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At least 325 records · Page 18Linked to original sources
PubMed2005

Endolymphatic perfusion with EGTA-acetoxymethyl ester inhibits asphyxia- and furosemide-induced decrease in endocochlear potential in guinea pigs.

We examined the effect of the Ca(2+) concentration in the endolymph ([Ca](e)) or in the endolymphatic surface cells ([Ca](i)) on the endocochlear potential (EP) by using an endolymphatic or perilymphatic perfusion technique, respectively. (i) A large increase in [Ca](e) up to approximately 10(-3) M with a fall in the EP was induced by transient asphyxia ( approximately 2 min) or by the intravenous administration of furosemide (60 mg/kg), and a significant correlation was obtained between the EP and p[Ca](e) (= -log [Ca](e), r = 0.998). (ii) Perfusion of the endolymph with 10 mM EGTA for 5 min neither produced any significant change in the EP nor altered the asphyxia-induced change in EP (DeltaEP(asp)), suggesting that neither [Ca](e) nor the Ca(2+) concentration gradient across the stria vascularis contributed directly to the generation of the EP in the condition of low [Ca](e). In contrast, endolymphatic perfusion with high Ca(2+) (more than 10 mM) produced a decrease in EP and a significant correlation was obtained between the EP and the Ca(2+) concentration of perfusion solution (r = 0.982), suggesting that Ca(2+) permeability may exist across the stria vascularis. (iii) The administration of a Ca(2+) chelator, EGTA-acetoxymethyl ester (AM, 0.3 mM), to the endolymph, which produced a gradual increase in EP, suppressed significantly, by 60-80%, DeltaEP(asp) or furosemide-induced changes in EP. In contrast, perilymphatic administration of 0.5 mM EGTA-AM caused no significant suppression of the DeltaEP(asp). These findings suggest that [Ca](i) plays an important role in generating/maintaining a large positive EP.

Animals↗
PubMed2001

Cupular response and functional anatomy to pressure application in the pigeon.

In this study, horizontal semicircular canal of the pigeon was inserted with a microfill, 164 micrometers in outer diameter, to gauge the pressure change in the canal and to clarify two things. One is whether the endolymph passes through the crista ampullaris or not. The other is as to the space where the endolymph passes through in the crista ampullaris if the endolymph goes through the crista. The pressure applications were performed by using Evans blue solution and as a result three pressure groups, i.e., 1) high, 2) moderate and 3) low were discriminated. Our results suggest that the endolymphatic fluid passes through the subcupular space or the top of the crista ampullaris when the pressure is enough small like the head rotates in daily life. Accordingly we present a new hypothesis as to the functional anatomy of the cupula in contrast to current hypotheses e.g. drum membrane or revolving door.

Animals↗
PubMedDate not supplied

Obliteration of the ductus reuniens.

The ductus reuniens was successfully obliterated in 52 guinea pig ears. Histopathological study showed that a majority of these specimens demonstrated cochlear hydrops, saccular collapse and normal utricle. These results support the theory of longitudinal flow of endolymph from the cochlea toward the endolymphatic sac via the ductus reuniens and saccule. A major source of endolymph in the saccule appears to be the scala media. In another set of 11 animals in which the ductus reuniens was first obstructed and two months later the endolymphatic duct was blocked, endolymphatic hydrops was shown in the cochleae, saccules, and utricles of all but one. The evidence suggests that cochlear hydrops was caused by obliteration of the ductus reuniens, and the saccular and utricular hydrops occurred subsequently as the result of blockage of the endolymphatic duct. Remnants of otolithic membrane which were attached to the distended saccular wall indicate that the membrane which had collapsed onto the macula after obliteration of the ductus reuniens is capable of subsequent distension. This experiment supports the concept of endolymph flow from the utricle and canals toward the endolymphatic sac. A blocked cutus reuniens might also explain the pathophysiological basis for the auditory form of Meniere's disease.

Animals↗
PubMed1982

Functional and morphological findings of endolymphatic sac.

After obliteration of endolymphatic sac and duct, no significant alteration in d.c. potential, K+ activity or protein content during the development of endolymphatic hydrops could be observed. The K+ activity of endolymphatic sac was only one-ninth of that in the cochlear part of the endolymph. After injection of Thorotrast into the endolymphatic sac, aggregated particles were found in the cochlear endolymph 2 days later. Ethacrynic acid (60 mg/kg) caused a decrease in K+ activity in the cochlear endolymph, but an increase in the endolymphatic sac. Intercellular edema was observed both in stria vascularis and in endolymphatic sac by light and electronmicroscopy after ethacrynic acid administration. These results suggest the existence of an active transport mechanism in the endolymphatic sac epithelium.

