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At least 91 records · Page 5Linked to original sources
PubMed1993

Relationship of monoclonal antibody (KHRI 3 epitope) to cochlear supporting cell microvilli in the guinea pig.

As reported previously, monoclonal antibodies can be generated that bind against guinea pig cochlear structures. Preliminary immunohistochemical characterization revealed that one of these monoclonal antibodies (KHRI 3) most probably binds against a surface structure of guinea pig cochlear supporting cells. This study was undertaken to further characterize the KHRI 3 epitope in the cochlea. Since KHRI 3 immunolabeling appeared to be punctate and epitope expression was most pronounced in the reticular lamina, we hypothesized that KHRI 3 epitopes are related to microvilli. To prove this hypothesis immunoelectron microscopy was used. Also investigated was how epitope expression is altered in the reticular lamina microvilli following drug or noise-induced changes. When immunocytochemical results were compared to scanning electron microscopy findings, a striking correlation could be seen between changes in KRHI 3 immunolabeling and changes in the distribution of microvilli. These findings support the assumption that KHRI 3 epitopes are related to microvilli of inner ear supporting cells.

Animals↗
PubMed1981

The combination of scanning and transmission electron microscopy techniques in pathology of the organ of Corti in guinea pigs.

The pathology of the organ of Corti in guinea pigs is studied by means of SEM and TEM. It was the purpose of this study to examine the surface of an experimentally altered organ of Corti by means of SEM screening method). As it was our main interest to find out the localization of acoustic stimulation regarding the tonotopicity on the surface of the organ of Corti, we always examined the whole cochlear by means of SEM first. In acoustic experiments we used long-time pure-tone stimulation beyond the directly damaging sound pressure level, as well as white noise or shots for experimental damage of hair cells and supporting cells. Specimens of particular interest underwent a special procedure for a supplementary TEM examination. A prolonged and modified technique of embedding the specimens in Epon 812 permitted us to obtain supplementary data from TEM without major artifacts in the fine structure of the cells.

Acoustic Stimulation↗
PubMed2003

Hair cell regeneration: winging our way towards a sound future.

The discovery of hair cell regeneration in the inner ear of birds provides new optimism that there may be a treatment for hearing and balance disorders. In this review we describe the process of hair cell regeneration in birds; including restoration of function, recovery of perception and what is currently known about molecular events, such as growth factors and signalling systems. We examine some of the key recent findings in both birds and mammals.

Animals↗
PubMed2003

Expression of VASP and zyxin in cochlear pillar cells: indication for actin-based dynamics?

Vasodilator-stimulated phosphoprotein (VASP) is a member of the ENA/VASP-protein family. VASP is considered to be a crucial factor in the regulation of actin dynamics, which involves processes such as motility and cell adhesion, e.g. in filopodia or growth cones. In these processes zyxin acts as an important partner of VASP and is particularly concentrated at sites where VASP-dependent actin dynamics occur. Based on indirect evidence that actin-mediated dynamics may effect the mechanical properties of the cochlea, we have investigated expression of VASP and zyxin in the postnatal and adult rat cochlea using polymerase chain reaction and Western blot approaches, as well as immunohistochemistry and confocal microscopy. Besides an expected expression in vessels and fibroblasts, VASP and zyxin expression was also observed in pillar cells. Here, the staining was restricted to the head and foot plate of the pillar cells. Onset of VASP expression in pillar cells coincided with the beginning of hearing. In pillar cells, VASP and zyxin were co-localised with pan-actin, suggesting actin-based dynamics in these cochlear cells, which until now were rather presumed to form a highly rigid bridge between the inner and outer sensory cells. Thus, pillar cells may be more dynamically involved in controlling longer-lasting mechanical properties of the cochlea as hitherto presumed.

Actins↗
PubMed1992

Neural regeneration in the noise-damaged chinchilla cochlea.

