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At least 469 records · Page 26Linked to original sources
PubMed1987

Histopathological study of experimentally induced endolymphatic hydrops with emphasis on Reissner's membrane.

We investigated the histopathological changes of the guinea pig cochlea in experimentally induced endolymphatic hydrops 1, 2, 4 and 8 months after obliteration of the endolymphatic sac. In this paper special attention is given to the morphological changes created in Reissner's membrane. Reissner's membrane showed various foldings, bony wall connections, local thickenings, duplications, mesothelial defects, ruptures and atrophy. The incidence of these changes increased with survival time. The stria vascularis and hair cells showed degeneration starting apically and proceeding towards the cochlear base. The possible implications of these findings are discussed.

Animals↗
PubMed1990

A method for changing the avian endocochlear potential by current injection.

The endocochlear potential (EP) in the pigeon was found to be +10 +/- 3 mV. A method for changing the EP by current injection into the scala media is described. The EP change brought about was 1.6-2.9 mV/microA and was dependent on the distance from the tip of the current electrode. Single fiber activity in the cochlear ganglion could be recorded simultaneously with the current injection. These experiments have shown that decreases in the EP reduce the sound-evoked activity of primary afferent nerves and elevate their threshold.

Acoustic Stimulation↗
PubMed1990

Mesothelium of Reissner's membrane in guinea pigs: an electron microscopic study.

The mesothelial cells of Reissner's membrane in guinea pigs were found to be connected by junctional complexes. No cell discontinuities or gaps were observed by scanning or transmission electron microscopy. These results are not in accordance with previous studies. They were achieved by in vivo vascular perfusion fixation, handling of cochleae in protective specimen carriers, thiocarbohydrazide treatment and continuous dehydration. Findings in the present study indicate that the interepithelial space between the epithelial and mesothelial cell layers constitutes a specific compartment which must be considered when examining solute transport over Reissner's membrane.

Animals↗
PubMed1997

Structural maturation of the interface region between the stria vascularis and spiral ligament in the neonatal rat cochlea.

The ultrastructural morphology of the interface region between the stria vascularis (SV) and spiral ligament (SL) was examined in the neonatal rat cochlea via transmission electron microscopy. At postnatal day (PND) 3, morphology of both basal cells and fibrocytes was simple and immature. Only a small number of fibrocytes was observed in the SL. Intercellular junctions between basal cells and fibrocytes, and between adjacent fibrocytes, were few. At PND 7, the number of fibrocytes increased, and more organelles appeared within their cytoplasm. From PND 11 to 14, nuclei of the basal cells appeared to be more spindle-shaped and contained more heterochromatin. The cytoplasm of the fibrocytes was pale, and a greater number of cytoplasmic vesicles and mitochondria emerged. More intercellular junctions were observed between basal cells and fibrocytes at the interface region and between fibrocytes in the SL. By PND 21, the morphology of basal cells and fibrocytes and their intercellular junctions appeared to be adult-like. These morphological observations correlate with previous reports on the functional maturation of the developing rat cochlea.

Animals↗
PubMed2002

Degeneration of the stria vascularis during development in melanocyte-deficient mutant rats (Ws/Ws rats).

Developmental changes in the stria vascularis of white spotting (Ws) rats were examined by scanning and transmission electron microscopes and by diaminobenzidine-staining techniques. The stria of Ws/Ws homozygote rats was found to have both pigmented and non-pigmented portions. While the pigmented portions possessed intermediate cells in the same manner as the stria of wild +/+ rats, the non-pigmented portions lacked the cells. Examination at 1, 2, 3, 4, 6, 8 and 14 weeks after birth revealed a progressive degeneration in the marginal cells and strial capillaries in the non-pigmented portions. At 1 week, no significant differences were seen in the marginal cells of any of the rats examined. At 2 weeks, the basolateral infoldings of the marginal cells were seen to be well developed and adult-like in the pigmented portions of Ws/Ws rats and in +/+ rats. In the non-pigmented portions, the basolateral infoldings of the marginal cells appeared well developed; however, vacant spaces were seen around the basolateral infoldings. At 3 weeks, the basolateral infoldings of the marginal cells in the non-pigmented portions had become more atrophic, and the empty spaces around the basolateral infoldings had enlarged. Also, the marginal cells themselves had become flatter or thinner. These findings became more prominent at 4 weeks and 6 weeks. At 8 weeks and 14 weeks after birth, the marginal cells appeared markedly flat, and no basolateral infoldings were seen in the non-pigmented portions. Pigmented portions of the stria in Ws/Ws rats, on the other hand, showed normal development throughout this period. A DAB-staining examination of the stria capillary net in Ws/Ws rats showed it to be well developed at 3 weeks in both pigmented and non-pigmented portions. At 8 weeks, a thickening of the capillary basement membrane was apparent. The above findings lead the authors to believe that intermediate cells play an important role in the development and maintenance of marginal cells and the strial capillary system.

Animals↗
PubMed2003

A voltage- and Ca2+-dependent big conductance K channel in cochlear spiral ligament fibrocytes.

