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PubMed1991

[Immunohistochemical localization of calcitonin gene-related peptide (CGRP) and neuropeptide Y (NPY) in the cochlea and middle ear of the guinea pig].

The avidin-biotin peroxidase complex immunostaining method combined with the glucose oxidase-nickel (ABC-GON) technique was applied to the guinea pig cochlea and middle ear, the fine structure of CGRP-containing fibers in the organ of Corti was also observed. The results demonstrated that the CGRP-containing fibers in the cochlea belonged to both the medial and lateral efferent systems of olivocochlear bundle. The CGRP positive nerve endings on outer hair cell base formed synaptic contacts with the cell body. No NPY-containing fibers were found in the cochlea. Numerous CGRP and NPY-containing fibers of a similar distribution pattern and density were seen in the middle ear mucosa. The pars tensa of ear drum was also innervated by moderate CGRP-containing fibers and a few NPY-containing fibers. Occasionally, the CGRP-containing fibers were observed along the radial fibers in the pars tensa. The role of two neuropeptides in the cochlea and middle ear are discussed.

Animals↗

PubMedDate not supplied

Regional blood flow patterns along the length of the rodent cochlea.

The cochlear blood flow within the different vascular beds of the cochlea was examined in rats and guinea pigs. Using a computer-assisted reconstruction technique, the position of the microspheres within the cochlea was determined and their percentage distribution along the length of the sensory epithelium was calculated. In the present experiments, differences in blood flow were observed along the length of the cochlea. Within one species the pattern in each of three vascular areas varied independently of the other. When the two species are compared, the pattern for blood flow to the individual vascular beds along the length of the sensory epithelium is similar. The differences observed may reflect differences in cochlear anatomy, or correlate with biochemical and metabolic longitudinal gradients known to exist in the cochlea.

Animals↗

PubMed1993

Electrical resonance of isolated hair cells does not account for acoustic tuning in the free-standing region of the alligator lizard's cochlea.

The cochlea of the alligator lizard is divided into two morphologically and physiologically distinct regions. In the "tectorial region," hair bundles of hair cells are draped by a tectorial membrane, whereas in the "free-standing region," hair bundles are said to be free-standing because there are no overlying tectorial structures. The acoustic tuning of the free-standing region depends at least in part on mechanical resonances of the hair bundles. In the turtle cochlea, in contrast, acoustic tuning depends in large part upon the electrical properties of the hair cells. We have investigated the electrical properties of hair cells isolated from the free-standing region of the alligator lizard's cochlea. When injected with steps of depolarizing current, these "free-standing hair cells" exhibited electrical resonances that were comparable in frequency and quality to electrical resonances in cochlear hair cells from turtles, chicks, and alligators, and in saccular hair cells from frogs and fish. In the lizard's free-standing hair cells, however, the electrical resonance frequencies (< 300 Hz) were a decade below the cells' acoustic characteristic frequencies (between 1 and 4 kHz), showing that the electrical resonance is not likely to contribute to acoustic tuning. The electrical resonances were not apparent at rest. The cells' resting potentials were significantly more negative than the activation voltage (approximately -40 mV) of the Ca(2+)-dependent K+ current upon which the electrical resonance has been shown to depend in other hair cells. At potentials more negative than -50 mV, an inwardly rectifying K+ conductance dominated. Because we observed no electrical tuning above 300 Hz, our results indirectly support a mechanical origin for acoustic tuning in the free-standing region of the alligator lizard cochlea. These results further show that acoustic tuning cannot be inferred solely from the electrical resonances of isolated hair cells.

Animals↗

PubMed1993

Effect on endocochlear potential of streptomycin perfusion of the cochlea in guinea pigs.

Perilymphatic perfusion of the cochlea with streptomycin was performed on 17 guinea pigs. The first and second group, consisting of five animals each, received streptomycin 150 micrograms and 1500 micrograms respectively. In a control group, consisting of seven animals, the perilymph was perfused with artificial perilymph only. The endocochlear potential (EP) was recorded from the second turn of the cochlea in each animal. The results indicate that streptomycin in a low dosage that will destroy the vestibular receptors was not harmful to the function of either the stria vascularis or the hair cells in the cochlea, as measured by changes in the EP after streptomycin perfusion of the cochlea.

