Effect of electroacupuncture on arginine vasopressin-induced endolymphatic hydrops

OBJECTIVE

To investigate the influence of electroacupuncture (EA) on experimentally induced endolymphatic hydrops (EH) in guinea pigs, and elucidate the association between the dehydrating effect of EA and changes in stria vascularis ultrastructure and expression of vasopressin type 2 receptor (V2R), cyclic adenosine monophosphate (cAMP), and aquaporin 2 (AQP2) in the endolymphatic sac (ES).

METHODS

The EH model was established by intraperitoneal injection of arginine vasopressin (AVP). As a treatment, EA was delivered to Baihui (GV 20) and Tinggong (SI 19) acupoints, once daily for 10 consecutive days. For histomorphological studies, degree of cochlear hydrops was evaluated by hematoxylin-eosin staining, and the ratio of scala media (SM) area to SM + scala vestibuli area was calculated. In mechanical studies, ultrastructural changes in stria vascularis tissue were examined by transmission electron microscopy. In addition, cAMP levels and mRNA expression levels of V2R and AQP2 in the ES were compared among groups.

RESULTS

EA treatment significantly reduced cochlear hydrops compared with hydropic guinea pigs (P = 0.015). Furthermore, EA attenuated ultrastructural changes in the stria vascularis tissue following EH, significantly upregulated the expression of V2R (P = 0.016), and attenuated AVP-induced upregulation of both cAMP (P = 0.038) and AQP2 expression (P = 0.017) in the ES.

CONCLUSION

Collectively, the results of the present study suggest that the dehydrating effect of EA is associated with improvement of stria vascularis ultrastructure and V2R-cAMP-AQP2 signaling pathway regulation in the ES.

Inner ear pathologies impair sodium-regulated ion transport in Meniere's disease

Meniere's disease (MD), a syndromal inner ear disease, is commonly associated with a pathological accumulation of endolymphatic fluid in the inner ear, termed "idiopathic" endolymphatic hydrops (iEH). Although numerous precipitating/exacerbating factors have been proposed for MD, its etiology remains elusive. Here, using immunohistochemistry and in situ protein-protein interaction detection assays, we demonstrate mineralocorticoid-controlled sodium transport mechanisms in the epithelium of the extraosseous portion of the endolymphatic sac (eES) in the murine and human inner ears. Histological analysis of the eES in an extensive series of human temporal bones consistently revealed pathological changes in the eES in cases with iEH and a clinical history of MD, but no such changes were found in cases with "secondary" EH due to other otological diseases or in healthy controls. Notably, two etiologically different pathologies-degeneration and developmental hypoplasia-that selectively affect the eES in MD were distinguished. Clinical records from MD cases with degenerative and hypoplastic eES pathology revealed distinct intergroup differences in clinical disease presentation. Overall, we have identified for the first time two inner ear pathologies that are consistently present in MD and can be directly linked to the pathogenesis of EH, and which potentially affect the phenotypical presentation of MD.

[Effects of electroacupuncture on cochlea morphology and expression of aquaporins in guinea pigs with endolymphatic hydrops]

OBJECTIVE

To observe the effects of electroacupuncture (EA) on cochlea morphology and expression of aquaporin 1 (AQP1) in guinea pigs with endolymphatic hydrops, so as to explore the possible mechanism of EA on endolymphatic hydrops.

METHODS

Forty guinea pigs were randomly divided into a blank group, a model group, a medication group and an EA group, 10 guinea pigs in each one. Model of endolymphatic hydrops was established by using intraperitoneal injection of aldosterone. Guinea pigs in the blank group and model group were treated with identical immobilization as EA group but no treatment was given; guinea pigs in the medication group were treated with intragastric administration of hydrochlorothiazide at a dose of 5 mg/kg, once a day for consecutive 10 days; guinea pigs in the EA group were treated with' EA at "Baihui" (GV 20) and "Tinggong"(SI 19), once a day for consecutive 10 days. The serum ionic concentration in each group was tested by turbidimetric method; hematoxylin-eosin staining was used to measure the severity of cochlea hydrops; immunohistochemical method was used to observe the expression of AQP1 in the cochlea.

