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PubMedDate not supplied

Some observations on negative endocochlear potential during anoxia.

The effects of anoxia on the endocochlear potential (EP) and +K and +Na concentrations in the endolymph were studied in three groups of guinea pigs: kanamycin-treated guinea pigs, waltzing guinea pigs and normal guinea pigs. The magnitude of the EP in kanamycin-treated guinea pigs and waltzing guinea pigs did not show marked deviation from that observed in normal animals. The +K and +Na concentrations in the endolymph in those animals with severe suppression of sound-evoked cochlear potentials were also within the normal range. The changes in +K and +Na concentrations in the endolymph in anoxic condition were similar in the three groups of animals. However, the rate of decline of the EP was slower in kanamycin-treated guinea pigs and old waltzing guinea pigs. In young waltzing guinea pigs showing moderate suppression on the cochlear microphonics, the decline of the EP during anoxia was comparable to that observed in normal guinea pigs. The results indicate that anoxia decreases +K and increases +Na concentrations in the endolymph in a similar fashion in kanamycin-treated guinea pigs, waltzing guinea pigs and normal guinea pigs. It is suggested that the decline of the EP during anoxia is correlated with the +K conductance of the organ of Corti.

Action Potentials↗
PubMed1998

The papilla neglecta of turtles: a detector of head rotations with unique sensory coding properties.

The turtle papilla neglecta (PN) is a small organ lying in the ventrolateral utricular wall between the posterior crista (PC) and the utriculosaccular foramen. Innervated by a branch of the posterior ampullary nerve, the organ is covered by a cupula extending only a small distance into the endolymphatic space. Although most rotation-sensitive units in the posterior division of the eighth nerve have sensory coding properties expected of PC fibers, a few have unique properties. Intra-axonal labeling studies show that the former are PC units and the latter are PN units. PC units are maximally responsive to head rotations in the posterior canal plane and are sensitive to a combination of angular velocity and angular acceleration. PN units respond maximally to pitch rotations and are sensitive to a combination of angular acceleration and angular jerk. A maximal response to pitches can be related to the location of the PN, which allows it to sample endolymph flow from both vertical semicircular canals. Differences in response dynamics may reflect macromechanics. Because the cupula of each vertical canal occludes the endolymphatic space, its displacement should be proportional to endolymph displacement. In contrast, the PN cupula is probably coupled to endolymph flow by viscous forces, in which case its displacement should be proportional to endolymph velocity. In many vertebrates, the PN is similar to that seen in turtles in its location and in the size and shape of its cupula, which suggests that its function in these other species is also similar.

Animal Structures↗
PubMedDate not supplied

Why do benign paroxysmal positional vertigo episodes recover spontaneously?

It is well known that most episodes of benign paroxysmal positional vertigo (BPPV), even in untreated, recover spontaneously in 2 to 6 weeks. In the present study, we put forward the hypothesis that this is mainly due to the fact that endolymph, owing to its low calcium content (20 microM) is able to dissolve otoconia. To support this, the fate of frog saccular otoconia immersed in normal endolymph (Ca2+ content 20 microM) and in Ca2+-rich endolymphatic fluids (up to 500 microM) was studied by observing the crystals at regular intervals for 3 weeks. The results demonstrated that normal endolymph can dissolve otoconia very rapidly (in about 20 hours). When the endolymphatic Ca2+ content was increased (50 to 200 microM) otoconia dissolution time was slowed down (about 100 to 130 hours, respectively) and completely stopped when the endolymphatic Ca2+ content was of 500 microM. The present results therefore suggest that the major process involved in the spontaneous recovery of BPPV episodes is the capability of the endolymph to dissolve dislodged otoconia.

Animals↗
PubMed2005

How can teleostean inner ear hair cells maintain the proper association with the accreting otolith?

