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PubMedDate not supplied

The ultrastructure of the basilar membrane in the cat.

A detailed study of the feline basilar membrane was performed in 13 cochleae with light microscopy and in six with electron microscopy. The distribution of the mesothelial cells and homogeneous ground substance with the filaments was recorded and plotted as a function of length along the cochlear duct. The width, thickness and number of filaments were also measured. In the lower basal turn the basilar membrane was narrowest and its entire thickness was occupied by filaments. In the apical region the width was maximal and the filaments were fewer. The density of the filaments counted in the bundles showed no significant difference along the cochlear duct or across the width of the basilar membrane, but the number of filaments decreased markedly (approximately a ten-fold difference) from base to apex. The number of mesothelial cells increased towards the apex. These morphological characteristics may be related to the different motion pattern of the basilar membrane along the length of the cochlear duct. A discontinuity of the basement membrane was noted in the apical region in all cochleae studied. These gaps seemed to provide structural evidence for the permeability of the basilar membrane in this area. The vas spiralis was present as a blood vessel in two specimens and only in the apical region. Thus, its function as the sole nutritional source for the organ of Corti is doubtful.

Age Factors↗
PubMed1985

Parameters of growth in the embryonic and neonatal chick basilar papilla.

The growth of the basilar papilla in the chick cochlear duct was studied utilizing light, scanning, and transmission electron microscopy. The ages of the cochleae investigated ranged from embryonic day 6 to post-hatching day 7. The changes in the length and width of the basilar papilla as well as the establishment of its spatula-like shape were correlated with the maturation of the hair cells' apical surfaces and the changes in the cellular organization of the sensory epithelium. The histological reorganization of the distal hair cell nuclei was concomitant with the broadening of the distal region of the basilar papilla and occurred at a later stage than the reorganization of the proximal hair cell nuclei. Since the stereociliary bundles on all the hair cells are differentiated quite early, it appears that the delayed reorganization of the distal nuclei is associated with anatomical constraints on the cochlear duct, rather than a later differentiation of the distal sensory epithelium. A clear understanding of how growth of the cochlear duct influences both the distribution of hair cells on the basilar papilla's surface and the cellular organization in the sensory epithelium is critical to future studies correlating ultrastructural development with functional maturation of the auditory system.

Animals↗
PubMedDate not supplied

Endolymphatic hydrops in children.

Apart from clinical observations of Ménière's disease in children, there have only been a few histological descriptions of endolymphatic hydrops (EH) as an incidental finding in children. In this paper we report on the incidence of EH in temporal bones of children. One hundred eighteen temporal bones from 70 infants between newborn and 10 years (average age 12.9 months) were analyzed by light microscopy for EH of the cochlear duct, which was defined as a bulging of Reissner's membrane into the scala vestibuli in more than one turn of the cochlea. All endolymph spaces were carefully examined for factors such as an obliterated ductus reuniens which may have contributed to the development of EH. In 64 (54.2%) of the 118 temporal bones, a bulging of Reissner's membrane in the cochlear duct was found. In 65.6%, the bulging was confined to the apical turn and since the significance of isolated apical hydrops is controversial, we elected not to consider this group as having hydrops. Twenty (16.9%) bones met our criteria for a diagnosis of EH. Compared to the high incidence of bulging in the cochlear duct, fewer saccules and utricles were dilated. In approximately half of the temporal bones (49.2%), the ductus reuniens was collapsed. The ductus reuniens seems to be closed in its normal position and might open when pressure occurs due to an increasing volume of endolymph. If there is a permanent closure, EH may result. Our investigation does not indicate that EH is associated with a specific disease; however, where there were congenital anomalies the incidence of EH was higher.(ABSTRACT TRUNCATED AT 250 WORDS)

Child↗
PubMed1985

Inner ear structure in the deaf and normally hearing Dalmatian dog.

