Mammalin cochlear supporting cells transdifferentiation into outer hair cells

Objective To study the recovery of the outer hair cells in the bat cochlea after gentamicin exposure. Methods Bats were injected with a daily dose of gentamicin for 15 consecutive days and bromodeoxyuridine (BrdU) was given from day 16 to day 40 of this recovery phase. Hearing was assessed by overt acoustic behavior and auditory brainstem responses analysis, which was performed one day prior to the first injection and a day after the last injection (day 16). On day 40 animals were sacrificed for detection of cells that could take up BrdU. Results After 15 days of gentamicin treatment, all of the animals were proved to be deafened with significant increases of ABR thresholds, compared with control group. The findings in immunocytochemical stained samples and scanning electron microscopy revealed that BrdU labeled nuclei were observed in the cochlea in all of the deafened animals most commonly in the regions of the first-row and second-row Deiter’s cells (DCs) and occasionally in the regions of the third-row DCs. Conclusion We suggest that, under sufficient drug and enough time, the bat cochlear supporting cells can directly transdifferentiate into the outer hair cells after aminoglycoside exposure. This transdifferentation process is essential for repair of outer hair cells and recovery of normal function after gentamicin exposure.

Acetylcholine-induced calcium oscillation in isolated outer hair cells in guinea pig

Objective This study is to explore the relationship between acetylcholine(ACh)-induced calcium release from intracellular Ca2+ stores and function of outer hair cell(OHC) motors, in an attempt to elucidate the mechanism of OHC electromotility at resting state. Methods OHCs were isolated from adult guinea pig (200-300 g) cochlea and loaded with Fluo-3/AM. The cells were treated with ACh/dHBSS, ACh/HBSS, dHBSS only or HBSS only. Intracellular [Ca2+]i variations in cells under the four treatments were observed using an Ar-Kr laser scan confocal microscope. Results [Ca2+]i oscillations were recorded in five OHCs treated with ACh/dHBSS but not in other cells. This is the first time that Ach-excited [Ca2+]i oscillations are reported in guinea pig OHCs independent of extracellular calcium. Conclusions ACh-excited [Ca2+]i oscillations in OHCs originates from intracellular calcium release and may play a crucial role in maintaining active mechanical motility of the OHC at resting and modulating OHC electromotility.

Protective effects of the cochlear efferent system on the outer hair cells against intense sound:evidences from DPOAEs

It has been revealed in recent years that contralateral acoustic stimulation can affect cochlear active mechanisms through activating medial olivocochlear system (MOC) of the cochlear efferent nerve fibers. The MOC is therefore postulated to exert protective effects on outer hair cells (OHCs) under intense sound condition. In this study the effects of 4 kHz intense tone exposure on distortion product otoacoustic emissions (DPOAEs) in guinea pigs with and without contralateral white noise stimulation were observed so that to investigate the protective effects of MOC on OHCs. The results showed that DPOAEs obviously deceased after the intense tone exposure in all animals, while both the amplitude reduction and the affected frequency range of DPOAEs were smaller in animals with simultaneously delivered contralateral white noise during the tone exposure than that in animals without colltralateral acoustic stimulation. The above results may suggest some protective nature of the contralateral sound stimulating effects which might be mediated through the activity of MOC. These perhaps can serve as the evidence that the protective mechanism against intense sound operates in the outer hair cells which are strongly innervated by MOC

Distribution of Prestin on Outer Hair Cell Basolateral Surface

Prestin has been identified as a motor protein responsible for outer hair cell (OHC) electromotility and is expressed on the OHC surface. Previous studies revealed that OHC electromotility and its associated nonlinear capacitance were mainly located at the OHC lateral wall and absent at the apical cuticular plate and the basal nucleus region. Immunofluorescent staining for prestin also failed to demonstrate prestin expression at the OHC basal ends in whole-mount preparation of the organ of Corti. However, there lacks a definitive demonstration of the pattern of prestin distribution. The OHC lateral wall has a trilaminate organization and is composed of the plasma membrane, cortical lattice, and subsurface cisternae. In this study, the location of prestin proteins in dissociated OHCs was examined using immunofluorescent staining and confocal microscopy. We found that prestin was uniformly expressed on the basolateral surface, including the basal pole. No staining was seen on the cuticular plate and stereocilia. When co-stained with a membrane marker di-8-ANEPPS, prestin-labeling was found to be in the outer layer of the OHC lateral wall. After separating the plasma membrane from the underlying subsurface cisternae using a hypotonic extracellular solution, prestin-labeling was found to be in the plasma membrane, not the subsurface cisternae. The data show that prestin is expressed in the plasma membrane on the entire OHC basolateral surface.

