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PubMed2004

Col11a1 and Col11a2 mRNA expression in the developing mouse cochlea: implications for the correlation of hearing loss phenotype with mutant type XI collagen genotype.

OBJECTIVE: Mutations in the fibrillar collagen genes COL11A1 and COL11A2 can cause sensorineural hearing loss associated with Stickler syndrome. There is a correlation of hearing loss severity, onset, progression and affected frequencies with the underlying mutated collagen gene. We sought to determine whether differences in spatial or temporal expression of these genes underlie this correlation, and to identify the cochlear cell populations expressing these genes and the structures likely to be affected by mutations. MATERIALS AND METHODS: We used in situ hybridization analysis of C57BL/6J mouse temporal bones. RESULTS: Similar, diffuse expression of Col11a1 and Col11a2 mRNA was first observed in the cochlear duct at embryonic Day 15.5, with increasingly focal hybridization being noted at postnatal Days 1 and 5 in the greater epithelial ridge and lateral wall of the cochlea. The greater epithelial ridge appeared to be the main, if not only, source of mRNA encoding Col11a1 and Col11a2 in the tectorial membrane. At postnatal Day 13, Col11a1 and Col11a2 expression became more focal and co-localized in the inner sulcus, Claudius' cells and cells of Boettcher. CONCLUSIONS: We did not observe spatial or temporal differences in mRNA expression that could account for the auditory phenotype genotype correlation. The expression patterns suggest essential roles for Col11a1 and Col11a2 in the basilar or tectorial membranes.

Animals↗

PubMed2006

Rupture of Reissner's membrane during acute endolymphatic hydrops in the guinea pig: a model for Ménière's disease?

CONCLUSION: The changes in cochlear function during a destructive acute endolymphatic hydrops were relatively small. This might be consistent with the hypothesis that an endolymphatic hydrops is a marker of disordered inner ear homeostasis rather than the cause of the clinical symptoms of Ménière's disease. OBJECTIVE: Assessment of cochlear function during induction of a destructive acute endolymphatic hydrops. MATERIALS AND METHODS: During repetitive microinjections of 0.5 microl of artificial endolymph at a rate of 50 nl/s the 2f1-f2 and f2-f1 cochlear microphonics distortion products (CMDP) and 2f1-f2 distortion products otoacoustic emissions (DPOAE) were recorded in the guinea pig. RESULTS: A 'catastrophe' occurred in the inner ear when 2.5-3.5 microl of artificial endolymph was injected. A rupture of Reissner's membrane was then found, most often in the apical turn of the cochlea. This rupture had only minor effects on the endocochlear potential, whereas it caused a marked decrease in 2f1-f2 DPOAE amplitude. The 2f1-f2 and f2-f1 CMDP amplitude increased during each injection prior to the rupture. After the rupture the f2-f1 CMDP amplitude decreased during each injection, possibly due to a shift of the cochlear transducer operating point position.

Animals↗

PubMed1998

Failure of forskolin to elevate the endocochlear potential in experimental endolymphatic hydrops of the guinea pig.

The effect of forskolin (FSK) on the endocochlear potential (EP) in scala media (SM) was examined in experimental endolymphatic hydrops of the guinea pig. Two weeks after obliteration of the endolymphatic sac the EP of hydroptic ears and that of the contralateral control ears were measured by means of microelectrodes. The perfusion of scala vestibuli (SV) with FSK (200 microM) produced EP elevation in the contralateral control ears but failed to do so in the experimental hydroptic ears. Histological examination of experimental endolymphatic hydrops showed mild hydrops with intact appearance of outer and inner hair cells, and the stria vascularis. The mechanism underlying the failure of FSK to elevate the EP in experimental endolymphatic hydrops is discussed.

Animals↗

PubMed1999

Changes in off-lesion endocochlear potential following localized lesion in the lateral wall.

