直流电脉冲刺激豚鼠耳蜗基底膜振动研究

为了在活体上研究哺乳类动物耳蜗基底膜的电－机械特性，将一对铂－铱电极分别置于３０只豚鼠耳蜗底回的前庭阶和鼓阶。用矩形直流脉冲电刺激蜗管，用激光多普勒测速仪测定电刺激诱发的耳蜗基底膜振动的幅度和速度。结果表明，在听敏度正常豚鼠的耳蜗，电刺激可诱发基底膜向正电极方向位移，其位移波形类似于电脉冲的矩形波。在矩形脉冲的起始沿和结束沿，由于外毛细胞的瞬态反应，可诱发与该部位特征频率一致的共振运动。据分析，这一共振运动是外毛细胞的主动耗能过程，并由耳蜗放大器参与。在听力受损的耳蜗，直流电刺激仍能引起基底膜的位移，但振铃运动明显减少或消失。这可能是受损毛细胞的能量代谢障碍所致。直流电刺激诱发的基底膜振动与声波一样，可通过行波沿基底膜向其它部位传输，这一特性奠定了电听觉和耳声发射的生理基础。     

蜗内直流电对耳蜗基底膜振动的影响

目的：探讨外加直流电流后对耳蜗基底膜振动的影响。方法：在豚鼠耳蜗底回距圆窗龛缘2．4mm处开一直径约0．4mm小孔，作为测量活体基底膜的振动速度测试窗，在测试窗上，下缘的鼓阶，前庭阶各开一小孔，将铂－铱电极置入鼓阶，前庭阶作为跨蜗管的电刺激电极，用激光多普勒干涉测速仪观察直流电流对纯音诱发的基底膜振动速度的影响。结果：当外加电流前庭阶极性为正，鼓阶极性为负时，可以看到基底膜振动速度显著增大，给相反极性电流时，基底膜振动速度减小。结论：生理状态下的正内淋巴电位是耳蜗将声音能量转变为神经冲动的必要条件，适当提高外毛细胞顶端正电位，有助于提高耳蜗放大器的增益，外加负电位则严重影响耳蜗放大器的增益。     

蜗内直流电对耳蜗基底膜振动的影响

目的探讨外加直流电流后对耳蜗基底膜振动的影响.方法在豚鼠耳蜗底回距圆窗龛缘2.4mm处开一直径约0.4mm小孔,作为测量活体基底膜的振动速度测试窗.在测试窗上、下缘的鼓阶、前庭阶各开一小孔,将铂-铱电极置入鼓阶、前庭阶作为跨蜗管的电刺激电极.用激光多普勒干涉测速仪观察直流电流对纯音诱发的基底膜振动速度的影响.结果当外加电流前庭阶极性为正,鼓阶极性为负时,可以看到基底膜振动速度显著增大,给相反极性电流时,基底膜振动速度减小.结论生理状态下的正内淋巴电位是耳蜗将声音能量转变为神经冲动的必要条件.适当提高外毛细胞顶端正电位,有助于提高耳蜗放大器的增益.外加负电位则严重影响耳蜗放大器的增益.     

耳蜗埋植病人的电诱发电位

为确定用电生理方法估价耳蜗功能的可靠性和难易度,本文作者进行了三个方面的试验:(一)比较豚鼠对声刺激和电刺激的反应;(二)比较耳蜗埋植病人用短声诱发的中潜伏期和主观行为反应;(三)比较耳蜗埋植病人对短声和声刺激的诱发听觉脑干反应。结果发现:电刺激引起豚鼠的反应类型与刺激电极和参考电极的放置部位无关;豚鼠耳蜗对电刺激和声刺激     

短纯音诱发的AP—SP复合波和滤波短声诱发AP的比较

本文用慢性园窗电极方法，记录豚鼠耳蜗电位，对短纯音诱发的AP－SP复合波和滤波短声诱发的AP波进行比较，结果提示用短纯音诱发的AP－SP复合波在各个频率波形分化清楚，具有较好的频率选择性，无论是正常听力，中耳疾患还是内耳病变的豚鼠，AP－SP复合波如同AP波一样，均可获得电反应的听力曲线，且AP－SP复合波对内耳病变更为敏感。     

