair Cells ◽  
Noise Exposure ◽  
Dynamic Range ◽  
Basilar Membrane ◽  
Organ Of Corti ◽  
High Sensitivity ◽  
Element Model ◽  
Outer Hair Cells ◽  
Displacement Amplitude ◽  
Cochlear Amplification

In the mammalian auditory system, the three rows of outer hair cells (OHCs) located in the cochlea are thought to increase the displacement amplitude of the organ of Corti. This cochlear amplification is thought to contribute to the high sensitivity, wide dynamic range, and sharp frequency selectivity of the hearing system. Recent studies have shown that traumatic stimuli, such as noise exposure and ototoxic acid, cause functional loss of OHCs in one, two, or all three rows. However, the degree of decrease in cochlear amplification caused by such functional losses remains unclear. In the present study, a finite element model of a cross section of the gerbil cochlea was constructed. Then, to determine effects of the functional losses of OHCs on the cochlear amplification, changes in the displacement amplitude of the basilar membrane (BM) due to the functional losses of OHCs were calculated. Results showed that the displacement amplitude of the BM decreases significantly when a single row of OHCs lost its function, suggesting that all three rows of OHCs are required for cochlear amplification.

scholarly journals The origin of mechanical harmonic distortion within the organ of Corti in living gerbil cochleae

2021 ◽  
Vol 4 (1) ◽  
Author(s):  
Wenxuan He ◽  
Tianying Ren
Keyword(s):  
Hair Cells ◽  
Outer Hair Cell ◽  
Basilar Membrane ◽  
Second Harmonic ◽  
Harmonic Distortion ◽  
Organ Of Corti ◽  
Outer Hair Cells ◽  
Experimental Animals ◽  
Cellular Origin ◽  
Low Coherence

AbstractAlthough 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.

scholarly journals Active outer hair cell motility can suppress vibrations in the organ of Corti

2020 ◽  
Author(s):  
T. Jabeen ◽  
J. C. Holt ◽  
J. R. Becker ◽  
J.-H. Nam
Keyword(s):  
Electrical Stimulation ◽  
Hair Cell ◽  
Hair Cells ◽  
Acoustic Pressure ◽  
Outer Hair Cell ◽  
Organ Of Corti ◽  
Sensory Epithelium ◽  
Outer Hair Cells ◽  
Cochlear Tuning ◽  
Cell Force

AbstractHigh sensitivity and selectivity of hearing require active cochlea. The cochlear sensory epithelium, the organ of Corti, vibrates due to external and internal excitations. The external stimulation is acoustic pressures mediated by the scala fluids, while the internal excitation is generated by a type of sensory receptor cells (the outer hair cells) in response to the acoustical vibrations. The outer hair cells are cellular actuators that are responsible for cochlear amplification. The organ of Corti is highly structured for transmitting vibrations originating from acoustic pressure and active outer hair cell force to the inner hair cells that synapse on afferent nerves. Understanding how the organ of Corti vibrates due to acoustic pressure and outer hair cell force is critical for explaining cochlear function. In this study, excised cochlear turns were freshly isolated from young gerbils. The organ of Corti in the excised cochlea was subjected to mechanical and electrical stimulation that are analogous to acoustical and cellular stimulation in the natural cochlea. Organ of Corti vibrations including those of individual outer hair cells were measured using optical coherence tomography. Respective vibration patterns due to mechanical and electrical stimulation were characterized. Interactions between the two vibration patterns were investigated by applying the two forms of stimulation simultaneously. Our results show that the interactions could be either constructive or destructive, which implies that the outer hair cells can either amplify or suppress vibrations in the organ of Corti. We discuss a potential consequence of the two interaction modes for cochlear frequency tuning.Statement of SignificanceThe function of the mammalian cochlea is characterized by sharp tuning and high-level of amplification. Both tuning and amplification are achieved mechanically through the action of cellular actuators in the sensory epithelium. According to widely accepted theory, cochlear tuning is achieved by ‘selectively amplifying’ acoustic vibrations. This study presents a set of data suggesting that the cochlear actuators can both amplify and suppress vibrations to enhance cochlear tuning. Presented results will explain why the actuator cells in the cochlea spend energy in the locations where there is no need for amplification.

