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At least 271 records · Page 15Linked to original sources

PubMed1996

Mechanical response characteristics of the hearing organ in the low-frequency regions of the cochlea.

1. With the use of an in vitro preparation of the guinea pig temporal bone, in which the apical turns of the cochlea are exposed, the mechanical and electrical responses of the cochlea in the low-frequency regions were studied during sound stimulation. 2. The mechanical characteristics were investigated in the fourth and third turns of the cochlea with the use of laser heterodyne interferometry, which allows the vibratory responses of both sensory and supporting cells to be recorded. The electrical responses, which can be maintained for several hours, were recorded only in the most apical turn. 3. In the most apical turn, the frequency locations and shapes of the mechanical and electrical responses were very similar. 4. The shapes of the tuning curves and the spatial locations of the frequency maxima in the temporal bone preparation compared very favorably with published results from in vivo recordings of hair cell receptor potentials and sound-induced vibrations of the Reissner's membrane. 5. Compressive nonlinearities were present in both the mechanical and the electrical responses at moderate sound pressure levels. 6. The mechanical tuning changed along the length of the cochlea, the center frequencies in the fourth and third turns being approximately 280 and 570 Hz, respectively. 7. The mechanical responses of sensory and supporting cells were almost identical in shape but differed significantly in amplitude radially across the reticular lamina.

Acoustic Stimulation↗

PubMed2000

Functional expression of three P2X(2) receptor splice variants from guinea pig cochlea.

ATP has been suggested to act as a neurotransmitter or a neuromodulator in the cochlea. The responses to ATP in different cell types of the cochlea vary in terms of the rate of desensitization and magnitude, suggesting that there may be different subtypes of P2X receptors distributed in the cochlea. Recently three ionotropic P2X(2) receptor splice variants, P2X(2-1), P2X(2-2), and P2X(2-3,) were isolated and sequenced from a guinea pig cochlear cDNA library. To test the hypothesis that these different splice variants could be expressed as functional homomeric receptors, the three P2X(2) receptor variants were individually and transiently expressed in human embryonic kidney cells (HEK293). The biophysical and pharmacological properties of these receptors were characterized using the whole cell patch-clamp technique. Extracellular application of ATP induced an inward current in HEK293 cells containing each of the three splice variants in a dose-dependent manner indicating the expression of homomeric receptors. Current-voltage (I-V) relationships for the ATP-gated current show that the three subtypes of the P2X(2) receptor had a similar reversal potential and an inward rectification index (I(50 mV)/I(-50 mV)). However, the ATP-induced currents in cells expressing P2X(2-1) and P2X(2-2) variants were large and desensitized rapidly whereas the current in those cells expressing the P2X(2-3) variant was much smaller and desensitized slower. The order of potency to ATP agonists was 2-MeSATP > ATP > alpha,beta -MeATP for all three expressed splice variants. The ATP receptor antagonists suramin and PPADS reduced the effects of ATP on all three variants. Results demonstrate that three P2X(2) splice variants from guinea pig cochlea, P2X(2-1), P2X(2-2), and P2X(2-3), can individually form nonselective cation receptor channels when these subunits are expressed in HEK293 cells. The distinct properties of these P2X(2) receptor splice variants may contribute to the differences in the response to ATP observed in native cochlear cells.

Adenosine Triphosphate↗

PubMed1987

The cochlea in gerbilline rodents.

The inner ears of 5 different gerbil species are compared on the basis of cochlear microphonic recordings, serial sections and computerized quantitative reconstructions of the cochleae and their specific morphological structures. The hearing range of most gerbils is below 20 kHz. Some species are extremely sensitive in the frequency range of 1-4 kHz. This special sensitivity is reflected in, among other features, the following cochlear structures and their suggested functions: (1) the rapid width increase of the basilar membrane in the basal portion of the cochlea provides additional space for the representation of lower frequencies at the expense of higher frequencies; (2) the large hyaline mass and the cells of Claudius and Hensen in the medial and apical portions of the cochlea influence the vibratory properties of the cochlear partition, and (3) the specialized structures of the cochlea may be an adaptation to the acoustical environment in arid habitats.

