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PubMed1995

Degenerative changes in the organ of Corti and lateral cochlear wall in experimental endolymphatic hydrops and human Menière's disease.

The pathogenesis of sensorineural hearing loss in Menière's disease and experimental endolymphatic hydrops is not fully understood. At the light microscopic level, there is poor correlation between the histopathology and loss of sensitivity and speech discrimination. The results of electron microscopic investigation of histopathology and alterations in immunoreactivity in the organ of Corti and lateral cochlear wall in the hydropic guinea pig are presented. Loss of outer and inner hair cells and spiral ganglion cells, particularly in the apical turn was evident by light microscopy. By electron microscopy, further evidence of degeneration was detected in the cuticular plate of outer hair cells, neural endings of both inner and outer hair cells, myelinated dendritic fibers, spiral ganglion cells, and types I and II fibrocytes of the lateral cochlear wall. There was a marked decrease in immunoreactivity for a variety of enzymes, calcium binding proteins, structural proteins, and integral membrane proteins of gap junctions, particularly among type I and type II fibrocytes of the lateral cochlear wall. The evidence suggests that dysfunction and degeneration of hair cells, afferent neurons and fibrocytes of the lateral cochlear wall are involved in the pathogenesis of hearing loss in endolymphatic hydrops.

Animals↗

PubMed2005

Argon protects hypoxia-, cisplatin- and gentamycin-exposed hair cells in the newborn rat's organ of Corti.

During the last few years, an important protective effect of the noble gas xenon against neuronal hypoxic damage was observed. However, argon (Ar), a gas from the same chemical group, but less expensive and without anesthetic effect at normobaric pressure, has not been studied in terms of possible biological effects on cell protection. Ar was tested for its ability to protect organotypic cultures of the organ of Corti from 3-5 day old rats against hypoxia, cisplatin, and gentamycin toxicity. Cultures were exposed to nitrogen hypoxia (5% CO2, 95% N2), Ar hypoxia (5% CO2, 95% Ar) or normoxia for 30 h. Ar protected the hair cells from hypoxia-induced damage by about 25%. Ar-oxygen (O2) mixtures (21% O2, 5% CO2, 74% Ar) had no effect on the hair cell survival. Cisplatin (7.5-25 microM) and gentamycin (5-40 microM) exposed in medium under air damaged the hair cells in a dose-dependent manner. The exposure of cisplatin- and gentamycin-treated cultures to the Ar-O2 atmosphere significantly reduced the hair cell damage by up to 25%. This protective effect of Ar might provide a new protective approach against ototoxic processes.

Animals↗

PubMed1985

Met-enkephalin-Arg6-Gly7-Leu8 in the organ of Corti: high performance liquid chromatography and immunoelectron microscopy.

The opioid octapeptide Met-enkephalin-Arg6-Gly7-Leu8 (MERGL) was identified and quantified in the guinea pig cochlea using high performance liquid chromatography and a specific radioimmunoassay. The presence of MERGL immunostaining in efferent endings (coming from the brainstem) within the inner spiral bundle and the tunnel spiral bundle was demonstrated using a pre-embedding immunoelectronmicroscopic technique. Axo-dendritic synapses were observed between the MERGL immunostained varicosities and auditory dendrites. It is hypothesized that MERGL could act, together with Met-enkephalin and other pro-enkephalin A-related peptides, as an efferent neuromodulator or neurotransmitter in the organ of Corti.

Animals↗

PubMed2005

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.

Cochlea↗

PubMed1983

Serial section reconstruction of the neural poles of hair cells in the human organ of Corti. I. Inner hair cells.