Animals↗

PubMed1995

Surgical techniques for insertion of a multi-electrode implant into a postmeningitic ossified cochlea.

Severe ossification within the cochlea occurs in more than 20% of children deafened by meningitis. A multi-electrode cochlear implant can dramatically restore useful hearing to such children, providing it can be inserted satisfactorily within the cochlea. Various surgical techniques for cochlear implantation into an ossifying cochlea are discussed. Partial ossification often can be negotiated by clearing the new bone from the scala tympani or by inserting the array through the scala vestibuli. Total ossification is not a contraindication to the use of a multi-electrode cochlear implant. A method of drilling out the basal cochlear turn without removal of the overlying promontory is proposed. The results of "inlay" insertion into a totally ossified cochlea are evaluated in five ears.

Child↗

PubMed1997

Macrophage activity in organ cultures of the avian cochlea: demonstration of a resident population and recruitment to sites of hair cell lesions.

The factors that regulate the repair and regeneration of the sensory hair cells of the inner ear are not understood. Previous studies of hair cell injury in the lateral line sensory organs of amphibians and the cochleae of mammals have demonstrated that macrophages and other leukocytes are recruited to sites of hair cell lesions. The present study examined the distribution and activity of macrophages in organ cultures of the avian cochlea, a system whose regenerative abilities have been widely studied. Cochleae were removed from chicks and placed in organ culture, and precise hair cell lesions were created using a laser microbeam. Macrophages in the cultures were identified using histochemical, immunocytochemical, and morphologic criteria. It was found that (a) cultured cochleae contained a resident population of macrophages, and (b) increased numbers of macrophages were recruited to the sites of hair cell lesions. Furthermore, the latency of macrophage recruitment to lesions is consistent with a suggested role for macrophages in the initiation of hair cell regeneration.

Animals↗

PubMed1998

[The cochlea: modern physiologic insights into sensorineural hearing loss].

The cochlea is organized tonotopically: each frequency between 20 Hz and 20 kHz has its own location on the basilar membrane. In addition the cochlea has a large dynamic range (sound intensity). Active movements of the outer hair cells of the sensory organ of Corti play a crucial part in determining hearing acuity and frequency selectivity. Long-known properties such as combination tones and more recent observations like spontaneous and evoked otoacoustic emissions (the cochlea as sound source) fit in the same concept of a cochlea acting as a non-linear fine-tuned amplifier. Most sensorineural losses in people with diminished hearing are caused by injury to the hair cells, e.g. by medicines. Damage of outer hair cells impairs the cochlear amplifier, leading to loss of sensitivity to soft sounds and loss of frequency selectivity. Damage to the inner hair cells has much the same effect as conductive hearing loss. Tinnitus is not caused by otoacoustic emissions, but probably by denervation hypersensitivity following loss of cochlear input.

Cochlea↗

PubMed1992

Effects of noise and salicylate on hair cell loss in the chinchilla cochlea.

Chinchillas were exposed to octave band noise, sodium salicylate (300 mg/kg per day intraperitoneally), or the combination of both agents for 15 days. The octave band noise exposure was centered at 500 Hz at an intensity of either 80 or 105 dB sound pressure level. The effects of the experimental treatments were evaluated by determining the number of missing hair cells after recovery as a function of location within the cochlea using a surface preparation technique. Average cochleograms were calculated for each of five experimental groups. Animals given salicylate alone showed little or no hair cell loss. Noise exposure at 80 dB resulted in a mild (less than 30%) outer hair cell loss in the apical turn of the cochlea, whereas exposure at 105 dB resulted in moderate (50%) outer hair cell loss (outer hair cell first row particularly) in the apical half of the cochlea, mild outer hair cell loss in the basal region of the cochlea, and a mild loss of inner hair cells. The amount of hair cell loss in the groups exposed to the combination of salicylates and noise was not significantly different from the corresponding groups exposed to noise alone. Statistical analysis of the data suggest that the combination of salicylate plus noise does not produce any greater hair cell loss than noise alone.