A technique for protecting delicate specimens during processing

1989 ◽  
Vol 47 ◽  
pp. 982-983
Author(s):  
R.J. Mount ◽  
R.V. Harrison
Keyword(s):  
Basilar Membrane ◽  
Low Cost ◽  
Organ Of Corti ◽  
Region Of Interest ◽  
Sensory Epithelium ◽  
Physical Damage ◽  
Air Drying ◽  
Specimen Handling ◽  
Two Component

The sensory end organ of the ear, the organ of Corti, rests on a thin basilar membrane which lies between the bone of the central modiolus and the bony wall of the cochlea. In vivo, the organ of Corti is protected by the bony wall which totally surrounds it. In order to examine the sensory epithelium by scanning electron microscopy it is necessary to dissect away the protective bone and expose the region of interest (Fig. 1). This leaves the fragile organ of Corti susceptible to physical damage during subsequent handling. In our laboratory cochlear specimens, after dissection, are routinely prepared by the O-T- O-T-O technique, critical point dried and then lightly sputter coated with gold. This processing involves considerable specimen handling including several hours on a rotator during which the organ of Corti is at risk of being physically damaged. The following procedure uses low cost, readily available materials to hold the specimen during processing ,preventing physical damage while allowing an unhindered exchange of fluids.Following fixation, the cochlea is dehydrated to 70% ethanol then dissected under ethanol to prevent air drying. The holder is prepared by punching a hole in the flexible snap cap of a Wheaton vial with a paper hole punch. A small amount of two component epoxy putty is well mixed then pushed through the hole in the cap. The putty on the inner cap is formed into a “cup” to hold the specimen (Fig. 2), the putty on the outside is smoothed into a “button” to give good attachment even when the cap is flexed during handling (Fig. 3). The cap is submerged in the 70% ethanol, the bone at the base of the cochlea is seated into the cup and the sides of the cup squeezed with forceps to grip it (Fig.4). Several types of epoxy putty have been tried, most are either soluble in ethanol to some degree or do not set in ethanol. The only putty we find successful is “DUROtm MASTERMENDtm Epoxy Extra Strength Ribbon” (Loctite Corp., Cleveland, Ohio), this is a blue and yellow ribbon which is kneaded to form a green putty, it is available at many hardware stores.

scholarly journals Effects of coiling on the micromechanics of the mammalian cochlea

2005 ◽  
Vol 2 (4) ◽  
pp. 341-348 ◽  
Author(s):  
Hongxue Cai ◽  
Daphne Manoussaki ◽  
Richard Chadwick
Keyword(s):  
Outer Hair Cell ◽  
Basilar Membrane ◽  
Travelling Waves ◽  
Organ Of Corti ◽  
Tectorial Membrane ◽  
Governing Equations ◽  
Element Analysis ◽  
Curvature Effects ◽  
Curvilinear Coordinate ◽  
Cochlear Partition

The cochlea transduces sound-induced vibrations in the inner ear into electrical signals in the auditory nerve via complex fluid–structure interactions. The mammalian cochlea is a spiral-shaped organ, which is often uncoiled for cochlear modelling. In those few studies where coiling has been considered, the cochlear partition was often reduced to the basilar membrane only. Here, we extend our recently developed hybrid analytical/numerical micromechanics model to include curvature effects, which were previously ignored. We also use a realistic cross-section geometry, including the tectorial membrane and cellular structures of the organ of Corti, to model the apical and basal regions of a guinea-pig cochlea. We formulate the governing equations of the fluid and solid domains in a curvilinear coordinate system. The WKB perturbation method is used to treat the propagation of travelling waves along the coiled cochlear duct, and the O (1) system of the governing equations is solved in the transverse plane using finite-element analysis. We find that the curvature of the cochlear geometry has an important functional significance; at the apex, it greatly increases the shear gain of the cochlear partition, which is a measure of the bending efficiency of the outer hair cell stereocilia.

scholarly journals Vibration of the organ of Corti within the cochlear apex in mice

2014 ◽  
Vol 112 (5) ◽  
pp. 1192-1204 ◽  
Author(s):  
Simon S. Gao ◽  
Rosalie Wang ◽  
Patrick D. Raphael ◽  
Yalda Moayedi ◽  
Andrew K. Groves ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Phase Difference ◽  
Basilar Membrane ◽  
Organ Of Corti ◽  
Lateral Compartment ◽  
Outer Hair Cells ◽  
Supporting Cells ◽  
Tuning Curves ◽  
Cochlear Amplification

