Deiters cells tread a narrow path--the Deiters cells-basilar membrane junction

Deiters cells extend from the basilar membrane to the reticular lamina and, together with pillar cells and outer hair cells, structurally define the micro-architecture of the organ of Corti. Studying vibrotome sections of the mouse organ of Corti with confocal and scanning electron microscopy we found that the basal pole of every Deiters cell, independently of their position in the organ of Corti and along the cochlear spiral, attached to the basilar membrane within a 15.1?±?0.3?μm-wide stripe running the length of the cochlear spiral adjacent to the row of outer pillar cells. All Deiters cells' basal poles had similar diameter and general morphology, and distributed on the stripe in a precise arrangement with a center-to-center distance of 7.1?±?0.3?μm between neighbor cells of the same row and 5.9?±?0.4?μm for neighbor cells in adjacent rows. Complete detachment of Deiters cells revealed an elliptical imprint on the top surface of the basilar membrane consisting of a smaller central structure with a very smooth surface surrounded by a rougher area, suggesting the presence of two different anchoring junctions. These previously unidentified morphological features of Deiters cells could be critical for the mechanical response of the organ of Corti.     

Cochlear micromechanics

On the basis of functional morphology, biomechanical properties and topographic relations of the cells of the Corti organ, a physical model was designed for the study of mechanical action in the cochlear partition during sound stimulation. The topographic relations between the supporting and the sensory cells of the organ of Corti transform the basilar membrane deviation into a complex movement of the reticular lamina, which enhances the differences in the deviation of stereocilia of the inner and outer hair cells.     

Direct visualization of living organ of Corti and studies of its extracellular fluids

Occlusion of all or parts of any of the three separate capillary systems supplying the organ of Corti and its related tissues could result in different audiometric symptoms; however, little is known about the functional relationship between these capillaries and the tissues, so a series of experiments has been carried out to provide some data. Sometime ago we reported an experiment that demonstrated a different role for the capillaries of the stria vascularis than for those underlying the osseous spiral lamina and basilar membrane. These latter capillaries care for the immediate demands of the organ of Corti. Probably the greatest handicap to more complete research has been the inability to observe the cells, spaces, and capillaries of the organ of Corti in the living state. This paper describes an approach to the inner ear of the guinea pig that provides a view of the sensory area without injuring essential capillaries. By means of a surgical approach to the round window a bit of bony promontory is removed to expose the basilar membrane. Removal of the stapes allows light from a cool fiber optics source to reflect from the walls of the vestibule to reveal the cells and spaces of the organ of Corti. Under this direct visualization, electrodes to monitor dc resting potentials or to measure oxygen concentrations are placed in the extracellular spaces. A motion picture shows the technique. Experiments that determined the boundaries of the organ of Corti fluids and capillaries that provide oxygen to these spaces and subsequently to the sensory cells are reviewed. The tectorial membrane seals the fluids of the organ of Corti spaces including the inner sulcus from endolymph, and the spiral vessels provide oxygen to these fluids. Occlusion of the spiral capillaries causes a relatively rapid degeneration of the organ of Corti in that region, whereas occlusion to capillaries of the spiral ligament and its structures may produce altered function of the organ of Corti and perhaps its degeneration over a longer period of time.     

Temporal bone histopathology in alport syndrome

OBJECTIVE: To determine the histopathologic abnormalities within the cochlea in Alport syndrome. BACKGROUND: Alport syndrome, which manifests as hereditary nephritis and sensorineural hearing loss (SNHL), is caused by mutations in genes that code for the proportional, variant3, proportional, variant4, and proportional, variant5 chains of type IV collagen. The proportional, variant3, proportional, variant4, and proportional, variant5 chains of type IV collagen are present in the basement membrane of the organ of Corti. Previous temporal bone studies have failed to identify histopathologic correlates for the SNHL. METHODS: We examined temporal bones from nine individuals with a clinical diagnosis of Alport syndrome. One of our cases also had genetic testing that showed a mutation in the type IV collagen proportional, variant5 chain gene. RESULTS: By light microscopy, eight of nine cases demonstrated two unique pathologic changes: 1) a "zone of separation" between the basilar membrane and overlying cells of the organ of Corti and 2) presence of cells filling the tunnel of Corti and extracellular spaces of Nuel. The cytologic losses of hair cells, stria vascularis, and cochlear neuronal cells were insufficient to account for the observed SNHL in our cases. Electron microscopy was performed in four cases; all four demonstrated the following: 1) the zone of separation that was observed at light microscopy occurred between the basement membrane and the basilar membrane, 2) the cells within the tunnel of Corti and spaces of Nuel were morphologically similar to supporting cells, and 3) the basement membrane of strial capillaries and the spiral vessel (under the basilar membrane) were normal. CONCLUSIONS: The histopathologic correlates of cochlear involvement in Alport syndrome are abnormalities of the basement membrane of cells of the organ of Corti and dysmorphogenesis (cellular infilling of the tunnel and extracellular spaces) of the organ of Corti. We hypothesize that these abnormalities result in SNHL by altering cochlear micromechanics.     

