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At least 109 records · Page 6Linked to original sources

PubMed1988

Scar formation following impulse noise-induced mechanical damage to the organ of Corti.

The terminal stages of the healing process of the organ of Corti in the chinchilla following exposure to blast-waves at 160 dB peak SPL, were studied by scanning electron microscopy (SEM) and by surface preparation technique. Extensive lesions of the sensory epithelia consisting in the absence of the OHC's, Deiter cells and Hensen cells, were replaced by scar tissue formed by single, flat, irregularly polygonal cells, arising from the Claudius cell area sealing off the endolymphatic spaces. When the pillar cells have been destroyed the scar epithelium from the Claudius cells has reached the IHC's, which show a remarkable resistance to acoustic trauma. Their presence in a large healed area may be the only remnants of a previous sensory region. When even the IHC's are absent, the entire organ of Corti can be replaced both by Claudius cells and by inner sulcus cells covering the denuded basilar membrane without any clear morphological difference between the two cellular sources.

Animals↗

PubMed1986

A computer-assisted morphometric analysis of the organ of Corti.

This paper describes a method for a computer-assisted morphometric analysis of the organ of Corti and presents normal morphometric data on the chinchilla cochlea. The computer-assisted light microscope system that we developed consists of commercially available equipment: an Olympus light microscope, Boeckler X, Y motorized stage micrometers, an IBM PC computer and a computer program written by the second author. The system was developed for the analysis of whole-mount, surface preparations of the organ of Corti. The procedure for producing suitable surface preparations for a computer-assisted analysis of hair cells was described in a previous paper (Santi, 1986). The analysis procedure requires 2 passes along the length of the basilar membrane. During the first pass, the system establishes an X, Y slide coordinate system and maps basilar membrane distance onto the coordinate system. This procedure was performed in approximately 10 min using an efficient, 3-point arc approximation method. During the second pass, the user scans along the length of the basilar membrane and measures organ of Corti structures (e.g., hair cell dimensions) or records abnormal or missing hair cells. In addition to providing distance along the length of the basilar membrane, the system could also determine which hair cell row the user was examining. Thus, recording damaged and missing hair cells consisted of merely pressing the appropriate footpedal to indicate the type and degree of hair cell damage. After assessing hair cell damage, a cytocochleogram with an accompanying table of descriptive statistics was produced. Since the X,Y coordinate system for each slide was stored on a disk along with its corresponding basilar membrane distance map, slides could be removed and later reevaluated without the loss of previously obtained data. Normal morphometric data on the chinchilla organ of Corti consisted of cell dimensions within the reticular lamina and a two-dimensional graphical reconstruction of the curvature of the basilar membrane.

Animals↗

PubMedDate not supplied

Organ of Corti in the human fetus: scanning and transmission electronmicroscope studies.

The organ of Corti in the five-month human fetus was studied by transmission and scanning electronmicroscopy. Differentiation of the surface organization of the organ of Corti into a single row of inner and three to four rows of outer hair cells was complete at this stage except at the apical end. The morphological aspects of the hair bundles changed with maturation of the sensory cells; the inner hair cells preceded the outer hair cells in cytodifferentiation at a given location.

Cell Differentiation↗

PubMed1998

Quantitative measures reflect degeneration, but not regeneration, in the deafness mouse organ of Corti.

The deafness mouse (dn/dn) is a well known model of hereditary deafness uncomplicated by behavioral and motor disturbances. The organ of Corti in this mouse develops a normal complement of sensory and supporting cell structures, yet animals homozygous for this gene never demonstrate any hearing capacity. They are profoundly deaf from birth. Soon after development, the organ of Corti rapidly degenerates, most sensory cells having vanished by 50 days of age. Published observations have suggested that apical regions of the organ of Corti may regenerate some supporting cell structures by 90 days of age. We have quantified changes in organ of Corti structure from 15 to 130 days of age using several different measures. Measures of peak height and total cross-sectional area. as well as a subjective rating scale, all demonstrate consistent degenerative changes during this time period. No evidence for regeneration of supporting or sensory cell structures is noted, although a surprising degree of variability is present in all regions of the organ of Corti which may account for previous claims.

Aging↗

PubMed1999

p27(Kip1) links cell proliferation to morphogenesis in the developing organ of Corti.

