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PubMed1985

Localization of dynorphin B-like and alpha-neoendorphin-like immunoreactivities in the guinea pig organ of Corti.

Antiserum to dynorphin B and antiserum to alpha-neoendorphin were used in an immunocytochemical examination of the guinea pig organ of Corti. Immunoreactive staining for these two proenkephalin B (prodynorphin)-derived peptides was seen in the lateral system of olivocochlear efferents in the organ of Corti: the inner spiral bundle, the tunnel spiral bundle and by the bases of inner hair cells. Immunoreactive staining with both antisera was also seen in efferent terminals on outer hair cells at or above the level of the nucleus, which may represent terminals of either the lateral or the medial system. No immunoreactive staining was seen in tunnel crossing fibers and at bases of outer hair cells corresponding to the medial system of efferents. The staining seen with antiserum to dynorphin B and to alpha-neoendorphin has similar distribution to that seen with antisera to methionine enkephalin; there may be co-localization of these neuropeptides in the lateral system of efferents. Choline acetyltransferase-like immunoreactivity (co-localized with enkephalin-like immunoreactivity in the lateral system in the brainstem) and glutamic acid decarboxylase (GAD)-like immunoreactivity have also been found in olivocochlear efferents. Further studies will be necessary to determine if the dynorphins are co-localized with other neurotransmitter candidates and what their interactions may be.

Animals↗

PubMed1998

Gap junction change in supporting cells of the organ of Corti with ryanodine and caffeine.

It has been demonstrated that the gap junctions of the supporting cells of the organ of Corti are controlled by H+ and Ca2+. Inside these cells there is a tubular structure. It is supposed that this network is endoplasmic reticulum. Calcium release from inside the cells, and the effect of calcium on the gap junctions of these cells, were investigated under whole cell clamping application of ryanodine and caffeine. Membrane capacitance and membrane resistance were calculated, with corrections for changes in whole cell parameters. Ryanodine-treated cells (1 microM-10 mM), caffeine-treated cells (5 mM 500 nM) and A23187-treated cells were uncoupled at their gap junctions. Therefore, Ca2+ plays a role in the uncoupling of the gap junctions in supporting cells of the organ of Corti from inside the cells.

Animals↗

PubMed1983

Holes in the reticular lamina after noise exposure: implication for continuing damage in the organ of Corti.

Three different histological techniques (scanning electron microscopy, phase contrast microscopy and light microscopy) were used to examine the organ of Corti after a damaging noise exposure. In the region of maximal injury, all outer hair cells were missing 1-2 h after the exposure had ended. Degenerated hair cells are eventually replaced by phalangeal scars. However, in these short-term recovery ears, a series of holes which were the exact size and shape of the missing outer hair cell apices were found in the reticular lamina. These holes may provide a communication route between the endolymphatic space and the fluid spaces of the organ of Corti for a period of time following a damaging noise exposure. The noise-related degeneration of supporting cells, nerve fibers and even some sensory cells may be secondary to contamination of the fluid spaces with potassium-rich endolymph.

Animals↗

PubMed1985

Qualitative assessment of postnatal maturation of the organ of Corti in two rat strains.

The radial width of three rows of cuticular plates of outer hair cells (width of the OHC triad), the distribution of inner hair cells along the organ of Corti, and postnatal maturation of the middle ear were examined in rats of the Srague-Dawley and Lewis strains aged 0-24 days and two months. The width of the OHC triad is a good indication of the course of maturation of the reticular lamina and the organ of Corti in different regions of the cochlea. The width of the OHC triad in adult rats decreases continuously from the apex toward the base, while in newborn pups the trend is just the reverse. Thus, there is a region of the cochlea in which the width of the OHC triad is the same, or changes insignificantly, from birth to adulthood. This particular region (where the process of postnatal maturation of the organ of Corti begins?) corresponds to the region of maximum density of inner hair cells and tonotopically to the region of 'best hearing'. The width of the OHC triad will reach its adult values earlier in the basal than in the apical regions. The time-course of middle ear maturation correlates well with the time-course of maturation of the reticular lamina. The parameters under study are in many respects strain-specific.

Animals↗

PubMed1986

Spike activity recorded from the organ of Corti.

During microelectrode passes through the inner hair cell region of the organ of Corti, spike activity is frequently encountered. We have obtained both extracellular and intracellular records from afferent terminals or dendrites. The response characteristics of all-or-none spike trains mimic those recorded from primary auditory axons. EPSPs may be identified, either associated with the spikes or in the absence of a spike. Inferences may be made about the nature of neurotransmitter quantum release from inner hair cells.

Action Potentials↗

PubMedDate not supplied

Efferent nerve fibers associated with the outermost supporting cells of the organ of Corti in the guinea pig.

