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At least 487 records · Page 27Linked to original sources
PubMed1986

Ionic environment of cochlear hair cells.

The scala media of the adult cochlea in mammals comprises a morphologically closed compartment sealed with tight junctions of the intermediate to tight types. The unique ionic composition of endolymph is maintained by the stria vascularis through active reabsorption of sodium and active secretion of potassium against ionic gradients. The subtectorial space is only a partially closed compartment which communicates with the endolymph via holes in the tectorial membrane at its outer insertion to the organ of Corti. Hardesty's membrane divides the subtectorial space into two compartments: one facing the surfaces of inner hair cells and one facing the surfaces of outer hair cells. In the study of comparative anatomy, hair cells, e.g. in the lizard, basilar papilla are of two types: those covered with a tectorial membrane and those being free-standing lacking the tectorial membrane. The ionic environment of the hair cell surface seems to be the same, independent of whether covered with a tectorial membrane or not. The tectorial membrane itself is semipermeable to ions in the endolymphatic space. Only the surface structures of the hair cell with the sensory hairs facing the subtectorial space are exposed to the high concentration of potassium, whereas the remaining parts of the hair cell are surrounded by a fluid having a more normal extracellular type of ionic composition (cortilymph/perilymph). During embryonic development the ionic composition of endolymph develops in parallel with the morphologic maturation of the stria vascularis. A completely mature composition of endolymph is reached before any electrophysiological potentials in the cochlea can be elicited. The sensory hair surface of hair cells has reached a mature morphology prior to the maturation of endolymph. In several species the tectorial membrane is morphologically only partially mature when the increase of the potassium concentration of endolymph starts. Drugs primarily affecting the stria vascularis causing a transient change of the ionic composition of endolymph result in a transient dysfunction of inner ear potentials. If the ionic changes persist for longer time, morphological changes can occur in both the stria vascularis and the hair cells of the organ of Corti. Whether such changes are primarily caused by the ototoxic drug itself or by changes in the ionic composition of endolymph has to be explored further.

Animals↗
PubMed1987

Electron microscopic autoradiographic demonstration of inositol incorporation in the cochlea.

[3H]Inositol was perilymphatically perfused into the guinea pig cochlea and the sites of its incorporation were autoradiographically identified by electron microscope. In the organ of Corti, distinct areas of inositol incorporation were observed at sites enriched with cytoskeletal proteins. In addition, a wide range of cell organelles incorporated inositol. Cell membrane/subsurface cisterna complex of the outer hair cells and the cell membrane/microvilli complex incorporated inositol more avidly than did other cell membranes. In the stria vascularis, intermediate cells incorporated inositol more frequently than cells in other areas.

Animals↗
PubMed1987

The low-frequency response of inner hair cells in the guinea pig cochlea: implications for fluid coupling and resonance of the stereocilia.

AC receptor potentials within the inner hair cells of the basal turn of the guinea pig cochlea have been recorded for stimuli in the frequency range 20 Hz to 3200 Hz. Comparison of these potentials with potentials recorded in scala media suggests that the stereocilia of many inner hair cells are stimulated by the transverse velocity of the cochlear partition for very low frequency, but above a transition frequency in the range 400 Hz to 1000 Hz they become entrained with partition displacement. It is suggested that such a transition is probably a simple consequence of the fluid coupling that drives these cells, and that mechanical resonance of the free-standing stereocilia of the inner hair cells does not occur in the basal turn of the guinea pig. These results do not, however, preclude the possibility of mechanical resonance involving the stereocilia of the outer hair cells. The results also indicate that the bodies of these cells low-pass filter the intracellular receptor potential, with a cutoff frequency of approximately 1000 Hz.

Acoustic Stimulation↗
PubMed1988

Acoustically induced hearing loss: intracellular studies in the guinea pig cochlea.