沙土鼠在听力学研究中的应用

听力学是二战后由Ｄａｖｉｓ将其发展成专门研究听觉生理、病理和听觉障碍诊断、处理的一门独立学科。近年来,人们发现沙土鼠耳蜗结构与豚鼠十分类似,但高频听力比豚鼠敏锐,尤其在高频听力具有优势,其高频听力可达到４０～５０ｋＨｚ;沙土鼠的耳声发射更易引出;沙土鼠对电刺激诱发更敏感,如电刺激诱发的耳声发射（ｅｌｅｃｔｒｉｃａｌｌｙ　ｅｖｏｋｅｄ　ｏｔｏａｃｏｕｓｔｉｃ　ｅ－ｍｉｓｓｉｏｎ,ＥＥＯＡＥ）、电刺激诱发的听性脑干反应（ＥＡＢＲ）等都更易引出,更稳定。另外,沙土鼠饲养成本较豚鼠更低廉,且抵抗力较豚鼠…     

刺激电极在鼓阶内位置对听神经兴奋性的影响

目的　通过记录电诱发听性脑干反应 (electricallyevokedauditoryresponse ,EABR)阈值变化 ,探讨植入刺激电极在豚鼠耳蜗鼓阶内的位置对听神经兴奋性的影响。方法　在手术显微镜下 ,将标准刺激电极放在靠近蜗轴位置 ,用压碎的肌肉轻轻封住圆窗口 ,记录二次EABR阈值 ,取均值。然后取出刺激电极 ,再次植入电极靠近耳蜗鼓阶的外侧壁 ,再记录二次EABR阈值 ,取均值 ,然后比较前后二次记录到的EABR阈值变化。结果　植入电极在耳蜗鼓阶外侧壁的EABR阈值为 1.14± 0 .4 5mA ,较耳蜗内侧壁EABR阈值 (0 .2 8± 0 .0 9mA)明显升高 ,二者有显著性差异 (P <0 .0 1)。结论　电刺激听神经如果采用间距不宽的双极电极 ,其有效性同电极在耳蜗鼓阶内的位置密切相关 :植入电极越靠近被刺激的听神经成份 ,被检测到的EABR的阈值就越低。此为实验室设计蜗旁多导电极提供了依据     

压电材料仿耳蜗感觉上皮功能

目的:耳蜗植入压电材料模仿耳蜗毛细胞的声电转换功能。方法:在耳聋的豚鼠耳蜗鼓阶植入40μm厚的聚偏二氟乙烯膜,将其感应电压放大1000倍刺激螺旋神经元,记录外耳道104.4dB强声诱导产生的听性脑干反应。结果:耳蜗植入的压电感应装置可在外耳道强声刺激下模仿耳蜗毛细胞功能,产生对应的听性脑干反应。     

耳蜗基底膜非线性运动和响度重振与外毛细胞机械一电转换非线性的关系

现认为正反馈机制能使声音引起的哺乳动物耳蜗的行波增强和锐利，进而使基底膜的被动线性运动方式变为非线性。既往基于圆窗区记录到的耳蜗微音器电位与和电位资料推测，基底膜的非线性运动与外毛细胞机械一电转换的非线性相关。为证实这一点，该文研究了离体耳蜗毛细胞的感受器电位。豚鼠耳蜗外毛细胞机械分离，以膜片精技术记录其感受器电位，并采用3HZ正弦喷射水流作为刺激源以引起外毛细胞纤毛的偏移。观察纤毛编移程度与感受器电位之间的关系。结果发现：当纤毛向最长纤毛方向偏移IOOnm以内时，随其偏移程度的增加感受器电位呈线性增…     

豚鼠螺旋神经节细胞中钙磷脂结合蛋白Ⅵ表达及意义

目的钙离子在耳蜗功能中具有重要作用。本实验探讨与钙离子结合蛋白相关annexin家族中重要成员annexinⅥ在螺旋神经节细胞中的表达和意义。方法用原位杂交的方法检测正常和经过倍频窄带噪声刺激6小时的豚鼠基底膜铺片和石蜡包埋中轴切片中annexinⅥmRNA表达,所选用的探针为经过FITC标记的寡核苷酸。结果在正常未经处理的和接受噪声刺激的豚鼠耳蜗螺旋神经节细胞中均可见annexinⅥmRNA表达。接受噪声刺激的豚鼠耳蜗螺旋神经节细胞的染色明显较正常豚鼠强烈。结论annexinⅥ参于内耳的生理活动,短期的噪声刺激后annexinⅥ在螺旋神经节细胞中表达增高。     

The radial pattern of basilar membrane motion evoked by electric stimulation of the cochlea.

