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At least 343 records · Page 19Linked to original sources

PubMed1987

Stereocilia and tectorial membrane development in the rat cochlea. A SEM study.

Maturation of the rat cochlea, from postnatal days 2 to 60, was studied using scanning electron microscopy (SEM), with emphasis on stereocilia and tectorial membrane (TM). Two days after birth, the organ of Corti was very immature. An adult appearance of its surface was observed by day 16 in the basal turn, and by the end of the 3rd postnatal week in the apex. Stereocilia started their development first on inner hair cells. By contrast, the apical pole of outer hair cells ended its maturation before that of inner hair cells. Top-links were detected very early in inner hair cell stereociliary development (postnatal day 2). Marginal pillars temporarily attached the TM to the organ of Corti; they disappeared first in the apical region. This transient attachment seems to play a role in the coupling of outer hair cells to the TM, as prints of their longest stereocilia appeared at the undersurface of the TM by the same time. Moreover, these prints were more clear and regular at the base than at the apex of the cochlea. Results are discussed in relation to ultrastructural and functional data on rat cochlea maturation.

Animals↗

PubMed1977

Receptor maturation and synaptogenesis in the golden hamster cochlea.

Maturation of hamster cochlea was studied using light and electron microscopy. Critical stages of receptor and neural structure development have been determined. At birth the hamster cochlea shows a pronounced immaturity, but innervation can already be found. 2 or 3 days later, characteristic afferent synapses can be recognized beginning at the inner hair cell level. Similarly, efferent endings first appear on the inner side at the end of the first week. The onset of auditory function must be related to structures depicted at around 10 days, and cochlear maturation is achieved at about 25 days. The sequence of synaptic development in the cochlea is discussed regarding the general morphogenesis of synapses within the nervous system. Some determinations of the timing of peripheral myelination are given. This process begins almost a week before the presumable date of the onset of function.

Age Factors↗

PubMed1981

X-ray microanalysis of fluid spaces in the frozen cochlea.

The cochlea is quick-frozen and then opened while under liquid nitrogen to expose the scalae of all turns in the mid-modiolar section. Still under liquid nitrogen, the cochlea is transferred to the cold stage of a pre-vacuum chamber especially constructed for attachment to the scanning electron microscope. Under partial vacuum, it is moved to the cold stage in the high vacuum chamber of a field-emission scanning electron microscope. Energy dispersive X-ray analysis demonstrates the relative levels of sodium, potassium, and chlorine in the fluid spaces of the cochlea.

Animals↗

PubMed1989

An immunohistochemical method for the study of aminoglycoside ototoxicity in the guinea pig cochlea using decalcified frozen sections.

An immunohistochemical technique with decalcified frozen sections was used to study aminoglycoside ototoxicity. Decalcified guinea pig cochleas were cut with a fine blade parallel to the plane of the modiolus to facilitate the penetration of inclusion material and the manipulation of frozen sections. Light microscopy was carried out and additional frozen sections were employed for an immuno-electron microscopic study. Twenty-four hours after a single transtympanic injection of 10 mg gentamicin, there was a definite distribution of the drug in only type I hair cells of the ampullae as well as in both inner and outer hair cells along the length of the cochlea. In those animals treated intraperitoneally with 200 mg/kg amikacin for 8 days, the drug was located in the outer hair cells of the cochlea, with a tendency to decrease from base to apex and in the inner hair cells towards the apex.

Amikacin↗

PubMed1983

Compartment analysis of the potassium fluxes in the cochlea.

The results obtained from tracer kinetics, measured by Konishi et al. (1978) and June (1979), are combined to construct a two-compartment model of the guinea-pig cochlea. The potassium fluxes are calculated using a mathematical two-compartment theory. For the basal turn, one finds a circulating flux between the endolymphatic and perilymphatic spaces of 190 pMol/min and 1 mm cochlea, whereas a minor value of 100 pmol/min/mm is calculated for the flux from the perilymphatic scales out of the cochlea.

Animals↗

PubMed1985

The effect of furosemide on glucose oxidation of the cochlea and other tissues.