Intracellular recordings were made from both inner and outer hair cells (IHC, OHC) in the basal coil of the guinea pig cochlea before, during and after the animal was exposed to loud, pure tones. Following multiple loud tones both types of sensory cells demonstrate a culmulative decrease in their voltage responses to a test tone. A loss in sensitivity of the compound action potential (CAP) of the eighth nerve co-incides with a decrease in both the amplitude of the IHC receptor potential and the positive summating potential (+SP) recorded at the round window. The largest decreases in sensitivity of IHCs are found at the characteristic or best frequency (CF) of each cell and this frequency selective loss of sensitivity results in a decrease in the tuning of the hair cell. During and following a loud tone the nonlinear properties of IHCs are also reduced.

Action Potentials↗
PubMed1989

Electrochemical profiles for monovalent ions in the stria vascularis: cellular model of ion transport mechanisms.

The electrochemical profiles for K+, Na+, and Cl- ions in tissues of the lateral wall of the cochlea in the chinchilla were measured using an ion-selective microelectrode. Based upon the changes of the d.c. resting potential and ion composition, five distinct compartments were identified in the lateral wall. The first compartment, corresponding to the spiral ligament, showed an ionic composition similar to perilymph. The second, corresponding to the basal cell layer of the stria vascularis, showed a characteristic recording of the ion-sensitive barrel: a spike-like change of the ion concentration (K+: 100.1 +/- 16.8 mM, Na+: 33.9 +/- 20.2 mM, Cl-: 70.2 +/- 9.4 mM). The third compartment, corresponding to the extracellular space of the stria vascularis, showed a higher d.c. potential (60.4 +/- 9.5 mV) than that of the second region, with a low K+ concentration (22.1 +/- 14.9 mM) and a high Na+ (78.3 +/- 5.7 mV) than the fifth compartment, corresponding to the scala media (78.1 +/- 4.1 mV), and K+ and Na+ concentrations similar to those of endolymph, while the Cl- concentration in the fourth compartment (117.6 +/- 21.5 mM) was lower than that of endolymph (143.3 +/- 13.9 mM). A thermodynamic study of electrochemical potential gradients suggests the possibility that the Na-K pump and Na-K-2Cl cotransport exist at the basolateral membrane of the marginal cells.

Animals↗
PubMed1991

Expression of intermediate filament proteins in the mature inner ear of the rat and guinea pig.

The expression of intermediate filament proteins was studied in the mature inner ear of the rat and guinea pig, using a panel of polyclonal and monoclonal antibodies directed against cytokeratins, desmin, neurofilament proteins and glial fibrillary acidic protein (GFAP). The epithelial lining of the endolymphatic space displayed a complex expression pattern of cytokeratin filament proteins, suggesting greater cell diversity than was known sofar from morphological studies. The cytokeratin antibodies when applied to the inner ear tissues revealed the presence of only cytokeratin polypeptides which are typical of simple epithelia (i.e. nos. 7, 8, 18, and 19). Profound differences in cytokeratin expression patterns were, however, found in the various cell types of both the cochlear and vestibular partition. Remarkably, the sensory cells appeared to be devoid of both cytokeratins and neurofilament proteins. Staining with a 200 kDa neurofilament antibody displayed the presence of different populations of ganglion cells in the spiral ganglion and the vestibular ganglion. There was no reaction with antibodies directed against desmin and GFAP. The great resemblance of the intermediate filament protein expression patterns in the inner ear of the rat and guinea pig indicates a close similarity between the different epitopes.

Animals↗
PubMed1991

Mechanically induced length changes of isolated outer hair cells are metabolically dependent.