Animals↗
PubMed1988

Calcium and the inner ear fluids.

Total calcium (Ca) concentration in inner ear fluids was determined by fluorimetry, emission and absorption spectrophotometry, and electron probe analysis. The ionized Ca was measured with selective microelectrodes. In perilymph, the total Ca concentration (1.2 mM) was similar to the ultrafiltrable Ca concentration in plasma. The fraction of ionized Ca was 80%. In endolymph, a total Ca concentration of 0.5 mM contrasted with a reported ionized Ca concentration of 0.02 mM, which suggests, as a working hypothesis, that most of the Ca could exist as bicarbonate and/or phosphate undissociated salts. The decrease in the endocochlear potential induced an increase of the ionized fraction of the Ca. The electrochemical potential of Ca across the perilymph-endolymph barrier implies an active entry of Ca into the endolymph.

Calcium↗
PubMed1989

The effects of glycerol on vestibular function and the endolymphatic sac after pre-treatment with colchicine.

The endolymphatic sac (ES) is believed to absorb endolymph. Recent studies have suggested that the ES also has a secretory capacity, a function that may be related to the regulation of inner ear fluid volume and pressure. Other studies indicate that hyperosmolar substances, such as glycerol and urea, may initiate a secretion of glycoprotein into the ES. This function was suggested to be related to a regulatory function of the ES by which it can compensate for a decrease in endolymph pressure. In order to investigate this regulatory potential of the ES, the effect of glycerol on the ES was investigated with or without the presence of pharmacological inhibition of glycoprotein secretion through colchicine treatment. Animals treated in such a way showed marked signs of impaired inner ear function, including loss of postural control and loss of Preyer's reflex. Significant ultrastructural changes were noted in the endolymphatic sac suggesting a disturbed secretory activity. The results may indicate that the endolymphatic sac may actively respond to changes in endolymph homeostasis through secretion of macromolecular substances and that alterations in this secretion may lead to functional disturbances of the inner ear.

Animals↗
PubMed1992

Adenylate cyclase modulation of ion permeability in the guinea pig cochlea: a possible mechanism for the formation of endolymphatic hydrops.

The pathophysiological mechanisms leading to endolymphatic hydrops in Meniere's disease are unknown. Changes in ionic permeability of the cellular membranes between the endolymph and the perilymph, which alter the composition and osmolarity of the inner ear fluid, may be a major factor in the etiology of endolymphatic hydrops. To determine the possible involvement of adenylate cyclase in the formation of endolymphatic hydrops, we measured the endolymphatic K+, Na+, Cl- activities (AK, ANa, ACl) and the endocochlear potential (EP) by means of ion-selective microelectrodes while inner ear adenylate cyclase was activated by perilymphatic perfusion with forskolin. We observed a large ACl increase accompanied by an EP increase during forskolin (2 x 10(-4) M) perfusion and a delayed AK decrease after perfusion. No measurable ANa change was observed. These results suggest that adenylate cyclase may regulate Cl- permeability of the endolymph-perilymph barrier and that adenylate cyclase plays a critical role in acute endolymphatic hydrops in Meniere's disease by altering the osmolarity of the endolymph.

Adenylyl Cyclases↗
PubMed1996

Hormonal modulation of inner ear fluids.

In the cochlea, hormones such as antidiuretic hormone and adrenocorticosteroid hormones are supposed to modulate the endolymph osmolality acting on the labyrinthine water permeability, on the one hand, and on the Na+, K(+)-ATPase, on the other hand. To test the hypothesis that these hormones are involved in the inner ear fluids homeostasis, the electrochemical composition of cochlear fluids was studied in control Long Evans rats, Brattleboro rats that are genetically deprived of antidiuretic hormone, and in adrenalectomized Long Evans rats. The results demonstrated that: i) in Brattleboro rats, the endocochlear K gradient was absent whereas the endocochlear potential and the Cl concentration gradients were maintained; the K gradient was restored by the dDAVP administration; ii) in adrenalectomized rats, no modification of the electrochemical composition of endolymph occurred; the injection of bumetanide (10 mg/kg) induced a larger decrease of the endocochlear potential in adrenalectomized rats than in control animals. These results suggest that the cellular transport systems involved in the endolymph secretion may be altered by different hormones such as antidiuretic hormone and/or adrenocorticosteroid hormones. Nevertheless, the hormonal modulation of the inner ear fluid homeostasis remains to be further documented.

