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PubMed1991

Transmission of cerebrospinal fluid pressure changes to the inner ear and its effect on cochlear microphonics.

Alterations in inner ear fluid pressure and cochlear microphonics (CM) associated with increased cerebrospinal fluid (CSF) pressure were studied in the guinea pig. Hydrostatic pressure in the endolymph and perilymph of the cochlea were measured by use of a servo-controlled micropipet system. Endolymphatic and perilymphatic pressure increased in a linear manner with little or no time lag following pressure increases of 0-50 mm Hg. There was no pressure gradient between the endolymph and perilymph. CM in response to 500 Hz and 4000 Hz tone bursts was recorded before, during and after CSF pressurization. The input-output function of CM showed suppression of 2-8 dB in both maximum output and sensitivity unless the increase in CSF pressure exceeded a level which reduced the cochlear blood flow.

Animals↗
PubMed1994

The effect of 6 kHz tone exposure on inner ear function of the guinea pig: relation to changes in cochlear microphonics, action potential, endocochlear potential and chemical potentials of K(+)-ions and Na(+)-ions, using a double-barrel glass electrode.

Using 97 male albino guinea pigs and applying electrophysiological methods, the effects of a 6 kHz tone were investigated at a moderate sound pressure level to the inner ear during a 24-h exposure time. Following exposure to the 6 kHz tone at 90 dB, cochleas showed decreased maximum output voltage of cochlear microphonics (CM) and action potential (AP). In the endolymph, K+ ion and Na+ ion concentrations remained unchanged during 40 min anoxia and 90 dB tone exposure. At 80 dB sound exposure decreases in maximum output voltage of CM and AP and decreases in the absolute value of EP could not be detected. Endolymph K(+)-ion Na(+)-ion concentrations were also unchanged. These findings indicate that diffusion potentials are induced at the same time as decreases of maximum output voltage in CM induced by exposure to sound at 90 dB.

Action Potentials↗
PubMed1976

[Formation of the inner ear lymphs. Permeability of inner ear membranes (author's transl)].

1. The endolymphatic system is morphologically a close system. The inner surface of the wall is tightly lined with an epithelium of ectodermal origin. The perilymphatic spaces are enlarged intercellular spaces which are built from the embryonic mesenchyme. 2. The perilymph ist an ultrafiltrate of plasma. There is probably a flow from the cerebrospinal fluid which is constantly renewed. The diffusion in the perilymph is dependent on the concentration and the size of the molecules. The endolymph is mainly a perilymph-filtrate. The "secretory" epithelia (e.g. stria vascularis cells and other tissues) of the endolymphatic system perform an important role to sustain the potassium and sodium concentrations. The ionic concentrations regulate the water movement also the volume of the endolymphatic spaces. They are maintained by anoxy-sensitive pumps. 3. The DC potential within the endolymphatic spaces represents the movement of certain electrical charge through membranes. By applying various inhibitors it is possible to distinguish the pumping mechanisms, and to observe the continuous changes of potassium and sodium concentrations with Na+ specific electrodes and K+ specific electrodes. There are probably three interdependent sources of driving-forces: a. A positively electrogenic K+-pump which is anoxia-sensitive and can be inhibited by Ethacrynic acid. This mechanism is more active in stria cells and less so in utricle and saccule. b. A negatively electrogenic Na+-K+ exchange-pump in all parts of the endolymphatic spaces is inhibited by Ouabain or anoxia. c. The passive diffusion of potassium-ions from endolymph to perilymph results an electro-negative effect.

Animals↗
PubMed1976

On the mechanism of the Menière attack.

Three theories are discussed dealing with the origin of the Menière attack: 1) The hypothesis of pressure induced changes is disproved. 2. The stimulation of the crista epithelium by a mechanical cupula deviation has been investigated. The results showed that the changes in action potential frequency of the ampullary nerve induced by maintained bending of the cupula, always declined and returned to resting potential frequency within a very short period of time usually within 1 min. Preventing the "elastic return" of the cupula did not change the time constant of this response decline. This proves that a Menière nystagmus lasting for hours, can not be elicited by a mechanical deformation of the cupula. 3) The paralyzing influence on vestibular nerve fibres by K+ ions in endolymph, leaking into perilymph spaces has earlier been demonstrated by the author. When the distended membranous labyrinth ruptures at predestined weak spots, leaking endolymph may reach and paralyze different nerve branches. This can explain all the main symptoms of a Menière attack.

