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PubMed1990

Ultrastructure of the intercalated body, a novel organelle associated with fluid forming cells in the organ of Corti.

The intercalated body is a newly discovered organelle in the inner and outer spiral sulcus cells of the mouse organ of Corti. The organelle was found in the cochleas of 14-day and older intact mice and in organs in culture of corresponding ages. The organelle consists of a stack of interconnected cisternae of endoplasmic reticulum and of membrane bound rodlets that are intercalated between, and run parallel to, the cisternae. The cisternal membranes are predominantly smooth, but some may display ribosomes. Most rodlets are from 1 to 2 microns long, about 0.1 micron wide, and contain electron dense material. Mitochondria are commonly associated with or incorporated into the organelle. Some electron micrographs suggest that the rodlets may originate from modified mitochondria. It is our impression that the formation of the organelle begins with the apposition of cisternae and mitochondria. Cisternal-associated mitochondria appear to constrict, elongate, and lose their inner membranes. In both the intact animal and in culture, the cells of the inner and outer spiral sulci display microvilli, apical junctional complexes, lateral intercellular spaces containing interdigitating cell processes, and appear to be involved in fluid formation. Moreover, in culture, the cells of inner and outer spiral sulci as well as some cells proliferating in the outgrowth zone participate in fluid formation, producing large fluid pockets. All these cells commonly contain intercalated bodies. It is possible that in the intact animal, as in culture, intercalated bodies may play a role in fluid regulation in the immediate vicinity of the hair cells.

Animals↗
PubMed1986

Cytoskeletal organization in the supporting cell of the guinea pig organ of Corti.

The rapid-freeze, deep-etch method was used to visualize the three-dimensional organization of cytoskeletons in the supporting cells of the guinea pig organ of Corti. Deep-etched replicas showed that both the head and basal portions of the pillar cell were composed of a filamentous network consisting of several kinds of fibrous elements, into which numerous microtubules and actin filaments were tightly inserted. Myosin S1-decoration showed that the main constituent element in such filamentous networks in the basal portion of the pillar cell was the actin and tiny cross-bridges interconnected the randomly oriented adjacent actin filaments.

Actin Cytoskeleton↗
PubMed1987

Surface aspects of the developing human organ of Corti.

Thirteen cochleas from human fetuses ranging in age from week 9 to week 22 were observed by scanning electron microscopy. The classical 'base-to-apex' and 'internal-to-external' gradients of maturation were confirmed by surface observations of the developing organ of Corti. The tectorial membrane begins to be secreted around week 9, i.e. 2 weeks before the onset of the ciliogenesis. Its structure appears to be first amorphous and then fibrillar. The surface of the organ of Corti looks mature around week 22, but, in fact, its complete maturation, especially at outer hair cell level, probably occurs during the last trimester of pregnancy.

Cell Differentiation↗
PubMed1975

Action of Corti's organ and the cochlea: a new theory.

An "engineer's model" of the labyrinth is derived from the monoclinic crystal and the avian egg. The anatomy of the human cochlea and of the semicircular canals is then related by diffraction theory and Fresnel's explanation of optic activity. Increased cochlear electric potential, which represents stored energy, is associated with mechanical translation of the basilar membrane and angular separation of Corti's rods and is effected by "pumping" by the endolymphatic sac and the muscles that act on the auditory ossicles. The semicircular canals function as valves; the utricular and saccular macules form holograms and reflect the energy into the cochlear duct. Incoming acoustic waves excite dipole resonance and stimulate emission of a fraction of the stored energy; further amplification is effected by the hair cells, which, together with the tectorial membrane, behave like a transistor. These findings lead to a new theory of static balance and the action of Corti's organ: the labyrinth functions as a traveling wave maser of which the cochlea is the slow wave structure. Cochlear geometry itself effects resolution of incoming sound pitch. Corti's organ corresponds to the melatopes of the crystal, and the inter-rod angle is critical for any particular frequency, since it is related to dispersion of the optic axes.

Acoustics↗
PubMed1985

A study of the nerve endings of the outer hair cells in the organ of Corti--using scanning electron microscopy.

