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.     

Spatial distribution of electrically induced high frequency vibration on basilar membrane

We reported that the electrically evoked basilar membrane (BM) vibration at frequencies above the best frequency (BF) showed a lowest BM velocity magnitude, called a "dip", in the velocity-frequency spectra, indicating a cancellation. In the present study, we measured the high frequency BM motion as functions of the longitudinal and radial locations. Measurements were taken at three longitudinal locations in the first turn and the hook region: 14.9, 15.8 and 16.8 mm from the apex, corresponding to the BFs of 17, 21.3 and 28.0 kHz calculated from Greenwood [J. Acoust. Soc. Am. 87, 2592], and at different radial locations across the width of the BM. It was found that the dip frequency (DF) varied with the longitudinal and radial locations. In the longitudinal direction, the average value of the DF was 49.6, 55.6 and 72.8 kHz, respectively. Thus, the longitudinal distribution of the high frequency BM vibration was correlated with the BF. In the radial direction, there was consistent variation of the response spectrum such that the dip was mainly evident in the pectinate zone of the BM. These results imply that the high frequency BM motion is related to mechanical properties of the cochlear partition, including the outer hair cells (OHCs) themselves. Data also indicate different vibration modes across the width of the organ of Corti.     

The ultrastructure of the basilar membrane in the cat

A detailed study of the feline basilar membrane was performed in 13 cochleae with light microscopy and in six with electron microscopy. The distribution of the mesothelial cells and homogeneous ground substance with the filaments was recorded and plotted as a function of length along the cochlear duct. The width, thickness and number of filaments were also measured. In the lower basal turn the basilar membrane was narrowest and its entire thickness was occupied by filaments. In the apical region the width was maximal and the filaments were fewer. The density of the filaments counted in the bundles showed no significant difference along the cochlear duct or across the width of the basilar membrane, but the number of filaments decreased markedly (approximately a ten-fold difference) from base to apex. The number of mesothelial cells increased towards the apex. These morphological characteristics may be related to the different motion pattern of the basilar membrane along the length of the cochlear duct. A discontinuity of the basement membrane was noted in the apical region in all cochleae studied. These gaps seemed to provide structural evidence for the permeability of the basilar membrane in this area. The vas spiralis was present as a blood vessel in two specimens and only in the apical region. Thus, its function as the sole nutritional source for the organ of Corti is doubtful.     

Measurement of Basilar Membrane Motion During Round Window Stimulation in Guinea Pigs

Driving the cochlea in reverse via the round window membrane (RWM) is an alternative treatment option for the hearing rehabilitation of a nonfunctional or malformed middle ear. However, cochlear stimulation from the RWM side is not a normal sound transmission pathway. The basilar membrane (BM) motion elicited by mechanical stimulation of the RWM is unknown. In this study, the BM movement at the basal turn was investigated in both reverse via RWM drive and acoustic stimulation in the ear canal or forward drive in postmortem isolated temporal bone preparations of guinea pigs. During reverse drive, a magnet-coil was coupled on RWM, and the BM vibration at the basal turn and the movement of the incus tip were measured with laser Doppler vibrometry. During forward drive, the vibration of the incus tip induced by sound pressure in the ear canal resulted in BM vibration and the BM movement at the same location as that in the reverse stimulation was measured. The displacement ratio of the BM to RWM in reverse drive and the ratio of the BM to incus in forward drive were compared. The results demonstrated that the BM response measured in both situations was similar in nature between forward and reverse drives. This study provides new knowledge for an understanding of BM movement induced by reverse drive via the RWM stimulation.     

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。     

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，用激光多普勒汛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     

Differences in the distribution of F-actin in outer hair cells along the organ of Corti

There is evidence of differences in the structure, innervation and physiological responses between outer hair cells (OHCs) of the basal and apical turns of the mammalian cochlea. In this study we have used rhodamine-labelled phalloidin to investigate the differential distribution of F-actin in OHCs along the organ of Corti of the guinea pig. Isolated OHCs and surface preparations and cryosections of the organ of Corti were studied. F-actin was observed in stereocilia and the cuticular plate of all OHCs. In addition, some OHCs had a network of F-actin extending from the cuticular plate towards the nucleus. This infracuticular network was observed in most OHCs of the apical cochlear turns but was not seen in any OHCs of the basal turn. These microstructural differences between OHCs of the base and apex could be related to differences in OHC function between the apical and basal portions of the cochlea.     

