Expression of AQP-10, -11 and -12 in the rat stria vascularis.

BACKGROUND: Water homeostasis is essential for inner ear function. Several aquaporins (AQPs), which are water transport proteins in the cell or plasma membrane, have been reported in the lateral wall of the rat inner ear (cochlea). However, the presence of AQP-10, -11 and -12 has not been reported in the rat stria vascularis (SV) to date. AIMS/OBJECTIVES: We have aimed to clarify the expression of AQP-10, -11 and -12 in the cochlea lateral wall. MATERIALS AND METHODS: Using Wistar rats, we examined the expression of AQP-10, -11 and -12 in the cochlea lateral wall using molecular approaches and immunohistochemistry. RESULTS: AQP-11 was molecular biologically expressed, but the expression of AQP-10 and -12 was not observed. Immunohistochemically, AQP-11 was diffusely localized in the basal cells and marginal cells of the rat SV but was not expressed at the apical site of marginal cells with double staining. The expression of AQP-10 and -12 was not observed. CONCLUSIONS AND SIGNIFICANCE: Only AQP-11 was expressed in the basal cells and marginal cells, but it was not expressed at the apical site of marginal cells. Based on this study, AQP-11 may not have an important role in water flux between the perilymph and endolymph.

Effects of Glucocorticoids on the Inner Ear.

Hypothesis: Recently, several lines of evidence have suggested that the inner ear is under hormonal control. It is likely that steroids have some influence on the inner ear. Background: Many clinicians have been empirically using steroids for the treatment of diseases associated with endolymphatic hydrops. The theoretical grounds for this are not clear, and there have been a number of debates on the effectiveness of steroid treatment. Furthermore, there are few reports on histological observations of the influences of steroids on the cochlea. Method: Fifteen guinea pigs (30 ears) were divided into three groups. In the control group, physiological saline solution was administered intra-peritoneally for 3 days. In two steroid groups, 40 mg/kg/day of hydrocortisone or 4 mg/kg/day of dexamethasone was administered intra-peritoneally for 3 days. Extension of Reissner's membrane and volume change of the scala media were checked 6 h after the last administration. The degree of Reissner's membrane extension and volumetric change of the scala media were quantitatively measured with the use of a video-digitizer. Results: We did not identify any distinct changes in the cochlea of the control group. In contrast, the extension of Reissner's membrane and endolymphatic hydrops were observed in the animals in the steroid groups. Statistical analysis revealed that Reissner's membrane extended significantly in the steroid groups, and that the volume of the scala media also increased significantly. Conclusion: This is the first report to investigate the effects of systemic administration of glucocorticoids on guineapig cochlea. The extension of Reissner's membrane and dilated endolymphatic space were evident in the steroid groups. However, the underlying mechanism of histological changes was not clear, marked care needs to be taken when administering steroids to patients with Meniere's disease whose histological feature is endolymphatic hydrops.

A possible mechanism of the formation of endolymphatic hydrops and its associated inner ear disorders.

The pathology of Meniere's disease (MD) is well established to be endolymphatic hydrops. However, the mechanism underlying deafness and vertigo of MD or idiopathic endolymphatic hydrops is still unknown. In order to evaluate the pathogenesis of deafness and vertigo in MD, it seems to be rational to investigate the interrelationship between hydrops and inner ear disorders using animals with experimentally-induced endolymphatic hydrops. In spite of intense efforts by many researchers, the mechanism of vertiginous attack has been unexplained, because animals with experimental hydrops usually did not show vertiginous attack. Recently, there are two reports to succeed to evoke vertiginous attack in animals with experimental hydrops. In the present paper were first surveyed past proposals about underlying mechanism of the development of hydrops and inner ear disorders associated with hydrops, and were discussed the pathogenetic mechanism of vertiginous attack in hydrops. In conclusion, abrupt development of hydrops was thought to play a pivotal role in the onset of vertiginous seizure.

