钙蛋白酶在卡那霉素致毒豚鼠耳蜗中的表达

目的探讨钙蛋白酶(calpain)在卡那霉素(kanamycin,KM)致耳中毒豚鼠耳蜗的表达。方法将豚鼠随机分成对照组、KM 3d组、KM 7d组和KM1 4d组,应用免疫组织化学SABC(streptavidin-biotin peroxidae complex,链霉亲合素-生物素过氧化物酶复合物)法和显微图像分析技术检测耳蜗中钙蛋白酶的表达,用药前后给予短纯音刺激检测听性脑干反应阈值,观察豚鼠听力的变化。结果对照组calpain 1阳性免疫反应主要见于耳蜗毛细胞、螺旋神经节、血管纹和螺旋韧带,以螺旋神经节的染色较深,而其它部位均呈阴性。肌肉注射KM后,calpain 1在耳蜗中的阳性反应部位与对照组大致相同,显微图像分析结果表明,随着给药天数的增加,calpain 1在耳蜗上述部位的阳性反应逐渐减弱。Calpain 2在各组豚鼠耳蜗中的表达部位与calpain 1的相同,显微图像分析结果提示,随着给药天数的增加,calpain 2在耳蜗上述部位的阳性反应逐渐增强。结论正常豚鼠耳蜗中有calpain 1和calpain 2的表达。注射KM后,随着给药天数的增加,calpain 1在耳蜗的表达逐渐减弱,而calpain 2的表达则逐渐增强,提示calpain 2可能参与了卡那霉素致耳中毒的过程。     

复方丹参抗耳蜗外毛细胞凋亡的实验观察

目的 探讨氨基甙类抗生素所致耳蜗外毛细胞凋亡与听力损害关系及复方丹参对其凋亡发生的影响。方法 对35只豚鼠行药物造模,测试ABR阈值,TUNEL技术观察耳蜗外毛细胞凋亡发生情况。结果 正常豚鼠耳蜗外毛细胞无凋亡发生,耳毒性药物应用1d,3d后耳蜗各转外毛细胞均可出现凋亡阳性染色,中药干预组动物耳蜗外毛细胞凋亡数目相对较少,此外,豚鼠ABR阈值皆无明显升高。结论 耳毒性药物可诱发耳蜗外毛细胞发生凋亡;复方丹参能够对抗凋亡发生;凋亡发生早期对豚鼠听力阈值无明显影响。     

两种神经营养因子对噪声性毛细胞损伤协同防护作用的观察

目的观察胶质细胞源性神经营养因子(glialcellline-derivedneurotrophicfactor,GDNF)和神经营养素-3(neurotrophin-3,NT-3)对噪声引起毛细胞肌动蛋白损伤的协同防护作用.方法采用改进的豚鼠耳蜗微渗透压泵慢性灌注技术,将GDNF和NT-3缓慢注入12只豚鼠左侧内耳,以左耳灌注人工外淋巴液的9只豚鼠为对照,检测噪声暴露后豚鼠听功能和耳蜗毛细胞缺失率的变化.结果动物术后14d(噪声暴露后10d)实验组手术耳和非手术耳的脑干诱发电位反应(auditorybrainstemresponses,ABR)阈值低于对照组(秩和检验,下同.P＜0.05,P＜0.01),毛细胞表皮板和纤毛肌动蛋白荧光染色计数发现实验组手术耳和非手术耳外毛细胞缺失率均低于对照组(P＜0.001,P＜0.01),内毛细胞缺失率也均低于对照组(P＜0.01,P＜0.01).结论GDNF和NT-3对噪声性聋具有较好的协同防护作用.     