RESULTS

(1) There was no endolymphatic hydrops in the blank group, moderate-severe endolymphatic hydrops in the model group and slight endolymphatic hydrops in the EA group and medication group. (2) The concentration of K+ and Ca2+ in the EA group was higher than that in the model group and medication group (all P<0. 01); the concentration of Na+ was lower than that in the model group (P< 0. 01) but higher than that in the medication group (P<0. 01); the concentration of Cl- was higher than that in the medication group (P<0. 01), but not significantly different from the model group (P>0. 05). (3) The ratio of expression area of AQP1 in the model group was lower than that in the blank group (P<0. 01); the ratio of expression area of AQP1 in the EA group was higher than that in the model group (P<0. 01), and lower than that in the medication group without significant difference (P>0. 05).

CONCLUSION

EA could relieve the endolymphatic hydrops in guinea pigs; the mechanism is likely to be related with up-regulating the expression of AQP1 in cochlea and ion concentration might be an important factor involved.

[Effects of intratympanic injection of dexamethasone on endolymphatic hydrops and changes in guinea pigs inner ear CFTR expression]

OBJECTIVE

To observe the effect of tympanic injection of dexamethasone in the guinea pig endolymphatic hydrops and the change CFTR expression, to explore the effect of glucocorticoid treatment endolymphatic and its possible mechanism.

METHOD

Thirty guinea pigs were divided into three groups: hormone group, water group, control group. The animals(hormone group, water group) in study were injected DDAVP 4 μg/kg in the first 7 d, and will increase to 6 μg/kg in the second 3 d. The control group was given normal saline, continuous 10 d. After twelfth days, the hormone group transtympanic injection of dexamethasone (5 mg/ml, 0.5 ml), and water group, control group transtympanic given normal saline (0.5 ml), continuous injection 5 d. Using immuno- histochemistry and Western blot to detect the cystic fibrosis transmembrane conductance regulator cochlear factor (CFTR) expression.

RESULT

The water group ABR thresholds was significantly higher than that before the experiment (P < 0.01), and the water group was significantly higher than the rest of the groups (P < 0.01); Hormone group compared with the control group increased threshold value (P < 0.05). The control group had no endolym- phatic hydrops, the water group showed varying degrees of endolymphatic hydrops, cochlear duct and vestibular plus cochlear duct area ratio compared with the control group, hormone group was significantly higher (P < 0.01). hormone group area ratio was higher than the control group (P < 0.05). CFTR was primarily expressed in the stria vascularis, Corti's, spiral ligament, basilar membrane, cochlear ganglion,etc . The expression of CFTR in the water group was increased than that in the control group, and the hormone group (P < 0.01); the expression of hormone group increased compared with the control group (P < 0.05).

CONCLUSION

Tympanic injection of dexa- methasone can alleviate the desmopressin acetatein guinea pigs caused by membranous labyrinth, and the improve- ment of the hearing; Tympanic injection of dexamethasone can make the endolymphatic hydrops cochlea of guinea pigs decreased CFTR expression, indicating that the expression and possible mechanisms of CFTR intratympanic steroids reduce endolymphatic hydrops changes.

Developmental changes of ENaC expression and function in the inner ear of pendrin knock-out mice as a perspective on the development of endolymphatic hydrops

Pendrin mutations cause enlarged vestibular aqueducts and various degrees of sensorineural hearing loss. The selective abolition of pendrin causes dilation of the membranous labyrinth known as endolymphatic hydrops, loss of the endocochlear potential, and consequently loss of hearing function. Because Na+ transport is one of the most important driving forces for fluid transport, the epithelial Na+ channel (ENaC) is believed to play an important role in fluid volume regulation in the inner ear. Therefore, the dysfunction of Na+ transport through ENaC by the acidification of endolymph in Pendred syndrome is one of the potential causes of endolymphatic hydrops. We investigated the changes of ENaC expression and function during the development of the pendrin knock-out mouse. In the cochlea, the expression of β and γENaC was significantly increased at P56 in Pds-/- mice compared with Pds+/+ mice. In the vestibule, the expression of βENaC was significantly increased at P56, and γENaC expression significantly increased from P6 to P56 in Pds-/- mice. The ENaC-dependent trans-epithelial current was not significantly different between Pds+/+ and Pds-/- mice in Reissner's membrane or the saccular extramacular roof epithelium at P0, but the current was significantly increased in Pds-/- mice at P56 compared with Pds+/+ mice. These findings indicate that the expression and function of ENaC were enhanced in Pds-/- mice after the development of endolymphatic hydrops as a compensatory mechanism. This result provides insight into the role of Na+ transport in the development and regulation of endolymphatic hydrops due to pendrin mutations.

