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PubMed1981

Elemental analysis of the early postnatal tectorial membrane.

The analytical electron microscope has revealed that the elemental composition of the early postnatal tectorial membrane is principally the same before and after the development of endolymph. The elemental composition of the tectorial membrane does not give absolute information on the permeability of the membrane to ions such as potassium and chlorine from the endolymphatic space. Such a permeability is, however, likely when comparing the relative peak intensities of chlorine and potassium before and after the development of endolymph.

Animals↗
PubMed1988

The effect of acoustic trauma on the tectorial membrane, stereocilia, and hearing sensitivity: possible mechanisms underlying damage, recovery, and protection.

The aim of the present investigation was to determine: 1) the relationship between changes in auditory sensitivity and alterations in stereocilia micromechanics and tectorial membrane morphology after acoustic overstimulation; 2) the rate of growth of a threshold shift in stereocilia following in vitro overstimulation; and 3) if the damaging effects of noise trauma can be reduced by pre-exposure to a low level acoustic stimulus. After exposure to a 1.0 kHz pure tone signal at 105 dB SPL for 72 hours, the threshold of the auditory brainstem response was broadly elevated by approximately 40-50 dB; the inner hair cell stereocilia became less stiff; and morphological alterations were observed in the middle zone of the tectorial membrane. The location of both the stereocilia and tectorial membrane alterations corresponded to the region of the cochlea demonstrating a threshold shift. Following a recovery period from overstimulation, the auditory brainstem response showed some improvement yet a 25 dB threshold shift remained. At this time, swelling of the afferent dendrites beneath the inner hair cells was observed together with scattered outer hair cell loss. Also, the inner hair cell stereocilia regained their normal stiffness characteristics. The in vitro experiments demonstrated that overstimulation reduced the stiffness of the inner and outer hair cell stereocilia bundles. A threshold shift increased systematically with exposure duration and intensity. After 6 minutes of overstimulation, the threshold shift exhibited a plateau whose magnitude was dependent upon the exposure intensity. Stereocilia micromechanics were shown to be dependent on the metabolism of the hair cell. The pre-treatment to a low level acoustic stimulus (81 dB SPL) prior to exposure to a stimulus known to yield a permanent threshold shift resulted in a 20 dB reduction in the threshold shift relative to the group not pre-exposed as well as complete recovery from the threshold shift after 2 months.

Animals↗
PubMed1990

An ultrastructural study of the guinea pig tectorial membrane 'type A' protofibril.

Fine structural features of the 'type A' protofibrils in the guinea pig tectorial membrane were examined using negative staining and deep-etching techniques. Negative-stained samples of fragmented tectorial membrane were composed of several fine filamentous subunits showing the clear banding pattern of the type A protofibrils. Deep-etched replicas of the EGTA (ethylene glycol bis-N,N,N',N'-tetraacetic acid)-treated samples showed fine surface structure consisting of several linear arrays of filamentous elements on the extracellular fibrils, which is interpreted to be type A protofibrils.

Animals↗
PubMed2003

Dynamic material properties of the tectorial membrane: a summary.

Dynamic material properties of the tectorial membrane (TM) have been measured at audio frequencies in TMs excised from the apical portions of mouse cochleae. We review, integrate, and interpret recent findings. The mechanical point impedance of the TM in the radial, longitudinal, and transverse directions is viscoelastic and has a frequency dependence of the form 1/(K(j2pif)(alpha)) for 10<or=f<or=4000 Hz, where f is frequency, K is a constant, j=-1, and alpha approximately 0.66. Comparison with other connective tissues shows that the TM is a relatively lossy viscoelastic material. The median magnitudes of the point impedance at 10 Hz in the radial, longitudinal, and transverse directions are 4.6 x 10(-3) N.s/m, 1.8 x 10(-3) N.s/m, and 2.7 x 10(-3) N.s/m. Consistent with osmotic responses (Freeman et al., 2003), the TM point impedance is anisotropic - the TM is stiffer in the radial than in the longitudinal and transverse directions. The mechanical space constant of the TM is approximately 20 microm. Comparisons reveal that in the apical region of the mouse cochlea, the TM dynamic stiffness at 10 Hz is 10 times larger than the static stiffness of the aggregate hair cells in a mechanical space constant and roughly comparable to the stiffness of the basilar membrane. We conclude that the TM provides a mechanical load on the basilar membrane and that the lability of the TM to changes in endolymph composition may well be reflected in changes in basilar membrane motion.

Animals↗
PubMed1992

Type II and type IX collagen form heterotypic fibers in the tectorial membrane of the inner ear.

