The influence of moderate-intensity noise on the click-evoked compound action potential of the guinea pig,Cavia porcellus

Summary Noise-induced alterations of the click-evoked compound potential (CAP) were studied by means of electrodes chronically implanted near the round window in 15 pigmented guinea pigs aged 3–6 months. The potentials were recorded before, during and after exposure to continuous pink noise maintained at an intensity of 80, 90 or 100 dB SPL for 120 h. During the exposure phase the CAP thresholds of all the animals tested increased exponentially, nearly leveling out by approximately 48 h to form an asymptotic threshold shift. Recovery after the end of exposure also occurred exponentially, with a return to the original threshold for neural excitation after at most 72 h. There was no detectable change in amplitude, latency or inter-peak interval of the CAP when correlated with the change in threshold.With the support of the Deutsche Forschungsgemeinschaft     

模拟失重和噪声复合因素对豚鼠内耳淋巴液容积的影响

目的探讨模拟失重和噪声复合因素对豚鼠内耳淋巴液容积的影响。方法健康豚鼠24只随机分为单纯失重组12只、单纯噪声组6只、失重+噪声组6只,分别测试实验前、实验5天及实验结束后3天听性脑干诱发电位(ABR)阈值及内耳MRI扫描,并用自制专用软件对内耳淋巴液容积进行计算。结果单纯噪声组实验前后内耳容积无差异(P>0.05);单纯失重组实验5天与实验前、实验结束后3天与实验5天相比有显著性差异(P<0.01),实验结束后3天与实验前相比无明显差异(P>0.05);失重+稳态噪声组实验5天及实验结束后3天豚鼠内耳容积较实验前明显增大(P<0.01),实验5天与实验结束后3天豚鼠内耳容积无显著差异(P>0.05)。结论失重环境可使豚鼠内耳淋巴液容积变大,但是短期单纯失重环境豚鼠内耳淋巴液容积变化可恢复,失重加噪声复合因素会加重内耳淋巴液容积变化,且实验后3天后内耳淋巴液容积无恢复。     

Age-related changes in the compound action potentials of the eighth nerve in guinea pigs

The eighth nerve compound action potential (CAP) in 95 guinea pigs was measured using click stimuli to investigate age-related changes in their neural auditory thresholds. The animals were separated into three groups: group A (n = 43, 86 ears; 2–4 months old); group B (n = 29; 58 ears, 13–15 months old); and group C (n = 23; 46 ears, 23–25 months old). With increasing age, a gradual elevation of CAP thresholds was clearly seen among the three groups. The negative peak (N1) latencies of the CAP were prolonged, and the N1 amplitudes of the CAP decreased. There were significant differences in N1 latencies among the three groups and in N1 amplitudes between groups A and B, and between groups A and C. However, the rate of decline of the thresholds as well as the input-output function curves of the CAP varied in some of the oldest animals, suggesting that there were some individual differences in degenerative aging processes of the auditory system.     

Frequency-dependence of early auditory evoked responses in the guinea pig

Summary Neural auditory responses in the guinea pig, monitored by surface electrodes (brain stem potentials and frequency-following responses) and by electrodes at the round window, were analyzed for evidence of frequency dependence in the range from 500 Hz to 15 kHz. The characteristics of the brain stem potentials and frequency-following responses with stimuli near threshold intensity for frequencies below 2 kHz indicate that this activity derives from the excitation of apical regions of the basilar membrane. The same interpretation applies to the potentials recorded at the round window. Comparison of the responses seen with surface electrodes and those appearing at the round window reveals that the broad potential P_I of the brain stem response to low-frequency stimuli corresponds to the compound action potential, while the frequency-following responses correspond to phase-locked responses in the acoustic nerve.     