Endocytosis of CF in marginal cells of stria vascularis regulated by ROCK and MLCK signaling cascade, but not G-proteins.

Objective The endocytosis of cationized feritin (CF) via a clathrin-mediated pathway is regulated by a signaling network. Marginal cells showed the active endocytosis of CF via a clathrin-mediated pathway. The internalization of receptors through this clathrin-mediated pathway is an important regulatory event in signal transduction. Numerous kinases are involved in endocytosis, and each endocytic route is subjected to high-order regulation by cellular signaling mechanisms. In this study, we investigated whether ROCK and MLCK signaling cascades and G-proteins regulate the endocytosis of CF in marginal cells of the stria vascularis. Methods CF was infused into the cochlear duct with pertussis toxin (PTX),Clostridium botulinum C3 toxin (BTX), guanosine(g-thio)-triphosphate (GTP-γS), ML-7, Y-27632. Endocytic activity was measured at 30 min after the start of infusion under an electron microscope. Results In marginal cells, CF was internalized via a clathrin-mediated pathway that depends on F-actin and microtubules (MT). Its processes were controlled by myosin light chain kinase (MLCK) and Rho-associated kinase (ROCK), but not affected by G-protein-coupled receptor (GPCR) or the RhoA signaling cascade. Conclusion Our previous study showed that the main endocytotic pathway of microperoxidase (MPO) did not depend on the Rho/ROCK molecular switch or actin/myosin motor system, but was mainly regulated by the RhoA signaling cascade. The present study results indicate that these signaling cascades regulating CF internalization completely differ from the cascades for MPO internalization.

Isosorbide-Induced Decompression Effect on the Scala Media: Participation of Plasma Osmolality and Plasma Arginine Vasopressin.

OBJECTIVE: The correlation between the isosorbide-induced decompression effect on the endolymphatic space and plasma osmolality (p-OSM) or plasma arginine vasopressin (p-AVP) was investigated on comparing two different dosages of isosorbide (2.8 and 1.4 g/kg) to elucidate why the decompression effect is delayed with a large dose of isosorbide. MATERIALS AND METHODS: Two experiments were performed using 80 guinea pigs. Experiment 1 was designed to morphologically investigate the sequential influence of the oral intake of 1.4- and 2.8-g/kg doses of isosorbide on the endolymphatic volume. The animals used were 50 guinea pigs (control: 10, experimental: 40). All animals underwent surgical obliteration of the endolymphatic sac of the left ear. One month after the surgery, control animals were sacrificed 3 hours after the intake of distilled water, and experimental animals were sacrificed 3 and 6 hours after the isosorbide intake. All of the left temporal bone served for the quantitative assessment of changes in the endolymphatic space, and the cross-sectional area of the scala media was measured from the mid-modiolar sections of the cochlea.Experiment 2 was designed to investigate changes in p-OSM and p-AVP levels 3 hours after the oral intake of isosorbide. Animals used were 15 guinea pigs (control: 5, experimental: 10). The control group received the oral administration of distilled water (4 ml/kg), and the experimental animals were subdivided into two groups consisting of 10 animals each by the dosage of isosorbide (1.4 or 2.8 g/kg). All animals were sacrificed for the measurement of p-OSM and p-AVP concentrations 3 hours after the intake of water or 70% isosorbide solution. RESULTS: Morphologically, an isosorbide-induced decompression effect was noted in animals with both 1.4- and 2.8-g/kg doses of isosorbide. According to the regression analysis, however, the volumetric decrease of the endolymphatic space was more evident in cases with the small dose (1.4 g/kg) 3 hours after the intake (analysis of covariance [ANCOVA], p < 0.001). Six hours after, the decompression effect was significantly greater in cases with the large dose (2.8 g/kg) (ANCOVA, p < 0.001).Isosorbide intake caused a rise in p-OSM levels dose-dependently. The Cochran-Cox test revealed that the differences in the mean values among control and isosorbide groups were significant (p < 0.01). Regarding the p-AVP level, a significant increase was evident in cases with the large dose (2.8 g/kg) (p < 0.01, Cochran-Cox test), and not in cases with the small dose (1.4 g/kg). CONCLUSION: An isosorbide-induced decompression effect of the endolymphatic space was evident in spite of two different dosages of isosorbide (2.8 and 1.4 g/kg). Three hours after the isosorbide intake, however, the decompression effect was more marked in the group with the small dose (1.4 g/kg). Since significant rises in p-OSM and p-AVP were evident in the group with the large dose, this early rise of p-AVP due to dehydration seems to be the major reason for the delayed decompression effect in cases with a large isosorbide intake.

