年龄相关听力损失BALB／c小鼠耳蜗形态学观察

目的 探讨年龄相关听力损失小鼠耳蜗毛细胞形态学变化,建立年龄相关听力损失动物模型.方法 分别取3、6、12、18月龄BALB/c小鼠测定其听性脑干反应(ABR)阈值,应用耳蜗铺片和扫描电镜技术,观察不同月龄鼠耳蜗毛细胞计数和形态的变化.结果 3、6、12月龄鼠8 kHz ABR反应阈分别为(24.8±5.1)、(51.5±6.7)和(92.5±7.5)dB SPL.18月龄组120 dB SPL刺激声无诱发反应.耳蜗铺片毛细胞计数自6月龄组外毛细胞出现显著缺失,随月龄增加而加重,由底回逐渐向顶回发展,至12月龄时耳蜗底回和中回外毛细胞几乎完全丧失,内毛细胞显著缺失.扫描电镜显示6月龄组小鼠耳蜗毛细胞静纤毛可见不同程度的缺失、转位、散乱、倒伏、融合、变短现象,随月龄增加而逐渐加重.结论 BALB/c小鼠听力损失、耳蜗毛细胞缺失和纤毛损害随年龄增加而逐渐加重,可作为年龄相关听力损失研究的合适动物模型     

老年性聋小鼠耳蜗带状突触损伤特点及机制研究

目的研究老年性聋耳蜗带状突触数量在耳蜗各回的变化特点及其可能机制的研究。方法根据年龄将C57BL/6J小鼠分为1月龄组和12月龄组(每组12只),听性脑干反应(Auditory Brain Response, ABR)检测两组小鼠听功能,免疫组织化学染色检测两组小鼠耳蜗带状突触数量,Western blot检测两组小鼠耳蜗Ucp2蛋白的表达。结果和1月龄小鼠相比较,12月龄小鼠ABR阈值在8kHz显著升高(t=12.226, P<0.01),在16kHz和32kHz阈值均超过90dB SPL;12月龄小鼠在90dB SPL声强下ABR I波幅值在8kHz显著降低(t=5.102, P<0.01);12月龄小鼠耳蜗带状突触数量在耳蜗顶回(t=10.230, P<0.01)、中回(t=3.386, P<0.05)和底回(t=17.076, P<0.01)均显著减少,其中耳蜗底回数量减少最明显;12月龄小鼠耳蜗Ucp2蛋白水平显著增加(t=11.429, P<0.01)。结论在小鼠老化的过程中,耳蜗底回的带状突触最容易损伤丢失,其次是耳蜗顶回和中回,线粒体Ucp2可能在耳蜗带状突触损伤过程中起到重要作用。     

PDCD5和caspase3在不同年龄段C57BL/6J小鼠耳蜗中的表达

目的 检测程序化细胞死亡分子5（programmed cell death 5,PDCD5）和半胱氨酸天冬氨酸蛋白酶3（caspase 3）在不同年龄段C57BL/6J小鼠耳蜗中的表达,初步探讨其在年龄相关性听力下降发生、发展中的作用。方法 选择3、6、9及12月龄段C57BL/6J小鼠各15只,即按月龄分为四组。检测各组小鼠双侧短声( click)及短纯音(6、8 kHz)听性脑干反应(ABR)阈值。采用免疫组化和蛋白质印迹杂交(Westem blotting)检测各月龄段小鼠耳蜗PDCD5和Caspase3蛋白的表达,实时荧光定量PCR( real-time PCR)检测各月龄段小鼠耳蜗PDCD5和caspase 3基因mRNA的表达。结果 随着年龄的增长,C57BL/6J小鼠各频率ABR阈值逐渐提高,耳蜗PDCD5和Caspase3蛋白的表达亦逐渐增强。3月龄和6月龄小鼠耳蜗毛细胞和血管纹细胞仅出现少量PDCD5和Caspase3蛋白表达,9月龄时表达有明显增加,至12月龄时表达最强,各月龄组间比较,差异具有统计学意义(P值均＜0.05)。Real-time PCR检测显示PDCD5和caspase3基因mRNA随着年龄的增长表达逐渐增强,与其蛋白变化趋势相一致。结论 C57 BL/6J小鼠耳蜗PDCD5和caspase3随着年龄的增长表达增强,与耳蜗的老化密切相关,可能是老年性聋发病机制中的一个重要因素。     

