Biomedical subjects

Y Raphael

Publications and source records attributed to Y Raphael.

12 recordsLinked to original sources

PubMed1992

Evidence for supporting cell mitosis in response to acoustic trauma in the avian inner ear.

Acoustic overstimulation can lead to sensory cell (hair cell) loss in the auditory epithelium. Damaged hair cells in the organ of Corti (the mammalian auditory end-organ) degenerate and are replaced by non-sensory cells (supporting cells) which construct an irreversible scar. In birds, however, auditory hair cells which are damaged by acoustic trauma or ototoxic drugs may be replaced by new hair cells. As first step in determining the mechanism of hair cell regeneration, we developed an assay for cell divisions in the auditory epithelium after acoustic trauma. The results of these experiments demonstrate that supporting cells in damaged regions of the auditory epithelium incorporate the DNA-specific marker bromodeoxyuridine as early as one day after noise exposure. We provide direct evidence that following acoustic insult to the avian inner ear, supporting cells which reside within the sensory epithelium divide near the luminal surface and repopulate the epithelium. These results suggest that supporting cells participate in scar formation during hair cell degeneration, and produce new cells for regeneration.

Animals↗

PubMed1992

Early microfilament reorganization in injured auditory epithelia.

Microfilaments (MFs) play an important role in wound healing and other regenerative events. The purpose of this study was to characterize changes in the distribution of MFs in traumatized auditory epithelia and compare these changes between avian (regenerating) and mammalian (nonregenerating) ears. Chicks and guinea pigs were acoustically overstimulated and their auditory epithelia analyzed fluorescence microscopy with phalloidin as a MF-specific marker. Immediately or several hours after overstimulation, we observed a substantial reduction of MFs in stereocilia and the cuticular plate. The circumferential belt of MF which is associated with the adherens junctional complex was constricted in damaged hair cells (HCs) as early as 1 day after the exposure. Concomitant with the junctional constriction, the apical surface area of supporting cells was increased relative to normal, whereas the surface area of HCs was decreased. We conclude the changes in the amount and distribution of MFs which characterize early responses to acoustic damage are similar in avian (regenerating) and mammalian (nonregenerating) auditory epithelia. We hypothesize that changes in MF-mediated tensile forces trigger the process of tissue repair in auditory epithelia in response to insult. In mammals the reorganization of MFs may help maintain the integrity of the reticular lamina and thereby prevent further damage. In contrast, early changes in MFs in chicks may play a role in regulating regenerative tissue responses.

Acoustic Stimulation↗

PubMed1991

The sensory epithelium and its innervation in the mole rat cochlea.

The mole rat (Spalax ehrenbergi) burrows throughout its life in subterranean tunnels. Several structural and functional features which adapt the mole rat to its habitat have been discerned. The goal of this study was to elucidate the structural basis for adaptation of the auditory end-organ to an environment where low-frequency acoustical signals prevail. For this purpose, cochleae of adult mole rats were studied with light and electron microscopy. Inner hair cells throughout the cochlea, and outer hair cells in the basal (high-frequency) portion of the cochlea, were similar in structure to those seen in other mammals. In contrast, outer hair cells in the apical (low-frequency) portion displayed unique structural features. These features resembled the structure of inner hair cells or immature outer hair cells. The innervation of outer hair cells was most uncommon, in that classical medial efferent innervation was not found throughout the cochlear spiral.

Animals↗

PubMed1991

Reorganization of cytoskeletal and junctional proteins during cochlear hair cell degeneration.

Experiments were carried out to elucidate changes in cytoskeletal elements and intercellular junctions in the organ of Corti, when hair cells degenerate and phalangeal scars form. Hair cell damage was induced by exposing guinea pigs to high intensity noise. The spatial and temporal changes in the organization of microfilaments, intermediate filaments, and tight junction-specific proteins were investigated using scanning and transmission electron microscopy and histochemistry. The results show that microfilaments, cytokeratins, adherens junctions, and tight junctions rearrange their distribution in damaged areas. From the temporal sequence of these changes it appears that phalangeal scars develop simultaneous with hair cell degeneration, and that the integrity of the luminal membranes in the organ of Corti is not interrupted. Each scar is formed by two supporting cells which expand and invade the sub-apical region of the dying hair cell. This region becomes cytokeratin-positive. The two supporting cells meet at the mid-line of the scar, where a new junctional complex is formed. The junctional complex consists of tight junction and adherens-type junction, but desmosomes are absent.