Dehydration effects of a V2 antagonist on endolymphatic hydrops in guinea pigs.

We investigated the influence of vasopressin type 2 receptor antagonist (OPC-41061; Tolvaptan) on experimentally induced endolymphatic hydrops (EH) in guinea pigs. In the first series, the endolymphatic sac (ES) of the left ear of all animals was electrocauterized. Four weeks after surgery, the animals were allocated to four groups: three systemic applications groups (saline, OPC 10 and 100 mg/kg) and a local round window (RW) OPC 1 mg/body application group. We examined the histopathology of the temporal bones and assessed volumetric changes of the endolymphatic space in the cochlea and saccule. In the second series, we investigated the effects of systemic and topical applications of OPC on plasma vasopressin (p-VP) concentrations and plasma osmolality (p-OSM). In the first series, we found that EH was reduced in the OPC 10 mg/kg systemic and OPC RW application groups. In contrast, EH increased in the OPC 100 mg/kg systemic application group. In the second series, neither p-VP levels nor p-OSM were significantly different among the non-OPC, OPC 10 mg/kg systemic, and OPC RW application groups. However, in the OPC 100 mg/kg systemic application group, the p-VP level was significantly higher than that in other groups, and p-OSM was higher than that in the non-OPC group. The systemic application of a low dose of OPC and topical application of OPC resulted in reduced EH in the face of minimal systemic effects (p-VP and p-OSM). These findings suggest that OPC-41061 may be one useful treatment option for EH.

Experimental studies on the recovery processes from severe facial palsy and the development of its sequelae.

OBJECTIVE: To experimentally elucidate the pathogenesis of inappropriate co-contraction of facially innervated muscles after severe facial palsy. METHODS: Twenty-two guinea pigs with severe facial palsy induced by the interruption of the petrosal artery were used to follow up behavioral facial movement, including the degree of facial palsy and abnormal hyperkinetic facial movement of synkinesis and mass contracture. At the end of the follow-up, the evoked facial compound muscle action potential (evoked FCMP) and antidromically evoked facial nerve response (AFNR) were examined in a few typical cases with complete recovery and with incomplete recovery accompanied by synkinesis. After the follow-up, all animals were sacrificed for morphological studies, which consisted of a light-microscopic study (by Luxol fast blue and hematoxylin and eosin staining or toluidine blue staining) and/or an electron-microscopic study. RESULTS: The initial sign of recovery was mass contracture or spasm. This condition continued for 2 weeks or more. As voluntary facial movement recovered, the mass contracture became unnoticeable. It could not be distinguished when the so-called synkinesis developed. Synkinesis usually developed during the recovery process from severe to moderate palsy, and synkinesis persisted or progressed once it appeared. Histologically, unmyelinated fibers were intermingled with myelinated fibers in an early stage of recovery with mass contracture. In the late stage with the development of synkinesis, however, such an intermingling of unmyelinated and myelinated axons was not observed. In this stage, axons became well myelinated, but they were irregular in shape in cases with synkinesis. Especially, axons irregularly ran at the level of the G1 (at the region of the second genu) segment, and bifurcated axons were sporadically found. The axon count had a tendency to increase toward the periphery. AFNR was not detected, although evoked FCMP could be clearly detected in cases with synkinesis. CONCLUSION: Misguidance of regenerated axons is an important cause of facial synkinesis in the ischemia-induced facial palsy model. Ephaptic transmission between unmyelinated and myelinated axons is also likely to be responsible for mass contracture manifested in the early stage of the recovery process.