年龄相关性听力损失小鼠耳蜗毛细胞的凋亡机制

目的观察年龄相关性听力损失小鼠耳蜗毛细胞的死亡方式,探讨老年性聋的分子机制。方法随机选用5～7只28、30和60天龄的NMF308nmf/nmf小鼠,应用ABR和DPOAE检测听功能,用免疫荧光染色组织化学技术TUNEL、Caspase-3和碘化丙啶（PI）染色标记并观察耳蜗毛细胞。结果NMF308nmf/nmf小鼠从1月龄开始发生听功能减退和毛细胞改变,到2月龄时出现明显的TUNEL阳性标记,是毛细胞凋亡的最早表现;Caspase-3阳性表达的毛细胞凋亡现象稍晚出现;PI标记可见2～3月龄开始出现毛细胞细胞核固缩和碎片;到3月龄时听功能基本丧失,耳蜗毛细胞严重缺失。结论老年性聋的早期首先出现耳蜗毛细胞出现DNA单链断裂,随后Caspase-3信号途径激活,导致耳蜗毛细胞凋亡。     

γ-Synuclein在不同年龄段C57小鼠内毛细胞中的差异表达

目的 观察不同年龄段C57BL/6J小鼠内毛细胞中γ-Synuclein的表达差异性,探讨其与老年性聋听力损失的可能关系。方法 随机选取出生后1月龄、3月龄、6月龄和9月龄C57BL/6 J小鼠各12只,对其进行ABR检测,取其耳蜗基底膜顶、底回进行免疫荧光染色,观察γ-Synuclein的表达差异情况。结果 各年龄段C57小鼠ABR32kHz（高频）听力阈值分别为38.75±7.42、45.00±7.39、66.25±9.80、79.58±8.38dB SPL,从6月龄开始32kHz听阈明显升高（P<0.05）,9月龄时相比6月龄进一步升高（P<0.05）。各年龄组免疫荧光染色耳蜗顶回γ-Synuclein染色完整未见缺失,底回γ-Synuclein出现选择性表达缺失,各年龄组选择性表达缺失数分别为1.08±1.00、1.25±1.22、2.75±1.91、4.42±2.11个,从6月龄开始γ-Synuclein在底回选择性表达缺失明显增加（P<0.05）,9月龄时相比6月龄进一步增加（P<0.05）。结论 γ-Synuclein选择性表达缺失增加的变化趋势与...     

快速老化小鼠的听功能和耳蜗螺旋神经元的增龄性变化

目的探讨快速老化小鼠听觉功能和耳蜗螺旋神经元的增龄性变化。方法选取1、3、5、7、9月龄的快速老化小鼠亚系1( Senescence accelerated mouse/prone 1, SAMP 1)作为实验组，而同龄抗快速老化小鼠亚系1(Senescence accelerated mouse/resistance 1, SAMR 1) 作为SAMP 1的正常对照组。分别观察其8kHz短纯音听觉脑干反应阈值、耳蜗螺旋神经节细胞透射电镜形态学、末端脱氧核苷酸转移酶介导的dUTP原位切口末端标记［terminal deoxynucleotidyl transferase(TdT) dUTP nick end labeling］ TUNEL免疫组化染色等方面的增龄性变化。结果① 听功能检测。第7、9个月龄SAMP 1小鼠跟同龄SAMR 1小鼠比较听觉脑干反应阈值差异有统计学意义；② 耳蜗螺旋神经节细胞形态学检测。第7、9个月龄SAMP 1小鼠可见螺旋神经元凋亡，而同龄SAMR 1小鼠罕见螺旋神经元凋亡；③ 耳蜗中轴位切片TUNEL染色。第7个月龄SAMR 1小鼠SGN细胞核基本上不着色［TUNEL染色阳性率为（2.27±2.43）%］，第7个月龄SAMP 1小鼠部分SGN胞核着色［染色阳性率为（11.36±4.96）%］，两者的染色阳性率差异有统计学意义。结论SAMP 1小鼠随月龄增长耳蜗螺旋神经元凋亡、听功能减退，7月龄SAMP 1小鼠即出现明显的听功能老化特征，可作为老年聋动物模型用于耳聋的相关研究。     