Study of the anatomy of the cochlea, and in particular the morphology of synaptic relationships between hair cells and cochlear neurons, is essential for elucidation of the mechanisms of transduction of mechanical acoustic signals into electrical neural events. Because considerable gaps remain in our understanding of the microscopic anatomy of these synapses, particularly in the human, a reconstruction of neural pole of inner hair cells of the human organ of Corti was performed. The data are based on 526 serial sections from the basal turn (10 mm region) and 356 serial sections from the middle turn (26 mm region). This provided complete data on 3 and partial data on 5 inner hair cells. Afferent terminals on inner hair cells were variable in size, ranging 1 to 20 micrometers in diameter. Branching of large fibers to produce multiple terminals innervating from 1 to 3 inner hair cells was common. Each inner hair cell received approximately 6 to 8 different nerve terminals. In addition, each terminal possessed a variable number of synaptic contacts. Junctional membrane specialization consisted of synapses, desmosomes, coated vesicles and arrays of microtubules and membrane cisternae. Specialization at synapses consisted of asymmetrical membrane thickening. At inner hair cells the postsynaptic membrane was thicker than the presynaptic membrane. Eighty-three percent of synapses had presynaptic bodies. Vesiculated efferent terminals synapsed on afferent fibers at the base of inner hair cells, but never directly on the inner hair cell. These anatomical data demonstrate distinct differences between the human and animal inner ear, which are important in the interpretation of neurophysiological data in animals and the formulation of hypotheses that involve assumptions crossing species.

Desmosomes↗

PubMed1983

Serial section reconstruction of the neural poles of hair cells in the human organ of Corti. II. outer hair cells.

Study of the anatomy of the cochlea, and in particular the morphology of synaptic relationships between hair cells and cochlear neurons, is essential for elucidation of the mechanisms of transduction of mechanical acoustic signals into electrical neural events. Because considerable gaps remain in our understanding of the microscopic anatomy of these synapses, particularly in the human, a reconstruction of the neural pole of outer hair cells of the human organ of Corti was performed. The data are based on 577 serial sections from the basal turn and 368 sections from the middle turn. This provided complete data on 11 and partial data on 9 outer hair cells. Terminal size of afferent fibers on outer hair cells was much more uniform than that found at the base of inner hair cells. Only small bouton-like terminals were found. Branching of afferent fibers was also seen at the base of outer hair cells. Each outer hair cell received approximately two to eight afferent nerve terminals. Multiple synaptic contacts between a single afferent terminal and an outer hair cell were common. Junctional membrane specialization consisted of synapses, desmosomes, coated vesicles and arrays of microtubules and membrane cisternae. Specialization at synapses consisted of asymmetrical membrane thickening. At outer hair cells the presynaptic membrane was thicker than the postsynaptic membrane. At inner hair cells the converse was true. At outer hair cells 35% of synapses had presynaptic bodies, compared to 83% of synapses at inner hair cells. Reciprocal synapses, with both hair cell to neuron and neuron to hair cell polarities, were found only on outer hair cells. Vesiculated efferent terminals were common at the base of outer hair cells. Both axosomatic and axodendritic efferent synapses were found. In addition, the same efferent fibers were found to synapse both on an outer hair cell and on an afferent dendrite. One example of a probable dendro-dendritic synapse in the outer spiral bundle is presented.

Cochlear Nerve↗

PubMed1993

Glutathione S-transferases in the organ of Corti of the rat: enzymatic activity, subunit composition and immunohistochemical localization.

Glutathione S-transferases (GSTs), a family of ubiquitous cytosolic isozymes, catalyze the detoxification of electrophilic substrates with reduced glutathione and participate in intracellular binding and transport of lipophilic substances. This study measured GST activity biochemically in the inner ear of the rat; determined the isozyme profile by Western blotting; and identified, immunohistochemically, the distribution of the mu and pi class GSTs in the organ of Corti. GST enzymatic activity in inner ear tissues ranged from 117 to 348 nmoles glutathione converted/min/mg protein, values somewhat higher than those found in brain (130) and much lower than in liver (1011). Of the GST isoforms, the pi class (identified by antibodies against the Yp subunit) was most prominent, the mu class (Yb1 subunit) clearly evident while the alpha class (Y(a) subunit) was barely detectable on Western blots. Immunocytochemical analysis showed differential distribution of the Yb1 and Yp subunits. The Yb1 subunit was present in the sensory cells, while supporting cells were not specifically stained. At the subcellular level, the isozyme was localized in the apical zones of inner (IHCs) and outer hair cells (OHCs) close to the cuticular plate. The extent of staining, however, varied between OHCs and IHCs. In the OHCs, staining appeared in discrete spots in the apical areas only, whereas in IHCs staining extended further towards the center of the cells. The Yp subunit was mainly localized to Deiters cell processes and pillar cells. Both Yb1 and Yp colocalized with tubulin-specific antibody. The functional significance of GST in the cochlear receptor cells is speculative. However, a role analogous to that in other tissues (detoxification, prostaglandin synthesis) can be assumed. In addition, an association of GST with the microtubule system is possible based on immunohistochemical colocalization with tubulin.