Forward masking in distinguishing inner and outer hair cell damage

Forward Masking Temporal audiotory resolution is the ability of the auditory system to resolve auditory signals in the time domain. Forward masking is a means of studying temporal resolution where one tone, the probe, is masked by a preceding tone, the masker. Forward masking is

Quantitative Relations between Outer Hair Cell Electromotility and Nonlinear Capacitance

The electrically evoked somatic motility of outer hair cells （OHC）, briefly termed OHC electromotility, plays a crucial role in cochlear amplification that underlies the remarkably high sensitivity and frequency selectivity of the mammalian hearing. Accompanying OHC electromotility is a voltage-dependent gating charge movement within the cell lateral membrane, manifested as a measurable nonlinear capacitance （NLC） in OHCs. The electromotility and NLC of OHCs are highly correlated by sharing a common molecular substrate, the motor protein prestin. In this study, we systematically characterized the quantitative relationship between OHC electromotility and NLC in their voltage dependences for the purpose of further understanding the electromechanical transduction in OHCs. The results demonstrated that the two possess differing voltage dependences with the V^2 of electromotility consistently being -20 mV depolarized in comparison with that of NLC although their slope factors a are statistically identical. Further investigations showed that the initial state of OHCs influences the voltage dependence of electromotility but not that of NLC, indicating that some biophysical factors other than the motor protein per se are involved in the process of OHC length changes. We proposed that the cytoskeletal spectrin-actin framework underneath the OHC plasma membrane and the cell＇ s turgor are the two most probable factors that cause the voltage-dependence discrepancy between OHC electromotility and NLC.

Measurement of Ca^(2+) Flow in Cochlear Cells Using Non-Invasive Micro-Test Technique

Objective To test Calcium ion(Ca2+) flow at the head and end of outer hair cells(OHCs) in resting state and in response to Nimodipine treatment.Methods Non-invasive micro-test techniques were used to study Ca2+ in isolated OHCs in adult guinea pigs.Results Four types of Ca2+ transport were identified in OHCs on basilar membrane tissue fragments:influx at the head of with efflux at the bottom(type 1):efflux at the head of OHCs with influx at the bottom(type 2);influx at the both head and bottom(type 3);and efflux at the both head and bottom(type 4).However,only type 1 and type 3 of Ca2+ ion transport were detected in the cochlea.We propose that Ca2+ ion transport exists in adult guinea pig cochlear OHCs in resting state and is variable.Ca2 + flow in OHC can be inhibited by Nimodipine in resting state.

Neurodynamics analysis of cochlear hair cell activity

There have been many studies on the effect of cochlea basal membrane movement on the resolution of different frequencies and intensities.However,these studies did not take into account the influence of power and energy consumption of the hair cells in the process of the electromotility movement,as well as the neurodynamic mechanism that produced this effect.This makes previous studies unable to fully clarify the function of outer hair cells(OHCs)and the mechanism of sound amplification.To this end,we introduce the gate conductance characteristics of the hair cells in the mechanical process of increasing frequency selectivity.The research finds that the low attenuation of OHCs membrane potential and the high gain in OHC power and energy consumption caused that OHC amplification is driven by electromotility.The research results show that the amplification of the OHCs is driven by low attenuation of membrane potential and high gain of power and energy consumption.This conclusion profoundly reveals the physiological mechanism of the electromotility movement.