Acoustic Stimulation↗

PubMed1985

Afferent influences on brain stem auditory nuclei of the chicken: neuron number and size following cochlea removal.

The consequences of cochlea removal on neuron number and soma cross-sectional area were examined in the second order auditory nucleus (n. magnocellularis) of chickens. Both the age of the subjects at the time of cochlea (basilar papilla) removal (1-66 weeks) and the survival period (1-45 days) were varied. Neuron number and soma cross-sectional area were determined from Nissl stained sections. Additional material was processed to examine the relationship of ganglion cell loss to changes in n. magnocellularis. Neuron number decreased by 25-30% and soma cross-sectional area decreased by 10-20% ipsilateral to the cochlea removal in chickens operated on during the first 6 weeks after hatching. In contrast, in chickens operated on at 66 weeks posthatch neuron number decreased less than 10% and there was no change in soma area. The changes were rapid, being nearly complete 2 days after cochlea removal. An initial change (1 and 2 days after surgery) observed in animals operated on up to 6 weeks posthatch was the presence of a large number of neurons in which no Nissl substance could be detected. These results demonstrate an age-dependent change in the susceptibility of NM neurons to deafferentation. This change is not temporally related to other measures of functional maturation of the auditory system.

Age Factors↗

PubMed1996

Sensory cells of the chick cochlea express synaptophysin.

Previous evidence has shown expression of synaptophysin by sensory cells of the auditory and vestibular systems in the human, but not in other mammalian species. Using a monoclonal antibody, SBI 20.10, we investigated the expression of synaptophysin in the sensory cells of the avian cochlea. We present immunohistochemical data showing synaptophysin expression by cochlear hair cells in both late stage embryos and adult chickens. Immunoblotting of cochleae confirmed an antigen with an apparent molecular weight appropriate for synaptophysin that increases with development. Immunoreactivity in the apex of the cochlea occurred in hair cells on both neural and abneural sides, whereas immunoreactivity in the base of the cochlea was relegated to hair cells on the neural side. These observations indicate that, in the avian auditory system, like the human, synaptophysin is expressed in the sensory cells of both the embryo and adult.

Age Factors↗

PubMed2005

A single dose of neurotrophin-3 to the cochlea surrounds spiral ganglion neurons and provides trophic support.

Degeneration of spiral ganglion neurons (SGNs) in the cochlea following sensorineural hearing loss is preventable by the infusion of neurotrophins into the scala tympani. This study investigates the trophic effects and distribution of a single bolus infusion of neurotrophin-3 (NT3) into the scala tympani of the cochlea. The left cochleae of 28-day deafened guinea pigs were infused with 0, 100 or 140 ng 125I NT3 via a cochleostomy in the scala tympani of the basal turn. Seven days post-infusion, cochlear sections were processed for measurements of trophic effects on SGNs and autoradiography. A single infusion of NT3 increased the soma size of SGNs in a dose-dependent and significant manner but did not contribute to SGN survival. Following infusion of 140 ng 125I NT3 into the cochlea, 0.31% of the total 125I NT3 signal in the basal turn was detected in Rosenthal's canal, 2.4% was in peripheral processes and 0.35% was in the modiolar auditory nerve. Despite influencing SGN soma size, 125I NT3 was not observed to accumulate in SGN cell bodies. The data suggest that only a small proportion of neurotrophins infused into the scala tympani diffuses to the SGNs and their processes and produces trophic effects on SGN cell bodies.

Animals↗

PubMed1990

Preferential expression of transient potassium current (IA) by 'short' hair cells of the chick's cochlea.