EGCG对阿米卡星诱导大鼠螺旋神经元诱导型一氧化氮合酶表达的影响

目的探讨表没食子儿茶素没食子酸酯［(-)-epigallocatechin-3-gallate,EGCG］对阿米卡星（amikacin,Amk）诱导的大鼠耳蜗螺旋神经元(spiral ganglion neuron;SGN) 诱导型一氧化氮合酶（inducible nitric oxide synthase, iNOS）表达的影响。方法将30只SD大鼠分为生理盐水对照组、Amk（450?mg/kg·d×14d）损伤组和Amk加EGCG（50?mg/kg·d×14d）保护组。各组动物均经深度麻醉后,半身灌注固定处死,取右侧耳蜗标本固定、脱钙、石蜡轴位包埋、轴位切片,近中轴位切片行iNOS免疫组化染色,光学显微镜下检测耳蜗SGN表达情况,并通过切片图像分析进行半定量处理比较。结果对照组SGN胞浆及细胞核基本上不着色（SGN iNOS染色平均灰度值为111.04±3.15）,损伤组SGN部分神经元胞浆内有棕黄色或黄色颗粒或斑片（SGN iNOS染色平均灰度值为90.32±5.26）,保护组胞浆及细胞核无明显着色（SGN iNOS染色平均灰度值为109.35±4.89）,图像分析结果显示,损伤组与对照组、损伤组与保护组之间的SGN iNOS染色平均灰度值差异有统计学意义。结论iNOS参与Amk耳中毒时耳蜗螺旋神经元的氧化损伤,EGCG可以减弱Amk耳中毒时耳蜗螺旋神经元iNOS的表达,从而减轻Amk耳毒性。     

丁胺卡那霉素诱发豚鼠耳蜗外毛细胞凋亡的实验研究

目的 探讨氨基糖苷类抗生素作用于耳蜗时外毛细胞凋亡现象及其凋亡发生特点。方法 用一定剂量的丁胺卡那霉素对15只豚鼠行耳蜗造模后利用光镜、TUNEL标记技术（teminal-deoxynucl eotidy transferase mediated d-UTP nick-end labeling)原位检测凋亡发生。结果 肌注丁胺卡那霉素1d后即可诱发豚鼠蜗底转外毛细胞发生凋亡,随着用药时间延长,其余各转外毛细胞亦发生凋亡,甚至出现部分外毛细胞丢失现象。结论 氨基糖苷类抗生素作用于耳蜗系统时可引起外毛细胞凋亡,细胞凋亡是豚鼠耳蜗听毛细胞损伤的一条途径;氨基糖苷类抗生素耳毒性作用机制可能与其引起耳蜗毛细胞凋亡有关。     

庆大霉素致豚鼠耳蜗毛细胞凋亡时Caspase-3的表达

目的探讨庆大霉素所致耳蜗外毛细胞的损伤特点及耳毒性机制。方法豚鼠随机分3个组,分别腹腔注射庆大霉素、庆大霉素加速尿、生理盐水各连续6天,比较用药前后各组豚鼠畸变产物耳声发射（distortion product otoacoustic emissions,DPOAE）变化、耳蜗铺片、毛细胞凋亡情况及Caspase-3在毛细胞的表达。结果注射庆大霉素和庆大霉素加速尿2个组,用药后DPOAE明显下降,耳蜗铺片见毛细胞损伤明显,细胞凋亡发生及Caspase-3免疫复合物阳性表达。结论庆大霉素可致豚鼠耳蜗毛细胞损伤并加速凋亡,Caspase-3在毛细胞凋亡过程中起重要作用。     

两种神经营养因子对噪声性毛细胞损伤协同防护作用的观察

目的：观察胶质细胞源性神经营养因子（glial cell line-derved neurotrophic factor,GDNF)和神经营养素－3（neurotrophin-3,NT-3)对噪声引起毛细胞肌动蛋白损伤的协同防护作用。方法：采用改进的豚鼠耳蜗微渗透压泵慢性灌注技术,将GDNF和NT－3缓慢注入12只豚鼠左侧内耳,在左耳灌注人工外淋巴液的9只豚为对照,检测噪声暴露后豚鼠听功能和耳蜗毛细胞缺失率的变化。结果：动物术后14d(噪声暴露后10d)实验组手术耳和非手术耳的脑干诱发电位反应（auditory brainstem responses,ABR)阈值低于对照组（秩和检验,下同,P＜0．05,P＜0．01）,毛细胞表皮板和纤毛肌动蛋白荧光染色计数发现实验组手术耳和非手术耳外毛细胞缺失率均低于对照组（P＜0．001,P＜0．01）,内毛细胞缺失率也均低于对照组（P＜0．01,P＜0．01）。结论：GDNF和NT－3对噪声性聋具有较好的协同防护作用。     