Noise exposure induced cochlear hair cell death pathways in guinea pig

Objective To understand the mechanism of noise exposure induced outer hair cells(OHCs) death pathways. Methods Thirty two guinea pigs were used in this study. The animals were either exposed for 4 h/day to broadband noise at 122 dB SPL (A-weighted) for 2 consecutive days or perfused with MNNG. After auditory test, the cochleae of animals were dissected. Propidium iodide (PI), a DNA intercalating fluorescent probe, was used to trace morphological changes in OHC nuclei. F-actin staining was used to determine missing OHCs. Caspase-3 was detected in living organ of Corti whole mounts using the fluorescent probe. The single strand DNA (ssDNA) in apoptotic OHCs in guinea pigs and apoptosis inducing factor (AIF) in hair cells in guinea pigs were examined by immunohistology method. Whole mounts of organ of Corti were prepared. Morphological and fluorescent changes were examined under a confocal microscope. Results (1) Both apoptotic and necrotic hair cells appeared following noise exposure. (2) Noise exposure induced single strand DNA in apoptotic OHCs but not in the normal OHCs. (3) Either after noise exposure or after MNNG perfusion, apoptotic OHCs were featured by nuclear condensation or fragmentation with caspase-3 activation, whereas necrotic OHCs were characterized by nuclear swelling without caspase-3 activation. (4) In normal organ of Corti, AIF was located in the mitochondria areas. After noise exposure, AIF was translocated from mitochondria in apoptotic and necrotic OHCs. Conclusion These findings indicate that noise exposure damages DNA in the OHC, which triggers action of Caspase-3. Subsequently, AIF is translocated to the nucleus, leading to DNA damage and OHCs death.

Characterization of spontaneous otoacoustic emissions in 2–4 day old neonates with respect to gender and ear

BACKGROUND： Spontaneous otoacoustic emissions （SOAEs） are regarded as a valuable audio- metric parameter that objectively reflects the function of outer hair cells （OHCs）. Many studies have reported that the incidence of SOAEs in adults is less than 50%. Therefore, measurement of SOAEs may be of little value to clinical examinations. However, the incidence of SOAEs in infants and neonates is higher than in adults. OBJECTIVE： To analyze the basic characteristics of SOAEs in 2–4 day old neonates, and to demonstrate the difference in OHC function between sexes and ears. DESIGN, TIME AND SETTING： Neurophysiological contrast study, performed in the Department of Neonates, Beijing Chaoyang Hospital, Capital Medical University, between December 2007 and August 2008. PARTICIPANTS： A total of 112 newborns （224 ears） consisting of 59 females and 53 males were included in this study. METHODS： The probe was adapted and embedded in the neonate external auditory canal with a foam rubber earplug after checking and clearing up the outer ear canal. The presence of SOAEs was determined when the signal amplitude had a clear peak exceeding –30 dB, or was 3 dB above the noise floor. MAIN OUTCOME MEASURES： The incidence of SOAEs, the number of SOAE signal peaks, and the maximal tension of SOAEs. RESULTS： The incidence in females （79.7%） was higher than males （76.4%） （P 〉 0.05）, and the incidence in right ears （86.6%） was higher than in left ears （69.6%） （P 〈 0.05）. There were no significant difference in the number of SOAE peaks between females and males （4.49 vs. 4.28）, or between right ears and left ears （4.62 vs. 4.12） （P 〉 0.05）. The mean maximum SOAE level per ear in females （–3.29 ± 9.28） dB sound pressure level （SPL） was slightly higher than that in males （–3.91 ± 9.14） dB SPL （P 〉 0.05）. Also, the mean maximum SOAE level in right ears （–2.03 ± 9.11） dB SPL was higher than in left ears （–5.50 ± 9.65） dB SPL （P 〈 0.05）. The maximum SOAE level showed a positive correlation with maximum SOAE number in emitting ears （r = 0.55, P 〈 0.01）. CONCLUSION： The incidence of SOAEs in neonates is high （78.1%） within 4 days of birth. The in-cidence of SOAEs and the maximum SOAE level exhibited a significant difference between right and left ears, but the difference between sexes was insignificant. Both the strongest SOAE signal peak and number of SOAEs per ear are representative of the function OHCs.