Evidence is accruing that spiral ligament fibrocytes (SLFs) play an important role in cochlear K(+) homeostasis, but little direct physiological data is available to support this concept. Here we report the presence and characterization of a voltage- and Ca(2+)-dependent big-conductance K (BK) channel in type I SLFs cultured from the gerbil cochlea. A single-channel conductance of 298+/-5.6 pS (n=28) was measured under symmetrical K(+). Membrane potentials for half-maximal open probability (P(o)) were -67, -45 and 85 mV with cytosolic free-Ca(2+) levels of 0.7 mM, 10 microM and 1 microM, respectively (n=8-14). The Hill coefficient for Ca(2+) affinity was 1.9 at a membrane potential of 60 mV (n=6). The BK channel showed very low activity (P(o)=0.0019, n=5) under normal physiological conditions, suggesting a low resting intracellular free [Ca(2+)]. Pharmacological results fit well with the profile of classic BK channels. The estimated half-maximal inhibitory concentration and Hill coefficient for tetraethylammonium were 0.086+/-0.021 mM and 0.99, respectively (n=4-9). In whole cell recordings, the voltage-activated outward K current was inhibited 85.7+/-4.5% (n=6) by 0.1 microM iberiotoxin. A steady-state kinetic model with two open and two closed stages best described the BK gating process (tau(o1) 0.23+/-0.08 ms, tau(o2) 1.40+/-0.32 ms; tau(c1) 0.26+/-0.09 ms, tau(c2) 3.10+/-1.2 ms; n=11). RT-PCR analyses revealed a splice variant of the BK channel alpha subunit in cultured type I SLFs and freshly isolated spiral ligament tissues. The BK channel is likely to play a major role in regulating the membrane potential of type I SLFs, which may in turn influence K(+) recycling dynamics in the mammalian cochlea.

Animals↗
PubMed2003

Distribution of gentamicin in the guinea pig inner ear after local or systemic application.

Uptake and retention of gentamicin by cells in the guinea pig inner ear after a single peritoneal injection or local application on the round window were investigated using immunocytochemistry to localize the drug. The cells that accumulated the drug under the two conditions were the same, but staining for the drug was more intense and was often accompanied by widespread cochlear degeneration following local application. Soon after drug administration by either route, there was diffuse staining for the drug throughout all tissue within the labyrinth, including bone. At later times when distinct cell staining became evident, virtually all cell types were found to be positive, with several cell types staining more darkly for the drug than hair cells, indicating that hair cells were not the most avid in accumulating gentamicin. The infracuticular portion of auditory and vestibular hair cells as well as type III fibrocytes of the spiral ligament were positively stained in almost all cases and these sites were found to be positive for as long as six months post administration. In animals with loss of the organ of Corti, there was unusually intense staining for gentamicin in root cells of the spiral ligament, in marginal cells of the stria vascularis, and in cells of the spiral limbus. Dark staining of surviving cells in cases with overt tissue destruction suggests that variability in the extent of damage caused by the drug was determined more by the degree of its local uptake than by differences in animals' capacities to metabolize the drug systemically. The present results show that gentamicin may damage or destroy all cochlear cells following a single round window application. The findings broaden the scope of our knowledge of cochlear gentamicin uptake and damage and have implications for treatment of patients with vestibular disorders by infusion of aminoglycosides into the middle ear, as well as implications for prospects of rehabilitating patients that have been deafened by aminoglycosides.

Administration, Topical↗
PubMed2003

Changes in cytochemistry of sensory and nonsensory cells in gentamicin-treated cochleas.

Effects of a single local dose of gentamicin upon sensory and nonsensory cells throughout the cochlea were assessed by changes in immunostaining patterns for a broad array of functionally important proteins. Cytochemical changes in hair cells, spiral ganglion cells, and cells of the stria vascularis, spiral ligament, and spiral limbus were found beginning 4 days post administration. The extent of changes in immunostaining varied with survival time and with cell type and was not always commensurate with the degree to which individual cell types accumulated gentamicin. Outer hair cells, types I and II fibrocytes of the spiral ligament, and fibrocytes in the spiral limbus showed marked decreases in immunostaining for a number of constituents. In contrast, inner hair cells, type III fibrocytes and root cells of the spiral ligament, cells of the stria vascularis, and interdental cells in the spiral limbus showed less dramatic decreases, and in some cases they showed increases in immunostaining. Results indicate that, in addition to damaging sensory cells, local application of gentamicin results in widespread and disparate disruptions of a variety of cochlear cell types. Only in the case of ganglion cells was it apparent that the changes in nonsensory cells were secondary to loss or damage of hair cells. These results indicate that malfunction of the ear following gentamicin treatment is widespread and far more complex than simple loss of sensory elements. The results have implications for efforts directed toward detecting, preventing, and treating toxic effects of aminoglycosides upon the inner ear.

Animals↗
PubMed1980

Nonlinear aspects of infrasonic pressure transfer into the perilymph.

