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PubMedDate not supplied

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.

Freeze Fracturing↗
PubMed1997

Specific proteins of the organ of Corti.

The mammalian organ of Corti has achieved a degree of perfection unequaled in other hair cell systems. Although cellular metabolism requires the coordinated action of thousands of proteins, the physical processes underlying auditory transduction in the OC are undoubtedly mediated by a much smaller subset of these. OCP1, OCP2, and CBP-15-identified by 2D-PAGE-are apparently members of this elite class. OCP1 and OCP2 are restricted to the supporting cells of the organ of Corti and adjacent epithelia. Their distribution closely parallels the boundaries of the epithelial gap junction system, implying a role in cochlear potassium and pH homeostasis. CBP-15 was recently shown to be identical to oncomodulin, the mammalian beta-parvalbumin, heretofore documented only in the placenta and neoplasms. Expression of this small calcium-binding protein in the OC is restricted to the outer hair cells, where it may function as a calcium-dependent regulatory protein.

Animals↗
PubMed1991

[Study of the mechanism of supporting cells repairing the organ of Corti in terms of cell kinetics--nuclear DNA synthesis of supporting cell of the organ of Corti in the cochlea damaged by nitromin administration].

3H-thymidine autoradiography in vivo was carried out on normal mature mice, whose organs of Corti were securely damaged by Nitrogen Mustard-N-oxide (nitromin). The cell kinetics of supporting cells of the organ of Corti were examined and relation between these changes and mechanisms of supporting cells to maintain the organ of Corti was discussed in this paper. A few grains in various kinds of supporting cells in S stage, which were not found in control mice without nitromin injection, were discovered. Those were detected in Hensen's cell, Deiters' cell, Claudius' cells, and inner phalangeal cell. Mitosis was seen in one Claudius' cell in addition. Therefore some supporting cells seem to be able to synthesize DNA and proliferate in the acutely damaged organ of Corti even in mature cochlea and those in G0 stage begin to go around cell cycle as occasion demands. Although labelled supporting cells decreased over time, the portion of supporting cell is likely to change in proportion as the extension of damage in the organ of Corti. If this new dynamic change of cell kinetics in the acutely damaged organ of Corti means the reaction to repair the organ of Corti, the supporting cells seem to have a reasonable role to maintain the organ of Corti including repairment of reticular lamina.

Animals↗
PubMedDate not supplied

[Receptor surface of Corti's organ in guinea pig embryos].

Using scanning electron microscope, studies have been made of the structure of the receptive surface of the organ of Corti in 48- and 57-day old embryos of the guinea pig. It was found that some structural modifications take place in this period: the size and the number of microvilli in the supporting cells decrease, the width of the organ of Corti increases, the number of ball-like cytoplasmic protrusions from the cellular surface decreases, the number of kinocilia in the receptor cells is reduced. These processes are associated presumably with the development of Nuel's space, Corti's tunnel, the origin of flexible connection between the tectorial membrane and the receptive surface, as well as with maturation of the ionic composition of the inner ear fluid.

Animals↗
PubMed1997

[Ultrastructural study of the organ of Corti in animals given kanamycin and ceruloplasmin].

10 guinea pigs of group 1 were injected subcutaneously kanamycin (400 mg/kg). The other 10 guinea pigs of group 2 received human ceruloplasmin as an intraperitoneal injection of 10% solution (0.25 ml of the protein preparation per 100 g body weight) 30 min before kanamycin administration. 7 days after the treatment the cochlease were isolated and examined electron microscopically. The Corti's organ was stained with alcyan blue and lanthanum hydroxide. In animals of group 1 there was mitochondrial vacuolization, enlargement of the cisterns of the endoplasmic network, Golgi apparatus, sub-superficial network; glycocalix layer on the surface of the receptor epithelium was unbroken but uneven, in the sensor cells of the Corti's organ of the group 2 animals only few mitochondria were vacuolized. A great number of ribosomes and mitochondrial contacts with membraneous cell structures were indicative of active protein synthesis and energetic processes. Glycocalix was less damaged. This was indicative of an otoprotective effect of ceruloplasmin which diminished kanamycin ototoxicity.

