Effects of exposure to an augmented acoustic environment on auditory function in mice: roles of hearing loss and age during treatment

The effects of exposure to an augmented acoustic environment (AAE) on auditory function were evaluated in mouse strains that exhibit various degrees and time courses of progressive hearing loss (BXD-22, BXD-12, BXD-16, BXD-14, BALB/cJ), and in normal-hearing CBA/CaJ mice. Beginning at age 25 days, mice were exposed 12 h every night to a 70 dB SPL broadband noise AAE. The AAE was maintained for at least 30 days in each strain. Same-strain control mice were age-matched and maintained under normal vivarium acoustic conditions. The auditory brainstem response (ABR), acoustic startle response amplitude, and prepulse inhibition (PPI) were used to assess the auditory system. Exposure to the AAE resulted in improved auditory performance (better PPI, lower ABR thresholds) when hearing impairment was present, but not when hearing was normal. The ameliorative effects occurred irrespective of a mouse's age at the onset of hearing loss, as long as initiation of AAE treatment preceded the occurrence of severe hearing loss. If AAE treatment was delayed beyond such a point, loss of threshold sensitivity progressed as usual, although PPI could still benefit. Finally, AAE treatment can slow, but not prevent, the occurrence of severe genetically determined hearing loss.     

Effects of exposing gonadectomized and intact C57BL/6J mice to a high-frequency augmented acoustic environment: Auditory brainstem response thresholds and cytocochleograms

Gonadectomized and surgically intact adult C57BL/6J (B6) mice of both sexes were exposed for 12h nightly to a high-frequency augmented acoustic environment (AAE): repetitive bursts of a half-octave noise band centered at 20 kHz, 70 dB SPL. The effects of sex, gonadectomy, and AAE treatment on genetic progressive hearing loss (exhibited by B6 mice) were evaluated by obtaining auditory brainstem response thresholds at ages 3-, 6-, and 9-months; hair cell counts (cytocochleograms) were obtained at 9 months. A sex difference in the rate of genetic progressive hearing loss in B6 mice (observed by earlier studies) was confirmed, with females exhibiting a faster rate of threshold elevations and more severe loss of hair cells at age 9 months. Gonadectomy had no consistent effects on the rate or severity of hearing loss in non-exposed mice of either sex. An unexpected finding was that the high-frequency AAE treatment caused additional ABR threshold elevations and hair cell loss. In an earlier study, the same high-frequency AAE treatment on DBA/2J mice ameliorated hearing loss. The most severe AAE-induced losses occurred in surgically intact females, suggesting a potentiating effect of ovarian hormone(s).     

Neural plasticity in the mouse inferior colliculus: relationship to hearing loss, augmented acoustic stimulation, and prepulse inhibition

C57BL/6J (C57) and DBA/2J (DBA) mice exhibit progressive high-frequency hearing loss. Extracellular recordings of responses of neurons in the inferior colliculus (IC) evoked by 70-dB SPL tones indicated that normal tonotopic organization was greatly disrupted in both strains: still-audible lower frequencies (4-12 kHz) evoked responses in a large percentage of recording sites in ventral tonotopic regions that normally respond strongly to high frequencies only. To relate the IC responses to an auditory behavior, prepulse inhibition (PPI) was measured using 70-dB tones as prepulses. As high-frequency hearing loss progressed in C57 mice, prepulses of 4-12 kHz elicited stronger PPI, and this was significantly correlated with changes in the percentage of IC recording sites responding to 70-dB tones (the neural pathway for PPI includes the IC). The analysis was extended to DBA mice that had been exposed to an augmented acoustic environment (AAE) - a procedure that improves PPI. In these mice, a higher percentage of IC recording sites responded to 70-dB tones, and this was correlated with improved PPI. The data suggest that responses of IC neurons reflect both hearing loss-induced plasticity and changes induced by exposure to an AAE, and these neural changes are correlated with the magnitude of PPI.     