Isolated outer hair cells from the organ of Corti of the guinea pig have been shown to change length in response to a mechanical stimulus in the form of a tone burst at a fixed frequency of 200 Hz (Canlon et al., 1988). In the present study, the threshold of movement for individual outer hair cells is related to the original length of the cell such that long cells are more sensitive than short cells for all cochlear locations studied. Length changes could be elicited when the stimulus was projected at any site along the longitudinal axis of the plasma membrane. Length changes were not elicited when the stereocilia were stimulated directly. These mechanically-induced length changes were found to be metabolically dependent. In the presence of either sodium cyanide or 2,4-dinitrophenol, the motile response of outer hair cells was completely blocked within 30 min. When the extracellular pH was altered in a graded fashion, the motile response decreased gradually. Furthermore, 3 microM poly-L-lysine or poly-D-lysine of different molecular weights were also effective in blocking the motile response, whereas the negatively charged polyaminoacid, poly-L-aspartate, was not effective. Fluorescently-labelled poly-lysine demonstrated that the plasma membrane, stereocilia, and nucleus were the most intensely stained structures of the outer hair cells. It is suggested that the passive influx of poly-lysine is responsible for the inhibition of the motile response. Finally, the finding that the bidirectional motile response of isolated outer hair cells induced by mechanical stimulation is dependent on the metabolic state of the cell distinguishes this type of motility from the electrically induced outer hair cell shape changes.

2,4-Dinitrophenol↗
PubMed1991

Atrophy of outer hair cell stereocilia and hearing loss in hydropic cochleae.

We have earlier described selective atrophy of short and middle stereocilia on outer hair cells of the three upper cochlear turns in hydropic cochleae of guinea pigs. The present study describes sequential early stages of stereocilia degeneration leading to this specific atrophy. Comparison of the morpho-pathology with the ultimate CAP audiograms taken before sacrifice indicated a close association between the low frequency hearing loss and this atrophy of stereocilia. The atrophy appeared to be associated first with the short and then the middle stereocilia of the 2nd and 3rd rows of outer hair cells between 0.5 kHz and 2 kHz and with time included the 1st row of all outer hair cells of the upper cochlear turns down to the 8 kHz region.

Acoustic Stimulation↗
PubMed1992

Development of the human stria vascularis.

Fifteen human fetal cochleas were investigated by light microscopy and transmission electron microscopy in order to observe the development of the stria vascularis. The earliest signs of strial cell differentiation take place during the 11th week of gestation. Subsequently, the first stages of the stria vascularis development occur quickly. At week 14 the three types of cells, namely, marginal, intermediate and basal cells are discernable. Moreover at this stage, signs of specific activity are already present. The adult-like appearance of the stria vascularis is reached by week 21 but its maturation is completed only during the last trimester of pregnancy. This is in good agreement both with the development of the organ of Corti structures and with the maturation of the human auditory function.

Adult↗
PubMed1992

Stage dependent development of intraocular cochlear grafts.

The intraocular grafting technique was employed to test whether the peripheral hearing organ, the cochlea, is capable of survival and an organized development in total isolation from the temporal bone. Rat cochleae obtained from gestation day 16, postnatal day 1 and 7 were chosen for transplantation into the anterior chamber of the eye of adult Sprague-Dawley rats. The grafts were maintained in the anterior chamber for 6, 10, or 15 weeks survival time. The salient features of this study is that 1) cochlear structures survive and, 2) the cochlear structures develop beyond their pre-grafted stage as determined from light and electron micrographs. In the present study, the grafts obtained at gestation day 16 (GD 16) and postnatal day 1 gave a much higher rate of survival and development than the postnatal day 7 grafts. In addition, grafts maintained for either 6 or 10 weeks had a better survival rate than those grafts left for 15 weeks. It is estimated from light and electron micrographs that the gestation day 16 otocysts that were maintained for 10 weeks, developed to the equivalent of a postnatal day 10 cochlea. The grafts obtained from postnatal day one rats developed to the equivalent of approximately 14 days after birth. Interestingly, in the absence of synaptic contact, the inner and outer hair cells were capable of survival, differentiation and maturation. It remains to be determined if the spiral ganglion cells require additional neurotrophic factors for survival in the anterior chamber of the eye.

Animals↗
PubMed1992

Characterization of marginal and Claudius' cells growing from cochlear explants in vitro.