Animals↗
PubMed2000

Cell coupling in Corti's organ.

The mammalian organ of Corti is responsible for the initial analysis of sound; injury leads to hearing loss. During the last two decades, the characteristics of cellular coupling in this specialized epithelium have been studied. In this review, data on both electrical and mechanical coupling are covered. While electrical coupling likely contributes to homeostasis in the organ, this concept is far from proven.

Animals↗
PubMed1994

Cell coupling in the supporting cells of Corti's organ: sensitivity to intracellular H+ and Ca+2.

The input capacitance of cell pairs or small groups can be used to gauge the degree of electrical coupling via gap junctions (Santos-Sacchi, 1991). In order to estimate junctional sensitivity to intracellular Ca+2 and H+ concentration, the input capacitance of supporting cell syncytia of the organ of Corti was measured with the whole cell voltage clamp technique, while directly modifying the cation concentrations via the patch pipette. Typically, a pH below 6.5 was capable of uncoupling Hensen cells. On the other hand, pCa levels as low as 3 were ineffective.

Animals↗
PubMed1992

[Immunohistochemical distribution and fine localization of the gamma-aminobutyric acid in the organ of Corti of normal guinea pigs].

This paper presents the distribution and fine localization of the gamma-aminobutyric acid (GABA) in the Corti's organ of normal guinea pigs by using immunohistochemical technique (ABC-GDN method) and immunoelectron microscopy. GABA-IR was found in axons of efferent neurons in all turns of the cochlear spiral, but no positive endings may be found in the apical. The positive immunoreactive products were seen in the efferent components, including inner spiral bundle, tunnel spiral bundle, tunnel-crossing fibers, and large nerve endings on outer hair cell bases. Some of the GABA-IR negative outer hair cells could be seen between the positive endings. One GABA-IR positive nerve fiber could form synapse with six or seven outer hair cell bases. The GABA-IR positive efferent endings, negative efferent endings and negative afferent endings could be seen on the out hair cell bases with transmission electronic microscope. The GABA-IR positive efferent endings and negative afferent endings could form the neuraxon-neurodendron synapse on the inner hair cells bases. These morphological distribution suggests that the GABA may be one of the cochlear efferent neurotransmitter or modulator.

Animals↗
PubMed2000

Nitric oxide uncouples gap junctions of supporting Deiters cells from Corti's organ.

Supporting cells of Corti's organ are electrically coupled via gap junctions. They probably serve to maintain the unique cochlear environment that is required for normal sensory function. In this study we used input capacitance measurements under whole-cell voltage-clamp conditions to evaluate the effects of nitric oxide on gap junctional communication between pairs of isolated supporting Deiters cells. We show that the nitric oxide (NO) donor sodium nitroprusside causes the uncoupling of Deiters cells, and that an NO synthase inhibitor blocks the effect. The cGMP analogue 8-bromo-cGMP also uncouples Deiters cells. With either treatment, the input capacitance of pairs of Deiters cells drops to single-cell levels within minutes of application, indicative of electrical uncoupling. We surmise that the NO/cGMP pathway may serve to modulate normal cochlear homeostasis and possibly plays a role in ototoxic mechanisms.

Animals↗
PubMed1996

Morphology of the monotreme organ of Corti and macula lagena.

The organ of Corti and macula lagena were studied by scanning and transmission electron microscopy in two species of monotreme, the platypus and echidna. In both species, the organ of Corti had a fundamentally mammalian conformation, with distinct outer and inner hair cells, separated by a tunnel of Corti. However, unlike eutherian mammals, the monotremes had three or four rows of pillar cells, and four to five rows of inner hair cells. The organ of Corti was much shorter than in eutherian mammals, at 4.4 mm (platypus), and 7.6 mm (echidna). While the total number of outer hair cells (3,350 platypus, 5,050 echidna) was many fewer than in most eutherian mammals, the total number of inner hair cells (1,600 platypus, 2,700 echidna) was comparable with that in eutherian mammals. The stereocilia on both inner and outer hair cells underwent a systematic change in orientation across the cochlear duct, with those nearest the tunnel of Corti having their axis of symmetry oriented transversely across the duct, and those on the outer edge of the organ having the axis oriented nearly longitudinally along the duct. The macula lagena had signs of a vestibular epithelium, with tall bundles of stereocilia, a division into areas with bundles of opposing orientation and type I and type II hair cells.