The perception of equilibrium and sound in fish depends on the deflection of hair bundles of hair cell by the otolith. However, the accreting nature of teleostean otoliths poses a problem for maintenance of proper contact between the hair bundle and the otolith surface. Immunocytochemical staining localizes abundant proton-secreting H(+)-ATPase in the apical membrane of the hair cells. The H(+)-ATPase-mediated proton secretion into the endolymph causes an approximately 0.4-unit pH decrease, which was quantified by an H(+)-selective microelectrode. Thus, the hair cells maintain the proper distance from the otolith by neutralizing the alkaline endolymph to retard CaCO(3) deposition on the otolith opposite the sensory macula. Carbonic anhydrase, which hydrolyses CO(2) and produces HCO(3) (-) and H(+), was also localized in the hair cells. Ionocytes showed prominent immunostaining of carbonic anhydrase and Na(+)-K(+)-ATPase, indicating its role in transepithelial transport of HCO(3) (-) across the membranous labyrinth into the endolymph. Ionocytes form a ring closely surrounding the sensory macula. HCO(3) (-) secreted from the ionocytes may serve as a barrier to neutralize H(+) diffused from the sensory macula while keeping the endolymph alkaline outside the sensory macula. The ingenious arrangement of ionocytes and hair cells results in a unique sculptured groove, which is a common feature on the proximal surface of all teleostean otoliths.

Animals↗
PubMed2004

Responses of the endolymphatic sac to perilymphatic injections and withdrawals: evidence for the presence of a one-way valve.

Although the endolymphatic sac (ES) is thought to be a primary site for endolymph volume regulation, we have limited knowledge of how it responds to volume and pressure changes. In a prior publication, we demonstrated changes of K(+), Na(+) and endolymphatic sac potential (ESP) resulting from volume injections into, and withdrawals from, scala media of the cochlea. In the present study, we compared the influence of injections into and withdrawals from scala tympani of the cochlea on the endolymphatic sac. It is assumed that similar pressure changes are induced in endolymph and perilymph of both the cochlear and vestibular compartments of the ear. Pressure changes induced by the perilymphatic injections and withdrawals did not induce similar K(+) changes in the ES. The majority of perilymph withdrawals caused K(+) and ESP reductions in the sac, but few injections caused any measurable changes in the sac. Pressure measurements from the ES demonstrated that transmission of labyrinthine pressures to the lumen was directionally sensitive, with negative pressure transmitted more effectively than positive. In other experiments, application of infrasonic stimulation to the ear canal resulted in K(+) increase in the ES. These physiological measurements suggest that the endolymphatic duct may be closed by sustained positive pressure in the vestibule but open during pressure fluctuations. Study of the anatomy where the endolymphatic duct enters the vestibule suggests that the membranous sinus of the endolymphatic duct could act as a mechanical valve, limiting the flow of endolymph from the saccule to the endolymphatic sac when pressure is applied. This structure could therefore play an important role in endolymph volume regulation.

Animals↗
PubMed2001

Cochlear distribution of Na,K-ATPase and corticosteroid receptors in two mouse strains with congenital hearing disorders.

As corticosteroid hormones, via their receptors, and Na,K-ATPase are thought to be involved in the regulation of endolymph production, two mouse models were used to investigate whether degeneration of the stria vascularis (SV) and disturbed endolymph composition are correlated with changes in the amounts and distribution of corticosteroid receptors and Na,K-ATPase in the cochlea. Both the shaker-2 mouse and the newly discovered mix mouse are deaf at birth and show vestibular dysfunction. In both mouse strains, the SV is degenerated and endolymph production is severely disturbed. In the shaker-2 mouse, using the C57Bl mouse as a normal control, immunohistochemical staining of mineralo- and glucocorticoid receptors (MR and GR) and the Na,K-ATPase subunits alpha1, alpha3 and beta1 showed a weaker reaction in all structures of the cochlea. The inner ear morphology of the mix mouse is described and compared to that of asymptomatic littermates. Immunostaining of MR, GR and the different Na,K-ATPase subunits in this mouse was considerably weaker in the SV, while staining intensities were normal in the remaining cochlea. The reduced corticosteroid receptor levels may lead to a reduction in Na,K-ATPase expression in the same tissues, although this conclusion should be treated with caution. The conclusion that reduced Na,K-ATPase levels in both mouse strains may be an important mechanism of the disturbed endolymph production is less controversial.