The tonotopic map of the mammalian cochlea is commonly thought to be determined by the passive mechanical properties of the basilar membrane. The other tissues and cells that make up the organ of Corti also have passive mechanical properties; however, their roles are less well understood. In addition, active forces produced by outer hair cells (OHCs) enhance the vibration of the basilar membrane, termed cochlear amplification. Here, we studied how these biomechanical components interact using optical coherence tomography, which permits vibratory measurements within tissue. We measured not only classical basilar membrane tuning curves, but also vibratory responses from the rest of the organ of Corti within the mouse cochlear apex in vivo. As expected, basilar membrane tuning was sharp in live mice and broad in dead mice. Interestingly, the vibratory response of the region lateral to the OHCs, the “lateral compartment,” demonstrated frequency-dependent phase differences relative to the basilar membrane. This was sharply tuned in both live and dead mice. We then measured basilar membrane and lateral compartment vibration in transgenic mice with targeted alterations in cochlear mechanics. Prestin499/499, Prestin−/−, and TectaC1509G/C1509G mice demonstrated no cochlear amplification but maintained the lateral compartment phase difference. In contrast, SfswapTg/Tg mice maintained cochlear amplification but did not demonstrate the lateral compartment phase difference. These data indicate that the organ of Corti has complex micromechanical vibratory characteristics, with passive, yet sharply tuned, vibratory characteristics associated with the supporting cells. These characteristics may tune OHC force generation to produce the sharp frequency selectivity of mammalian hearing.

scholarly journals Early appearance of key transcription factors influence the spatiotemporal development of the human inner ear

2019 ◽  
Vol 379 (3) ◽  
pp. 459-471 ◽  
Author(s):  
Lejo Johnson Chacko ◽  
Consolato Sergi ◽  
Theresa Eberharter ◽  
Jozsef Dudas ◽  
Helge Rask-Andersen ◽  
...  
Keyword(s):  
Transcription Factors ◽  
Inner Ear ◽  
Hair Cells ◽  
Transforming Growth Factor ◽  
Expression Patterns ◽  
Organ Of Corti ◽  
Sensory Epithelium ◽  
Receptor Expression ◽  
Cell Phenotype ◽  
Type I

AbstractExpression patterns of transcription factors leucine-rich repeat-containing G protein-coupled receptor 5 (LGR5), transforming growth factor-β-activated kinase-1 (TAK1), SRY (sex-determining region Y)-box 2 (SOX2), and GATA binding protein 3 (GATA3) in the developing human fetal inner ear were studied between the gestation weeks 9 and 12. Further development of cochlear apex between gestational weeks 11 and 16 (GW11 and GW16) was examined using transmission electron microscopy. LGR5 was evident in the apical poles of the sensory epithelium of the cochlear duct and the vestibular end organs at GW11. Immunostaining was limited to hair cells of the organ of Corti by GW12. TAK1 was immune positive in inner hair cells of the organ of Corti by GW12 and colocalized with p75 neurotrophic receptor expression. Expression for SOX2 was confined primarily to the supporting cells of utricle at the earliest stage examined at GW9. Intense expression for GATA3 was presented in the cochlear sensory epithelium and spiral ganglia at GW9. Expression of GATA3 was present along the midline of both the utricle and saccule in the zone corresponding to the striolar reversal zone where the hair cell phenotype switches from type I to type II. The spatiotemporal gradient of the development of the organ of Corti was also evident with the apex of the cochlea forming by GW16. It seems that highly specific staining patterns of several transcriptions factors are critical in guiding the genesis of the inner ear over development. Our findings suggest that the spatiotemporal gradient in cochlear development extends at least until gestational week 16.

scholarly journals Cochlear progenitor number is controlled through mesenchymal FGF receptor signaling

eLife ◽  
2015 ◽  
Vol 4 ◽  
Author(s):  
Sung-Ho Huh ◽  
Mark E Warchol ◽  
David M Ornitz
Keyword(s):  
Growth Factors ◽  
Hair Cells ◽  
Fibroblast Growth Factors ◽  
Organ Of Corti ◽  
Sensory Epithelium ◽  
Feedback Mechanism ◽  
Outer Hair Cells ◽  
Fibroblast Growth ◽  
Supporting Cells ◽  
Fgf Receptor

The sensory and supporting cells (SCs) of the organ of Corti are derived from a limited number of progenitors. The mechanisms that regulate the number of sensory progenitors are not known. Here, we show that Fibroblast Growth Factors (FGF) 9 and 20, which are expressed in the non-sensory (Fgf9) and sensory (Fgf20) epithelium during otic development, regulate the number of cochlear progenitors. We further demonstrate that Fgf receptor (Fgfr) 1 signaling within the developing sensory epithelium is required for the differentiation of outer hair cells and SCs, while mesenchymal FGFRs regulate the size of the sensory progenitor population and the overall cochlear length. In addition, ectopic FGFR activation in mesenchyme was sufficient to increase sensory progenitor proliferation and cochlear length. These data define a feedback mechanism, originating from epithelial FGF ligands and mediated through periotic mesenchyme that controls the number of sensory progenitors and the length of the cochlea.

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