神经营养因子对噪声引起豚鼠耳蜗外毛细胞损伤的防护作用

目的 定量观察胶质细胞源性神经营养因子(glial cell ine-derived neurotrophic factor,GDNF)和神经营养-3(neurotrophin-3,NT-3)对噪声引起豚鼠耳蜗外毛细胞损伤的防护作用。方法 将微渗透压泵埋置于豚鼠背部,经固定于耳蜗底回鼓阶内的改良微导管将GDNF(100ng/ml)和NT-3(2.5μg/ml)的混合液缓慢注入12只豚鼠左侧内耳,以左侧内耳灌注人工外淋巴液的9只豚鼠为对照,检测噪声暴露后豚鼠听功能和耳蜗外毛细胞形态、数量的变化。结果 噪声暴露10天后,实验组手术耳和非手术耳的脑干诱发电反应阈值低于对照组(P<0.05,p<0.01)。毛细胞表皮板和纤毛肌动蛋白荧光染色计数发现,实验组手术耳和非手术耳的外毛细胞缺失率低于对照组(p<0.001,p<0.01)。毛细胞核荧光染色计数发现,实验组手术耳和非手术耳的外毛细胞核肿胀率低于对照组(p<0.01,p<0.01)。结论 GDNF和NT-3对噪声引起豚鼠耳蜗外毛细胞损伤具有较好的防护作用。     

川芎嗪对卡那霉素耳中毒抗氧化作用的研究

通过检测豚鼠耳蜗组织超氧化物歧化酶（SOD）活力、丙二醛（MDA）含量、听神经复合动作电位（CAP）及扫描电镜观察，评价川芎嗪对卡那霉素（KM）耳中毒的抗氧化作用。结果显示：KM能 明显增加SOD活力、MDA含量及CAP阈值。同时应用KM和川芎嗪后，与KM组对比，听力有改善，SOD活力、MDA含量显著下降；与正常组相比，SOD、MDA无明显变化，听力轻度下降。推测脂质过氧化反应参与了KM耳中毒的过程。并探讨了川芎嗪对KM耳中毒抗氧化作用的可能机制。     

卡那霉素对豚鼠耳蜗碳酸酐酶活性的影响

本实验对豚鼠在卡那霉索(KM)致聋后和对照组进行了碳酸酐酶(CAH)组织化学活性研究，结合图象分析技术和听觉脑干反应(ABR)测试，观察豚鼠用KM后听力发生变化时耳蜗CAH的变化。探讨了耳蜗内、外毛细胞区及血管纹CAH的变化及其与听功能的关系。结果指示，KM所致听力损伤与耳蜗CAH的变化有关。     

特异性损伤内耳螺旋神经元小鼠模型的建立

目的：建立小鼠内耳螺旋神经元损伤的耳聋模型,为研究干细胞移植治疗感音神经性聋奠定基础。方法成年雌性SPF级CBA／J小鼠60只,随机分为实验组和生理盐水组,每组30只,实验组动物经圆窗渗透给予10μl哇巴因（ouabain）,生理盐水组同法给予等量生理盐水。每组于给药前及给药后7、14及30天分别检测小鼠听性脑干反应（ABR）和畸变产物耳声发射（DPOAE）,并用免疫组织荧光技术和基底膜铺片技术分别观察耳蜗螺旋神经元（spiral ganglion neurons ,SGNs）细胞及内耳毛细胞（hair cells ,HCs）的变化。结果①与生理盐水组比较,实验组给药后各时间点 ABR反应阈均明显升高,波Ⅰ潜伏期延长,振幅明显降低,差异有统计学意义（ P＜0．05）。②实验组及生理盐水组小鼠DPOAE均可正常引出。③与生理盐水组相比,实验组耳蜗各回螺旋神经元的数量及密度显著降低,差异有统计学意义（P＜0．05）。④实验组在给药后不同时间点,耳蜗各回内、外毛细胞均排列整齐、形态完整、未见明显损伤或丢失。结论哇巴因经圆窗渗透给药可特异性损伤CBA／J小鼠内耳螺旋神经元及其功能,而不损伤内、外毛细胞,是一种理想的研究干细胞移植治疗感音神经性聋的动物模型。     

Adenovirus-mediated expression of brain-derived neurotrophic factor protects spiral ganglion neurons from ototoxic damage

Hair cell loss, the most common cause of deafness, is often associated with auditory nerve degeneration. Our goal was to determine the influence of combined ciliary-derived neurotrophic factor (CNTF) and brain-derived neurotrophic factor (BDNF) gene therapy on the survival of spiral ganglion neurons (SGNs) after elimination of inner hair cells in the mature guinea pig ear. Seven days after bilateral deafening, a 5-microl suspension of CNTF and/or BDNF adenovirus vectors was injected into the left scala tympani through the round window. Animals were sacrificed 28 days after deafening, and their inner ears were prepared for SGN counts. The SGN counts revealed that BDNF alone and the combined CNTF and BDNF treatment significantly enhanced SGN survival. CNTF did not significantly enhance the protective effect of BDNF. These data present possible strategies for enhancing SGN survival in cochlear implant procedures.     

