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PubMed2001

Thyroid hormone-deficient period prior to the onset of hearing is associated with reduced levels of beta-tectorin protein in the tectorial membrane: implication for hearing loss.

The genes for alpha- and beta-tectorin encode the major non-collagenous proteins of the tectorial membrane. Recently, a targeted deletion of the mouse alpha-tectorin gene was found to cause loss of cochlear sensitivity (). Here we describe that mRNA levels for beta-tectorin, but not alpha-tectorin, are significantly reduced in the cochlear epithelium under constant hypothyroid conditions and that levels of beta-tectorin protein in the tectorial membrane are lower. A delay in the onset of thyroid hormone supply prior to onset of hearing, recently described to result in permanent hearing defects and loss of active cochlear mechanics (), can also lead to permanently reduced beta-tectorin protein levels in the tectorial membrane. beta-Tectorin protein levels remain low in the tectorial membrane up to one year after the onset of thyroid hormone supply has been delayed until postnatal day 8 or later and are associated with an abnormally structured tectorial membrane and the loss of active cochlear function. These data indicate that a simple delay in thyroid hormone supply during a critical period of development can lead to low beta-tectorin levels in the tectorial membrane and suggest for the first time that beta-tectorin may be required for development of normal hearing.

Animals↗
PubMed2004

Displacement of the reticular lamina with and without the tectorial membrane in the guinea pig cochlea.

OBJECTIVE: In an attempt to establish the mechanical relationships between the reticular lamina and tectorial membrane, we studied the morphological changes of the reticular lamina on a micrometer scale when an in vitro preparation of guinea pig cochlea with and without tectorial membrane was exposed to a potassium-rich medium. MATERIAL AND METHODS: Using video-enhanced differential interference contrast microscopy, the radial displacement of the inner hair cells (IHCs) and outer hair cells (OHCs) in the reticular lamina was measured in real time after exposure to the potassium-rich medium for 3 min. RESULTS: The amplitude of the displacement of the OHCs in preparations with an intact tectorial membrane was half of that observed in those in which the tectorial membrane had been removed. A similar displacement response was also observed for the IHCs, although it was smaller than that for the OHCs. There was no significant difference in the amplitude of the displacement among the three rows of OHCs. CONCLUSIONS: These results suggest that the structure linking the OHCs to the pillar cells is very elastic and that the movement of the OHCs in situ is weakly mechanically coupled to the IHCs. The tectorial membrane provides increased compliance in the motion of the IHCs and OHCs.

Action Potentials↗
PubMed1994

The osmotic response of the isolated tectorial membrane of the chick to isosmotic solutions: effect of Na+, K+, and Ca2+ concentration.

Changes in the size, shape, and structure of the isolated tectorial membrane of the chick were measured in response to isosmotic changes in the ionic composition of the perfusion solution. Substitution of artificial perilymph (AP) for artificial endolymph (AE) caused a small (approximately 15%), slow (time constants tau approximately 12 min) shrinkage of the thickness of the tectorial membrane that was largely reversed on return to AE. Substitution of AP for AE alters not only the predominate cation (from K+ to Na+) but also the Ca2+ concentration (from < 7 mumol/l to 2 mmol/l). Additional experiments were performed to separate effects of each of these changes. When a high-Na+, low-Ca2+ solution was substituted for a high-K+, low-Ca2+ solution (AE), the tectorial membrane swelled significantly, often to more than twice its original thickness (the largest swelling was 337%), with a slow time course (tau approximately 23 min). Addition of the Ca2+ to either high-K+ or high-Na+ solutions caused rapid shrinkage of the tectorial membrane (tau approximately 2-3 min). Addition of the Ca2+ chelator EGTA caused rapid swelling (tau approximately 4 min). Large osmotic responses were only partially reversible and caused long-lasting changes. For example, long-duration solution changes that produced large, rapid osmotic responses early in an experiment tended to produce smaller and slower responses later in the experiment. In contrast, the small osmotic responses to short-duration solution changes were repeatable for tens of hours. Changes in ionic composition of the bath affected not only the thickness of the tectorial membrane but also its other dimensions. Responses were not generally isotropic; both the size and shape of the tectorial membrane generally changed. Consistent changes in microstructure accompanied the osmotic changes.