晚期糖基化终产物受体在小鼠耳蜗中表达的初步探讨

目的通过研究晚期糖基化终产物受体(RAGE)在小鼠耳蜗中的表达,初步探讨RAGE与老年性聋关系。方法将C57BL/6J小鼠分为2月龄、10月龄组,分别行ABR阈值检测,组织学切片观察耳蜗形态结构,免疫组化和realtime PCR检测RAGE在耳蜗中的定位和定量表达,半定量RT-PCR检测其配体S100B在耳蜗中的表达情况。结果 :(1)10月龄小鼠较2月龄ABR阈值明显提高;(2)RAGE主要在两组小鼠耳蜗的螺旋神经节细胞,内外毛细胞和血管纹中表达,10月龄C57BL/6J小鼠耳蜗中RAGE平均光密度值比2月龄小鼠大,两组间差异有统计学意义;(3)2月龄组耳蜗中RAGE相对表达量为1±0.15,10月龄组小鼠耳蜗中RAGE相对表达量为2.0816±0.117,两组间差异有统计学意义;(4)配体S100B在10月龄小鼠耳蜗中表达增高。结论 RAGE在C57BL/6J小鼠耳蜗中有表达且随年龄增大表达增强,可能与配体S100B相互作用导致听力下降,提示RAGE可能与老年性聋的发病机制有关。     

X-连锁低磷酸盐血症Pug小鼠的听力学和耳形态学研究

目的Phex基因点突变Pug小鼠是典型的人类X-连锁低磷酸盐血症小鼠模型。通过研究Pug小鼠的听力学表型,探讨Phex基因点突变对小鼠听觉功能与内耳形态的影响。方法运用听性脑干诱发电位（ABR）对4月龄Pug小鼠和野生型小鼠进行听功能测试,取小鼠耳蜗进行大体形态观察,运用石蜡切片观察小鼠耳蜗骨壁、前庭膜、血管纹、螺旋韧带、盖膜、Corti器、螺旋神经节等结构。运用扫描电镜观察小鼠耳蜗Corti器上的内、外毛细胞及其表皮板等结构。结果Pug小鼠的ABR在短声和8kHz、16kHz、32kHz短纯音刺激的反应阈值均有提高,在短声和16kHz、32kHz频率,其差异具有统计学意义（P〈0.05）。小鼠耳蜗骨壁增厚,骨质过度增长,有大量骨质矿化不完全区域;耳蜗底转部位螺旋神经节出现明显退化,神经元数目大量减少;耳蜗顶转到底转内、外毛细胞静纤毛散在性缺失,静纤毛形态异常。结论Phex基因点突变引起的基因功能缺失导致了Pug小鼠的听觉功能减退和耳蜗形态异常。     

KCNQ1在小鼠耳蜗血管纹的表达及在听觉中的意义

目的探讨KCNQ1在耳蜗侧壁血管纹的表达及其在听觉中的作用。方法以不同基因型小鼠KC-NQ1-/-(突变纯合子)、KCNQ1 /-(杂合子)和KCNQ1 / (野生型)以及C57BL/6J小鼠为实验对象,采用免疫组织化学和ABR检测技术,检测KCNQ1在小鼠耳蜗血管纹的表达及其听力。结果KCNQ1蛋白阳性颗粒集中在小鼠耳蜗血管纹边缘细胞顶膜。KCNQ1 / 小鼠的听力正常,短声ABR的阈值为36.67±7.13dBSPL;KCNQ1 /-小鼠听力低于同窝KCNQ1 / 野生型鼠,短声ABR的阈值为38.25±9.35dB SPL;KCNQ1-/-小鼠呈现全聋,ABR在100dB SPL时仍无反应。结论KCNQ1是位于耳蜗侧壁血管纹边缘细胞的重要通道蛋白,在维系耳蜗听觉功能中有重要作用。KCNQ1通道蛋白的缺失或功能受限可以不同程度地影响耳蜗的听觉功能。     

