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Results for “Tectorial Membrane”

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PubMed1993

[Immunohistochemical study of proteoglycans and collagens in the mouse cochlear duct].

Immunohistochemical studies of proteoglycans and collagens (type I and type IV) in the cochlear duct, and of the effects of cisplatin (CDDP), were performed. In cells of the organ of Corti and in the middle layer of the stria vascularis, heparan sulfate proteoglycan (HSPG) and collagens (type I and IV) or collagen-like substances were found. HSPG in these locations appeared to play important roles in the production of auditory sense. The tectorial membrane contained HSPG and collagens (type I and IV). However, no data supporting the concept that elements of the tectorial membrane are derived from interdental cells was obtained. In the basilar membrane, no HSPG, chondroitin sulfate (Chs), or collagens (type I and IV) were detected. The unique structures containing these substances reacted strongly with anti-HS (heparan sulfate), anti-HSPG-CP (core protein) and anti-collagen (type I and IV) antibodies that developed in the middle layer of the stria vascularis after the administration of CDDP. However, no change was observed in the tectorial membrane, the spiral prominence, the basilar membrane, or the spiral limbus. The decrease in HSPG in cells of the organ of Corti, and the changes in the stria vascularis, may help solve the well known contradiction between the severity of morphological damage and of the hardness of hearing.

Animals↗

PubMed1998

Evidence for a medial K+ recycling pathway from inner hair cells.

K+ effluxed from outer hair cells and their nerves is thought to flow laterally to strial marginal cells for recycling into scala media. Observations reported here provide evidence that K+ effluxed from inner hair cells and inner radial nerves travels medially through border cells, inner sulcus cells (ISCs), limbal fibrocytes and interdental cells (IDCs) for return to endolymph. Morphologic features of ISCs in the medial route resembled those of Hensen and Claudius cells in the lateral indicating an ion transport role for ISCs like that of Hensen and Claudius cells. Na,K-ATPase in plasmalemma of IDCs testified to their capacity to resorb and transport K+ through their known gap junctions. IDCs were differentiated into three subgroups. The most lateral IDCs formed short and long columns. Long columns contacted the medialmost ISC inferiorly and the undersurface of the tectorial membrane superiorly providing thereby a potential transcellular route for K+ transit from ISCs to endolymph. Short columns faced inner sulcus below and tectorial membrane above and accordingly possessed cells with opposite polarity at the bottom and top of the column. Short columns thus appeared situated to resorb electrolytes from limbal stroma for release into inner sulcus and beneath tectorial membrane at opposite ends of the column. The central IDCs were positioned for resorbing and transporting K+ effluxing from the Na,K-ATPase-rich stellate fibrocytes which spread toward the IDCs from near the inner sulcus. The most medial IDCs lined cuplike invaginations near the attachment of Reissner's membrane and lay apposed to light fibrocytes located between supralimbal fibrocytes and the medial IDCs. Content of Na,K-ATPase and position in the K+ transport route likened the limbal stellate fibrocytes to the spiral ligament type II fibrocytes and supralimbal fibrocytes to suprastrial fibrocytes in the lateral wall. From content of creatine kinase and position in the transport path, limbal light fibrocytes appeared analogous to spiral ligament type I fibrocytes. The additional finding that limbal fibrocytes showed unchanged or upregulated Na,K-ATPase immunoreactivity in aged gerbils with strial atrophy provided further evidence for an independent medial transport route and for the survival of inner hair cells in presbyacusis.

Aging↗

PubMed2005

Type IX collagen knock-out mouse shows progressive hearing loss.

Type IX collagen is one of the important components, together with type II, V, and XI collagens, in the tectorial membrane of the organ of Corti. To confirm the significance of type IX collagen for normal hearing, we assessed the detailed morphological and electrophysiological features of type IX collagen knock-out mice, which have recently been reported as a deafness model. Through assessment by auditory brainstem response (ABR), knock-out mice were shown to have progressive hearing loss. At the light microscopic level, the tectorial membrane of knock-out mice was found to be abnormal in shape. These morphological changes started in the basal turn and were progressive toward the apical turn. Electron microscopy confirmed disturbance of organization of the collagen fibrils. These results suggest that mutations in type IX collagen genes may lead to abnormal integrity of collagen fibers in the tectorial membrane.