Both cochleae of two 6-week-old Dalmatian dogs of the same litter were examined by means of surface specimens and histological section techniques. Basic quantitative data on the morphometry of the cochlear duct in the hearing (though hypopigmented) pup are presented. The cochlear ducts of the deaf (though normally coloured) pup exhibited in general the same alterations (collapse of the scala media) as described in the literature. In addition, we describe also the coalescence of membranous structures, projection of the tectorial membrane up to the spiral ligament and preservation of inner hair cells in the second (i.e. middle) cochlear coil. These new findings complement the previous data and indicate an alternative possible course of hereditary inner ear degeneration in the Dalmatian dog.

Animals↗
PubMedDate not supplied

Intercellular fluid pathways in the organ of Corti of cat and man.

The intercellular junctions in the organ of Corti of cat and man were examined with the electron microscope. In contrast to the zone of tight junctions, or zonulae occludentes, which were present at the surface of cells lining the scala media, there was no tight junctional specialization among the cells of the tympanic lamina, perilymphatic lining cells of the scala vestibuli, basal processes of the supporting cells of the organ of Corti or cells of the spiral limbus and spiral ligament. These findings suggest the possibility of fluid continuity between the scala vestibuli and scala tympani all along the cochlear duct. Morphological evidence for an intercellular diffusion barrier was present only at the endolymphatic surfaces of the cochlear duct and between the processes of the basal cells of the stria vascularis in cat and man.

Animals↗
PubMed1985

Morphologic changes in the guinea pig cochlea following cochleostomy--a preliminary scanning electron microscope study.

Fistulization of the membranous labyrinth via a surgically created endolymphatic-perilymphatic shunt (cochleosacculotomy) is currently being advocated as a treatment for endolymphatic hydrops. As a preliminary study to the investigation of the effects of labyrinthine fistulization on the hydropic condition, we sought first to reproduce the cochleosacculotomy procedure in a series of normal animals. Fistulization of the cochlear duct was performed in 15 normal animals using a tungsten wire directed via the round window through the cochlear partition in the region of the organ of Corti. The animals were sacrificed at regular intervals and the cochleas examined for histopathologic changes with the scanning electron microscope. Observations suggest that discrete permanent fistulization of the cochlear duct in the normal guinea pig results in progressive sensory cell degeneration. The implication of these observations and the apparent difference between these results and the experience thus far reported in humans are discussed.

Animals↗
PubMed1991

Effect of isepamicin dosing scheme on concentration in cochlear tissue.

To investigate the possible effect of the dosing scheme of aminoglycosides on their concentration in the cochlear tissue, we gave two groups of 12 guinea pigs subcutaneous doses of 45 mg of isepamicin (ca. 30 mg of active product) per kg of body weight daily for eight consecutive days. The first group received the drug by continuous infusion, while the second group received it by single daily injection. On the final day of administration, the animals were sacrificed and the cochlear tissue was removed. The tissues from the cochleas of pairs of guinea pigs were pooled. The isepamicin concentrations in the cochlear duct tissue (organ of Corti plus lateral wall) and the cochlear nerve tissue were determined separately. Hearing levels before and after treatment were assessed by means of frequency-specific auditory brain stem responses (ABR). The creatinine level in serum was determined on the last day of the administration. None of the animals in either group showed signs of renal insufficiency or of hearing impairment. The median isepamicin concentration in the cochlear duct was 2.40 micrograms/mg of protein after continuous administration and 2.50 micrograms/mg of protein after once-daily administration, compared with the concentration in the cochlear nerve, where it was 1.93 micrograms/mg of protein after continuous administration and 2.59 micrograms/mg of protein after once-daily administration. These differences are statistically insignificant. The results give evidence for linear uptake kinetics of isepamicin in the inner ear tissue and may be directly relevant to the clinical dosing of the drug.

Animals↗
PubMed2005

Pathological alterations of strial capillaries in dominant white spotting W/Wv mice.