Spontaneous and impulsively evoked otoacoustic emission: indicators of cochlear pathology?

The first author's right ear produces a spontaneous otoacoustic emission (SOAE) at 7529 Hz and 16 dB SPL. An external continuous tone is able to suppress the SOAE. The 3 dB iso-suppression curve is broadly tuned and displaced, relative to the SOAE, toward higher frequencies. An audiogram notch exists at frequencies just below that of the SOAE.

We explain the occurrence of both spontaneous and impulsively evoked OAEs in terms of disruption of active feedback mechanisms of the OHCs upon basilar membrane vibration. According to this hypothesis, each segment of the organ of Corti feeds back positively upon its segment of basilar membrane and negatively upon adjacent segments. If a patch of OHC loss exists, adjacent segments of the basilar membrane are released from the negative feedback and respond to an impulsive stimulus with exaggerated oscillations at their resonance frequencies, thus producing OAEs. At particularly sharp transitions between normal and abnormal regions of the organ of Corti SOAEs may be generated.     

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.     

Calcium-binding proteins in organ of Corti and basilar papilla: CBP-15, an unidentified calcium-binding protein of the inner ear

In a previous paper (Thalmann et al., 1993) we reported that the amino acid sequence of OCP2, a low molecular weight acidic protein present in extremely high concentrations in the organ of Corti and absent in the basilar papilla, exhibits a rudimentary EF-hand — a potential calcium-binding domain. The present study was undertaken to determine whether OCP2 binds 45-calcium under non-denaturing conditions following separation by isoelectric focusing and transblotting. The same criterion was used to determine whether the EF-hands of several other calcium-binding proteins (CBP) are functional in organ of Corti and basilar papilla. OCP2 exhibited no 45-calcium binding. Calmodulin, present in the organ of Corti in extremely high concentrations and lower in basilar papilla, showed strong 45-calcium binding in both structures. While calbindin represents a major protein in basilar papilla and binds 45-calcium, this protein is a minor component in the organ of Corti; whether it binds 45-calcium remains to be decided.

By extending the pI range in the acidic region of isoelectric focusing, a 15 kDa, highly acidic (pI ≈ 3.1) protein was revealed that constitutes a major protein in the organ of Corti; the protein was not detectable in the basilar papilla, spiral ligament/stria vascularis complex and numerous other organs tested. It remains to be resolved whether this protein represents an isoform of parvalbumin or a novel CBP. The differential make-up of CBPs between the mammalian organ of Corti and the avian basilar papillar is discussed.     

Location of small cochlear lesions by phase contrast microscopy prior to thin sectioning

A new technique for the study of the inner ear is described. Cochleae are fixed, dehydrated and infiltrated with plastic while their bony walls are intact except for small holes at the third turn and near the round window. After the plastic polymerizes, the cochlear bone is removed so that half turns of cochlear duct can be separated from the modiolus. These specimens are re-embedded in a thin layer of plastic after trimming so that their basilar membrane sides lie close to the surface of the plastic layer. Using phase contrast microscopy, the entire organ of Corti is examined by focusing through the surface of the plastic and through the specimens from the basilar membrane up to the tectorial membrane. Segments of organ of Corti containing small lesions are divided in such a way that cross-sections of those areas for study by light and electron microscopy are obtained readily using an ultrotome.     