Animals↗
PubMed2002

Spatial orientation of caloric nystagmus.

The spatial orientation of the slow-phase eye velocity of caloric nystagmus was investigated in cynomolgus monkeys after all six semicircular canals had been plugged. Normal animals generate responses that have dominant convective components produced by movement of the endolymph in the lateral canal toward or away from gravity. As a result, the direction of horizontal slow-phase velocity induced by cold-water irrigation changes direction with changes in head position with regard to gravity. Plugging produced a dense overgrowth of bone that blocked the flow of endolymph, but the end organs were intact. Robust caloric nystagmus was elicited after recovery, but the horizontal (yaw) component was now always toward the stimulated (ipsilateral) side, regardless of head position re gravity. The induced caloric nystagmus had strong spatial orientation properties after canal plugging. With animals upright, the three-dimensional velocity vector of the caloric nystagmus was close to the yaw axis with small vertical and roll components. Roll components became stronger in supine and prone positions and vertical components were enhanced in the right- and left-side down positions. In each instance, the addition of the roll and vertical components moved the velocity vector of the nystagmus closer to the spatial vertical. Modeling supported the postulate that the caloric nystagmus after canal plugging is influenced by three factors: (1) a reduction in neural activity in the ampullary nerves on the stimulated side due to cooling of the nerves; (2) contraction of the endolymph in the closed space between the cupula and the plug due to cooling, which resulted in deflection of the cupula and hair cells toward the plug (ampullofugal deflection); and (3) alignment of eye velocity to gravity due to the orientation properties of velocity storage. Although convection is the most prominent factor in producing caloric responses in the normal state, our results suggest that alteration of nerve activity due to thermal effects, endolymph contraction or expansion, and velocity storage are also likely to contribute to the total response.

Animals↗
PubMed1981

Radioimmunoassay of gentamicin in microliter and nanoliter samples of biological fluids.

A gentamicin radioimmunoassay is described for microliter and nanoliter samples. The assay was performed in the inner ears' fluids (perilymph and endolymph) of rats. Endolymph and perilymph samples were collected under oil with a glass capillary micropipette. The absolute threshold of sensitivity was 20 . 10(-12) g. Considering the maximum sampling volume, 15--400 . 10(-9) and 10 . 16(-6) l for endolymph and perilymph respectively, the limit of detection is 4.19 . 10(-4) microM . ml-1 in endolymph, 1.26 . 10(-4) microM . ml-1 in perilymph. Clinical applications of this method are suggested.

Animals↗
PubMed2004

Compartmentalization established by claudin-11-based tight junctions in stria vascularis is required for hearing through generation of endocochlear potential.

Claudins are cell adhesion molecules working at tight junctions (TJs) that are directly involved in compartmentalization in multicellular organisms. The cochlea includes a rather peculiar compartment filled with endolymph. This compartment is characterized by high K+ concentration (approximately 150 mM) and a positive endocochlear potential (approximately 90 mV; EP), both indispensable conditions for cochlear hair cells to transduce acoustic stimuli to electrical signals. These conditions are thought to be generated by the stria vascularis, which is adjacent to the endolymph compartment. The stria vascularis itself constitutes an isolated compartment delineated by two epithelial barriers, marginal and basal cell layers. Because TJs of basal cells are primarily composed of claudin-11, claudin-11-deficient (Cld11-/-) mice were generated with an expectation that the compartmentalization in stria vascularis in these mice would be affected. Auditory brainstem response measurements revealed that Cld11-/- mice suffered from deafness; although no obvious gross morphological malformations were detected in Cld11-/- cochlea, freeze-fracture replica electron microscopy showed that TJs disappeared from basal cells of the stria vascularis. In good agreement with this, tracer experiments showed that the basal cell barrier was destroyed without affecting the marginal cell barrier. Importantly, in the endolymph compartment of Cld11-/- cochlea, the K+ concentration was maintained around the normal level (approximately 150 mM), whereas the EP was suppressed down to approximately 30 mV. These findings indicated that the establishment of the stria vascularis compartment, especially the basal cell barrier, is indispensable for hearing ability through the generation/maintenance of EP but not of a high K+ concentration in the endolymph.