The nerve endings on the outer hair cells of the guinea pig organ of Corti were studied using a scanning electron microscope. The nerve endings in the basal turn were entirely exposed in the space of Nuel, whereas in the upper turns almost all nerve endings were covered by the Deiters' cell bulge. The number and the size of the nerve endings gradually decreased from the basal turn toward the apical turn. The shape of the nerve endings was spindle-shaped in the basal turn, while it was round in the upper turn. Some nerve endings were found to locate close to the outer hair cell surface. No pathological change was observed in the nerve endings 25 hr after completion of series treatments of streptomycin or kanamycin. However, the outer hair cells consistently showed shrinkage, especially in the basal turn.

Animals↗
PubMed1984

Glutamic acid decarboxylase immunoreactivity of olivocochlear neurons in the organ of Corti of guinea pig and rat.

The distribution of glutamic acid decarboxylase (GAD)-like immunoreactivity in the organ of Corti of guinea pig and rat was studied under the light microscope. Indirect immunohistochemical techniques were used. Cochleae were first incubated with a specific antiserum to rat brain GAD and then stained through an avidin-biotin-horseradish peroxidase (HRP) procedure. GAD-like immunoreactivity was visualized as staining with HRP reaction product. Surface preparations were prepared from the immunoreacted cochleae. GAD-like immunoreactivity was found in the inner spiral bundle, tunnel spiral bundle, tunnel crossing fibers, outer hair cell synaptic regions and outer spiral bundles. Little staining was seen in the basal turn. Most of the immunoreactivity was seen in the third and lower fourth turn of the guinea pig cochlea, but even there many efferent fibers and endings were unstained. It is concluded that GAD-like immunoreactivity is present in a subpopulation of cochlear efferents that contains elements from both the medial and the lateral olivocochlear system. Future studies are needed to determine whether this subpopulation is GABA-ergic (i.e. uses gamma-aminobutyric acid as a neurotransmitter) and/or cholinergic.

Animals↗
PubMed1987

Use of phase contrast microscopy to determine the height of the organ of Corti in whole-mount preparations.

A technique has been developed to measure the height of the organ of Corti (OC) in the whole-mount preparations of the cochlear duct. The technique corrects for variations in the microscope system, such as the magnification of the objective lens and the mechanical properties of the fine-focus knob, as well as the refractive index of the embedding medium and the angle of specimens with respect to the optical axis of the microscope. At 11 percentage locations from apex to base, the height of the OC in ten chinchilla cochleas was measured at three positions: (1) the lateral edge of the inner hair cell (IHC); (2) the medial edge of the first row outer hair cell (OHC1); and (3) the lateral edge of the third row outer hair cell (OHC3). These measurements were compared to measurements made on radial sections from five other cochleas, with very good agreement at IHC and OHC3, and fairly good agreement at OHC1. The height at OHC3 varied almost linearly with percentage distance along the OC, ranging from 96 microns (apical end) to 51 microns (basal end). The height at the OHC1 varied from 77 to 49 microns, but did not vary linearly. The height of the IHC was relatively constant, from 50 to 60 microns, except at the basal end, where it decreased to 42 microns.

Animals↗
PubMed1991

Degeneration of the organ of Corti following intravenous administration of cisplatin.

The development of acute morphological changes in the cochlea was studied in guinea pigs given one intravenous high-dose injection of cisplatin. In the light microscope three major stages of degeneration in the organ of Corti could be recognized: 1) an initial swelling of the Hensen's cells and protrusion of the Deiters' cells into the space of Nuel enclosing the outer hair cells, 2) a gradual degeneration of the outer hair cells together with a vacuolization in the region of the base of the inner hair cells, 3) a collapse of the Reissner's membrane and the entire organ of Corti with different degrees of damage to the inner hair cells. Sporadic bulging of the marginal cells of the stria vascularis into the endolymphatic space could be observed 4 days after injection.

Animals↗
PubMed2006

Microscale analysis of proteins in inner ear tissues and fluids with emphasis on endolymphatic sac, otoconia, and organ of Corti.