CBA小鼠内耳感觉上皮的参考数据

目的测量成年CBA小鼠耳蜗和前庭的有关数据,为内耳感受器定量分析提供参考依据。方法将6只出生后3个月左右的成年CBA小鼠(12耳)的耳蜗和前庭各终器取出并制备成全耳蜗基底膜铺片和全前庭终器铺片。测量全耳蜗基底膜的总长度,以及基底膜和Corti器在耳蜗不同部位的宽度。观察并记录全耳蜗毛细胞的总数和基底膜上不同区间的毛细胞密度。观察并记录椭圆囊斑和球囊斑毛细胞的总数及其微纹区和周边区的毛细胞密度,记录壶腹嵴上的毛细胞密度。结果正常成年CBA小鼠的耳蜗基底膜长度为(5.76±0.196)毫米(平均数±标准差,下同),基底膜的宽度在耳蜗底部距起始端约1.5毫米处为(339.1±9.87)微米,在耳蜗中部距起始端约3毫米处为(304.5±11.82)微米,在耳蜗顶部距起始端约5毫米处为(300.1±7.22)微米,说明小鼠耳蜗基底膜的宽度从底回到顶回逐渐变窄。Corti器的宽度在耳蜗底部距起始端1.5毫米处为(37.80±2.24)微米,在耳蜗中部距起始端约3毫米处为(45.00±2.67)微米,在耳蜗顶部距起始端约5毫米处为(52.20±3.16)微米,可见Corti器的宽度从底回到顶回逐渐变宽。CBA小鼠全耳蜗毛细胞的总数为(3116.41±151.91)个,其中内毛细胞总数为(680.67±17.50)个,而外毛细胞的总数是(2435.8±143.46)个。耳蜗内、外毛细胞的平均密度为(541.1±9.36)个/毫米,其中内毛细胞的平均密度为(118.3±2.68)个/毫米,外毛细胞的平均密度为(422.8±11.87)个/毫米,耳蜗毛细胞在耳蜗基底膜上不同区间的毛细胞密度无明显差异(P>0.05)。小鼠椭圆囊斑上的毛细胞总数为(3300±177.51)个,球囊斑上的毛细胞总数为(3045±361.57)个。前庭球囊斑和椭圆囊斑微纹区和周边区的毛细胞密度基本相同(P>0.05),两个囊斑微纹区的平均毛细胞密度为(40.2±6.59)个/0.0025mm2,两个囊斑周边区的平均毛细胞密度为(53.2±7.18)个/0.0025mm2,可见囊斑微纹区的毛细胞密度低于周边区。尽管小鼠上半规管和后半规管壶腹嵴的毛细胞区被位于嵴中央的上皮细胞分隔为两个区域,但三个壶腹嵴上的毛细胞密度基本相同,其平均密度为(44.7±7.15)个/0.0025mm2。结论本实验所得CBA小鼠耳蜗和前庭测量数据,为进一步定量观察CBA小鼠内耳病理学改变提供了重要的参考依据。     

Tubulin expression in the developing and adult gerbil organ of Corti

In the late stages of inner ear development, the relatively undifferentiated cells of Kollicker's organ are transformed into the elaborately specialized cell types of the organ of Corti. Microtubules are prominent features of adult cells in the organ of Corti, particularly supporting cells. To test the possible role of microtubules in organ of Corti development, the microtubule organization in the organ of Corti has been examined using indirect immunofluorescence to beta-tubulin in the developing gerbil cochlea. Tubulin first appears at post-natal day 0 (P0) as filamentous asters in inner hair cells and by P2, asters are also seen in outer hair cells. Tubulin appears at P3 in inner pillar cells in a tooth crown-like figure. By P6, tubulin expression is also evident in outer pillar cells and by P9, it is seen in Deiters cells. Elaboration of microtubules in pillar cells was observed to proceed from the reticular lamina towards the basilar membrane. The pattern of tubulin expression in the apical organ of Corti lags the base by about 3 days until P6, but by P9, apical and basal organ of Corti appear substantially the same.     

The inner ear as an electrosensory sense organ]

A model for cochlear perception is introduced based on the consideration that the organ of Corti is an electrosensory organ like that found in fish physiology during phylogenetic development. The inner hair cells work as electroreceptors, the outer hair cells as electrocytes. A layer of potassium ions on the lower surface of the tectorial membrane causes the excitation of the inner hair cells as soon as contact with a stereocilium occurs. A model for the basilar membrane motion, based on mathematical considerations and in accordance with the typical tuning curves of single auditory nerve fibres can serve as basis to explain the results of frequency and intensity analyses if we assume an electric excitation of the inner hair cells.     