Dominant white spotting W/W(v) and W(v)/W(v) mice are well-known mutants that lack strial intermediate cells in their cochlea and manifest hereditary sensorineural hearing loss. We recently reported marked thickening of and IgG deposition on the basement membrane of strial capillaries in W/W(v) mutant mice, similar to observations made in aged animals and in animals with autoimmune sensorineural hearing loss. The present study aimed to clarify the age-dependent changes in these pathological findings of strial capillaries in the W/W(v) mice. Male WBB6F1 +/+ and dominant white spotting W/W(v) mutant mice were sacrificed by transcardiac perfusion with paraformaldehyde solution. The cochlear ducts were isolated and subjected to light- and electron-microscopy, immunohistochemistry, immunoelectron microscopy. Alternatively, lanthanum chloride tracer examination in the isolated cochlear ducts was performed in order to compare the permeability of the strial capillaries between +/+ and W/W(v) mice. In the W/W(v) mice, thickening of and IgG deposition on the basement membrane of strial capillaries were observed as early as 1 week after birth and became more noticeable with age. Deposited IgG was preferentially localized to the thickened basement membrane and was also observed in partially the intercellular space between adjacent of endothelial cells. In addition, pinocytotic vesicles both in the apical and basal lesions of such cells also showed IgG deposition. Lanthanum chloride was retained along apical plasma membrane of the endothelial cells in the +/+ mice but penetrated through the endothelial layer in the W/W(v) mice. These results indicate that active transport via pinocytotic vesicles as well as increased permeability of strial capillaries in the W/W(v) mice occur in the early stage after birth, resulting in the morphological alterations in the strial capillaries of these mice.

Aging↗
PubMed1983

Intracellular and extracellular ion content of the endolymphatic sac.

The Cl- activity in the endolymph of the endolymphatic sac and in the cochlear duct was measured with Cl- sensitive double-barreled microelectrodes. The Cl- activity in the endolymphatic sac fluid was lower than in the cochlear duct. A small, positive, DC potential was recorded in the endolymphatic sac. During anoxia, the DC potential decreased while the Cl- activity in the endolymphatic sac increased. The K/Na ratio in the epithelial cells and subepithelial tissue of endolymphatic sac was measured using the LAMMA technique. The K/Na ratio in the epithelial cells decreased after ethacrynic acid injection (60 mg/kg i.v.). These findings suggest that chloride in the endolymphatic sac is actively transported inward and outward.

Animals↗
PubMed1983

Clinical implications of experiments on alteration of the labyrinthine fluid pressures.

Hearing is affected by changes in hydrostatic pressure of the perilymph, but very high pressures are required to produce a significant loss. Among the observed findings in cats are a rapidly reversible decrease in the sensitivity of the cochlear microphonic that is greater for low frequencies, harmonic distortion and reduction of dynamic range as measured by the input-output function for the cochlear microphonic, and a change in the summating potential from negative to positive. These changes are attributed to a temporary reduction in the size of the cochlear duct due to a shift of water molecules out of the cochlear duct into the blood until the resulting increase in osmotic pressure balances the increase in hydrostatic pressure. Consequently, the organ of Corti is biased "upward" away from the scala tympani. Increasing the hydrostatic pressure of the endolymph produces a "downward" biasing of the organ of Corti and has an opposite effect upon the summating potential. Presumably this is what happens in Meniere's disease. Because of the presence of the perilymphatic canaliculi, the locus of the hydrostatic pressure effect is assumed to be in the region of the reticular lamina. A theory has been developed to explain why cochlear function is very sensitive to relative differences between the hydrostatic pressures of the perilymph and the endolymph but is resistant to large variations in the absolute magnitudes of those pressures. Some of the clinical implications of this theory are discussed.

Animals↗
PubMed1978

[Distribution pattern in the guinea pig cochlea of intravitally injected peroxidase].

Following perilymphatic perfusion and injection into the cisterna cerebello-medullaris, respectively, the distribution pattern of horseradish peroxidase in the cochlea of the guinea pig was studied light and electron microscopically. The findings prove effective tight junctions (zonulae occludentes) between the cells of the epithelial lining of the endolymphatic compartment. At the level of the reticular membrane the tight junctions are far more extended than elsewhere at the cochlear duct epithelium. From the findings a fairly rapid exchange is suggestive between the lymphatic space of the organ of Corti and the tympanic scale. Various types of cells of the cochlear duct actively take up considerable amounts of peroxidase. However, endocytosis of peroxidase by hair cells and particularly by the outer ones is rather scanty. Passive permeation of the tracer through the membran of undamaged hair cells was disproven.