We tested the hypothesis that furosemide interferes with energy generation in the cochlea, and determined its effect on CO2 formation from glucose and glyceroaldehyde-3-phosphate dehydrogenase (GAPDH) activity by examining biochemical and histochemical changes in the cochlea, the kidney, and the liver. We found that furosemide suppressed CO2 formation in vitro at relatively low concentrations in all tissues examined. GAPDH was inhibited as soon as 2 min after its administration (80 mg/kg, i.v.). Recovery of this enzyme activity was most rapid in the liver. We concluded that furosemide does interfere with energy generation in the cochlea, kidney, and liver as a result of its inhibition of GAPDH.

Animals↗

PubMed1984

Localization of triphosphoinositide in the cochlea. An electronmicroscopic immunocytochemical study.

Triphosphoinositide (TPI) has been demonstrated to be a receptor for aminoglycosides in the cochlea and may regulate ionic permeability by its binding with Ca++. This phospholipid was localized by a protein A-gold technique in the cochlea at the electronmicroscopic level. TPI was prepared by a neomycin column and antibodies to it were raised in rabbits. The antibody used in this study reacted virtually only to TPI among the tested lipids. TPI was localized mainly at stereocilia, cuticular plates, head plates of Deiters' cells, plasma membrane, and mitochondria of various cells in the organ of Corti. In the vascular stria, TPI was found mainly at the plasma membrane of basal infoldings of the marginal cells. Possible physiological and pathophysiological roles of TPI in the cochlea are briefly discussed.

Animals↗

PubMed1989

Development of acetylcholinesterase-positive neuronal pathways in the cochlea of the mouse.

Development of the cholinergic enzymes, choline acetyltransferase (ChAT) and AChE, and of the AChE-positive innervation in the cochlea was studied biochemically and morphologically in the postnatal mouse up to 26 days. Both ChAT and AChE are already present at birth in levels comparable to 50 and 20% of near-adult values, respectively. Increases in the enzymatic activities occur mainly during the second postnatal week. ChAT increases primarily in the basal turn; the specific activities in the basal and mid turns become about equal and at least twice of the values found in the apex. AChE increase continues throughout the entire cochlea; at all times its activity is highest in the base and lowest in the apex. In the light microscope, AChE-positive fibres are seen to enter the organ in the intraganglionic bundle during late foetal development and travel upwards via radial bundles. The fibres destined for outer hair cells usually differentiate first and take a separate route. They either cross the prospective tunnel of Corti directly or take a spiral course in front of inner pillar cells to form the inner pillar bundle. The tunnel fibres are radially oriented and provide the innervation to outer hair cells in narrow vertical sectors. In most cases, the outer hair cells are being innervated by the 4th day. Between the 4th and the 6th day, the tunnel fibres reach the outer hair cells in the third row; the first and second outer spiral bundles are formed. The AChE-positive innervation of the inner spiral bundle and plexus forms in short segments, and the bundle may be still discontinuous even by the 6th day. By the 12th day the innervation is complete. In the electron microscope, the stain for AChE may allow identification of growing efferent fibres before their ultrastructural differentiation. Both ChAT and AChE activities are early markers of the differentiating efferent system. An ingrowth of the cholinergic fibres to the entire cochlea occurs before birth. The greatest increase of AChE occurs between the 4th and 10th day, relating in time to efferent synaptogenesis.

Acetylcholinesterase↗

PubMed1989

GABA-like immunoreactivity in the cochlea of the developing mouse.