Type 1 allergy-induced endolymphatic hydrops and the suppressive effect of H1-receptor antagonist (olopatadine hydrochloride).

OBJECTIVE: To investigate whether endolymphatic hydrops (EH) is experimentally induced by type 1 (or immediate) hypersensitivity allergic reaction and to investigate the inhibitory action of a histamine H(1)-receptor antagonist (olopatadine hydrochloride [OLO-Hy]) on allergic EH induced by systemic immune challenge with 2,4-dinitrophenylated-Ascaris (DNP-As). METHODS: The experimental animals were actively sensitized with DNP-As twice at a 4-week interval and were provoked by an injection of DNP-BSA including DNP-As 1 week after the second sensitization. The OLO-Hy (+) group received oral administration of OLO-Hy (30 mg/kg) 1 hour before the provocation, whereas the OLO-Hy (-) group received distilled water. The temporal bones in all animals were light microscopically examined to assess the degree of EH quantitatively and the expression of degranulated mast cells in the endolymphatic sac. RESULTS: Endolymphatic hydrops was observed 1, 6, 12, and 24 hours after the last sensitization in the OLO-Hy (-) group but was not observed in the OLO-Hy (+) group. Quantitative analysis of the increase ratios (IRs) of the cross-sectional area of the scala media revealed that the IRs of the OLO-Hy (-) group were significantly greater compared with those of the control group (p < 0.001). There was also a significant difference in the IRs between the OLO-Hy (-) and OLO-Hy (+) groups (p < 0.001). CONCLUSION: The systemic sensitization with DNP-As produced allergy-induced experimental EH by type 1 hypersensitivity allergic reaction, and the development of this EH was prevented by histamine H(1)-receptor antagonists.

Morphological and functional changes in a new animal model of Ménière's disease.

The purpose of this study was to clarify the underlying mechanism of vertiginous attacks in Ménière's disease (MD) while obtaining insight into water homeostasis in the inner ear using a new animal model. We conducted both histopathological and functional assessment of the vestibular system in the guinea-pig. In the first experiment, all animals were maintained 1 or 4 weeks after electrocauterization of the endolymphatic sac of the left ear and were given either saline or desmopressin (vasopressin type 2 receptor agonist). The temporal bones from both ears were harvested and the extent of endolymphatic hydrops was quantitatively assessed. In the second experiment, either 1 or 4 weeks after surgery, animals were assessed for balance disorders and nystagmus after the administration of saline or desmopressin. In the first experiment, the proportion of endolymphatic space in the cochlea and the saccule was significantly greater in ears that survived for 4 weeks after surgery and were given desmopressin compared with other groups. In the second experiment, all animals that underwent surgery and were given desmopressin showed spontaneous nystagmus and balance disorder, whereas all animals that had surgery but without desmopressin administration were asymptomatic. Our animal model induced severe endolymphatic hydrops in the cochlea and the saccule, and showed episodes of balance disorder along with spontaneous nystagmus. These findings suggest that administration of desmopressin can exacerbate endolymphatic hydrops because of acute V2 (vasopressin type 2 receptor)-mediated effects, and, when combined with endolymphathic sac dysfunction, can cause temporary vestibular abnormalities that are similar to the vertiginous attacks in patients with MD.

Type 1 allergy-induced endolymphatic hydrops and the suppressive effect of leukotriene receptor antagonist.