Action Potentials↗
PubMed1983

[Experimental studies on the effect of labyrinth anesthesia].

Injection of tetracaine into the tympanic cavity inhibits, independently of histologic lesions of the round window membrane, the active electrogenic pump in the stria vascularis cells. The DC potential in the endolymph is reduced with increasing doses of tetracaine, while the K+-Cl- activity is unchanged for 120 min. This drug does not alter the permeability of Reissner's membrane. Near the stria vascularis area, the oxygen pressure in the endolymph increases significantly after the effects of 4% tetracaine.

Anesthesia, Local↗
PubMed1977

Experimental study of sacculotomy in endolymphatic hydrops.

Thirty-nine guinea pigs were used for four groups of experiments: 1. sacculotomy only, 2. sacculotomy and simultaneous obliteration of the endolymphatic duct, 3. sacculotomy followed by obliteration of the endolymphatic duct, and 4. obliteration of the endolymphatic duct followed by sacculotomy. Sacculotomy alone caused only minimal cochlear pathology, whereas sacculotomy on hydropic ears produced severe atrophy of the organ of Corti and cochlear neurons as well as connective cells of the limbus. There was histological evidence that Reissner's membrane in hydropic ears was ruptured by the sacculotomy procedure. The primary cause for the severe atrophic changes is thought to be the toxic effect of intermixing perilymph with a large volume of endolymph. The surgically induced saccular tears appeared to be healed in all ears, and the procedure had no significant effect on the course of endolymphatic hydrops. Although two out of eleven specimens in which sacculotomy was performed on hydropic ears showed tears and collapse of Reissner's membrane, since others with similar tears showed extensive hydrops, the possibility of artifact could not be ruled out. In one specimen with simultaneous sacculotomy and obliteration of the duct, persisting fistulae were noted at the sites of accidental fracture of the osseous spiral lamina; this ear is the only one which failed to develop hydrops following obliteration of the duct. The results of this experiment, namely sacculotomy on hydropic guinea pig ears, suggest that sacculotomy is not a rational procedure for the control of endolymphatic hydrops in Ménière's disease for the following reasons: 1. surgically induced tears in the saccular wall are followed by rapid healing and 2. intermixing of perilymph and a large volume of endolymph causes toxic atrophy of the limbus, organ of Corti and cochlear neurons.

Animals↗
PubMed1977

[Pharmacokinetical, histological, and histochemical investigation on the ototoxicity of gentamicin, tobramycin, and amikacin (author's transl)].

The pharmacokinetics of gentamicin, tobramycin, and amikacin in the inner ear fluids and serum of the guinea pig were studied. The concentrations of these antibiotics were determined by a microbiological method and could be confirmed by the use of 14C-labeled gentamicin. Retention was clearly demonstrated in perilymph and endolymph, whereas there was no retention in the cerebrospinal fluid and the compartments of the eye. A linear relation between concentrations in the perilymph and dosage of gentamicin was ascertained. There was no difference between the concentration of drug in endolymph and that in perilymph. The concentrations of these antibiotics in the perilymph were symmetrical and many times higher than those in the brain. Long-term treatment did not influence the pharmacokinetics of the three antibiotics in the inner ear. However, increased levels of drug in the inner ears in animals with uremia and in some animals with otitis media explained the increased ototoxicity that was observed in histological investigations of these two conditions. Cisternal puncture and diuretics did not change the concentrations of aminoglycoside antibiotics in the inner ear. In large experimental series the hair cell degeneration pattern of the new aminoglycoside antibiotics was determined by the surface preparation technique as well as the influence of the different factors upon this pattern. A prophylactic effect on the ototoxicity of the aminoglycoside antibiotics could not be found in the 2,3-dimercaptopropanol, but by dividing the daily dosage administered. Young guinea pigs were generally not very sensitive to gentamicin, in some cases however much more. Late ototoxicity could not be found after administration of gentamicin. The pharmacokinetical and especially the histological investigations allowed an evaluation of the ototoxicity of the new aminoglycoside antibiotics. By histochemical investigations no influence of the new aminoglycoside antibiotics upon the amount of unspecific esterases and alkaline phosphatase in the inner ear could be detected, but an increase of the amount of acid phosphatase in slightly damaged outer hair cells.