Here we describe preparatory techniques adapted for the study of proteins of inner ear tissues and fluids that have allowed us to apply state-of-the-art analytical techniques in spite of the minute size and anatomical complexities of this organ. Illustrative examples address unresolved issues of functional and clinical significance. First, we demonstrate how quick-freezing and freeze drying prevents artifacts that arise from sampling endolymphatic sac (ES) content in the liquid state. This set the stage for the generation of the first protein profile of the ES. Identification of crucial proteins will help elucidate mechanisms of endolymph volume regulation and pathogenesis of Meniere's disease. Second, we show how a unique situation allowed identification of otoconial proteins by mass spectrometric analysis without prior separation and we discuss possible roles for these minor otoconins in otoconial development and prevention of degenerative diseases that affect balance. Finally, we demonstrate techniques for the precise dissection of organ of Corti and its substructures, while preserving their near normal chemical state. We extended an earlier study in which we identified a novel calcium-binding protein by IEF, oncomodulin, localized in the outer hair cells and show here the applicability of prefractionation for the screening of calcium-binding proteins of organ of Corti. These studies demonstrate how advanced preparatory and analytical techniques can be applied to studies of the inner ear.

Animals↗
PubMed1991

Finding the impedance of the organ of Corti.

Measurements of the nonlinear response of the basilar membrane to a pure tone are shown to have a simple form for moderate membrane velocities: V(x,f;Vu)/Vu approximately [V(x,f)/Vu]v(x,f), f less than or equal to fc(x), where the response V is the velocity of the membrane at measurement position x, Vu is the umbo velocity, f is the frequency of the stimulus, and fc(x) is the local characteristic frequency. The frequency dependence of the functions v(x,f) and V(x,f) is determined from the data, and v(x,f) and ln V(x,f) are shown to be analytic functions in the lower half of the complex frequency plane, with Re [v(x,f)] a monotonically increasing function of f at fixed x. The linear limit of basilar membrane motion is characterized by a transfer function T(x,f) = (V/V1)v/(1-v), estimated by extrapolating V(x,f;Vu)/Vu to a small membrane velocity V1.T(x,f) and ln T(x,f) are shown to be analytic functions in the lower half of the complex frequency plane. The inverse of the amplitude of the transfer function, which has both a deep dip at f approximately fc(x) and a broad shoulder at lower frequencies, bears a striking resemblance to the neural threshold tuning curve. The functional form of T(x,f) is used to deduce the equation governing the motion of a section of the organ of Corti. Each section acts like a negatively damped harmonic oscillator stabilized at time t by a feedback force proportional to the velocity at the previous time t-tau. The time delay tau is proportional to the oscillator period [tau approximately 1.75/fc(x)]. Like a laser, the organ of Corti pumps energy into harmonic traveling waves. Unlike the laser, the direction of energy flow abruptly reverses as the traveling wave approaches the point of maximum membrane velocity [fc(x) approximately f]. All accumulated wave energy is then pumped back into a small section of the organ of Corti where transduction presumably occurs. Outer hair cells are conjectured to be active elements contributing to the negative damping and feedback of the cochlear amplifier.

Animals↗
PubMed1989

Effect of acoustic overstimulation on the glycocalyx and the ciliary interconnections in the organ of Corti: high resolution scanning electron microscopic investigation.

Changes in ciliary interconnections in the organ of Corti are described after acoustic overstimulation using a special high resolution scanning electron microscope and tannic acid-osmium staining technique, giving an almost three dimensional view. Guinea pigs were exposed to a 3.85 kHz pure tone at an intensity of 120 dB for 22.5 minutes. The first detectable change was a disarrangement of the cilia with a loosening of the interconnections. The ciliary plasma membrane presented with an abnormally smooth appearance. The tip links connecting the tips of the stereocilia to their taller neighbours were also affected showing elongation or even disappearance. The fine granules which cover the tips of the tallest stereocilia of the outer hair cells were decreased. These findings suggest that acoustic overstimulation may affect the carbohydrate metabolism exceeding to degeneration of ciliary interconnections resulting in a disarrangement and detachment of cilia. The tip links, which may participate in sensory cell transduction, seem also to be affected by acoustic overstimulation.

