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.     

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.     

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.     

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.     

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.     

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.     

Loss of stereocilia in the human organ of Corti

Summary The process of disappearance of the stereocilia at the top of the outer hair cell was described by observing aged human cochlea under scanning electron microscope. After loss of hair, remnants of hair could be recognized at the top of outer hair cells. As the process continued, the remnants of the stereocilia increase in percentage, while the remaining abnormal hair decrease.As remnants gradually disappear, the W-configuration faded away. At the same time, the diameter of the hair cell top decreased by shrinking. Before the supporting cells made a complete cover, there may be a depression in the reticular lamina due to shrinking of the top of the hair cell. However, if the depression persists, there is the potential danger of reticular lamina rupture.Existence of a breaking point in the stereocilia of the outer hair cell was proposed.This study was supported by the Research Grant for Specific Diseases of the Ministry of Health and Welfare, Idiopathic Bilateral Sensorineural Hearing Loss Research Committee of Japan     

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     

Cross-links between stereocilia in the human organ of Corti

Human cochleae were fixed in glutaraldehyde, without the use of osmium. Cross-links were seen between the stereocilia, similar to those we have previously reported for the guinea pig: first, stereocilia of the same row on each hair cell were joined by horizontally-running links; secondly, the shorter stereocilia had pointed tips, each giving rise to a single, vertically-pointing link, which ran upwards to join the adjacent taller stereocilium of the next row. We suggest that distortion of this link is involved in sensory transduction. The links were sparser than had been seen in the guinea pig which may be a reflection of the vulnerability of the links to non-optimal fixation, and the greater difficulty in producing good fixation in human specimens.     

Hensen's cell cyst of the organ of Corti

The temporal bone collection at the Massachusetts Eye and Ear Infirmary contains the bones of two subjects with bilaterally symmetrical cyst formations in the Hensen's cell areas of the organs of Corti. In both subjects the cysts are located in the 8-14-mm regions of the cochlear ducts. Both cochleas of one subject show pressure atrophy of the outer hair cells, demonstrating that the cysts may have the potential for producing high-tone hearing loss. While the genesis and contents of the cysts are unknown, it is postulated that they may represent the coalescence of lipid droplets extruded from Hensen's cells.