GABA-like immunoreactivity was studied in surface preparations of cochleas from postnatal developing mice, and GAD-like immunoreactivity was studied in the adult. GABA-positive fibres are already present at birth; they innervate both the inner and outer hair cells and some spiral ganglion cells. The GABA-positive fibres that enter via the intraganglionic bundle send collaterals to the spiral ganglion and to the hair cell region. Fibres that enter along the central processes of spiral neurons end predominantly among the spiral ganglion cells. A few spiral neurons display pericellular rings of GABA-positive boutons at birth. In older animals, the endings occur on a small number of spiral ganglion cells either as rings or as brush formations. The early GABA-positive fibres reach the inner hair cells around the second day and the outer hair cells (of the upper turns only) around the seventh day. In 12-day animals, tunnel fibres arborize in the outer hair cell region; their collaterals make contacts with the outer hair cells within four to eight cell-wide segments, distributing the endings high, up to the reticular plate. In older animals, fibres (both GABA-and GAD-positive) may innervate single vertical rows of outer hair cells. In the maturing and the adult cochlea, the GABA-positive component of the inner spiral bundle is conspicuous and extends along the entire cochlear length, but the innervation of the outer hair cells comprises only the mid and apical turns. GABA-positive nerve cells occur among the small vestibular neurons, occasionally among the cells of eighth nerve nucleus and only exceptionally in the spiral ganglion. In the adult animal, GAD-positive cells, although uncommon, were observed among the spiral neurons. In the developing animal, GABA-positive fibres give rise to transitory formations: (1) a convoluted plexus running beneath and among the radial bundles and (2) a sparse plexus, continuous with the inner spiral bundle and running in the upper plane of the inner spiral sulcus. GABA-like immunoreactivity was also observed in neuronal growth cones and in some fibres running along blood vessels. In conclusion, GABA immunoreactive fibres appear to reach the cochlea by two routes: via the intraganglionic bundle and to a much lesser extent via the central bundles of the spiral ganglion. The fibres innervate sensory cells and also some spiral neurons. The occasional presence of GABA-positive neurons in the vestibular ganglion, in the VIIIth nerve nucleus, and exceptionally among the spiral neurons raises the possibility of a local GABAergic circuitry within the inner ear.

Animals↗

PubMed1998

Distances between the cochlea and adjacent structures related to cochlear implant surgery.

A sound knowledge of the topographic anatomy of the cochlea, especially of the distances between it and the adjacent structures, is essential for otosurgery in general, and in surgical procedures for cochlear implantation in particular. One hundred temporal bones of humans aged from one month to 71 years, of either sex, taken from both body sides (but not bilaterally) were studied by dissection under the operating microscope and exposing the cochlea and its neighbourhood. The minimal distances were measured between the cochlear turns and the internal carotid artery, the bulb of the jugular vein, the facial nerve and the floor of the internal acoustic meatus. It was found that in children aged up to 4 years most of the measured distances were significantly smaller than in older individuals. Only the minimal distance between the basal turn of the cochlea and the floor of the internal acoustic meatus was shorter in small children without statistical significance.

Adolescent↗

PubMed1997

[Microlight-guided spectrophotometry of the cochlea].

BACKGROUND: Intraoperative measurements of local intracapillary hemoglobin oxygenation of the human cochlea via the round window membrane have been shown to be possible using the Erlangen microlight-guided spectrophotometer. The aim of the present study was to develop a new microlight guide suitable for measurements in the round window niche and to evaluate electrophysiologically the possible impact of the procedure on the cochlea. METHODS: Measurements were made for wavelengths of 450 to 900 nm at a total power of 5.3 mW. The exit diameter of the light guide was 200 microns and the angle used was 20 degrees. The recording depth was about 250 microns. The atraumatic character of the spectrophotometry was demonstrated by monitoring the compound action potential (CAP) threshold tuning curve from 1 to 34 kHz in ketanest-anesthetized guinea pigs. RESULTS: CAP thresholds remained constant (0.3 +/- 3.9 dB SPL) during 3 to 30 min of exposure to the light. CONCLUSIONS: These results suggest that the spectrophotometry may be useful as a new technique for intraoperative monitoring of intracapillary hemoglobin without causing physiological deterioration of the cochlea.

Animals↗

PubMed2005

Inhibition of Notch/RBP-J signaling induces hair cell formation in neonate mouse cochleas.

Mammalian inner ear hair cells in cochleas are believed to be incapable of regeneration after birth, which hampers treatment of sensorineural hearing impairment mainly caused by hair cell loss. Sensory epithelia of cochleas are composed of hair cells and supporting cells, both of which originate from common progenitors. Notch/RBP-J signaling is an evolutionally conserved pathway involved in specification of various cell types in developmental stage and even in some of postnatal mammalian organs. The specification of hair cell fate from the progenitors is inhibited by Notch/RBP-J signaling in embryonic inner ears. However, its function in postnatal inner ears is unknown. We showed that inhibition of Notch/RBP-J signaling, by either conditional disruption of the Rbpsuh gene or treatment with a gamma-secretase inhibitor, could give rise to ectopic hair cells in the supporting cell region in organs of Corti from neonatal mouse cochleas where hair cells have not been considered to regenerate after birth. We also showed that down-regulation of Hes5 and up-regulation of Math1 were associated with ectopic hair cell induction. These results suggest that Notch/RBP-J signaling inhibits supporting cells from differentiation into hair cells even in postnatal days, implying that inhibitors of Notch/RBP-J signaling can be used to help regenerating hair cells after birth and thus serve for potential treatment of intractable sensorineural hearing impairment caused by hair cell loss without genetical manipulation.