Comparison of various short noise exposures in albino and pigmented guinea pigs

Summary Albino and pigmented guinea pigs were exposed to 20 kHz at 120 dB SPL for exposure durations of 30, 7.5, 6.5, 5 and 3.25 min. In a second series of experiments, the two shortest exposures were repeated after an interval of 6 or 24 h. Sensory hair cell loss was assessed 3 weeks post-exposure by surface preparations and quantified as percentage cell loss per segment per row, total numbers of outer and inner hair cells lost and the area of total outer hair cell damage. A variable but discrete area of damage resulted from these exposures. The main differences between the two strains were that in albino guinea pigs fewer ears were damaged after the shortest single exposures and generally more damage occurred after repeated exposures. However, no differences were detected in either strain when the interval between repeated exposures was changed.     

Age-dependent changes of the compound action potential in the guinea pig

Summary As a measure of age-related changes in the most peripheral neural part of the auditory pathway, the compound action potential of the guinea pig was analyzed. In addition to a marked threshold elevation, there was a significantly lower potential amplitude in old animals. By contrast, the latency of the compound action potential was unchanged. In view of the fact that the relative amplitude increase in the intensity range tested was the same in old as in young animals, the implication is that the auditory-nerve neurons that are still excited do not exhibit functional deterioration with aging.With the support of the Deutsche Forschungsgemeinschaft (DFG)     

豚鼠噪声暴露后畸变产物耳声发射与外毛细胞的改变

为观察豚鼠噪声暴露后畸变产物耳声发射（ＤＰＯＡＥ）与内耳毛细胞的改变，将１６只健康豚鼠分为３组，正常对照组３只，噪声后即刻组３只，７ｄ组１０只。暴露于１１５ｄＢ ＳＰＬ模拟潜艇机舱噪声中４ｈ，暴露后即刻及７ｄ检测ＤＯＰＡＥ听力图及Ｉ／Ｏ函数曲线，光镜及扫描电镜观察耳蜗毛细胞的改变。暴露即刻组ＤＰＯＡＥ振幅消失（Ｐ〈０．０１），７ｄ后又恢复至暴震前的基线水平（Ｐ〉０．０５）。光镜及扫描电镜显示耳蜗２     

The effect of impulse noise exposure on distortion product otoacoustic emissions in the awake guinea pig

Distortion product otoacoustic emissions (DPOAE) are a sensitive detector of outer hair cell (OHC) function and were monitored in awake guinea pigs before and after impulse noise damaging the cochlea (peak intensity 153 dB SPL, rise time < 0.1 ms). Animals had stable DPOAE levels before noise exposure. In the first hours after noise exposure DPOAE levels were reduced significantly. Three different patterns of recovery of DPOAE were seen in the post-exposure period: restitution exceeding controls, partial recovery and no recovery. In general, DPOAE levels declined and types of recovery closely corresponded to changes in amplitudes of cochlear microphonics after noise exposure. These data suggest that the monitoring of DPOAE is a suitable method for diagnosing impaired OHC function. Received: 25 February 1999 / Accepted: 1 July 1999     

Latencies of eighth nerve fibre responses with respect to their relative contribution to the compound action potential in the guinea pig

Summary We present a study of the latencies of click-evoked post-stimulus time histograms (PSTHs) in the guinea pig in the context of the auditory nerve fibre's contribution to the compound action potential (CAP) recorded at the round window. The latencies of the dominant PSTH peak were studied as a function of relevant physiological fibre properties, in particular the characteristic frequency (CF) and the spontaneous discharge rate (SR). We found that high-SR fibres have shorter latencies than low-SR fibres. These findings are discussed in the context of correlation between synaptic morphology and SR as described in the literature. The PSTH latency as a function of CF is described separately for low- and high-CF fibres for each of the two SR sub-groups. Finally, we discuss to what extent the various subgroups of fibres contribute to the N₁ peak of the CAP, the most commonly studied component.Presented at the 25th Workshop on Inner Ear Biology in London, England, 4–7 September 1988     