Elektromechanische Transduktion

BACKGROUND: The somatic electromotility of the outer hair cells can be induced by an extracellular electrical field. This enables us to investigate the electromechanically induced motion of the organ of Corti. METHODS: The electrically induced motion of the guinea-pig organ of Corti was measured with a laser Doppler vibrometer in three cochlear turns at ten radial positions on the reticular lamina (RL) and six on each of the upper and lower surfaces of the tectorial membrane (TM). RESULTS AND CONCLUSIONS: We found a complex vibration pattern of the RL and TM, leading to a stimulus synchronous modulation of the depth of the subtectorial space in the region of the inner hair cells (IHCs). This modulation causes radial fluid motion inside the space up to at least 3 kHz. This motion is capable of deflecting the IHC stereocilia and provides an amplification mechanism additional to that associated with basilar-membrane motion.     

Evaluating cochlear implant trauma to the scala vestibuli

Objectives: Placement of cochlear implant electrodes into the scala vestibuli may be intentional, e.g. in case of blocked scala tympani or unintentional as a result of trauma to the basilar membrane or erroneous location of the cochieostomy. The aim of this study was to evaluate the morphological consequences and cochlear trauma after implantation of different cochlear implant electrode arrays in the scala vestibuli. Design: Human temporal bone study with histological and radiological evaluation. Setting: Twelve human cadaver temporal bones were implanted with different cochlear implant electrodes. Implanted bones were processed using a special method to section undecalcified bone. Main outcome measures: Cochlear trauma and intracochlear positions. Results: All implanted electrodes were implanted into the scala vestibuli using a special approach that allows direct scala vestibuli insertions. Fractures of the osseous spiral lamina were evaluated in some bones in the basal cochlear regions. In most electrodes, delicate structures of the organ of Corti were left intact, however, Reissner's membrane was destroyed in all specimens and the electrode lay upon the tectorial membrane. In some bones the organ of Corti was destroyed. Conclusions: Scala vestibuli insertions did not cause severe trauma to osseous or neural structures, thus preserving the basis for electrostimulation of the cochlea. However, destruction of Reissner's membrane and impact on the Organ of Corti can be assumed to destroy residual hearing.     

The cochlea of the spontaneously diabetic mouse

Summary We used transmission electron microscopy to examine the cochleae of non-obese diabetic mice as animal models for human type I or non-insulin-dependent diabetes mellitus. Pathological changes were observed in the organ of Corti of the basal turn and in the stria vascularis of each turn. Major findings in the stria vascularis were protrusion or condensation of marginal cells, swelling of intermediate cells, and widening of the intercellular spaces. Principal findings in the organ of Corti involved degenerative changes of the outer and inner hair cells and replacement of hair cells by supporting cells. No prominent pathological changes were observed in the capillaries. The possible mechanism of diabetic involvement in cochlear pathology is discussed.     

The cochlea of the spontaneously diabetic mouse. II. Electron microscopic observations of non-obese diabetic mice

We used transmission electron microscopy to examine the cochlea of non-obese diabetic mice as animal models for human type I or non-insulin-dependent diabetes mellitus. Pathological changes were observed in the organ of Corti of the basal turn and in the stria vascularis of each turn. Major findings in the stria vascularis were protrusion or condensation of marginal cells, swelling of intermediate cells, and widening of the intercellular spaces. Principal findings in the organ of Corti involved degenerative changes of the outer and inner hair cells and replacement of hair cells by supporting cells. No prominent pathological changes were observed in the capillaries. The possible mechanism of diabetic involvement in cochlear pathology is discussed.     

Distribution of F-actin and fodrin in the hair cells of the guinea pig cochlea as revealed by confocal fluorescence microscopy.

We double-stained paraformaldehyde fixed guinea pig cochleas with rhodaminated phalloidin to detect F-actin and with a monoclonal antibody against non-erythroid spectrin (fodrin). The hair cells were studied in surface specimens of the organ of Corti with confocal fluorescence microscopy. In serial optical sections, phalloidin stained the stereocilia, cuticular plate, and a circumferential ring beneath it in the inner and outer hair cells (IHCs and OHCs). The cytoplasm of the IHCs and the OHCs was unlabelled, but the infracuticular network of the OHCs in the upper turns showed a strong reaction. The lateral plasma membrane was unreactive with phalloidin in the IHCs and OHCs, except in the basal turn, where a moderate reaction, probably representing actin of Deiter's cups, was seen along the lateral walls of the basal pole of the OHCs. Fodrin was similarly seen in the cuticular plate, in a circumferential ring beneath it, and in the infracuticular network of the apical OHCs. The most interesting finding was the fodrin-specific distinct labelling of the lateral cell surface in the OHCs of the basal cochlear turn. This staining diminished towards the apex and was practically absent in the OHCs located above the level of 15 mm from the round window. The lateral cell surface of IHCs showed moderate fodrin labelling in all cochlear turns. This staining was much weaker than that seen in the basal OHCs. Fodrin labelling revealed deformation from the regular cylindrical shape in midportion of the OHC bodies in the basal turn of the cochlea.     

