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PubMed2005

Paget disease and sensorineural hearing loss associated with spiral ligament degeneration.

HYPOTHESIS: Previously unreported cystic degeneration of the spiral ligament in cases of Paget disease. BACKGROUND: About 70% of cases of Paget disease involve the skull, with hearing affected in approximately 50% of these. The hearing impairment may be sensorineural, mixed, or, rarely, only conductive. The etiology and pathogenesis of the hearing loss are not yet understood, and reports in the literature are inconsistent regarding the pathologic changes responsible for sensorineural hearing loss. Of six pairs of temporal bones from patients with Paget disease in the temporal bone collection of a research institution, two pairs have abnormalities not previously associated with sensorineural hearing loss or Paget disease. We report the histopathologic findings in these temporal bones. METHODS: The temporal bones were fixed in formalin, decalcified in ethylenediaminetetraacetic acid, embedded in celloidin, and sectioned in the horizontal plane at a thickness of 20 microm. Every 10th section was stained with hematoxylin-eosin and mounted on glass slides. The sections were examined by light microscopy. RESULTS: Cystic degeneration of the spiral ligament, primarily in the basal segment, was found in both cases. Endolymphatic hydrops and a small endolymphatic sac with calcification of the perisaccular tissue were found in one case. CONCLUSIONS: Cystic degeneration of the spiral ligament has not been previously reported and may be unique to Paget disease. This is consistent with recent literature showing a previously unsuspected role of the spiral ligament in sensorineural hearing loss.

Aged↗
PubMed2002

Transcript profiling of functionally related groups of genes during conditional differentiation of a mammalian cochlear hair cell line.

We have used Affymetrix high-density gene arrays to generate a temporal profile of gene expression during differentiation of UB/OC-1, a conditionally immortal cell line derived from the mouse cochlea. Gene expression was assessed daily for 14 days under differentiating conditions. The experiment was replicated in two separate populations of cells. Profiles for selected genes were correlated with those obtained by RT-PCR, TaqMan analysis, immunoblotting, and immunofluorescence. The results suggest that UB/OC-1 is derived from a population of nonsensory epithelial cells in the greater epithelial ridge that have the potential to differentiate into a hair-cell-like phenotype, without the intervention of Math1. Elements of the Notch signaling cascade were identified, including the receptor Notch3, with a transient up-regulation that suggests a role in hair cell differentiation. Several genes showed a profile similar to Notch3, including the transcriptional co-repressor Groucho1. UB/OC-1 also expressed Me1, a putative partner of Math1 that may confer competence to differentiate into hair cells. Cluster analysis revealed expression profiles for neural guidance genes associated with Gata3. The temporal dimension of this analysis provides a powerful tool to study genetic mechanisms that underlie the conversion of nonsensory epithelial cells into hair cells.

Animals↗
PubMed1993

Dynamic formant tracking of noisy speech using temporal analysis on outputs from a nonlinear cochlear model.

In this paper we take a modeling approach to studying representation of formant frequencies of spoken speech and speech in noise in the temporal responses of the peripheral auditory system. On the basis of the properties of the representation, we have devised and evaluated a cross-channel correlation algorithm and an interpeak interval analysis for automatic formant extraction of speech which is strongly dynamic in acoustic characteristics and is embedded in noise. The basilar membrane model used in this study contains laterally coupled damping elements, which are made monotonically dependent on the spatial distribution of the short-term power in the outputs of the model. Efficient digital implementation and the related salient numerical properties of the model are described. Simulation results from the model in response to speech and speech in noise illustrate temporal response patterns that are tonotopically organized in relation to speech formant parameters with little influence by the noise level. By utilizing such relations the devised cross-channel correlation algorithm is shown to be capable of accurately tracking formant movements in spoken syllables and sentences.

Algorithms↗
PubMed1986

Congenital cerebrospinal fluid fistulae of the petrous temporal bone.

Spontaneous cerebrospinal fluid fistulae from the subarachnoid space into the middle ear cavity may be classified as perilabyrinthine or translabyrinthine. The very rare perilabyrinthine group, through bony defects close to but not involving the labyrinth, usually have normal hearing initially. The commoner translabyrinthine group are nearly always associated with anacusis, severe labyrinthine dysplasia and a route via the internal auditory meatus. The labyrinthine deformity is more severe than the type classically described by Mondini, and evidence of a dilated cochlear aqueduct in these cases is also unconvincing.