Characterization of neuronal cell death in the spiral ganglia of a mouse model of endolymphatic hydrops

HYPOTHESIS

Spiral ganglion neurons (SGN) in the Phex male mouse, a murine model of postnatal endolymphatic hydrops (ELH) undergo progressive deterioration reminiscent of human and other animal models of ELH with features suggesting apoptosis as an important mechanism.

BACKGROUND

Histologic analysis of the mutant's cochlea demonstrates ELH by postnatal Day (P) 21 and SGN loss by P90. The SGN loss seems to occur in a consistent topographic pattern beginning at the cochlear apex.

METHODS

SGN were counted at P60, P90, and P120. Semiquantitative reverse transcriptase-polymerase chain reaction (RT-PCR), quantitative PCR, and immunohistochemical analyses of activated caspase-3, caspase-8, and caspase-9 were performed on cochlear sections obtained from mutants and controls. Terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick-end labeling assay (TUNEL) was carried out on 2 mutants and 2 controls.

RESULTS

Corrected SGN counts in control mice were greater in the apical turn of the cochleae at P90 and P120, respectively (p < 0.01). Increased expression of activated caspase-3, caspase-8, and caspase-9 was seen in the mutant. At later time points, activated caspase expression gradually declined in the apical turns and increased in basal turns of the cochlea. Quantitative and semiquantitative PCR analysis confirmed increased expression of caspase-3, caspase-8, and caspase-9 at P21 and P40. TUNEL staining demonstrated apoptosis at P90 in the apical and basal turns of the mutant cochleae.

CONCLUSION

SGN degeneration in the Phex /Y mouse seems to mimic patterns observed in other animals with ELH. Apoptosis plays an important role in the degeneration of the SGN in the Phex male mouse.

Expression of osmotic stress protein 94 in murine endolymphatic hydrops model

CONCLUSION

The up-regulation of osmotic stress protein 94 (OSP94) in the murine endolymphatic hydrops (EH) models suggests that OSP94 might be involved in cellular adaptation in response to ionic and osmotic stress in the murine inner ear.

OBJECTIVES

The purpose of the present study was to investigate the expression of OSP94 in cochlear tissues of the murine EH models and control animals.

METHODS

Nine adult BALB/c mice were treated with both intratympanic injection of lipopolysaccharide and intraperitoneal administration of aldosterone to induce EH. Nine mice were used as control animals. The expression level of OSP94 in the EH and control groups was compared using immunohistochemistry and real-time RT-PCR.

RESULTS

Immunohistochemical staining of tissues in the EH group showed an up-regulation of OSP94 expression in the cochlea, especially in the stria vascularis and Reissner's membrane. Quantitative real-time PCR analysis also showed that transcription of the OSP94 gene in the cochlea was significantly up-regulated in the EH group.

[Effect of vasopressin on aquaporin 7 expression in rat inner ear]

OBJECTIVE

To study the effect of vasopressin on aquaporin 7 (AQP7) expression in rat inner ear and reveal the possible role of aquaporins in the formation of endolymphatic hydrops induced by vasopressin.

METHODS

Wistar rats were intraperitoneally injected with 50 microg/kg arginine vasopressin once a day for one week. Differentially expressed genes of aquaporins induced by vasopressin injection in rat inner ear were filtered by cDNA microarray. The changes of mRNA expression level of AQP7 in inner ear of rats treated with vasopressin injection were measured by RT-PCR.

RESULTS

Differentially expressed gene AQP7 of aquaporins induced by vasopressin injection was screened out in rat inner ear. The expression level of AQP7 mRNA in inner ear of rats treated with vasopressin injection was significantly lower.