In whold-mount preparations of the organ of Corti nerve fibers are sometimes seen peripheral to the third-row outer hair cells where they appear to wander among the Hensen cells. These fibers were studied in the guinea pig by both light and electron microscopy. In the upper second, third and fourth cochlear turns nerve fibers were seen between and on the peripheral side of the third-row Deiters cells as well as in the floor of the outer tunnel space. They were not found in the intercellular spaces between the Hensen cells. These nerve fibers are continuous with the spiral efferent fibers beneath the outer hair cells. Also their ultrastructural and histochemical characteristics indicate that they are efferent neural elements. This identification was confirmed by the finding that they degenerate following interruption of the olivo-cochlear bundle in the brain stem.

Animals↗

PubMedDate not supplied

Immediate alterations in the impulse noise exposed organ of Corti of the guinea pig.

Cochlear microphonics and morphological changes in the organ of Corti were examined in guinea pigs exposed to 1 or 10 impulses of 164 dB SPL. Immediately after noise exposure the CM amplitudes of frequencies between 500 and 10000 Hz delcined severly with an accelerating tendency during the next 2 hours. The decrease in CM in two groups differed insignificantly. 10 minutes after impulse exposure, whole-mount specimens showed mainly swollen and translocated nuclei of outer hair cells. After 2 hours we found large quantities of pyknotic nuclei, karyorrhexis, and gaps in the normal OHC pattern. Despite minor numerical differences in injured cells of either group, exposure to 10 impulses caused a greater degree of irreversible alteration. Altogether, altered hair cells were only localized in the basal and lower second turn, and their numbers were relatively small. This stands in contrast to severe decrease of CM from low to high frequencies. Hair cell injury and additional mechanical lesion of the reticular membrane caused many sites of leakage, allowing interchange of endo-and peri-lymph. This effect is considered to be the main cause of functional damage indicated by rapid CM decline.

Animals↗

PubMed1983

Some electrical circuit properties of the organ of Corti. I. Analysis without reactive elements.

A simplified network model of the organ of Corti is analyzed with the assumption of parametric excitation via resistance changes in the hair cells' apical membrane. Pertinent network variables (intracellular resting and receptor potentials, cellular input resistance, extracellular potentials) depend on the ratios of basal (perilymphatic face) and apical (endolymphatic face) receptor cell resistances, denoted as shape factors. In the Appendix two methods are suggested for the computation of shape factors; both are based on the geometrical properties of hair cells. Various electrical quantities computed on the basis of shape factors are consistent with recent recordings from third turn inner and outer hair cells (Dallos et al. (1982): Science 218, 582-584). The model provides a plausible explanation for the experimentally observed discrepancy between inner and outer hair cell resting and receptor potentials. One potentially significant result of the analysis is the demonstration that since shape factors for outer hair cells are probably longitudinally graded, so must be all cellular electrical characteristics. Another interesting finding is that electrical interaction among neighboring hair cells is unlikely. A large-signal analysis of the circuit demonstrates that even in the absence of a non-linear input, the parametrically excited circuit itself generates pronounced distortion. The most significant consequence of this nonlinearity is a response asymmetry in which the depolarizing phase is greater than the hyperpolarizing one. Thus the circuit nonlinearity may, at least in part, account for the large positive d.c. response seen in both types of receptor cell (Dallos et al. (1982): Science 218, 582-584; Russell and Sellick (1978): J. Physiol. Lond. 284, 261-290).

Animals↗

PubMed2003

Localization of the P2Y4 receptor in the guinea pig organ of Corti.

Cochleae of guinea pigs were evaluated for the presence of the metabotropic receptor, P2Y4. Evidence is presented that P2Y4 protein is expressed in the guinea pig cochleae using Western blot analysis. A single protein band of 35 kDa was detected with P2Y4 receptor-specific antibody. The cellular distribution of P2Y4 purinoceptor protein was determined by immunohistochemistry of the whole organ of Corti. Immunoreactive staining for P2Y4 was seen in most cells of the organ of Corti. Staining of Hensen's cells and Deiters' cells, especially the outer Deiters' cells, was more intense than staining of the outer hair cells, inner hair cells, and pillar cells. Staining intensity was greatest at the basal turn and progressively decreased in the upper turns with the apex showing the weakest staining pattern. This is the first demonstration of a metabotropic P2Y receptor in the guinea pig organ of Corti.

Adenosine Triphosphate↗

PubMed1985

A technique for freeze-fracturing of the organ of Corti.

A modification of the conventional method of freeze-fracturing is described. By the use of polyvinyl-alcohol, a high viscous fluid, the organ of Corti is better stabilized in the specimen holder. This fluid also facilitates a clean fracture through the organ of Corti proper and in a high number of cases gives a large replica void of contaminating biological tissue and free of folds. Examples of results produced with this technique are demonstrated.