We have made a comparative study of the membrane properties of tall and short hair cells isolated from a selected region of the chick's cochlea. Tall hair cells are analogous to inner cochlear hair cells of mammals, and like those, are presynaptic to the majority of afferent neurons in the cochlea. Short hair cells, like mammalian outer hair cells, are the postsynaptic targets of efferent neurons that inhibit the cochlea. Voltage-clamp recordings have revealed that short hair cells have an inactivating potassium (K) current, IA, whereas tall hair cells have little or none. Short hair cells are also sensitive to the cholinergic agonist carbachol, whereas tall hair cells are not. This pattern is in accord with the selective distribution of efferent cholinergic synapses in the cochlea. Although IA is completely inactivated at the resting potential of the short hair cells, cholinergic agonists can hyperpolarize these cells by as much as 30 mV. This hyperpolarization removes inactivation and allows IA to modulate subsequent voltage-dependent processes in short hair cells. It is concluded that IA could increase the high frequency response of the hair cell by decreasing membrane resistance and thus the membrane time constant after inhibition. This will be of particular importance to cochlear function if short hair cells produce voltage-dependent movements, as do mammalian outer hair cells.

Animals↗

PubMed1988

Electrical tuning in hair cells isolated from the chick cochlea.

Tall (inner) hair cells were isolated from specific locations in the chick cochlea. The electrical membrane properties of these cells were recorded using the tight-seal whole-cell technique. Depolarizing current steps elicited damped voltage oscillations that ranged in frequency from 100 to 250 Hz among cells from the middle third of the cochlea (basal cells). The current-voltage relation obtained under voltage clamp was dominated by calcium-activated potassium current in the voltage range over which these oscillations occurred. Tall hair cells isolated from the apical tip of the cochlea (apical cells) exhibited action potentials and lower frequency voltage oscillations (5-14 Hz) during depolarizing current steps. Outward currents in these cells were 20-fold slower than those found in the basal cells. These results suggest that electrical tuning of hair cells may play a role in determining the frequency selectivity of the chick cochlea.

Animals↗

PubMed1980

Autoradiographic localization of vitamin A in the stria vascularis of the rat cochlea.

Vitamin A is present in the membranous cochlea at a higher concentration than in most other mammalian tissues. In order to localize this substance in the cochlea, 11(3)[H] retinyl acetate was administered to vitamin A-deficient rats. An autoradiographic study of these cochleas revealed labelling of the stria vascularis; the sensory cells and ganglion cells were not labelled.

Animals↗

PubMed1999

Differential expression of trkB.T1 and trkB.T2, truncated trkC, and p75(NGFR) in the cochlea prior to hearing function.

Prior to the onset of hearing, synchronous cellular, neuronal, and morphogenetic processes participate in the development of a functional cochlea. We have studied the expression of different splice forms of trkB and trkC as well as p75(NGFR) in rat and mouse cochlea within this critical developmental period, using in situ hybridization, PCR, Northern blotting, and immunohistochemical analyses. An antibody to full-length trkB receptors proved to detect full-length trkB receptors as well as truncated trkB.T2 but not trkB. T1 isoforms. Full-length trkB and trkC isoforms as well as trkB.T2 but not trkB.T1 receptors were noted in cochlear neurons. A transient expression of trkB.T1 and trkB.T2 was observed at the epithelial-mesenchymal border of the spiral ligament during this time. A sequential appearance of trkB.T1, the low-affinity neurotrophin receptor p75(NGFR), and trkB.T2 in epithelial cochlear cells correlated with the formation of the inner sulcus of the organ. A differential expression of presumptive trkB.T2 in hair and supporting cells was observed concomitant with the maturation of the distinct innervation pattern of these cells. A gradual shift from p75(NGFR) to truncated trkC receptors in Pillar cells occurred during the formation of the tunnel of Corti. A distinct expression of full-length trkC correlated with the time of differentiation of the stria vascularis. Finally, an expression of trkB.T1 and trkB.T2 in oligodendrocytes, full-length trkB and trkC in nerve fibers, and p75(NGFR) in Schwann cells was noted at the glial interface of the VIIIth nerve during the establishment of the glial transition zone. These various transitory neurotrophin receptor expression patterns, which were related to final maturation processes of the cochlea, may provide new insights into the as yet obscure role of neurotrophin receptors in nonneuronal tissue.

Animals↗

PubMed1997

Golgi-canalicular reticulum system in ion transporting fibrocytes and outer sulcus epithelium of gerbil cochlea.