Acoustic Stimulation↗

PubMed1997

Otogelin: a glycoprotein specific to the acellular membranes of the inner ear.

Efforts to identify the specific components of the mammalian inner ear have been hampered by the small number of neuroepithelial cells and the variety of supporting cells. To circumvent these difficulties, we used a PCR-based subtractive method on cDNA from 2-day-old mouse cochlea. A cDNA encoding a predicted 2910-amino acid protein related to mucin has been isolated. Several lines of evidence indicate, however, that this protein does not undergo the O-glycosylation characteristic to mucins. As confirmed by immunocytochemistry and biochemical experiments, this protein is specific to the inner ear. Immunohistofluorescence labeling showed that this protein is a component of all the acellular membranes of the inner ear: i.e., the tectorial membrane of the cochlea, the otoconial and accessory membranes of the utricule and saccule, the cupula of the semicircular canals, and a previously undescribed acellular material covering the otoconia of the saccule. The protein has been named otogelin with reference to its localization. A variety of nonsensory cells located underneath these membranes could be identified as synthesizing otogelin. Finally, this study revealed a maturation process of the tectorial membrane, as evidenced by the progressive organization of otogelin labeling into thick and spaced radial fiber-like structures.

Amino Acid Sequence↗

PubMed1998

Mutations in the human alpha-tectorin gene cause autosomal dominant non-syndromic hearing impairment.

The tectorial membrane is an extracellular matrix of the inner ear that contacts the stereocilia bundles of specialized sensory hair cells. Sound induces movement of these hair cells relative to the tectorial membrane, deflects the stereocilia, and leads to fluctuations in hair-cell membrane potential, transducing sound into electrical signals. Alpha-tectorin is one of the major non-collagenous components of the tectorial membrane. Recently, the gene encoding mouse alpha-tectorin (Tecta) was mapped to a region of mouse chromosome 9, which shows evolutionary conservation with human chromosome 11q (ref. 3), where linkage was found in two families, one Belgian (DFNA12; ref. 4) and the other, Austrian (DFNA8; unpublished data), with autosomal dominant non-syndromic hearing impairment. We determined the complete sequence and the intron-exon structure of the human TECTA gene. In both families, mutation analysis revealed missense mutations which replace conserved amino-acid residues within the zona pellucida domain of TECTA. These findings indicate that mutations in TECTA are responsible for hearing impairment in these families, and implicate a new type of protein in the pathogenesis of hearing impairment.

Alternative Splicing↗

PubMed2005

Development and properties of stereociliary link types in hair cells of the mouse cochlea.

The hair bundles of outer hair cells in the mature mouse cochlea possess three distinct cell-surface specializations: tip links, horizontal top connectors, and tectorial membrane attachment crowns. Electron microscopy was used to study the appearance and maturation of these link types and examine additional structures transiently associated with the developing hair bundle. At embryonic day 17.5 (E17.5), the stereocilia are interconnected by fine lateral links and have punctate elements distributed over their surface. Oblique tip links are also seen at this stage. By postnatal day 2 (P2), outer hair cell bundles have a dense cell coat, but have lost many of the lateral links seen at E17.5. At P2, ankle links appear around the base of the bundle and tectorial membrane attachment crowns are seen at the stereociliary tips. Ankle links become less apparent by P9 and are completely lost by P12. The appearance of horizontal top connectors, which persist into adulthood, occurs concomitant with this loss of ankle links. Treatment with the calcium chelator BAPTA or the protease subtilisin enabled these links to be further distinguished. Ankle links are susceptible to both treatments, tip links are only sensitive to BAPTA, and tectorial membrane attachment crowns are removed by subtilisin but not BAPTA. The cell-coat material is partially sensitive to subtilisin alone, while horizontal top connectors resist both treatments. These results indicate there is a rich, rapidly changing array of different links covering the developing hair bundle that becomes progressively refined to generate the mature complement by P19.

Animals↗

PubMed1997

The development of the reticular lamina in the hamster: an examination of transitory features and their functional roles.

