Ionic coupling among cells in the organ of Corti.

Gap junctions have been demonstrated morphologically among the supporting cells of the mammalian organ of Corti but, in contradistinction to reptiles, evidence for their existence between the supporting cells and hair cells is equivocal. The literature is ambiguous with respect to electrical coupling and dye coupling among the supporting cells, and no coupling of either kind has been demonstrated for the hair cells. We found strong coupling of both kinds among the supporting cells in the cochleas of live Mongolian gerbils and a less stable coupling between the supporting cells and the outer hair cells. The electrical coupling was established by recording alternating receptor potentials in the hair cells and following their decrement in the population of Hensen's cells; the dye coupling, by injecting Lucifer yellow electrophoretically into the hair cells or the supporting cells and investigating its spread to the neighboring cells. The electrical recordings were made by means of microelectrodes filled with either 1.5 or 3 M KCl or 1 M LiCl with 6% Lucifer yellow, the latter used for dye injection. The electrode resistances ranged from about 20 to 60 M omega in the first instance, and from about 50 to 110 M omega, in the second. The electrodes were inserted into the organ of Corti through scala media according to the method of Dallos, Santos-Sacchi and Flock (1982) modified by us. The alternating potential in Hensen's cells was usually larger than in the outer tunnel of Corti and remained practically constant up to the outer margin of the Hensen's-cell population. Its phase was the same as in the outer hair cells. When the dye was injected into a Hensen's cell, it always spread to neighboring Hensen's cells and often to Deiter's cells. Dye injected into outer hair cells (identified according to anatomical and physiological criteria) also spread to Deiter's and Hensen's cells and, usually, to other outer hair cells. Stained cells were identified in surface preparations and, on two occasions, in serial sections from plastic embedded cochleas.     

A re-evaluation of cell coupling in the organ of Corti

Intercellular electrical coupling was assessed in an in vitro organ of Corti preparation using separate electrodes to inject current and record voltage drops in Hensen's cells. The results demonstrate much better coupling among these supporting cells than previously thought. Coupling ratios between adjacent Hensen's cells are greater than 0.6.     

The temperature dependence of electrical coupling in the organ of Corti

Electrical coupling in an in vitro preparation of the organ of Corti was evaluated during changes in temperature of the bathing media. The effect of cooling the organ from 35 +/- 2 degrees C to 17 +/- 3 degrees C is to reduce membrane potentials, increase input resistance and decrease coupling ratios. Decreases in coupling ratios ranging from 15 to 75% have been observed. The effects are reversible upon warming. Membrane potentials are very susceptible to depolarization caused by cooling. The reduction in coupling is not due to depolarization nor is it dependent upon extracellular Ca2+. It is conceivable, however, that intracellular stores of Ca2+ are released or that intracellular pH is altered.     

The effects of cytoplasmic acidification upon electrical coupling in the organ of Corti

The supporting cells of the organ of Corti are joined to one another by gap junctions, and electrical coupling among them is known to be good. It is demonstrated here, using an in vitro preparation, that electrical communication between Hensen's cells can be modified by treatments which are known to cause cytoplasmic acidification. Treatment of the preparation with 100% CO2-saturated medium causes a drop in membrane potential, increase in input resistance, and decrease in steady-state coupling ratio. These measures return to pretreatment levels upon washout of the CO2 medium. Also, direct injection of H+ into a Hensen's cell uncouples that cell from the supporting cell network. An increase in coupling ratio is sometimes observed immediately before and after uncoupling due to CO2 treatment. In fact, in some cases it is possible to solely increase coupling ratios with limited CO2 treatments, although prolonged treatment with CO2 invariably produces uncoupling. This phenomenon may be due to an increase in cell resistance without a change in junctional conductance. A few possible roles for gap junctions in the inner ear are suggested, and the significance of the present results discussed.     

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.     

重组腺病毒Ad-GFP转染新生小鼠离体耳蜗基底膜的实验分析

目的观察重组腺病毒Ad-GFP转染新生小鼠离体耳蜗基底膜培养组织的情况。方法取新生1～5 d小鼠的耳蜗基底膜,离体培养1 d后,加入重组腺病毒Ad-GFP继续培养1 d,在荧光显微镜及Confocal显微镜下观察病毒对离体耳蜗基底膜的转染情况。结果耳蜗基底膜离体培养1 d后,在显微镜下观察,可见基底膜贴壁生长良好,外周有新生上皮细胞和成纤维细胞长出;高倍显微镜下可见耳蜗内外毛细胞和支持细胞等结构。离体耳蜗基底膜培养组织加入重组腺病毒Ad-GFP继续培养1 d后,可见重组腺病毒Ad-GFP能高效转染新生小鼠离体耳蜗基底膜及其外周长出的新生上皮细胞和成纤维细胞;在新生小鼠离体耳蜗基底膜上,不仅大上皮嵴细胞区域、小上皮嵴细胞区域的细胞能被高效转染,毛细胞也能被高效转染。结论重组腺病毒Ad-GFP能高效转染新生小鼠离体耳蜗基底膜培养组织。     

Hydrops of the organ of Corti

Objectives: The authors would like to confirm a fluid pathway from the scala tympani to the organ of Corti, and to observe its morphological changes.

Methods: A staining solution for succinic dehydrogenase was perfused with phenazine methosulfate in the scala tympani of living guinea pigs (n?=?5) under deep anesthesia. After fixation, the cochleas were eventually embedded in epon. Sections were observed under a light microscope.

Results: Blue-stained tissue is indicative of the pathway taken by the solution. The staining solution entered the organ of Corti through Hensen-Deiters’ slit. The slit widened and Hensen’s cells were pushed laterally. A new space was formed medial to Hensen’s cells. Cortilymphatic hydrops developed.