Animals↗
PubMed1997

Development of 11 beta-hydroxysteroid dehydrogenase expression in the rat cochlea.

11 beta-hydroxysteroid dehydrogenase (11 beta-HSD) catalyzes the transformation of active glucocorticoid (GC) steroids to inactive 11-oxosteroids, as well as the reverse reaction. 11 beta-HSD was previously demonstrated specifically in the spiral ligament of the lateral cochlear wall where it was co-localized with adrenal steroid receptors. These findings imply that 11 beta-HSD regulates binding of corticoids to their inner ear receptors. The GC receptor expression initially occurs around the critical maturation period of the cochlear duct. 11 beta-HSD, which is an integral part of the cochlear steroid receptor system, could indirectly affect glucocorticoid-mediated induction processes. In this study the expression of 11 beta-HSD was studied in the postnatal rat cochlea from the 3rd to 30th postnatal day. Bouin's fixed, paraffin-embedded cochlear sections were processed for immunocytochemical detection of 11 beta-HSD using polyclonal antibodies against 11 beta-HSD. 11 beta-HSD expression appeared at the 12th postnatal day at low levels in spiral ligament tissues. From the 15th postnatal day, 11 beta-HSD expression was stronger and similar to that of the adult cochlea. No additional inner ear tissue region expressed 11 beta-HSD enzyme during the observed period. 11 beta-HSD expression coincides with the onset of functional maturity of the rat cochlear duct. The expression of 11 beta-HSD is preceded by the expression of GC receptors which appeared at the 7th postnatal day in the rat cochlea. These results further suggest an integrative role of the cochlear steroid receptor system in the homeostasis and functional maturation of the cochlea.

11-beta-Hydroxysteroid Dehydrogenases↗
PubMed1982

[The dynamic behavior of inner ear fluids].

To study the movement of the endolymph and the exchange of substances between serum and endolymph or perilymph, fluorescent dyestuffs were applied directly into the endolymph of the cochlear duct or were given intraperitoneally. In addition, glucose concentrations in endolymph and perilymph were determined after experimental alteration of blood glucose levels. The bulk flow of the endolymph in the cochlear duct in the direction towards the saccule is much quicker in the basal coil than has been described up to now. At the base of the cochlea the perilymph of the scala tympani hardly shows any movement. Fluorescein applied parenterally was demonstrated in the upper coils of the scala tympani more intensively than in the scala vestibuli. In the basal portion of the scala tympani it is practically undetectable. The changes in the glucose concentration of the endolymph were less than in the perilymph. The movement (bulk flow) of the inner ear fluids and the exchange of different substances from the serum is different in the cochlea not only between endolymph and perilymph but also between basal and the apical parts.

Animals↗
PubMedDate not supplied

Influences on the coiling of the cochlea.

The growth and shape of the cochlea appears to be controlled by the formation of the cartilaginous capsule. Coiling of the cochlear duct is apparently the result of the physical barrier and support provided by the cartilage cells differentiating from mesenchyme surrounding the ventral portion of the otocyst. In addition, tissue interactions between this mesenchyme and the developing cochlear duct will influence the formation of the cartilaginous capsule and they may also be the origin of one of the controlling agents for the coiling mechanism.

Animals↗
PubMed1983

Stria vascularis in acoustic trauma.

Mechanical energy of noise destroys not only the organ of Corti, Reissner's membrane, and the basilar membrane but also the lateral wall of cochlear duct. The damage is characterized by ruptures running parallel to the attachment of the basilar membrane in the prominentia spiralis or sulcus spiralis externus. The other signs of injury after acoustic overstimulation are blisterlike detachments of the stria vascularis from the spiral ligament. The mechanism of injury is interpreted as the result of interaction of given mechanical properties of exposed tissues and of the kinetic energy of sound in narrow segments of cochlear duct.

Acoustic Stimulation↗
PubMed1991

Hair cell differentiation in the developing chick cochlea and in embryonic cochlear organ culture.