The presence of type II and IX collagen in the adult gerbil inner ear was probed by use of preembedding and post-embedding immunocytochemistry. Monoclonal antibodies to type II and IX collagen both label the tectorial membrane, an acellular structure which lies over the cochlear sensory hair cells and plays an essential role in the transduction process. At the light microscopic level, the antibodies are localized throughout the tectorial membrane. At the electron microscopic level, antibodies against types II and IX collagen are co-localized over the thick unbranched (Type A) radial fibers but not over the thin highly branched (Type B) fibers in which the thick fibers are embedded. Thus, the tectorial membrane of the cochlea represents another non-cartilaginous structure in which type II and IX collagen are present and arranged in heterotypic fibers. The organization of these fibers into bundles, meshworks and layers results in the formation of a structure with the unique properties necessary to withstand mechanical stresses associated with sensory transduction.

Animals↗
PubMed1997

Ultrastructural organization of proteoglycans and fibrillar matrix of the tectorial membrane.

The molecular and supramolecular structure of the tectorial membrane (TM) was studied by transmission electron microscopy (TEM). Collagen (type A) fibrils in the TM were found associated with proteoglycans (PGs) and type B fibrils. Most PGs were orthogonally oriented and attached D-periodically to collagen fibrils. Computer averaged projections of PG particles and linear aggregates of PGs in crystalline arrays, stained with Cuprolinic blue, showed an elongated, electron-dense structure 50-65 nm in length and 10 nm in width. Image analysis of type B fibrils showed that they are constructed of globular domains arranged with a periodicity of 12-14 nm. Each globular domain contains two thin 'arms', extended in opposite directions, which contact the 'arms' of adjacent fibrils. Numerous type B fibrils were found between collagen fibrils. They are attached to adjacent collagen fibrils by the 'arms' of their globular domains. An association of type B fibrils and PGs with collagen seems to result in the local ordered arrangement of the TM matrix. A hypothetical model of the TM matrix supramolecular structure is presented.

Animals↗
PubMed1990

Effects of perinatal hypothyroidism in the carbohydrate composition of cochlear tectorial membrane.

The presence of carbohydrates in the cochlear tectorial membrane (TM) of normal and hypothyroid rats was analyzed using fluorescent lectin probes. SBA and WGA lectins exhibited a similar reactivity in both normal and hypothyroid TMs. DBA, RCA1, UEA1 and Con A lectins were also reactive, although they showed a different distribution pattern between normal and hypothyroid TMs. Lastly, one of the lectins, PNA, was only labeled in hypothyroid TMs. These findings suggest that carbohydrate chains containing residues of N-acetyl-D-galactosamine (GalNAc) and N-acetyl-D-glucosamine, are similarly distributed in normal and hypothyroid TMs. Other carbohydrate residues as GalNAc alpha 1,3 GalNAc, D-galactose (Gal), L-fucose and D-mannose, are present, but are abnormally distributed in hypothyroid TMs. The Gal beta 1,3GalNAc residues, recognized by PNA, could be present only in the hypothyroid TMs. Alterations in glycosylation of the glycoproteins in the hypothyroid TM could be responsible for the abnormal distribution pattern of carbohydrate residues here described, and for the distorted shape of the hypothyroid TM.

Animals↗
PubMed1990

Ultrastructure of proteoglycans in the tectorial membrane.

The ultrastructure of proteoglycans (PGs) in the tectorial membrane (TM) of the mature chinchilla cochlea was investigated using the cationic dye Cuprolinic blue. When used at a high critical electrolyte concentration, Cuprolinic blue has been shown specifically to bind to the glycosaminoglycan residues of sulfated PGs. After Cuprolinic blue treatment, PGs were observed in the TM which were represented as rod-shaped, electron-dense structures. A perifibrillar, primarily orthogonal, array of PGs was associated with the type A protofibrils. These PGs were distributed in 50 nm intervals along the length of the type A protofibrils. A less common orientation was parallel to the axis of the type A protofibrils. PGs did not appear to be associated with the type B protofibrils. Based upon previous results by other investigators, the TM contains types II and IX collagen, and it appears likely that the type A protofibrils are composed of collagen type II. PGs visualized in the TM in this study thus may represent the glycosaminoglycan residue of type IX collagen which is associated with the type II collagen fibrils. Alternatively, the TM PGs may be small dermatan or chondroitin sulfate PGs.

Animals↗
PubMed1978

[Light and electron microscopic studies of the greater epithelial ridge and its relationship to the developing tectorial membrane in the cochlear duct of the guinea pig (author's transl)].