This study examines the development of the reticular lamina in the Syrian golden hamster postriatally from birth to adulthood at 2 day intervals using the scanning electron microscope. During this period, numerous transitory features emerged whose roles were concerned primarily with the development of the tectorial membrane (TM). The principal findings were as follows. (1) The surface of the developing organ of Corti produced all the fibrous material composing the minor tectorial membrane (mTM) including radial and longitudinal fiber bundles which formed the skeleton of the TM, and spongy, amorphous material which formed its intervening ground substance. (2) Throughout most of the cochlear spiral, radial fiber bundles were seen extending from the microvilli of supporting cells and projecting toward the major tectorial membrane (MTM). In most of the basal turn, but not in the apical turn, these radial bundles were interwoven with longitudinal fiber bundles which emerged from the surface of Hensen's cells. These findings indicate that the architecture of the TM is more complex in the basal turn than in the apex. (3) Increases in the dimensions of the reticular lamina resulted from the emergence of pillar cell headplates and growth in the diameter of hair cells and supporting cells. The emergence of pillar cell headplates was the principal factor contributing to increases in the radial dimension of the reticular lamina. This emergence was most dramatic between 10 and 12 days after birth (DAB) after the mTM completed its growth. Since the mTM appears to be bound medially to the MTM and laterally to the marginal pillars by 10 DAB, it seems likely that the growth of the reticular lamina after 10 DAB causes some stretching of the mTM both radially and longitudinally. (4) Completion of outer hair cell stereocilia growth at 8 DAB was followed by loss of supporting cell attachments of the TM (trabeculae) by 10 DAB, and coincided with the formation of marginal pillars from the third row of supporting cells. It is suggested that the formation of marginal pillars may be required for coupling of the TM to the tips of outer hair cell stereocilia and for induction of radial tension of the mTM. (5) Removal of the marginal pillar attachments occurred following completion of hair cell growth. (6) All structures on the reticular lamina appeared to have adult-like characteristics by 20 DAB.

Animals↗

PubMed1983

Morphological basis for tonotopy in the anuran amphibian papilla.

The amphibian papilla of the more-recently derived frogs and toads is similar to the mammalian cochlea in at least three ways: 1. Its sensory surface is a slender, curved structure. 2. It exhibits tonotopy, with the highest-frequency sensitivity located at the end apparently closest to the source of acoustical excitation. 3. Its single-axon tuning curves exhibit extremely steep high-frequency slopes and gentle low-frequency slopes, consistent with selection by a distributed-parameter, low-pass filter with cutoff frequency that decreases as one moves farther from the source of acoustical excitation. The filter operation in the cochlea is centered around the basilar membrane, a structure whose profound taper is largely responsible for the decreasing cutoff frequency. Although the amphibian papilla lacks a basilar membrane, it does possess a conspicuously tapered tectorial membrane, which might serve a similar function. In this paper, after reviewing briefly an old and simple model of the cochlear filter and the morphology of the amphibian papilla and its tectorial membrane, we are unable to reconcile the structure of the latter with the topological requirements for realization of a filter analogous to the former. In fact, we are unable to deduce the principles of frequency selectivity in the frog auditory endorgan.

Acoustic Stimulation↗

PubMed1999

Micromechanical responses to tones in the auditory fovea of the greater mustached bat's cochlea.