Animals↗
PubMed1983

An ultrastructural study of the development of afferent and efferent synapses on outer hair cells of the guinea pig organ of Corti.

The guinea pig organ of Corti was studied using transmission electron microscopy, the second turn of the cochlea being examined at various ages between 20 days before birth and 30 days postnatal. Outer hair cells were examined at each of these ages. At all ages studied, the efferent (presynaptic) terminals are large and are packed with synaptic vesicles, whereas the afferent (postsynaptic) terminals are generally smaller, with a relatively small number of vesicles. During development, the subsynaptic cistern changes from a fragmented, diffuse profile extending over 50-70% of the length of the efferent contact zones, to a continuous, compact structure spanning neighbouring synapses. Synaptic vesicles in the efferent terminals are predominantly rounded in early development, flattened vesicles appearing postnatally. The synaptic bodies at afferent synapses do not change noticeably during development. Quantitative analysis revealed that the area of efferent terminals and the length of their active zone increase with increasing age, the same parameters decreasing in afferent terminals. Synaptic vesicles in the efferent terminals decrease in diameter, but remain constant in afferent terminals, with increasing age. The number of hair cell membrane invaginations decreases as development proceeds.

Afferent Pathways↗
PubMedDate not supplied

The efferent innervation in the region of inner hair cells in the organ of Corti.

The efferent innervation of the inner hair cells in Corti's organ of the laboratory rat and of a bat was investigated with help of histochemical staining of the inner spiral bundle. The area of acetylcholinesterase-positive fibres in the inner spiral bundle regions was measured. The bulk of the efferent fibres lie in the middle part of the cochlea. Towards the apical and lower basal turns a distinct decrease in the number of fibres was observed.

Acetylcholinesterase↗
PubMed2000

Three-dimensional motion of the organ of Corti.

The vibration of the organ of Corti, a three-dimensional micromechanical structure that incorporates the sensory cells of the hearing organ, was measured in three mutually orthogonal directions. This was achieved by coupling the light of a laser Doppler vibrometer into the side arm of an epifluorescence microscope to measure velocity along the optical axis of the microscope, called the transversal direction. Displacements were measured in the plane orthogonal to the transverse direction with a differential photodiode mounted on the microscope in the focal plane. Vibration responses were measured in the fourth turn of a temporal-bone preparation of the guinea-pig cochlea. Responses were corrected for a "fast" wave component caused by the presence of the hole in the cochlear wall, made to view the structures. The frequency responses of the basilar membrane and the reticular lamina were similar, with little phase differences between the vibration components. Their motion was rectilinear and vertical to the surface of their membranes. The organ of Corti rotated about a point near the edge of the inner limbus. A second vibration mode was detected in the motion of the tectorial membrane. This vibration mode was directed parallel to the reticular lamina and became apparent for frequencies above approximately 0.5 oct below the characteristic frequency. This radial vibration mode presumably controls the shearing action of the hair bundles of the outer hair cells.

Animals↗
PubMedDate not supplied

A quantitative study of the sequence of topographical changes in the organ of Corti following acoustic trauma.

The organs of Corti of 30 guinea pigs were examined quantitatively by scanning electron microscopy either immediately or 1, 3, 7 or 14 days after exposure to 3 kHz at 125 dB SPL for 30 min. Lesions (0.1-4.15 mm in length) were observed in 70% of the organs of Corti. There was no significant change in lesion length with recovery from the exposure. Early changes in hair cells consisted of stereocilia abnormalities, predominantly amongst inner hair cells and the first row of outer hair cells. The proportion of affected cells increased towards the centre of lesions, where supporting cells were affected also. Subsequent to exposure, affected hair cells were either lost or remained with stereocilia abnormalities but did not recover. Regions showing supporting cell damage were replaced within 3 days by inner sulcus and Claudius cells. Despite similar changes to stereocilia, inner hair cells were more resistant to necrosis than outer hair cells, suggesting that the nature of stereocilia damage does not necessarily indicate the fate of hair cells.

Animals↗