Cerebrospinal Fluid Otorrhea↗
PubMed1993

Vulnerability and adaptation of distortion product otoacoustic emissions to endocochlear potential variation.

The endocochlear potential (EP) was reversibly decreased in adult gerbils by the intraperitoneal injection of furosemide, while cochlear functioning was monitored by measurement of distortion production otoacoustic emissions (DPE) at a range of stimulus intensities. Stimulus frequencies for DPEs were f1 = 6.8 and f2 = 8 kHz (f2/f1 = 1.18). Emissions monitored in the ear canal and scala media were 2f1-f2, 3f1-2f2, 2f2-f1, and f2-f1. Typically, the EP decreased smoothly, reached a minimum one-half hour after injection, then recovered slowly over several hours. Emissions at 2f1-f2 and 3f1-2f2 at low stimulus levels were particularly vulnerable to the change in EP. These vulnerable emissions showed characteristic trajectories in which the amplitudes changed little with the initial EP decrease, then dropped sharply as the EP continued to decrease. However, the amplitudes then began to recover even before the EP reached minimum, and recovered completely while the EP remained subnormal. The trajectories of the other odd order emissions were similar, but lacked the abrupt decrease. The variation of the even order (f2-f1) component was completely different, but appeared related to the odd order trajectories in a complex fashion. During the initial decrease for the vulnerable components, the decrease in emission amplitude (in dB) was found to be proportional to the square of the change in EP (in mV). The recovery with a subnormal EP was interpreted as an adaptive effect with a time constant of about 15 min.

Acoustic Stimulation↗
PubMed1999

Altered cochlear fibrocytes in a mouse model of DFN3 nonsyndromic deafness.

DFN3, an X chromosome-linked nonsyndromic mixed deafness, is caused by mutations in the BRN-4 gene, which encodes a POU transcription factor. Brn-4-deficient mice were created and found to exhibit profound deafness. No gross morphological changes were observed in the conductive ossicles or cochlea, although there was a dramatic reduction in endocochlear potential. Electron microscopy revealed severe ultrastructural alterations in cochlear spiral ligament fibrocytes. The findings suggest that these fibrocytes, which are mesenchymal in origin and for which a role in potassium ion homeostasis has been postulated, may play a critical role in auditory function.

Animals↗
PubMed1983

Alternating current delivered into the scala media alters sound pressure at the eardrum.

Alternating current delivered into the scala media of the gerbil cochlea modulates the amplitude of a test tone measured near the eardrum. Variations in the electromechanical effect with acoustic stimulus parameters and observed physiological vulnerability suggest that cochlear hair cells are the biophysical origin of the process. Cochlear hair cells have traditionally been thought of as passive receptor cells, but they may play an active role in cochlear micromechanics.

Acoustic Stimulation↗
PubMed1995

High-frequency motility of outer hair cells and the cochlear amplifier.

Outer hair cells undergo somatic elongation-contraction cycles in vitro when electrically stimulated. This "electromotile" response is assumed to underlie the high sensitivity and frequency selectivity of amplification in the mammalian cochlea. This process, presumably operating on a cycle-by-cycle basis at the frequency of the stimulus, is believed to provide mechanical feedback in vivo. However, if driven by the receptor potential of the cell, the mechanical feedback is expected to be severely attenuated at high frequencies because of electrical low-pass filtering by the outer hair cell basolateral membrane. It is proposed that electromotility at high frequencies is driven instead by extracellular potential gradients across the hair cell, and it is shown that this driving voltage is not subject to low-pass filtering and is sufficiently large. It is further shown that if the filtering properties of the cell membrane are canceled, taking advantage of the electrical characteristics of isolated outer hair cells in a partitioning glass microchamber, then the lower bound of the motor's bandwidth is approximately 22 kilohertz, a number determined only by the limitations of our instrumentation.

Acoustic Stimulation↗
PubMed2005

CT of the ear in Pendred syndrome.