A short history of hearing research. IV: Physiology]

In 1863, Hensen concluded from measurements of the width of the basilar membrane that tones of high and low pitch were represented at the base and apex of the cochlea, respectively. According to his calculations on the tonotopic representation of sound stimuli in the cochlea Helmholtz proposed additional resonators that would transmit the amplified signal to the afferent nerve endings. He speculated that the pillar cells of the tunnel of Corti or strands of the basilar membrane might be these proposed resonators. The resonance theory was contradicted by Wien in 1905. However, further experiments by Held and Kleinknecht in 1927 and by Békésy in 1928 demonstrated that Helmholtz's ideas on the tonotopic dispersion of the vibration of the basilar membrane were correct. Békésy measured the vibration of the cochlear partition in human and animal cadavers and discovered the travelling-wave of the basilar membrane. At the turn of the century Ter Kuile noted that the vibration of the cochlear partition caused a deflection of the sensory hairs of the hair cells, the auditory receptor cells. Wever and Bray described in 1930 stimulus-evoked electrical currents near the cochlea with a wave form similar to that of the original sound stimulus. It was Adrian who later coined the term "cochlear microphonics" for this phenomenon. According to calculations of Gold (1948) and others active mechanical amplification would be required for such a sharp tuning in the cochlea. The first to measure action potentials of the afferent auditory nerve was Tasaki (1954).(ABSTRACT TRUNCATED AT 250 WORDS)     

The Coxsackievirus and Adenovirus Receptor: a new adhesion protein in cochlear development

Interferometric measurement of the vibration of the organ of Corti in the isolated guinea pig cochlea was conducted using low-coherence light (1310 ± 47 nm wavelength) from a superluminescent diode. The short coherence length of the light source localized measurements along the axial direction to within a 10-μm window (in tissue), even when using a low numerical-aperture lens. The ability to accomplish this is important because measurement of the vibration of the basal-turn organ of Corti is generally done via a small hole in the bone of the cochlea, which effectively limits the numerical aperture. The axial localization, combined with the inherent sensitivity of the method, allowed distinct measurements of the basilar membrane (BM) and the putative reticular lamina (RL) vibration using only the native tissue reflectance, that is without requiring the use of reflective particles. The system was first operated in a scanning mode as an optical coherence tomography (OCT) system to yield an image of the organ of Corti. The reflectance of intensity from the BM and RL was 8 × 10⁻⁵ and 8 × 10⁻⁶, respectively. The internal structure between the BM and RL presented a variable reflectivity of about 10⁻⁷. A mirror would define a reflectance of 1.00. Then the instrument was operated as a homodyne interferometer to measure the displacement of either the BM or RL. Vibration at 16 kHz was induced by a piezoelectric actuator, causing whole movement of a dissected cochlea. After calibration of the system, we demonstrated clear measurement of mechanically driven vibration for both the BM and RL of 0.30 nm above a noise floor equivalent to 0.03 nm. OCT interferometry, when adapted for in vivo organ of Corti measurements, appears suitable to determine the micromechanical vibration of cells and tissue elements of the organ.     

Basilar membrane and osseous spiral lamina motion in human cadavers with air and bone conduction stimuli

It is generally accepted that bone conduction (BC) stimuli yield a traveling wave on the basilar membrane (BM) and hence stimulate the cochlea by the same mechanisms as normal air conduction (AC). The basis for this is the ability to cancel or mask a BC tone with an AC tone and the ability to generate two tone distortion products with a BC tone and an AC tone. The hypothesis is proposed that BC stimulates the BM not only through the hydrodynamics of the scala vestibuli and scala tympani, but also through osseous spiral lamina (OSL) vibrations. To test this hypothesis the BM and OSL response with AC as well as BC stimulation was measured with a laser Doppler vibrometer. Human temporal bones mounted on a shaker were used to record the velocities of the bone per se, the BM and the OSL. The measurements were then converted to relative BM and OSL velocities. The results from the basal turn of the cochlea show similar behavior with AC and BC stimulation. The motion of the OSL at the edge where it connects to the BM is in phase and is typically 6 dB lower than the BM motion. With BC stimulation, there is less phase accumulation in the OSL after the cochlea is drained; the OSL moves due to inertial forces and resonates at approximately 7 kHz. Inertial vibration of the OSL may partially contribute to the total response of BC sound, especially at the high frequencies, although current models of the cochlea assume a rigid OSL. The measurements reported here can be used to include a flexible OSL in cochlear models.     