Strict control of cellular proliferation is required to shape the complex structures of the developing embryo. The organ of Corti, the auditory neuroepithelium of the inner ear in mammals, consists of two types of terminally differentiated mechanosensory hair cells and at least four types of supporting cells arrayed precisely along the length of the spiral cochlea. In mice, the progenitors of greater than 80% of both hair cells and supporting cells undergo their terminal division between embryonic day 13 (E13) and E14. As in humans, these cells persist in a non-proliferative state throughout the adult life of the animal. Here we report that the correct timing of cell cycle withdrawal in the developing organ of Corti requires p27(Kip1), a cyclin-dependent kinase inhibitor that functions as an inhibitor of cell cycle progression. p27(Kip1) expression is induced in the primordial organ of Corti between E12 and E14, correlating with the cessation of cell division of the progenitors of the hair cells and supporting cells. In wild-type animals, p27(Kip1) expression is downregulated during subsequent hair cell differentiation, but it persists at high levels in differentiated supporting cells of the mature organ of Corti. In mice with a targeted deletion of the p27(Kip1) gene, proliferation of the sensory cell progenitors continues after E14, leading to the appearance of supernumerary hair cells and supporting cells. In the absence of p27(Kip1), mitotically active cells are still observed in the organ of Corti of postnatal day 6 animals, suggesting that the persistence of p27(Kip1) expression in mature supporting cells may contribute to the maintenance of quiescence in this tissue and, possibly, to its inability to regenerate. Homozygous mutant mice are severely hearing impaired. Thus, p27(Kip1) provides a link between developmental control of cell proliferation and the morphological development of the inner ear.

Animals↗

PubMed1998

Nonlinear mechanics of the organ of Corti caused by Deiters cells.

Though the organ of Corti (OC) has been an object of experimental and theoretical hearing research, open questions remain concerning the processing of acoustic signals by the cochlea where the OC is located. Today there is extensive knowledge about single parts of the organ but a lack of understanding as to how these elements act together. One of the reasons for this is the missing analysis of the mechanics of the OC in three dimensions. In order to fill this gap, we have analyzed a short section (0.06 mm) of the basilar membrane including the OC and evaluated its nonlinear finite element model numerically. The Deiters cells are idealized as thin elastic beams with a comparably low modulus of elasticity of actin. Therefore, they show nonlinear mechanical behavior generating additional frequency components with two-tone stimulation.

Basilar Membrane↗

PubMed1977

[To Wittmaack's theory of "hearing without the organ of Corti" (author's transl)].

1911 Wittmaack had shown by experiments in cats that the organ of Corti is independent from the cochlear nerve but dependent from a normal internal auditory artery. Similar findings he could observe in his temporal bone collection in cases of acoustic nerve tumors. On the other hand many human cases with the compression phenomenon of the organ of Corti had intact cochlear nerve fibers and neurons, and nearly normal hearing. Thus Wittmaack concluded that some parameters of hearing are transmitted by the nerve endings in the organ of Corti without the haircells. This hypothesis is discussed by means of examples of Wittmaack's temporal bone collection in the light of our present knowledge.

Cochlea↗

PubMed1984

The accuracy of hair cell counts in determining distance and position along the organ of Corti.

The relationship between the density of hair cells (cells/mm) and measured distance along the guinea pig organ of Corti was determined using light microscopy and the surface specimen technique. It was demonstrated that the density of inner hair cells (IHC; mean 92.0 +/- 2.4) and 1st row of outer hair cells (OHC1; mean 118.7 +/- 2.3) did not show significant variation along the organ of Corti except within 0.5-1.0 mm of the apex and base where there was considerable variation between animals in the density of cells. There was a close relationship between the accumulated number of either IHC or OHC1 and distance from the base along the organ of Corti. Distances estimated by hair cell counts were similar to those determined by direct measurement. It is concluded that hair cell counts can be used to reliably estimate distances along the organ of Corti where accurate direct measurement is not possible, such as in scanning electron microscopy.

Animals↗

PubMed1993

Cellular localisation of taurine in the organ of Corti.

The cellular localisation of taurine in the organ of Corti has been established using a monoclonal antibody and confocal fluorescence microscopy. The bulk of the taurine was found in the outer hair cells with very little present in the inner hair cells and supporting structures. The outer hair cells which probably function as an amplification/attenuation gain system, control inner hair cell output to the brain. Taurine is tentatively postulated as being related to calcium fluxes involved in outer hair cell response to sound or olivocochlear bundle stimulation. Other possibilities are also discussed.

Acoustic Stimulation↗

PubMed1995

Sound-induced displacement responses in the plane of the organ of Corti in the isolated guinea-pig cochlea.

