Ultrastructure of the normal human organ of Corti. New anatomical findings in surgical specimens

Conclusion A thorough scanning electron microscopy (SEM) investigation of immediately fixed human adult cochleae obtained during surgery for petro-clival meningiomas conveyed new information about morphology.

Objective To investigate the ultrastructure of human adult cochleae using SEM.

Material and methods Two human cochleae were decalcified, fixed with glutaraldehyde and osmium and prepared for SEM.

Results The excellently preserved morphology showed the pathways of nerve fibres through the organ of Corti. Undulating lateral cell membranes of Hensen and Claudius cells created an enlarged surface that may be important for homoeostasis. The distal attachment of the tectorial membrane to the reticular lamina was present in the shape of a marginal net, which was extended through marginal pillars. Stereocilia imprints extended as far as the distal end of the marginal pillars. The presence of an irregularly distributed fourth row of outer hair cells attached to the marginal pillars raises questions about differences in the excitation of the last row of outer hair cells as a result of differences in the composition of the tectorial membrane.     

Ultrastructure of the normal human organ of corti. new anatomical findings in surgical specimens

CONCLUSION: A thorough scanning electron microscopy (SEM) investigation of immediately fixed human adult cochleae obtained during surgery for petro-clival meningiomas conveyed new information about morphology. OBJECTIVE: To investigate the ultrastructure of human adult cochleae using SEM. MATERIAL AND METHODS: Two human cochleae were decalcified, fixed with glutaraldehyde and osmium and prepared for SEM. RESULTS: The excellently preserved morphology showed the pathways of nerve fibres through the organ of Corti. Undulating lateral cell membranes of Hensen and Claudius cells created an enlarged surface that may be important for homoeostasis. The distal attachment of the tectorial membrane to the reticular lamina was present in the shape of a marginal net, which was extended through marginal pillars. Stereocilia imprints extended as far as the distal end of the marginal pillars. The presence of an irregularly distributed fourth row of outer hair cells attached to the marginal pillars raises questions about differences in the excitation of the last row of outer hair cells as a result of differences in the composition of the tectorial membrane.     

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.     

Repair pattern of the reticular lamina of the organ of corti in human ears

The repair pattern of the reticular lamina of the organ of Corti was studied in the cochleae of human ears. The inner ears were obtained at autopsy from the individuals who had no evidence of auditory or vestibular disorders or therapy with ototoxic drugs:

• After a loss of outer or inner hair cells, the framework of the reticular lamina was distorted but no gaps were detected. The supporting cells were hypertrophied but no reparative proliferation of the supporting cells was found in the organ of Corti.
• Defects due to the collapse of outer hair cells of the first row were filled in mainly by the hypertrophied heads of the outer pillar cells.
• Defects due to the collapse of outer hair cells of the second, third and fourth row were filled in mainly by the hypertrophied phalanges of Deiters' cells of the first, second and third row respectively.
• The space due to inner hair cell loss was filled in by the nearest inner supporting cells which were hypertrophied and extended toward the space.
• The distortion of the reticular lamina and the aging degeneration were regarded as two possible causes for the total loss of the organ of Corti near the end of the first turn.

     