B细胞淋巴瘤-2蛋白在年龄相关性聋小鼠耳蜗中的表达

目的　了解B 细胞淋巴瘤- 2（B c e l l lymphoma-2,Bcl-2）在不同年龄段年龄相关性小鼠内耳中的表达量及部位的差异,为后续研究Bcl-2信号通路做准备。方法　采用听性脑干反应（ABR）行听力水平测试,耳蜗基底膜铺片行毛细胞形态,数量观察,实时荧光定量、免疫荧光组织化学法和蛋白质印迹分析进行不同年龄段（“年轻”组、“老年”组）C57BL/6小鼠耳蜗Bcl-2在mRNA和蛋白表达水平检测。结果　ABR两组比较,老年组小鼠平均阈值均高于年轻组,各频率差异均有统计学意义。耳蜗基底膜铺片两组比较,老年组耳蜗底转毛细胞排列紊乱且部分缺失,螺旋神经节细胞稀疏,排列凌乱。实时荧光定量结果提示Bcl-2在mRNA水平“老年”鼠耳蜗表达降低。免疫荧光组织化学法和蛋白质印迹分析提示Bcl-2在蛋白水平“老年”鼠耳蜗表达降低,且Bcl-2表达位于胞浆,内毛细胞表达高于外毛细胞。结论　Bcl-2在“老年”鼠耳蜗表达降低,且Bcl-2表达降低与耳蜗毛细胞缺失、听力下降可能具有相关性。     

Vulnerability to noise-induced hearing loss in 'middle-aged' and young adult mice: a dose-response approach in CBA, C57BL, and BALB inbred strains

Vulnerability of the cochlea to noise-induced permanent threshold shifts (NIPTS) was examined in young adult (1-2 months) and 'middle-aged' (5-7 months) CBA/CaJ, C57BL/6J, and BALB/cJ inbred mice. For each age and strain, a dose-response paradigm was applied, whereby groups of up to 12 animals were exposed to intense broadband noise (110 dB SPL) for varying durations. Exposure durations reliably associated with <10% and >90% probability of a criterion amount of NIPTS (determined 2 weeks post-exposure) were identified, and the minimum NIPTS exposure and the slope of the dose-response relation were then derived by numerical modeling. For all three strains, young adult mice were more susceptible to NIPTS than older adults; That is, a shorter exposure was able to cause NIPTS in the younger mice. Strain comparisons revealed that C57 mice were more susceptible than CBAs in the older age group only. At both ages examined, however, BALB mice were most susceptible to NIPTS. When animals with a similar amount of NIPTS were compared, outer hair cell loss in the cochlear base was more widespread in the younger animals. BALB mice appear particularly susceptible to noise-induced outer hair cell loss throughout life. Our data suggest that the mechanism or site of noise injury differs between young adults and older adults, and may depend on genetic background. The finding that both BALB and C57 mice, which show pronounced age-related hearing loss, are also especially vulnerable to noise supports the notion that genes associated with age-related hearing loss often act by rendering the cochlea susceptible to insults.     

Age-related auditory pathology in the CBA/J mouse

Commercially obtained aged male CBA/J mice presented a complex pattern of hearing loss and morphological changes. A significant threshold shift in auditory brainstem responses (ABR) occurred at 3 months of age at 4kHz without apparent loss of hair cells, rising slowly at later ages accompanied by loss of apical hair cells. A delayed high-frequency deficit started at 24kHz around the age of 12 months. At 20-26 months, threshold shifts at 12 and 24kHz and the accompanying hair cell loss at the base of the cochlea were highly variable with some animals appearing almost normal and others showing large deficits. Spiral ganglion cells degenerated by 18 months in all regions of the cochlea, with cell density reduced by approximately 25%. There was no degeneration of the stria vascularis and the endocochlear potential remained stable from 3 to 25 months of age regardless of whether the animals had normal or highly elevated ABR thresholds. The slow high-frequency hearing loss combined with a modest reduction of ganglion cell density and an unchanged endocochlear potential suggest sensorineural presbycusis. The superimposed early hearing loss at low frequencies, which is not seen in animals bred in-house, may complicate the use of these animals as a presbycusis model.     