CONCLUSION

Vasopressin may down-regulate the expression of AQP7 mRNA in the endolymphatic sac and induce a decreased absorption of endolymph, which decreases the water permeability in the potassium ions recycle pathway in the organ of Corti and disturbs the circulation of endolymph, resulting in endolymphatic hydrops.

Protective effect of edaravone against endolymphatic hydrops

CONCLUSION

Our findings suggest that edaravone prevented the production of reactive oxygen species (ROS). Edaravone also delayed the formation of endolymphatic hydrops in guinea pigs, but had no effect on endolymphatic hydrops.

OBJECTIVE

To analyse the protective effect of a free radical scavenger, edaravone, on endolymphatic hydrops.

MATERIALS AND METHODS

Guinea pigs were subjected to surgical obliteration of the endolymphatic duct (ED). For the detection of ROS, group 1 received intraperitoneal injections of edaravone (3 mg/kg/day) for 2 days, group 2 received edaravone for 2 weeks, group 3 saline for 2 days, and group 4 saline for 2 weeks. ROS production by the organ of Corti and stria vascularis was examined by using dihydrotetramethylrosamine. For the morphological analysis, guinea pigs were divided into five groups, i.e. 2 or 4 weeks after ED obliteration, 2 weeks with edaravone, first or last 2 weeks with edaravone and sacrificed 4 weeks after ED obliteration. Increases in the ratios of the cross-sectional area of scala media were analysed quantitatively to assess the degree of endolymphatic hydrops among the above-mentioned five groups of the hydropic cochlea.

RESULTS

ROS was detected both in the organ of Corti and in the lateral wall of cochleae 2 days after ED obliteration. Edaravone prevented the production of ROS and also attenuated the formation of endolymphatic hydrops in the acute hydrops group.

Molecular Changes Associated With the Endolymphatic Hydrops Model

HYPOTHESIS

Hearing loss and cochlear degeneration in the guinea pig model of endolymphatic hydrops (ELH) results, in part, from toxic levels of excitatory amino acids (EAAs) such as glutamate, which in turn leads to changes in the expression of genes linked to intracellular glutamate homeostasis and apoptosis, leading to neuronal cell death.

BACKGROUND

EAAs have been shown to play a role in normal auditory signal transmission in mammalian cochlea, but have also been implicated in neurotoxicity when levels are elevated. Changes in the expression of specific genes involved in the glutamatergic and apoptotic pathway would serve as evidence for excitotoxicity linked to elevated levels of glutamate.

METHODS

Guinea pigs underwent surgical obliteration of the endolymphatic duct, and then a timed harvest of the treated (right) and control (left) cochlea and subsequent quantification of gene expression via real-time quantitative polymerase chain reaction.

RESULTS

Quantitative polymerase chain reaction data show significant upregulation of glutamate aspartate transporter and neuronal nitric oxide synthase mRNA levels 3 weeks postsurgery and Caspase 3 mRNA levels 1 week postsurgery. No significant changes were detected in glutamine synthetase expression levels.

CONCLUSION

Upregulation of genes involved in glutamate homeostasis and the apoptotic pathway in animals treated with endolymphatic duct obstruction (usually associated with secondary ELH) support the hypothesis that EAAs may play a role in the pathophysiology of ELH-related cochlear injury. Inhibitors to these pathways can be useful for the study of new avenues to delay or prevent ELH-related hearing loss.

[Expression of aquaporin 1 in two types of animal model of endolymphatic hydrops]

OBJECTIVE

To study the expression of aquaporin 1 (AQP1) in cochlea and endolymphatic sac of guinea pig of two types of animal model of endolymphatic hydrops.

METHODS

Thirty guinea pigs were divided into three groups at random: surgery group; aldosterone group and control group. Each group included 10 animals. Surgical endolymphatic sac obstruction or aldosterone intraperitoneal injection was used to build the animal models of endolymphatic hydrops. Immunohistochemistry and western blot were used to examine the expression of AQP1 in cochlea and endolymphatic sac of animal models. Image processing soft (Image Tool) was used to do the semiquantitative analysis.

