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PubMed2004

Expression of Islet1 marks the sensory and neuronal lineages in the mammalian inner ear.

Several basic helix-loop-helix (bHLH) genes have been shown to be essential for the generation of the auditory sensory hair cells or the spiral ganglion (SG) neurons that innervate the hair cells in the cochlea, as well as a variety of cell types in the other nervous systems. However, it remains elusive what cellular context-dependent mechanisms confer the inner ear-specific neuronal or sensory competency/identities. We explored the possibility that one of the mechanisms responsible for generating cellular diversity in the nervous system through cooperative action of bHLH and LIM-homeodomain (LIM-HD) transcriptional factors might also contribute to the inner ear-specific sensory and/or neuronal competency. Here, we show that Islet1 (Isl1), a LIM-HD protein, is expressed early in the otocyst in the region that gives rise to both the auditory sensory organ, the organ of Corti, and SG neurons. Subsequently, the expression of Isl1 is maintained in SG neurons but is transitory in the sensory lineage. At embryonic day 12 (E12) in mice, the expression of Isl1 marks distinctively the ventral portion of the nascent cochlear epithelium encompassing the primordial organ of Corti. At E13, Isl1 is maintained at relatively high levels in the sensory primordium while down-regulated in the other regions of the cochlear duct. As the sensory epithelium starts to differentiate, it is down-regulated in the entire cochlear epithelium. The expression of Isl1 in the developing inner ear reveals an early and likely a common step in the development of both sensory and neuronal lineages of the inner ear, and suggests its potential role in the inner ear-specific sensory and neuronal cell development.

Animals↗
PubMed1993

Temporal bone histopathology 14 years after cytomegalic inclusion disease: a case study.

Temporal bones were examined from a 14-year-old male who died of sequelae of congenital cytomegalic inclusion disease (CID). Cytomegalovirus (CMV) was not isolated from inner ear fluid or multiple systemic tissues at the time of death. Examination of temporal bones revealed chronic pathology of both cochlear and vestibular sensory and nonsensory tissues. Endolymphatic hydrops was observed in the basal turn of the cochlear duct, while Reissner's membrane was collapsed in the more apical turns. Strial atrophy and a loss of cochlear hair cells were observed along the entire length of the basilar membrane. Vestibular neuroepithelial regions were degenerated and fibrosis was seen within the vestibular perilymphatic tissue spaces, suggesting prior labyrinthitis within the perilymph compartment in addition to the more typical pattern of endolabyrinthitis associated with human CMV infection. Distention of the saccular membrane was evident. In both cochlear and vestibular tissues, there were isolated regions of calcifications that appeared characteristic to that reported in other organ systems of individuals with CID. Collectively, these chronic, pathological findings in this case of CID demonstrate more extensive injury than has been identified in the previously reported acute temporal bone pathology of CID.

Cochlea↗
PubMed1995

Monoclonal antibody markers for early development of the stereociliary bundles of mammalian hair cells.

Two monoclonal antibodies, SC1 and SC2, were raised in vitro against antigens from the stereocilia of guinea-pig hair cells. They both labelled stereociliary antigens that were not detected in any other cell within the cochlear duct or the vestibular epithelial. SC1 cross-reacted with the tectorial membrane in the cochlea and labelled both cochlear and vestibular hair cells from both the mouse and the rat. In the mouse the SC1 antigen was labelled from embryonic days 16-18, coincident with the development of the stereociliary bundles. SC1 cross-reacted with neuromuscular junctions from striated muscle and with basal keratinocytes in skin. SC2 did not cross-react cleanly with hair cells from the mouse or the rat but it cross-reacted with proximal tubules of the guinea-pig kidney. Both antibodies can be used as cellular markers within the guinea-pig cochlea and SC1 should be particularly useful for studies of hair cell differentiation in the mouse.

Animals↗
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↗
PubMedDate not supplied

Effects of topical sodium potassium ATPase inhibitors upon endocochlear potential in chinchilla.