Sound-induced displacement responses in the plane of the organ of Corti were studied in the apical turn in the isolated temporal-bone preparation of the guinea-pig cochlea. Swept sinusoidal sound stimuli (100-500 Hz) were delivered closed-field to the external auditory meatus. The surface of the organ of Corti was continuously monitored using a CCD video camera. Displacement responses in the plane of the organ of Corti were determined by analyzing the change of the location of the cells (pixel-by-pixel) within the visual field of the microscope. Displacement responses followed the stimulus amplitude and were observable at Hensen's cells, three rows of outer hair cells and inner hair cells. The most prominent displacement responses were over the outer hair cells; the maximum amplitude was 0.6-1.7 microns at 100 dB SPL. Tuned displacement responses were found; the Q10 dB was 1.3 +/- 0.6. The best frequency was tonotopically organized, decreasing toward the apex with a space constant of 0.4-0.9 mm/oct. The motion was directed either strial-apically or strial-basally in a frequency dependent manner. With the aid of laser interferometric measurements of the transverse displacement, it was concluded that sound stimulation does not induce slow DC motion in the organ of Corti for the isolated temporal-bone preparation.

Acoustic Stimulation↗

PubMed2000

Vibrations of the guinea pig organ of Corti in the apical turn.

Vibrations of the organ of Corti were measured in response to sound applied to the ear in the apical turn of a living guinea pig. Measurements were made at 29 points on the Reissner's membrane (RM) at 10 micro spacing along a radial track. Measurements also included 22 points on the reticular lamina (RL), Claudius' cells and osseous spiral lamina. Our goal was to characterize the vibration of the RM and the RL with high spatial resolution along a radial axis. The tuning and spatial patterns of the RM are compared in the radial direction with those for the RL at the fundamental frequency and at the second harmonic. The shape of the RM tuning curve changes with radial position, and differ significantly from those observed at the RL. These results support our earlier findings (Hao and Khanna, Hear. Res. 99 (1996) 176-189).

Animals↗

PubMedDate not supplied

Electrophysiological and morphological changes in the guinea pig cochlea following mechanical trauma to the organ of Corti.

Small discrete lesions were produced in the organ of Corti of the guinea pig cochlea using fine probes to produce direct mechanical insult. The electrophysiological state of the cochlea was assessed using N1 electrocochleography and loss of receptor cells determined by scanning electron microscopy. Principal findings were: 1) Excellent agreement between the location of hair cell losses and the frequency of maximum sensitivity change in the N1 audiogram; 2) The spatial extent of the mechanically induced lesion appears to be more important than the total number of hair cells lost, in determining the magnitude of N1 sensitivity loss; 3) Hair cell losses extending over only 72 micrometers could be detected as significant changes in N1 sensitivity. These results further emphasize the accuracy and usefulness of the N1 electrocochleogram for assessing the functional status of the cochlea; 4) Lesions involving only outer hair cell loss also produced marked elevations of N1 threshold.

Action Potentials↗

PubMed1994

[Pseudo-three dimensional observation of the organ of Corti in the guinea pig using scanning electron microscopy].

The entire organ of Corti of guinea pig was investigated by scanning electron microscopy (SEM), using it's high resolving power to observe the three dimensional fine structure of the cochlea. Inner ear tissue of the normal guinea pig was conductively stained (OTOTO-method) for SEM. The relationship between the sensory cells and supporting cells was shown. SEM gives a nice overview of the surface structure of three dimensional organs like the inner ear. We conclude that bulk specimens of the organ of Corti are more advantageous than piece specimens in acoustic physiological as well as pathological research studies.

Animals↗

PubMed1992

Strategies for constructing a guinea pig organ of Corti cDNA library and its potential use.

Mutations of genes common to several tissues or organs can lead to cellular damage, which may result in hearing impairment as part of a syndromic disorder. Mutations of genes that are unique to the organ of Corti would have a high probability of causing nonsyndromic hearing impairment. It is expected that such genes are involved in auditory transduction as well as in maintaining specific hair cell and supporting cell functions in the organ of Corti. Cloning and describing genes involved with nonsyndromic hearing impairment thus require the construction of a guinea pig cDNA library of the organ of Corti.

Amino Acid Sequence↗

PubMed1999

Establishment and characterization of conditionally immortalized organ of corti cell lines.

A culture of cells was isolated from the organ of Corti of 2-week-old H-2Kb-tsA58 (Immortomouse) transgenic mice. All cells of these mice harbor a mutant of the simian virus 40 A-gene, encoding a thermolabile large T-antigen (Tag) protein. At 33 degrees C the Tag protein is functional and induces cell proliferation, but at 39 degrees C it is rapidly denatured and inactivated. Isolated organ of Corti cells growing at 33 degrees C were predominantly small, rounded or fusiform and proliferated rapidly. When moved to 39 degrees C, the cells reduced their rate of proliferation and differentiated into specific morphological phenotypes. Four cell lines were cloned by limiting dilution and characterized by immunofluorescence microscopy and Western blot. The cell lines, named OC-k1, OC-k2, OC-k3 and OC-k4, have been passaged at least 50 times with retention of a stable phenotype. These cell lines were all positive for the neuroepithelial precursor cell marker nestin and for the inner ear cell marker OCP2. In addition, the cells showed reactivity to epithelial and neuronal cell markers, but with a pattern of protein expression different for each clone and different between cells of the same clone growing at 33 degrees C or 39 degrees C. Some of the clones exhibited asymmetric cell division which is a characteristic commonly ascribed to stem cells. These cell lines can be used advantageously to study mechanisms and signals involved in the control of cell differentiation and morphogenesis of the mammalian inner ear and to isolate inner ear specific proteins.