PURPOSE: To prospectively determine the structural anomalies of the inner ear by using thin-section computed tomography (CT) in an extended family with Pendred syndrome. MATERIALS AND METHODS: Ethics committee approved the study, and informed consent was obtained from every patient or from parents of patients under legal age. Twelve patients (three females and nine males aged 7-47 years) with Pendred syndrome (all from the same ethnic isolate and with the same mutation in the PDS gene) were evaluated for inner-ear malformation at thin-section CT. Both ears were evaluated. Presence or absence of interscalar septum between upper and middle turns of the cochlea was evaluated, and vestibule and vestibular aqueduct were examined for enlargement. Modiolus was determined to be present or absent (modiolar deficiency). CT scans were evaluated in consensus by two radiologists (M.G., J.M.G.). RESULTS: All patients had inner ear malformation on both sides. Modiolus was absent and vestibule was enlarged on both sides in all 12 patients. Interscalar septum was absent in 18 (75%) of 24 ears. In eight patients, interscalar septum was absent in both ears, whereas in two patients, it was absent on only one side. Aqueduct was enlarged in 20 (80%) of 24 ears. In nine patients, both ears had enlarged aqueducts, while in two patients, only one side was abnormal. CONCLUSION: Inner ear malformation is an invariable finding in Pendred syndrome. Modiolus deficiency and vestibular enlargement were the most consistent anomalies in this population with Pendred syndrome.

Adolescent↗
PubMed1998

A cationic nonselective stretch-activated channel in the Reissner's membrane of the guinea pig cochlea.

The Reissner's membrane (RM) separates in the mammalian cochlea the K(+)-rich endolymph from the Na(+)-rich perilymph. The patch-clamp technique was used to investigate the transport mechanisms in epithelial cells of RM freshly dissected from the guinea pig cochlea. This study shows a stretch-activated nonselective cationic channel (SA channel) with a linear current-voltage relationship (23 pS) highly selective for cations over anions [K+ approximately Na+ (1) > Ba2+ (0.65) > Ca2+ (0.32) >> Cl- (0.14)] and activated by the intrapipette gradient pressure. The open probability-pressure relationship is best fitted by a Boltzmann distribution (half-maximal pressure = 37.8 mmHg, slope constant = 8.2 mmHg). SA channels exhibit a strong voltage dependency and are insensitive to internal Ca2+, ATP, and fenamates but are blocked by 1 microM GdCl3 in the pipette. They are reversibly activated by in situ superfusion of the cell with hyposmotic solutions. Kinetic studies show that depolarization and mechanical or osmotic stretch modify the closed and open time constants probably by a different mechanism. These channels could participate in pressure-induced modifications of ionic permeability of the RM.

Animals↗
PubMedDate not supplied

4-aminopyridine in scala media reversibly alters the cochlear potentials and suppresses electrically evoked oto-acoustic emissions.

Iontophoresis of 4-aminopyridine into scala media of the guinea pig cochlea caused elevation of the thresholds of the compound action potential of the auditory nerve, loss of amplitude of the extracellular cochlear microphonic response (CM), increase in the endocochlear potential (EP) and reduction in the amplitude of electrically evoked oto-acoustic emissions (EEOAEs). These changes were reversible over 10-20 min. The reciprocity of the changes in the CM and the EP was consistent with an interruption of both DC and AC currents through outer hair cells (OHCs), probably by blockade of mechano-electrical transduction (MET) channels in OHCs. Reductions in EEOAEs were consistent with the extrinsically applied generating current entering the OHC via the MET channels. Implications for the activation of OHC electromotility in vivo are discussed.

4-Aminopyridine↗
PubMed2004

Time course of dehydrating effects of isosorbide on experimentally induced endolymphatic hydrops in guinea pigs.

Osmotic diuretics are therapeutic agents used to reduce endolymphatic hydrops. However, glycerol-induced change in endolymph volume is followed by a rebound phenomenon. In this study, we investigated the rebound phenomenon occurring with isosorbide, an osmotic diuretic used as a therapeutic agent for Ménière's disease in Japan. Forty guinea pigs underwent surgical obliteration of the endolymphatic sac. Thirty received isosorbide orally 1 month after surgery. These animals were sacrificed 3, 6, or 12 h after isosorbide intake. The remaining 10 animals served as controls. Quantitative assessment of changes in the endolymphatic space was performed light-microscopically. Isosorbide reduced cochlear endolymph volume, with a peak reduction 6 h after intake. Thereafter, no prominent rebound phenomenon was noted. Clinically, since isosorbide is orally administered every 8 h, rebound phenomenon need not be considered in the treatment with isosorbide.

