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PubMed2006

Mice doubly deficient in the midkine and pleiotrophin genes exhibit deficits in the expression of beta-tectorin gene and in auditory response.

alpha-Tectorin and beta-tectorin are major noncollagenous proteins of the tectorial membrane, which plays a crucial role in the reception of sonic signals in the cochlea. Midkine and pleiotrophin are closely related proteins that serve as growth factors and cytokines. In mice doubly deficient in the midkine gene and pleiotrophin gene, expression of beta-tectorin mRNA was nearly abolished in the cochlea on day 1 and 7 after birth. Expression of alpha-tectorin mRNA was unaffected in the double knockout mice, and expression of beta-tectorin mRNA was not altered in mice deficient in only the midkine or pleiotrophin gene. In newborn wild-type mice, both midkine and pleiotrophin were expressed in the greater epithelial ridge of the cochlea, in which beta-tectorin mRNA was strongly expressed. These results indicate that either midkine or pleiotrophin is required for significant expression of beta-tectorin. In agreement with the view that beta-tectorin is essential for normal auditory function, mice doubly deficient in both midkine and pleiotrophin genes exhibited very severe auditory deficits. We observed that mice deficient in either midkine or pleiotrophin gene were also impaired in their auditory response, but the level of the deficit was generally low or moderate. The present finding illustrates the importance of growth factor expression in the cochlea for auditory function.

Animals↗

PubMed1996

Further studies on the mechanics of the cochlear partition in the mustached bat. II. A second cochlear frequency map derived from acoustic distortion products.

It has been proposed that acoustic 2f1-f2 distortions reflect the frequency characteristics of a secondary cochlear filter mechanism (Brown et al., 1992; Allen and Fahey, 1993). This concept was used to construct a second cochlear frequency map that may represent aspects of tectorial membrane (TM) tuning. Within the frequency range of 15-105 kHz, for a given f2 frequency, f1 was varied and the frequency ratio f2/f1 determined that produced maximum levels of the 2f1-f2 distortion (best ratio). The second cochlear frequency map was derived by plotting the distortion frequency that corresponded to the best ratio f2/f1 against the cochlear place of f2 which was obtained from the HRP-frequency map of Pteronotus (Kössl and Vater, 1985b). Minimum best ratios of 1.0005 and hence practically identical characteristic frequencies of the putative tuning of basilar membrane (HRP) and TM (2f1-f2) were found at about 45% distance from the base, a point at which 62 kHz are represented on the BM. This frequency is associated with strong cochlear resonance and large evoked and spontaneous otoacoustic emissions. Between 45% and 20% distance from the base, the basilar membrane (BM) tuning progressively increases to about 70 kHz whereas the calculated TM tuning remains constant at a frequency close to 62 kHz. The range of constant TM tuning coincides with the sparsely innervated cochlear region of Pteronotus where BM thickness is maximal and TM mass and limbal attachment are reduced (Vater and Kössl, 1996). We suggest that here the TM oscillates strongly at 62 kHz and may carry most of the energy of cochlear resonance which is transferred into movement of the organ of Corti at and apical to the 45% location where the BM is tuned to 62 kHz.

Acoustic Stimulation↗

PubMed2001

Ultrastructure of the inner ear of NKCC1-deficient mice.

The transduction of the auditory signal is dependent on the flow of ions within the inner ear. We have generated mice deficient in NKCC1, an ion cotransporter that is thought to be involved in the secretion of K+ by the strial marginal cells. Inner ear histology revealed partial to almost total absence of the scala media and collapse of Reissner's membrane. Ultrastructural analysis showed that Reissner's membrane consists of 3-4 cell layers instead of the usual two, and a substance of unknown composition is present between Reissner's membrane and underlying structures. Within the tunnel of Corti, hair cells and supporting cells were difficult to identify. The location of the tectorial membrane was altered, and a precipitate was observed surrounding it. Severe structural defects were noted in the interdental cells and Boettcher cells, and mild defects were observed in the stria vascularis and in type II and type IV fibrocytes. The finding that major defects occur predominantly in cells that are not known to express NKCC1 suggests that loss of NKCC1 results in functional defects in cells expressing NKCC1 and a morphological effect on cell populations downstream in the proposed K+ recycling pathway.

Animals↗

PubMed2000

Three-dimensional motion of the organ of Corti.