Animals↗
PubMedDate not supplied

Mechanical properties of the tectorial membrane in situ.

According to the classical model of cochlear hair-cell stimulation, the tectorial membrane moves in cross-section like a stiff beam, rotating around the lip of the spiral limbus. This produces a shearing motion against the reticular lamina and, as a result, a radial deflection of the hair-cell stereocilia. The deflection can be effectively produced by the tectorial membrane only if its stiffness in the radial direction is greater than that of the stereocilia. We were able to manipulate the tectorial membrane through a scala-media access in live Mongolian gerbils and to measure its transverse and radial stiffness. We found the membrane to behave like a rubber band and to be much less stiff than the stereocilia. This is incompatible with the classical model. The tectorial membrane must act on the stereocilia as a mass load rather than a stiff anchor.

Animals↗
PubMed1987

Acoustic overstimulation alters the morphology of the tectorial membrane.

After a permanent threshold shift was induced by exposing guinea pigs to a 1 kHz pure tone at 105 dB(A) for 72 h, light microscopic observations of freshly dissected and stained tectorial membranes showed an increased waviness and clumping of the fibers of the middle zone. Hensen's stripe was not seen as a continuous dense structure running through the middle zone but was at times discontinuous and curved. As measured from cross-sections of the cochlea, the thickness of the tectorial membrane was decreased after acoustic overstimulation. The stereocilia of the inner and outer hair cells lie directly under the middle zone. Visual detection levels of threshold of tectorial membrane movement was determined by stimulating the marginal zone of the tectorial membrane of isolated cochlear coils by an oscillating water jet. After acoustic overstimulation the tectorial membrane became more complaint. The tectorial membrane abnormalities were restricted to the regions of the cochlea that demonstrated a 40-50 dB hearing loss.

Animals↗
PubMed1994

Pilocarpine-induced changes in the saccharide composition of the tectorial membrane and interdental cells of the organ of Corti: a study with gold-labeled lectins.

The glycoconjugates in the cytoplasm of inner ear interdental cells and those constituting the limbal tectorial membrane were identified by a post-embedding cytochemical method using low-temperature embedding in Lowicryl K4M and labeling with biotinylated lectins, goat anti-biotin antibody, rabbit anti-goat antibody, and gold-labeled protein A in control animals, and after the systemic injection of pilocarpine. The lectins used were ConA, PHA-E, PSA, RCA, SBA, Succ-WGA, UEA, and WGA. In control animals, a semiquantitive analysis of gold particles showed that Succ-WGA produced the strongest labeling on the tectorial membrane, followed by SBA, ConA, WGA, RCA, PHA-E, and PSA. The lowest values were obtained with UEA. The cytoplasm of the interdental cells was also labeled with all the lectins, but the number of particles/microns2 was lower than on the tectorial membrane. The concentration of gold particles on the limbal tectorial membrane in pilocarpine-treated animals was higher than in control animals for some lectins (RCA, PSA, UEA) but lower for others (WGA, SBA, PHA-E, Succ-WGA). The changes in the labeling pattern of the cytoplasm of the interdental cells paralleled those in the tectorial membrane. These results demonstrate that the saccharide composition of the limbal tectorial membrane can be modified by systemic injection of pilocarpine. This action may take place through a change in either the secretion rate or the amount of some glycoconjugates by the interdental cells.

Acrylic Resins↗
PubMed1988

The ultrastructural organization and properties of the mouse tectorial membrane matrix.