In early stages of fetal development (36th day, 3rd turn) the thickening of the epithelium at the basal side of the cochlear duct forms two ridges. Later in fetal development the laterally situated lesser epithelial ridge forms the major part of the organ of Corti, whereas the medially situated greater epithelial ridge contributes only a small part to this organ. The medial part of the greater ridge consists of the columnar inner supporting cells, which bear a border of closely packed microvilli at their upper surface. Up to the time of the opening of the internal spiral sulcus in the 48th day of fetal development, there is a close spacial relationship between microvilli and filaments of the tectorial membrane. We conclude that the inner supporting cells contribute to the formation of the tectorial membrane. However, thus far we cannot entirely exclude a different possibility, that the inner supporting cells absorb material of the tectorial membrane. During the opening of the sulcus spiralis internus the inner supporting cells become considerably smaller, some of them undergo complete destruction by cytolysis, with pyknosis and karyorrhexis.

Animals↗
PubMed1998

Inner ridge cells may be the main source of tectorial membrane type II collagen: evidence from quantitative mRNA in situ hybridization.

In a previous study we showed that COL2A1 mRNA is expressed in both ectodermally and mesodermally derived structures of second trimester human fetal cochlea, whereas type II collagen is present in mesodermally derived structures and in tectorial and basilar membranes. Because the tectorial membrane is acellular and therefore does not make its own proteins, the source of type II collagen and proteoglycans in this membrane has been of interest. We have attempted to address this issue, at least in part, by performing quantitative cRNA mRNA in situ hybridization on second trimester human fetal cochlear sections using a COL2A1 probe. By counting the number of silver grains cell in the interdental cells, inner sulcus cells and inner ridge Kolliker organ cells and by an analysis of variance of these quantitative data. inner ridge cells were found to have significantly higher levels of COL2A1 mRNA than interdental and inner sulcus cells (p < 0.0001). On the basis of significantly higher COL2A1 mRNA levels in inner ridge cells and their higher numbers than interdental and inner sulcus cells we postulate that type II collagen for human fetal tectorial membrane is derived mostly from inner ridge Kolliker organ cells. The lower COL2A1 mRNA in interdental cells appears to provide type II collagen for the spiral limbus and the tectorial membrane. The inner sulcus cells, hair cells. Deiter's and Hensen's cells also appear to contribute lesser amounts of type II collagen to the tectorial membrane. In analogy to these findings it is possible that other tectorial membrane proteins, including proteoglycans and other collagens, are also largely derived from these cells during human fetal development.

Cochlea↗
PubMedDate not supplied

Guinea pig tectorial membrane profile in an in vitro cochlear preparation.

The guinea pig cochlea was examined under high-magnification light microscopy in an in vitro preparation. After extraction of the otic capsule, the bulla was opened widely and a small hole made into the fourth turn of the scala vestibuli. The organ of Corti was visualized under artificial endolymph at 600 X magnification. Added 1-micron titanium dioxide particles settled on the upper surface of the transparent tectorial membrane. Particle positions showed that much of this upper surface lay in a flat sheet that extended centrifugally almost to the Hensen's cells, giving the impression it was attached there. The sheet extended at least to the level of the inner hair cells, where a tectorial membrane thickness of about 40 micron was reached. Titanium dioxide particles were seen regularly in immediate proximity to the hair cell cilia, indicating that scala media is continuous with the subtectorial space. Upon mechanical manipulation, Hensen's cells proved to be extremely cohesive and elastic. It is suggested that hair cell stereocilia provide major mechanical connections for the tectorial membrane.

Animals↗
PubMed1979

Tectorial membrane: a possible effect on frequency analysis in the cochlea.

Mathematical analysis and computer and network simulations of the cochlea show that, given appropriate values of specific physical constants, radial shear motion between the tectorial membrane and the reticular lamina may provide the sharpening of frequency analysis observed in cochlear nerve fibers in comparison with the mechanical amplitude distribution on the basilar membrane. According to the analysis, the sharpening occurs through an interaction of the longitudinal mechanical propagation constant of the tectorial membrane with the wavelength on the basilar membrane.

Basilar Membrane↗
PubMed1987

Glycoconjugates of the tectorial membrane.

The type and quantity of carbohydrate present in the tectorial membrane (TM) was analysed using gas-liquid chromatography and lectin staining of TM protein subunits previously separated by electrophoresis. A relatively large amount of carbohydrate was found, and glucose, N-acetylglucosamine, N-acetylgalactosamine, galactose, mannose and N-acetylneuraminic acid were detected. The presence of mannose and the reaction of many of the protein bands with lectins suggest that at least part of the carbohydrate present is in the form of glycoprotein. The reaction of the main protein band with the lectins RCA1 and ConA is consistent with the suggestion [Thalmann et al. (1985) J. Acoust. Soc. Am. Suppl. 1, Vol. 78, S66] that this band is similar to collagen type II. The failure to detect any uronic acid in these experiments indicates that the more common proteoglycans are probably not a major component of the TM (although keratan sulphate might be present).