Assessment of hearing in 80 inbred strains of mice by ABR threshold analyses

The common occurrence of hearing loss in both humans and mice, and the anatomical and functional similarities of their inner ears, attest to the potential of mice being used as models to study inherited hearing loss. A large-scale, auditory screening project is being undertaken at The Jackson Laboratory (TJL) to identify mice with inherited hearing disorders. To assess hearing sensitivity, at least five mice from each inbred strain had auditory brainstem response (ABR) thresholds determined. Thus far, we have screened 80 inbred strains of mice; 60 of them exhibited homogeneous ABR threshold values not significantly different from those of the control strain CBA/CaJ. This large database establishes a reliable reference for normal hearing mouse strains. The following 16 inbred strains exhibited significantly elevated ABR thresholds before the age of 3 months: 129/J, 129/ReJ, 129/SvJ, A/J, ALR/LtJ, ALS/LtJ, BUB/BnJ, C57BLKS/J, C57BR/cdJ, C57L/J, DBA/2J, I/LnJ, MA/MyJ, NOD/LtJ, NOR/LtJ, and SKH2/J. These hearing impaired strains may serve as models for some forms of human non-syndromic hearing loss and aid in the identification of the underlying genes.     

Low-Frequency Tone Pips Elicit Exaggerated Startle Reflexes in C57BL/6J Mice with Hearing Loss

The strength of the acoustic startle reflex (ASR) as a function of age was studied in adult C57BL/6J and CBA/CaJ mice, because altered ASR levels are a potential behavioral consequence of the neural reorganization that accompanies the early-onset hearing loss of the C57BL, in contrast to the normal-hearing CBA. For C57BL mice at 14–36 weeks of age, compared with 7-week-old mice, high-frequency thresholds measured with the auditory brainstem response (ABR) were less sensitive by about 25–30 dB while the hearing loss at low frequencies was 10–15 dB, but by 60 weeks losses of 45–50 dB were present across the entire spectrum. Their ASR amplitudes for 16 kHz tone pips were highest at 7 weeks and then declined with age, but, for 4 kHz tones the ASR increased in strength at 18 weeks and beyond to levels above that of the younger mice. This hyperreactivity persisted even in 60-week-old mice. The ASR for 16 kHz stimuli was positively correlated with hearing sensitivity, but the ASR for 4 kHz stimuli was positively correlated with hearing loss for mice that were 18–36 weeks of age. Furthermore, ASR amplitudes for 4 kHz stimuli were positively correlated with the 16 kHz ASR in young C57BL mice but negatively correlated in older mice. There were no similar ASR or ABR changes in adult CBA mice through 19 weeks of age. Correlations between ASR and ABR scores were always weakly positive, and correlations between 4 kHz and 16 kHz ASR amplitudes were always strongly positive. The ASR data in older C57BL mice with hearing loss are consistent with reports describing their increased neural representation of low-frequency sounds and reinforce the value of this strain for studying the functional consequences that accompany age-related cochlear degeneration.     

封闭环境对C57BL/6J小鼠听功能及听皮层GABA能神经元凋亡的影响

目的探讨封闭环境对老年性聋动物模型C57BL/6J小鼠听皮层GABA能神经元凋亡的影响。方法构建封闭环境,将2、10月龄C57BL/6J小鼠(实验组,各20只)放入其中,并将另2、10月龄C57BL/6J小鼠各20只设立为开放环境对照组,饲养2月后比较不同环境各组动物ABR反应阈变化,免疫荧光法及tunel法检测听皮层GABA能神经元凋亡水平。结果实验组各频率ABR阈值明显高于对照组,尤其以高频明显(P<0.05);tunel检测证实实验组动物听皮层GABA能神经元凋亡显著增多。结论封闭环境能促进老年性聋动物模型C57BL/6J小鼠听皮层GABA能神经元的凋亡,可能是老年性聋的重要环境因素。     

Ameliorative Effects of Exposing DBA/2J Mice to an Augmented Acoustic Environment on Histological Changes in the Cochlea and Anteroventral Cochlear Nucleus

DBA/2J (D2) mice, which exhibit very early progressive sensorineural hearing loss, were treated nightly with an augmented acoustic environment (AAE) initiated before the onset of hearing, and consisting of repetitive bursts of a 70-dB sound pressure level (SPL), 4–25 kHz noise band. At 55 days of age, AAE-treated mice exhibited less elevation of auditory brainstem response thresholds, fewer missing hair cells, and greatly reduced loss of anteroventral cochlear nucleus (AVCN) volume and neuron number compared to untreated control mice. It was hypothesized that the central neuroprotective effect was associated with increased afferent input to AVCN neurons evoked by the AAE as well as a healthier cochlea.     