Elemental composition of individual cells and tissues in the cochlea

Localization of elements at the cellular and sub-cellular levels was performed with the energy dispersive X-ray microanalysis technique, using shock-frozen, freeze-dried and araldite-embedded mouse (CBA/CBA) cochleae sectioned dry. Anatomical identification occurred in the STEM (scanning transmission electron microscopy) mode. In inner hair cell stereocilia the K/Na ratio was 70:1 but only 20:1 in the cytoplasm. In outer hair cell cytoplasm the K/Na ratio was 11:1 while the ratio in stereocilia was similar to that in inner hair cells. Ca was identified in stereocilia and the upper part of the cytoplasm of both outer and inner hair cells. The elemental composition in the subtectorial space is endolymph-like and that in the inner tunnel of the organ of Corti is similar to extracellular fluid. Considerable regional differences in elemental composition occur in the tectorial membrane with regard to P, K and Ca. The highest concentration of Ca occurs in the basal part of the tectorial membrane towards the sensory hairs. The highest concentration of K occurs in the basal and outer parts whereas the middle part of the tectorial membrane contains low levels of both K and Ca. The elemental composition changes in two main directions: 1) from the limbal (growing) region to the tip of the tectorial membrane, and, 2) from upper to lower surfaces. The three cell types of the stria vascularis differ considerably in elemental composition. The highest concentration of K occurs in marginal cells. The basal cells contain more K than do the intermediate cells. A significantly higher concentration of Ca, Cl and Na occurs in marginal cell cytoplasm than in any other cell type in the stria vascularis.     

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.     

小鸡和豚鼠耳蜗毛细胞β-肌动蛋白分布比较

目的 :比较小鸡基底乳头和豚鼠耳蜗毛细胞 β-肌动蛋白 (β- actin)分布的特点。方法 :应用免疫组织化学方法观察小鸡和豚鼠耳蜗中β- actin免疫反应活性。结果 :鸡基底乳头高、矮毛细胞的静纤毛 ,盖膜根部附着处缘上皮细胞胞浆 ,豚鼠耳蜗三排外毛细胞胞浆 ,内、外支柱细胞胞浆和指状突β- actin免疫反应阳性。结论 :小鸡和豚鼠耳蜗毛细胞具有相同结构蛋白β- actin,但两种动物之间存在明显的分布差异。     

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.     

Wheat germ agglutinin binding sites in the organ of Corti as revealed by lectin-gold labeling

The distribution of wheat germ agglutinin(WGA)-binding sites in the organ of Corti of the guinea pig and mongolian gerbil was studied. WGA was conjugated with gold particles and applied on thin sections of the cochlea embedded in Spurr's resin and in Lowicryl K4M. WGA-binding sites were found on the plasma membrane, lysosomes and cytoskeletons of hair and supporting cells as well as on the tectorial and basilar membranes. No distinct difference was discovered between hair cells and supporting cells in terms of WGA-binding activities.     

A newly identified surface coat on cochlear hair cells

Routine electron microscope methods do not well preserve or stain the surface coat or glycocalyx on cochlear hair cells. In other tissues, enhanced preservation and staining of these glycoconjugates was obtained following fixation with glutaraldehyde containing a cationic dye (e.g., Alcian blue and ruthenium red). When cochleas were fixed with glutaraldehyde containing Alcian blue, the endolymphatic surface of hair cells, but not the supporting cells, displayed an extensive (approximately 90 nm thick) surface coat. Alcian blue positive material was also observed in the tectorial and basilar membranes and in a portion of the spiral ligament. In addition, acellular bands of Alcian blue positive material were observed between the tectorial membrane and the reticular lamina or inner sulcus cells. Although the function of these cochlear glycoconjugates is not yet known, it is proposed that they serve to attach the tectorial membrane to the organ of Corti, and they are involved in stereocilia fusion following sound exposure and ototoxic drug administration.     

Morphological changes in the cochlea of the mouse after the onset of hearing

The cochleae of 5, 10, 12 and 15 day old mice and of adults (Mus musculus, strain NMRI) were studied by light and electron microscopy. In each case the same part of the organ of Corti (2.8–3.3 mm from the helicotrema) was examined. The results were correlated with the development of auditory thresholds (in mice of the same strain) obtained by Ehret (Ehret G. (1971) J. Am. Audiol. Soc. 1, 179–184). It was demonstrated that morphological development of the organ of Corti is by no means complete at the onset of behavioural responses to acoustic stimuli. After this event the following morphological changes occur: (1) The basilar membrane filaments stain more intensly and the tympanic cover layer is greatly reduced in thickness and almost completely disappears. (2) The filaments of the pillar cells stain more intensly and apparently increase in number, and the angle between the outer and inner pillar cells increases so that the cross-sectional area of the tunnel of Corti expands. (3) Hook-shaped connections (marginal pillars) between the reticular membrane and the tectorial membrane disappear. The consequences of these morphological changes for the cochlear mechanics are discussed, especially in respect to the increase of sensitivity of hearing.     