Effect of age on click-evoked otoacoustic emission A systematic review

OBJECTIVE：The aims of this study were to investigate the changes of the total intensity of transient evoked otoacoustic emission（TEOAE） and signal-to-noise ratio in various frequency bands as a function of aging,and to explore the role of age-related decline of cochlear outer hair cells.DATA SOURCES：The literature was searched using the PubMed database using ＇transient-evoked otoacoustic emissions＇ as a keyword.Articles were limited as follows：Species was ＇Humans＇;languages were ＇English and Chinese＇;publication date between 1990-01-01 and 2010-12-31.The references of the found were also searched to obtain additional articles.DATA SELECTION：Inclusion criteria：（1） Articles should involve the total TEOAE level or signal-to-noise ratio.（2） The measurement and analysis system used was Otodynamics ILO analysis system（ILO88,ILO92,ILO96 or ILO292）.（3） Studies involved groups of greater than 10 subjects and TEOAE results were from normally hearing ears.（4） If more papers from the same author or laboratory analyzed the same subjects,only one was used.MAIN OUTCOME MEASURES：The correlations of the age scale with the total level and signal-to-noise ratio of TEOAE was determined,respectively.RESULTS：（1） TEOAE total level gradually increased until 2 months of age,and then decreased with increasing age.Significant negative correlations between total TEOAE level and age were found（r =-0.885,P = 0.000）.（2） The most rapid decrease of TEOAE amplitude occurred at 1 year old.The total TEOAE level decreased about 4.25 dB SPL between 2 months to 1 year old,then about 0.26-0.52 dB SPL from 1 year to 10 years old,about 0.23 dB SPL from 11 years to 25 years old,and about 0.14 dB SPL from 26 years to 60 years old.（3） The signal-to-noise ratio in the frequency bands centered at 1.5,2,3 and 4 kHz decreased with increasing age after 2 months of age.Significant negative correlations between the signal-to-noise ratio and age were found for frequency bands ranging from 1.5 kHz to 4 kHz,with the highest correlations at 4 kHz（r =-0.890,P 〈 0.01）,then at 3 kHz（r =-0.889,P 〈 0.01）,at 2 kHz（r =-0.850,P 〈 0.01） and at 1.5 kHz（r =-0.705,P 〈 0.05）.Conversely,a positive correlation between the signal-to-noise ratio centered at 1 kHz and age was found,but was not statistically significant（r = 0.298,P = 0.374）.CONCLUSION：The total TEOAE response level decreased with increasing age after the first 2 months of age.The signal-to-noise ratio also decreased with increasing age in frequency bands above 1.5 kHz.The signal-to-noise ratio in higher frequencies decreased faster than in lower frequencies,leading to the maximum signal-to-noise ratio shift form 3.2-4.0 kHz in neonates to 1.5 kHz in adults,and further decreasing the total TEOAE response level.The age-related TEOAE spectrum peak shift is most likely because the outer hair cells functioning in higher frequencies are more prone to damage than those for lower frequencies.

Otoacoustic emissions value in patients with idiopathic sudden sensorineural hearing loss

Objectives:This study aimed to determine the prognostic value of otoacoustic emissions(OAEs)in idiopathic sudden sensorineural hearing loss patients.Methods:The study included 30 subjects with unilateral idiopathic sudden sensorineural hearing loss(ISSNHL).Each patient was evaluated four times:at baseline and after one week,one month,and three months of treatment.During each visit,each patient was subjected to full audiological history,otoscopic examination,basic audiological evaluations,and transiently evoked and distortion product otoacoustic emission(TEOAEs&DEOAEs).Results:The hearing thresholds(frequency range 250e8000 Hz)and word recognition scores of patients with detectable TEOAEs and DPOAEs improved significantly,whereas no significant improvements were observed in those with no response.Conclusion:Hearing improvement is better in patients with detectable TEOAEs and DPOAEs.As a result,TEOAEs and DPOAEs are recommended as routine tests in all SSNHL patients to predict outcomes and monitor treatment as TEOAEs and DPOAEs reflect the cochlear OHCs activity.

Mechanical model of organ of Corti

According to the vibration characteristics of the organ of Corti （OC）, seven hypotheses are made to simplify the structure of the model, and a mechanical OC model is established. Using the variational principle, a displacement analytical expression is solved under a certain pressure. The results are in good agreement with experimental data, showing the validity of the formula. Combined with the damage caused by noise in clinic, it is found that the hardening of outer hair cells and outer stereocilia can lead to loss of hearing and generation of threshold shift. In addition, the results show that high frequency resonance occurs at the bottom of the basilar membrane （BM）, and low frequency resonance occurs at the top of the BM. This confirms the frequency selective characteristics of the BM. Further, using this formula can avoid interference of the envi- ronment and the technical level of the test personnel, and can evaluate performance of the OC objectively.