Effects of exposing C57BL/6J mice to high- and low-frequency augmented acoustic environments: auditory brainstem response thresholds, cytocochleograms, anterior cochlear nucleus morphology and the role of gonadal hormones

Gonadectomized and intact adult C57BL/6J (B6) mice of both sexes were exposed for 12h nightly to an augmented acoustic environment (AAE): repetitive bursts of a 70dB SPL noise band. The high-frequency AAE (HAAE) was a half-octave band centered at 20kHz; the low-frequency AAE (LAAE) was a 2-8kHz band. The effects of sex, gonadectomy, and AAE treatment on genetic progressive hearing loss (a trait of B6 mice) were evaluated by obtaining auditory brainstem response (ABR) thresholds at ages 3-, 6-, and 9-months. At 9-months of age, hair cell counts (cytocochleograms) were obtained, and morphometric measures of the anteroventral cochlear nucleus (AVCN) were obtained. LAAE treatment caused elevation in ABR thresholds (8-24kHz), with the highest thresholds occurring in intact females. LAAE treatment caused some loss of outer hair cells in the basal half of the cochlea (in addition to losses normally occurring in B6 mice), with intact females losing more cells than intact males. The loss of AVCN neurons and shrinkage of tissue volume that typically occur in 9-month-old B6 mice was lessened by LAAE treatment in intact (but not gonadectomized) male mice, whereas the degenerative changes were exacerbated in intact (but not gonadectomized) females. These LAAE effects were prominent in, but not restricted to, the tonotopic low-frequency (ventral) AVCN. HAAE treatment resulted in some loss of neurons in the high-frequency (dorsal) AVCN. In general, LAAE treatment plus male gonadal hormones (intact males) had an ameliorative effect whereas HAAE or LAAE treatment plus ovarian hormones (intact females) had a negative effect on age-related changes in the B6 auditory system.     

C57BL/6J 小鼠耳蜗血管纹Na-K-2Cl联合转运子-1的年龄相关性变化

目的观察不同周龄C57BL/6J(C57)小鼠听力及血管纹Na-K-2Cl联合转运子-1(Na-K-2Cl co-transporter-1,NKCC1)表达的情况。方法应用听性脑干反应(auditory brainstemresponse,ABR)分别检测4、8、16、32、48、64周龄组C57小鼠的听力;采用免疫组织化学染色法观察其血管纹NKCC1表达的变化。结果C57小鼠随年龄增大出现听力下降,自16周龄时ABR阈值出现显著性增高(P<0.05);血管纹NKCC1表达也出现年龄相关性减少,其灰度值自16周龄时显著增高(P<0.01)。结论C57小鼠血管纹NKCC1蛋白表达随年龄增长而减少,可能与年龄相关性听力损失具有一定相关性。     

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.     

Influence of genotype and age on acute acoustic trauma and recovery in CBA/Ca and C57BL/6J mice.

Two inbred strains of mice, CBA/Ca (with a moderate auditory impairment starting late in life) and C57BL/6J (with a progressive auditory degeneration starting during young adulthood), were exposed to a 120 dB SPL broadband noise (2-7 kHz) for 5 min at the age of 1, 3, or 6 months. Compound and permanent threshold shifts (CTS and PTS) were determined by auditory brainstem response during the first day (CTS) and 1 month (PTS) after exposure. With increasing age, susceptibility to CTS at middle frequencies (8 and 12.5 kHz) decreased in CBA mice, yet was retained in C57 mice. C57 mice were more severely affected by CTS than age-matched CBA mice. Noise-induced CTS was positively correlated to pre-exposure thresholds in C57 mice and to PTS over all ages and strains. The amount of recovery from CTS to PTS was, however, independent of age and strain. There was only a 2% risk of classifying CBA mice as C57 mice by pre-exposure thresholds at high frequency, while there was about 40% risk by CTS. The results indicate that genetic predisposition can affect susceptibility to auditory degeneration and noise impairment in a systematic manner, allowing the identification of susceptible individuals by pre-exposure audiometric examination, especially at high frequencies.     