We have defined a method for growing chick embryonic cochleae in organ culture that preserves many aspects of hair cell differentiation. Cochlear ducts were isolated from embryonic day 8 chicks, placed in organ culture, and incubated for 48 hours (to a point equivalent to embryonic day 10). The cultured ducts were then fixed and processed for scanning electron microscopy. As controls, cochlear ducts at embryonic days 8 and 10 were dissected and immediately fixed and processed for scanning electron microscopy. We chose this period to culture cochleae because at the corresponding time in vivo hair cells undergo a dynamic phase of differentiation. During this time, the number of stereocilia in the stereociliary bundle increases, and two to three rows of stereocilia nearest the kinocilium elongate, initiating the staircase pattern of the bundle. Also, the orientation of many hair cells shifts from nonpolarized at embryonic day 8 to polarized toward the inferior edge of the basilar papilla at embryonic day 10. Many of these aspects of hair cell differentiation proceed normally in organ culture. The appropriate distal-to-proximal gradients of hair cell density, apical surface area, and stereociliary number are preserved. Elongation of the 1-2 stereociliary rows next to the kinocilium continues, and more stereociliary bundles are oriented toward the inferior edge in cultured cochleae than in embryonic day 8 chicks. It appears that cochlear organ culture can serve as an effective method with which to study how hair cell differentiation is regulated.

Animals↗
PubMed1993

Analyses of Mössbauer mechanical measurements indicate that the cochlea is mechanically active.

Using the results of Mössbauer measurements, mechanical activity in the cochlea was tested for by comparing the measured basilar membrane (BM) transverse velocity amplitude with that calculated for a lossless mechanically passive system, derived from the measured BM velocity phase. If the cochlea is considered to be a lossless mechanically passive system, then the transverse velocity amplitude can be calculated from the group velocity and the relative variation of stiffness along the BM. The group velocity can be derived from the Mössbauer phase measurements, and the relative variation of stiffness along the BM can be derived from the frequency map of the cochlea. Making some general assumptions, the actual transverse velocity amplitudes are then compared from the Mössbauer amplitude data with those derived from the Mössbauer phase data, to determine if there is a significant transverse velocity gain. This operation was performed on several sets of Mössbauer data. From Mössbauer data showing sharp tuning, differences were found of up to 40 dB between the actual transverse velocity amplitude and the calculated lossless passive transverse velocity amplitude derived from the phase data. Examination of the assumptions made during the calculation of the lossless passive transverse velocity amplitude showed that none could account for a 40-dB transverse velocity gain. Thus, it is concluded that this transverse velocity gain can only be accounted for by the contribution to the amplitude of the transverse BM velocity by mechanically active elements along the cochlear duct. From Mössbauer data showing much less sharp tuning, it was found that the actual transverse velocity amplitude was approximately equal to the calculated lossless passive transverse velocity amplitude, basal to the characteristic place. This result is attributed to the disabling of the mechanically active elements along the cochlear duct. Apical to the characteristic place, the actual transverse velocity amplitude is shown to behave in a manner that suggests that the effective damping increases markedly in this region. This increase in effective damping is not necessarily due to an increase in viscous damping but could be due to any mechanism removing energy from the BM traveling wave. As an example, this paper discusses how this effective damping could be accounted for the transfer of energy to another mode of vibration at the characteristic place.

Acoustic Stimulation↗
PubMed1991

Radiology for cochlear implants.

One fifth of patients selected for cochlear implants have such bony irregularities in the cochlear duct that full insertion of a multichannel electrode array is impossible. Three cases of cochlear deafness are presented where pre- and post-operative radiology played an important part in the management. Standard CT at 2 mm cuts is compared with ultra high resolution CT at 1 mm cuts. The pitfall of poor definition is that the inexperienced surgeon may find himself unexpectedly drilling out an obliterated cochlear duct. Sections 30 degrees caudal to Reid's infra orbito-meatal base line at 1 mm intervals give maximum information for minimum radiation. Plain films show the placement of individual platinum electrode contacts in relation to the spiral 'frequency map' of the cochlea. This is vital information for the audiologist who has to route specific frequencies to specific sites within the ear for a good hearing result.

Adult↗