OBJECTIVE: To investigate allergic endolymphatic hydrops (EH) and the effect of leukotriene receptor antagonist (LTRA). METHODS: Experiment 1: Thirty-six guinea pigs were actively sensitized with DNP-ascaris twice and were provoked with DNP-bovine serum albumin 1 week after the second sensitization. Alterations in the inner ear were investigated histologically at 1, 12, 24, and 36 hours after the provocation, and changes of the endolymphatic space were quantitatively assessed. The animals in the control group received no sensitization but only distilled water. Experiment 2: Twenty-four guinea pigs were actively sensitized and provoked in the same manner. Animals received oral administration of LTRA 1 hour before the provocation. Alterations in the inner ear were investigated as same manner as in Experiment 1. Experiment 3: Eleven of 19 guinea pigs were actively sensitized and provoked in the same manner. Eight animals in the control group received distilled water. One hour after these procedures, the changes in p-AVP levels were investigated. RESULTS: Experiment 1: EH was observed 12, 24, and 36 hours after the last sensitization. In these groups, their cross-sectional areas of the scala media were significantly larger than that of the control group. Degranulation of mast cells was observed in the endolymphatic sac. Experiment 2: In animal groups with LTRA, EH was not observed at all. Experiment 3: P-AVP levels were significantly elevated in animals with the sensitization. CONCLUSION: The sensitization with DNP-Ascaris produced allergic EH and elevation of p-AVP, and allergic EH was inhibited by LTRA.

Endocytosis of cationized ferritin in marginal cells of the stria vascularis is regulated by protein kinase, protein phosphatase, and MEK/ERK and PI3-K signaling pathways.

HYPOTHESIS: The endocytosis of cationized ferritin (CF) via a clathrin-mediated pathway is regulated by a signaling network. BACKGROUND: Marginal cells showed the active endocytosis of CF via a clathrin-mediated pathway. The internalization of receptors through the clathrin-mediated pathway is an important regulatory event in signal transduction. Numerous kinases are involved in endocytosis, and each endocytic route is subjected to high-order regulation by cellular signaling mechanisms. METHODS: CF was infused into the cochlear duct with phorbol 12-myristate 13 acetate, okadaic acid, staurosporin, phenylarsine oxide, PD98059, SB20580 and wortmannin. Endocytic activity was measured at 30 minutes post-infusion by transmission electron microscopy. RESULTS: The endocytosis of CF was stimulated by a protein kinase C activator (phorbol 12-myristate 13 acetate) and a protein kinase A activator (8-bromoadenosine-3', 5'-cyclic monophosphate). It was inhibited by protein phosphatase inhibitors (okadaic acid and phenylarsine oxide), mitogen-activated protein kinase/extracellular signal-related kinase inhibitors (PD98059 and SB20580), and a phosphatidylinositol 3-kinase inhibitor (wortmannin). CONCLUSION: Our previous study showed the endocytosis of microperoxidase to be strongly dependent on protein kinase C, protein phosphatase, extracellular signal-related kinase, and phosphatidylinositol 3-kinase signaling networks but not on protein kinase A and mitogen-activated protein kinase signaling networks. The present study indicated that the signaling cascade regulating CF's internalization differed from the cascade for microperoxidase's endocytosis.

Endocytosis of microperoxidase in marginal cells is mainly regulated by RhoA signaling cascade, but not by Rho-associated protein kinase, myosin light-chain kinase and myosin phosphatase.

Endocytosis plays an important role in cell function and the activation and propagation of signaling pathways. Signaling occurs on endocytic pathways and signaling endosomes, and endocytosis is subjected to high-order regulation by cellular signaling mechanisms. Marginal cells showed active endocytosis of microperoxidase (MPO) via the clathrin-independent pathway. We examined the signaling pathway that regulates MPO endocytosis in marginal cells using specific inhibitors and activators of signaling molecules. The results showed that pertussis toxin - which inhibits the ribosylation of G-protein-coupled receptor - did not affect MPO endocytosis, but Clostridium botulinum C3 toxin - which induces RhoA inactivation resulting in extracellular-signal-related kinase inactivation - inhibited MPO endocytosis. The main endocytotic pathway of MPO did not depend on the Rho-associated protein kinase molecular switch or actin/myosin motor system, but was mainly regulated by the RhoA signaling cascade.