BACKGROUND: Five types of highly specialized fibrocytes have been identified in the spiral ligament of the gerbil cochlea. Type I, II, and IV fibrocytes function in cycling back to the stria vascularis K+ effluxed from outer hair cells and nerves during auditory transduction. Thus, evidence exists for a transcellular path of K+ movement from outer sulcus cells through fibrocytes to the strial interstitial space, but a mechanism for facilitating such ion flow within the cells has not been elucidated. METHODS: The spiral ligament of glutaraldehyde-osmium tetroxide-fixed and Epon-embedded gerbil cochlea was examined by transmission electron microscopy. RESULTS: Ultrastructural examination disclosed an extensive membrane limited reticulum in the cytoplasm of type I, II, IV, and V fibrocytes of the lateral wall and in outer sulcus cells and their root processes. This system resembled the tubulocisternal endoplasmic reticulum present in some ion-transporting epithelia but appeared more to constitute a network of canaliculi and is referred to as the canalicular reticulum (CR). Many typical small Golgi complexes invariably accompanied the CR in the fibrocytes and sulcus cells, as we have found to be true of other epithelia known to contain CR and function in ion transport. Numerous mitochondria populated cytosol-containing CR. CONCLUSIONS: The data support the concept of transcellular K+ flux in type I, II, IV, and V fibrocytes and outer sulcus cells in the cochlea and lend credence to the view of CR as functioning in the movement of ions through cells. The constant and precise association of Golgi complexes with CR in the different cell types implies a functional relationship possibly concerned with biosynthesis of CR by Golgi elements, and the abundance of mitochondria near CR indicates an energy requirement for function of the reticulum or its biosynthesis.

Animals↗

PubMed1999

Determination of free calcium in guinea-pig cochlea perilymph by capillary electrophoresis with direct injection.

At present, the tinnitus mechanism is still not clear. Our experiments demonstrated that the concentration of free calcium in cochlea perilymph of tinnitus model guinea-pigs is lower than that in normal guinea-pigs. However, the volume of cochlea perilymph is so small that only 5-10 microL of sample can be obtained from each animal. We describe the application of CE to the detection of free calcium in guinea-pig cochlea perilymph. Direct injection was employed in this study. The separation was carried out at 10 kV. The capillary temperature was maintained at 20 degrees C, and indirect UV detection at 214 nm was employed. The samples were vacuum injected for 3 s. The run buffer was 0.005 mol/L imidazole with a pH of 4.30-4.50. The concentration of free calcium in the normal group was found to be in accordance with the reference data. The method has been applied to research on the tinnitus mechanism and for medical treatment.

Animals↗

PubMed2002

WDR1 colocalizes with ADF and actin in the normal and noise-damaged chick cochlea.

Auditory hair cells of birds, unlike hair cells in the mammalian organ of Corti, can regenerate following sound-induced loss. We have identified several genes that are upregulated following such an insult. One gene, WDR1, encodes the vertebrate homologue of actin-interacting protein 1, which interacts with actin depolymerization factor (ADF) to enhance the rate of actin filament cleavage. We examined WDR1 expression in the developing, mature, and noise-damaged chick cochlea by in situ hybridization and immunocytochemistry. In the mature cochlea, WDR1 mRNA was detected in hair cells, homogene cells, and cuboidal cells, all of which contain high levels of F-actin. In the developing inner ear, WDR1 mRNA was detected in homogene cells and cuboidal cells by embryonic day 7, in the undifferentiated sensory epithelium by day 9, and in hair cells at embryonic day 16. We also demonstrated colocalization of WDR1, ADF, and F-actin in all three cell types in the normal and noise-damaged cochlea. Immediately after acoustic overstimulation, WDR1 mRNA was seen in supporting cells. These cells contribute to the structural integrity of the basilar papilla, the maintenance of the ionic barrier at the reticular lamina, and the generation of new hair cells. These results indicate that one of the immediate responses of the supporting cell after noise exposure is to induce WDR1 gene expression and thus to increase the rate of actin filament turnover. These results suggest that WDR1 may play a role either in restoring cytoskeletal integrity in supporting cells or in a cell signaling pathway required for regeneration.

Actin Depolymerizing Factors↗