Animals↗
PubMed2000

Deformations of the isolated mouse tectorial membrane produced by oscillatory forces.

Mechanical properties of the isolated tectorial membrane (TM) of the mouse were measured by applying oscillatory shear forces to the TM with a magnetic bead (radius approximately 10 mcm). Sinusoidal forces at 10 Hz with amplitudes from 5 to 33 nN were applied tangentially to the surfaces of 11 TMs. The ratio of force to bead displacement ranged from 0.04 to 0.98 N/m (median: 0.18 N/m, interquartile range: 0.11-0.30 N/m, n=90). Increasing frequency from 10 to 100 Hz decreased the magnitude of the displacement of the magnetic bead by 6-7.3 dB/decade. The phase of the displacement lagged that of the stimulus current by approximately 27-44 degrees across frequencies. Displacement of the adjacent tissue decreased as the distance from the magnetic bead increased. Space constants were of the order of tens of micrometers. Forces with equal amplitude and frequency were applied radially and longitudinally. Longitudinal displacements in response to longitudinal forces were 1-10 times as large as radial displacements in response to radial forces in 85% of 560 paired measurements. These results suggest that the following mechanical properties of the TM are important. (1) Viscoelasticity: The frequency dependence of TM displacement lies between that of a purely viscous and a purely elastic material, suggesting that both are important. (2) Mechanical coupling: Space constants indicate that hair bundles could interact mechanically with adjacent hair bundles via the TM. (3) Anisotropy: The mechanical impedance is greater in the radial direction than it is in the longitudinal direction. This mechanical anisotropy correlates with anatomical anisotropies, such as the radially oriented fibrillar structure of the TM.

Animals↗
PubMed1991

The effect of bacterial endotoxin upon the morphology of the tectorial membrane and stereocilia in the guinea pig cochlea.

Endotoxin of E coli was microperfused into scala tympani or injected into the cerebrospinal fluid in anaesthetised pigmented guinea pigs. The effects of endotoxin on the cochlea were studied using electrophysiological techniques and scanning electron microscopy. We found a drop in the amplitude of the cochlear microphonics and compound action potentials 2 to 2.5 hours after injection. There were also changes in the morphology of stereocilia and the tectorial membrane. The stereocilia lost their rigidity and the tectorial membrane appeared swollen. These effects were less severe in animals which were pretreated with dexamethasone.

Action Potentials↗
PubMed1979

The limbus spiralis and its relationship to the developing tectorial membrane in the cochlear duct of the Guinea pig fetus.

The development of the interdental cells of the limbus spiralis and of the inner spiral sulcus cells as well as the formation of the mesenchymal teeth of Huschke are described during fetal life up to the day of birth in the guinea pig. Additionally, the changes of the developing tectorial membrane are studied. The ultrastructural observations allow the conclusion that during fetal development at least a considerable part of the material of the tectorial membrane is secreted by the interdental cells of the limbus spiralis.

Animals↗
PubMed1988

Gelsolin immunoreactivity and development of the tectorial membrane in the cochlea of normal and hypothyroid rats.

Gelsolin was localized by immunocytochemistry in the developing cochlea of the rat. In normal animals, the protein appeared at 18 th day in utero in cells of the Kölliker's organ, which are involved in the secretion of the tectorial membrane. The Kölliker's organ cells were not immunoreactive after the first postnatal week, which is when they cease their secretory activity. Gelsolin immunoreactivity was similar in thyroid-deficient rats until the second postnatal week but, at this age, Kölliker's organ did not transform and its gelsolin immunoreactivity persisted, together with its secretory activity. As a result, the tectorial membrane was greatly distorted and out of contact with the hair cells, which dramatically impaired the mechanical properties of the organ of Corti. The developing cochlea thus provides an example of the involvement of gelsolin in a secretory process that is of importance in the development of hearing.

Animals↗
PubMed1990

Morphological changes of hair cell stereocilia and tectorial membrane in guinea pigs with experimentally induced hydrops.

Endolymphatic hydrops was surgically induced in guinea pigs. Atrophy of middle and short stereocilia on the outer hair cells in the upper 13 mm of the cochlea was systematically observed by scanning electron microscopy in guinea pigs with hydrops between 5-22 months. Light microscope and scanning electron microscope observations indicated that the tectorial membrane in the apical three turns was often abnormally elevated, and could be vertically positioned in longstanding hydrops. The atrophy of outer hair cell middle and short stereocilia and the elevation of the tectorial membrane certainly contribute to the pathophysiology of experimental hydrops and might be implicated in Menière's disease.

Animals↗