Sodium orthovanadate (vanadate) is a recently discovered inhibitor of the enzyme sodium potassium adenosine triphosphatase, which has properties similar to ouabain in peripheral tissues. The effects of topical application of vanadate and ouabain to the round window membrane of the chinchilla were studied using endocochlear potential (EP) and action potential as measures of cochlear function. The EP demonstrated an initial elevation followed by a secondary decline after topical application of 2 mmol vanadate to the round window membrane. During the EP elevation, the resistance was unchanged, but the action potential response declined, with a greater effect on responses to 8-kHz tone bursts than to 2-kHz tone bursts. Thus, it does not appear that the initial increase of endocochlear potential that was observed was due to a change in the resistance of the cochlear duct; rather, some other mechanism must be involved. The round window topical application of potentially ototoxic drugs accompanied by cochlear function monitoring appears to be a useful method for testing drugs with marked systemic effects such as ouabain or vanadate and is simpler to perform than perilymphatic or vascular perfusion.

Administration, Topical↗
PubMed1988

Appearance and distribution of neuron-specific enolase and calbindin (CaBP 28 kDa) in the developing human inner ear.

The onset and development of neuron-specific enolase (NSE) and calbindin immunoreactivities were studied in the inner ear of human fetuses aged from 6-7 to 14 weeks of gestation. NSE occurred very early in ganglion neurons. Its appearance in vestibular sensory cells at 8 weeks coincided with the formation of the first afferent synapses, and showed an apex/base gradient in the cristae. Calbindin was found in vestibular ganglion neurons at 6-7 weeks and in the cochlear ganglion neurons at 8-9 weeks. Vestibular sensory cells and the whole ventral wall of the cochlear duct were stained from 8-9 weeks. At 14 weeks, calbindin staining occurred only in the sensory cells of the cochlear neuroepithelium. Non-neuronal secretory structures, i.e. Kölliker's organ and some cells of the transitional zone of the utricle, were also reactive. Staining appeared in Kölliker's organ with a base to apex gradient and disappeared from it with an internal to external gradient. Calbindin appeared in vestibular sensory cells later than NSE staining, synapse formation and sensory hair bundle differentiation. By contrast in the cochlea, calbindin staining appeared in the neuroepithelium before sensory cell differentiation, but remained only in the hair cells after they had differentiated and been contacted by the afferent fibers.

Antibodies↗
PubMedDate not supplied

Fistulae in the membranous labyrinth.

Fistulization at various parts of the membranous labyrinth has been currently in use as one of the treatments for the symptoms of Meniere's disease. The present report concerns our experience with membranous fistulae in experimental animal ears with and without manifestation of endolymphatic hydrops. The materials presented are mostly new; however, our previous data are also incorporated in order to bring this issue into better perspective. The first part describes the nonproduction aspect of endolymphatic hydrops in the rat, chinchilla, and squirrel monkey after obliteration of the endolymphatic duct in relation to the occurrence of spontaneous fistulae. The second part describes surgical fistulization of the vestibular membranous labyrinth and cochlear duct in order to prevent or control development of endolymphatic hydrops in the guinea pig, the species in which hydrops can be produced consistently. These results are tabulated and analyzed in terms of the pathological consequences that can be expected in performing fistulization of the membranous labyrinths in animals as well as in humans.

Animals↗
PubMed1989

Spiral ganglion cell density in young and old gerbils.