Alleles↗
PubMed1984

[Physical dimensions influence the functional property of the semicircular canal].

The functional dependence of the semicircular canal upon its physical dimensions was evaluated by measuring the internal radius (r), the radius of curvature (R) and the cupula radius (rC) of the posterior canal in 10 freshly dissected frog labyrinths. These values have been compared to the same parameters of the cat labyrinth. The coefficients I, B, K in the Steinhausen equation were determined for both animals. The A ratio between cupula deflection and endolymph displacement was also calculated by utilizing the Bernard equation. The A ratio is three times larger in the frog than in the cat. It follows that if the same acceleration produces similar endolymph displacements in the posterior canal of both animals, the cupula deflection will be larger in the frog. The solution of the Steinhausen equation in the presence of a constant acceleration, however, reveals that the same stimulus intensity will result in a larger endolymph displacement in the cat posterior canal; similarly, the endolymph displacement directly depends on the duration of the stimulating period in both animals. Contrary to the Bernard assumption, these effects generate a G ratio (psi frog/psi cat) which is less than the Q ratio (A frog/A cat). Moreover, G decreases on increasing the duration of the stimulating period. For stimuli of short duration the semicircular canal of a small animal is expected to exhibit a higher sensitivity than that of a larger one. However, the definitive primary afferent discharge will be largely controlled by the receptor/generator potential properties.

Acoustic Stimulation↗
PubMed1993

Intracellular and extracellular elemental composition of the endolymphatic sac studied by X-ray microanalysis.

X-ray microanalysis was performed along with light microscopy (LM) on rapidly frozen and cryo-sectioned endolymphatic sac tissues of adult guinea pigs, to determine the elemental composition of the different cell types in this tissue as well as the content of the sac lumen. The morphological preservation and spatial resolution of cryo-sectioned endolymphatic sac was found adequate for the identification of the different cell types of the sac in the transmission electron microscope. Further cell type identification was performed by comparing scanning transmission electron microscopy images with LM images on adjacent serial sections. X-ray microanalysis demonstrated differences between epithelial and sub-epithelial cells in the intracellular concentrations of sodium, chlorine, potassium, calcium, phosphorus and sulphur. Measurements performed in the lumen of the endolymphatic sac showed elevated sodium and decreased potassium levels as compared with the known levels of these elements in cochlear or vestibular endolymph. High phosphorus and sulphur levels were also found in the endolymph of the sac. Other morphological and analytical findings on the luminal content point out that otoconial destruction and cleaning of the endolymph from the cell debris and other products such as lipids and proteins take place in the endolymphatic sac. Our results suggest that the endolymphatic sac participates in fluid absorption (osmoregulation), ion transport and otoconial destruction. The data support the longitudinal flow theory of the endolymph.

Animals↗
PubMed1979

Localization of the marginal zone of the tectorial membrane in situ, unfixed, and with in vivo-like ionic milieu.

In order to determine the normal positional relationship between the tectorial membrane and the organ of Corti, a preparation method was developed which made it possible to study the unfixed tectorial membrane in its normal position in relation to the cochlea and with in vivo-like ionic conditions. With this method, post-mortem changes visible with the light microscope were detectable after 60 to 90 min instead of the normal 30 min. When endolymph of artifical endolymph are present in the scala media, the marginal zone lies in close contact with the surface of the organ of Corti. If the endolymph is replaced by artificial perilymph, first the marginal zone of the tectorial membrane, and later the whole membrane shrinks. At this stage, latex particles suspended in the perilymph are free to enter the subtectorial space.

Animals↗
PubMed1977

Time course of anoxia-induced K+ concentration changes in the cochlea measured with K+ specific microelectrodes.