Adrenal Cortex Hormones↗
PubMedDate not supplied

Pathogenesis of Menière's disease.

While endolymphatic hydrops is a characteristic pathologic feature of Menière's disease, there are exceptions to this rule. There is evidence that hydrops develops as a result of malabsorption of endolymph. This implies dysfunction of the endolymphatic sac and duct, which normally absorb endolymph. In approximately 20% of cases of Menière's disease, a specific pathologic condition in the temporal bone can be associated as a cause of endolymphatic hydrops. Syphilis, fractures of the temporal bone, otosclerosis, and preceding chronic otitis media are some of the more commonly encountered pathologic conditions so associated. Hypoplasia of the mastoid air-cell system and of periaqueductal air cells, and especially displacement medially but also anteriorly of the sigmoid (lateral) sinus are commonly observed in patients with Menière's disease. Evidence is available to substantiate the etiologic bases of Menière's disease as including multifactorial inheritance (1). The clinical symptoms and findings result from both chemical and physical mechanisms. Pathogenesis appears to be due to malabsorption of endolymph in the environment of the endolymphatic sac, primarily affecting longitudinal flow. The possible role of such processes as autoimmune reactions and viral inflammation, especially in the endolymphatic sac, should be further investigated in the future.

Endolymph↗
PubMed1991

[Mechanisms of development of endolymphatic hydrops following secondary immune response in the endolymphatic sac of guinea pigs].

Previously the author reported the immediate development of endolymphatic hydrops (e. hydrops) following direct challenge of secondary antigen to the endolymphatic sac (ES) in guinea pigs, during the early phases of postchallenge, ranging from 1 to 5 weeks. The present study reports the results of specimens taken up to 10 weeks postchallenge, and correlation of e.hydrops to perilymph in antigen-specific antibody levels. From the present results, mechanisms of e.hydrops induced ES immune reaction are suggested as follows. 1) In the early stage of e.hydrops, an acute inflammatory reaction in the ES may produce endolymph by an increased vascular permeability of the inner ear and may impair endolymph absorption from the ES. 2) In the latter stage of e.hydrops, the moderate cellular infiltration in the ES may cause chronic impairment of endolymph absorption in the ES.

Animals↗
PubMed1988

The effects of cetrimide and potassium bromate on the potassium ion concentration in the inner ear fluid of the guinea-pig.

The mammalian inner ear is located deep within the temporal bone. The organ of Corti, the delicate sensory system for sound, is surrounded by two fluid systems; the potassium-rich endolymph and the sodium-rich perilymph. The pathogenesis of inner ear deafness is thought to be largely due to an imbalance of potassium and sodium ions in the inner ear fluids. Dynamic changes in K+ in the endolymph and perilymph were studied in the guinea-pig following cetrimide (cetrimonium bromide, a powerful cationic detergent which shows ototoxicity) applications on the round window membrane, intramuscular injection of potassium bromate (bread whitener, known to cause renal damage and permanent deafness in animals and man). Maximum fall in K+ concentration in the endolymoh (mM/min) and maximum K+ conductance (mM/min/mV) were 3.54 +/- 1.65 and 0.036 +/- 0.02 in cetrimide, and 1.85 +/- 0.35 and 0.021 +/- 0.009 in potassium bromate, respectively. In view of these findings, the influence of the active transport mechanism to K+ concentrations are discussed in comparison with dynamic changes in endolymph K+ induced by asphyxia and ethacrynic acid.

Animals↗
PubMed1999

Characterization of ootolith soluble-matrix producing cells in the saccular epithelium of rainbow trout (Oncorhynchus mykiss) inner ear.

Although the organic matrix may play an important role in the growth of teleost otoliths, cellular contributions to the production of the organic matrix have been studied in only a small number of teleost species with limited methods, and are still poorly understood. In order to characterize saccular epithelial cells which produce otolith matrix, antiserum was raised against an EDTA-soluble fraction of otolith matrix (otolith soluble-matrix, OSM) of the rainbow trout. The components in the OSM and in the endolymph were characterized by immunoblotting. The saccular epithelium was immunohistochemically stained with the antiserum and the ultrastructure of OSM immunoreactive cells was studied. By immunoblotting, multiple components (> 94.0 kDa [smeared] and 43.0 kDa) in the OSM reacted with the antiserum, whereas only one band (> 94.0 kDa) was detected in the endolymph. Under immunohistochemical staining, reactions to the antiserum were observed in columnar cells lined at the most peripheral region of the sensory epithelium, transitional epithelial cells, and squamous epithelial cells. Electron microscopic observations revealed that all three types of cells were equipped with extended rough endoplasmic reticulum and prominent Golgi apparatus, suggesting the active production of organic material(s). Dilations of translucent vesicles, apocrine-like extrusions of cytoplasm, and vesicles containing many minute globules were frequently associated with the apical surface of these cells. Some ruptured vesicles were observed, releasing their contents into the endolymphatic space. The present study identified columnar cells lining the most peripheral region of the sensory epithelium, transitional epithelial cells, and squamous epithelial cells as the OSM-producing cells. We suggest that the OSM components are secreted and dissolved into the endolymph and subsequently deposited onto the otolith.