Actins↗

PubMed1991

Scar formation after drug-induced cochlear insult.

Structural and molecular changes in the guinea pig organ of Corti were studied using histochemistry and electron microscopy in the course of drug-induced hair cell degeneration. Actin filaments disappear from the cuticular plate and the stereocilia. An actin-rich bridge appears in the apical region of dying hair cells. Two supporting cells form a scar for a given hair cell. The supporting cells expand and invade the spaces of Nuel and then the region previously occupied by the hair cell. The scar region becomes cytokeratin-labeled. In this study, the apical domain of the hair cell is the last part of the cell to degenerate. Hair cell degeneration coincides temporally with scar formation. We define the resulting scar as a 'type I' scar. The results provide preliminary information about the molecular composition of the type I scar and suggest a structural basis for the dynamics of scar formation.

Actin Cytoskeleton↗

PubMed1991

Pure-tone overstimulation protects surviving avian hair cells from acoustic trauma.

It was found that intense pure-tones which damage hair cells in chicks, also result in damage to the tectorial membrane (TM). This study was designed to elucidate the effects of a second pure-tone insult on hair cells which survived a priming pure-tone exposure. Chicks were exposed to a pure-tone of 1.5 kHz at 124 dB SPL. Lesion was found in both TM and hair cells, but the area of damage to the TM was much larger than that to the hair cells. Following this exposure, chicks were exposed to a second intense pure-tone at 2.2 kHz 124 dB SPL. The frequency of the second exposure corresponded to a region where the TM did, but hair cells did not appear to be injured by the first exposure. The second exposure caused significantly less hair cell damage in chicks already exposed to the 1.5 kHz pure-tone than in controls which were not primed with the first exposure. This finding suggests that the first exposure provides a degree of protection for the surviving hair cells, perhaps by uncoupling them from the TM.

Acoustic Stimulation↗

PubMed1991

First appearance and development of motile properties in outer hair cells isolated from guinea-pig cochlea.

Cochleae from fetal guinea-pigs (37 to 64 gestation days, gd) were used to correlate the appearance of motile properties of isolated outer hair cells (OHCs) with the development of specific morphological features. Both the 'fast' electrically-driven and the 'slow' calcium-induced motilities appeared first in OHCs from basal turn of 52 gd fetuses. At 56 gd, most of basal and some apical OHCs responded positively to both types of stimulation. All tested cells were positive at 64 gd. It is noteworthy that this period closely corresponds to the onset and maturation of the gross cochlear potentials. Some structural changes in the organ of Corti may be correlated with the development of OHC motile properties: the acquisition of an adult-like cylindrical shape by the OHC, its lateral detachment from neighboring Deiters cells, and its surrounding by fluid spaces. At the ultrastructural level, the formation of a first layer of laminated cisternae regularly aligned along the OHC plasma membrane from the cuticular plate down to the nuclear level, temporally coincided with the onset of in vitro motility (52 gd). The following days, pillars and a sub-membrane lattice were clearly noticed between the outermost cisternal membrane and the plasma membrane. The results support the ideas that: motile properties observed in vitro reflect the in vivo active mechanisms, and that one single layer of laminated cisternae and its associated sub-plasma membrane material may be needed for OHC motility.

Animals↗

PubMed1991

Hereditary deafness occurring in cd/1 mice.

Different strains of mice provide a valuable research tool for studying both hereditary and acquired forms of deafness. The cd/1 strain has been found to demonstrate hereditary cochlear pathology. The characteristics of hearing loss in cd/1 mice have not previously been reported. In this investigation auditory thresholds were obtained by measuring evoked brain stem responses in subjects of three different ages: 3 weeks, 10 weeks and 6 months. The results were compared with thresholds obtained from CBA/Ca mice (which have normal hearing) and C57BL/6 mice (which are known to have a genetically determined pre-senile progressive cochlear hearing loss). A significant hearing loss was observed which progressed from high to low frequencies, and with age. Extensive degeneration was observed throughout the organ of Corti. cd/1 mice may provide a useful model for studying genetically determined deafness.

Age Factors↗

PubMed1988

The modulation of cell adhesion molecule expression and intercellular junction formation in the developing avian inner ear.