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。     

NKCC1和Na-K-ATPase通道蛋白与老年性耳聋的关系及其在老年性耳聋不同阶段中的作用

目的：通过对C57BL/6J小鼠耳蜗中NKCC1和Na-K-ATPase的年龄相关性表达的研究，分析其与老年性耳聋的关系并进一步探讨其在老年性耳聋发生发展不同阶段中的作用。方法通过听性脑干反应（ABR）分别检测C57BL/6J小鼠在4、24和48周年龄段的听力水平。采用实时免疫荧光定量逆转录聚合酶链反应（RT-PCR）法分别检测NKCC1和Na-K-ATPase mRNA在各年龄段小鼠耳蜗中的表达水平。结果随着C57BL/6J鼠龄的增加，其ABR反应阈值逐渐升高（P〈0.05）。RT-PCR显示NKCC1和Na-K-ATPase mRNA在耳蜗的表达水平存在随鼠龄增加逐渐下降的趋势（P＜0.01）。结论 C57BL/6J小鼠的ABR反应阈值随鼠龄增加逐渐增高，具有老年性耳聋的特征；NKCC1和Na-K-ATPase两种通道蛋白随鼠龄的增加逐渐下降，与C57BL/6J小鼠的年龄相关性听力下降密切相关，可能与老年性耳聋后期发展及恶化有关。     

Age-Related Hearing Loss in C57BL/6J Mice has both Frequency-Specific and Non-Frequency-Specific Components that Produce a Hyperacusis-Like Exaggeration of the Acoustic Startle Reflex

Auditory brainstem-evoked response (ABR) thresholds were obtained in a longitudinal study of C57BL/6J mice between 10 and 53 weeks old, with repeated testing every 2 weeks. On alternate weeks, acoustic startle reflex (ASR) amplitudes were measured, elicited by tone pips with stimulus frequencies of 3, 6, 12, and 24 kHz, and intensities from subthreshold up to 110 dB sound pressure level. The increase in ABR thresholds for 3 and 6 kHz test stimuli followed a linear time course with increasing age from 10 to 53 weeks, with a slope of about 0.7 dB/week, and for 48 kHz a second linear time course, but beginning at 10 weeks with a slope of about 2.3 dB/week. ABR thresholds for 12, 24, and 32 kHz increased after one linear segment with a 0.7 dB slope, then after a variable delay related to the test frequency, shifted to a second segment having slopes of 3–5 dB/week. Hearing loss initially reduced the ASR for all eliciting stimuli, but at about 6 months of age, the response elicited by intense 3 and 6 kHz stimuli began to increase to reach values about three times above normal, and previously subthreshold stimuli came to elicit vigorous responses seen at first only for the intense stimuli. This hyperacusis-like effect appeared in all mice but was especially pronounced in mice with more serious hearing loss. These ABR data, together with a review of histopathological data in the C57BL/6 literature, suggest that the non-frequency-specific slow time course of hearing loss results from pathology in the lateral wall of the cochlea, whereas the stimulus-specific hearing loss with a rapid time course results from hair cell loss. Delayed exaggeration of the ASR with hearing loss reveals a deficit in centrifugal inhibitory control over the afferent reflex pathways after central neural reorganization, suggesting that this mouse may provide a useful model of age-related tinnitus and associated hyperacusis.     

The acoustic startle response in DBA/2 and C57BL/6 mice: relationship to auditory neuronal response properties and hearing impairment

The acoustic startle response (ASR) was elicited with tone pips in sensorineural hearing-impaired DBA/2 mice and in non-impaired C57BL/6 mice. The influence of stimulus frequency and intensity on ASR amplitude varied as a function of both strain and age. Previous neurophysiological findings indicate that ASR amplitude is correlated with the proportion of neurons in the cochlear nucleus and inferior colliculus that respond to the ASR stimulus frequencies and to the excitability of neurons in these structures. ASR amplitude is not highly correlated with threshold sensitivity. These observations suggest several neural correlates of ASR amplitude and have implications regarding central neuronal response properties associated with sensorineural hearing loss.     

Aging and the auditory brainstem response in mice with severe or minimal presbycusis

Threshold, latency, and amplitude of the auditory brainstem response (ABR) were obtained with filtered noise pips in young and aging C57BL/6J mice (to 16-months), which undergo severe progressive age-related sensorineural hearing loss (presbycusis) and CBA/J mice (to 19-months), which show only mild loss late in life. Aging per se (CBA mice) is not associated with significant changes in ABR parameters. Presbycusis, in aging C57 mice, is associated with increased thresholds; there is a trend toward increased latencies, but only when threshold elevations are substantial. Amplitudes of early waves, but not late waves, decrease greatly in aging C57 mice. In young C57 mice, amplitudes of early ABR waves vary monotonically with intensity, while amplitudes of later waves (IV and V) have a relatively flat, or even nonmonotonic, relationship to intensity; in older C57 mice, all waves have monotonie intensity functions. ABR parameters are not affected by gender in either strain. The mouse models can help to clarify some inconsistencies in the human literature on aging and the ABR.     