Acoustic Stimulation↗
PubMed1987

Tyrosine hydroxylase immunoreactivity identifies possible catecholaminergic fibers in the organ of Corti.

Antibodies to tyrosine hydroxylase, dopamine beta-hydroxylase and phenylethanolamine N-methyltransferase were used in an immunocytochemical examination of catecholamines in the cochlea. In cryostat sections, tyrosine hydroxylase and dopamine beta-hydroxylase-like immunoreactivities fibers were seen in the modiolus that did not extend to the organ of Corti. These corresponded to blood vessel-associated and non-blood vessel-associated fibers that have been previously described with histofluorescence. In surface preparations, tyrosine hydroxylase-like immunoreactivity was seen in the organ of Corti, in the inner and tunnel spiral bundles, suggesting an efferent component may be catecholaminergic.

Animals↗
PubMed2000

Age-related changes in microtubules in the guinea pig organ of Corti. Tubulin isoform shifts with increasing age suggest changes in micromechanical properties of the sensory epithelium.

Biochemical and immunocytochemical analyses have been used to provide new insights into age-related changes in the sensory and supporting cells of the guinea pig organ of Corti. Quantitative densitometry of immunoblots showed that, while levels of alpha-tubulin remained relatively constant in guinea pigs from 3 weeks to 18 months old, there were progressive shifts in some tubulin isoforms. Levels of tyrosinated tubulin increased with age, nontyrosinatable tubulin (delta2-tubulin) showed a compensatory decrease, but detyrosinated tubulin did not change; acetylated, polyglutamylated, and glycylated tubulin levels also decreased. Immunolabeled tissue sections showed that cell type-specific distribution of tubulin seen in young guinea pigs (tyrosinated in the microtubules of the sensory cells, and post-translationally modified isoforms in the supporting cells) did not change as animals aged. However, there were age-related decreases in labeling for alpha-tubulin and all post-translationally modified isoforms. Biochemical and immunocytochemical results both support an age-related decrease in the number and/or length of microtubules as well as an increase in the pool of soluble tyrosinated and detyrosinated tubulin. They further suggest that microtubules containing nontyrosinatable tubulin from older animals are the sites for further modification of tubulin by acetylation, polyglutamylation, and glycylation. Changes in tubulin isoform levels and stability of microtubules in the organ of Corti may alter its micromechanical properties; the resulting changes in conduction of sound-induced vibration would provide one mechanism for age-related hearing loss.

Acetylation↗
PubMed1988

Light- and electron-microscopic study of gamma-aminobutyric-acid-like immunoreactivity in the guinea pig organ of Corti.

With light and electron microscopy, gamma-aminobutyric-acid (GABA)-like immunoreactivity was examined in the guinea pig organ of Corti. In whole-mount preparations, although GABA-like immunoreactivity was present within efferent components in all turns of the cochlea, it was more intense apically. At the ultrastructural level, GABA-like immunoreactivity was clearly restricted to the efferent system, appearing in axons of the inner and tunnel spiral bundles, in axons crossing the tunnel of Corti, and in terminals filled with numerous labeled vesicles synapsing on outer hair cells.

Animals↗
PubMed1991

Progress in electron microscopic diagnostics: semi-quantitative determination of precipitable calcium in different cell types of the organ of Corti in the guinea-pig.

Potassium antimonate was used to precipitate calcium in the cochlea of the guinea-pig. The distribution of the calcium antimonate precipitates was analysed by electron microscopy. The precipitate density was determined in different cell types in the organ of Corti by counting the number of calcium binding sites in a 10-micron 2 area. The size of the precipitates varied considerably, and thus the relative amount of the precipitable calcium was estimated only semi-quantitatively. As the prominent carbon signal is superimposed over the nearby small Ca(2+)-edge signals, the combined signal of the antimony M4,5-edge and the oxygen K-edge of the calcium antimonate salt formed was chosen for the semi-quantitative estimation. Images of the inelastically scattered electrons of the precipitates at delta E = 570 eV were recorded by electron spectroscopic imaging. The area covered by the calcium precipitates within a given cell type was determined in different ultrathin sections of the same organ of Corti by an image processing system.