The Mongolian gerbil, like other mammalian species, has a decreased number of spiral ganglion cells as a function of age. This loss of cells was first seen in 24- to 30-month old animals in the basal end of the ganglion. In the oldest individuals the apical end of the ganglion was also affected. There were approximately 15-25% fewer cells in the affected areas in the 36- to 42-month old animals. In the oldest animals degeneration of the stria vascularis was seen in the apical turn and some degenerative changes in the organ of Corti were seen throughout the length of the cochlear duct. The aging pattern in the gerbil cochlea, is similar to that described for other species. Vacuoles, previously described in the gerbil cochlear nucleus, were also seen in the auditory nerve within the modiolus, but central to the Schwann-glial border in all animals. Vacuoles were not present within the spiral ganglion or the peripheral processes of the ganglion cells. Because the ganglion cell axons should be similar on either side of the Schwann-glial border, but the vacuoles were confined to the central nervous system, it is concluded that the degenerative process affects glial cells as opposed to neurons.

Aging↗
PubMed1993

Reduced Na(+)-K(+)-ATPase activities in the cochleae of guinea pigs with experimental endolymphatic hydrops.

Normal auditory function depends on the maintenance of the unique ion composition in the endolymph. The Na(+)-K(+)-ATPase in the lateral wall of the cochlear duct has been suggested to play an important role in maintaining the endolymphatic ion concentration and in generating a positive endocochlear potential. Cochlear dysfunction may indicate changes in the biochemical components and osmotic pressure of the inner ear fluids as well as inadequate generation of intracellular metabolic energy. Dysfunction of the stria vascularis and spiral prominence was investigated in the early stages of endolymphatic hydrops. Vibratome sections of hydropic and normal cochleae were stained histochemically for Na(+)-K(+)-ATPase activity in this study. Decreased activity of this enzyme was shown in the stria vascularis and spiral prominence of the hydropic cochlea in the early stage of endolymphatic hydrops. The results coincide with those of studies of electrophysiologic changes in cochlear function in hydropic animals by others. The results of the present study provide further information concerning a possible deficit in ion transport activity and decreased enzymatic activity in the cochlea.

Animals↗
PubMed1995

MR imaging of intralabyrinthine schwannoma, labyrinthitis, and other labyrinthine pathology.

This article reviews recent imaging developments in various diseases of the membranous labyrinth. Membranous labyrinth is the initial receptor for acoustic stimuli. Exciting progress has been made in the imaging evaluation of the normal and diseased labyrinth. Structures of the membranous labyrinth, such as the cochlea, vestibule, semicircular canals, and endolymphatic duct and sac can be visualized on routine MR scans. Using high-resolution MR imaging techniques, researches have been able to visualize the cochlear duct, scala tympani, scala vestibuli, and even the otolithic mass. The sensitivity of gadolinium-enhanced MR imaging is such that labyrinthitis or other labyrinthine pathology, including small intralabyrinthine schwannomas, can be diagnosed on routine MR study.

Ear Neoplasms↗
PubMed2006

Inhibitors of differentiation and DNA binding (Ids) regulate Math1 and hair cell formation during the development of the organ of Corti.

The basic helix-loop-helix (bHLH) transcription factor Math1 (also called Atoh1) is both necessary and sufficient for hair cell development in the mammalian cochlea (Bermingham et al., 1999; Zheng and Gao, 2000). Previous studies have demonstrated that a dynamic pattern of Math1 expression plays a key role in regulating the number and position of mechanosensory hair cells. However, the factors that regulate the temporal and spatial expression of Math1 within the cochlea are unknown. The bHLH-related inhibitors of differentiation and DNA binding (Id) proteins are known to negatively regulate many bHLH transcription factors, including Math1, in a number of different systems. Therefore, Id proteins are good candidates for regulating Math1 in the cochlea. Results from PCR and in situ hybridization indicate that Id1, Id2, and Id3 are expressed within the cochlear duct in a pattern that is consistent with a role in regulation of hair cell development. In particular, expression of Ids and Math1 overlapped in cochlear progenitor cells before cellular differentiation, but a specific downregulation of Id expression was observed in individual cells that differentiated as hair cells. In addition, progenitor cells in which the expression of Ids was maintained during the time period for hair cell differentiation were inhibited from developing as hair cells. These results indicate a key role for Ids in the regulation of expression of Math1 and hair cell differentiation in the developing cochlea.