稳态强噪声暴露后听神经动作电位及神经丝蛋白表达的观察

目的 观察豚鼠暴露于稳态强噪声后听神经复合动作电位(CAP)及神经丝蛋白(NFP)的变化。方法 选用20只(40耳)Preyer反射正常的健康豚鼠，分为4组，噪声暴露后存活7天组(N-7d)、14天组(N-14d)和2个月组(N-2m)各5只，空白对照组(C)5只。噪声强度130dB(A)SPL，连续暴露5小时，于暴露前、暴露后3、7、14天、暴露后2个月分别测试CAP—N1波反应阈。免疫组化反应分别检测对照组、暴露后7、14天组、暴露后2个月组动物耳蜗内NFP的表达。结果稳态强噪声暴露后CAP—N1波反应阈明显增高，于暴露后7天基本稳定。暴露后7、14天NFP表达无明显变化，暴露后2月NFP表达显著减弱。结论 130dB(A)SPL稳态强噪声暴露5小时可以导致豚鼠CAP中重度永久性阈移，噪声损伤的早期NFP改变不明显，耳蜗NFP染色反应随着存活时间延长逐渐减弱，反映了损伤后神经纤维中骨架蛋白存在变性过程。     

短期铅暴露对成年豚鼠听性脑干反应的影响

摘要：目的观察短期铅暴露对成年豚鼠听性脑干反应（auditory brainstem response, ABR）的影响。方法将24只听力正常的成年黑目花色豚鼠随机分为4组（A、B、C、D组,每组6只）,分别用含醋酸铅浓度为2 mmol/L的铅水进行喂养0、15、30及60 d,所有动物均在实验结束时测试双耳ABR并断头采血检测血铅浓度。结果各组动物的血铅浓度分别为A组（58.91±7.76）μg/L、B组（659.00±62.71）μg/L、C组（733.00±68.96）μg/L、D组（701.80±54.75）μg/L。各组动物由click诱发的ABR阈值分别为A组（25.91±3.75）dB SPL、B组（23.57±5.56）dB SPL、C组（26.88±5.94）dB SPL、D组（25.63±5.00）dB SPL,各组动物之间比较,差异无统计学意义（P>0.05）。在70 dB SPL 的click声刺激下,随着铅暴露时间的延长,I波潜伏期出现延长的趋势,但差异无统计学意义（P>0.05）;30 d及60 d与对照组相比,III波振幅出现减小,其差异具有统计学意义（P<0.01）。结论短期铅暴露（2个月内）对成年豚鼠ABR阈值无明显影响,但铅暴露时间超过30 d,从耳蜗传导到中脑的听觉信号强度开始出现下降。     

Adrenergic innervation in the Eustachian tube of guinea pigs

Summary We have succeeded in demonstrating for the first time adrenergic innervation in the Eustachian tube of guinea pigs. The approach was histochemical using the fluorescence method with glyoxylic acid. There was an apparent regional variation with a greater number of axon terminals in the pharyngeal area of the Eustachian tube as compared to the tympanic area.This work was supported in part by a research grant from the Scientific Research Fund of the Ministry of Education, Science and Culture, Japan     

次声波对豚鼠畸变产物耳声发射幅度的影响

目的观察强次声波暴露后豚鼠畸变产物耳声发射(DPOAE)的变化情况.方法将15只豚鼠置于频率8Hz、强度为135dB SPL的次声声场中连续暴露90分钟.分别于强次声波暴露前及暴露后即刻(2h内)、2天和5天做畸变产物耳声发射测试.结果强次声波暴露后豚鼠DPOAE的幅度值在各个频率段与暴露前相比均有明显的降低(p＜0.01),随着时间的推移,各个频率的幅度虽有一定的恢复,但仍明显低于暴露前水平(p＜0.01).结论强次声波可导致豚鼠耳蜗外毛细胞功能明显减退.     