Amikacin↗
PubMed1997

Altered calcium homeostasis in the rat cochlear duct and endogenous corticosteroid insufficiency.

Free calcium concentration (CCa2+) profiles were evaluated in perilymph, endolymph, marginal cells, spiral ligament and blood serum of adrenalectomized (ADX) rats. Free CCa2+ was significantly greater in perilymph and significantly reduced in the serum of the ADX animals as compared to sham-operated animals. In addition, higher levels of free CCa2+ were found in the spiral ligament in ADX animals. Free CCa2+ did not appear to be affected by ADX in marginal cells and endolymph. These data suggest that marked reductions in endogenous levels of corticosteroids may have a systematic effect on free CCa2+ that is detectable in blood serum as well as cochlear fluids and tissues.

Adrenal Cortex Hormones↗
PubMed1980

Embryogenesis of the inner ear. IV. Post-natal maturation of the secretory epithelia of the inner ear in correlation with the elemental composition in the endolymphatic space.

The rise of the potassium concentration in the endolymphatic space occurred between the 4th and 8th day after birth (DAB). During this time morphological maturation of the stria vascularis was ended. The increasing concentration of potassium in the developing endolymph parallelled in the vestibular and cochlear parts of the labyrinth. The dark cell epithelium surrounding vestibular organs was, however, ultrastructurally mature at birth except for an increase of the number of intercellular digitations toward the basal membrane maturing during the first days postpartum. The maturation of endolymph thus took place prior to the development of the endocochlear potential.

Animals↗
PubMed2001

Occurrence of NaK-ATPase isoforms during rat inner ear development and functional implications.

This study examined the presence of NaK-ATPase isoforms in the developing inner ear of the rat and studied the importance of functional subunit combinations in endolymph homeostasis. The findings were: (a) the combination alpha 1 beta 1 is found in epithelial, mesenchymal, and neural inner ear cells with an early starting expression 14 days postconception (dpc) in some endolymphatic sac cells; (b) from 1 day after birth (dab) expression of alpha 1 beta 2 is observed in marginal cells, vestibular dark cells, and certain vestibular nonsensory cells; (c) a transient expression of alpha 2 beta 1 is found in suprastrial fibrocytes and spiral ligament fibrocytes type II between 10 and 15 dab; (d) starting at 16 dpc the combination alpha 3 beta 1 is uniquely expressed in inner ear neural cells (as in other neural tissues). In conclusion, during development a switch from alpha 2 beta 1 towards alpha 1 beta 1 is observed in suprastrial fibrocytes and in spiral ligament fibrocytes type II. Thus, according to the biochemical characteristics of these combinations, a switch towards a NaK-ATPase with higher capacity takes place. In addition, prominent expression of the alpha 1 beta 2 combination in predominantly K+ ion transporting marginal and dark cells is in accordance with the characteristic of this combination and thus with the presumed function of these cells as important K+ suppliers for the endolymph. We believe this combination in certain vestibular nonsensory cells to be involved in K+ sensing. Early expression of the alpha 1 beta 1 combination in the endolymphatic sac, prior to that in the other parts of the inner ear, suggests that this structure may be involved to some extent in the development of the vestibulum and cochlea.

Animals↗
PubMed2006

Large Na(+) influx and high Na(+), K (+)-ATPase activity in mitochondria-rich epithelial cells of the inner ear endolymphatic sac.

Fluid in the mammalian endolymphatic sac (ES) is connected to the endolymph in the cochlea and the vestibule. Since the dominant ion in the ES is Na(+), it has been postulated that Na(+) transport is essential for regulating the endolymph pressure. This study focused on the cellular mechanism of Na(+) transport in ES epithelial cells. To evaluate the Na(+) transport capability of the ES epithelial cells, changes in intracellular Na(+) concentration ([Na(+)](i)) of individual ES cells were measured with sodium-binding benzofurzan isophthalate in a freshly dissected ES sheet and in dissociated ES cells in response to either the K(+)-free or ouabain-containing solution. Analysis of the [Na(+)](i) changes by the Na(+) load and mitochondrial staining with rhodamine 123 showed that the ES cells were classified into two groups; one exhibited an intensive [Na(+)](i) increase, higher Na(+), K(+)-ATPase activity, and intensive mitochondrial staining (mitochondria-rich cells), and the other exhibited a moderate [Na(+)](i) increase, lower Na(+), K(+)-ATPase activity, and moderate mitochondrial staining (filament-rich cells). These results suggest that mitochondria-rich ES epithelial cells (ca. 30% of ES cells) endowed with high Na(+) permeability and Na(+), K(+)-ATPase activity potentially contribute to the transport of Na(+) outside of the endolymphatic sac.