The perilymphatic pressure was studied in response to various low frequency pressure changes in the ear canal. The pressure transfer was analysed and found to be nonlinear in many aspects. The pressure response was found to contain two time constants representing the inner ear pressure regulating mechanisms. The time constants showed an asymmetry in response to positive and negative going inputs--the effects to some extent proportional to input levels. Further nonlinearities were found when infrasonic sine waves were applied to the ear. Harmonic distortion and modulation appeared. When short bursts of infrasound were introduced a clear d.c. shift was observed as a consequence of an asymmetry in the response to positive and negative going pressure inputs. A temporary change in mean perilymphatic pressure was thus achieved and continued throughout the duration of the signal. At very low frequencies a distinct phase shift was detected in the sine waves. This appeared as a phase lead, breaking the continuity of the output sine wave.

Acoustic Stimulation↗
PubMed1981

Adenylate cyclase activity in the fetal and the early postnatal inner ear of the mouse.

The adenylate cyclase activity was analyzed in fetal, early postnatal and adult inner ears of the CBA/CBA mouse and also in approximately one month old inner ears from Shaker -1 and Shaker -2 mice. A comparison was made with the maturation of potassium levels in endolymph as investigated with the X-ray energy dispersive technique. Adenylate cyclase activity in the developing normal inner ear shows two significant periods of increases: from the 16th to the 19th gestational day in both the cochlear and vestibular parts of the labyrinth, and from birth to day 6 after birth in the lateral wall tissues of the scala media. During the first period the anatomical boundaries of the secretory epithelia are developing. The postnatal rise in adenylate cyclase activity correlates with the morphological maturation of stria vascularis at the cellular and subcellular levels and the rise in potassium content of endolymph. The rise of enzyme activity in the cochlear during the maturation of endolymph supports a link between adenylate cyclase and the control of inner ear fluids. Adenylate cyclase activity in stria vascularis/spiral ligament of Shaker -1 and Shaker -2 mice were at normal levels and correlated better with the rather normal morphology of the tissues than the abnormal composition of endolymph in these mutants.

Adenylyl Cyclases↗
PubMed1982

Influence of blood viscosity on cochlear action potentials and oxygenation.

Impairment of the cochlear blood supply of guinea pigs was induced in order to study the effects of hypoxia on the cochlear action potentials. The oxygenation of the cochlear structures was decreased by perfusing the ears with polycythemic hyperviscous blood. The validity of using this model of cochlear blood flow was based on the propensity of the blood to flow in a laminar way. Because of the streamlined flow pattern, the blood supplied by the two vertebral arteries does not mix within the common trunk of the basilar artery. The retrograde injection of polycythemic hyperviscous blood into one vertebral artery will affect the ear on the injected side only. The high viscosity of the polycythemic blood decreases the rate of flow of blood through the cochlear vessels; the high oxygen content of this blood, however, avoids hypoxia of the cochlea. Therefore, in order to make the slowdown in the blood flow evident, its oxygen content was reduced to a 'precritical level' before it was infused. Injecting normoviscous blood with a 'precritical level' of oxygen caused a mild reduction in the scala media pO2 of 15.2% for the whole group of twenty animals. The hyperviscous blood with the same level of oxygenation, however, reduced the pO2 in the scala media to 53.3% of normal. These findings explain the difference in the altered click-evoked action potentials in the two groups of animals.

Action Potentials↗
PubMed1983

Basilar membrane tuning properties in the specialised cochlea of the CF-bat, Rhinolophus ferrumequinum.

The greater horseshoe bat has greatly expanded frequency mapping, and morphological specialisations, in the first half turn of its cochlea and a sudden transition to normal mapping. Amplitude and phase of vibration have been measured on various structures in the expanded and normal regions and have not revealed any sharply tuned responses. Amplitudes are much lower than those found in other species and frequently show a deep notch in the 77-84 kHz region. The high-frequency cut-off frequencies are tonotopically organised but deviate from the Bruns map, so that hair-cell tuning appears to occur at a frequency at which basilar membrane vibration is small. In the basal region, phase differences were frequently found between the inner and outer parts of the basilar membrane. These appear to be due to interaction between two components of motion and are probably not indicative of a further filtering mechanism. There is no evidence for reflection of the travelling wave at the transition.

Acoustic Stimulation↗
PubMed1985

Carbohydrates detected by lectins in the vestibular organ.

In the vestibular organ the presence of carbohydrates in the cupula and otoconia of young (6-day-old) and adult rats was investigated using fluorescent lectins. The following sugars have been identified in both young and adult rats: N-acetyl-glucosamine, galactose, mannose and fucose. In contrast, N-acetyl-galactosamine was not detected. In order to demonstrate the specificity of the reaction, control experiments were performed after preincubation of the lectin with its specific inhibitory sugar. The same sugars were identified in calcified (i.e. otoconia) and non-calcified (i.e. cupula) structures. The role of these sugars in the mineralization and fusion process of otoconia is discussed.

Animals↗
PubMed1986

The developmental appearance of a major basilar papilla-specific protein in the chick.

The sensory epithelium of the chick cochlea, the basilar papilla, contains a major protein of approximately 23,000 daltons. This protein was as abundant as actin in the papilla, yet could not be found in significant quantities in any other cochlear tissue. The protein appeared at a time in development when other studies have shown that the chick embryo develops peripheral auditory competence. These observations suggest a role for this protein in cochlear function.

Age Factors↗