p-ERK5在快速衰老小鼠耳蜗血管纹中的增龄性变化

目的探讨快速衰老小鼠耳蜗血管纹中磷酸化的细胞外信号调节激酶5（phosphorylated extracellular signal regulated kinase 5, p ERK5）表达的增龄性变化。方法选用3、5、7月龄的快速衰老小鼠亚系８（senescence accelerated mouse, ＳＡＭＰ８）各６只,分别进行８ｋＨｚ短纯音听性脑干反应（ＡＢＲ）检测,并用免疫组化染色方法分别检测各月龄组小鼠耳蜗血管纹细胞中p ERK5的表达,分析其增龄性变化。结果3、５、７月龄小鼠耳蜗血管纹细胞中p ERK5平均光密度值分别为0.3838±0.0020、0.3646±0.0010、0.3423±0.0036; p ERK5在不同月龄快速衰老小鼠耳蜗组织中的表达光密度值随着月龄增加而显著降低（P＜０.０５）。结论随着年龄相关性功能减退,快速衰老小鼠耳蜗血管纹中p ERK5的表达水平逐渐降低,推测p ERK5可能与维持正常的耳蜗功能及听觉有关。     

Comparison of cochlear morphology and apoptosis in mouse models of presbycusis

Objectives

Morphological studies on presbycusis, or age-related hearing loss, have been performed in several different strains of mice that demonstrate hearing loss with auditory pathology. The C57BL/6 (C57) mouse is a known model of early onset presbycusis, while the CBA mouse is characterized by relatively late onset hearing loss. We performed this study to further understand how early onset hearing loss is related with the aging process of the cochlea.

Methods

We compared C57 cochlear pathology and its accompanying apoptotic processes to those in CBA mice. Hearing thresholds and outer hair cell functions have been evaluated by auditory brainstem response (ABR) recordings and distortion product otoacoustic emission (DPOAE).

Results

ABR recordings and DPOAE studies demonstrated high frequency hearing loss in C57 mice at P3mo of age. Cochlear morphologic studies of P1mo C57 and CBA mice did not show differences in the organ of Corti, spiral ganglion, or stria vascularis. However, from P3mo and onwards, a predominant early outer hair cell degeneration at the basal turn of the cochlea in C57 mice without definitive degeneration of spiral ganglion cells and stria vascularis/spiral ligament, compared with CBA mice, was observed. Additionally, apoptotic processes in the C57 mice also demonstrated an earlier progression.

Conclusion

These data suggest that the C57 mouse could be an excellent animal model for early onset ''sensory'' presbycusis in their young age until P6mo. Further studies to investigate the intrinsic or extrinsic etiologic factors that lead to the early degeneration of organ of Corti, especially in the high frequency region, in C57 mice may provide a possible pathological mechanism of early onset hearing loss.     

Cu/Zn superoxide dismutase and age-related hearing loss

Mice, in which the genetics can be manipulated and the life span is relatively short, enable evaluation of the effects of specific gene expression on cochlear degeneration over time. Antioxidant enzymes such as Cu/Zn superoxide dismutase (SOD1) protect cells from toxic, reactive oxygen species and may be involved in age-related degeneration. The effects of SOD1 deletion and over-expression on the cochlea were examined in Sod1-null mice, Sod1 transgenic mice and in age- and genetics-matched controls. Auditory brainstem responses (ABR) were measured and cochleae were histologically examined. The absence of SOD1 resulted in hearing loss at an earlier age than in wildtype or heterozygous mice. The cochleae of the null mice had severe spiral ganglion cell degeneration at 7-9 months of age. The stria vascularis in the aged, null mice was thinner than in the heterozygous or wildtype mice. Over-expression of SOD1 did not protect against hearing loss except at 24 months of age. In conclusion, SOD1 seems important for survival of cochlear neurons and the stria vascularis, however even half the amount is sufficient and an over abundance does not provide much protection from age-related hearing loss.     