An extended region of the greater mustached bat's cochlea, the sparsely innervated (SI) zone, is located just basally to the frequency place of the dominant 61-kHz component of the echolocation signal (CF2). Anatomic adaptations in the SI zone are thought to provide the basis for cochlear resonance to the CF2 echoes and for the extremely sharp tuning throughout the auditory system that allows these bats to detect Doppler shifts in the echoes caused by insect wing beat. We measured basilar membrane (BM) displacements in the SI zone with a laser interferometer and recorded acoustic distortion products at the ear drum at frequencies represented in the SI zone. The basilar membrane in the SI region was tuned both to its characteristic frequency (62-72 kHz) and to the resonance frequency (61-62 kHz). With increasing stimulus levels, the displacement growth functions are compressive curves with initial slopes close to unity, and their properties are consistent with the mammalian cochlear amplifier working at high sound frequencies. The sharp basilar membrane resonance is associated with a phase lag of 180 degrees and with a shift of the peak resonance to lower frequencies for high stimulus levels. Within the range of the resonance, the distortion product otoacoustic emissions, which have been attributed to the resonance of the tectorial membrane in the SI region, are associated with an abrupt phase change of 360 degrees. It is proposed that a standing wave resonance of the tectorial membrane drives the BM in the SI region and that the outer hair cells enhance, fine tune, and control the resonance. In the SI region, cochlear micromechanics appear to be able to work in two different modes: a conventional traveling wave leads to shear displacement between basilar and tectorial membrane and to neuronal excitation for 62-70 kHz. In addition, the SI region responds to 61-62 kHz with a resonance based on standing waves and thus preprocesses signals which are represented more apically in the CF2 region of the cochlea.

Acoustic Stimulation↗

PubMed1987

Auditory stereocilia in the alligator lizard.

The normal anatomy of stereociliary tufts in the basilar papilla of the alligator lizard is described and demonstrated with scanning electron micrographs. Stereociliary tufts in the tectorial region differ from those in the free-standing region in several ways. Tectorial stereociliary tufts are short (less than 10 micron in height), unidirectional in orientation, and covered with a tectorial membrane. Free-standing stereociliary tufts are very tall (up to 38 micron in height), bidirectional in orientation and not covered by a tectorial membrane or any other tectorial substance. The heights of the stereociliary tufts along the length and across the width of the basilar papilla were measured in serial light and transmission electron micrographs. Free-standing stereociliary tufts decrease progressively in height along the length of the basilar membrane, being tallest at the apical end and shortest at the basal end. Tectorial stereociliary tufts do not increase progressively along the length of the basilar membrane but do increase progressively across the width of the basilar membrane, being shortest on the neural side. Free-standing stereociliary tufts are structurally simple being a prominent specialization of the lizard cochlea. Tectorial stereociliary tufts are structurally more complicated conforming more closely to the general anatomical pattern of vertebrate auditory hair cells.

Animals↗

PubMed1990

Two different secretion mechanisms in the inner ear's interdental cells.

Fixation with a mixture of tannic acid and glutaraldehyde reveals a darkly stained substance in the intercellular clefts between juxtapposed interdental cells, where it is included by pynocytotic vesicles. Over the interdental cells, similar-sized vesicles (35-45 nm) are present in clear spaces of the amorphous layer of the limbal portion of the tectorial membrane. Some images suggest that they may be secreted through small disruptions of the membrane of the interdental cells' microvilli. In addition, a TA-unstained, amorphous material is present inside both basal ducts and apical cavities of the interdental cells, thus suggesting another secretory route from the basal region of the interdental cells towards either the endolymph, or the tectorial membrane. These two secretion processes coexist in a single interdental complex, and the two secretion products may be involved in the turnover of the adult tectorial membrane and/or the secretion of some component of the endolymph.

Animals↗

PubMed1990

Scanning electron microscopy of the auditory teeth along the mouse cochlear duct.

The auditory teeth in the spiral limbus of the cochlear duct are located under the limbal portion of the tectorial membrane and separated by furrows lodging the interdental cells. In this study, the shape, arrangement and distribution of the auditory teeth in the cochlear duct of adult mice were examined by scanning electron microscopy after removing the tectorial membrane and the interdental cells with chemical maceration methods. The auditory teeth appeared on the top face of the spiral limbus between the edge of the vestibular lip and the Reissner membrane. The teeth on the vestibular lip side possessed elongated upper plates and formed a continuous row resembling the keyboard of a piano; the teeth were separated by radially oriented parallel slits. The elongated teeth decreased in length from the base to the apex of the cochlear duct. The teeth on the Reissner membrane side showed star-shaped upper plates separated by slits and gaps. The population density of the star-shaped teeth decreased from the base to the apex, widening the gaps to hold the interdental cells. The upper plates of the teeth occupied about 75% of an extent of the tooth zone in the hook and first basal half turn, and about 55% in the apical turn. The regional differences of the auditory teeth are considered to be closely related to local functions of the tectorial membrane and the interdental cells.