Endocytosis of MPO in marginal cells is regulated by PKC, protein phosphatase, ERK and PI3-K signaling cascades, but not by PKA and MEK signaling cascades.

Endocytosis of marginal cells plays a key role in maintaining the homeostasis of endocytosis and function of the organ of Corti. How the signaling cascade is involved in the regulation of endocytosis is an important issue at present. To investigate the regulation of endocytosis in marginal cells of the stria vascularis by the signaling network, we perfused MPO, an endocytosis tracer, with PMA, OA, staurosporin, PAO, PD98059, SB20580 or wortmannin into the cochlear duct. After 30 min endolymphatic perfusion, the tissues were fixed and the distribution of MPO was examined by electron microscopy. We explored the functions of PKC, RTK, PI3-K, PTP, and PP1/2A in MPO endocytosis and defined the MPO endocytic route. MPO endocytosis was strongly dependent on PKC, ERK, PTP, PP1/2A and PI3-K signaling networks, but not on PKA and MEK signaling networks. The MPO endocytic pathways are clathrin-, GPI-AP-, and caveolae-independent.

The clinical value of extratympanic electrocochleography in the diagnosis of Ménière's disease.

OBJECTIVE: To evaluate the clinical conditions causing an elevation in the click-evoked summation potential (SP)/action potential (AP) amplitude ratio (SP/AP ratio), the cause of the SP enhancement in Ménière's disease (MD) and the diagnostic efficacy of electrocochleography (ECoG) were discussed. STUDY DESIGN: Retrospective case review. SETTING: An outpatient clinic of the Otolaryngology Department of Kochi Medical School. PATIENTS: ECoG testing was performed in 632 patients (727 ears) with vertigo/dizziness and/or deafness over a 10-year period (1995-2005). Among them, 334 patients had diagnoses of definite MD, including 95 cases of bilateral involvement. MAIN OUTCOME MEASURES: Audiological thresholds and SP/AP ratio. RESULTS: An enhanced SP was observed in 56.3% of patients with MD. The incidence of an enhanced SP was low in patients for whom the disease duration was 2 years or less and the frequency of attacks was once a year or less, but was significantly higher in cases where the disease duration was 2 years or longer and/or the frequency of attacks was several times a year (Games-Howell test, p < 0.05). The incidence of an enhanced SP was significantly elevated in cases with pure-tone average exceeding 31 dB (Kendall's rank correlation test, p < 0.001). However, the enhanced SP, once it appeared, did not always disappear in spite of hearing improvement. Hearing improvement induced by the glycerol test also produced no alteration in an SP/AP ratio, and there was no significant difference between the glycerol test results and the incidence of an enhanced SP (chi2 goodness-of-fit test). CONCLUSIONS: The longer the patients were symptomatic or the severer the ear symptoms, the more likely the ECoG was to be positive. The abnormally elevated SP, once it had appeared, persisted for long periods. Spontaneous and glycerol-induced hearing gains did not result in a decrease in SP/AP ratio. These clinical characteristics of ECoG seem to indicate that the enhanced SP in MD might be caused by the malfunction of hair cells, not by the displacement of the basilar membrane toward the scala tympani.

Hormonal aspects of Ménière's disease on the basis of clinical and experimental studies.

CONCLUSIONS: Endolymph homeostasis is thought to be mediated by the vasopressin-aquaporin-2 (VP-AQP2) system in the inner ear. Endolymphatic hydrops, the morphological characteristics of Ménière's disease (MD), seems to reflect the malregulation of the VP-AQP2 system in inner ear fluid. The elevation of plasma vasopressin (p-VP) level, which is often observed in MD and its related diseases, might be one of the causative factors underlying these diseases. PURPOSE OF REVIEW: Review of the role of the VP-AQP2 system in the inner ear fluid homeostasis and in the formation and development of endolymphatic hydrops. RECENT CLINICAL AND EXPERIMENTAL FINDINGS: A clinical survey has revealed that the p-VP level is often elevated in MD and its related diseases and that the increase in the p-VP level was closely linked to vertigo attacks in MD. Experimental studies have revealed that proteins and mRNAs of aquaporin-2 and vasopressin type 2 receptor were expressed in the stria vascularis of the cochlea and the epithelium of the endolymphatic sac, and that the volume of the endolymphatic compartment was mediated by the activity of the VP-AQP2 system in the inner ear.