Administration, Oral↗
PubMed2005

Communication between the perilymphatic scalae and spiral ligament visualized by in vivo MRI.

We evaluated the transport of Gadolinium-diethylenetriaminepentaacetate-bismethylamide (Gd-DTPA-BMA) through the round window (RW) membrane into the perilymphatic space with 4.7-T MRI in an animal study and 1.5-T MRI in humans. After administration of Gd-DTPA-BMA onto the intact RW membrane of guinea pig, Gd-DTPA-BMA uptake was observed in the basal turn and part of the second turn within 40 min. The scala tympani, scala vestibuli, the fibrous part of the spiral ligament and semicircular canal all showed uptake of Gd-DTPA-BMA. All turns of the cochlea were filled with Gd within 10 min in the perforated RW membrane administration group and within 30 min in the intravenous administration group. In patients who accepted middle ear injection of Gd-DTPA-BMA, uptake was observed within 2 h in the basal turn and semicircular canal. After 12 h the apex did still not show any uptake. Gd-DTPA-BMA is transported from the RW to the semicircular canal, the scala tympani and scala vestibuli without passing the helicotrema.

Animals↗
PubMed2005

BAPTA induces frequency shifts in vivo of spontaneous otoacoustic emissions of the bobtail lizard.

Spontaneous otoacoustic emissions (SOAEs) are indicators of active processes in the inner ear and are found in all classes of land vertebrates. In the Australian bobtail lizard, earlier work showed that otoacoustic emissions are generated by an active motility process in the hair-cell bundle. This is likely to be driven by calcium-sensitive mechanisms implicated in other non-mammalian hair cell systems. If so, it should be fundamentally influenced by the extracellular calcium concentration. In in vitro studies, the rate of force generation in hair cell stereovilli is linked to the extracellular calcium concentration. In such preparations, low-calcium solutions, buffered by the calcium chelator BAPTA, were reported to change the frequency of hair cell bundle oscillations. In the present study, BAPTA was iontophoresed into the endolymph of the bobtail skink in vivo, and SOAEs were monitored. Application of BAPTA resulted in a prolonged downward shift in the frequency of individual SOAE spectral peaks. Recovery took more than 1 h, consistent with a slow clearance of BAPTA from endolymph. SOAE peak amplitudes were most often enhanced, suggesting there was no functional disruption of tip links. The direction and degree of frequency shifts were consistent with in vitro and in vivo data showing the effects of changing calcium concentrations in the endolymph directly.

Anesthesia↗
PubMed1976

Surface morphology of the bullfrog amphibian papilla.

The bullfrog amphibian papilla, which has been identified as the peripheral source of two of the three types of auditory axon in that animal, is shown to have a continual distribution of receptor types based on surface topography, but a dichotomy of types based on the adjacent tectorium and its apparent mechanical linkage to the receptors and their supporting cells and a second dichotomy based on receptor polarization patterns. Each dichotomy divides the receptors into two approximately equal populations and thus might correspond to the previously observed division of primary axons into two frequency-response types.

Animals↗
PubMed1976

Attachment of the inner sensory cell hairs to the tectorial membrane. A scanning electron microscopic study.

The residue of tectorial membrane insertion of cochlear inner sensory cell hairs was studied under a scanning electron microscope. In addition to the clear imprints resulting from outer sensory cell hair insertions, an adjacent medial row of bow-shaped imprints was noted on the base of the tectorial membrane. The relative position of these imprints corresponded to the location and the size of the inner cell hairs. These imprints were thus thought to arise from the insertion of the inner sensory hair cells. Such imprints were found only in the lower turns of the cat's cochlea, but not on the guinea pig tectorial membrane. Thus an actual physical contact between the tectorial membrane and the inner sensory cell hiars may exist in some species but not in others, and when there is physical contact, it is thought to be less firm than that of the outer sensory hair cells.

Animals↗