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.     

Membrane specializations in the human organ of Corti

The human organ of Corti was investigated with the freeze fracturing technique with the purpose of analysing membrane specializations. Tight junctions were found on hair cells as well as on supporting cells. Inner and outer hair cells were coupled to the supporting cells by rather extensive tight junctions. The tight junctions between the Deiter's cells were comparable to those of the hair cells, while the tight junctions between the Hensen's cells were considerably less extensive. Gap junctions were present coupling all supporting elements in the organ of Corti, small ones preferably in the apical regions of the cells and large ones in the basal region.     

Supporting and membrane structures of human outer hair cells: evidence for an isometric contraction

The supporting elements of the human organ of Corti express a number of cytokeratins, and it is obvious that the presence of cytokeratins provides mechanical stability to the framework of the entire organ of Corti. In the basal part of the outer hair cells and in the apical part of the Deiters cells, there is a significant expression of actin. In the human outer hair cells, the system of subsurface cisterns is not only restricted to the lateral cell wall but is also continuous to the basal region where the hair cells are closely attached to the supporting Deiters cells. In contrast to the well-known organization of the subsurface cisterns and pillar structures at the lateral outer hair cell wall of rodents, the pillars at the base of human outer hair cells can form channels. These channels allow a direct communication between the lumen of the subsurface cisterns and the intercellular space which separates outer hair cells and Deiters cells. At the apical part of the Deiters cells, a condensation of microfilaments is present which displays morphological similarities to actin fibers. These well-organized structural configurations between outer hair cells and Deiters cells imply that this region has special contractile properties. The human outer hair cells are therefore firmly stabilized not merely apically but also at the cell base, a situation which would permit a mainly isometric contraction under in vivo physiological conditions.     

出生后大鼠听毛细胞纤毛发育过程

目的观察新生大鼠（P1、P7、P14、P21）耳蜗Corti器的形态结构及排列方式,以便了解听毛细胞纤毛发育的过程。方法取新乍SD大鼠四个阶段的耳蜗,采刖扫描电镜对出生后大鼠耳蜗Corti器形态结构进行系统观察。结果发现这四个阶段在体犬鼠耳蜗毛细胞从出生至毛细胞完全发育成熟,绝大部分都是以一排内毛细胞和三排外毛细胞的方式排列的,只有少部分在局部发现多出几个外毛细胞形成第四排。毛细胞的形态结构及排列方式随着时间的改变逐渐发育成熟。P14这个阶段是个重要的时期,Corti器表面柱细胞头板增宽,表面的微绒毛减少,Deiter细胞表面微绒毛也减少,动纤毛从底圄至顶圈逐渐退化已经基本结束,P14这个阶段Corti器各个部分发育已经完全成熟：结论出生后14天之内。大鼠听毛细胞静纤毛和动纤毛与听器其他细胞形态结构仍不同程度地处于由不成熟到成熟的逐渐发育过程,为研究大鼠出生后Corti器的发育、听觉功能的建立和完善提供了比较可靠的形态学证据。     

Electron microscopic temporal bone histopathology in experimental pneumococcal meningitis.

