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.

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.

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.

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.

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

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.

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.

传出神经对听力发育早期耳蜗放大功能影响的研究

目的利用外毛细胞乙酰胆碱受体α9亚基敲除(Knock-out,Chrna9 KO)与功能获得性敲入(Knockin,Chrna9 KI)的点突变小鼠,重点关注Prestin蛋白水平与耳蜗频率编码方面的差异,研究耳蜗传出神经支配对听力发育的影响。方法选取出生后18 d的KO、KI小鼠与其各自对照组,采用听性脑干反应(auditory brainstem responses,ABR)检测听觉功能;通过耳声发射畸变产物(distortion product otoacoustic emission,DPOAE)群延时实验技术评估基底膜上固定频率的编码位置;通过免疫荧光染色分别观察小鼠的传出神经突触与带状突触;全细胞膜片钳技术测量非线性膜电容来评估外毛细胞的功能及Prestin蛋白的表达情况。结果4.0~45.0 kHz的9个频率中,KO Homo组ABR阈值与KO WT组比较,KI Homo组ABR阈值与KI WT组比较,差异均无统计学意义(P>0.05)。22.6、16.0、8.0 kHz频率的90、85、80 dB SPL处,KI Homo组ABR的Ⅰ波波幅高于KI WT组,差异有统计学意义(P<0.05)。KO Homo组各频率、各刺激声的Ⅰ波波幅与KO WT组比较,差异均无统计学意义(P>0.05)。在13 kHz频率上的60 dB SPL,KI Homo组群延时短于KI WT组,差异有统计学意义(P<0.05)。在各频率上,KO Homo组群延时与KO WT组比较,差异均无统计学意义(P>0.05)。KI Homo组传出神经MOC终末计数顶圈第1、3排外毛细胞多于KI WT组,差异有统计学意义(P<0.05),中、底圈外毛细胞与KI WT组比较,差异无统计学意义(P>0.05)。KO Homo组传出神经MOC终末计数顶、中圈第3排外毛细胞数量少于KO WT组,底圈第3排少于KO WT组,差异均有统计学意义(P<0.05)。KI Homo组、KO Homo组外毛细胞非线性膜电容曲线、Qmax值、Vh值、Clin值、Qsp值与KI WT组、KO WT组比较,差异无统计学意义(P>0.05)。结论在听觉发育早期,传出神经支配末梢数量的降低不影响正常的听觉功能、内毛细胞带状突触与外毛细胞电能动性。然而,传出神经调控功能的增强,在不干扰毛细胞发育的情况下,可能功能性地改变了耳蜗的行波与基底膜频率编码模式。

二甲胺四环素拮抗新霉素致小鼠耳蜗外毛细胞损伤的机制研究

目的通过体内实验探究二甲胺四环素对新霉素导致外毛细胞损伤的保护作用及其机制。方法选用C57小鼠45只,雌雄不限,将小鼠随机分为对照组,新霉素处理组及新霉素+二甲胺四环素处理组,每组15只,测试3组小鼠听性脑干反应(auditory brainstem response,ABR)阈值;通过免疫荧光染色,比较3组外毛细胞存活情况;采用cleaved caspase-3染色及原位末端标记法(TdT-mediated dUTP-nick end labeling assay,TUNEL)染色,比较3组外毛细胞凋亡情况。结果新霉素+二甲胺四环素处理组ABR阈值在各个频率均显著低于新霉素处理组,且ABR阈值在各个频率比较,差异均有统计学意义(P<0.05)。基底膜铺片显示,二甲胺四环素处理能显著减轻新霉素导致的外毛细胞损失。在对照组基底膜中,未检测到cleaved caspase-3和TUNEL阳性细胞;新霉素处理组,cleaved caspase-3和TUNEL阳性细胞数量显著上升;新霉素+二甲胺四环素处理组,cleaved caspase-3和TUNEL阳性细胞数量显著下降。结论二甲胺四环素对新霉素导致的外毛细胞损伤具有显著的保护作用,且这种保护作用是通过抑制外毛细胞凋亡通路而介导的。

茯苓对豚鼠卡那霉素中毒性耳聋的对抗作用

为了更好地预防卡那霉素中毒性耳聋的发生，通过给豚鼠灌服茯苓煎剂，以一般中毒症状、耳廓反射阈、脑干听觉诱发电位阈及外毛细胞缺失率为指标，观察了茯苓对卡那霉素中毒性耳损害的影响。结果发现服用茯苓煎剂可明显减轻卡那霉素耳损害，服药组和未服药组动物的４ｋＨｚ、６ｋＨｚ、８ｋＨｚ的耳廓反射阈在用药第７天时分别为４．７±１．５ｄＢ、５．７±２．４ｄＢ、２．７±１．２ｄＢ和１０．５±３．２ｄＢ、１２．１±３．７ｄＢ、８．５±２．７ｄＢ。脑干听觉诱发电位阈分别较实验前升高２２．７±９．７ｄＢ和５１．３±１４．４ｄＢ。柯蒂氏器底圈外毛细胞缺失率分别为３９．４％和６７．４％。表明茯苓对卡那霉素中毒性耳损害有对抗作用。