Animals↗
PubMed1990

Adenylate cyclase and carbonic anhydrase in the semicircular canal epithelium of the frog Rana esculenta. An ultrastructural cytochemical localization.

Because the secretion of endolymph has been localized in the ampullar part of the frog semicircular canal, we attempted to determine by cytochemical methods the ultrastructural localization of two enzymes that are assumed to play a role in endolymph secretion: carbonic anhydrase and adenylate cyclase. Functionally, the epithelium of the frog semicircular canal can be schematically divided into three areas: sensory (crista ampullaris), secretory (dark cells), and non-sensory and nonsecretory (transitional and undifferentiated cells) areas. Carbonic anhydrase activity was widely distributed in dark cells. Dark cell labeling disappeared in the presence of acetazolamide. The other cells of the canal did not show any carbonic anhydrase labeling except for the supporting cells of the sensory cells. Adenylate cyclase activity was found on the basolateral and apical membranes of dark cells, and on the apical membrane of sensory cells; weak labeling was also observed in the other epithelial cells. In the apical membrane of the dark cells, adenylate cyclase labeling was dependent on the presence of vasotocin, the frog antidiuretic hormone. The dark cells of the frog semicircular canal thus possess the enzyme equipment needed for the secretion of endolymph and its possible hormonal regulation.

Adenylyl Cyclases↗
PubMed1996

Enzyme-histochemical localization of carbonic anhydrase in the inner ear of the guinea pig and several improvements of the technique.

We have made several improvements in the method of fixation of the inner ear and the enzyme-histo-chemical technique for carbonic anhydrase (CA) detection. The results confirmed that CA is localized in the hair cells of the organ of Corti, Deiters' cells or nerve endings, inner pillar cells, Boettcher's cells, stria vascularis, spiral ligament, spiral limbus, and spiral ganglion cells. These results generally agree with previous histochemical observations but showed some differences. Our method preserved tissue morphology and showed more detailed localization of CA activity in the inner ear. In particular, the marginal zone of stria vascularis and the epithelial cells of spiral prominence, facing the endolymph, showed no CA activity, while the suprastrial region of the spiral ligament and the supralimbal region of the spiral limbus, juxtaposed to the perilymph, showed CA activity. In outer hair cells, the cuticular plate, which faces the endolymph showed CA activity, but the lateral membrane, which faces the perilymph showed no CA activity. In contrast, the inner hair cell cytoplasm showed diffuse CA activity. These results will be useful in considering ion exchange between endolymph and its adjacent cells, and between perilymph and its adjacent structures.

Animals↗
PubMed1998

MRI of enlarged endolymphatic sacs in the large vestibular aqueduct syndrome.

We studied ten inner ears of five patients with a bilateral large vestibular aqueduct syndrome, using CT and MRI. Although the large vestibular aqueduct varied in size, a markedly dilated endolymphatic sac extending to the sigmoid sinus was demonstrated bilaterally on MRI in all patients. The cause of hearing loss in this syndrome is unclear. However, it is suggested that reflux of the protein-rich, hyperosmolar endolymph from the enlarged endolymphatic sac (EES) into the cochlea through a widely patent endolymphatic duct may damage the neuroepithelium. CT density and spin-echo MRI signal intensity of the endolymph in EES were markedly higher than those of CSF in eight inner ears of four patients. Increased density and high signal may indicate protein-rich, hyperosmolar endolymph. In some patients with sensorineural hearing loss and EES, the vestibular aqueduct may not appear dilated on CT. MRI is therefore necessary for correct diagnosis of this syndrome, which should more correctly be termed "large endolymphatic duct and sac syndrome". Prominent EES may predict poor prognosis in this syndrome.