Electric current applied to the cochlea can evoke in situ electromotile responses of the organ of Corti. These nonsound-generated responses can give insight into the mechanics of the organ as the putative forces produced by outer hair cells (OHC) must couple to the modes of vibration of the basilar membrane (BM). In this study, platinum-iridium wire electrodes were positioned into the scala vestibuli and scala tympani of the first cochlear turn in the guinea pig. Current (1.5 ms rectangular-shaped pulses) was applied to these electrodes at levels to 500 microA peak. A laser Doppler velocimeter was used to record the velocity or displacement of the basilar membrane at the tonotopic 18 kHz place via an opening into the scala tympani of the first cochlear turn. Beads were positioned across the width of the BM so that the velocity or displacement of the BM could be studied in the radial direction. It was found that the current pulses evoked linear displacements of up to 2 nm for current levels of 500 microA (higher levels were damaging to the organ of Corti). The pattern of motion across the width of the BM was such that maximum displacement and velocity was located near the first row of OHCs and the position of the outer pillar cell footplate. The BM motion was biphasic in that the zona arcuata moved in the opposite direction to that of the zona pectinata. The results of this study demonstrate that the level of force produced by OHCs is effective in moving the BM and that the distribution of force within the organ of Corti leads to a multimodal motion pattern of the BM for this experimentally artificial means of evoking OHC motion.     

Effects of lidocaine on basilar membrane vibration in the guinea pig.

The effects of lidocaine on basilar membrane (BM) vibration and compound action potential (CAP) were studied in guinea pigs in order to elucidate the site of lidocaine action in the cochlea. BM vibration was measured with a laser Doppler vibrometer through an opening made in the lateral bony wall of the scala tympani at the basal turn. Ten min after local administration of lidocaine (250 microg) into the scala tympani, the velocity of BM vibration and the CAP amplitude decreased significantly at around the characteristic frequency of the stimulus sound (p < 0.05). The maximum decreases were 4 dB in the velocity of the BM vibration and 40 dB in the CAP amplitude. In contrast, such changes were not observed after i.v. injection of lidocaine (1.5 mg/kg). These results suggest that when lidocaine is administered locally in the cochlea it acts not only on the cochlear nerve but also on the outer hair cells.     

Effects of Lidocaine on Basilar Membrane Vibration in the Guinea Pig

The effects of lidocaine on basilar membrane (BM) vibration and compound action potential (CAP) were studied in guinea pigs in order to elucidate the site of lidocaine action in the cochlea. BM vibration was measured with a laser Doppler vibrometer through an opening made in the lateral bony wall of the scala tympani at the basal turn. Ten min after local administration of lidocaine (250 &#119 g) into the scala tympani, the velocity of BM vibration and the CAP amplitude decreased significantly at around the characteristic frequency of the stimulus sound ( p <0.05). The maximum decreases were 4 dB in the velocity of the BM vibration and 40 dB in the CAP amplitude. In contrast, such changes were not observed after i.v. injection of lidocaine (1.5 mg kg). These results suggest that when lidocaine is administered locally in the cochlea it acts not only on the cochlear nerve but also on the outer hair cells.     

Phase opposition between inner and outer hair cells and auditory sound analysis.

Recordings of single-unit responses in the auditory nerve of normal and kanamycin-treated Mongolian gerbils indicate that inner and outer hair cells of the cochlea interact in phase opposition. After kanamycin treatment, the firing rate in some fibers is increased during the basilar membrane motion toward scala vestibuli, in others, during its motion towards scala tympani. Because of statistical correlation with anatomical changes and characteristic time patterns, the first response polarity is associated with inner hair cells, the second, with outer hair cells. It is shown that normal responses can be reconstructed from the two kinds of responses seen after kanamycin treatment. The phase opposition between inner and outer hair cells, in connection with the expected effect of spiral fibers, provides an explanation for neural sharpening of mechanical filter action in the cochlea.     

The low-frequency response of inner hair cells in the guinea pig cochlea: implications for fluid coupling and resonance of the stereocilia

AC receptor potentials within the inner hair cells of the basal turn of the guinea pig cochlea have been recorded for stimuli in the frequency range 20 Hz to 3200 Hz. Comparison of these potentials with potentials recorded in scala media suggests that the stereocilia of many inner hair cells are stimulated by the transverse velocity of the cochlear partition for very low frequency, but above a transition frequency in the range 400 Hz to 1000 Hz they become entrained with partition displacement. It is suggested that such a transition is probably a simple consequence of the fluid coupling that drives these cells, and that mechanical resonance of the free-standing stereocilia of the inner hair cells does not occur in the basal turn of the guinea pig. These results do not, however, preclude the possibility of mechanical resonance involving the stereocilia of the outer hair cells. The results also indicate that the bodies of these cells low-pass filter the intracellular receptor potential, with a cutoff frequency of approximately 1000 Hz.     