Tissue specimens of stria vascularis together with spiral ligament were transferred from the guinea pig cochlea to tissue culture dishes. To characterize and identify cells growing out from the explants, indirect immunofluorescence microscopy was used. The expression of the intermediate-sized filaments vimentin and cytokeratin 18 in cells on the surface of tissue specimens and in cells growing out from the explants after different cultivation periods were compared. Basically, three types of cells grew from the explants during several days: marginal cells, Claudius' cells and fibroblast-like cells. In primary cultures of explants, growth of marginal cells was observed in 25% of the dishes. Their proliferative activity, estimated by the use of the BrdUrd-DNA antibody, started in the stria vascularis and continued across the attachment of Reissner's membrane down to the bottom of the cell culture dish. The newly-formed marginal cells expressed cytokeratin 18 in the same way that original marginal cells on the tissue specimen do. If the newly-formed marginal cells were in contact with fibroblast-like cells or were forming groups (domes) on the bottom, they expressed vimentin. In 3% of the dishes growth of Claudius' cells was observed. Proliferative activity of these cells was found at the point where the basilar membrane was attached to the spiral ligament. New Claudius' cells spread at the opposite side of an explant when compared with the location of new marginal cells. Original as well as newly-formed Claudius' cells contained cytokeratin 18. Fibroblast-like cells were commonly present in cultures and contained only vimentin.

Animals↗
PubMed1993

Involvement of Cl- transport in forskolin-induced elevation of endocochlear potential.

To determine the possible involvement of Cl- transport in the forskolin-induced endocochlear potential (EP) elevation, the effect of forskolin on the EP was examined in Cl(-)-free artificial perilymph (aPL) as well as in the presence of Cl- channel blockers. The perfusion of scala vestibuli (SV) with forskolin (200 microM) dissolved in Cl(-)-free aPL failed to produce an EP elevation, while SV perfusion of forskolin dissolved in normal aPL elevated the EP. The application of DPC and IAA-94 (blockers of cAMP-activated Cl- channel) into SV completely suppressed the forskolin-induced EP elevation, while niflumic acid (a Ca(2+)-activated Cl- channel blocker) failed to do so. IAA-94 applied into scala tympani (ST) did not suppress this EP elevation. The results suggest that adenylate cyclase may modulate the EP by changing Cl- transport between SV and scala media (SM) across Reissner's membrane.

Adenylyl Cyclases↗
PubMed1995

Nonlinear mechanics at the apex of the guinea-pig cochlea.

A heterodyne laser interferometer was used to observe the sound-evoked displacement patterns of Reissner's membrane and various other structures in the apical turn of the guinea-pig cochlea. Most structures (including the basilar membrane) were similarly tuned, and had best frequencies in the 200-350Hz range. A distinct notch was usually observed approximately 0.7 octaves above the best frequency, and amplitude- and phase-plateaus were observed at higher frequencies. In most other respects, however, the mechanical tuning resembled the frequency-threshold curves of low frequency cochlear nerve fibers. In five reasonably intact, in vivo preparations, the frequency of the mechanical sensitivity notch was intensity-dependent: Compressive nonlinearities were observed above approximately 80 dB SPL on the low-frequency side of the notch, with antagonistically expansive nonlinearities on the high-frequency side. Two-tone suppression was observed in one of these preparations. Stimulus-related baseline position shifts were observed in another in vivo preparation. No such nonlinearities were observed in structurally damaged and/or > 1 hour post-mortem preparations. However, more robust nonlinearities were observed in all preparations at higher levels of stimulation (e.g. > 100-110 dB SPL). These high-level nonlinearities diminished only slowly after death, and gave rise to various effects, including time-dependent (i.e. adapting) and severely distorted (e.g. peak-split and/or dc-shifted) responses.

Acoustic Stimulation↗
PubMed1995

Role of endolymphatic anion transport in forskolin-induced Cl- activity increase of scala media.