Age-related loss of auditory sensitivity in two mouse genotypes.

Frequency-specific auditory brainstem responses (ABR) (frequency range 2-31.5 kHz) were used to describe age-dependent alterations in frequency sensitivity in CBA/ca (to 30 months) and C57BL/6J (to 16 months) mouse genotypes. The two strains displayed an age-related loss similar to that of humans, with a primary decline in high-frequency sensitivity. CBA mice showed a slow, yet gradual decrease in sensitivity to high- followed by low-frequency until 18 months of age and a rapid deterioration at all frequencies thereafter. C57 mice demonstrated precocious aging in auditory sensitivity in an unsteady rather than gradual manner. By testing the same individuals on repeated occasions it was shown that, for C57 mice, the degenerative process was more precipitous with three phases, and that the individual variability was larger than that of CBA mice. It is suggested that the two mouse genotypes can be used to express the different aspects of human presbycusis in individual variability and modes of gradual or staggered progression.     

Sex- and age-related elevation of cochlear nerve envelope response (CNER) and auditory brainstem response (ABR) thresholds in C57BL/6 mice

The C57BL/6 mouse has long been considered, in scores of published studies, as a model of early adult-onset, progressive sensorineural hearing loss (presbycusis). The auditory brainstem response (ABR) has most often been used in these studies as a measure of functional loss. Whereas the ABR measures the response to a rapid acoustic onset, the cochlear nerve envelope response (CNER) measures the ability of cochlear nerve axons to respond to the low frequency modulations of the entire acoustic waveform, acoustic changes that are utilized in vocalizations and music. The present study compared the ability of these two measures to assess presbycusis in male and female C57BL/6 mice, at ages ranging from 50 to 400 days. Thresholds to the CNER were almost invariably more sensitive than the ABR, in response to stimulus frequencies ranging from 8 to 56 kHz. By 100 days of age, mice showed elevation of thresholds in response to high frequency stimuli, and this loss was greater in females than in males. These trends persisted for both measures over the next 300 days, involving successively lower frequencies.     

C57BL/6J小鼠在不同剂量氨基糖甙类药物暴露下听力损害的特点

目的探讨C57BL/6J小鼠在不同剂量氨基糖甙类药物毒性作用下听力损害的特点。方法采用不同剂量的庆大霉素对成年C57BL/6J小鼠进行腹腔注射,小鼠随机分成五组,药物剂量浓度分别为300mg/kg,200mg/kg,100mg/kg和50mg/kg。对照组为等量的注射用0.9%生理盐水,药物注射连续应用7天。分别于用药前(p0,对照组)以及用药后第2天(P2)、第4天(P4)、第7天(P7)检测动物的听功能(Click&Tonebrust),并进组间差异的比较分析。结果 (1)在50mg/kg组,用药后第7天的听阈值和对照组听阈分别为48.33±10.33(P7)和41.67±11.20(P0),两者相比具有显著性差异(P<0.05)。在100mg/kg组,用药后第4天的听阈值和对照组相比具有显著性差异(P4:48.89±9.16;P0:40.83±10.07,P<0.05)。在200mg/kg和300mg/kg组,用药后第2天的听阈值和对照组相比有显著上升(200mg/kg,P2:50.56±5.39;P0:40.42±9.66,P<0.05),(300mg/kg,P2:50.50±6.85,P0:40.00±11.00,P<0.05)。(2)各剂量组药物在Click和Toneburst(4kHz,8kHz&t16kHz)频率中,听力损害程度存在区别,损害程度依次为:200mg/kg组>300mg/kg组>100mg/kg组>50mg/kg组。(3)在8kHz&16kHz频率上,①50mg/kg与300mg/kg剂量组在给药后第2、4、7天均无明显听力变化(P>0.05)。②在100mg/kg组:与对照组相比,给药后第4天、第7天的听阈出现明显升高(P<0.05)。③在200mg/kg组:给药后第2、4、7天的听阈值亦出现显著升高(P<0.05)。(4)在给药后第7天,各剂量组的听阈均达到峰值。结论本研究表明:(1)随着给药剂量的增加,C57BL/6J小鼠听力损害出现的时间提前,但听力损害的程度并非同步加重;(2)以200mg/kg浓度给药后,小鼠听力在Click&Toneburst上均可以产生明显变化,同时小鼠的生理状态依然保持良好,因而200mg/kg(庆大霉素)浓度可能是C57BL/6J小鼠药物性致聋的理想剂量。