Animals↗

PubMed2000

Mechanical nonlinearity in the apical turn of the guinea pig organ of Corti.

Confocal microscopy was used to view the sealed apical turn of the cochlea in a living guinea pig, and to identify the cochlear structures through the intact Reissner's membrane. X, Y and Z coordinates for each point of interest were recorded. A confocal laser heterodyne interferometer measured the cellular vibration in response to acoustical signals applied to the ear. Velocity time waveforms were recorded at 32 frequencies between 25 and 2500 Hz at each point of measurement. To characterize the vibration pattern of the organ of Corti, vibrations at multiple locations along a radial track of the reticular lamina were measured before and after sacrificing the animal. Amplitude and phase tuning curves of the fundamental and the second harmonic, velocity time waveforms, and FFTs of time waveforms are compared before and after sacrifice. The results show that a sharply tuned nonlinear part of the response disappears shortly after sacrifice.

Acoustic Stimulation↗

PubMed1990

Intracellular distribution of actin in cells of the organ of Corti: a structural basis for cell shape and motility.

Immunofluorescence staining and phalloidin labeling have provided localization of actin in the sensory and supporting cells of the inner ear at the light microscopic level. However, with electron microscopy, neither actin nor actin filaments have been found in the outer hair cell body. This paper describes various techniques utilized to preserve and identify cytoplasmic actin at the ultrastructural level. Post-embedding staining of Lowicryl K4M sections, pre-embedding staining of permeabilized cells of the organ of Corti, pre-embedding staining of vibratome sections, and pre-embedding staining of permeabilized dissociated cells documented the presence of actin, but each of these techniques was best suited to localize actin in specific parts of the cell. Cytoplasmic actin was labeled when isolated cells were lightly fixed and membranes were permeabilized with detergent--conditions under which the cell ultrastructure was compromised. Under conditions of optimal fixation, cytoplasmic filaments embedded in the dense granular matrix of the hair cell cytoplasm were observed.

Actins↗

PubMed1984

Enkephalin-like immunoreactivity in the guinea pig organ of Corti: ultrastructural and lesion studies.

Enkephalin-like immunoreactivity (ELI) was examined in a light and electron microscopic study of the normal guinea pig cochlea and of cochlea de-efferented through evulsion of the vestibular nerve. Antiserum to methionine enkephalin, 164, which gives immunoreactive labeling of only the lateral system of efferents, and antiserum 163, which gives immunoreactive labeling of lateral and medial efferents, were used. In de-efferented cochleae no immunoreactive labeling was seen with either antiserum, confirming that in the organ of Corti ELI is confined to efferents. At the ultrastructural level antiserum 163 but not 164 showed ELI in efferent terminals at the base of outer hair cells. ELI with 164 was seen in efferents ending on outer hair cells at the level of the nucleus. Medially, ELI was seen with both antisera in the inner and tunnel spiral bundles. Efferent terminals containing ELI were seen apposing afferent dendrites, other efferents and the inner hair cell. However, only rarely could synaptic contacts be unambiguously identified and then only with afferent dendrites.

Acetylcholinesterase↗

PubMed2004

Impedance analysis of the organ of corti with magnetically actuated probes.