Recent studies in the bird ear have shown that degenerated hair cells are sometimes replaced by regenerated receptor cells. The present study evaluated the adult mammalian cochlea for evidence of hair-cell and nerve-fiber regeneration. Eighty-eight noise-damaged chinchilla cochleas were examined as plastic-embedded whole mounts by phase-contrast and bright-field microscopy. No signs of hair-cell regeneration were found. However, 32 (70%) of 46 cochleas damaged by high-intensity noise and 20 (48%) of 42 cochleas damaged by moderate-intensity noise contained a variable number of nerve fibers which appeared to be regenerated. These fibers, which were located in severely damaged areas of organ of Corti, differed from residual fibers with respect to their diameters, the degree and pattern of myelination, and by the abnormal paths they followed within the osseous spiral lamina and on the basilar membrane. The number of regenerated fibers varied with type of exposure and length of recovery. The strongest response was found in ears exposed to a high-intensity, low-frequency noise. The results described here indicate that a potential exists for the biological restoration of the mammalian inner ear.

Animals↗
PubMed1998

Keratin filament deployment and cytoskeletal networking in a sensory epithelium that vibrates during hearing.

The intricate and spatially precise ways in which keratin intermediate filaments are deployed in certain cochlear epithelial cells, called supporting cells, suggests that these filaments make a micromechanically important contribution to the functional design of the guinea pig organ of Corti. Filament arrays that include keratins 8, 18, and 19 are confined mainly to regions close to the ends of large transcellular microtubule bundles in supporting cells. These cells and their microtubule bundles link sensory hair cells to a specialized basement membrane that vibrates during hearing. The keratin filament arrays apparently help anchor the ends of the microtubule bundles to cell surfaces. Filaments are concentrated at the apices and bases of most cells that contact hair cells. Substantial arrays of adherens junctions link the apices of these cells. Hence, keratin filaments may contribute to a cytoskeletal network that distributes mechanical forces from cell to cell and that coordinates the displacement of neighboring hair cells. However, high concentrations of keratin filaments have not been detected at the apices of one of the supporting cell types, which apparently has a mechanical role that is different from that of the others. Transmission electron microscopy has revealed previously undescribed filament networks at all the locations where the binding of antibodies to keratins is most marked. There is evidence that intercellular linkage of the keratin networks via their association with actin-containing meshworks and adherens junctions is more extensive than linkage provided by desmosomes.

Animals↗
PubMed2002

ATP-gated ion channels assembled from P2X2 receptor subunits in the mouse cochlea.

Extracellular ATP has several neuro-humoral actions on cochlear physiology, many of which involve P2X receptor-mediated signal transduction. The present study extends the molecular physiology of P2X receptor gene expression in the cochlea to the principal platform for transgenic studies, the mouse model. P2X receptor subunits, which assemble to form ATP-gated ion channels, were localised in cryosections and whole-mount tissues from the adult mouse cochlea using a specific antiserum and immunoperoxidase histochemistry. Whole-cell voltage clamp recordings functionally correlated immunolocalisation of ATP-gated ion channels in isolated hair cells and supporting cells. P2X immunoreactivity was widespread throughout the epithelial lining of the cochlea (except vascular stria); spiral ganglion neurons, organ of Corti supporting cells, and outer hair cell (OHC) stereocilia exhibited strong P2X immunolabelling. Localisation of ATP-gated ion channels on the endolymphatic surface (cuticular plates and stereocilia) of outer hair cells was confirmed electrophysiologically. In contrast, Deiters' cells exhibited an even distribution of both immunolabelling over the whole cell membrane and inward currents could be evoked by localised ATP application anywhere on these cells. In both OHC and Deiters' cells, the slowly-desensitising inward currents were blocked by the P2X-selective antagonist pyridoxal-phosphate-6-azophenyl-2',4'-disulphonic acid (PPADS), compatible with P2X subunits contributing to the ATP-gated ion channels. Our immunohistochemical and functional localisation of P2X receptors in the mouse cochlea extends previous studies to verify and characterise extracellular ATP signalling in the cochlea and extends support for P2X receptor-mediated regulation of endolymphatic ionic homeostasis, sound transduction, auditory neurotransmission and cochlear mechanics.

Adenosine Triphosphate↗
PubMed1983

Intercellular communication in the supporting cells of the organ of Corti.

We have directly tested the concept that the supporting cells of the organ of Corti are functionally coupled through gap junctions. In vitro and in vivo preparations were evaluated. Electrical measurements clearly show that the cells are coupled ionically. Voltage drops measured in neighboring cells in response to intracellular current injections indicate that current spread decays rapidly. Despite the existence of electrical coupling, fluorescent dye injection studies revealed no dye spread into adjacent cells, other than a few instances which were clearly artifactual. However, it is possible that dye spread is very slow and that dye in adjacent cells is diluted below visual detectability. In any case, dye coupling is remarkably poor compared to other electrically coupled tissues. The role of coupling in the supporting cells may be nutritive, considering the avascular nature of Corti's organ.