Sirtuin 1激活在氯化钴诱导的离体耳蜗缺氧损害中的作用研究

目的观察氯化钴（CoCl2）对耳蜗毛细胞和神经节细胞的损伤模式并探讨Sirtuin 1（SIRT1）在耳蜗缺氧过程中的作用。方法采用CoCl2作用于离体培养的新生大鼠耳蜗组织，通过细胞化学染色和免疫荧光染色确定CoCl2对耳蜗毛细胞存活的影响，采用实时定量PCR方法检测CoCl2作用耳蜗组织后Sirtuin 1mRNA表达的变化。同时使用Sirtuin1激活剂白藜芦醇和Sirtuin 1抑制剂Sirtinol，观察SIRT1在缺氧介导的耳蜗损伤过程中的作用。结果300μmol／L以上浓度CoCl2作用于耳蜗24h可引起内外毛细胞缺失。细胞肿胀明显，神经元胞体变得不规则，数目明显减少，有些神经纤维甚至断裂。CoCl2处理后可引起早期耳蜗组织Sirtuin1基因表达增强，6h达到峰值。白藜芦醇预处理可以显著提高外毛细胞（P〈0．01）和内毛细胞的存活率（P〈0．05）。同时给予Sirtuin1抑制剂Sirtinol，白藜芦醇的保护效应被抵消。结论CoCl2导致耳蜗组织缺氧损害。耳蜗在缺氧过程中Sirtuin1早期上调，可保护耳蜗组织对抗缺氧诱导的细胞损伤。     

N-acetylcysteine and N-nitroarginine methyl ester attenuate Carboplatin-induced ototoxicity in dissociated spiral ganglion neuron cultures

Objectives

Carboplatin, a platinum-containing anti-cancer drug used to treat a variety of cancers, induces ototoxicity. Since, reactive oxygen species (ROS) and nitric oxide (NO) seem to be responsible for this toxicity, the antioxidant, N-acetyl-L-cysteine (L-NAC), and NO synthetase inhibitor, N-nitro-L-arginine methyl ester (L-NAME) were predicted to have protective effects against carboplatin ototoxicity. The aim of this study was to test for the protective effects of L-NAC and L-NAME on cochlear hair cells and spiral ganglion neurons (SGNs).

Methods

Cochlear organotypic cultures and dissociated spiral ganglion neuron cultures, from mice postnatal day 5 cultures were used in this study. The cultures were treated with carboplatin alone or in combination with L-NAC or L-NAME, and carboplatin-induced damage was monitored.

Results

Treatment with carboplatin induced a significant loss of outer hair cells, while inner hair cells were preserved in the cochlear organotypic cultures. Addition of L-NAC or L-NAME reduced the amount of carboplatin-induced hair cell damage; the differences did not reach statistical significance. However, carboplatin significantly decreased the number of surviving SGNs in dissociated cultures. The toxic effects were significantly reduced by addition of L-NAC or L-NAME. In addition, carboplatin induced the loss of neurites from the SGN somata, and this was not blocked with L-NAC or L-NAME.

Conclusion

The results of this study suggest that ROS and NO are involved in carboplatin-induced damage to hair cells and SGNs, and administration of L-NAC/L-NAME can be used to attenuate the toxicity.     

Novel strategy for treatment of inner ears using a biodegradable gel

OBJECTIVE: The present study aimed to evaluate the efficacy of a biodegradable hydrogel as a drug-delivery medium for the inner ear. Brain-derived neurotrophic factor (BDNF) was chosen as the agent to be administered. METHOD: First, we used an enzyme-linked immunosorbent assay to measure BDNF concentrations in the cochlear fluid after placing a hydrogel containing this agent onto the round-window membrane of the ear. Second, the functional and histologic protection of the auditory primary neurons (spiral ganglion neurons [SGNs]) by BDNF applied through the hydrogel was examined using an animal model of SGN degeneration. RESULTS: The results revealed sustained delivery of BDNF into the cochlear fluid by way of the hydrogel. Second, the functional and histologic protection of the auditory primary neurons (SGNs) by BDNF applied through the hydrogel was examined using an animal model of SGN degeneration. The measurement of electrically evoked auditory-brainstem responses demonstrated that BDNF delivered by way of the hydrogel significantly reduced the threshold elevation. Immunohistochemistry for neurofilament 200 kD demonstrated increased survival of SGNs because of BDNF application through the hydrogel. CONCLUSION: These findings indicate that biodegradable hydrogels can be used for drug delivery to the inner ear.     