Endocochlear potential (EP) was measured at various off-lesion sites after a small focal lesion was made in the lateral wall of the guinea pig cochlea. Lesions were produced by a photochemical reaction between systemically administered rose bengal and focused green light illumination. In 21 ears, continuous measurement for 30 min after onset of the reaction at turns apical or basal to the site of illumination revealed no significant changes in EP compared with the control value (p < 0.01). In another group of 43 ears, EP was measured at 3 days post-illumination. A significant decline was seen at every site located apical to the lesion (p < 0.001). Conversely, no significant change was measured at any site located basal to the lesion. These findings suggest that the decrease in EP assumes the form of a gradient from the lower to upper turns in the guinea pig cochlea.

Analysis of Variance↗

PubMed2002

Mutation of a transcription factor, TFCP2L3, causes progressive autosomal dominant hearing loss, DFNA28.

We ascertained a large American family with an autosomal dominant form of progressive non-syndromic sensorineural hearing loss. After excluding linkage to known deafness loci, we performed a genome-wide scan and found linkage to marker GAAT1A4 on chromosome 8q22 (LOD=5.12 at theta=0), and this locus was designated DFNA28. Sequencing of six candidate genes in the 1.4 cM linked region identified a frameshift mutation (1609-1610insC) resulting in a premature translation stop codon in exon 14 of the gene TFCP2L3 (transcription factor cellular promoter 2-like 3). TFCP2L3 is a member of a family of transcription factor genes whose archetype is TFCP2, a mammalian homolog of the Drosophila gene grainyhead. Northern blot analyses and in situ hybridization studies show that mouse Tfcp2l3 is expressed in many epithelial tissues, including cells lining the cochlear duct, at embryonic day 18.5 and postnatal day 5.

Adolescent↗

PubMed1986

Recent developments in cochlear physiology.

Recent findings in cochlear physiology have caused many of our long held ideas about how sound is analyzed by the ear to be reevaluated. This article describes changes which have occurred in three classical ideas of cochlear transduction: (1) There is a gradient of frequency representation along the cochlea with high frequencies being represented at the base and lower frequencies represented progressively toward the apex. It is now known that the specific frequency which is represented at a given location along the cochlea is not invariant but changes systematically during the normal development of hearing. (2) The place code and frequency tuning along the cochlea are due to the conventional traveling wave of von Békésy and basilar membrane mechanics. Experiments in nonmammalian vertebrates which lack a traveling wave have shown that other mechanisms, including the mechanical resonance of hair cell stereocilia, may contribute to tonotopic organization and frequency tuning. It is possible that hair cell stereocilia also contribute to frequency representation and tuning in the mammalian cochlea. (3) The vibration of the basilar membrane to sound is determined by its passive mechanical properties. It is now known that the response of the basilar membrane, and that of the cochlear partition as a whole, is influenced by physiological processes which utilize metabolic energy. The active processes are likely expressed through the motile activity of outer hair cells.

Audiometry, Pure-Tone↗

PubMed2000

Developmental expression of aquaporin 2 in the mouse inner ear.

OBJECTIVES: The maintenance of endolymph homeostasis is critical for the inner ear to perform its functions of hearing and maintaining balance. The identification and cloning of aquaporins (a family of water channel proteins) has allowed the study of a novel cellular mechanism potentially involved in endolymph homeostasis. The objective of the present study was to define the developmental temporal and spatial expression pattern of aquaporin 2 (Aqp2) in the developing mouse inner ear. STUDY DESIGN: A systematic immunohistochemical study of Aqp2 protein expression was performed on embryonic mouse inner ears ranging from embryonic day 10 (otocyst stage) to embryonic day 18 (just before birth). METHODS: Serial cryosections of embryonic mouse inner ears were used for immunohistochemical experiments. A rabbit polyclonal antisera raised against a synthetic Aqp2 peptide was used with a standard nickel intensified 3,3-diaminobenzidine reaction protocol for immunolocalization of Aqp2 in tissue sections. RESULTS: Aquaporin 2 is expressed diffusely in the early otocyst, then becomes progressively restricted as the inner ear matures. During early cochlear duct formation (embryonic days 12 and 13), expression of Aqp2 is homogeneous; later, it becomes restricted to specific regions of the endolymphatic compartment (embryonic days 15 and 18). Similar restriction of expression patterns could be noted for the vestibular structures. Endolymphatic duct and sac and stria vascularis expression of Aqp2 was noted to occur fairly late during development but demonstrated a distinct pattern of immunolabeling. CONCLUSIONS: Aquaporin 2 shows an early and specific pattern of expression in the developing mouse inner ear, suggesting a significant role for this water channel protein in the development of endolymph homeostasis and meriting further functional studies of Aqp2 in the inner ear.