RESULTS

Middle to high grade endolymphatic hydrops were found in surgery group. It was most significant in the apical coil, and lessened from the apical coil to the basal coil. Low to middle expression grade in endolymphatic hydrops was found in aldosterone group. Most of them were found in the basal coil. The positions of AQP1 expression in two animal models of endolymphatic hydrops were identical with the control group. In cochlea, no difference of AQP1 expression was found in the surgery and control group (t = 0.718 , P > 0.05) , but the expression of AQP1 was down regulated in the cochlea of aldosterone group (t = 6.609, P < 0.01) while the expressions of AQP1 in endolymphatic sac of aldosterone and control group were no difference between them (t = 0.998, P > 0.05). The quantization of AQP1 protein in the lateral wall of cochlea of aldosterone group was lower than that of control group (t = 13.626 , P < 0.01).

CONCLUSIONS

The expression of AQP1 is no change in surgery and control group, but decreased in aldosterone group. The expression of AQP1 may be regulated by the ionic concentration in inner ear of guinea pig.

Optimization of ribonucleic acid detection from archival Guinea pig temporal bone specimens

HYPOTHESIS

The choice of ribonucleic acid (RNA) isolation protocol coupled with modifications to RNA extraction and detection procedures may result in a more reliable method to detect gene expression in archived temporal bones.

BACKGROUND

A large number of archival temporal bones exist. Retrospective analysis of these specimens using techniques of RNA extraction will greatly enrich our understanding of the pathophysiology of specific otologic diseases. However, archival human temporal bones are aged and embedded in paraffin or celloidin, rendering isolation and manipulation of nucleic acid in preserved specimens difficult, especially as it pertains to RNA degradation. Despite some reports of moderate success in the recent past, RNA isolation and gene expression using polymerase chain reaction (PCR) analysis continues to be challenging and unreliable. Archival guinea pig temporal bone specimens were used to develop and optimize a protocol for RNA extraction and gene expression analysis using PCR and quantitative PCR methods. The genes amplified comprise housekeeping genes and genes associated with the glutamate pathway.

METHODS

Archival celloidin-embedded guinea pig temporal bones were collected from the senior author's collection of experimental hydropic inner ear specimens. RNA from this tissue was extracted using the protocol described previously in 16animals and using a modified trizol extraction technique in 10 animals. Gene expression analysis was performed on the extracted RNA. Analysis included two housekeeping genes, GAPDH and 18S, as well as three mediators of the glutamate pathway, glutamate aspartate transporter, glutamate synthetase, and inducible nitric oxide synthase.

RESULTS

Compared with the standard extraction protocol, the trizol-based extraction technique showed greater reliability and reproducibility of RNA detection. The housekeeping gene GAPDH or 18S was detected in 7 of 36 attempts with the standard protocol versus 9 of 9 using the modified extraction method (P < 0.001). The gene of interest, glutamate aspartate transporter, was detected in 3 of 26 attempts with the standard protocol versus 12 of 13 attempts using the modified extraction method (P < 0.001). Quantification of messenger RNA levels was then achieved using quantitative PCR methods.

CONCLUSION

Improved reliability for detection of gene expression and demonstration of reproducibility were accomplished by modification of RNA extraction technique and standard reverse transcriptase PCR protocol. In addition, we also showed that gene expression from archival material can be quantified by real-time PCR.

