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781 records · Page 44Linked to original sources
PubMed1999

Morphological changes of the endolymphatic sac induced by microinjection of artificial endolymph into the cochlea.

Morphological changes of the endolymphatic sac were analyzed in guinea pigs following microinjection of artificial endolymph into the cochlea or withdrawal of a quantity of native endolymph. Injections were performed into the second turn of scala media with a micro-pump at a rate of 60-100 nl/min, lasting for a period of 4, 7. 5, 15 or 18 min. In withdrawal experiments, endolymph was aspirated from the second cochlear turn over a period of 8 min. For each procedure the contralateral (non-treated) ear served as a histological control. Following artificial endolymph injections of 7. 5 min or more there was an almost total absence of the normal intraluminal homogeneous substance (HS) on the injected side. Our observations suggest that the disappearance of the HS occurs by both enzymatic and macrophagic activity. After endolymphatic withdrawals the ES was found to contain increased amounts of HS. The results could suggest that the volume of fluid in the ES, and hence the volume of the entire membranous labyrinth, may be regulated by a dynamic relationship between active secretion and enzymatic degradation of a lumen-expanding substance that is intimately related to the intraluminal macrophages. The exact mechanism governing these regulatory systems, and their relationship to ion and water movements across the epithelium of the sac, remain to be elucidated.

Animals↗
PubMed1982

Minimal concentrations of metabolic substrates capable of supporting cochlear potentials.

The objective of this study was to determine the capability of glucose analogues, as well as lactate and pyruvate, to maintain the endolymphatic potential and the cochlear microphonics. In addition, the minimum concentration at which different substrates (including D-glucose) were able to sustain the potentials ("critical' concentration) was determined. Synthetic blood containing various substrates at different concentrations was perfused via the anterior inferior cerebellar artery. The critical concentration for D-glucose was found to be 15 mg% (0.83 mM). L-Glucose, galactose and fructose were not able to support the potentials at concentrations as high as 200 mg%. On the other hand, mannose was capable of supporting the potentials; however, the critical concentration (50 mg% or 2.8 mM) was substantially higher than that of D-glucose. Both lactate and pyruvate could support the potentials, but the critical concentrations (8.5 mM and 6.5 mM, respectively) were markedly higher than in the case of glucose, even when the difference of carbon equivalents was taken into consideration. The data are discussed in the context of the intermediary metabolism and possible carrier systems of the stria vascularis.

Action Potentials↗
PubMed1987

Rapidly fluctuating thresholds at the onset of experimentally-induced hydrops in the guinea pig.

Pigmented guinea pigs were chronically implanted bilaterally with a platinum electrode on each round window. After recovery the endolymphatic sac was destroyed and the duct blocked on one side only; the other side was employed as a control. The round window response thresholds on both sides were recorded several times per week over a three month period. There were three main results. A sensitivity loss of up to 20 dB was observed for frequencies between 250 Hz and 6.4 kHz within two weeks post-op. At the end of three months the threshold elevation for these frequencies was as much as 50 dB. On the other hand the thresholds for frequencies between 8 and 16 kHz remained within 10 dB of their pre-operative value for at least two months. The thresholds fluctuated with a shift of as much as 25 dB within 24 h. The threshold elevation was associated with a decrease in the latency, at threshold, of the round window AP response which at frequencies between 250 Hz and 6.4 kHz was as short as that for 8 kHz. This observation suggested that it was the base, only, of the cochlea which responded. The present study has indicated that experimentally induced endolymphatic hydrops in the guinea pig mimics well the progressive and fluctuating hearing loss characteristic of Ménière's disease.

Animals↗
PubMed1995

[Measurement of Ca2+ concentration and endocochlear potential in experimental endolymphatic hydrops in vivo].

This study was based on observations on 14 normal guinea pigs and 17 guinea pigs in which the left endolymphatic duct and sac had been surgically obliterated to induce endolymphatic hydrops. Three groups of hydropic animals were tested 1, 2 and 3 months after surgery. The Ca2+ concentration and endocochlear potential (EP) were recorded by means of double-barrelled ion selective micro-electrode in the third turn of the cochlea. The results indicated that a decrease in EP and an increase in Ca2+ in hydropic cochlea, a negative correlation was present. In the control ear, the values of Ca2+ and EP were 26.4 +/- 0.33 microns/L (n = 14) and 72.78 mV (n = 14), respectively; in the hydropic ear, the value of Ca/+ was 404.47 +/- 79.74 microns/L (n = 17), while the EP was 55.82 +/- 3.28 mV (n=17). According to Nerstian formula, the slope of electrochemical gradient in the control was 31 mV/decade (n = 14), but in the hydropic ear it increased to 72.5 mV/decade change in Ca2+ (n = 17). The statistical analysis showed significant difference between the control and hydropic ears. The changes were progressive and became more pronounced as the duration of hydrops prolonged. The cause of hearing loss in the Ménière's disease and the relation between the EP and CA2+ concentration had been discussed.