Animals↗

PubMed2002

Specification of the mammalian cochlea is dependent on Sonic hedgehog.

Organization of the inner ear into auditory and vestibular components is dependent on localized patterns of gene expression within the otic vesicle. Surrounding tissues are known to influence compartmentalization of the otic vesicle, yet the participating signals remain unclear. This study identifies Sonic hedgehog (Shh) secreted by the notochord and/or floor plate as a primary regulator of auditory cell fates within the mouse inner ear. Whereas otic induction proceeds normally in Shh(-/-) embryos, morphogenesis of the inner ear is greatly perturbed by midgestation. Ventral otic derivatives including the cochlear duct and cochleovestibular ganglia failed to develop in the absence of Shh. The origin of the inner ear defects in Shh(-/-) embryos could be traced back to alterations in the expression of a number of genes involved in cell fate specification including Pax2, Otx1, Otx2, Tbx1, and Ngn1. We further show that several of these genes are targets of Shh signaling given their ectopic activation in transgenic mice that misexpress Shh in the inner ear. Taken together, our data support a model whereby auditory cell fates in the otic vesicle are established by the direct action of Shh.

Animals↗

PubMed1981

Scanning electron microscopy of the normal human cochlea.

Preservation of the fine structures of the human cochlea has been achieved by perfusing the cochlea with fixative shortly after death. Following the dissection of the temporal bone the surface of the organ of Corti and stria vascularis has been examined in the scanning electron microscope. The surfaces of the inner and outer hair cells can be seen and the stereocilia projecting from their surfaces closely examined. The number and length of the stereocilia of the outer hair cells changes linearly with distance along the cochlear duct. The surface of the stria vascularis is similar to that seen in other animals.

Adult↗

PubMedDate not supplied

Low-field magnetic resonance imaging of the canine middle and inner ear.

A series of low-field magnetic resonance images of the normal canine middle and inner ear are presented to serve as a reference. A completely balanced steady-state gradient echo pulse sequence with a slice thickness of 0.9 mm can be used to acquire images of the relevant structures within and neighboring the inner ear. These were the cochlear duct, semicircular ducts, vestibule, facial and vestibulocochlear nerves, as well as the temporal sinus. Within the middle ear, no applied sequence was able to allow identification of the auditory ossicles or the tympanic membrane.

Animals↗

PubMed2001

Development of the vertebrate inner ear.

The inner ear, also called the membranous labyrinth, contains the cochlea, which is responsible for the sense of hearing, and the vestibular apparatus, which is necessary for the sense of balance and gravity. The inner ear arises in the embryo from placodes, which are epithelial thickenings of the cranial ectoderm symmetrically located on either side of hindbrain rhombomeres 5 and 6. Placode formation in mice is first visible at the 12-somite stage and is controlled by surrounding tissues, the paraxial mesoderm and neural ectoderm. Diffusible molecules such as growth factors play an important role in this process. The activity of several genes confers the identity to the placodal cells. Subsequent cellular proliferation processes under influences from the adjacent hindbrain cause the inner ear epithelium to invaginate and form a vesicle called the otocyst. Combinatorial expression of several genes and diffusible factors secreted from the vesicle epithelium and hindbrain control specification of distinct inner ear compartments. Transplantation studies and inner ear in vitro cultures show that each of these compartments is already committed to develop unique inner ear structures. Later developmental periods are principally characterized by intrinsic differentiation processes. In particular, sensory patches differentiate into fully functional sensory epithelia, and the semicircular canals along with the cochlear duct are elaborated and ossified.

Animals↗

PubMed1971

A study of the electrochemistry and osmotic relationships of the cochlear fluids in the neonatal rat at the time of the development of the endocochlear potential.