Prestin forms tetramer with each subunit being mechanically independent

Prestin is the motor protein of cochlear outer hair cells （OHCs）. It is able to perform rapid and reciprocal electromechanical conversion that underlies OHC electromotility. Due to the inadequate size of a single prestin molecule to form the2 nm intramembraneous protein particles （IMPs） in the OHC lateral membrane （LM）, the possibility of prestin oligomerization has been proposed. It has been suggested that prestin molecules form highorder oligomers, most likely as the tetramer, in heterologous systems. In OHCs, however, the oligomeric structure of prestin remains unclear. Here we calculated the prestin-related charge density in both gerbil and guinea pig OHCs through measuring their nonlinear capacitance （NLC） and LM surface area, showing that the average charge density （22, 608 μm-2 in gerbils; 19, 460 μm-2 in guinea pigs） is statistically 4 times the average density of IMPs （5,686 μm-2 in gerbils; 5, 000 μm-2 in guinea pigs）. This suggests that each IMP contains four prestin molecules based upon the notion that each prestin transfers a single elementary charge, implying that prestin forms tetramers in OHCs. To determine whether the prestin tetramer functions as a mechanical unit, we subsequently compared the slope factors （α） of electromotility and NLC simultaneously measured from the same OHC, showing that the α values of the two are statistically the same. This suggests that each prestin molecule in the tetramer is mechanically independent and equally contributes to OHC electromotility.

Zinc-finger protein A20 protects hair cells from damage made by high-power microwave

Inner ear hair cells are important for maintaining hearing.Irreversible damage to hair cells is an important cause of sensorineural deafness.Electromagnetic radiation,especially high-power microwave,is an important threat to human health in modern society and war.However,it is not clear whether high-power microwave has an effect on cochlea hair cells.This study aimed to assess the effects of high-power microwave on cochlear hair cells in guinea pigs,and investigate the potential protection of these cells against high-power microwave-induced damage by recombinant adenovirus A20.Based on experimental results,a 65 W/cm^(2) irradiation density applied to guinea pigs in this study to establish a high-power microwave inner ear injury model.In addition,pAdEeay-1/A20 was injected via a round window into experimental guinea pig cochlea,whereas artificial perilymph was injected into the control group.Auditory function was assessed by testing the auditory brainstem response threshold,and damage to cochlear hair cells was investigated by cell counting and scanning electron microscopy observations of the basilar membrane.Inner ear injury was observed 6 hours after 65 W/cm^( 2 ) of irradiation and the auditory brainstem response threshold was significantly higher in the irradiation group(P<0.05)compared with other groups.Propidium iodide staining and scanning electron microscopy results indicated that significant morphological changes occurred after radiation,especially to inner hair cells,which exhibited remarkable damage and the presence of several unknown spherical substances.Auditory brainstem response threshold was decreased in the pAdEeay-1/A20 group compared with the artificial perilymph group;moreover,damage to hair cells was milder in the pAdEeay-1/A20 group compared with the control group(P<0.01).Thus,high-power microwave can cause damage to cochlear hair cells,as well as hearing loss with prolonged exposure and/or high dosage.In this regard,65 W/cm^( 2 ) of irradiation for 6 hours is a reliable target dose for observation of damage.The zinc finger protein A20 can protect cochlear hair cells from high-power microwave-induced damage and prevent further hearing loss.This study was approved by the Laboratory Animal Welfare and Ethics Committee of the Third Military Medical University,China on April 18,2017.

Noise-induced nitrotyrosine increase and outer hair cell death in guinea pig cochlea

Background Modern research has provided new insights into the biological mechanisms of noise-induced hearing loss, and a number of studies showed the appearance of increased reactive oxygen species （ROS） and reactive nitrogen species （RNS） during and after noise exposure. This study was designed to investigate the noise exposure induced nitrotyrosine change and the mechanism of outer hair cells death in guinea pig cochlea. Method Thirty guinea pigs were used in this study. The experimental animals were either exposed for 4 hours per day to broadband noise at 122 dB SPL （A-weighted） for 2 consecutive days or perfused cochleae with 5 mg/ml of the SIN1 solutions, an exogenous NO and superoxide donor, for 30 minutes. Then the cochleae of the animals were dissected. Propidium iodide （PI）, a DNA intercalating fluorescent probe, was used to trace morphological changes in OHC nuclei. The distribution of nitrotyrosine （NT） in the organ of Corti and the cochlear lateral wall tissue from the guinea pigs were examined using fluorescence immunohistochemistry method. Whole mounts of organ of Corti were prepared. Morphological and fluorescent changes were examined under a confocal microscope. Results Either after noise exposure or after SIN1 perfusion, outer hair cells （OHCs） death with characteristics of both apoptotic and necrotic degradation appeared. Nitrotyrosine immunolabeling could be observed in the OHCs from the control animals. After noise exposure, NT immunostaining became much greater than the control animals in OHCs. The apoptotic OHC has significant increase of nitrotyrosine in and around the nucleus following noise exposure. In the normal later wall of cochleae, relatively weak nitrotyrosine immunolabeling could be observed. After noise exposure, nitrotyrosine immunoactivity became stronger in stria vascularis. Conclusion Noise exposure induced increase of nitrotyrosine production is associated with OHCs death suggesting reactive nitrogen species participation in the cochlear pathophysiology of noise-induced hearing loss.