The polyphenolic compound tannic acid and the cationic stains ruthenium red, Alcian blue and lanthanum chloride have been used to reinvestigate the ultrastructural organization of the tectorial membrane matrix. Tannic acid treatment reveals that the matrix both in between and within the Type A protofibril bundle system has a high degree of structural organization. The basic unit of this matrix is best described as a 'striated sheet'. These striated sheets are formed by alternating 'dark' and 'light' fibrils which run parallel to one another and lie within the plane of each sheet. In sodium based buffers both light and dark fibrils have diameters of approximately 7 nm and the distance between each dark fibril in a sheet varies from 30 to 46 nm. Dark and light fibrils are coupled by periodic, staggered cross-bridges which occur at approximately 12 nm intervals along the fibrils. Fibril diameters in tectorial membranes prepared and fixed in potassium based buffers are from 10-20% greater than they are in tectorial membranes prepared and fixed in sodium based buffers. Fine fibrils can also be resolved in the matrix with the cationic stains lanthanum chloride and ruthenium red, but the organization of these fibrils into a regular matrix structure is most clearly resolved with tannic acid treatment. The striated sheets are largely destroyed by treating the tectorial membranes with neutral trypsin and are insensitive to treatment with bacterial collagenase. In contrast, the Type A protofibril system is trypsin resistant and collagenase sensitive. Treatment of tectorial membranes with salt solutions containing either 5 nM EDTA or 5 mM EGTA and 2 mM MgCl2 results in a complete loss of organized striated sheets and the appearance of randomly dispersed fibrillar material and small particles. Re-addition of Ca2+ ions causes the striated sheets to reform, indicating that the structure can undergo at least one cycle of depolymerization and polymerization in vitro. Reduction of disulphide bonds with beta-mercaptoethanol causes a loss of structural organization similar to that observed after EDTA or EGTA treatment. The results demonstrate that the non-collagenous components of the tectorial form a matrix with a degree of organization that has been previously unrecognised.

Alcian Blue↗
PubMed1990

SEM analysis of the developing tectorial membrane in the chick cochlea.

The development of the tectorial membrane in the embryonic chick cochlea was studied using scanning electron microscopy. Chick embryos ranged in age from embryonic day 7 (E7) to post-hatching day 15. Our studies revealed that a fine filamentous matrix arose on the apical surface of the basilar papilla at approximately E7. This matrix was secreted by the supporting cells which encircled the hair cells. By E9, the early matrix had increased in volume but remained filamentous in structure, except at the inferior edge of the basilar papilla where it was condensed into a layer of laterally-oriented columns. At E9 the TM exhibited an additional layer of matrix, called the amorphous component. It appeared to originate from the homogene cell population, and attached to the early columnar matrix at the inferior edge of the basilar papilla. The two components of the TM were separated by a longitudinal ridge, called the 'track', which marked the inferior edge of the amorphous component. As the cochlea developed, the basilar papilla increased in width, the columnar component elongated and the track appeared to recede. These morphological findings point to separate developmental origins for the two components of the tectorial membrane.

Animals↗
PubMed2004

Evidence and implications of inhomogeneity in tectorial membrane elasticity.

The motion of the tectorial membrane (TM) with respect to the reticular lamina subserves auditory function by bending the outer hair cell bundles and inducing fluid flows that shear the inner hair bundles in response to sound energy. Little is currently known about its intrinsic elasticity or about the relation between the mechanical properties and function of the membrane. Here we subdivide the TM into three longitudinal regions and five radial zones and map the shear modulus of the TM using atomic force microscopy, and present evidence that the TM elasticity varies radially, after the distribution of type A collagen fibrils. This is seen most dramatically as a decrease in shear modulus in the neighborhood of the sensory hair cells; we argue that this inhomogeneity of properties not only protects the hair bundles but also increases the energy efficiency of the vibrational shearing during sound transduction.

Animals↗
PubMed1976

[Postnatal development of the tectorial membrane's marginal net of the rabbit. Correlations with the typical marginal structures of the adult squirrel monkey].