Freeze Fracturing↗

PubMed1999

Postnatal development of the organ of Corti in cats: a light microscopic morphometric study.

This study quantitatively characterizes the development of the major morphological features of the organ of Corti during the first 2 weeks postnatal, the period when the cat auditory system makes the transition from being essentially non-functional to having nearly adult-like responses. Four groups of kittens (n = 3) were studied at one day postnatal (P1), P5, P10, P15, and compared to adults. Measurements were made of the organ of Corti at 3 cochlear locations: 20%, 60% and 85% of basilar membrane length from the base cochlear locations which in the adult correspond to best frequencies of approximately 20 kHz, 2 kHz and 500 Hz, respectively. In addition, measurements of basilar membrane length and opening of the tunnel of Corti were made in 20 cochlear specimens from kittens aged P0-P6. Results indicate that: (i) at P0 the basilar membrane has attained adult length, and the tunnel of Corti is open over approximately the basal one-half of the cochlea; (ii) the initial opening of the tunnel of Corti occurs at a site about 4 mm from the cochlear base (best frequency of approximately 25 kHz in the adult cochlea); (iii) the thickness of the tympanic cell layer decreases markedly at the basal 20-kHz location; (iv) the areas of the tunnel of Corti and space of Nuel and the angulation of the inner hair cells (IHC) relative to the basilar membrane all show marked postnatal increases at both the middle and apical locations; (v) IHC are nearly adult-like in length and shape at birth, whereas the OHC (at 2-kHz and 500-Hz locations) undergo marked postnatal changes; (vi) disappearance of the marginal pillars and maturation of the supporting cells are not yet complete by P15.

Animals↗

PubMed2004

[Expression of substance P receptor positive cells in the Corti's organ with acute middle ear infection in guinea pigs].

OBJECTIVE: To investigate the expression of substance P receptor(SPR), SPR positive cells in the Corti's organ with acute middle ear infection in guinea pigs using the polyclonal antibody of SPR. METHODS: Twelve healthy guinea pigs were employed in the experiment. After general anesthesia, by injecting 1 x 10(8)/L staphylococcosis aureus into the middle cavity of right ear with the left ear serving as control, the acute middle ear infection model was established. Then three days later, immunohistochemical staining of SPR was performed in the Cochlear base membrane preparation. RESULTS: Microscopic examination of whole cochlear preparation revealed a number of SPR positive cells expression in the cochlear base membrane, these labeled cells usually did not exist in normal cochlear tissue. Obvious difference in morphology and distribution could be identified with inner hair cells, outer hair cells vascular endothelial cell and spiral ganglion neurons. Labeled SP receptor positive cells were similar to "neurons", scattering distributed in the free margin of cochlear base membrane, with larger size and multiple projections which was 6-12 times than the erythrocyte. There were the vesicle and granular substances in the cytoplasm of the labeled cells. CONCLUSIONS: Acute middle ear infection could induce the expression of SP receptor positive nonspecific cells in the Corti's organ of guinea pigs. These cells did not exist in the normal base membrane and might participate in initiating or inducing the immune response of inner ear.

Acute Disease↗

PubMed1996

Shape deformation of the organ of Corti associated with length changes of outer hair cell.

Cochlear outer hair cells (OHC) are commonly assumed to function as mechanical effectors as well as sensory receptors in the organ of Corti (OC) of the inner ear. OHC in vitro and in organ explants exhibit mechanical responses to electrical, chemical or mechanical stimulation which may represent an aspect of their effector process that is expected in vivo. A detailed description, however, of an OHC effector operation in situ is still missing. Specifically, little is known as to how OHC movements influence the geometry of the OC in situ. Previous work has demonstrated that the motility of isolated OHCs in response to electrical stimulation and to K(+)-gluconate is probably under voltage control and causes depolarisation (shortening) and hyperpolarization (elongation). This work was undertaken to investigate if the movements that were observed in isolated OHC, and which are induced by ionic stimulation, could change the geometry of the OC. A synchronized depolarization of OHC was induced in guinea pig cochleae by exposing the entire OC to artificial endolymph (K+). Subsequent morphometry of mid-modiolar sections from these cochleae revealed that the distance between the basilar membrane (BM) and the reticular lamina (RL) had decreased considerably. Furthermore, in the three upper turns OHC had significantly shortened in all rows. The results suggest that OHC can change their length in the organ of Corti (OC) thus deforming the geometry of the OC. The experiments reveal a tonic force generation within the OC that may change the position of RL and/or BM, contribute to damping, modulate the BM-RL-distance and control the operating points of RL and sensory hair bundles. Thus, the results suggest active self-adjustments of cochlear mechanics by slow OHC length changes. Such mechanical adjustments have recently been postulated to correspond to timing elements of animal communication, speech or music.