1. Changes in the endocochlear potential between the 8th and 18th days after birth were investigated in the rat. Initially the potential was low but its magnitude increased rapidly between the 11th and 16th day. During the 13th and 14th days the rate of increase was approximately 1 mV/hr.2. The rapid potential increase arose virtually simultaneously in all three turns of the cochlea.3. Histological examination revealed the cochlea, including the hair cells of Corti's organ and the stria vascularis, to be fully mature before the period of rapid change in the endocochlear potential, apart from the cells of Claudius, whose final development coincided with the latter part of this phase.4. The endolymphatic sodium concentration (average 1.0 m-equiv/l.) had attained the very low adult level in the earliest period studied. The potassium and chloride concentrations were slightly below the normal adult levels, the result of some degree of general hypo-osmolality present at this time.5. The endolymphatic ionic concentrations remained unchanged during the phase of rapid increase in the endocochlear potential.6. The findings thus indicate that the distinctive endolymphatic ionic composition and the endocochlear potential arise largely independently and in succession during cochlear maturation.7. No differences in osmotic pressure were demonstrated between endolymph, perilymph and serum. The problems concerning the homoeostasis of the inner ear fluids do not consequently seem to be complicated by unusual hydrodynamic aspects.8. Alterations in body fluid osmolality, produced by intraperitoneal injection of water or hypertonic glycerol, were accompanied by simultaneous changes in the osmotic pressures of the inner ear fluids. Some portion of the membranes bounding the endolymphatic space is therefore considered to be freely permeable to water.9. The investigations provide no further information about the nature of the endocochlear potential, although an increase in the electrical resistance of the cochlear duct membranes is thought responsible for its appearance. The time relationships of this period support the concept that the potential is an essential feature of the mechano-electric transduction process.

Animals↗

PubMed1979

The spectral content of the cochlear microphonic measured in scala media of the guinea pig cochlea.

Cochlear microphonic (CM) in response to low-frequency tonal stimuli, measured as a function of sound-pressure level (SPL) in scala media of the guinea pig cochlea, was averaged and Fourier analyzed. The slope of the amplitude of the Nth CM harmonic versus sound intensity in log-log coordinates was approximately N (1 less than or equal to N less than or equal to 5) in the first three cochlear turns, but notable variations on such a slope rule were found to apply to CM in turn I. CM harmonic phases plotted versus SPL were found to group into two distinctive categories expressly delimited by whether the order of the harmonic was even or odd. Some difference between CM recorded between scala media and scala tympani and recorded between scala media and the animal's neck could be attributed to neural contamination. We also found CM in its saturation region to have a hysteretic relation to the input sound pressure. At high sound levels, large, physiologically produced acoustic harmonics existed at the animal's eardrum. Our data support an asymmetrical, saturating, single-valued nonlinearity as a model for CM generation at low sound levels. At higher sound levels a different, more complex, hysteretic nonlinearity seems mandatory.

Acoustic Stimulation↗

PubMed1979

Comparison of the spectra of the cochlear microphonic and of the sound-elicited electrical impedance changes measured in scala media of the guinea pig.

The harmonic structure of the cochlear microphonic (CM) and that of a sound-elicited signal which we have considered as an (apparent) changing resistance (CR) were simultaneously determined in scala media of the first turn of the guinea pig cochlea. We analyzed our data in the context of the Davis variable resistance hair-cell model (1965), which predicts CM and CR to be proportional to each other. But, plotted as functions of the sound-pressure level, CM and CR were found to have qualitatively similar but quantitatively disproportionate spectra. The preparations with the highest endolymphatic potential showed the least correspondence between the spectra of the two measured quantities. The phase angles of the fundamental components in CM and CR were equal within approximately 10 degrees, but the phase of the even harmonics of the two independent measures commonly differed by approximately 180 degrees at lower SPLs. Although most data were collected using 160-Hz tonal stimulation, tones with frequencies up to 1280 Hz produced qualitatively similar results. The CM and the CR both varied slightly with the level of the alternating current used to probe the CR. Considered on a quantitative basis, consistent with the accuracy of our measurements, any model which reduces to a fixed source, a fixed resistance, and a single linear, time-varying resistance cannot mimic the most significant, commonly found aspects of our CM and CR data. An alternate model incorporating a nonlinear, time-invariant resistance is able to account for some of the data. The output of the model is correctly considered a (time) changing resistance, or apparent changing resistance; but the model demonstrates that similar experimental results are not necessarily evidence for a time-varying resistor as originally proposed by Davis.