Effect of artificial endolymph injection into the cochlear duct on perilymph potassium.

OBJECTIVE: To investigate the relationship between endolymphatic hydrops and perilymphatic potassium. METHODS: 20 pigmented guinea pigs were used: 10 for scala vestibuli study and 10 for scala tympani study. Acute endolymphatic hydrops was produced by microinjection of an artificial endolymph into the scala media. Injections were performed in the second turn at rates up to 500 nl/min for a period of 10 min. The injection volume was up to 5 microl. Endocochlear potential (EP) was monitored during injections. Simultaneous with the injections, the potassium concentrations in scala vestibuli (K(SV)) or tympani (K(ST)) perilymph were measured with ion-sensitive double-barreled microelectrodes sealed into in the scalae in the 3rd turn with cyanoacrylate glue. RESULTS: For endolymphatic injections of

Bumetanide-induced enlargement of the rat intrastrial space and effects of a vasopressin type 2 antagonist.

OBJECTIVE: Water homeostasis is essential for the inner ear to maintain the function of hearing and equilibrium. Bumetanide inhibits Na(+)-K(+)-2Cl(-) co-transporter (NKCC), which is expressed in the basolateral membrane of stria vascularis marginal cell, and it causes the enlargement of intrastrial space. Aquaporin (AQP) 2 is expressed in the perilymph side of stria vascularis basal cell, and the vasopressin type 2 antagonist OPC-31260 produces downregulation of AQP2 mRNA levels in the inner ear. The aim of this study is to investigate the influence of OPC-31260 on experimentally induced enlargement of the intrastrial space caused by bumetanide. MATERIALS AND METHODS: Wistar rats were divided into two groups, a BUM group and an OPC-BUM group. The BUM group was exposed to bumetanide, and the OPC-BUM group was exposed to bumetanide after being premedicated with OPC-31260. The specimens of the stria vascularis were observed using transmission electron microscopy and analyzed quantitatively and statistically. RESULTS: Morphological changes of intrastrial space enlargement occurred in both the BUM and OPC-BUM groups. The ratio of the areas of the intrastrial space area to the stria vascularis were calculated, and the OPC-BUM group mean showed a minimal difference from the BUM-group mean. However, there is no statistical difference. CONCLUSIONS: Premedication of rats with OPC-31260 tended to reduce bumetanide-induced enlargement of the intrastrial space. This may indicate that the effect of bumetanide on the stria vascularis is much stronger than that of OPC-31260.

Time course of vestibular function changes of experimental endolymphatic hydrops in guinea pigs.

OBJECTIVE: To investigate the relationship between endolymphatic hydrops and vestibular dysfunction. METHODS: 20 pigmented guinea pigs were used: 15 for a hydrops group and 5 for a sham group. Endolymphatic hydrops was produced by electrocauterization of the endolymphatic sac on the left ears. In the horizontal vestibuloocular reflex (HVOR) study, HVOR responses were recorded before and 1, 2, and 4 weeks after surgery in 9 animals of the hydrops group and 5 animals of the sham group. HVOR gain under sinusoidal rotation with a maximal head velocity of 45 degrees /s and frequencies of 0.05, 0.1, 0.2, 0.4 and 0.8 Hz was analyzed. In the nystagmus study, spontaneous nystagmus was recorded in all animals of the hydrops and the sham groups for 1 h in the dark and the maximum slow-phase velocity was measured before and 1, 2, 4 weeks after surgery. Morphological changes in the inner ear were measured light microscopically. RESULTS: In the hydrops group, the HVOR gains at all stimulation frequencies seemed to decrease 1 week after surgery and recover 2 or 4 weeks after surgery; however, there were no statistical differences among HVOR gains in any periods after surgery. The incidence of spontaneous nystagmus gradually increased after surgery and the direction and onset showed large variation. The duration of nystagmus was approximately 10 min. The degree of endolymphatic hydrops showed large variation. In the sham group, HVOR gains at all stimulation frequencies showed no statistically different change in any period after surgery. In the sham group, no animal showed spontaneous nystagmus. CONCLUSION: Experimentally induced endolymphatic hydrops seems to contribute to vestibular dysfunction to some extent. We speculated that when endolymphatic hydrops is progressing, vestibular dysfunction might occur.