Animals↗

PubMed1978

Scanning electron microscope studies of the papilla basilaris of some turtles and snakes.

The papillae basilares of three species of turtles and four species of snakes were studied by SEM. The papillae of turtle are relatively large among reptiles and are characterized by a long, horizontal middle section resting on wide basilar membrane. Both terminal ends of the papilla extend onto the surrounding limbus in the form of a forked or "T" -shaped end or as a curved, "hook"- like processes. Details vary with the species. In the three species of turtles studied, there were between 1,100 and 1,400 hair cells on a papilla. The tectorial membrane covering the horizontal portion of the papilla is heavy in appearance and tightly attached to the kinocilial bulbs. The terminal ends of the papilla are covered by a thin gelatinous material. In addition, mat-like tectorial network covers the supporting cells and extends from the microvilli of the supporting cells to the overlying tectorial membrane. All hair cells are unidirectionally and abneurally oriented. The supporting cell surfaces form a large part of the papilla and, thus, hair cell density is low. The papillae of the two boid snake species studied are moderately long among snakes and contain a moderate number of hair cells (574 in Epicrates and 710-780 in Constrictor). Papillar form is elongate, avoid, or canoe-shaped. The tectorial membrane may be either highly fenestrated or moderately dense and covers all but a few of the terminal hair cells. A tectorial-like mat covers all but a few of the terminal hair cells. Most hair cells are unidirectionally and abneurally oriented. A few terminal cells in boids may show reverse orientation. Hair cell density is similar to that of turtles.

Animals↗

PubMed1997

Immunohistochemical localization of keratan sulfate in the chinchilla inner ear.

Keratan sulfate (KS) was immunolocalized in the chinchilla cochlea and vestibular system using indirect immunohistochemistry and a monoclonal antibody (clone 5-D-4) directed against a proteoglycan core antigen. As a positive control, anti-KS Mab reactivity was found in the pericellular matrix and lacuna walls of temporal bone osteocytes. In the cochlea, anti-KS Mab reactivity was abundant in the basal cell layer of the stria vascularis and in the marginal band and Hensen's stripe of the tectorial membrane. Less anti-KS Mab reactivity was present in the cover net, Hardesty's membrane and the upper fibrous zone of the limbal layer of the tectorial membrane. In the vestibular system, anti-KS Mab reactivity was immunolocalized to a portion of the epithelium overlying the cupula of the crista ampullaris, in the apical surface of crista ampullaris epithelium, crista ampullaris stereocilia and in the otoconia. Elucidating the distribution of KS in the cochlea will improve our understanding of cochlear anatomy and is a first step toward understanding the etiology of hearing loss observed in diseases involving KS metabolism, namely, mucopolysaccharidosis type IV (Morquio's syndrome).

Animals↗

PubMed1999

Chick alpha-tectorin: molecular cloning and expression during embryogenesis.

The avian and mammalian tectorial membranes both contain two non-collagenous glycoproteins, alpha and beta-tectorin. To determine whether variations in the primary sequences of the chick and mouse alpha-tectorins account for differences in subunit composition and matrix structure of the tectorial membranes in these two species, cDNAs spanning the entire open reading frame of chick alpha-tectorin were cloned and the derived amino acid sequence was compared with that of mouse alpha-tectorin. Chick alpha-tectorin shares 73% amino acid sequence identity with mouse alpha-tectorin and, like mouse alpha-tectorin, is composed of three distinct modules: an N-terminal region similar to the G1 domain of entactin, a central region that shares identity with zonadhesin and contains three full and two partial von Willebrand factor type D repeats, and a C-terminal region containing a zona pellucida domain. The central region of chick alpha-tectorin contains fewer potential N-glycosylation sites than that of mouse alpha-tectorin and is cleaved at two additional sites. Differences in the glycosylation and proteolytic processing of chick and mouse alpha-tectorin may therefore account for the variation observed in the composition and structure of the collagenase-insensitive matrices of the avian and mammalian tectorial membranes. In situ hybridisation and Northern blot analysis of chick inner ear tissue indicate that the spatial and temporal patterns of alpha and beta-tectorin mRNA expression in the developing chick inner ear are different, suggesting the two tectorins may each form homomeric filaments.