To determine the role of anion transport in the forskolin-induced Cl- increase of scala media (SM), effects of forskolin on the EP (endocochlear potential) and Cl- activity (ACl) in SM were examined with double-barrelled Cl(-)-selective microelectrodes. The experiments were carried out on guinea pig cochleae, using a few anion transport inhibitors: IAA-94 for a Cl- channel blocker, bumetanide (BU) for an Na+/K+/2Cl- cotransport blocker, and SITS and DIDS for Cl-/HCO3- exchange blockers. The application of forskolin (200 microM) into scala vestibuli (SV) caused a 20 mEq increase of endolymphatic ACl and a 15 mV elevation of EP, and IAA-94 with forskolin completely abolished these responses. Although each application of BU, SITS or DIDS did not completely suppress EP elevation, the concurrent application of these inhibitors completely suppressed EP with endolymphatic ACl increase. The results indicate the involvement of Cl- channels, Na+/K+/2Cl- cotransport and Cl-/HCO3- exchange in forskolin-induced increase of ACl and EP. The role of adenylate cyclase activation and Cl- transport in endolymph homeostasis was discussed.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1995

Differentiation of the rat stria vascularis.

The differentiation of the rat stria vascularis (SV) was investigated by light- and electron microscopy and by immunocytochemistry. Loss of the basal lamina at the epithelial-mesenchymal interface of SVs as indicated by immunoreactions of laminin and fibronectin induces the formation of vascular feet by basal infoldings of the marginal cells (MCs), and the development of the strial capillaries (SCs) by mesenchymal cells in a manner of vasculogenesis is progressing at the same time. The production of fibronectin in the rough endoplasmic reticulum of mesenchymal cells and the involvement of this glycoprotein in a mechanical linkage between the vasoformative mesenchymal cells and endothelial ones of the SCs are indicated by immunocytochemistry. The plasma membrane of the marginal cells (MCs) begins to show immunoreactions of Na+.K+ ATPase at postnatal day 5 and is conjugated to each other by tight junctions at postnatal day 14. The apical tubules of the differentiating MCs do not seem to be involved in the endocytotic activity but are involved in the plasma membrane supply for the rapid differentiation.

Animals↗
PubMed1995

Detection and quantification of endolymphatic hydrops in the guinea pig cochlea by magnetic resonance microscopy.

Three-dimensional magnetic resonance microscopy (MRM) was used to study normal and hydropic cochleae of the guinea pig. With this technique consecutive serial slices representing the entire volume of isolated, fixed cochleae were obtained. The voxels (volume elements) making up the contiguous slices were isotropic (25 microns 3) and in each slice the boundaries of scala media, including the position of Reissner's membrane, were clearly delineated. Three-dimensional reconstructions of the endolymphatic and perilymphatic scale were generated. Custom software was developed to quantify cross-sectional area (CSA) of all scalae. In the normal cochlea all 3 scalae, including scala media, showed a gradual decrease in CSA from base to apex. Marked differences existed between our findings and previously reported cochlear dimensions, especially for the perilymphatic scalae in the basal turn. In hydropic cochleae the scala media was enlarged to a varying extent in different turns and marked changes in the degree of distension of Reissner's membrane occurred along the cochlea. MRM and subsequent computer analysis of the isotropic data provide excellent methods for imaging and quantifying the fluid spaces of normal and hydropic cochleae.

Animals↗
PubMed1995

Acoustic enhancement of electrically evoked otoacoustic emissions reflects basilar membrane tuning: a model.

A simple model for the acoustic enhancement of electrically evoked otoacoustic emissions (EEOEs) is presented in this paper. The model is based on the assumption that the enhancement is a result of the local interaction between the electrical current spreading in the scala media and the basilar membrane (BM) response to acoustic input. The analytical, steady-state response of the 1-dimensional linear cable to sinusoidal current injection is derived and is used to predict the current spreading in the cochlea. Acoustic enhancement at an emission generator is modeled as a magnitude change that is a sigmoid function of the local BM motion. The model results are in good agreement with the experimental findings and support our interpretation that the acoustic enhancement of EEOEs reflects BM tuning.

Acoustic Stimulation↗