The difference in endolymphatic hydrostatic pressure elevation induced by isoproterenol between the ampulla and the cochlea.

OBJECTIVE: The purpose of the study was to investigate the difference in the responses of endolymphatic hydrostatic pressure to isoproterenol, ß-adrenergic receptor agonist, between pars superior and pars inferior. METHODS: The hydrostatic pressure of endolymph and perilymph and endolymphatic potential in the ampulla and the cochlea during the intravenous administration of isoproterenol were recorded using a servo-null system in guinea pigs. RESULTS: The hydrostatic pressure of endolymph and perilymph in the ampulla and cochlea was similar in magnitude. Isoproterenol significantly increased hydrostatic pressure of ampullar and cochlear endolymph and perilymph with no change in the ampullar endolymphatic potential and endocochlear potential, respectively. The isoproterenol-induced maximum change of endolymphatic hydrostatic pressure in ampulla was significantly (p<0.01) smaller than that in the cochlea. In ears with an obstructed endolymphatic sac, the action of isoproterenol on endolymphatic hydrostatic pressure in the ampulla disappeared like that in the cochlea. CONCLUSION: Isoproterenol elevates endolymphatic hydrostatic pressure in different manner between the vestibule and the cochlea.

Effect of inner ear blood flow changes on the endolymphatic sac.

CONCLUSIONS: That the endolymphatic sac (ES) reacts to changes in inner ear blood flow may be important for homeostasis of the inner ear fluid volume and pressure. OBJECTIVES: To elucidate the effect of changes in inner ear blood flow on the ES and to learn more about the volume and pressure regulatory function of the ES. MATERIALS AND METHODS: Epinephrine or sodium nitroprusside (SNP) was injected into the middle ear cavity of adult CBA/J mice. The ES were analyzed morphologically by light microscopy. RESULTS: Epinephrine reduced the luminal size of the ES leading to an accumulation of intraluminal homogeneous substance. Injection of SNP increased the size of the ES lumen, accompanied by a collapse of the lateral intercellular space (LIS) and dense perisaccular tissue. These changes were almost reversed 4 h after injection.

A new animal model for Ménière's disease.

CONCLUSION: A new murine model for the study of Ménière's disease has been developed by treatment with both lipopolysaccharide (LPS) and aldosterone. Induction of vestibular dysfunction in the hydropic animal model may entail additional stress such as reduced inner ear blood flow, and sudden acute changes in endolymph volume and/or pressure. OBJECTIVE: The purpose of this study was to develop a more suitable animal model, showing closer resemblance to the pathophysiological process in Ménière's disease. MATERIALS AND METHODS: Adult CBA/J mice were treated by intratympanic injection of LPS, intraperitoneal injection of aldosterone, or injection of both LPS and aldosterone. Morphological analyses were performed in the cochlea and endolymphatic sac. RESULTS: All experimental animals showed mild to moderate endolymphatic hydrops. Those treated with both LPS and aldosterone showed reversible vestibular dysfunction after the intratympanic injection of epinephrine.

Aquaporin-2 regulation by vasopressin in the rat inner ear.

Our previous studies have suggested a close relationship between vasopressin and endolymphatic hydrops, or the increased volume of endolymph in the inner ear. Endolymphatic hydrops is also thought to occur in Ménière's disease patients. In the kidney collecting duct, vasopressin induces the expression of aquaporin-2 (AQP2), resulting in increased water reabsorption. We explored the possibility, using a quantitative PCR method, that vasopressin regulates the expression of AQP2 mRNA in the rat inner ear, as it does in the kidney. The levels of AQP2 mRNA in the cochlea and endolymphatic sac were significantly higher in rats treated with vasopressin than the levels in control animals. We speculate that over-expression of AQP2 may be involved in the formation of endolymphatic hydrops.

Effect of isosorbide on distortion-product otoacoustic emissions and endocochlear DC potential in experimentally induced hydropic ears.

The effects of isosorbide on distortion-product otoacoustic emissions (DPOAEs) and endocochlear DC potential (EP) were examined in experimentally induced endolymphatic hydropic ears and untreated control ears using 20 albino guinea pigs. DPOAEs and EP in the hydropic ears decreased after obliteration of the endolymphatic duct and sac. The administration of isosorbide restored DPOAEs to the normal level, whereas EP was further reduced. In control ears there was no significant change in DPOAEs and EP after the administration of isosorbide. The results obtained in the present study indicate that the effect of isosorbide on DPOAEs is different from that on EP, and the recovery of DPOAEs in hydropic ears is not a secondary phenomenon due to the recovery of EP.

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.

Effect of glycerol on the guinea pig inner ear after removal of the endolymphatic sac.

The effects of glycerol were investigated in guinea pigs in which the endolymphatic sac (ES) and duct (ED) had been obliterated unilaterally. Twenty-four hours after obliteration of the right ES and ED, glycerol was injected intraperitoneally. One to two hours after administration of glycerol, collapse or folding of Reissner's membrane was observed in the operated cochlea. No remarkable change was found in the nonoperated ear. The lumen of the ES of the nonoperated ear collapsed with intraluminal stainable substance within 1 h. The volume of the stainable substance increased with time and could still be seen 4 h after the injection of glycerol. Twenty-four hours after the injection of glycerol, the configuration of the ES was normal again. In addition, the animals showed marked unilateral (operated side) vestibular dysfunction after injection of glycerol. These findings suggest that the ES also has a secretory capacity and plays an important role in inner ear fluid volume and pressure regulation.

The effect of glycerol on short-term experimental endolymphatic hydrops.

The aim of this paper was to evaluate the effect of one month of treatment with different dosages of glycerol on experimental endolymphatic hydrops produced by obliteration of endolymphatic sac and duct through an extradural approach. Forty-two guinea pigs were used. The animals, divided into six groups, received 0.5-2 gr/kg body weight of the drug per day for one month. The activity of glycerol was determined by statistical analysis of volumetric changes of scala media. Glycerol demonstrated the effect of reducing endolymphatic hydrops. The decrease in hydrops was influenced by the dosage suggesting a stria metabolic response.

Early effects of gentamicin on inner ear glycocalyx cytochemistry.

The early effects of gentamicin treatment on the inner ear glycocalyx were investigated using two cationic probes, colloidal thorium and cationized ferritin. Gentamicin treatment resulted in a diminished thorium reactivity of both the endolymphatic and perilymphatic glycocalyx of the hair cells after 1 day and complete abolishment of reactivity after 5 days. Cationized ferritin reactivity of the perilymphatic and endolymphatic glycocalyx was not significantly influenced. The cytochemistry of the inner ear glycocalyx and the possible biochemical changes induced by gentamicin are discussed.

The nature of the ototoxic actions of ethacrynic acid upon the mammalian endolymph system. II. Structural-functional correlates in the stria vascularis.

The relationship of the ultrastructural changes in the stria vascularis to the functional alterations in the endolymph system was investigated in 23 rats at various times up to 120 min after a single intravenous injection of ethacrynic acid (60 mg kg-1). The overall effect upon the marginal cells, revealed by the development and regression of marked cytoplasmic swelling, was reasonably well correlated with the derangements produced in the strial ion-transporting mechanisms. The pathophysiological relationships of the action upon the intermediate cells was less exact and no unequivocal structural correlates were found for the diminution in membrane permeability and the probable late decrease in energy production. The size of the interstitial spaces was determined mainly by the variations in volume of the marginal and intermediate cells.