Diagnostic value of plasma antidiuretic hormone, electrocochleography, and glycerol test in patients with endolymphatic hydrops.

OBJECTIVE: To investigate the relationship between the plasma antidiuretic hormone (p-ADH) level, electrocochleogram (ECoG), and the glycerol test in patients with endolymphatic hydrops (ELH). PATIENTS AND METHODS: The subjects were 60 patients, including 51 with Ménière's disease (except for cochlear Ménière's disease), 7 with delayed ELH, and 2 with syphilitic ELH. The time period for measurements of the p-ADH level, ECoG and the glycerol test was within 4 weeks. RESULTS: 13 patients showed positive results for all tests. 58 patients showed positive results for at least one of three tests. Only 2 patients showed negative results for all tests. CONCLUSION: The p-ADH level, ECoG and the glycerol test show different selectivity of ELH detection. It is useful to perform all three tests to diagnose ELH.

Electrical recording of otoacoustic emission.

CONCLUSION: Otoacoustic emissions (OAEs) could be detectable as cochlear AC potentials. Spontaneous otoacoustic emissions (SOAEs) were detected either electrically or acoustically, while evoked otoacoustic emissions (EOAEs) could be detected electrically but not acoustically. OBJECTIVE: Many lines of evidence support the hypothesis that SOAEs are produced by spontaneous mechanical oscillation within the cochlea, and perhaps motile properties of the outer hair cells. If this is the case, SOAEs, emitted acoustically in the external auditory meatus, could also be recorded electrically as cochlear AC potential. EOAE is also thought to be produced by vibration of the basilar membrane, generated by the backward-traveling waves. EOAE thus seems to be detectable electrically as cochlear AC potential. In the present study, SOAE and EOAE were recorded both acoustically and electrically in the guinea pigs to examine the correlation between electrically recorded SOAE (ER-SOAE) and acoustically recorded SOAE (AR-SOAE). In addition, a microphonics response (MPR) to tone pip was recorded to analyze the characteristics of the non-linear component and linear component of the AC responses. RESULTS: (1) In 4 out of 20 guinea pigs (20%), SOAE could be detected both acoustically and electrically. (2) Electrical signals of SOAE had a better S/N ratio than acoustical signals. Generally, only some ER-SOAE could be detected acoustically. (3) Almost without exception, the prominent frequencies of multiple ER-SOAEs corresponded to the intermodulation distortion product, or harmonics. (4) ER-SOAEs were suppressed by hypoxia or intense sound exposure and reappeared upon rebreathing or discontinuation of the external tone. During recovery, prominent frequencies showed a transient downward shift in frequency. (5) SOAEs were synchronized in phase with an external tone in the spectral neighborhood of SOAE. The averaged waveform of SOAE synchronized with the external tone was the same with either acoustic or electrical signals. (6) The MPR to tone pip is composed of two components with different frequency characteristics and input/output functions. (7) The non-linear component delayed to cochlear microphonics was markedly saturated at the intensity level of 40 dB peak equivalent SPL. This component was a phase-lock response, not a frequency-locked one. (8) The non-linear component could be separated with Probst's non-linear differential extraction technique. In the MPR to a 4-kHz tone pip, high-cut filtration at 3.5 kHz produced a waveform similar to the non-linear component separated by Probst's method.