Bacterial meningitis is one of the most common causes of acquired profound sensorineural deafness in children. Measurement of hearing and examination of the cochlea is limited in patients suffering from acute meningitis. A rabbit model of pneumococcal meningitis was developed to identify the temporal bone histopathologic changes that occur in meningogenic labyrinthitis caused by Streptococcus pneumoniae. Light microscopy was previously performed on temporal bones from acutely meningitic rabbits with profound hearing loss as determined electrophysiologically. Extensive inflammation of the cochlea with endolymphatic hydrops was observed. The organ of Corti, however, showed preserved architecture in the majority of these animals. In order to further investigate these findings, a protocol was used to create meningitic rabbits with hearing loss ranging from early high-frequency loss to profound deafness. The temporal bones from 7 rabbits were examined by transmission electron microscopy. In cases of mild hearing loss, partial degeneration of the inner row of outer hair cells, as well as edema of efferent cochlear nerve endings and marginal cells of the stria vascularis, was seen. With increasing degrees of hearing loss, the remainder of the organ of Corti and intermediate cells of the stria showed ultrastructural abnormalities. Spiral ganglion cells and basal cells of the stria vascularis remained intact in all subjects. This study provides unique information regarding the histology and pathophysiology of meningogenic deafness. The clinical implications of these findings are discussed, with an emphasis on potentially reversible changes and therapeutic intervention.     

豚鼠耳蜗盖膜下面的超微结构

目的 利用扫描电镜技术详细地观察豚鼠盖膜下的超微结构,为耳蜗的感音机制提供新的认识.方法 用S-4800型超高分辨率扫描电子显微镜观察了6只豚鼠12只耳蜗的盖膜.结果 (1)耳蜗各圈盖膜下面均可观察到外毛细胞静纤毛压迹,这种压迹多半与静纤毛最高排的形态一致,第一圈呈“W”型,由基底圈到顶圈,逐渐由“W”型渐变为“V”型及不规则的簇状.压迹为一排圆形的小凹,将盖膜下表面表层辐射状纤维断开,只有最高排的静纤毛才与盖膜接触形成压迹,压迹排列呈串珠一样.(2)盖膜下内毛细胞相应的位置有一条较深的波浪状沟槽,呈线性结构,沟槽比外毛细胞静纤毛的压迹浅而宽,由耳蜗的基底圈到顶圈这种压迹逐渐呈带状.(3)盖膜下的纤维由盖膜的外缘到盖膜与内毛细胞静纤毛压迹之间以蜗轴呈辐射状排列,但在外毛细胞静纤毛压迹的位置被这些压迹所阻断,而总的辐射方向和纤维走行并没有改变,纤维非常的精细,每根纤维之间又相互交错相连.内、外毛细胞压迹之间,柱细胞顶部的盖膜纤维很细,均匀呈细丝状.而内毛细胞与螺旋缘之间,即内沟上方的盖膜下方的纤维更加细长.结论 通过对盖膜超微结构的观察,盖膜下内外毛细胞静纤毛的压迹充分说明毛细胞静纤毛与盖膜的接触.盖膜下的纤维由盖膜的外缘到柱细胞和柱细胞到盖膜下内毛细胞静纤毛带状压迹之间也就是内、外毛细胞压迹之间,柱细胞顶部的盖膜的纤维与内毛细胞顶部盖膜带状结构到螺旋缘之间的纤维的粗细都不一样.这种纤维的分布特点,可能与盖膜在声音调谐方面所起的作用有一定的关系.     

Structural relationships of the unfixed tectorial membrane

Although the tectorial membrane has a key role in the function of the organ of Corti, its structural relationship within the cochlear partition is still not fully characterised. Being an acellular structure, the tectorial membrane is not readily stained with dyes and is thus difficult to visualise. We present here detailed observations of the unfixed tectorial membrane in an in vitro preparation of the guinea pig cochlea using confocal microscopy. By perfusing the fluid compartments within the cochlear partition with fluorochrome-conjugated dextran solutions, the tectorial membrane stood out against the bright background. The tectorial membrane was seen as a relatively loose structure as indicated by the dextran molecules being able to diffuse within its entire volume. There were, however, regions showing much less staining, demonstrating a heterogeneous organisation of the membrane. Especially Hensen's stripe and regions facing the outer hair cell bundles appeared more condensed. Whereas no connections between Hensen's stripe and the inner hair cell bundles could be observed, there was clearly a contact zone between the stripe and the reticular lamina inside of the inner hair cell.