The endocochlear potential (EP), potassium concentration in the endolymph (Ke+) and in the perilymph (Kp+) were measured in guinea-pigs during anoxia of different duration. Specific K+ double-barrel microelectrodes with liquid ion exchanger were used. The resting K+ concentration in the endolymph was 146.8 +/- 9.2 mM and in the perilymph 3.2 +/- 0.5 mM. The following time course of events was observed in the cochlea during anoxia: 40-50 s after the arrest of ventilation the K+ concentration decreased by 0.1-0.2 mM in the scala vestibuli, which was time related to a rapid fall of EP to negative values. Perilymphatic K+ started to increase in both scalae with a latency of 2-2.5 min, reaching a concentration of about 14 mM 60 min after the arrest of ventilation. The endolymphatic K+ began to decrease after a latency of 2.5-3 min, and 60 min after the arrest of ventilation an 80% concentration (average 112 mM K+) was reached as compared to the initial value. From the comparison of K+ concentration changes with the experimental values of the negative EP, it may be assumed that the negative EP is mainly generated by the K+ gradient between the perilymph and endolymph.

Animals↗
PubMed1998

Importance of type IV collagen, laminin, and heparan sulfate proteoglycan in the regulation of labyrinthine fluid in the rat cochlear duct.

The distribution of major components of the basement membrane, such as type IV collagen, laminin, and heparan sulfate proteoglycan (HSPG), was investigated in the rat cochlear duct. Immunofluorescence demonstrated that type IV collagen, laminin and HSPG were distributed along capillaries in the cochlear duct, including the stria vascularis, spiral ligament, spiral prominence and spiral limbus. Additionally, type IV collagen, laminin and HSPG were found to be distributed from the basement membrane of Reissner's membrane to that of the spiral prominence in a linear pattern. The scala media was surrounded by these basement membrane components, demarcating endolymph from perilymph, along epithelial cells except at the stria vascularis. These findings suggest that type IV collagen, laminin and HSPG create the anatomical separation between endolymph and perilymph, thus indicating that they may be involved in the regulation of fluid transport between the endolymph and perilymph.

Animals↗
PubMed2003

Localization and functional studies of pendrin in the mouse inner ear provide insight about the etiology of deafness in pendred syndrome.

Immunolocalization studies of mouse cochlea and vestibular end-organ were performed to study the expression pattern of pendrin, the protein encoded by the Pendred syndrome gene (PDS), in the inner ear. The protein was restricted to the areas composed of specialized epithelial cells thought to play a key role in regulating the composition and resorption of endolymph. In the cochlea, pendrin was abundant in the apical membrane of cells in the spiral prominence and outer sulcus cells (along with their root processes). In the vestibular end-organ, pendrin was found in the transitional cells of the cristae ampullaris, utriculi, and sacculi as well as in the apical membrane of cells in the endolymphatic sac. Pds-knockout (Pds-/-) mice were found to lack pendrin immunoreactivity in all of these locations. Histological studies revealed that the stria vascularis in Pds-/- mice was only two-thirds the thickness seen in wild-type mice, with the strial marginal cells showing irregular shapes and sizes. Functional studies were also performed to examine the role of pendrin in endolymph homeostasis. Using double-barreled electrodes placed in both the cochlea and the utricle, the endocochlear potential and endolymph potassium concentration were measured in wild-type and Pds-/- mice. Consistent with the altered strial morphology, the endocochlear potential in Pds-/- mice was near zero and did not change during anoxia. On the other hand, the endolymphatic potassium concentration in Pds-/- mice was near normal in the cochlea and utricle. Together, these results suggest that pendrin serves a key role in the functioning of the basal and/or intermediate cells of the stria vascularis to maintain the endocochlear potential, but not in the potassium secretory function of the marginal cells.

Animals↗
PubMed2002

Relationship between inner-ear fluid pressure and semicircular canal afferent nerve discharge.