Adolescent↗
PubMed2005

Observation of contrast enhancement in the cochlear fluid space of healthy subjects using a 3D-FLAIR sequence at 3 Tesla.

In animals, the enhancement of perilymph in the cochlea has been reported using 1.25 mmol/kg of Gd-DTPA, allowing the separate visualisation of perilymph and endolymph for the diagnosis of Meniere's disease. The purpose of this study was three-fold: (1) to determine the optimal timing for detecting cochlear fluid enhancement using 3D-FLAIR (fluid-attenuated inversion recovery) after intravenous administration of 0.1 mmol/kg of Gd-DTPA in healthy human subjects; (2) to examine the reliability of enhancement in multiple healthy subjects; and (3) to investigate whether endolymph and perilymph space can be visually discriminated. In two healthy subjects, 3D-FLAIR images were obtained before, immediately after and 2 h, 4 h and 6 h after the injection. Three more healthy subjects were scanned before and 4 h after the injection. In all four ears of the initial two subjects, cochlear fluid was found to be most intensely enhanced 4 h after the injection. In all of the additional three subjects, the cochlear fluid signal had increased after 4 h from injection. However, visual differentiation of endolymph and perilymph fluid could not be achieved. Using 3D-FLAIR and Gd-DTPA, cochlear fluid enhancement can be observed in healthy human ears, even with a single dose of contrast-medium injection.

Cochlea↗
PubMed1999

Vestibular semicircular canal epithelium of the rat in culture on filter support: polarity and barrier properties.

The inner ear of mammals contains the vestibular apparatus which is involved in the maintenance of posture and balance. The tubular structure of the apparatus is bathed by the potassium-rich endolymph and sodium-rich perilymph in the luminal and abluminal compartments, respectively. The luminal compartment is lined by a continuous epithelium with islets of receptor organs, which separates the luminal from the abluminal compartment. The present work focuses on the epithelium, without the receptor organs, and shows that it can be reconstituted in culture. The epithelium from 4-day-old Wistar rats was grown on microporous membranes. High transepithelial electrical resistances (4000-6000 Omega.cm2) were achieved after 4-8 days in culture. The epithelium was characterized by the presence of cytokeratin, ZO-1 protein, occludin, and the presence of tight junctions and kinocilia. The transepithelial resistance of the cell monolayer withstood endolymph/perilymph dual bathing when the apical pole of the cells was in contact with endolymph, but collapsed in the reverse configuration. Weak but statistically highly significant basal to apical rubidium (86Rb) transport was observed. These findings show that this epithelium maintains its in vivo polarity and could enhance the potassium composition of endolymph up to maturity. This new culture model, in which dual bathing is possible, should enable further in vitro studies of the sensory vestibular epithelia.

Animals↗
PubMed1986

Functional structure of the organ of Corti: a review.

The mammalian auditory organs have a dual sensory system (inner vs. outer hair cells) with distinctly different cellular organizations and innervation patterns. However, the inner (IHCs) and outer (OHCs) hair cells are mechanoreceptors sharing similar general characteristics such as organization of stereocilia (including linkage system) and a gradation of stereociliary height along the length of the cochlea. This gradation of stereociliary height may be the single most important anatomic feature in the tuning capability of the sensory cell. Several lines of evidence suggest that the stereociliary stiffness may be modulated by the sensory cells themselves, most likely via the cuticular plate-rootlet complex. The stereociliary bundles of both types of hair cell are organized in a 'W' formation with a steplike arrangement. In the OHCs, the 'W' formation is sharply angulated and slanted toward the apex, coinciding with the slanted fiber arrangement of the overlying tectorial membrane, which is firmly coupled to the tips of the tallest row of the stereociliary bundles. However, in the IHCs, the 'W' formation is wide and its long axis is linear and arranged at a right angle to the radial axis of the organ of Corti; also, the ciliary bundles are freestanding (with a few exceptions in the basal turn). This arrangement in the IHCs would be best suited for deflection by the radial flow of the endolymph. Present evidence suggests that the subtectorial fluid space exists, is filled with endolymph, and freely communicates with endolymph. Because of the discovery of the phenomenon of 'cochlear emission', the possible motility of the sensory cells, particularly of the OHCs, has drawn intense interest in recent years. Recent investigations with dissociated sensory cells (OHCs) indicate some motile capability under various experimental conditions, although it has not been established that this motility is present in vivo. For this reason, the specialized cellular organization for motility and localization of contractile and cytoskeletal proteins have been investigated. These results support the possibility that the OHCs may have cellular facilities for this function.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