The vibration of the organ of Corti, a three-dimensional micromechanical structure that incorporates the sensory cells of the hearing organ, was measured in three mutually orthogonal directions. This was achieved by coupling the light of a laser Doppler vibrometer into the side arm of an epifluorescence microscope to measure velocity along the optical axis of the microscope, called the transversal direction. Displacements were measured in the plane orthogonal to the transverse direction with a differential photodiode mounted on the microscope in the focal plane. Vibration responses were measured in the fourth turn of a temporal-bone preparation of the guinea-pig cochlea. Responses were corrected for a "fast" wave component caused by the presence of the hole in the cochlear wall, made to view the structures. The frequency responses of the basilar membrane and the reticular lamina were similar, with little phase differences between the vibration components. Their motion was rectilinear and vertical to the surface of their membranes. The organ of Corti rotated about a point near the edge of the inner limbus. A second vibration mode was detected in the motion of the tectorial membrane. This vibration mode was directed parallel to the reticular lamina and became apparent for frequencies above approximately 0.5 oct below the characteristic frequency. This radial vibration mode presumably controls the shearing action of the hair bundles of the outer hair cells.

Animals↗

PubMed1984

Quantitative light and scanning electron microscopic study of the developing auditory organs in the bullfrog: implications on their functional characteristics.

During postmetamorphic development in the bullfrog, there is a downward shift in the distributions of best excitatory frequencies (BEFs) of the three populations of primary auditory fibers. This decrease in BEF distribution suggests that concurrent morphological changes occur in the peripheral auditory system during postmetamorphic growth. The postmetamorphic development of the auditory organs in the bullfrog was quantitatively investigated with light and scanning electron microscopy. In the basilar papilla, there are dramatic increases in the lumen volume, contact membrane area, and mass of the tectorial membrane (TM). The area of the sensory epithelium and the total number of hair cells also increase slightly. In the amphibian papilla, the mass of the TM is spatially graded in a step-wise fashion along the length of the organ in both juvenile and adult bullfrogs, but there is an increase in the absolute mass of the TM throughout the papilla with age. The height of the tallest stereocilia of the predominant hair cell type systematically decreases caudally in the juvenile amphibian papilla, but is uniform throughout the adult papilla. The increase in stereociliary height in the caudal end of the organ presumably results in a decrease in stereociliary stiffness with postmetamorphic age. The length of the amphibian papilla sensory epithelium and the number of hair cells also increase during postmetamorphic development. Theoretically, the observed morphological changes alter the micromechanical tuning properties of the auditory organs so that there is a decrease in the BEFs of the auditory fibers that innervate the two papillae.

Animals↗

PubMed1980

Five decades of research on cochlear mechanics.

A review of Békésy's experiments on postmortem preparations shows the fundamental features of cochlear macromechanics. Early mathematical theory was able to explain Békésy's observations in terms of the hydrodynamics of surface waves and to account for some experimental artifacts. More recent experiments in vivo have shown that the cochlear frequency analysis is sharper than observed by Békésy and may occur in two interacting stages. It is suggested that the second stage may result in part from a resonance of hair-cell stereocilia loaded by the mass of the tectorial membrane, and it is calculated that the damping is small enough to allow such a resonance. The resonance would make the basilar membrane with the organ of Corti appear as a fourth- rather than a second-order system.

Animals↗

PubMed1992

Antibodies against a 30 kilodalton cochlear protein and type II and IX collagens in the serum of patients with inner ear diseases.

Collagen molecules are major extracellular matrix proteins involved in the development and support of delicate auditory sensory organs. Type II collagen is widely distributed within inner ear tissues, while type IX is found only within the labyrinthine membrane and dense fibers of the tectorial membrane. Antibody specific for type II collagen has been shown to be elevated in some patients with hearing loss due to several presumably autoimmune illnesses (including Meniere's disease, otosclerosis, chronic progressive sensorineural hearing loss, and relapsing polychondritis). Purified human type II and IX collagens and an extract of human cochlear tissue were subjected to isolation by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and transferred to nitrocellulose. The sera of 21 patients with inner ear disease were examined for the presence of anticollagen and anticochlear antibodies; the sera were used to probe Western blots of purified human collagens II, IX, and XI, and cochlear protein extract with peroxidase-conjugated goat anti human polyvalent immunoglobulin as the second antibody. Anti-type II collagen antibodies were seen in 12 of 21 (57%) patients, while 13 of 21 (62%) had anti-type IX antibodies detectable by Western blot. A previously unreported 30 kd (probably noncollagen) protein was 21 (62%) had anti-type IX antibodies detectable by Western blot. A previously unreported 30 kd (probably noncollagen) protein was found by SDS-PAGE of human cochlear tissue extracts, with 3 patients, all with Meniere's disease, having antibody activity to this protein detected by Western blot.(ABSTRACT TRUNCATED AT 250 WORDS)

Blotting, Western↗

PubMed2001

Cochlear dimensions obtained in hemicochleae of four different strains of mice: CBA/CaJ, 129/CD1, 129/SvEv and C57BL/6J.