An innovative method is presented to measure the mechanical driving point impedance of biological structures up to at least 40 kHz. The technique employs an atomic force cantilever with a ferromagnetic coating and an external magnetic field to apply a calibrated force to the cantilever. Measurement of the resulting cantilever velocity using a laser Doppler vibrometer yields the impedance. A key feature of the method is that it permits measurements for biological tissue in physiological solutions. The method was applied to measure the point impedance of the organ of Corti in situ, to elucidate the biophysical basis of cochlear amplification. The basilar membrane was mechanically clamped at its tympanic surface and the measurements conducted at different radial positions on the reticular lamina. The tectorial membrane was removed. The impedance was described by a generalized Voigt-Kelvin viscoelastic model, in which the stiffness was real-valued and independent of frequency, but the viscosity was complex-valued with positive real part, which was dependent on frequency and negative imaginary part, which was independent of frequency. There was no evidence for an inertial component. The magnitude of the impedance was greatest at the tunnel of Corti, and decreased monotonically in each of the radial directions. In the absence of inertia, the mechanical load on the outer hair cells causes their electromotile displacement responses to be reduced by only 10-fold over the entire range of auditory frequencies.

Acoustic Impedance Tests↗

PubMed2006

Intracochlear pressure and organ of corti impedance from a linear active three-dimensional model.

Intracochlear pressure and basilar membrane (BM) velocity are calculated from a physiologically based chinchilla cochlea model . The model includes three-dimensional viscous fluid and the pectinate zone of the elastic BM with dimensional and material property variation along its length. The passive response shows excellent agreement with measurement at high sound pressure levels. The active process is represented by adding the motility of the outer hair cells (OHCs) to the passive model with the feed-forward approximation of the organ of Corti (OC), as was done previously. The current model explains recent observations including: (1) agreement with characteristic frequency (CF)-to-place map, (2) CF shift in the active model, (3) BM displacement gain from OHC motility, (4) lower intracochlear pressure gain than BM displacement gain, and (5) OC impedance (Z(OC)).

Animals↗

PubMed2002

Localization of gamma-aminobutyric acid A receptor subunits in the rat spiral ganglion and organ of Corti.

Gamma-aminobutyric acid (GABA) is thought to be the major inhibitory neurotransmitter in the central nervous system. Although it is distributed in the olivo-cochlear bundles, which constitute the mammalian cochlear efferent system, its function in the cochlea is still obscure. In this study, we investigated the localization of GABAa receptor subunits (alpha1-6, beta1-3, gamma) in the rat cochlea in order to determine the role of GABA in the cochlea. Most spiral ganglion cells were intensely immunolabeled with all the anti-GABAa receptor subunit antibodies. In the organ of Corti, punctate immunoreactivities were observed in inner hair cell regions corresponding to the distribution of GABA. These data suggest that GABAa receptor was present in afferent nerve terminals in inner hair cell regions, and that GABA regulated afferent nerve transmission contacting efferent nerve endings by means of the axo-dendritic synapse function.

Animals↗

PubMed1985

Ultrastructural changes in the organ of Corti and in the ganglion spiral cochleae after vitamin A deficiency.

Guinea pigs were fed a vitamin A free diet and the cochleae of these animals were studied with the light and electron microscope. No changes could be found after ten weeks of vitamin A deficiency, but after 19 weeks the experimental animals showed a slight hypertrophy of the otic capsule, an accumulation of lysosomes in the sensory cells and a disruption and disintegration of the Hensen body. In the ganglion spiral cochleae ganglion cells appeared, filled with different myelin figures or honeycomb-like inclusions. Furthermore, the myelin sheath was split and sometimes filled with circular lamellar complexes and glycogen. These morphological findings together with the evidence of high concentrations of vitamin A in the organ of Corti support the hypothesis that vitamin A may be important for the function of the n. acusticus.

Animals↗

PubMed2000

Lipopolysaccharide-induced expression of inducible nitric oxide synthase in the guinea pig organ of Corti.

The purpose of the investigation was to ascertain whether inoculation of bacterial lipopolysaccharide (LPS) into the cochlea of the guinea pig could elicit formation of inducible nitric oxide synthase (iNOS). Immunohistochemical study revealed that immunoreactivity to iNOS was seen below outer hair cells representing nerve fibers and synaptic nerve endings. iNOS-staining could also be observed in phalangeal dendrites of Deiter's cells pointing to the cuticular membrane, Hensen's cells and on stria vascularis 48 h after inoculation with LPS. Immunohistochemical investigation with a specific anti-nitrotyrosine antibody also revealed intense immunoreactivity identical to that of iNOS, suggesting formation of peroxynitrite in the organ of Corti by the reaction of NO with O(2)(-). On the basis of these findings, it can be concluded that NO together with O(2)(-), which form the more reactive peroxynitrite, are the most important pathogenic agents in LPS-induced damage of cochlea in the guinea pig.