Animals↗

PubMed2000

Noise-induced aspartate and glutamate efflux in the guinea pig cochlea and hearing loss.

Aspartate and glutamate were monitored in the scala tympani of the guinea pig cochlea using in vivo microdialysis before and during noise exposure. Moderate level broad band noise [105 dB sound pressure level (SPL), 30 min] neither altered the levels of aspartate or glutamate, nor auditory brainstem response (ABR) thresholds. High level noise exposure (135 dB SPL, 30 min) caused a large increase in aspartate (330%), a smaller increase in glutamate (150%), and a permanent ABR threshold shift of 60-75 dB between 2.0 and 12.5 kHz. Morphological analysis of the cochlea revealed a collapse of supporting structures, swelling of the afferent dendrites under the inner hair cells, and outer hair cell loss. Pretreatment with the NMDA antagonist, MK 801 (1 mg/kg body weight, i.p.) 1 h before noise exposure protected the afferent dendrites from swelling but did not protect the collapse of supporting structures, outer hair cell loss, or auditory thresholds. In conclusion, the noise-induced increase in aspartate and glutamate release in the cochlea and the protective effect of NMDA antagonism suggest that these two neurotransmitters are involved in noise-induced hearing loss.

Acoustic Stimulation↗

PubMed1998

Sound-evoked efflux of excitatory amino acids in the guinea-pig cochlea in vitro.

We have used the perfused guinea-pig temporal-bone preparation to study the sound-evoked efflux of aspartate and glutamate, which are putative afferent transmitters in the cochlea. The cochlea was stimulated with white noise at 89, 95, and 101 dB SPL. Cochlear function was monitored by recording the endocochlear potential, the cochlear microphonic, and the summating potential. In silence, there was a low basal efflux of both amino acids. A significant and intensity dependent sound-evoked efflux of aspartate was observed at all levels, whereas a significant efflux of glutamate was found only at the 101 dB SPL level. Immunohistochemistry of sections from the organ of corti showed an ubiquitous distribution of glutamate-like immunoreactivity in the sensory organ and ganglion, whereas aspartate-like immunoreactivity was found in the region of the inner hair cells and in the spiral ganglion. In view of these findings, we suggest that not only glutamate, but also aspartate may have a neurotransmitter role in the afferent pathway of the cochlea.

Acoustic Stimulation↗

PubMed2007

Tuning the cochlea: wave-mediated positive feedback between cells.

Frequency analysis by the mammalian cochlea is traditionally thought to occur via a hydrodynamically coupled 'travelling wave' along the basilar membrane. A persistent difficulty with this picture is how sharp tuning can emerge. This paper proposes, and models, a supplementary or alternative mechanism: it supposes that the cochlea analyses sound by setting up standing waves between parallel rows of outer hair cells. In this scheme, multiple cells mutually interact through positive feedback of wave-borne energy. Analytical modelling and numerical evaluation presented here demonstrate that this can provide narrow-band frequency analysis. Graded cochlear tuning will then rely on the distance between rows becoming greater as distance from the base increases (as exhibited by the actual cochlea) and on the wave's phase velocity becoming slower. In effect, tuning is now a case of varying the feedback delay between the rows, and a prime candidate for a wave exhibiting suitably graded phase velocity-a short-wavelength 'squirting wave'-is identified and used in the modelling. In this way, resonance between rows could supply both amplification and high Q, characteristics underlying the 'cochlear amplifier'-the device whose action has long been evident to auditory science but whose anatomical basis and mode of operation are still obscure.

Acoustic Stimulation↗

PubMed1999

Transient expression of an inwardly rectifying potassium conductance in developing inner and outer hair cells along the mouse cochlea.