Adaptation, Biological↗

PubMedDate not supplied

Activity elicited in the auditory pathway of the rat by electrical stimulation of the cochlea.

The activity elicited by electrical stimulation of the cochlea in the auditory pathway was assessed in an animal model of cochlear implants on the basis of the induction of the immediate early gene c-fos and single neuron recordings. Electrical stimulation of the cochlea induced Fos-like immunoreactivity in the cochlear nucleus, mainly in its dorsal nucleus, in the superior olivary complex, in the lateral lemniscus, but not in the central nucleus of the inferior colliculus, the main relay nucleus in the auditory midbrain. However, single unit recordings from the inferior colliculus, ipsilateral and contralateral to the electrically stimulated cochlea, showed clear responses of single neurons, reminiscent of those elicited by acoustic stimulation. These findings provide immunocytochemical and electrophysiological evidence that the various nuclei of the auditory pathway are activated by electrical stimulation of the cochlea.

Animals↗

PubMedDate not supplied

Efferent innervation of the cochlea.

The origin of the efferent innervation of the cochlea was investigated in the guinea pigs. Horseradish peroxidase (HRP) was injected into the cochlea and transported to the brainstem by retrograde axonal transport of the efferent fibers, showing the origin of the crossed an uncrossed olivocochlear bundles of Rasmussen. HRP-labeled neurons were found in various nuclei of the superior olivary complex bilaterally. Ipsilateral to the injected cochlea ther were three times more cells than on the contralateral side. About 40% of the total number of labeled neurons, a remarkable quantity, occurred in the ipsilateral lateral superior olivary nucleus. Moreover, extraolivary origin of the efferent innervation of the cochlea could be demonstrated bilaterally in the ventral nucleus of the lateral lemniscus.

Animals↗

PubMedDate not supplied

Frozen-section autoradiography of the cochlea: evidence for differential distribution of amino acids.

A histological method is described for embedding the whole cochlea in an egg yolk medium that permits frozen sectioning in the mid-modiolar plane. Resulting tissues can be processed using standard autoradiographic techniques and stained with Nissl or silver impregnation methods. Following identical intracochlear injections of tritiated proline or leucine and frozen sectioning of embedded cochleae, differential uptake patterns within the cochlea were revealed for these amino acids. Frozen sectioning of the cochlea promises to provide an efficient means to examine specific labeling patterns within the cochlear duct for compounds suspected of contributing to cochlear function by permitting the application of multiple histological techniques including routine stains and anterograde and retrograde tracers.

Animals↗

PubMedDate not supplied

Effect of high intensity impulse noise on the vascular system of the chinchilla cochlea.

Changes in the vasculature of the chinchilla cochlea were quantitatively assessed 45 days after impulse noise exposure of either 155- or 160-dB peak sound pressure level. The condition of the vessels in the lateral wall and spiral lamina of each cochlea was evaluated in terms of 20 morphological parameters. Multivariate statistical analysis identified the parameters that were significantly affected by the noise exposure. Evaluation of these significant parameters indicated a net reduction in blood flow to the cochlea. All of the noise-exposed cochleas showed vascular changes when compared to controls, and the magnitude of these changes was related to the amount of hair cell loss. The vascular changes are presumed to be permanent.

Animals↗

PubMedDate not supplied

Multichannel cochlear implants in partially ossified cochleas.

Deposition of bone within the fluid spaces of the cochlea is encountered commonly in cochlear implant candidates and previously has been considered a relative contraindication to the use of multichannel intracochlear electrodes. This contraindication has been based on possible mechanical difficulty with electrode insertion as well as uncertainty about the potential benefit of the multichannel device in the patient. Fifteen profoundly deaf patients with partial ossification of the basal turn of the cochlea received implants with long intracochlear electrodes (11, Nucleus; 1, University of California at San Francisco/Storz; and 3, Symbion/Inneraid). In 11 cases, ossification had been predicted preoperatively by computed tomographic scan. Electrodes were completely inserted in 14 patients, and partial insertion was accomplished in one patient. All patients currently are using their devices and nine of 12 postlingually deaf patients have achieved some degree of open-set speech discrimination. This series demonstrates that in experienced hands, insertion of long multichannel electrodes into partially ossified cochleas is possible and that results are similar to those achieved in patients who have nonossified cochleas.