The cells that constitute the membranous labyrinth in the vertebrate inner ear are all derived from a single embryonic source, namely, the otocyst. The mature inner ear epithelia contain different regions with highly differentiated cells, displaying a highly specialized cytoarchitecture. The present study was designed to determine the presence of adherens-type intercellular junctions in this tissue and study the expression of cell adhesion molecules (CAMs) associated with these junctions, namely, A-CAM and L-CAM, in the developing avian inner ear epithelia. The results presented here show that throughout the early otocyst, A-CAM is coexpressed with L-CAM. The formation of asymmetries between sensory and nonsensory areas in the epithelium is accompanied by the modulation of CAMs expression and the assembly of intercellular junctional complexes. A-CAM and L-CAM display reciprocal expression patterns, the former being expressed mostly in the mosaic sensory epithelium, while L-CAM becomes conspicuous in the nonsensory areas but its expression in the sensory region is markedly reduced. Adherens-type junctions and numerous desmosomes are found in the junctional complexes of early otocyst cells. The former persist to maturity of the various inner ear epithelia, whereas desmosomes disappear from junctional complexes of hair cells but remain in the intercellular junctional complexes of all other cell types in the membranous labyrinth. Thus, adherens type intercellular junctions comprise the only defined cytoskeleton-bound junction in mature hair cells. A-CAM-positive cells are also found in the region of the acoustic ganglion in early developmental stages but not in the mature neural elements.

Actins↗

PubMed1987

Modulation of intermediate-filament expression in developing cochlear epithelium.

The present study was designed to characterize the expression and distribution of intermediate filaments (IFs) in the diverse cellular elements of inner-ear epithelium in guinea pig and man. Using immunofluorescence microscopy with a battery of IF-specific monoclonal antibodies, we show that the epithelium of the otocyst expresses cytokeratin (CK) polypeptides typical of simple epithelia. Cells in the early otic ganglion were also positively labelled for cytokeratins, suggesting that they are of otocystic epithelial origin. Cytokeratin distribution was largely homogeneous in the early cochlear duct as the epithelium differentiated, differences in the distribution of cytokeratin between the various cell types became detectable. Characteristically, cochlear hair cells became devoid of cytokeratin labelling, and remained unlabelled with antibodies specific for all other IF classes. The neural tissue of the inner ear was also devoid of cytokeratins and was typically positive for neurofilaments. Vimentin IFs were abundant in the mesenchymal tissues around the membranous labyrinth. Desmin and glial fibrillary acidic protein were not detectable in the cochlea. The apparent absence of all IFs from the cochlear hair cells in both guinea pig and man, as revealed by immunofluorescence and electron microscopy, and the possible significance of their absence for cochlear physiology, are discussed.

Animals↗

PubMed1986

Linkage of sub-membrane-cisterns with the cytoskeleton and the plasma membrane in cochlear outer hair cells.

The fine structure of the organ of Corti in the mole-rat (Spalax sp.) was studied. All outer hair cells possessed a single layer of membrane bound vesicles which lined the plasma membrane along the lateral aspect of the cell, except in the cuticular plate and in synapse areas. This organization of vesicles was not observed in inner hair cells. Most of the vesicles were laterally linked to the cell membrane by pairs of 25 nm long 'arms' while medially they were connected to microtubules. The three-dimensional organization and the possible role of the sub-membrane vesicles in the process of auditory transduction are discussed.

Animals↗

PubMedDate not supplied

Effect of glycerol on furosemide-caused EP decrease in guinea pig neonates.

Furosemide, a loop diuretic, reduces the endocochlear potential in guinea pigs. In our previous experiment using adult guinea pigs, glycerol was thought to open the blood-cochlea barrier and to help furosemide to reach its site of action in the stria vascularis. The present study was designed to determine whether or not the same potentiation by glycerol occurs in neonate guinea pigs. In one group, furosemide (10-30 mg/kg) was administered, while in another group, 50 v/v% glycerol (1 ml/kg) was administered 15 minutes prior to the injection of furosemide. Furosemide reduced the EP significantly more in neonates than in adults. This effect was not potentiated in the glycerol-pretreated group. From these findings, it seemed conceivable that the neonate blood-cochlea barrier still remains immature in some functions.

Animals↗