To date the structure of the marginal net of the tectorial membrane has not been sufficiently described, its function is unclear and can only be understood after further detailed analysis. The limiting factor in these experiments is that mostly the applied routine preparation techniques always unspecifically change the tectorial membrane. The preparation techniques have now been modified so far that the induced changes can be kept at a minimum. Examinations were carried out parallely with the stereo microscope, the light microscope, the scanning and transmission electron microscopes; results were compared and ensured. 1. The normal structure of the marginal net of the adult squirrel monkey was compared with that of the adult rabbit. The similarity suggests to study for the first time the development of the marginal net in the embryologically more easily accessable rabbit by means of scanning electron microscope. 2. The refined preparation technique enables a reproducable investigation of the tectorial membrane in a lifted off state and subsequently in a large area even in a not lifted off state. 3. During the various steps of preparation the marginal zone is deformed much stronger than the rest of the membrane. 4. In the squirrel monkey a distinctly developed marginal net seems to be combined with the presence of a fourth row of other hair cells. To this conclusion leads the following observation: the impressions of the sensory cell hairs on the bottom side of the tectorial membrane are found predominately in the cross connections of the marginal net. 5. The marginal net of the rabbit shows a development from basal to apical. Thereby the hair cells are covered with fibres of the tectorial membrane up to the Hensen's cells. 6. On the fifth day characteristic holes are growing in the marginal area and the fibres withdraw from the Hensen' cells. This development proceeds in the rabbit more than in the squirrel monkey, the emerged net structure is reduced to the advantage of the marginal band. 7. A new technique allows the same spot to be observed by the scanning as well as the transmission electron microscopes. The interdental cells examinated in this way showed a strong activity of synthesis in the "3d" stage.

Animals↗
PubMed2006

Measurement of the mechanical properties of isolated tectorial membrane using atomic force microscopy.

The tectorial membrane (TM) is an extracellular matrix situated over the sensory cells of the cochlea. Its strategic location, together with the results of recent TM-specific mutation studies, suggests that it has an important role in the mechanism by which the cochlea transduces mechanical energy into neural excitation. A detailed characterization of TM mechanical properties is fundamental to understanding its role in cochlear mechanics. In this work, the mechanical properties of the TM are characterized in the radial and longitudinal directions using nano- and microindentation experiments conducted by using atomic force spectroscopy. We find that the stiffness in the main body region and in the spiral limbus attachment zone does not change significantly along the length of the cochlea. The main body of the TM is the softest region, whereas the spiral limbus attachment zone is stiffer, with the two areas having averaged Young's modulus values of 37 +/- 3 and 135 +/- 14 kPa, respectively. By contrast, we find that the stiffness of the TM in the region above the outer hair cells (OHCs) increases by one order of magnitude in the longitudinal direction, from 24 +/- 4 kPa in the apical region to 210 +/- 15 kPa at the basilar end of the TM. Scanning electron microscopy analysis shows differences in the collagen fiber arrangements in the OHC zone of the TM that correspond to the observed variations in mechanical properties. The longitudinal increase in TM stiffness is similar to that found for the OHC stereocilia, which supports the existence of mechanical coupling between these two structures.

Animals↗
PubMed2007

Sharpened cochlear tuning in a mouse with a genetically modified tectorial membrane.

Frequency tuning in the cochlea is determined by the passive mechanical properties of the basilar membrane and active feedback from the outer hair cells, sensory-effector cells that detect and amplify sound-induced basilar membrane motions. The sensory hair bundles of the outer hair cells are imbedded in the tectorial membrane, a sheet of extracellular matrix that overlies the cochlea's sensory epithelium. The tectorial membrane contains radially organized collagen fibrils that are imbedded in an unusual striated-sheet matrix formed by two glycoproteins, alpha-tectorin (Tecta) and beta-tectorin (Tectb). In Tectb(-/-) mice the structure of the striated-sheet matrix is disrupted. Although these mice have a low-frequency hearing loss, basilar-membrane and neural tuning are both significantly enhanced in the high-frequency regions of the cochlea, with little loss in sensitivity. These findings can be attributed to a reduction in the acting mass of the tectorial membrane and reveal a new function for this structure in controlling interactions along the cochlea.

Animals↗
PubMed1979

Localization of the marginal zone of the tectorial membrane in situ, unfixed, and with in vivo-like ionic milieu.