Adolescent↗

PubMed1990

Endoscopy of the cochlea during cochlear implantation.

We have previously demonstrated that multichannel cochlear implants may be effective in partially obstructed cochleas. In practice, however, it may be difficult to determine whether electrode insertion is feasible prior to attempting it. Initial trials with a flexible fiberoptic otologic endoscope on 10 cadaver temporal bones were previously reported. On the basis of these trials, endoscopy of the inferior segment of the cochlea during cochlear implantation seemed feasible. In the present study, the same endoscope was used on eight subjects undergoing cochlear implantation, six of whom had partially obstructed cochleas. Endoscopy was found to be helpful in visualizing obstructed segments, determining patency after the obstruction was removed, and identifying normal structures of the cochlea. Documentation with videotape and 35-mm photography constitutes the majority of this paper.

Adolescent↗

PubMedDate not supplied

Ototoxicity: an argument for evaluation of the cochlea in safety testing in animals.

The cochlea is one of the more common targets for toxic effects, yet current toxicologic screening in animals does not routinely evaluate the cochlea as a potential target organ. Although histopathologic sections are routinely taken from the eye and the optic nerve and tract and most studies include at least 1 section through the nasal cavity and olfactory mucosa, the cochlea is not histopathologically examined in routine toxicity studies. Unfortunately, routine clinical examinations frequently miss ototoxicity because rodents and other species can lose most of their high-frequency hearing and still respond to most ambient noises. Ototoxicity as a deficiency in toxicologic screening can be remedied by using well-established histopathologic and behavioral methods or electrophysiologic methods, such as brain stem auditory evoked responses (BAERs). Once the equipment is in place, BAERs can be obtained quickly and easily for ototoxicity screening (approximately 15 minutes for paired testing of 2 rats and 30 minutes each for dogs). BAERs also can be used in virtually all mammalian species. Three or 4 probe frequencies (eg, 4, 8, 16, and 32 kHz), representing different areas of the cochlea, can be tested in a few minutes with subcutaneous electrodes under short-acting chemorestraint. Given the availability of several approaches to screening for ototoxicity and the importance of the auditory function in human health, safety tests of chemicals and drugs should include an effective screening test for ototoxicity.

Animals↗

PubMed1989

Distribution of immunoreactive Na+,K+-ATPase in gerbil cochlea.

The distribution of Na+,K+-ATPase was mapped in cochleas of mature gerbils with normal hearing, using a specific and sensitive immunocytochemical method. Na+,K+-ATPase was abundant in the basolateral plasma membrane of marginal cells in the stria vascularis. Considerable levels of enzyme were also associated with the surfaces of spiral ganglion neurons and their central and peripheral processes. An unexpected finding was the detection of high levels of immunoreactive Na+,K+-ATPase in three different populations of cells lying in the inferior portion of the spiral ligament and at the medial and lateral border of the scala vestibuli just superior to the attachment of Reissner's membrane. Cells in these areas shared the morphological characteristics of cells specialized for active transport but appeared to be nonpolarized, suggesting a uniform distribution of Na+,K+-ATPase over their entire plasmalemma. The presence of these three distinct cell populations in the cochlea of several mammalian species suggests that they play an important role in cochlear function, perhaps that of regulating the cation content of perilymph. The absence of discrete concentrations of Na+,K+-ATPase-rich cells in the perilymphatic connective tissue of the bird cochlea and the mammalian vestibular system suggests further that these cells may be involved with generating and maintaining the high endolymphatic potential unique to the mammalian cochlea.