Animals↗
PubMed1993

[Morphological changes in the supporting cells of the utricular macula due to streptomycin intoxication].

Morphological changes in cultured utricular supporting cells following streptomycin sulfate (SM) intoxication were investigated using an organ culture system. Utricles of guinea pig were exposed to 30 and 3mg/ml of SM for 1-3 days in culture. The number of lysosomes in the supporting cells increased daily, and mitochondria, myeloid bodies, granules and vesicles were observed within the lysosomes. As these components accumulated in the lysosomes, the number of granules and vesicles in the cytoplasma decreased. Acid phosphatase (AcPase) activity also decreased. After 1-3 days culture with SM, the culture medium was changed to a medium without SM. After removal of SM, the Golgi apparati appeared more developed and AcPase activity was higher. At the same time, lysosomes were markedly decreased in number and the endoplasmic reticulum showed a gradual reproduction. These findings suggest close relationships among the Golgi apparatus, lysosomes, secretory granules and the endplasmic reticulum.

Acid Phosphatase↗
PubMed1990

Argon laser irradiation of the otolithic organ.

An argon laser was used to irradiate the otolithic organs of guinea pigs and cynomolgus monkeys. After stapedectomy, the argon laser (1.5 W x 0.5 sec/shot) irradiated the utricle or saccule without touching the sensory organs. The stapes was replaced over the oval window after irradiation. The animals used for acute observation were killed immediately for morphologic studies; those used for long-term observation were kept alive for 2, 4, or 10 weeks. Acute observation revealed that sensory and supporting cells were elevated from the basement membrane only in the irradiated area. No rupture of the membranous labyrinth was observed. Long-term observation revealed that the otolith of the macula utriculi had disappeared in 2-week specimens. The entire macula utricili had disappeared in 10-week specimens. No morphologic changes were observed in cochlea, semicircular canals, or membranous labyrinth. The saccule showed similar changes.

Acoustic Maculae↗
PubMed2004

Impaired permeability to Ins(1,4,5)P3 in a mutant connexin underlies recessive hereditary deafness.

Connexins are membrane proteins that assemble into gap-junction channels and are responsible for direct, electrical and metabolic coupling between connected cells. Here we describe an investigation of the properties of a recombinantly expressed recessive mutant of connexin 26 (Cx26), the V84L mutant, associated with deafness. Unlike other Cx26 mutations, V84L affects neither intracellular sorting nor electrical coupling, but specifically reduces permeability to the Ca(2+)-mobilizing messenger inositol 1,4,5-trisphosphate (Ins(1,4,5)P(3)). Both the permeability to Lucifer Yellow and the unitary channel conductance of V84L-mutant channels are indistinguishable from those of the wild-type Cx26. Injection of Ins(1,4,5)P(3) into supporting cells of the rat organ of Corti, which abundantly express Cx26, ensues in a regenerative wave of Ca(2+) throughout the tissue. Blocking the gap junction communication abolishes wave propagation. We propose that the V84L mutation reduces metabolic coupling mediated by Ins(1,4,5)P(3) to an extent sufficient to impair the propagation of Ca(2+) waves and the formation of a functional syncytium. Our data provide the first demonstration of a specific defect of metabolic coupling and offer a mechanistic explanation for the pathogenesis of an inherited human disease.

Animals↗
PubMed2002

Innervation of supporting cells in the guinea pig cochlea detected in bloc-surface preparations.

We immunohistochemically examined the distribution of nerve fibers among supporting cells of the cochlea by using the bloc-surface preparation. The existence of these nerve fibers was not very clear in the standard avidin-biotin complex (ABC) method. However, the standard ABC method complemented with silver intensification procedure provided very fine details of the nerve fibers. The nerves started to appear at low density about 55% of the distance from the apex, and their density gradually increased toward the upper turn. In each portion, the nerve fibers increased in thickness and length as well as the number of synapses made with the nuclei. Moreover, the distribution of these nerves in the fetal cochlea was similar to that in the adult. However, the functional significance and importance of these nerves remains to be determined. Our study also indicates that the silver intensification procedure combined with the standard ABC method is useful for the detailed observation of stereoscopic innervation in thick tissue preparations like such as the cochlea.