Because homologies between mice and human genomes are well established and hereditary abnormalities are similar in both, mice present a valuable animal model to study hereditary hearing disorders in humans. One of the manifestations of hereditary hearing disorders might be in the structure of cochlear elements, such as the gross morphology of the cochlea. Cochlear dimensions, however, are one factor that determines inner ear mechanics and thus hearing function. Therefore, gross cochlear dimension might be important when different strains of mice are compared regarding their hearing. Although several studies have examined mouse inner ear structures on a sub-cellular level, only few have studied cochlear gross morphology. Moreover, the sparse data available were acquired from fixed and dehydrated tissue. Dehydration, however, produces severe distortion of gel-like cochlear structures such as the tectorial membrane and the basilar membrane hyaline matrix. In this study, the hemicochlea technique, which allows fresh mouse cochlear material to be viewed from a radial perspective, was used to provide an itemized study of the dimensions of gross cochlear structures in four mouse strains (CBA/CaJ, 129/SvEv, 129/CD1 and C57BL/6J). Except for the CBA/CaJ, these strains are known to possess genes for age-related hearing loss. The measurements showed no major differences among the four strains. However, when compared with previous data, the thickness measures of the basilar membrane were up to 10 times larger. Such differences are likely to result from the different techniques used to process the material. The hemicochlea technique eliminates much of the distortion caused by dehydration, which was present in previous experiments.

Animals↗

PubMed2002

Structure of outer hair cell stereocilia side and attachment links in the chinchilla cochlea.

The structure and symmetry of chinchilla outer hair cell (OHC) stereocilia side and attachment links were investigated by transmission electron microscopy using tannic acid and Cuprolinic blue histochemical procedures. The side links run laterally between and across the rows of the stereocilia and connect the stereocilia together within the bundle. Attachment links form a crown-like array around the tips of only the tallest OHC stereocilia and attach these stereocilia to the Type B fibrils of the tectorial membrane. Computer averaging of the side links from tannic acid-treated tissues showed a central dense region of the link between adjacent stereocilia and a smaller dense portion at the plasma membrane end of the link. Computer averaging of Cuprolinic blue-treated tissues showed low electron density of the central region of the link, and the plasma membrane ends of the link were electron dense. After tannic acid treatment, the attachment links showed a diffused radial distribution around the tips of the tallest OHC stereocilia. After Cuprolinic blue treatment, the attachment links appeared as electron-dense, membrane-bound granular structures arranged with radial symmetry. The central regions of the side links are reactive to tannic acid. These regions appear to contain neutral and basic residues of proteins and participate in side-by-side association of the side links in regular aggregates. Cuprolinic blue-reactive regions of the side and attachment links appear to contain acidic sulfated residues of glycoproteins or proteoglycans, which may be involved in the attachment of these links to the stereocilium membrane.

Animals↗

PubMed1980

CM tuning can be compatible with sharply tuned receptor potentials.

There is convincing evidence that cochlear microphonics (CM) arise primarily from outer hair cells and have a frequency distribution that is much broader than that measured in inner hair cells by Russel and Sellick [6,7]. The broad tuning results from the fact that CM generated at each location decays exponentially along the cochlear duct. This implies that the sources of CM (the outer hair cells) must be more sharply tuned than the CM itself. We modeled approximately the tuning of outer hairs on the assumption that it is proportional to the shear motion between the tectorial membrane and the reticular lamina. At each frequency the spatial distribution of CM is computed by convolving the shear distribution with an exponential decay function. The frequency dependence of CM at a given location can then be found by making a cut through a family of such frequency curves. The resulting CM tuning is much flatter than that of the modeled outer hair-cell receptor potentials and roughly parallels basilar-membrane tuning below the best frequency. Above the best frequency, the theoretical curves show a frequency-dependent plateau similar to that found in physiological CM measurements.

Basilar Membrane↗

PubMed1985

Role of inner and outer hair cells in mechanical frequency selectivity of the cochlea.