Acoustic Stimulation↗

PubMed1979

Loss of auditory sensitivity following exposure to spectrally narrow impulses.

Damage-risk criteria (DRC) for impulse noise do not presently take the spectrum of an impulse into direct account; yet it is clear that the ear is spectrally tuned. In order to establish the sensitivity of various sections of the cochlear duct to trauma from impulses, ears were exposed to 100 spectrally narrow impulses (1.0, 5.0, or 10.0 kHz) delivered in 10 min. Changes in auditory sensitivity were measured by an electrocochleographic technique in 43 cat ears and a threshold of loss established for each type of impulse. Expressed in SPL at the ear drum, the loss threshold rose at 3.2 dB/octave between 1.0 and 10.0 kHz. Expressed in stapes displacements, the loss threshold fell at 5.4 dB/octave in the same region. This curve was used to establish a tentative shape for a DRC for the human ear for impulse noise. The patterns of loss, rates of loss, lack of recovery, and loss thresholds are discussed with respect to their probable physiological basis with conclusion that mechanical displacement rather than metabolic exhaustion is the most reasonable causative factor.

Animals↗

PubMed1987

Use of phase contrast microscopy to determine the height of the organ of Corti in whole-mount preparations.

A technique has been developed to measure the height of the organ of Corti (OC) in the whole-mount preparations of the cochlear duct. The technique corrects for variations in the microscope system, such as the magnification of the objective lens and the mechanical properties of the fine-focus knob, as well as the refractive index of the embedding medium and the angle of specimens with respect to the optical axis of the microscope. At 11 percentage locations from apex to base, the height of the OC in ten chinchilla cochleas was measured at three positions: (1) the lateral edge of the inner hair cell (IHC); (2) the medial edge of the first row outer hair cell (OHC1); and (3) the lateral edge of the third row outer hair cell (OHC3). These measurements were compared to measurements made on radial sections from five other cochleas, with very good agreement at IHC and OHC3, and fairly good agreement at OHC1. The height at OHC3 varied almost linearly with percentage distance along the OC, ranging from 96 microns (apical end) to 51 microns (basal end). The height at the OHC1 varied from 77 to 49 microns, but did not vary linearly. The height of the IHC was relatively constant, from 50 to 60 microns, except at the basal end, where it decreased to 42 microns.

Animals↗

PubMed2000

Three-dimensional numerical modeling for global cochlear dynamics.

A hybrid analytical-numerical model using Galerkin approximation to variational equations has been developed for predicting global cochlear responses. The formulation provides a flexible framework capable of incorporating morphologically based mechanical models of the cochlear partition and realistic geometry. The framework is applied for a simplified model with an emphasis on application of hybrid methods for three-dimensional modeling. The resulting formulation is modular, where matrices representing fluid and cochlear partition are constructed independently. Computational cost is reduced using two methods, a modal-finite-element method and a boundary element-finite-element method. The first uses a cross-mode expansion of fluid pressure (2.5D model) and the second uses a waveguide Green's-function-based boundary element method (BEM). A novel wave number approach to the boundary element formulation for interior problem results in efficient computation of the finite-element matrix. For the two methods a convergence study is undertaken using a simplified passive structural model of cochlear partition. It is shown that basilar membrane velocity close to best place is influenced by fluid and structural discretization. Cochlear duct pressure fields are also shown demonstrating the 3D nature of pressure near best place.

Auditory Perception↗

PubMedDate not supplied

Cochlear model with three-dimensional fluid, inner sulcus and feed-forward mechanism.

A three-dimensional model of the guinea pig cochlea using the phase-integral method is presented. This model incorporates the viscous fluid effects in the cochlea, dimensional and material property variation along the cochlear duct and the active feed-forward mechanism of the outer hair cells. Two degrees of freedom of the basilar membrane are considered, which results in two traveling waves propagating along the duct for a given frequency. Basilar membrane response with the active feed-forward mechanism compares favorably with published experimental measurements.

Acoustic Stimulation↗