The present study was designed to determine (1) the transcupular fluid pressure (deltaP) generated across the semicircular canal cupula in response to sinusoidal head rotation, (2) the translabyrinthine dilational pressure (P0) generated across the membranous labyrinth in response to an increase in endolymph fluid volume (hydrops), (3) afferent nerve discharge patterns generated by these distinct pressure stimuli and, (4) threshold values of deltaP and P0 required to elicit afferent neural responses. The experimental model was the oyster toadfish, Opsanus tau. Micromechanical indentation of the horizontal canal (HC) duct and utricular vestibule was used to simulate sinusoidal head rotation and fluid volume injection. Single-unit neural spike trains and endolymph pressure within the ampulla, on both sides of the cupula, were recorded simultaneously. deltaP averaged 0.013 Pa per 1 degrees/s of sinusoidal angular head velocity and P0 averaged 0.2 Pa per 1 nL of endolymph volume injection. The most responsive afferents had a threshold sensitivity to deltaP of 10(-3) Pa and to P0 of 5 x 10(-2) Pa based on a discharge modulation criterion of 1 impulse/s per cycle for 2 Hz pressure stimuli. Neural sensitivity to AP was expected on the basis of transverse cupular and hair bundle deflections. Analysis of mechanics of the end organ, neuronal projections into the crista, and individual neural firing patterns indicates that P0 sensitivity resulted from pressure-induced distension of the ampulla that led to a nonuniform cupular deformation pattern and hair bundle deflections. This explanation is consistent with predictions of a finite element model of the end organ. Results have implications regarding the role of deltaP in angular motion transduction and the role of P0 under transient hydropic conditions.

Action Potentials↗
PubMed1979

Effects of exposure to noise on ion movement in guinea pig cochlea.

Healthy guinea pigs were exposed to broad band noise at levels between 95 and 115 dBA for 7 days. A significant decrease of the sound-induced cochlear responses, together with a substantial increase of the endocochlear potential, was observed in guinea pigs exposed to noise at 105 or 115 dBA. Microsamples of the endolymph obtained from these guinea pigs showed a significant increase of K+ and Cl- concentrations and a decrease of Na+ concentration, when compared with those from control animals. The K+, Na+ and Cl- concentrations in the perilymph were not markedly affected by noise exposure. When the perilymphatic space was perfused with artificial perilymph containing 43K, 22Na or 36 Cl, the uptake of radiotracers into the endolymph showed a single exponential function of the perfusion time. When compared with rate constants in normal animals, the value of rate constant for K+ was significantly decreased in animals exposed to noise. These results indicate that ionic permeability changes of the endolymph-perilymph barrier are a significant factor in the physiological mechanisms underlying noise-induced hearing loss.

Animals↗
PubMed1993

Mechanism of lack of development of negative endocochlear potential in guinea pigs with hair cell loss.

The endocochlear potential (EP), and the concentration of K+, Na+ and Cl- were measured simultaneously in endolymph of guinea pigs. The EP was 85.6 +/- 0.8 mV in normal guinea pigs, 90.7 +/- 0.8 mV in the kanamycin-treated animals, and 91.6 +/- 1.2 mV in those treated with nitrogen mustard-N-oxide (NMNO). Thirty minutes after the onset of anoxia, the EP (negative EP) was -29.3 +/- 1.0 mV in the normal group, -0.2 +/- 1.0 mV in the kanamycin-treated group, and -1.9 +/- 1.3 mV in the NMNO-treated group. The permeability coefficients of K+ (Pk), Na+ (Pna) and Cl- (Pcl) across the endolymph-perilymph barrier during the period of 20-30 min after the onset of anoxia in the normal group were (341.6 +/- 38.2) x 10(-9) cm3 sec-1, (53.0 +/- 8.1) x 10(-9) cm3 sec-1 and (111.8 +/- 27.2) x 10(-9) cm3 sec-1, respectively. Pk was decreased in the kanamycin- and NMNO-treated groups. Pna did not differ between the normal and treated groups. Pcl was increased in the kanamycin- and NMNO-treated groups. The K+:Na+:Cl- permeability ratio was 1:0.16:0.32 in the normal group, 1:1.12:11.6 in the kanamycin-treated group, and 1:0.44:5.60 in the NMNO-treated group. The results indicate that the lack of development of a negative EP in the kanamycin- and NMNO-treated guinea pigs was attributable to the increased Pcl and the decreased Pk across the endolymph-perilymph barrier, probably the organ of Corti, during anoxia.

Animals↗