Inwardly rectifying K+ currents in inner and outer hair cells (IHCs, OHCs) were studied during post-natal development of the mouse cochlea. Hyperpolarizing steps from a holding potential of -64 mV induced a rapidly activating current in both cell types. This current showed strong inward rectification around the K+ equilibrium potential and, at potentials negative to -130 mV, partial inactivation. The activation range varied with extracellular K+ concentration. External application of Ba2+ and Cs+ reversibly blocked the elicited current. The results are consistent with the presence of an IK1-type inwardly rectifying potassium conductance in these cells. The maximum current was 60% larger in IHCs than in OHCs. In OHCs, but not IHCs, the amplitude of IK1 varied significantly with the cells' position along the cochlea. IK1 was maximal in cells located in the most basal region of the cochlea and its amplitude decreased in the apical coil. IK1 disappeared upon functional maturation: in OHCs at the end of the first postnatal week, and in IHCs at the onset of auditory function 12 days after birth. The current is active at the resting potential of the cells and plays a role in regulating the spiking behaviour characteristic of developing hair cells.

Algorithms↗

PubMed2005

Postnatal developmental expression of the PDZ scaffolds Na+ -H+ exchanger regulatory factors 1 and 2 in the rat cochlea.

Sensory transduction in the mammalian cochlea requires the maintenance of specialized fluid compartments with distinct ionic compositions. This is achieved by the concerted action of diverse ion channels and transporters, some of which can interact with the PDZ scaffolds, Na(+)-H(+) exchanger regulatory factors 1 and 2 (NHERF-1, NHERF-2). Here, we report that NHERF-1 and NHERF-2 are widely expressed in the rat cochlea, and that their expression is developmentally regulated. Reverse transcription/polymerase chain reaction (RT-PCR) and Western blotting initially confirmed the RNA and protein expression of NHERFs. We then performed immunohistochemistry on cochlea during various stages of postnatal development. Prior to the onset of hearing (P8), NHERF-1 immunolabeling was prominently polarized to the apical membrane of cells lining the endolymphatic compartment, including the stereocilia and cuticular plates of the inner and outer hair cells, marginal cells of the stria vascularis, Reissner's epithelia, and tectorial membrane. With maturation (P21, P70), NHERF-1 immunolabeling was reduced in the above structures, whereas labeling increased in the apical membrane of the interdental cells of the spiral limbus and the inner and outer sulcus cells, Hensen's cells, the inner and outer pillar cells, Deiters cells, the inner border cells, spiral ligament fibrocytes, and spiral ganglion neurons (particularly type II). NHERF-1 expression in strial basal and intermediate cells was persistent. NHERF-2 immunolabeling was similar to that for NHERF-1 during postnatal development, with the exception of expression in the synaptic regions beneath the outer hair cells. NHERF-1 and NHERF-2 co-localized with glial fibrillary acidic protein and vimentin in glia. The cochlear localization of NHERF scaffolds suggests that they play important roles in the developmental regulation of ion transport, homeostasis, and auditory neurotransmission.

Animals↗

PubMed2006

Supporting cell proliferation after hair cell injury in mature guinea pig cochlea in vivo.

In cold-blooded animals, lost sensory hair cells can be replaced via a process of regenerative cell proliferation of epithelial supporting cells. In contrast, in mammalian cochlea, receptor (hair) cells are believed to be produced only during embryogenesis; after maturity, sensory or supporting cell proliferation or regeneration are thought to occur neither under normal conditions nor after trauma. Using bromodeoxyuridine (BrdU) as a proliferation marker, we have assessed cell proliferation activity in the mature organ of Corti in the cochlea of young guinea pigs following severe damage to the outer hair cells induced by kanamycin sulfate and ethacrynic acid. Although limited, we have found BrdU-labeled nuclei in the regions of Deiters cells when BrdU is given for 3 days or longer. When BrdU is given for 10 days, at least one labeled nucleus can be observed in the organ of Corti in approximately half of the ears; proliferating cells typically appear as paired daughters, with one nucleus being displaced away from the basement membrane to the position expected of the hair cells. Double-staining with antibodies to cytokeratin, vimentin, and p27 have shown that the BrdU-labeled nuclei are located in cells phenotypically similar to Deiters cells. Most of the uptake of BrdU occurs 3-5 days following ototoxic insult, and the number of BrdU-labeled cells does not decrease until 30 days following insult. These findings indicate that Deiters cells in the mature mammalian cochlea maintain a limited competence to re-enter the cell cycle and proliferate after hair cell injury, and that they can survive at least for 1 month.

Animals↗