Ototoxic effects of mefloquine in cochlear organotypic cultures

Mefloquine is a widely used anti-malarial drug. Some clinical reports suggest that mefloquine may be ototoxic and neurotoxic, but there is little scientific evidence from which to draw any firm conclusion. To evaluate the ototoxic and neurotoxic potential of mefloquine, we treated cochlear organotypic cultures and spiral ganglion cultures with various concentrations of mefloquine. Mefloquine caused a dose-dependent loss of cochlear hair cells at doses exceeding 0.01 mM. Hair cell loss progressed from base to apex and from outer to inner hair cells with increasing dose. Spiral ganglion neurons and auditory nerve fibers were also rapidly destroyed by mefloquine in a dose-dependent manner. To investigate the mechanisms underlying mefloquine-induced cell death, cochlear cultures were stained with TO-Pro-3 to identify morphological changes in the nucleus, and with carboxyfluorescein FAM-labeled caspase inhibitor 8, 9 or 3 to determine caspase-mediated cell death. TO-Pro-3-labeled nuclei in hair cells, spiral ganglion neurons and supporting cells were shrunken or fragmented, morphological features characteristic of cells undergoing apoptosis. Both initiator caspase 8 (membrane damage) and caspase 9 (mitochondrial damage), along with executioner caspase 3, were heavily expressed in cochlear hair cells and spiral ganglions after mefloquine treatment. These three caspases were also expressed in support cells, although labeling was less widespread and less intense. These results indicate that mefloquine damages both the sensory and neural elements in the postnatal rat cochlea by initially activating cell death signaling pathways on the cell membrane and in mitochondria.

Anatomy and physiology of peripheral auditory system and commen causes of hearing loss

For Otolaryngologist,it is the most important to know the principle of anatomy,physiology and common ototoxicity.Short but more concise summary has been sum up in the following review in order to help young ENT doctor to understand the importance of this basic knowledge.

Prestin-Mediated Frequency Selectivity Does not Cover Ultrahigh Frequencies in Mice

In mammals,the piezoelectric protein,Prestin,endows the outer hair cells(OHCs)with electromotility(eM),which confers the capacity to change cellular length in response to alterations in membrane potential.Together with basilarmembrane resonance and possible stereociliary motility,Prestin-based OHC eM lays the foundation for enhancing cochlear sensitivity and frequency selectivity.However,it remains debatable whether Prestin contributes to ultrahigh-frequency hearing due to the intrinsic nature of the cel's low-pass features.The low-pass_property of mouse OHC eM is based on the finding that eM magnitude dissipates within the frequency bandwidth of human speech.In this study,we examined the role of Prestin in sensing broad-range frequencies(4-80 kHz)in mice that use ultrasonic hearing and vocalization(to>100 kHz)for social communication.The audiometric measurements in mice showed that ablation of Prestin did not abolish hearing at frequencies>40 kHz.Acoustic associative behavior tests confirmed that Prestin-knockout mice can learn ultrahigh-frequency sound-coupled tasks,similar to control mice.Ex vivo cochlear Ca2+imaging experiments demonstrated that without Prestin,the OHCs still exhibit ultrahigh-frequency transduction,which in contrast,can be abolished by a universal cation channel blocker,Gadolinium.In vivo salicylate treatment disrupts hearing at frequencies<40 kHz but not ultrahigh-frequency hearing.By pharmacogenetic manipulation,we showed that specific ablation of the OHCs largely abolished hearing at frequencies>40 kHz.These findings demonstrate that cochlear OHCs are the target cells that support ultrahigh-frequency transduction,which does not require Prestin.