Animals↗
PubMed1999

Immunological identification of an inward rectifier K+ channel (Kir4.1) in the intermediate cell (melanocyte) of the cochlear stria vascularis of gerbils and rats.

The cochlear stria vascularis produces the positive endocochlear potential (EP) and the endolymph. Both the EP and the endolymph are essential for the physiological function of hair cells. The intermediate cell is one of several cell types constituting the stria vascularis. It is known that inward rectifier K+ channels can play a constitutive role in the determination of the resting membrane potential. Localization of a member of the inward rectifier K+ channel family, Kir4.1, in the stria vascularis of gerbils and rats was investigated by immunological methods. A polyclonal antibody specific to the C-terminus of the rat Kir4.1 channel was raised in rabbits. Immunostaining of dissociated cells revealed that the Kir4.1 channel was localized to the intermediate cell, but not to the epithelial marginal cell. Subcellular localization of the Kir4.1 channel to the plasma membrane of the intermediate cell was confirmed by immunoelectron microscopy. Immunostaining of whole-tissue preparations revealed a network-like structure composed of intermediate cells. It seems likely that the Kir4.1 channel mediates the inwardly rectifying K+ current in the intermediate cell as shown previously by electrophysiological methods, and that this channel plays key roles in the production of the EP and K+ transport in the stria vascularis.

Amino Acid Sequence↗
PubMedDate not supplied

Gm(1) factor in human inner ear fluid.

The authors carried out investigations on the possibility of determining the Gm(1) factor in endolymph taken from human cadavers, as compared with tests of the blood. No difficulties or anomalies were found in the determination of Gm(1) factor either in the endolymph or the blood taken from cadavers.

Blood Group Antigens↗
PubMed1996

Na+,K(+)-ATPase activity in the cochlear lateral wall of the gerbil.

We examined Na+,K(+)-ATPase activity in four regions of the gerbil cochlear lateral wall by measuring intracellular Na+ concentration ([Na+]i). The application of 1 mM ouabain and removal of external K+ caused a most striking increase in [Na+]i of the suprastrial fibrocytes, followed by the stria vascularis and the type II fibrocytes, but no detectable response in the type I fibrocytes. These results may imply the potency of the Na+,K(+)-ATPase activity. The high values of the resting [Na+]i in these cells under perilymph-like solution returned to the [Na+]i within physiological values after exposure to low-Na+ conditions similar to endolymph. Our results are interpreted in the light of recent morphological findings with regard to the roles in the secretion of K+ into endolymph of several cell types within the lateral wall.

Animals↗
PubMed1979

The effect of changes in endolymphatic ion concentrations on the tectorial membrane.

The development of a new preparation technique has allowed the effects of fluid-substitution experiments on the tectorial membrane (t.m.) to be studied morphologically and not only, as previously, electrophysiologically. The organ of Corti and t.m. were examined in situ, unfixed and with in vivo-like ionic conditions under light-microscopical control (differential-interference-contrast, magnification 400--800X). An irreversible shrinkage of the marginal and middle zones of the t.m. was observed under the influence of Na+ ions (substitution of endolymph with artificial perilymph). This shrinkage is also seen in specimens prepared for scanning electron microscopy after perfusion of scale media with perilymph. If endolymph is replaced by an isotonic solution of EDTA (ethylenediaminetetraacetate) the t.m. can swell in its vestibulo-tympanal extent, e.g. from 39 to 72 microns. This swelling is reversible on addition of CaCl2. Although the size of the t.m. is not influenced to any great extent by changes in fluid osmolarity, reduction of H+ ion concentration leads to a minimal state of hydration of the protobril system at pH 4.3 (i.e. region of isoelectric point). The mechanism of Na+ and Ca2+ effects are discussed. These results indicate that the subtectorial space is morphologically separated from the scala media proper by the marginal zone.

Animals↗
PubMed1985

A model for signal transmission in an ear having hair cells with free-standing stereocilia. III. Micromechanical stage.