Amino Acid Sequence↗

PubMed1992

Localization of type II, IX and V collagen in the inner ear.

Types II and IX collagen are traditionally considered cartilage collagens; however, within the inner ear, types II and IX collagen have a more diverse distribution. In the adult gerbil, type II collagen is the major fibrillar component. In the otic capsule it is present surrounding the osteocytes embedded and branching in the periosteal layer, in the cartilaginous rests of the enchondral layer, and in the endosteal layer bordering the membranous labyrinth. In the regions of the sensory cells, type II collagen is found in the osseous spiral lamina, the connective tissue of the spiral limbus, the subepithelial tissue of the maculae in the vestibule and the cristae in the ampullae, and in the spiral ligament. It is present in the non-cartilaginous and acellular structures of the tectorial membrane over the cochlear hair cells and the vestibular membrane lining the semicircular canals. Type IX collagen, when present, in all cases co-localizes with type II collagen but is found in more limited regions. It is found only in the cartilaginous rests of the enchondral bone, the tectorial membrane and the vestibular membrane. Type V-like collagen, a connective tissue collagen, is found to have a complementary localization to types II and IX collagen within the interstitial bone of the otic capsule, the osseous spiral lamina and the tectorial membrane, but it is absent from the vestibular membrane. This report is the first documenting the co-localization of types II and IX collagen.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1994

Visualisation of domains in the avian tectorial and otolithic membranes with monoclonal antibodies.

The staining patterns observed with six monoclonal antibodies (mAbs) raised in vitro against a fraction derived from the utricular macula were examined with cryosections of the auditory and vestibular organs of the avian inner ear. These antibodies revealed several distinct domains within the gelatinous membranes. Three different labelling patterns were observed in the tectorial membrane. Staining was seen either throughout the entire tectorial membrane, restricted to its core, or in a narrow zone lying close to the surface of the basilar papilla. In the maculae, the mAbs stained either the striolar region of the otolithic membrane or the entire structure. One monoclonal which labelled otoconia, stained small otoconia in their entirely, whilst larger otoconia were only labelled around their periphery. Only one of the mAbs stained the cupulae of the semi-circular canal ampullae and this antibody stained neither the tectorial nor the otolithic membranes. These results suggest that there are biochemically distinct regions in the gelatinous membranes of the inner ear and indicate that these matrices are not simply homogeneous extracellular structures.

Animals↗

PubMed1997

Two-tone rate suppression boundaries of cochlear ganglion neurons in chickens following acoustic trauma.

The purpose of the present study was to examine the effects of acoustic trauma and hair cell loss and regeneration on the two-tone rate suppression (TTRS) boundaries of cochlear ganglion neurons in chickens. Chickens were exposed for 48 hours to a 525-Hz, 120-dB SPL tone which destroyed the hair cells and tectorial membrane in a crescent-shaped patch along the abneural side of the basilar papilla. Afterwards, TTRS boundaries were recorded from cochlear ganglion neurons at 0-1, 5, 14, and 28 days postexposure. Acoustic trauma reduced the percentage of neurons with TTRS boundaries below CF (TTRSb) (52.6% to 8.2%) and above CF (TTRSa) (88.4% to 46.6%). In addition, the exposure reduced TTRS boundary slopes, elevated best suppression threshold (BST), and increased the frequency separation between the tips of the TTRS boundaries and CF. All the TTRS measures started to recover by 5 days postexposure and by 14 days and 28 days postexposure, most measures had recovered to normal levels. However, the BST, TTRS slopes, and the frequency separation of TTRSb boundaries from CF were still slightly abnormal near the exposure frequency. In addition, the percentage of neurons with TTRS below CF was reduced significantly. The partial recovery of TTRS boundaries is presumably due to the regeneration of hair cells and the lower honeycomb layer of the tectorial membrane. The residual TTRS deficits observed 28 days postexposure were most closely associated with the missing upper fibrous layer of the tectorial membrane.

Animals↗