Animals↗

PubMed2005

Influence of carbon dioxide laser irradiation on the morphology and function of guinea pig cochlea.

Both experimental and clinical studies have demonstrated that carbon dioxide laser is suitable for stapedotomy. The aim of this study was to investigate morphological, electrophysiological and functional changes in the inner ear after irradiation with CO(2) laser set with different energy parameters. A cochleostomy in the basal cochlear turn of guinea pig cochleae was performed with CO(2) laser of 1, 2 and 3 w, respectively. The cochleae were removed three weeks after laser irradiation. The auditory evoked brainstem response (ABR) was measured before and after laser application and immediately before removal of the cochlea. Immunohistochemical methods were used to examine inducible nitric oxide synthase (iNOS/NOSII) and heat-shock protein 70 (Hsp70) concentrations in the cochlea after laser application. The organ of Corti was studied by scanning electron microscopy. Worse hearing loss was observed in animals receiving higher-power CO(2) laser. These findings correlated with more intense injury of the cochlear ultrastructure and with positive expression of iNOS and Hsp70 in spiral ganglion cells, nerve fibres, supporting cells of the organ of Corti and cells of the spiral ligament. The CO(2) laser as a noncontact procedure is shown to be effective and safe if the total amount of energy is kept within the limits applied in this study. Nitric oxide and stress proteins play important roles in the traumatic mechanism of the inner ear, which are related to hearing loss and injury of the ultrastructure of the inner ear.

Animals↗

PubMed1989

Development of morphological and physiological changes in the cochlea induced by cytomegalovirus.

The effect of viral infection in the cochlea was investigated by inoculation of live cytomegalovirus or inactivated virus. Auditory thresholds were measured on the day of inoculation and on the terminal day. Two to 8 days following inoculation, the animals were killed and the cochleas were evaluated histologically. The compound nerve potential showed an increase in threshold prior to the cochlear microphonic, indicating the nerve was affected prior to the outer hair cells. All experimental cochleas contained inflammatory and cytomegalic inclusion cells and showed degenerative changes. The number of infected cells was small relative to the histopathology. Control cochleas had normal structure and function. The degeneration, therefore, might be mediated by inflammation as well as by the cytopathic effect of the virus. Viral infections, therefore, might be better managed with anti-inflammatory therapy in addition to antiviral agents.

Animals↗

PubMed1992

Effects of bacterial endotoxin applied to the guinea pig cochlea.

The ototoxic potential of bacterial endotoxin present in middle ear effusions was evaluated by inoculating endotoxin solutions of 10 micrograms/mL or 1000 micrograms/mL directly into the scala tympani of the guinea pig cochlea. Median auditory brainstem response threshold shifts of 12.5 and 20 dB were observed in the experimental ears exposed to the higher dose at days 2 and 4, respectively, with gradual improvement to near baseline by day 28. Histologic examination revealed inflammatory infiltrates in the scala tympani and scala vestibuli of several of these cochleas. The lower concentration, closer to that found in human effusions, elicited no significant loss of hearing and a milder inflammatory response. It is concluded that brief exposure of the cochlea to endotoxin from middle ear effusions is insufficient to cause hearing loss. Under chronic conditions, however, persistent inflammation within the cochlea may result in a sensorineural deficit.

Animals↗

PubMed1992

Neural regeneration in the noise-damaged chinchilla cochlea.

Recent studies in the bird ear have shown that degenerated hair cells are sometimes replaced by regenerated receptor cells. The present study evaluated the adult mammalian cochlea for evidence of hair-cell and nerve-fiber regeneration. Eighty-eight noise-damaged chinchilla cochleas were examined as plastic-embedded whole mounts by phase-contrast and bright-field microscopy. No signs of hair-cell regeneration were found. However, 32 (70%) of 46 cochleas damaged by high-intensity noise and 20 (48%) of 42 cochleas damaged by moderate-intensity noise contained a variable number of nerve fibers which appeared to be regenerated. These fibers, which were located in severely damaged areas of organ of Corti, differed from residual fibers with respect to their diameters, the degree and pattern of myelination, and by the abnormal paths they followed within the osseous spiral lamina and on the basilar membrane. The number of regenerated fibers varied with type of exposure and length of recovery. The strongest response was found in ears exposed to a high-intensity, low-frequency noise. The results described here indicate that a potential exists for the biological restoration of the mammalian inner ear.