Animals↗

PubMedDate not supplied

Fas ligand expression in the organ of Corti.

We have previously demonstrated by FACS analysis and histochemistry that Fas ligand (FasL) increases on cochlear cell surfaces after immune response or stimulation with gamma-interferon (IFN-gamma). To determine whether the appearance of FasL on cochlear cell membranes is related to gene expression or to posttranslational events, cochlear cells were treated with IFN-gamma. They were evaluated for FasL gene expression by real-time PCR and for FasL protein localization by confocal microscopy of permeabilized and immunolabeled cells. Real-time PCR analysis of cDNAs generated from unstimulated or IFN-gamma-stimulated organ of Corti demonstrated no change in the transcription of the gene encoding FasL. In contrast, confocal microscopy revealed dramatic changes in the cellular distribution of FasL, consistent with movement from the endoplasmic reticulum to the cytoplasm and cell membrane. The results suggest that recruitment of preformed FasL from intracellular compartments, rather than its biosynthesis, is responsible for the increase in FasL on the cell surface following IFN-gamma stimulation. This is similar to the response of cytotoxic T lymphocytes in which gene expression is not involved in FasL surface appearance. Presumably, the use of preformed FasL increases the rapidity of this response. FasL localization to the membrane may be involved in protecting the inner ear from autoimmunity or inflammation. Alternatively it may be related to cochlear cell death in response to inflammatory stress.

Actins↗

PubMed2003

Transgenic expression of a dominant-negative connexin26 causes degeneration of the organ of Corti and non-syndromic deafness.

Hereditary deafness affects about 1 in 2000 children and mutations in the GJB2 gene are the major cause in various ethnic groups. GJB2 encodes connexin26, a putative channel component in cochlear gap junction. However, the pathogenesis of hearing loss caused by the GJB2 mutations remains obscure. The generation of a mouse model to study the function of connexin26 during hearing has been hampered by the fact that Gjb2 knockout mice are embryonic lethal. To establish viable model mice we generated transgenic mice expressing a mutant connexin26 with R75W mutation that was identified in a deaf family with autosomal-dominant inheritance. The previous expression analysis revealed that the R75W connexin26 inhibited the gap channel function of the co-expressed normal connexin26 in a dominant-negative fashion. We established two lines of transgenic mice that showed severe to profound hearing loss, deformity of supporting cells, failure in the formation of the tunnel of Corti and degeneration of sensory hair cells. Despite robust expression of the transgene, no obvious structural change was observed in the stria vascularis or spiral ligament that is rich in connexin26 and generates the endolymph. The high resting potential in cochlear endolymph essential for hair cell excitation was normally sustained. These results suggest that the GJB2 mutation disturbs homeostasis of cortilymph, an extracellular space surrounding the sensory hair cells, due to impaired K(+) transport by supporting cells, resulting in degradation of the organ of Corti, rather than affecting endolymph homeostasis in mice and probably in humans.

Amino Acid Substitution↗

PubMed1988

Postnatal development of the organ of Corti in the wild house mouse, laboratory mouse, and their hybrid.

Length of the basilar membrane, number and distribution of cochlear receptors, and the width of the triad of outer hair cells were analyzed in the course of the postnatal development and in adult individuals in wild and laboratory house mice and in hybrids of these species. While in newborn animals the triad of outer hair cells was wide at the base and narrow at the apex, the opposite was true for adult animals. The parameter decreased at the base and increased at the apex during postnatal development. The center of differentiation of (the reticular lamina of) the organ of Corti was localized at 40-50% of the basilar membrane length from the base and corresponded to the region with the maximum density of inner hair cells. The reticular lamina in the apical half of the cochlea matured earlier than in the basal half. Distribution of receptors did not change after birth. The shortest basilar membrane and the slowest rate of maturation were found in wild mice. Hybrids had the longest basilar membrane and the highest rate of maturation. These facts are considered an effect of heterosis.

Animals↗