Animals↗

PubMed1975

Mechanism of sound susceptibility in organ of Corti - inference of contrary recruitment phenomenon (hypothesis) and the application to diagnosis -.

In order to make the mechanism concerned with the sound-susceptibility in the organ of Corti clear, we observed the organ of Corti with the phase-contrast microscope, after the microdissection of the cochleae in human, dogs, guinea pigs and hamsters by Engstroöm's surface preparation technique. As a result, we have formulated a hypothesis for the mechanism of the sound-susceptibility in the organ of Corti. Further, we have inferred the contrary recruitment phenomenon (hypothesis), by explaining theoretically such a clinical fact as the recruitment phenomenon or the cochlear hearing loss by applying our first formula of hypothesis. Finally, we described the application of the contrary recruitment phenomenon (hypothesis) to the early discovery or diagnosis of the false normal ear or cochlea, in other words, latent hearing loss.

Acoustic Stimulation↗

PubMed1997

Use of organotypic cultures of Corti's organ to study the protective effects of antioxidant molecules on cisplatin-induced damage of auditory hair cells.

HYPOTHESIS: Cisplatin causes the generation of reactive oxygen species (ROS), which interferes with the antioxidant defense system of Corti's organ and results in damage to the hair cells. BACKGROUND: Cisplatin is a widely used chemotherapeutic agent with the dose-limiting side effect of ototoxicity. Evidence is accumulating that cisplatin interferes with the antioxidant defense system of Corti's organ. METHODS: Organotypic explants of P-3 rat organ of Corti were the in vitro model system. Presence of intact auditory hair cells and stereocilia bundle integrity was assayed by phalloidin-FITC staining. Fluorescent dye probes detected H2O2 and intracellular thiol [e.g., glutathione (GSH)]. Spectrophotometric analysis determined antioxidant enzyme levels. RESULTS: There was a rapid dose-dependent cisplatin cytotoxicity in the explants after 48 h of exposure. An accumulation of H2O2 and a reduction of GSH levels were observed within cisplatin-exposed hair cells. L-buthionine sulfoximine, an inhibitor of GSH formation, enhanced cisplatin ototoxicity, whereas N6-(2-phenylisopropyl) adenosine, an adenosine agonist, elevated antioxidant enzyme levels and ameliorated cisplatin toxicity. The following molecules protected hair cells from cisplatin-induced damage: GSH; glutathione diethyl ester (GSHe); ebselen (EBS); 4-methylthiobenzoic acid (MTBA); and D-methionine (D-MET). EBS, MTBA, and D-MET in vitro protection correlates with in vivo protection in rats. CONCLUSIONS: Organotypic culture of Corti's organ has been validated as a model for studying cisplatin toxicity and for screening otoprotective molecules. Some of the events that contribute to cisplatin's ability to damage auditory hair cells are generation of ROS (e.g., H2O2), depletion of intracellular GSH, and interference with antioxidant enzymes within the cochlea. Agents that bolster the cochlea's antioxidant system can prevent cisplatin destruction of auditory hair cells. Identified protective agents may prove to be clinically useful in limiting or completely protecting from cisplatin ototoxicity.

Analysis of Variance↗

PubMed2006

Distribution of pendrin in the organ of Corti of mice observed by electron immunomicroscopy.

The distribution of pendrin, which is encoded by the Pendred syndrome gene, has been investigated immunohistochemically in the inner ear. In the cochlea, pendrin has been found in the spiral prominence, external sulcus cells, Hensen's cells and Claudius cells, but its expression in the organ of Corti remains unclear. We examined whether pendrin localizes in the organ of Corti by postembedding immunogold analysis. In the organ of Corti, gold particles were clearly observed in outer and inner hair cells, including the stereocilia. The density of the particles was especially high in the cuticular plates of the hair cells. Gold particles were also detected in the external sulcus, in part of the spiral ligament adjacent to the external sulcus, in supporting cells, and in the spiral ganglion of the cochlea. Our study revealed that pendrin occurs in the organ of Corti. The role of pendrin in the organ of Corti and its association with the Cl- or pH regulation of neurotransmission require further study.

Analysis of Variance↗