Spiral ganglion neuron survival and function in the deafened cochlea following chronic neurotrophic treatment

Cochlear implants electrically stimulate residual spiral ganglion neurons (SGNs) to provide auditory cues for the severe-profoundly deaf. However, SGNs gradually degenerate following cochlear hair cell loss, leaving fewer neurons available for stimulation. Providing an exogenous supply of neurotrophins (NTs) has been shown to prevent SGN degeneration, and when combined with chronic intracochlear electrical stimulation (ES) following a short period of deafness (5 days), may also promote the formation of new neurons. The present study assessed the histopathological response of guinea pig cochleae treated with NTs (brain-derived neurotrophic factor and neurotrophin-3) with and without ES over a four week period, initiated two weeks after deafening. Results were compared to both NT alone and artificial perilymph (AP) treated animals. AP/ES treated animals exhibited no evidence of SGN rescue compared with untreated deafened controls. In contrast, NT administration showed a significant SGN rescue effect in the lower and middle cochlear turns (two-way ANOVA, p < 0.05) compared with AP-treated control animals. ES in combination with NT did not enhance SGN survival compared with NT alone. SGN function was assessed by measuring electrically-evoked auditory brainstem response (EABR) thresholds. EABR thresholds following NT treatment were significantly lower than animals treated with AP (two-way ANOVA, p = 0.033). Finally, the potential for induced neurogenesis following the combined treatment was investigated using a marker of DNA synthesis. However, no evidence of neurogenesis was observed in the SGN population. The results indicate that chronic NT delivery to the cochlea may be beneficial to cochlear implant patients by increasing the number of viable SGNs and decreasing activation thresholds compared to chronic ES alone.     

Structural and Ultrastructural Changes to Type I Spiral Ganglion Neurons and Schwann Cells in the Deafened Guinea Pig Cochlea

Sensorineural hearing loss is commonly caused by damage to cochlear sensory hair cells. Coinciding with hair cell degeneration, the peripheral fibres of type I spiral ganglion neurons (SGNs) that normally form synaptic connections with the inner hair cell gradually degenerate. We examined the time course of these degenerative changes in type I SGNs and their satellite Schwann cells at the ultrastructural level in guinea pigs at 2, 6, and 12 weeks following aminoglycoside-induced hearing loss. Degeneration of the peripheral fibres occurred prior to the degeneration of the type I SGN soma and was characterised by shrinkage of the fibre followed by retraction of the axoplasm, often leaving a normal myelin lumen devoid of axoplasmic content. A statistically significant reduction in the cross-sectional area of peripheral fibres was evident as early as 2 weeks following deafening (p < 0.001, ANOVA). This was followed by a decrease in type I SGN density within Rosenthal’s canal that was statistically significant 6 weeks following deafening (p < 0.001, ANOVA). At any time point examined, few type I SGN soma were observed undergoing degeneration, implying that once initiated, soma degeneration was rapid. While there was a significant reduction in soma area as well as changes to the morphology of the soma, the ultrastructure of surviving type I SGN soma appeared relatively normal over the 12-week period following deafening. Satellite Schwann cells exhibited greater survival traits than their type I SGN; however, on loss of neural contact, they reverted to a non-myelinating phenotype, exhibiting an astrocyte-like morphology with the formation of processes that appeared to be searching for new neural targets. In 6- and 12-week deafened cochlea, we observed cellular interaction between Schwann cell processes and residual SGNs that distorted the morphology of the SGN soma. Understanding the response of SGNs, Schwann cells, and the complex relationship between them following aminoglycoside deafening is important if we are to develop effective therapeutic techniques designed to rescue SGNs.     