The reaction of the guinea pig cochlea to perforations of the round window membrane with and without perilymph aspiration

Summary The influence of simple opening of the round window (RW) membrane and the effect of aspiration of perilymph on the electrophysiological characteristics of the cochlea was tested in guinea pigs by measurement of the compound action potentials. We found that perforations of the RW membrane failed to lead to either shortterm or long-term damage in cochlear function. There was only a slight spontaneous escape of perilymph but without measurable functional loss. Additional aspiration of perilymph led to entry of air into the basal turn and to an immediate loss of function of the cochlea. This regressed within 4 weeks in the middle- and low-frequency ranges. Measurable long-term damage persisted only in the high-frequency ranges. We attribute contradictory results of other authors to methodological errors which we avoided by a specific selection of healthy animals and the development of standardized operation, recording and measurement procedures.     

Effects of anoxia on the cochlear summating potential in the guinea pig

Summary The cochlear summating potential (SP) was recorded extracochlearly from the apex and the round window in 25 guinea pigs, applying anoxia during periods of 1–2 min. For 2 and 8 kHz tone pips at 80 and 60 dB SPL, respectively, the initially negative SP at the apex diminished and even became positive during oxygen cut-off. After restoration of oxygenation, the change in SP reversed direction and was followed by a large negative undershoot. At the round window, the initially positive SP evoked by 8 kHz, 60 dB SPL tone pips followed exactly the same time course, but with inverted polarity, while the majority of the recordings of the initially negative SP evoked by 2 kHz, 80 dB SPL tone pips followed a course similar to the apical negative SP. However, the negative round window SP showed only slight polarity reversal and no undershoot. A small number of the recordings at the round window for 2 kHz showed an increase of the negative SP during anoxia followed by a decline of the SP and recovery after anoxia. The similar time course of the initially negative SP at the apex and the initially positive SP at the round window failed to support the hypothesis of a multi-component SP. However, the polarity reversal during anoxia and the different reactions to anoxia of the 2 kHz round-window SP suggest that the SP may consist of several different components.     

噪声对豚鼠耳蜗电位及其超微结构的影响

目的观察噪声暴露对豚鼠耳蜗电位和超微结构的影响。方法选用健康杂色豚鼠10只,以右耳为噪声暴露耳,以左耳为对照耳,右耳持续给白噪声100dBSPL2小时。于噪声暴露前及噪声暴露后测量右耳耳蜗电位,并于噪声暴露后取噪声暴露耳和对照耳的耳蜗,应用透射电镜进行形态学的观察。结果噪声暴露后耳蜗微音电位幅度下降并且其非线性特点消失,听神经复合动作电位阈值明显升高;内毛细胞及其下方传入神经末梢空化,外毛细胞溶酶体增多、胞浆内出现空泡。结论噪声暴露不仅引起外毛细胞的损伤,还可以引起内毛细胞及传入神经纤维的损伤。     

镫骨全切除和吸引噪声对豚鼠耳蜗功能与超微结构的影响

本实验应用耳蜗电图和扫描、透射电镜等技术观察了6组(44只)豚鼠镫骨全切除后,前庭窗开放时间的长短和听泡内使用吸引器对耳蜗功能和超微结构的影响程度.结果如下:①随前庭窗开放时间的延长、复合蜗神经动作电位(compound action potential.CAP)反应阈进行性提高,开放180min可导致底回部分外毛细胞变性或破坏;②镫骨全切除后,听泡内较长时间地(60min)应用吸引器可引起CAP明显阈移和耳蜗底回部分外毛细胞的不可逆病变;③镫骨未切除时,听泡内吸引60min,仅引起CAP阈移,但外毛细胞未见损伤.结果提示:术中长时间开放前庭窗和鼓室内应用吸引器可能是引起镫骨全切除术后感音神经性聋的因素之一,但鼓室成形术中鼓室内吸引噪声可能因其强度不够大,不足以引起术后感音神经性聋.     