Effects of vasopressin on gene expression in rat inner ear

Vasopressin regulates water excretion from the kidney by increasing water permeability of the collecting duct as a hormone secreted from the posterior pituitary. A clinical study reported that plasma levels of arginine vasopressin were significantly higher in patients suffering from Meniere's disease. It was histologically confirmed that chronic administration of vasopressin induced endolymphatic hydrops in guinea pigs. However, the mechanism of endolymphatic hydrops induced by vasopressin is still unclear. We use cDNA microarray to study the effects of vasopressin on gene expression profiles in rat inner ear to elucidate the possible mechanism of the induced hydrolabyrinth. Wistar rats were intraperitoneally injected with 50 microg/kg arginine vasopressin once a day for one week. Hydrolabyrinth in rat inner ear induced by administration of vasopressin was detected by HE stain. The bullae were dissected out for total RNA extraction. cDNAs were synthesized by reverse transcription and labeled with Cyanine3 (Cy3) or Cyanine5 (Cy5). The BiostarR-40s cDNA microarray was hybridized with the above cDNAs and the changes of mRNA expression intensity were showed by data analysis. Furthermore, the changes of aquaporins expression level were measured by reverse transcription polymerase chain (RT-PCR). Endolymphatic hydrops were present in rats intraperitoneally injected with vasopressin. 226 known differentially expressed genes were screened out in rat inner ear induced by vasopressin injection. Of the 226 genes, 18 transcripts were increased by 5-fold or more, and 7 transcripts were decreased to 0.2-fold or less. Ten differentially expressed genes were identified that associate with cell signal transduction, 14 differentially expressed genes were identified that relate to ion transport, 7 differentially expressed genes were involved in vesicle-mediated transport, and 2 differentially expressed genes were aquaporin 2 (AQP2) and aquaporin 7 (AQP7). The expression level of AQP2 was significantly higher and AQP7 was significantly lower. These results suggest that there are obvious differences in gene expression profiles in inner ear between vasopressin injected rats and normal control rats. Vasopressin may disturb fluid homeostasis in inner ear by way of signal transduction, ion transport, vesicle-mediated transport and aquaporins. It is likely that up-regulated expression of AQP2 mRNA and down-regulated expression of AQP7 mRNA in the rat inner ear caused by vasopressin induce an increased production and a decreased absorption of endolymph, resulting in endolymphatic hydrops.

Effects of lithium on endolymph homeostasis and experimentally induced endolymphatic hydrops

There is evidence to suggest that water homeostasis in the inner ear is regulated via the vasopressin (VP)-aquaporin 2 (AQP2) system in the same fashion as in the kidney. The VP-AQP2 system in the kidney is well known to be inhibited by lithium, resulting in polyuria due to a decrease in reabsorption of water in the collecting duct of the kidney. Therefore, lithium is also likely to inhibit the VP-AQP2 system in the inner ear, and consequently exert some influence on inner ear fluid homeostasis. In this study, we investigated the effects of lithium on AQP2 expression in the rat inner ear, and on the cochlear fluid volume in hydropic ears of guinea pigs. A quantitative PCR study revealed that lithium reduced AQP2 mRNA expression in the cochlea and endolymphatic sac. Lithium application also decreased the immunoreactivity of AQP2 in the cochlea and endolymphatic sac. In a morphological study, lithium intake significantly reduced endolymphatic hydrops dose-dependently. These results indicate that lithium acts on the VP-AQP2 system in the inner ear, consequently producing a dehydratic effect on the endolymphatic compartment.

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.

Acute endolymphatic hydrops generated by exposure of the ear to nontraumatic low-frequency tones

Low-frequency sounds presented at high nontraumatizing levels induce temporary hyperacusis in humans and animals. One explanation of this finding is that the basilar membrane operating point may be disturbed by an endolymph volume change. This possibility was investigated using volume and flow markers iontophoresed into the endolymphatic space of guinea pigs. Marker concentrations were measured with ion-selective microelectrodes placed apically and basally to the iontophoresis site during exposure of the ear to low-frequency tones. Concentration changes were interpreted quantitatively using a finite-element model of the endolymphatic space that allowed changes of endolymph cross-sectional area and flow to be derived. Stimulation with a 200 Hz tone at 115 dB SPL for 3 min produced marker concentration changes consistent with the induction of transient endolymphatic hydrops and a basally directed displacement of endolymph. Endocochlear potentials were greater than normal after the exposure when hydrops was present. During identical tone exposures of animals without marker, we found that action potential (AP) threshold changes and endolymph potassium changes associated with the hydropic state were small. Marker concentration changes were compared with changes in endocochlear potential and AP thresholds for a range of exposure frequencies and levels. AP hypersensitivity occurred with 200 Hz exposure levels below those inducing endolymph volume disturbances. Endolymph volume changes are thought to be the result of, rather than the cause of, changes in operating point of the cochlear transducer. The observations that auditory threshold and endolymph potassium changes are minimal under conditions where substantial endolymphatic hydrops is present is relevant to our understanding of the hearing loss in patients with Meniere's disease.

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.