Animals↗
PubMed1992

Scanning electron microscopy of the mammalian organ of Corti: assessment of preparative procedures.

Different fixation, drying and coating procedures have been applied in preparation of the organ of Corti for scanning electron microscopy (SEM), and structural features of the apical surface of the tissue in unfixed, freeze-fractured preparations used in assessing their effects on morphology. Fixation with glutaraldehyde alone or osmium tetroxide alone causes artefacts that are substantially avoided when tissue is doubly fixed in glutaraldehyde followed by osmium. Significant improvements in preservation are also obtained when tissue is additionally processed through thiocarbohydrazide-osmium (TOTO) processing. In addition to providing a conducting coat, it stabilises the tissue against deformations that might otherwise occur during drying, and reduces the extent of tissue shrinkage. Freeze-drying of TOTO processed tissue produces less tissue distortion than critical point drying (CPD) but is not so easy to apply routinely. The distortions of structure in TOTO-processed CPD tissue are not significant and this may be the preferred procedure for routine use, but air drying from hexamethyldisilazane is a useful alternative, producing results as good as those from CPD samples if TOTO processing is applied beforehand. One particular advantage of freeze-drying, though, is that after freezing, brittle fracture through the tissue can occur making examination of intracellular structure by SEM relatively easy. However, again, TOTO processing prior to freezing is of value as this appears to prevent the formation of large ice-crystal during freezing. Examination of isolated outer hair cells by SEM shows that isolation procedures do not cause significant damage to the stereociliary bundles.

Animals↗
PubMed1995

Cytoskeletal and calcium-binding proteins in the mammalian organ of Corti: cell type-specific proteins displaying longitudinal and radial gradients.

Whole mounts and tissue sections of the organ of Corti from two representative mammalian species, the Mongolian gerbil (Meriones unguiculatus) and the guinea pig (Cavea porcellus) were probed with antibodies to cytoskeletal and calcium-binding proteins (actin, tubulin, including post-translational modifications, spectrin, fimbrin, calmodulin, parvalbumin, calbindin, S-100 and calretinin). All of the proteins tested were expressed in both species. New findings include the following. Actin is present in large accumulations in cell bodies of the Deiters cells under the outer hair cells (OHC), as well as in the filament networks previously described. These accumulations are more prominent in the apical turns. Tubulin is present in sensory cells in the tyrosinated (more dynamic) form, while tubulin in the supporting cells is post-translationally modified, indicating greater stability. Fimbrin, present in the stereocilia of both IHCs and OHCs, is similar to the isoform of fimbrin found in the epithelial cells of the intestine (fimbrin-I), which implies that actin bundling by fimbrin is reduced in the presence of increased calcium. Parvalbumin appears to be an IHC-specific calcium-binding protein in the gerbil as well as in the guinea pig; labeling displays a longitudinal gradient, with hair cells at the apex staining intensely and hair cells at the base staining weakly. Calbindin displays a similar longitudinal gradient, with staining intense in the IHCs and OHCs at the apex and weak to absent in the base. In the middle turns of the guinea pig cochlea, OHCs in the first row near the pillar cells lose immunoreactivity to calbindin before those in the second and third rows. Calmodulin is found throughout the whole cochlea in the IHCs and OHCs in the stereocilia, cuticular plate, and cell body. Calretinin is present in IHCs and Deiters cells in both species, as well as the tectal cell (modified Hensen cell) in the gerbil. S-100 is a supporting cell-specific calcium-binding protein which has not been localized in the sensory cells of these two species. The supporting cells containing S-100 include the inner border, inner phalangeal, pillar, Deiters, tectal (in gerbil) and Hensen cells, where labeling displays a longitudinal gradient decreasing in intensity towards the apex (opposite to what has been seen with labeling for other proteins in the cochlea).

Actins↗