模拟失重条件下飞船内噪声对豚鼠耳蜗形态与功能的影响

目的探讨模拟失重条件下,飞船内稳态噪声对豚鼠耳蜗形态与功能的影响。方法32只豚鼠随机分为单纯失重组16只、失重＋稳态噪声组16只。后肢悬吊法模拟失重,暴露于模拟飞船内在天飞行段的噪声环境,共5天。实验前、实验结束后即刻和实验结束后3天测试脑干诱发电位（ABR）阈值,取耳蜗标本行扫描电镜和透射电镜观察。结果实验组实验结束后即刻ABR阈值较实验前及实验结束后3天均增高（P〈0.01）;实验结束后3天ABR阈值较实验前高（P〈0.05）;实验结束后即刻及实验结束后3天失重＋稳态噪声组ABR阈值均较单纯失重组高（P〈0.01）。扫描电镜观察实验组实验结束后即刻耳蜗内、外毛细胞均受损。实验结束后3天,单纯失重组少数耳蜗各回内、外毛细胞的损伤程度比实验结束即刻加重;失重＋稳态噪声组耳蜗各回内毛细胞损伤较实验结束即刻重,外毛细胞损伤较实验结束即刻轻。实验组各时间段内毛细胞的损伤均重于外毛细胞,自第一回至第四回毛细胞损伤逐渐加重。透射电镜观察实验组耳蜗毛细胞及神经节细胞均可见空泡样改变,线粒体分布减少,细胞核固缩,可见细胞凋亡和细胞坏死两种细胞死亡现象。结论失重及失重＋稳态噪声均可造成豚鼠耳蜗形态和功能损伤,后者造成的损伤更重。失重对耳蜗毛细胞损伤以内毛细胞为重,损伤从底回至顶回逐渐加重。实验结束后3天较实验后即刻的听功能有所恢复但内毛细胞损伤加重。     

Auditory function in guinea pigs treated with netilmicin and other aminoglycoside antibiotics

Summary The following aminoglycoside antibiotics netilmicin, sisomicin, gentamicin, and kanamycin were submitted to a comparative study of their ototoxicity using both reflexological (Preyer's pinnareflex) and electrophysiological (near and far field) methods. The daily s.c. administration of sisomicin, gentamicin, and kanamycin for 21 days provoked a dose-related impairment of the cochlear function, detected with all the employed techniques. On the other hand, a very low ototoxic effect of netilmicin was demonstrated with electrophysiological but not with the reflexological evaluation.The reliability of the methods used in these experiments is also compared.     

Transient focal cooling at the round window and cochlear nucleus shows round window CAP originates from cochlear neurones alone

We have measured the compound action potential (CAP) evoked by very brief high-frequency tone-bursts (20 kHz, 1/4 ms) at the round window (RW) and at the surface of the cochlear nucleus (CN) in guinea pigs before, during and after a localised chilling of either the cochlea or CN, with a non-toxic ‘freeze spray’. CN chilling almost abolished the negative-going component of the CAP measured in the CN (generated by the CN and here called the cochlear nucleus response or CNR), leaving a positive-going localised response from the cochlear neurones as they leave the internal auditory meatus. Within 3 min, the CNR recovered to control values. During that time, the N₁ component of the RW CAP was slightly increased and the P₁ was larger, even though the CNR was abolished, indicating that the P₁ was not due to electrotonic spread of current from the CN. The N₂ and successive peaks at the RW were also abolished, but returned after 30 s. When the cochlea was chilled, the RW CAP was initially reduced in amplitude, presumably due to a drop in the number of cochlear neurones spiking in response to sound, but recovered within 3 min to be larger than the control waveform, with a more prominent N₁ peak which was delayed slightly, making the CAP more monophasic. At the same time, the CNR was smaller, presumably due to fewer cochlear neurones responding, but overall the CN CAP was altered little in waveshape. These experiments indicate that that RW CAP is generated almost solely by cochlear neurones. We also suggest that some of the changes in the RW CAP during the chills were due to changes in the firing of the lateral olivo-cochlear system of efferent neurons.