Modulation of responses of spiral ganglion cells in the guinea pig cochlea by low frequency sound

Period histograms were generated from single unit data obtained from the spiral ganglion of the first turn of the guinea pig cochlea in response to continuous tones between 40 and 500 Hz. With the lowest intensities used, spontaneous activity was suppressed during basilar membrane displacement (inferred from cochlear microphonic phase) towards scala vestibuli and activity was enhanced during displacement towards scala tympani. At higher intensities the response changed to excitation during maximal basilar membrane velocity towards scala vestibuli. These patterns were delayed by about 0.5 ms producing large phase delays at the higher frequencies. We postulate that the displacement response is produced by cochlear microphonic originating from the outer hair cells acting on the inner hair cell membrane. In contrast, the velocity response is produced by the inner hair cell receptor potential. The effect of a 40 Hz tone on activity evoked by tones above, at, and below the characteristic frequency was investigated by generating period histograms synchronous with the 40 Hz tone. We found that activity evoked by tones around the characteristic frequency of the cell was suppressed during displacement of the basilar membrane towards scala tympani and enhanced in the opposite direction at 40 Hz intensities that had no effect on spontaneous activity. Further increase in the 40 Hz intensity produced suppression during scala vestibuli displacement with activity remaining only during the zero crossings. Still further increase produces the 40 Hz tone alone response. Activity evoked by tones in the low frequency ‘tails’ of the frequency threshold curve was not similarly modulated. This phenomenon is thought to be related to basilar membrane nonlinearity for frequencies close to the cut-off. Investigation of the effect of a 40 Hz tone on the threshold of the compound action potential confirmed data obtained from single units.     

Modifications of cochlear microphonic frequency responses following transient changes of hydrostatic pressure in the perilymph

Cochlear microphonic potential was recorded with differential electrodes implanted in the various turns of the guinea-pig cochlea. Isointensity frequency responses were plotted in normal conditions and after excessive displacements of the cochlear partition. These displacements were provoked by changes of hydrostatic pressure in the perilymph of scala tympani or scala vestibuli. Typical modifications of the frequency response were observed. The most noticeable was a division in two parts of the response zone which suggested the existence of two resonance peaks. Scanning electron microscopy revealed that changes of hydrostatic pressure provoked alterations of the stereocilia in the outer rows of external hair cells, probably in relation with a decoupling of the tectorial membrane from the organ of Corti. These results are discussed in terms of possible alterations of cochlear micromechanics.     

The modulation of the sensitivity of the mammalian cochlea by low frequency tones. II. Inner hair cell receptor potentials

Intracellular receptor potentials from inner hair cells and extracellular potentials within the tunnel of Corti immediately outside inner hair cells have been recorded in the first turn of the guinea pig cochlea. The a.c. and d.c. components of these receptor potentials elicited by high frequency tones within the tip of the isoamplitude tuning curve were modulated in synchrony with a simultaneously applied low frequency suppressor tone. The observed suppression was largest for peak low frequency displacements of the cochlear partition towards scala tympani and less pronounced for displacements towards scala vestibuli. Little suppression was observed at intermediate phases of the low frequency suppressor tone corresponding to the zero crossings of the low frequency motion of the cochlear partition. Receptor potentials elicited by high frequency tones in the tail region of the isoamplitude curve were also modulated, but less strongly and in the opposite phase (scala vestibuli) to the response to frequencies close to the characteristic frequency of the inner hair cell. The modulation for frequencies much below the characteristic frequency also occurred only over a very limited range of high frequency tone intensity. Suppression of the microphonic response to the low frequency tone by the high frequency stimulus was also observed.     

Intracochlear pressure and organ of corti impedance from a linear active three-dimensional model

Intracochlear pressure and basilar membrane (BM) velocity are calculated from a physiologically based chinchilla cochlea model . The model includes three-dimensional viscous fluid and the pectinate zone of the elastic BM with dimensional and material property variation along its length. The passive response shows excellent agreement with measurement at high sound pressure levels. The active process is represented by adding the motility of the outer hair cells (OHCs) to the passive model with the feed-forward approximation of the organ of Corti (OC), as was done previously. The current model explains recent observations including: (1) agreement with characteristic frequency (CF)-to-place map, (2) CF shift in the active model, (3) BM displacement gain from OHC motility, (4) lower intracochlear pressure gain than BM displacement gain, and (5) OC impedance (Z(OC)).