Animals↗

PubMed2003

Expression of glutamate transporter GLAST in the developing mouse cochlea.

The immunohistochemical localization of glutamate transporter GLAST in the developing mouse cochlea was studied at different ages between 0 and 30 days after birth (DAB). In the adult mouse cochlea, intense GLAST-like immunoreactivity was found in the supporting cells adjacent to the inner hair cells of the organ of Corti, the type II and suprastrial fibrocytes of the cochlear lateral wall, the fibrocytes of the spiral limbus and the satellite cells surrounding the spiral ganglion cells. At 0 DAB, weak GLAST-like immunoreactivity was found in the supporting cells around the immature inner hair cells. Immature fibrocytes in the cochlea were also positively immunostained. At 3 DAB, weak immunostaining of GLAST appeared in the immature satellite cells in the spiral ganglion. The GLAST-like immunoreactivity in the supporting cells around the inner hair cells, in the fiborocytes in the spiral ligament and the spiral limbus and in the satellite cells in the spiral ganglion increased progressively during the second postnatal week, and reached the adult level at 15 DAB. This time course correlates with the electrophysiological onset and maturation of the mouse auditory function, which is mediated by glutamatergic neurotransmission. These results suggest that the expression of GLAST may be needed for the efficient removal and metabolism of the released glutamate in the cochlea and may play important roles in the onset and maturation of the auditory system.

Amino Acid Transport System X-AG↗

PubMed2006

Distinct population of hair cell progenitors can be isolated from the postnatal mouse cochlea using side population analysis.

In mammals, the permanence of hearing loss is due mostly to the incapacity of the cochlea to replace lost mechano-receptor cells (i.e., hair cells [HCs]). The generation of new HCs from a renewable source of progenitors is a principal requirement for developing a cell therapy within this sensory organ. A subset of stem cells, termed side population (SP), has been identified in several tissues of mammals. The ATP-binding cassette transporter Abcg2/Bcrp1 contributes to the specification of the SP phenotype and is proposed as a universal marker for stem/progenitor cells. A defining character of these SP cells is a high efflux capacity for Hoechst dye. Here, we demonstrate that Abcg2 transporter is expressed with two other stem/progenitor cell markers (i.e., Nestin and Musashi1) in distinct and overlapping domains of the supporting cells within the postnatal cochlea. We have developed and describe a fluorescence-activated cell sorting (FACS) technique that enables the purification of a discrete subpopulation of SP-supporting cells from the early postnatal mouse cochlea based on their ability to exclude Hoechst dye. These FACS-isolated cells can divide and express markers of stem/progenitor cells such as Abcg2, a determinant of the SP phenotype, and Musashi1, a neural stem/progenitor cell marker. These markers can differentiate cells expressing markers of HCs and supporting cells in vitro. Our observation that these SP cells are capable of differentiating into HC-like cells implies a possible use for such cells (i.e., the replacement of lost auditory HCs within damaged cochlea).

ATP Binding Cassette Transporter, Subfamily G, Mem↗

PubMed1987

Hair cell distributions in the normal human cochlea. A report of a European working group.

Cochlear hair cell counts from individuals who had clinically normal hearing prior to their death have been plotted for various age bands as a function of the number of hair cells per millimetre against their position in the cochlea. Position has been expressed as the distance of that observation of hair cell density from the base of the cochlea, divided by the total length of the cochlea, thereby giving a proportional representation of the cochlea in the range of 0.0 to 1.0 with 20 subdivisions of 0.05. There is an age-related decrease in the number of hair cells in the normal population, and this is more marked for the outer hair cells.

Adolescent↗