Induction of endolymphatic hydrops by directly infused monoclonal antibody against type II collagen CB11 peptide

Autoimmune ear disease induced by type II collagen has been investigated by Yoo et al. In the present study, we investigated the effects of direct chronic infusion of type II collagen-specific monoclonal antibodies into guinea pig cochlea. Type II collagen fragment CB11 peptide-specific monoclonal antibodies (anti-CB11 Mabs) were infused directly into the scala tympani of guinea pigs with an Alzet mini-osmotic pump (anti-CB11 Mab group). As a control, normal mouse serum was infused by the same method (control group). To evaluate the auditory function, we recorded brain stem auditory-evoked potentials (BAEPs). In the anti-CB11 Mab group, 80% of the animals showed an increased hearing threshold of more than 25 dB at 7 days after infusion. The hearing threshold shift observed in the guinea pigs of the control group was minimal (15 dB or less). To detect the structural changes, we performed histopathologic studies using hematoxylin and eosin staining. Inflammatory cell migration was detected mainly in the scala tympani of the guinea pigs of both groups. In the anti-CB11 Mab group, endolymphatic hydrops was also observed. The results of this experiment suggest that type II collagen autoimmunity is responsible for the production of hearing loss and endolymphatic hydrops.

Summating potential in the guinea pig cochlea after perilymphatic perfusion with arginine-vasopressin

We hypothesized that arginine-vasopressin (AVP), the natural vasopressin in the guinea pig, might increase the cochlear summating potential, indicating an increase in endolymphatic volume. Guinea pig cochleas were perfused with artificial perilymph for 15 min, with or without AVP (2 x 10(-6) M). In 1 group of animals, summating potentials (SP), compound action potentials and cochlear microphonics evoked by 2, 4 and 8 kHz tone bursts were measured with an apically placed electrode 15 min, 1 and 2 h after perilymphatic perfusion. In another group of animals the SP and endocochlear potential (EP) were measured simultaneously in the scala media during and after perfusion. In both groups the SP had increased significantly 15 min after perfusion with AVP and this increase was reversible. At the concentration of AVP used the increase in SP was not related to EP alterations. On light microscopic examination of the cochlea no evident increase in scala media volume could be detected. The increase in the SP (a sensitive indicator of acute endolymphatic hydrops) after perfusion with AVP suggests that this neuropeptide plays a role in the regulation of the ion and fluid balance in the cochlea.

Aldosterone assessment in patients with Menière's disease

Since 1938 endolymphatic hydrops has generally been accepted as the basic histopathological substrate of Menière's disease. In animal studies it has been found that exogenous administration of aldosterone resulted in endolymphatic hydrops. Manifestations of Menière's disease are frequently observed in times of emotional stress. Mediated through the hypothalamus, stress leads to an increased secretion of adrenocorticotropic hormone from the anterior pituitary gland, followed by an increased adrenocortical production of glucocorticoids (cortisol and corticosterone) and mineralocorticoids (aldosterone). We addressed the question whether plasma aldosterone levels, like in guinea pigs, would be increased in patients with Menière's disease. As part of a diagnostic protocol a clinical prospective cohort study was therefore performed on 89 patients with Menière's disease to assess plasma aldosterone levels. Plasma aldosterone was not elevated in Menière patients compared to plasma aldosterone in a control group of 27 normal subjects. No statistically significant differences were found in plasma aldosterone between uni- and bilateral Menière's disease. Plasma aldosterone levels did not correlate with age, average hearing loss, duration or perceived severity of subjective complaints (vertigo, hearing loss, tinnitus and aural pressure). In this study plasma aldosterone was not elevated in patients with Menière's disease compared to normal subjects. Plasma aldosterone can thus not be used as a diagnostic tool for Menière's disease.

IN CONCLUSION

No anomalous plasma aldosterone levels were found in Menière patients during an attack-free period. The question whether plasma aldosterone and cortisol levels show variations before, during and after an attack remains to be answered. If so, this might contribute to a better understanding of the pathophysiological mechanism of Menière's disease.