In order to determine the normal positional relationship between the tectorial membrane and the organ of Corti, a preparation method was developed which made it possible to study the unfixed tectorial membrane in its normal position in relation to the cochlea and with in vivo-like ionic conditions. With this method, post-mortem changes visible with the light microscope were detectable after 60 to 90 min instead of the normal 30 min. When endolymph of artifical endolymph are present in the scala media, the marginal zone lies in close contact with the surface of the organ of Corti. If the endolymph is replaced by artificial perilymph, first the marginal zone of the tectorial membrane, and later the whole membrane shrinks. At this stage, latex particles suspended in the perilymph are free to enter the subtectorial space.

Animals↗
PubMed1985

Lectins demonstrate the presence of carbohydrates in the tectorial membrane of mammalian cochlea.

Histological sections of rat and guinea pig cochleas were exposed to lectins to identify the carbohydrates present in the tectorial membranes. N-Acetylglucosamine, galactose, mannose and fucose were found to be present in both rats and guinea pigs, but N-acetylgalactosamine was not detected. In addition, two control experiments were performed. In the first, each lectin was preincubated with its specific inhibitory sugar. In the second, the unfixed tectorial membranes were exposed to lectins. Radioautographic studies confirmed the presence of glucosamine and fucose in the tectorial membrane of 1-day-old rats.

Acetylglucosamine↗
PubMed1981

Imprints of the inner sensory cell hairs on the human tectorial membrane.

Imprints indicating possible direct inner sensory cell hair contact with the tectorial membrane were observed in the cochlea of a 77-year-old woman under a scanning electron microscope (SEM). The imprints were seen in the lower and upper basal cochlear turns but not in the apical and middle turns. The small dot of imprints numbered from a few up to l2 and were arranged in various forms rather than straight lines. Contact between the tectorial membrane and inner and outer sensory cell hairs of the humancochlea was discussed from the SEM findings found in this case.

Aged↗
PubMedDate not supplied

Attachment of the tectorial membrane revealed by scanning electron microscope.

Our present-day descriptions of the causes of many forms of sensorineural deafness are based on what is known about the morphology of the organ of Corti. Unfortunately, this information is still woefully inadequate for a complete interpretation of normal events within this structure. Nevertheless there has been no shortage of theories based, in part at least, on assumptins of what the unknown morphology might be. One of the least understood structures is the tectorial membrane, for which the extent and position have had many descriptions. A review of these reveals that the observations vary with the techniques used, and different techniques have various effects on the sticky gel of the tectorial membrane which is reported to be 90% water. Here is described a technique whereby the bulk frozen-hydrated tectorial membrane is viewed by scanning microscopy. In its natural living state the tectorial membrane is sealed to the Hensen's cells, protecting the reticular lamina from endolymph.

Animals↗
PubMed2000

A targeted deletion in alpha-tectorin reveals that the tectorial membrane is required for the gain and timing of cochlear feedback.

alpha-tectorin is an extracellular matrix molecule of the inner ear. Mice homozygous for a targeted deletion in a-tectorin have tectorial membranes that are detached from the cochlear epithelium and lack all noncollagenous matrix, but the architecture of the organ of Corti is otherwise normal. The basilar membranes of wild-type and alpha-tectorin mutant mice are tuned, but the alpha-tectorin mutants are 35 dB less sensitive. Basilar membrane responses of wild-type mice exhibit a second resonance, indicating that the tectorial membrane provides an inertial mass against which outer hair cells can exert forces. Cochlear microphonics recorded in alpha-tectorin mutants differ in both phase and symmetry relative to those of wild-type mice. Thus, the tectorial membrane ensures that outer hair cells can effectively respond to basilar membrane motion and that feedback is delivered with the appropriate gain and timing required for amplification.

Acoustic Stimulation↗
PubMedDate not supplied

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

Excitation of cochlear hair cells is believed to be produced by radial deflection of their stereocilia as a result of shear motion between the reticular lamina and the tectorial membrane. The shear motion must depend on the mechanical coupling between the organ of Corti and the tectorial membrane. It is shown that, because longitudinal stiffness of the tectorial membrane, the shear motion must be enhanced as the wavelength decreases toward the cochlear vibration maximum. The resulting sharpening of the vibration maximum agrees with the frequency selectivity found in the inner hair cells and cochlear-nerve afferents.

Basilar Membrane↗