Animals↗
PubMed1990

[Experimental endolymphatic hydrops and its related morphological and functional changes in guinea pigs].

The endolymphatic hydrops was induced successfully in 13 guinea pigs by blocking the endolymphatic duct and sac, and the morphological and functional alterations (especially on semicircular canal function) after hydrops were studied by means of ENG, EcochG and serial section techniques. Hydrops in the cochlear duct was evident in the apical and/or near apical turns, especially in earlier stages. Dilation of the saccule was seen in all samples, but was barely noticeable in the utricle and semicircular canal's endolymphatic space. Degeneration in the corti's apparatus, stria vasculi and spiral ganglion occurred late. No evident changes of the sensory components in the saccule, utricle and semicircular canals were seen under the light microscope. The hearing loss in earlier stages of hydrops was evident at lower frequencies: later stages showed effects at all frequencies. The cochlear recruitment and fluctuation phenomena were observed in a few of the operated animals. The value of -SP/CAP in a few animals was significantly after operation. The functional changes of semicircular canals were demonstrated by the semicircular paralysis (CP), directional preponderance (DP), vestibular recruitment (VR) and elevated threshold of nystagmus to angular acceleration stimuli. There was no significant correlation between the degrees of hearing loss and impaired semicircular function. The criteria of ENG elicited by the quantitative angular acceleration stimuli for evaluating the semicircular canal function in guinea pigs is proposed for the first time in our experiment.

Animals↗
PubMed2001

[Pendred's syndrome. Current features].

Introduction Pendred's syndrome is a recessive autosomal disease, traditionally defined as the association of deaf-mutism, goiter and dysfunctional iodide organization revealed by the perchlorate discharge test. It represents 4 to 10% of the causes of congenital hypoacusis. Although described more than a 100 years ago, the association of thyroid and cochleo-vestibular damage remained unclear for many years. Genetic abnormalities Progress in molecular biology has revealed that the disease is related to alterations in the PDS gene situated on chromosome 7. The PDS gene is responsible for the production of pendrine, protein involved in anion (l-, Cl-) transportation, notably in the apical pole of the thyreocyte and the cochlear duct, where the endolympha is produced. Practical implications The truncation of pendrine related to the genetic alterations be responsible for the morpho-functional alterations in the cochlear apparatus and the thyroid. In this perspective, Pendred's syndrome would appear as a genetic disorder in anion transportation.

Carrier Proteins↗
PubMed1980

Saccule otoconia displacement into cochlea in cochleosaccular degeneration.

Eight human temporal bones from five patients demonstrated varying degrees of cochleosaccular degeneration. Otoconial debris, with tissue reaction, was demonstrated within the ductus reuniens and cochlear duct, as far distal as the middle of the ascending basal limb. Saccule degeneration could be the primary lesion in cochleosaccular degeneration related to heredity or aging, with cochlear changes secondary to the presence of displaced otoconia. In cochleosaccular degeneration of viral cause, if saccule otoconial displacement occurs, it may possibly produce additional damage in a cochlea involved by viral infection. Cochlear damage might be related to the severity of otoconial displacement and/or to impaired clearing mechanisms of the cochlea. Retrograde cochlear hydrops, secondary to collapse of the saccule, occurs first in the cecum vestibulare and may extend distally.

Adult↗
PubMed2005

Effects of coiling on the micromechanics of the mammalian cochlea.