Resonant frequencies of inner (IHC) and outer (OHC) hair cell systems in the guinea pig cochlea were computed using data on sensory-hair stiffness obtained from in vitro organ of Corti preparations (D. Strelioff and A. Flock (1984): Hearing Res. 15, 19-28). IHC stereocilia were modelled as stiff, free-standing, uniform cylinders which rotate about their elastic attachments to the apical surfaces of IHC. OHC, with the overlying tectorial membrane (TM), were modelled as a resonant mechanical system with the TM providing mass and the three rows of OHC sensory-hair bundles providing elasticity for linear, simple harmonic motion parallel to the reticular lamina. Since computed IHC resonant frequencies increase from 128 kHz at the apex to 300 kHz at the base, it is unlikely that they contribute to frequency selectivity. In contrast, computed frequencies of the OHC-TM system are within the audio range, increasing from 1.2 kHz at the apex to 22 kHz at the base. The results of these computations support the hypothesis that the OHC-TM system contributes to mechanical frequency selectivity of the cochlea whereas IHC are passive receptors which respond to mechanical movements of the cochlear partition.

Animals↗

PubMed2006

Does the geometrical arrangement of the outer hair cell stereocilia perform a fluid-mechanical function?

CONCLUSIONS: Our experiments qualitatively show that the geometrical structure of the inner ear may have the features of a micro-pump. To further substantiate this hypothesis, additional experiments, particularly on in vivo preparations, are needed. OBJECTIVE: To introduce some new ideas about the functional purpose of the geometric arrangement of the outer hair cell stereocilia. Analogies to some recently developed valveless micro-pumps are pointed out. To illustrate these points, comparative experiments were performed using a simplified macro model. METHODS: Specific structures of the organ of Corti were simulated in a partially open, partially closed acrylic tank. This rough approximation allows the visualization of fluid flows that are generated as a result of the relative motions between the tectorial membrane and the reticular lamina. RESULTS: It was shown that the arrangement of the cochlear elements not only forces fluid to flow in a one-way direction, but also generates a fluid stream that flows through the "outlets" between each two V or W formations of stereocilia. These fluid streams are directed towards the inner hair cells.

Basement Membrane↗

PubMed1982

Tectorial and basal membranes in experimental hypothyroidism.

The aim of the study was to trace subtle changes in the membranous labyrinth after experimental hypothyroidism that, at least in part, could explain how a reversed hearing impairment can occur, as is often clinically encountered in hypothyroid patients after thyroid substitution therapy. Adult Sprague-Dawley rats were made hypothyroid during six weeks by the use of methimazole in their drinking water. Their inner ears were investigated morphologically at the end of this period. The tectorial membrane is the first structure of the inner ear to show morphologic changes in hypothyroidism. Changes in the normal position and structure constantly were found. A thickening of the basilar membrane was indicated in many, but not all, specimens and in some control animals and may be coincidental. The initial morphologic changes are likely to be reversible after substitution therapy.

Animals↗

PubMed1994

Morphological changes in the tectorial and basilar membranes of aged rats.

Using both light and transmission electron microscopy presbycusic degeneration of the cochlea was observed in particular in the tectorial and basilar membranes, in naturally aged rats. These animals showed a descending auditory pattern as determined by auditory brainstem response. Ultrastructurally, the number of collagen fibers in the tectorial membrane was reduced and straight type A fibers were increased relative to branched, coiled type B fibers. The basilar membrane in the basal turn was also thickened by an increased homogeneous ground substance. These findings indicate that the specificity of vibration of the tectorial and basal membranes is very different in aged and young rats.

Aging↗

PubMed1996

Impediment of basilar membrane motion reduces overload protection but not threshold sensitivity: evidence from clinical and experimental hydrops.

The mechanical function of the basilar membrane (BM) in the mammalian cochlea has been newly debated after the discovery of frequency selectivity of single hair cells. Decisive information on this matter can be expected from hydropic ears, since hydrops presumably alters cochlear mechanics by (1) impeding BM motion and (2) uncoupling outer hair cell (OHC) stereocilia from the tectorial membrane (TM). Therefore hearing in Menière's disease (MD) was examined analysing data on epidemiology of MD types and audiogram types, 2f thresholds, over-recruitment, loudness intolerance, and otoacoustic emissions. Further, hearing in experimental hydrops (XH) was examined analysing data on: morphological changes on TM and OHCs in relation to hydrops duration; morphological and electrophysiological changes upon acoustic overstimulation. The results were unequivocal on two points: (1) co-occurrence of hydrops and normal hearing thresholds can appear both in MD and XH, (2) co-occurrence of non-hearing-loss hydrops and loudness hypersensitivity is typical both in MD and XH. The conclusion is that BM motion apparently is no necessary element in the chain of cochlear sound transmission but obviously is an auxiliary element for overload protection through resonant absorption. The results are further indicative of audiometric methods for an early detection of incipient MD.