Animals↗
PubMed1984

A re-evaluation of cell coupling in the organ of Corti.

Intercellular electrical coupling was assessed in an in vitro organ of Corti preparation using separate electrodes to inject current and record voltage drops in Hensen's cells. The results demonstrate much better coupling among these supporting cells than previously thought. Coupling ratios between adjacent Hensen's cells are greater than 0.6.

Animals↗
PubMedDate not supplied

Regulation of p27Kip1 during gentamicin mediated hair cell death.

The INK4 and Kip/Cip families of Cyclin Dependent Kinase inhibitors (CKIs) are regulators of the cell cycle. In addition, CKIS including p27(Kip1) can protect cells from apoptosis in vitro. However, little is known about protective effect of p27(Kip1) in vivo. We used systemic treatment with aminoglycosides to induce hair-cell death in the basilar papilla (BP), the auditory organ of the avian inner ear, and characterised the expression of p27(Kip1) with confocal and immunofluorescence microscopy. In contrast to the adult mammalian cochlea where p27(Kip1) is expressed only in supporting cells, p27(Kip1) is found in the nuclei of both hair cells and supporting cells in the BP of the normal, mature bird. Forty-eight hours after gentamicin treatment, hair cells with TUNEL positive nuclei and hair cells with pyknotic nuclei were both detected, suggesting many hair cells die by apoptosis. When the BP was double labelled for p27(Kip1) and myosin VIIa, a hair-cell specific protein, all dying hair cells that had been ejected from the epithelium were found to be myosin VIIa positive but negative for p27(Kip1) even though nuclear remnants were still visible. In the transition zone where partial hair-cell loss occurs, freshly ejected hair cells lying immediately above the surface of the BP no longer expressed p27(Kip1). Damaged hair cells within the epithelium in the transition zone contained p27(Kip1) in their cytoplasm but not in their nuclei. These data support recent in vitro findings suggesting that p27(Kip1) protects cells from apoptosis and that its downregulation may be a general feature of programmed cell death.

Animals↗
PubMedDate not supplied

Intercellular fluid pathways in the organ of Corti of cat and man.

The intercellular junctions in the organ of Corti of cat and man were examined with the electron microscope. In contrast to the zone of tight junctions, or zonulae occludentes, which were present at the surface of cells lining the scala media, there was no tight junctional specialization among the cells of the tympanic lamina, perilymphatic lining cells of the scala vestibuli, basal processes of the supporting cells of the organ of Corti or cells of the spiral limbus and spiral ligament. These findings suggest the possibility of fluid continuity between the scala vestibuli and scala tympani all along the cochlear duct. Morphological evidence for an intercellular diffusion barrier was present only at the endolymphatic surfaces of the cochlear duct and between the processes of the basal cells of the stria vascularis in cat and man.

Animals↗
PubMed1997

Further evidence for supporting cell conversion in the damaged avian basilar papilla.

Two lines of evidence suggested that a process other than supporting cell divisions may give rise to new hair cells in the bird inner ear injured by either noise or ototoxic drugs. This process, supporting cell conversion, occurs when non-dividing supporting cells transdifferentiate into hair cells. First, noise-exposed chicks received zero, one or two daily i.p. injections of cytosine arabinoside (a DNA synthesis blocker), as well as two daily intraperitoneal injections of bromodeoxyuridine, for four days. Following sacrifice, the papillae were processed for bromodeoxyuridine immunocytochemistry. All the ears demonstrated dividing cells, but increasing the number of cytosine arabinoside injections decreased the number of labeled cells. Indeed, two cytosine arabinoside injections per day nearly completely blocked supporting cell divisions in the short hair cell region within the sound-induced lesion. This suggested that unpaired, immature cells observed in a similar region with scanning electron microscopy, despite the presence of cytosine arabinoside, may have been products of supporting cell conversion. In the second experiment, birds were treated with gentamicin for three days. Upon sacrifice at 6 days post-treatment, papillae were processed for light and transmission electron microscopy. Several unusual cells were observed with phenotypic features of both hair cells and supporting cells. The peculiar cells may be in a transition from the supporting cell phenotype to that of a hair cell.

Animals↗