人神经营养因子3和绿色荧光蛋白基因共表达腺病毒载体对耳蜗组织的转染

目的:构建一个神经营养因子3(NT3)和绿色荧光蛋白(EGFP)基因共表达重组腺病毒载体,确定Ad/NT-3对离体耳蜗的转染效率和NT3对螺旋神经元存活的作用.方法:使用pAdeasy-1和pAdTrack CMV腺病毒载体系统,产生带绿色荧光标记的NT3重组腺病毒.转染培养新生的大鼠耳蜗基底膜,观察病毒的转染效率.对培养15 d的耳蜗进行神经丝蛋白200免疫荧光染色,计数螺旋神经元.观察NT3对神经存活的影响.结果:重组NT3病毒能够转染整个耳蜗组织中的各型细胞.以外沟细胞最高.约为49%,其次为齿间细胞,为27%.仅有少量的毛细胞和螺旋神经元被转染.Ad/NT-3重组腺病毒处理15 d的耳蜗螺旋神经元存活的数目多于Ad/EGFP腺病毒转染的耳蜗.结论:构建的Ad/NT-3重组腺病毒能够同时在耳蜗组织中表达EGFP和NT3蛋白,主要表达于外沟细胞和齿问细胞,这些细胞释放NT3能够维持耳蜗神经元存活.     

Neurotrophins and electrical stimulation for protection and repair of spiral ganglion neurons following sensorineural hearing loss

Exogenous neurotrophins (NTs) have been shown to rescue spiral ganglion neurons (SGNs) from degeneration following a sensorineural hearing loss (SNHL). Furthermore, chronic electrical stimulation (ES) has been shown to retard SGN degeneration in some studies but not others. Since there is evidence of even greater SGN rescue when NT administration is combined with ES, we examined whether chronic ES can maintain SGN survival long after cessation of NT delivery. Young adult guinea pigs were profoundly deafened using ototoxic drugs; five days later they were unilaterally implanted with an electrode array and drug delivery system. Brain derived neurotrophic factor (BDNF) was continuously delivered to the scala tympani over a four week period while the animal simultaneously received ES via bipolar electrodes in the basal turn (i.e., turn 1) scala tympani. One cohort (n=5) received ES for six weeks (i.e., including a two week period after the cessation of BDNF delivery; ES(6)); a second cohort (n=5) received ES for 10 weeks (i.e., a six week period following cessation of BDNF delivery; ES(10)). The cochleae were harvested for histology and SGN density determined for each cochlear turn for comparison with normal hearing controls (n=4). The withdrawal of BDNF resulted in a rapid loss of SGNs in turns 2-4 of the deafened/BDNF-treated cochleae; this was significant as early as two weeks following removal of the NT when compared with normal controls (p<0.05). Importantly, there was not a significant reduction in SGNs in turn 1 (i.e., adjacent to the electrode array) two and six weeks after NT removal, as compared with normal controls. This result suggests that chronic ES can prevent the rapid loss of SGNs that occurs after the withdrawal of exogenous NTs. Implications for the clinical delivery of NTs are discussed.     

Basic fibroblast growth factor protects auditory neurons and hair cells from glutamate neurotoxicity and noise exposure

OBJECTIVE: To determine the protective effects of basic fibroblast growth factor (bFGF) on cochlear neurons and hair cells in vitro and in vivo. MATERIAL AND METHODS: In Experiment I, cultured spiral ganglion neurons (SGNs) prepared from postnatal Day 3 mice were exposed to 20 mM glutamate for 2 h before the culture medium was replaced with fresh medium containing 0, 25, 50 or 100 ng/ml bFGF. Fourteen days later, all cultures were fixed with 4% paraformaldehyde and stained with 1% toluidine blue. The number of surviving SGNs was counted and the length of the neurites of the SGNs was measured. In Experiment II, in vivo studies were carried out with guinea pigs in which bFGF or normal saline was injected intramuscularly to assess possible protective effects of bFGF on cochlear hair cells and to accelerate the recovery of the auditory brainstem response (ABR). The ABRs were measured before, immediately after and 2 and 4 weeks after exposure to noise. RESULTS: Exposure to 20 mM glutamate for 2 h resulted in an inhibition of neurite outgrowth of SGNs and an increase in cell death. Treatment of the cultures with bFGF led to promotion of neurite outgrowth and an increase in the number of surviving SGNs. In Experiment II, significant (p < 0.05) differences in ABR thresholds were observed between the groups injected with bFGF and saline (t = 2.689) at 4 weeks after noise exposure. Cochleae were removed and hair cell loss analyzed in surface preparations prepared from all experimental animals. Acoustic trauma caused loss of 240 and 2160 inner hair cells in the groups injected with bFGF and saline, respectively. Similarly, more outer hair cells were lost in the normal saline injection group (99,291) than in the group treated with bFGF (70,377). CONCLUSIONS: Our results demonstrate that bFGF protects SGNs against glutamate neurotoxicity in vitro. In addition, treatment with bFGF protects hair cells from acoustic trauma.