Candidate's Thesis: Platelet‐Activating Factor–Induced Hearing Loss: Mediated by Nitric Oxide?

Objectives/Hypothesis Platelet‐activating factor (PAF)in middle ear effusion is thought to induce hearing loss. The purpose of this study is to investigate the role of nitric oxide (NO) in the mechanism of PAF‐induced hearing loss by studying the effects of PAF application on the round window membrane (RWM) with and without PAF‐antagonist NO‐blocker. Study Design Longitudinal study on randomized guinea pigs using PAF to induce hearing loss. Methods Guinea pigs were divided into four groups: PBS, PAF, PAF‐antagonist, and L‐NAME. The PBS group received phosphate buffered saline (PBS) and the PAF groups received 10, 20, and 40 μg of PAF soaked into gelfoam and placed on the RWM. PAF‐antagonist (WEB 2170) and NOS inhibitor NG‐nitro‐l‐arginine‐methylester (L‐NAME) were injected intraperitoneally prior to PAF 20 μg application on the RWM. The following three tests were performed on each animal group: Hearing was tested with an auditory brainstem response (ABR) test over 24 hours. At the end of 24 hours, cochlear hair cells were examined by scanning electron microscopy (SEM) and immunohistochemistry was carried out on the cochlea to test the expression of inducible nitric oxide synthase (iNOS). Results The PAF group developed significant elevation of ABR threshold and cochlear hair cell damage in the SEM group as compared with the PBS control group. The PAF‐antagonist (WEB 2170) and the L‐NAME groups did not show significant elevation of ABR threshold and cochlear hair cell damage compared with the group administered PAF 20 μg, but in the PAF‐antagonist group, the elevation of ABR threshold was significant compared with that of the PBS control group, whereas it was not significant compared with the PBS group in the L‐NAME group. Strong expression of iNOS on cochlea was observed in the PAF group and lighter expression was seen in PBS, WEB 2170, and L‐NAME groups. Conclusions This study demonstrated that PAF placed on the RWM induced hearing loss and cochlear hair cell damage. The PAF‐antagonists and L‐NAME prevented the PAF‐induced hearing loss and inhibited iNOS expression in the cochlea. These findings suggest that the PAF‐induced hearing loss caused by cochlear hair cell damage may have been mediated by NO. PAF‐antagonists and L‐NAME may have future therapeutic implications in preventing sensorineural hearing loss associated with chronic otitis media. The results of this study have significant potential clinical application.     

Targeted Mutation of the Gene for Cellular Glutathione Peroxidase (Gpx1) Increases Noise-Induced Hearing Loss in Mice

Reactive oxygen species (ROS) and oxidative stress have been implicated in cochlear injury following loud noise and ototoxins. Genetic mutations that impair antioxidant defenses would be expected to increase cochlear injury following acute insults and to contribute to cumulative injury that presents as age-related hearing loss. We examined whether genetically based deficiency of cellular glutathione peroxidase, a major antioxidant enzyme, increases noise-induced hearing loss in mice. Two-month-old "knockout" mice with a targeted inactivating mutation of the gene coding for glutathione peroxidase (Gpx1) and wild type controls were exposed to broadband noise for one hour at 110 dB SPL. Auditory brainstem response (ABR) thresholds at test frequencies ranging from 5 to 40 kHz were obtained two and four weeks after exposure to determine the stable permanent component of the hearing loss. Depending on test frequency, Gpx1 knockout mice showed up to 16 dB higher ABR thresholds prior to noise exposure, and up to 15 dB greater noise-induced hearing loss, compared with controls. Within the cochlear base, there was also a significant contribution of the knockout to inner and outer hair cell loss, as well as nerve fiber loss. Our results support a link between genetic impairment of antioxidant defenses, vulnerability of the cochlea injury, and cochlear degeneration. Such impairment produces characteristics expected of some mutations associated with age-related hearing loss and offers one possible mechanism for their action.     

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).琥珀酸脱氰酶染色显示,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足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.