The organ of Corti in the bat Hipposideros bicolor

The bat Hipposideros bicolor (Hipposideridae, Microchiroptera) is the mammalian species with the highest upper limit of hearing in which the structure of the organ of Corti has been studied. H. bicolor emits pure tone echo-locating signals of 153 kHz, compensates for Doppler shifts in the echo and hears ultrasonic frequencies up to 200 kHz (Neuweiler et al., 1984). The organ of Corti was investigated qualitatively and quantitatively using the technique of semi-thin sectioning. Some complementary ultra-thin sections were also examined. Length, width and cross-sectional area of the basilar membrane, the tectorial membrane, the hair cells with their stereocilia and the organ of Corti were measured at equi-distant positions on the basilar membrane. The organ of Corti of H. bicolor is composed of elements similar to those found in the cochleae of other eutherian mammals studied. However, in H. bicolor some of these elements show species-specific differences when compared to auditorily unspecialized mammals. The most basal region of the cochlea is characterized by miniaturization and re-inforcement of macro- and micro-mechanically important elements. This is interpreted as an adaptation for hearing extremely high frequencies. Specialized structures as well as local maxima of 'normal' elements in the basal and middle cochlear region are associated with evaluation of the echos of emitted pure tones. Besides the basal specializations. Hipposideros also shows specializations in the apical, low frequency, region which can be correlated with passive acoustic orientation.     

Temporal bone histopathology of noise-induced hearing loss

To examine the relationship between hearing and changes in the inner ear, we investigated human temporal bone specimens from 2 patients with noise-induced hearing loss and prepared audio-cytocochleograms as described by Schuknecht et al. Patient 1 was a 50-year-old male who died of thyroid cancer and had worked at a printing house for 38 years. Patient 2 was a 58-year old male who died of maxillary sinus cancer and had worked in construction for 22 years. A pure-tone audiogram showed high-tone sensorineural hearing loss with c5-dip-type hearing disorder in both ears in Patient 1, and a high-tone abrupt form of sensorineural hearing loss in Patient 2. Pathological examination of the temporal bone revealed degeneration and disappearance of the organ of Corti at the basal turn and disappearance of cochlear neurons in both patients. Audio-cytocochleograms revealed hearing disorder consistent with the changes in the inner ear in both patients. Marked degeneration and disappearance of the organ of Corti and stria vascularis were present in patient 1. It is generally known that disorders of the organ of Corti for a long period is involved in the etiology of noise-induced hearing loss. This degeneration of the organ of Corti is produced at a basilar membrane with the maximum amplitude related to exposure to noise according to a physical and mechanical factors. Moreover, animal experiments have shown that exposure to noise decrease cochlear blood flow. In Patient 1 both the organ of Corti and the stria vascularis exhibited degeneration, suggesting that not only physical and mechanical factors but a cochlear circulatory disorder related to exposure to noise was involved in the etiology of the pathological changes in the temporal bone related to noise-induced hearing loss.     

Postnatal development of the organ of Corti in cats: a light microscopic morphometric study

This study quantitatively characterizes the development of the major morphological features of the organ of Corti during the first 2 weeks postnatal, the period when the cat auditory system makes the transition from being essentially non-functional to having nearly adult-like responses. Four groups of kittens (n=3) were studied at one day postnatal (P1), P5, P10, P15, and compared to adults. Measurements were made of the organ of Corti at 3 cochlear locations: 20%, 60% and 85% of basilar membrane length from the base – cochlear locations which in the adult correspond to best frequencies of ≈20 kHz, 2 kHz and 500 Hz, respectively. In addition, measurements of basilar membrane length and opening of the tunnel of Corti were made in 20 cochlear specimens from kittens aged P0–P6. Results indicate that: (i) at P0 the basilar membrane has attained adult length, and the tunnel of Corti is open over approximately the basal one-half of the cochlea; (ii) the initial opening of the tunnel of Corti occurs at a site about 4 mm from the cochlear base (best frequency of ≈25 kHz in the adult cochlea); (iii) the thickness of the tympanic cell layer decreases markedly at the basal 20-kHz location; (iv) the areas of the tunnel of Corti and space of Nuel and the angulation of the inner hair cells (IHC) relative to the basilar membrane all show marked postnatal increases at both the middle and apical locations; (v) IHC are nearly adult-like in length and shape at birth, whereas the OHC (at 2-kHz and 500-Hz locations) undergo marked postnatal changes; (vi) disappearance of the marginal pillars and maturation of the supporting cells are not yet complete by P15.     

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.     

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.