Mechanical transduction in outer hair cells

The outer hair cells are responsible for the exquisite sensitivity, frequency selectivity and dynamic range of the cochlea. These cells are part of a mechanical feedback system involving the basilar membrane and tectorial membrane. Transverse displacement of the basilar membrane results in relative motion between the tectorial membrane and the reticular lamina, causing deflection of the stereocilia and modulation of the open probability of their transduction channels. The resulting current causes a change of membrane potential, which in turn produces mechanical force, that is fed back into the motion of the basilar membrane. Experiments were conducted to address mechanical transduction mechanisms in both the stereocilia and the basolateral cell membrane, as well as modes of coupling of the outer hair cell force to the organ of Corti.     

Pathological findings in the human auditory system following long-standing gentamicin ototoxicity

Summary The clinical, audiovestibular and histopathological findings in a patient who suffered from a long-standing gentamicin-induced deafness are reported. In both temporal bones, the organ of Corti was completely absent, with only a few nerve fibres remaining in the apical part of the cochlea. Regenerative ingrowth of nerve fibers into the area of the degenerative organ of Corti was present apically in both ears. The stria vascularis exhibited considerable degeneration in all turns and loss of microvasculature was found in the basilar membrane. The spiral ganglion cells, the cochlear nerve and the central auditory pathways and nuclei appeared to be unaffected.     

Pathological findings in the human auditory system following long-standing gentamicin ototoxicity

The clinical, audiovestibular and histopathological findings in a patient who suffered from a long-standing gentamicin-induced deafness are reported. In both temporal bones, the organ of Corti was completely absent, with only a few nerve fibres remaining in the apical part of the cochlea. Regenerative ingrowth of nerve fibers into the area of the degenerative organ of Corti was present apically in both ears. The stria vascularis exhibited considerable degeneration in all turns and loss of microvasculature was found in the basilar membrane. The spiral ganglion cells, the cochlear nerve and the central auditory pathways and nuclei appeared to be unaffected.     

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.     

耳蜗图的绘制及应用进展

位于耳蜗基底膜上的Corti器是接受声振动刺激的初级感受器，作为Corti器中的感觉细胞，毛细胞的损害将引起不同程度及频率范围的听力损失。对耳蜗毛细胞在基底膜不同部位的丢失情况进行定量分析是内耳组织病理学研究中最常用的手段，将全耳蜗毛细胞损害的定量定位分析结果与听功能相结合将有益于对疾病机制的探索和对治疗方法的评价。目前对全耳蜗毛细胞定位定量分析常采用耳蜗图来表示，但在听力学研究中耳蜗图的绘制方法并不完全相同，尚缺乏统一的绘制标准及原则，使得各个实验结果之间缺乏可比性。为更精准地对全耳蜗毛细胞的损伤情况进行定位定量分析，需要统一耳蜗图的绘制方法及原则。本文就目前文献报导中常用的耳蜗图绘制方法及绘制原则进行了综述。     

Endolymphatic hydrops: mechanical causes of hearing loss

Summary An explanation for the mechanical origin of the hearing loss in endolymphatic hydrops is presented that is based on studies in mechanical cochlear models. An elastic bias of the basilar membrane and/or a mass loading of the cochlear duct account for the low-frequency hearing loss, diplacusis, and evenharmonic distortion. In addition, the static shearing displacement between the tectorial membrane and the organ of Corti, caused by the displacement of the basilar membrane, may partially decouple the hair cells from the tectorial membrane, an event that would explain the tinnitus, recruitment, and perhaps even the disportional loss of speech intelligibility associated with endolymphatic hydrops.     

In vivo micromechanical measurements of the organ of Corti in the basal cochlear turn

Cochlear mechanical measurements of organ of Corti motion are generally accomplished in the apical or basal turn as in vivo or in vitro studies. In the apex it is possible to observe and measure tectorial membrane vibration as well as vibrations of structures such as the reticular lamina or the basilar membrane (BM). However, compared to the basal turn, cochlear amplification and nonlinearity are not strong in the apex. Basal turn studies have typically been limited to point location measurements of the BM but improved technology for laser interferometry is now making possible the spatial mapping of BM motion. The 'complexity' of BM motion in the radial direction (particularly the phase variation) is important to new models of cochlear wave amplification. In future work it may be possible to learn about vibration of structures within the organ of Corti.