Conclusion: The Hensen-Deiters’ slit is a pathway of a certain staining solution from the scala tympani to inside the organ of Corti of the guinea pig. The influx of the fluid pushes Hensen’s cells laterally and upward, resulting in a formation of hydrops of the organ of Corti or cortilymphatic hydrops. The hydrops is observed in animals with experimental perilymphatic fistula and with viral labyrinthitis. At the end stage of the hydrops, only the surface of the organ of Corti remains as a thin layer without any cellular elements.     

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.     

Serotonergic innervation of the organ of Corti

The olivocochlear efferent system of the mammalian cochlea, which is divided into two lateral and medial bundles, contains numerous neuroactive substances (acetylcholine, GABA, dopamine, enkephalins, dynorphins and CGRP). These have been located at the brainstem in neurons belonging to the lateral superior olive (lateral efferent system) or in neurons of the periolivary region around the medial superior olive and the trapezoid body (medial efferent system). All of these substances were found in well-characterized projections corresponding to lateral and medial nerve fibres and terminals which connect to the type I afferent dendrites and the outer hair cells, respectively. All could be involved in the modulation of the auditory process, as is suggested by the cochlear turnover increases observed in some of them (i.e. enkephalins or dopamine) induced by sound stimulation. Recently, the presence and distribution of serotonin-containing fibres has been included in the long list of cochlear neuroactive substances. However, its highly particular peripheral pattern of distribution together with the lack of response to sound stimulation could suggest that serotonergic fibres constitute a previously unknown cochlear innervation.     

Giant cilia in the human organ of Corti

Fusion of cilia, the growth of clumps of fused cilia and giant cilium formation have been studied in the normal human organ of Corti using the scanning electron microscope. These unusual forms are found mainly in the apical portions of the cochlea and appear to precede the loss of normal apical cilia which increases and extends in a basal direction with age. These changes may be due to low frequency noise damage or be a phenomenom of ageing. The mechanism of their formation is discussed in the light of recent experimental work on cell fusion.     

Actin-binding and microtubule-associated proteins in the organ of Corti.

Actin-binding and microtubule-associated proteins regulate microfilament and microtubule number, length, organization and location in cells. In freeze-dried preparations of the guinea pig cochlea, both actin and tubulin are found in the sensory and supporting cells of the organ of Corti. Fodrin (brain spectrin) co-localized with actin in the cuticular plates of both inner and outer hair cells and along the lateral wall of the outer hair cells. Alpha-actinin co-localized with actin in the cuticular plates of the hair cells and in the head and foot plates of the supporting cells. It was also found in the junctional regions between hair cells and supporting cells. Profilin co-localized with actin in the cuticular plates of the sensory hair cells. Myosin was detected only in the cuticular plates of the outer hair cells and in the supporting cells in the region facing endolymph. Gelsolin was found in the region of the nerve fibers. Tubulin is found in microtubules in all cells of the organ of Corti. In supporting cells, microtubules are bundled together with actin microfilaments and tropomyosin, as well as being present as individual microtubules arranged in networks. An intensely stained network of microtubules is found in both outer and inner sensory hair cells. The microtubules in the outer hair cells appear to course throughout the entire length of the cells, and based on their staining with antibodies to the tyrosinated form of tubulin they appear to be more dynamic structures than the microtubules in the supporting cells. The microtubule-associated protein MAP-2 is present only in outer hair cells within the organ of Corti and co-localizes with tubulin in these cells. No other MAPs (1,3,4,5) are present. Tau is found in the nerve fibers below both inner and outer hair cells and in the osseous spiral lamina. It is clear that the actin-binding and microtubule-associated proteins present in the cochlea co-localize with actin and tubulin and that they modulate microfilament and microtubule structure and function in a manner similar to that seen in other cell types. The location of some of these proteins in outer hair cells suggests a role for microfilaments and microtubules in outer hair cell motility.     

Interaction of light with the organ of Corti

Summary A cochlear postmortem preparation has been developed which allows for hydromechanical studies of the transilluminated organ of Corti. It was found that cochlear hair cells act as optical waveguides. This property of hair cells is important for optical cochlear investigations. It may be used in the study of the motion of single hair cells.     

Ultrastructure of the organ of Corti in experimental hydrops

The early ultrastructural changes of the organ of Corti in the guinea pig after obliteration of the endolymphatic sac and duct were examined in a time-sequence study. Initial loss of outer hair cells was followed by inner hair cell degeneration, both starting at the apical part of the cochlea. Morphological changes of the sensory cells were found to start at the endolymphatic surface and were characterized by a variety of sterociliary pathologies, distortion of the cuticular plate and a less prominent contrast-staining of glycocalyx. Further degeneration was marked by pathological changes of intracellular organelles and the afferent and efferent nerve endings. Details of the ultrastructural changes in the organ of Corti are discussed with regard to the pathophysiology of experimental hydrops.     

Vascular supply to the organ of Corti in man

Summary The capillary distribution in the basilar membrane and the osseous spiral lamina was studied in 40 human temporal bones. The capillaries were made visible using a histochemical technique for demonstrating alkaline phosphatase activity. High tone sensorineural hearing loss can be explained by capillary distribution, length of a segment in the outer spiral vessel and the distance between the inner and the outer spiral vessels in different cochlear turns.A portion of this paper was read at the First International Workshop on Sensorineural Deafness on December 2, 1974 in Nashville, Tenn., USA. This research was supported by the Research Grant for Specific Disease of the Ministry of Health and Welfare, Sudden Deafness Research Committee of Japan