Animals↗
PubMed2005

Activation of caspase-3 is associated with oxidative stress in the hydropic guinea pig cochlea.

The aim of this study was to investigate the involvement of oxidative stress and apoptosis in an animal model of Meniere's disease. Endolymphatic hydrops (ELH) is generally accepted as the decisive histological characteristic of Meniere's disease. Closure of the endolymphatic duct (Kimura's method) was used to induce endolymphatic hydrops in guinea pigs. Sham-operated animals served as controls. After 4 weeks the animals operated showed a significant elevation of the hearing thresholds as measured by audiometric brainstem responses (ABR) pre- and postoperatively. Immediately after the second ABR measurement, the animals were sacrificed for further immunohistological examinations of the inner ear with specific antibodies to active caspase-3 (cas-3) as a marker for apoptosis and antibodies to 8-isoprostane (8-iso) and nitrotyrosine (NT) as indicators of oxidative stress. Compared with the sham-operated controls, hydropic cochleae showed strong immunostaining for both oxidative stress markers in spiral ganglion cells, in the blood-vessels and fibrocytes of the lateral wall, as well as in supporting cells of the organ of Corti. Activation of cas-3 in spiral ganglion cells and the lateral wall was found exclusively in hydropic cochleae. Our findings suggest that oxidative stress is involved in the development of endolymphatic hydrops and may lead to cellular damage which induces apoptosis by activation of cas-3. Apoptotic cell death might contribute to the sensorineural hearing loss found in later stages of Meniere's disease.

Animals↗
PubMed1995

Disturbance of regulation of sodium by cis-diamminedichloroplatinum in perilymph of the guinea pig cochlea.

We studied the acute effects of cis-diamminedichloroplatinum (CDDP) on the cochlear partition and inner ear fluid in the guinea pig. At 48 hours after the administration of a single intramuscular injection of CDDP, 12.5 mg/kg of body weight, the endocochlear resting potential (EP) was significantly decreased to 32.1 +/- 1.8 mV in the treated animals, versus 80.6 +/- 1.0 mV in the control animals. There was a significant rise in potassium (K+), sodium (Na+), and chlorine (Cl-) in the endolymph of the animals treated with CDDP as compared with the control animals. Only Na+ was found to increase significantly in the perilymph, reaching more than twice the level of the control animals; both K+ and Cl- remained within the normal range. Serum electrolytes also remained within the normal range. Evaluation of modified ionic permeabilities across the endolymph-perilymph barrier showed an apparent increase in Na+ permeability and a normal range of K+ and Cl- permeabilities. Histopathologic examination of the cochlea showed a moderate collapse of the endolymphatic space, with atrophy of the stria vascularis and destruction of the outer hair cells. The findings suggest that the acute changes produced in the cochlea by administration of CDDP were attributable to a breakdown in the regulation of Na+ metabolism in the perilymph.

Animals↗
PubMed1992

Dependence of endocochlear potential on basolateral Na+ and Cl- concentration: a study using vascular and perilymph perfusion.

Inside-positive endocochlear potential (EP) and high potassium concentration in the endocochlear duct are generated by transepithelial K+ transport in marginal cells of the stria vascularis. In order to estimate the degree of involvement of Na+ and Cl- in K+ transport in marginal cells, EP in guinea pigs was measured under artificial vascular and perilymphatic perfusion in situ. Na+ depletion due to both vascular and perilymphatic perfusion decreased EP by -10.0 +/- 4.1 mV (delta EP = -86 +/- 5.2 mV, n = 5) from the control value of 78 +/- 4.3 mV (p < 0.01). Cl- depletion due to vascular and perilymphatic perfusion also decreased EP by -10.0 +/- 4.9 mV (delta EP = 8.5 +/- 4.8 mV, n = 6) from the control value of 77 +/- 5.1 mV (p < 0.01). However, under either vascular or perilymphatic perfusion, even lowering of Na+ or Cl- concentration in the perfusate decreased EP only slightly compared to the results under both vascular and perilymphatic perfusion. Furosemide, a blocker of Na+/K+/2Cl- symport, decreased EP under vascular perfusion. This dependency of EP on basolateral Na+ and Cl- concentration strongly suggests that K+ transport by the marginal cell is dependent on the basolateral Na+ and Cl- concentration, and that Na+/K+/2Cl- symport is raised as a possible mechanism for Na+ and Cl- dependency of EP.

Animals↗