The cochlea transduces sound-induced vibrations in the inner ear into electrical signals in the auditory nerve via complex fluid-structure interactions. The mammalian cochlea is a spiral-shaped organ, which is often uncoiled for cochlear modelling. In those few studies where coiling has been considered, the cochlear partition was often reduced to the basilar membrane only. Here, we extend our recently developed hybrid analytical/numerical micromechanics model to include curvature effects, which were previously ignored. We also use a realistic cross-section geometry, including the tectorial membrane and cellular structures of the organ of Corti, to model the apical and basal regions of a guinea-pig cochlea. We formulate the governing equations of the fluid and solid domains in a curvilinear coordinate system. The WKB perturbation method is used to treat the propagation of travelling waves along the coiled cochlear duct, and the O(1) system of the governing equations is solved in the transverse plane using finite-element analysis. We find that the curvature of the cochlear geometry has an important functional significance; at the apex, it greatly increases the shear gain of the cochlear partition, which is a measure of the bending efficiency of the outer hair cell stereocilia.

Animals↗
PubMed1988

Otic pathology of caprine beta-mannosidosis.

Caprine beta-mannosidosis is an autosomal recessive defect of glycoprotein catabolism with a deficiency of tissue and plasma beta-mannosidase activity and tissue accumulation of oligosaccharides within lysosomes. This rapidly fatal genetic disorder of Nubian goats is expressed at birth by a variety of clinical signs including deafness. Affected goats had folded pinnas, and the tympanic cavity was decreased due to multiple, polypoid projections of bone covered by middle ear mucosa which obstructed the view of the cochlear promontory. Numerous cells of the cochlear duct including mesothelial and epithelial cells of Reissner's membrane, mesothelial cells lining the scala tympani, cells of the stria vascularis, numerous supportive cells of the organ of Corti, cochlear hair cells, endothelial cells, perithelial cells, fibroblasts, macrophages, and neurons of the spiral ganglion contained numerous nonstaining intracytoplasmic vacuoles which resulted in distention of affected cells and caused thickening of involved structures. Ultrastructurally, the vacuoles were membrane-bound and consistent with lysosomes. Vacuolated cells were desquamated into the scala vestibuli and scala tympani. This is one of few reports describing light and electron microscopic otic alterations of a storage disease. Goats with beta-mannosidosis appear to be good models of hearing loss in patients with storage disease.

Animals↗
PubMed1978

Remote masking in presbycusis.

Remote Masking (RM) (a rise in threshold for low-frequency tones when the ear is exposed to a high intensity noise band of high frequency) has been attributed to mechanical nonlinear distortion of the cochlear partition, as an effect of the envelope of a nonuniform signal. Clinical studies using RM have revealed RM is normal only when both the endolabyrinthine pressure and the cochlear hydrodynamics are normal. Increasing the stiffness of the cochlear partition affects adversely the mechanism of motion of the cochlear duct and reduces RM values. We studied RM in normal young Ss and in patients with presbycusis in order to determine whether aging of the inner ear also induces stiffness of the cochlear partition. In presbycusic Ss the RM values were indeed reduced symmetrically in both ears and progressively as a result of aging. Thus RM demonstrates the existence of cochlear conductive presbycusis and can be considered a useful test of stiffness of the cochlear partition.

Adolescent↗
PubMed2002

Dynamics of noise-induced cellular injury and repair in the mouse cochlea.

To assess the dynamics of noise-induced tissue injury and repair, groups of CBA/CaJ mice were exposed to an octave-band noise for 2 hours at levels of 94, 100, 106, 112, or 116 dB SPL and evaluated at survival times of 0, 12, 24 hours or 1, 2, or 8 weeks. Functional change, assessed via auditory brainstem response (ABR), ranged from a reversible threshold shift (at 94 dB) to a profound permanent loss (at 116 dB). Light microscopic histopathology was assessed in serial thick plastic sections and involved quantitative evaluation of most major cell types within the cochlear duct, including hair cells (and their stereocilia), supporting cells, ganglion cells, spiral ligament fibrocytes, spiral limbus fibrocytes, and the stria vascularis. Morphometry allowed patterns of damage to be systematically assessed as functions of (1) cochlear location, (2) exposure level, and (3) postexposure survival. Insights into mechanisms of acute and chronic noise-induced cellular damage are discussed.

Acute Disease↗