Measurements have shown that the sound-induced motion of free-standing stereocilia of hair cells in the alligator lizard cochlea exhibits tonotopically organized frequency selectivity that is correlated with the geometry of the stereociliary tuft. We propose a model in which basilar-membrane motion causes vibration of the receptor organ which drags the stereocilia back and forth through the endolymph. The stereociliary tuft is represented as a rigid rod attached to the cuticular plate by a compliant hinge. Viscous and inertial forces exerted by the endolymph on the rod are computed approximately. A transfer function, H mu(f), is derived that relates rod angular displacement to basilar-membrane velocity. H mu(f) has low- and high-frequency slopes of 10 and -20 dB/decade, respectively. The resonant frequency of H mu(f) depends on the dimensions of the rod because this frequency is inversely proportional to the square root of the product of the moment of inertia of the rod, which depends on rod dimensions, and the compliance of the hinge, which does not. In most respects, measurements of frequency selectivity and tonotopic organization of hair cells and cochlear neurons in the alligator lizard, can be accounted for by an input transfer function, HI(f) = Hm(f)H mu(f)Ha(f), where Hm(f) is the macromechanical transfer function that relates sound pressure at the tympanic membrane to basilar-membrane velocity (Rosowski et al., 1985, Hearing Res. 20, 139-155), and Ha(f) is a first-order lowpass filter. Mechanisms that could produce the additional lowpass filter process are discussed.

Animals↗
PubMed1987

Vasopressin entry into the inner ear fluids of the rat.

The entry of arginine-vasopressin (AVP) and sucrose into cochlear endolymph, perilymph of scala vestibuli (PLV), perilymph of scala tympani (PLT), and cisternal cerebrospinal fluid (CSF) was studied, in anesthetized rats, after the administration into the cerebral lateral ventricle of a 10 microliter solution containing the radioactive tracers. Both tracers were detected in PLV, PLT, and CSF but not in endolymph. Monoexponential decay curves were calculated for PLV, PLT, and CSF, and for each tracer no difference was found between the regression lines calculated for the different fluids. These results indicate that (i) injection into the cerebral lateral ventricle is a useful tool to study the permeability of the cochlear epithelium to different solutes and (ii) no specific transport system exists for AVP across the cochlear epithelium, suggesting that AVP may exert its effect via the perilymphatic side of the stria vascularis.

Animals↗
PubMed1994

The effect of nimodipine on cochlear potentials and Na+/K(+)-ATPase activity in normal and hydropic cochleas of the albino guinea pig.

In experimental endolymphatic hydrops (EEH) a decrease in the endocochlear potential (EP) has been reported and is thought to be due to decreased activity of the enzyme Na+/K(+)-ATPase in the stria vascularis. By stimulating Na+/K(+)-ATPase, the EP, and thereby cochlear function as a whole, might be restored. On the other hand, stimulation of stria vascularis Na+/K(+)-ATPase might result in excessive production of endolymph and thus produce or augment hydrops. In this study we have investigated the effect of intraperitoneally applied nimodipine on cochlear potentials and on Na+/K(+)-ATPase activity in the stria vascularis, both in normal cochleas (control) and in cochleas with EEH. Nimodipine is an L-type Ca(2+)-channel blocking agent with Na+/K(+)-ATPase stimulating properties at concentrations as low as 1.5 nM. The compound action potential (CAP), evoked by 2,4 and 8 kHz tone bursts was found to be depressed in the EEH ears with and without nimodipine treatment, and in the nimodipine treated control ears. Statistical analysis (ANOVA) showed that the effects of EEH and nimodipine on the CAP were additive. The negative summating potential (SP), measured extracochlearly at the apex, in response to 4 and 8 kHz tone bursts was significantly enhanced in the EEH ears. Nimodipine treatment did not affect the SP, neither in the control, nor in the EEH ears. Cytochemically, Na+/K(+)-ATPase activity appeared to be decreased in the oedematous stria vascularis of hydropic cochleas. No effect of nimodipine on Na+/K(+)-ATPase activity could be established ultracytochemically, neither in the controls nor in the EEH ears. In the lower turns of some of the nimodipine treated control cochleas a mild hydrops was seen during light-microscopic evaluation. Although it was not possible to prove a stimulatory effect of nimodipine on the enzyme Na+/K(+)-ATPase cytochemically, the finding of mild endolymphatic hydrops in nimodipine treated control ears suggests (a history of) increased endolymph production. This hydrops might be responsible for the depression of the CAP in the nimodipine treated ears.

Animals↗