Animals↗

PubMed1994

The effect of acoustic overexposure on the tonotopic organization of the nucleus magnocellularis.

We assessed the effect a sound-induced cochlear lesion had on the tonotopic organization of the nucleus magnocellularis (NM) immediately after acoustic overexposure and following a twelve day recovery period. The acoustic overexposure was a 0.9 kHz tone at 120 dB sound pressure level (SPL) for 48 h. Initially after the acoustic overexposure, the tonotopic organization of the NM was statistically different from that of age-matched controls. Specifically, it appeared that the center frequencies of units in the frequency region of the NM associated with the acoustic overexposure had higher center frequencies than their control counterparts. Following a twelve day recovery period, when threshold sensitivity and frequency selectivity were operating normally, the tonotopic organization of the NM was not statistically different from age-matched controls. We suggest that the sound-induced changes in the tonotopic organization of the NM reflect peripheral damage in the basilar papilla. It has been well documented that similar exposure paradigms produce a loss of short hair cells and a degeneration of the tectorial membrane in the region of the basilar membrane associated with the overexposure. We postulate that the loss of these structures alters the micromechanics and tuning of the basilar membrane which is reflected in the observed changes in NM tonotopy. Following the recovery period, when those structures destroyed by the overexposure had regenerated and basilar membrane micromechanics were operating normally, the tonotopic organization of the NM returned to normal.

Acoustic Stimulation↗

PubMed1993

The sulcus connection. On a mode of participation of outer hair cells in cochlear mechanics.

Motile outer hair cells (OHCs) can only participate well in cochlear mechanics when one end of the hair cells is more restrained in its movements than the other. On this thought a model of the organ of Corti (OoC) is developed in which (in every cross section) the tectorial membrane (TM) is considered to consist of two stiff segments connected by a hinge. Movements of the TM then induce movements of the fluid contained in the inner spiral sulcus (ISS) and the fluid dynamics of the sulcus will play an important part in restraining the top ends of the hair cells. Since the model is meant to reflect low-level phenomena, it is conceived as linear. For simplicity, it operates in the long-wave mode. The sulcus is considered as a narrow channel that is closed at both ends. Since the sulcus fluid is an independent energy-storage element of the system, the entire cochlear model, consisting of two main fluid channels, the organ of Corti (OoC), the three-element TM and the sulcus, and equipped with motile OHCs, can be described by a fourth-order differential equation, with four boundary conditions. It is shown that the model can ideally produce response curves that reflect more than 40 dB of cochlear gain. When the actual effect of the sulcus is taken into account, however, the maximum gain is reduced to approximately 30 dB. The main reason for the reduction is that the sulcus cannot produce a large enough pressure to restrain the upper ends of the OHCs.

Acoustics↗

PubMed1994

Immunohistochemical localization of keratan sulfate and chondroitin 4- and 6-sulfate proteoglycans in subregions of the tectorial and basilar membranes.

Proteoglycans containing keratan sulfate (KSPG) and 4- and 6-sulfated epitopes of chondroitin sulfate (CSPG) were identified in distinct domains of the tectorial and basilar membranes by ultrastructural immunogold labeling with monoclonal antibodies. In the tectorial membrane (TM), the highest concentration of gold particles was present in the upper fibrous layers of the limbal, middle and marginal zones with all three antibodies. Reactivity with anti-KSPG exceeded that with anti-4S and anti-6S CSPG, especially in the marginal zone. The cover net showed no reactivity for any antibody. Labeling density of gold particles with all three antibodies increased markedly from base to apex. In the basilar membrane (BM), all three PGs were most highly concentrated in regions of amorphous ground substance bordering the upper and lower filamentous bands. As in the TM, reactivity for anti-KSPG in the BM exceeded that for either CSPG antibody and staining with all three antibodies was stronger and more widespread in the apical as compared to the basal turns. These results provide the first ultrastructural demonstration of KSPG and CSPG in distinct subregions of the TM and BM. The preferential distribution and marked increase in PGs from base to apex in both TM and BM supports a role for these macromolecules in regulating structural and mechanical properties of these highly specialized extracellular membranes.

Aggrecans↗