水杨酸钠急慢性注射致豚鼠耳蜗形态学的改变

目的 :研究水杨酸钠对豚鼠耳蜗形态学改变的急慢性作用。方法 :采用单次和长期注射水杨酸钠建模分别在光镜、电镜 (扫描、透射 )下观察 1次及多次注射水杨酸钠组和生理盐水对照组豚鼠耳蜗基底膜Corti器 ,特别是外毛细胞形态的改变。结果 :以相应的生理盐水组为对照 ,急性水杨酸钠注射 2h主要引起透射电镜下豚鼠外毛细胞侧壁表面下池发生扩张性空泡形成 ;慢性水杨酸钠注射 2周主要引起豚鼠外毛细胞在透射电镜下出现表面下池肿胀、扩张、空泡形成 ,以及透射和扫描电镜下均出现静纤毛柔软、弯曲。结论 :急慢性水杨酸钠注射引起豚鼠耳蜗形态学改变可能为耳蜗功能改变的原因 。

一次性大剂量^(60)钴辐射对豚鼠耳蜗影响的实验研究

目的观察一次大剂量６０钴（６０Ｃｏ）辐射对耳蜗功能与结构的影响。方法应用６０Ｃｏ５０Ｇｙ对豚鼠耳颞部一次照射，在辐射后４小时及以后７天中应用ＡＰ反应阈观察其听功能变化，并应用光镜及电镜作耳蜗基底膜损害的形态学观察。结果实验发现在接受辐射后第２天至第７天实验豚鼠听力呈渐进性下降，第７天ＡＰ反应阈达５８．７ｄＢ。光镜及电镜观察可见耳蜗基底膜毛细胞出现损害且内毛细胞的病损比外毛细胞更为明显和严重。结论一次性应用６０Ｃｏ５０Ｇｙ对豚鼠耳颞部照射可造成耳蜗功能与结构的损害。

川芎嗪抗链霉素耳毒性作用及其对豚鼠耳蜗外毛细胞钾通道的影响(英文)

本文旨在研究川芎嗪(tetramethylpyrazine,TMP)拮抗链霉素耳毒性作用及其对豚鼠耳蜗外毛细胞K^+通道的影响,探讨TMP拮抗链霉素耳毒性的离子通道机制。60只豚鼠随机分为6组,应用听觉脑干反应(auditory brainstem response,ABR)技术检测豚鼠ABR听阈,观测TMP的抗链霉素耳毒作用;并采用全细胞膜片钳技术观察TMP对耳蜗外毛细胞Ca^(2+)敏感K^+电流的影响。结果显示,TMP明显降低链霉素导致的豚鼠ABR听阈升高,提示TMP具有抗链霉素耳毒性作用;TMP能明显增大豚鼠耳蜗外毛细胞Ca^(2+)敏感K^+电流,并呈浓度依赖关系。结果提示,TMP通过增大K^+通道电导而拈抗链霉素耳毒性作用。

C57BL/6J小鼠听力及耳蜗毛细胞活性的年龄相关性研究

目的建立年龄相关性听力损失（age-related hearing loss,AHL）的小鼠动物模型,探讨C57BL/6J小鼠发生AHL与毛细胞活性变化的关系,并初步对C57BL/6J小鼠AHL模型进行AHL的病理分类。方法按3、8、9、10、17、18月龄段分6组培育C57BL/6J小鼠,各组分别进行听性脑干反应（ABR）测试,对耳蜗毛细胞行琥珀酸脱氢酶染色并作基底膜硬铺片,观察各年龄段小鼠内外毛细胞线粒体琥珀酸脱氢酶的活性。结果C57BL/6J小鼠随年龄增大,ABR阈值明显增高,在3月龄到9月龄期间ABR平均反应阈值增大比较缓慢,差异无统计学意义;在10月龄时,出现明显的听力下降,平均阈值比3月龄时约高18-23 dB,差异有统计学意义（click：t=5.78,P〈0.01;6 kHz：t=3.93,P〈0.01;8 kHz：t=3.01,P〈0.05）。10月龄后小鼠听力继续下降,21月龄时平均阈值比3月龄时增高约60-68 dB,差异有显著统计学意义（click：t=31.23,P〈0.01;6 kHz：t=30.44,P〈0.01;8 kHz：t=33.83,P〈0.01）。琥珀酸脱氢酶染色显示,随年龄增大,毛细胞线粒体活性丧失逐渐加重：先是底回外毛细胞活性下降,接着发生活性消失,并逐渐向顶回发展,最后累及内毛细胞。结论C57BL/6J小鼠具有典型的年龄相关性听力损失特点,其听力下降的原因早期可能主要是外毛细胞及内毛细胞活性的丧失,晚期可能是由于基底膜结构混乱,导致电生理屏障消失,致耳蜗内电位（EP）不能维持而引起。C57BL/6J小鼠可作为感音型老年性听力损失动物模型。

外源性谷氨酸对豚鼠耳蜗内、外毛细胞易损性的比较

目的观察外源性谷氨酸对豚鼠耳蜗电位及耳蜗内、外毛细胞的影响。方法将健康豚鼠30只随机分为3组,应用豚鼠全耳蜗灌流技术,分别经耳蜗灌流人工外淋巴液和不同浓度的谷氨酸2小时,记录灌流前和灌流后的耳蜗电位(CM、CAP);同时应用透射电镜技术观察灌流前后耳蜗形态学的变化。结果灌流人工外淋巴液后豚鼠耳蜗电位及形态学无改变;灌流10 mmol/L谷氨酸后CM幅度虽有下降,其非线性特点无改变,CAP阈值平均升高了35 dB;灌流20 mmol/L谷氨酸后CM幅度明显下降但仍保持其非线性特点,CAP阈值平均升高了48 dB,灌流谷氨酸后耳蜗内毛细胞及传入神经纤维出现空化。结论谷氨酸是耳蜗主要的兴奋性传入神经递质,应用外源性谷氨酸可以引起耳蜗内毛细胞及传入神经的损伤,但对耳蜗外毛细胞无影响。