Animals↗

PubMed2006

[Electromechanical transduction: influence of the outer hair cells on the motion of the organ of Corti].

BACKGROUND: The somatic electromotility of the outer hair cells can be induced by an extracellular electrical field. This enables us to investigate the electromechanically induced motion of the organ of Corti. METHODS: The electrically induced motion of the guinea-pig organ of Corti was measured with a laser Doppler vibrometer in three cochlear turns at ten radial positions on the reticular lamina (RL) and six on each of the upper and lower surfaces of the tectorial membrane (TM). RESULTS AND CONCLUSIONS: We found a complex vibration pattern of the RL and TM, leading to a stimulus synchronous modulation of the depth of the subtectorial space in the region of the inner hair cells (IHCs). This modulation causes radial fluid motion inside the space up to at least 3 kHz. This motion is capable of deflecting the IHC stereocilia and provides an amplification mechanism additional to that associated with basilar-membrane motion.

Animals↗

PubMed2001

The mouse slalom mutant demonstrates a role for Jagged1 in neuroepithelial patterning in the organ of Corti.

The Notch signalling pathway has recently been implicated in the development and patterning of the sensory epithelium in the cochlea, the organ of Corti. As part of an ongoing large-scale mutagenesis programme to identify new deaf or vestibular mouse mutants, we have identified a novel mouse mutant, slalom, which shows abnormalities in the patterning of hair cells in the organ of Corti and missing ampullae, structures that house the sensory epithelia of the semicircular canals. We show that the slalom mutant carries a mutation in the Jagged1 gene, implicating a new ligand in the signalling processes that pattern the inner ear neuro-epithelium.

Animals↗

PubMedDate not supplied

The role of macrophages in the disposal of degeneration products within the organ of corti after acoustic overstimulation.

We analysed the ultrastructure of scavenger cells in the organ of Corti of 10 guinea pigs at five different intervals (5 min, 4 h, 24 h, 5 days and 28 days) after acoustic overstimulation. There was evidence of phagocytic cells only at 5 days after noise exposure. Dendritic macrophages were seen phagocytosing degenerating cells and debris in the tunnel of Corti and in the region of the outer hair cells. Transforming monocytes in this area and leukocytic accumulation within the spiral lamina vessel suggest that these cells may be derived from blood-borne monocytes. These cells may contribute to local disposal of intracochlear cell degeneration products and thus to healing of organ of hearing after induction of noise-induced damage.

Animals↗

PubMedDate not supplied

Intercellular junctions in the organ of Corti as revealed by freeze fracturing.

The junctions between the cells of the organ of Corti have been investigated with the freeze-fracture method in the chinchilla inner ear. Numerous gap junctions have been found among all the supporting cells, particularly at the level of their basal part. This means that the supporting cells have their cytoplasm electrotonically and metabolically coupled. Gap junctions were not observed between supporting and sensory cells nor between sensory cells and nerve endings. At this level the transmission should be chemically mediated.

Animals↗

PubMed2000

[Regenerative potential in the organ of Corti after otic intoxication].

The auditory sensory cells are sensitive to a variety of influences such as noise, ototoxic drugs and aging. In the cochlea of mammals, the destroyed sensory cells are not replaced by new sensory cells. That leads to cochlear deafness, a frequent disease in human. Unfortunately, such auditory impairment is out of reach of treatment. The development of new therapeutic strategies in this field requires a precise knowledge of the mechanisms involved in auditory sensory cells disappearance and in organ of Corti's degeneration. The aim of our study was to characterize cellular and molecular changes in the cochlea of rats which had been intoxicated with the ototoxic antibiotic amikacin. The animals were sacrificed at different survival times during and after the antibiotic treatment and their cochleas were investigated using transmission and scanning electron microscopy and using confocal microscopy after tissue labellings with different fluorescent probes. The results revealed the existence of three periods. The first one corresponds to the disappearance of the sensory cells which die by apoptosis. During the second period, the organ of Corti undergoes a scarring process; concomitantly, a contingent of nonsensory supporting cells attempts to transdifferentiate directly into sensory cells. This process however fails, and the supporting cells never reach the status of hair cells. A general process of dedifferentiation of all the epithelial cells of the organ of Corti followed by a massive apoptosis of numerous epithelial cells and of most ganglion cells occurs during the third period. After that, the organ of Corti is definitely reduced to a simple monolayered epithelium. On the basis of these data, experimental strategies aimed i) to protect the sensory cells against apoptosis and ii) to promote sensory cell regeneration are now under study. They might have important implications in human therapy.

Amikacin↗