Different regulation of connexin26 and ZO-1 in cochleas of developing rats and of guinea pigs with endolymphatic hydrops

Using confocal microscopy and morphometry, we analyzed the expression of connexin26 (Cx26) and ZO-1 in rat cochlea during the postnatal period to elucidate spatiotemporal changes in gap junctions and tight junctions during auditory development. We also studied changes in these junctions in experimental endolymphatic hydrops in the guinea pig. In the adult rat cochlear lateral wall, Cx26 was detected in fibrocytes in the spiral ligament and in the basal cell layer of the stria vascularis, whereas ZO-1 was detected in the apical surfaces of marginal cells and in the basal cell layer. During postnatal development, Cx26 expression increased mainly in the spiral ligament, whereas ZO-1 expression increased in the basal cell layer. The morphometry of Cx26 showed a sigmoid time course with a rapid increase on postnatal day (PND) 14, whereas that of ZO-1 showed a marked increase on PND 7. In experimental endolymphatic hydrops, the expression of Cx26 significantly decreased, whereas there were no obvious changes in the expression of ZO-1. These results indicate that gap junctions and tight junctions in the cochlea increase in a different spatiotemporal manner during the development of auditory function and that gap junctions and tight junctions in the cochlea are differentially regulated in experimental endolymphatic hydrops. (J Histochem Cytochem 49:573-586, 2001)

Detection of single-stranded DNA in the hydropic vestibule after the direct injection of antigen into the endolymphatic sac of guinea pigs

Immunohistochemical study for single-stranded DNA (ssDNA) with vestibule of guinea pigs was performed after the injection of keyhole limpet hemocyanin (KLH) into the right endolymphatic sac. Endolymphatic hydrops became evident by expansion of the Reissner's membrane in the cochlea of all animals 1 day after the injection of KLH. Increased ssDNA expression was detected in the sensory epithelium and transitional area, while temporal bones in the control group did not show any ssDNA immunoreactivities. ssDNA is accompanied with the apoptotic change in the vestibule. Our results suggest that apoptotic changes could be involved in the hydropic vestibule and these phenomena lead inner ear disturbance as seen in endolymphatic hydrops.

The rebound phenomenon of glycerol-induced changes in the endolymphatic space

Volumetric changes of the scala media were histologically investigated in normal guinea pigs to see whether glycerol-induced volumetric change of the scala media followed a biphasic course similar to the auditory threshold in the glycerol test. Glycerol was administered orally in a 12 ml/kg dose. The volume of the scala media was assessed by examining the cross-sectional area of the scala media in the mid-modiolar sections of the cochlea. Histological study revealed that the time-course of the change in the volume of the scala media after glycerol intake showed biphasic changes. Specifically, the early phase of the glycerol effect is a decrease in endolymph volume. The volume of the scala media significantly decreased by 11.4+/-2.9% 2 h after glycerol intake. Thereafter, the volume began to increase, and reached its peak 6-12 h after intake. In addition, the volume of the scala media significantly increased by 17.6+/-1.1% after 6 h. The present study indicated that the secondary increase in the volume of the scala media following glycerol intake played an important role in the rebound phenomenon in the glycerol test, although the mechanism underlying the hearing loss with the endolymphatic hydrops remains to be elucidated.

[Effect of furosemide on the ampullar endolymphatic potential and endolymphatic Ca2+ activity]

The ampullar endolymphatic potential (AEP) and the endolymphatic Ca2+ activity were measured with double-barred Ca2+ selective microelectrodes in the experimental hydrops of guinea pigs. They showed 3.16 +/- 0.42 mV (n = 9) and (4.10 +/- 1.22) x 10(-4) M, respectively. The AEP decreased significantly at about 6 min after intravenous administration of 10 mg/kg furosemide. Its minimal value was 3.04 +/- 0.53 mV at about 40 min. But there was no significant difference between that and the value before injection. The Ca2+ activity increased significantly and reached (7.10 +/- 1.32) x 10(-4) M at about 60 min. The changes indicate that Ca2+ may play an important role in the mechanism of the furosemide test.

Preliminary study of the role of endothelin-1 in the homeostasis of the inner ear

Endothelin (ET), originally characterized as a 21-residue vasoconstrictor peptide from endothelial cells, has been reported to act as a local hormonal regulator of pressure, fluid, ions, and neurotransduction. Our previous studies suggested an important role of ET-1 in the inner ear. The present study investigated the time kinetics of ET-1 in the epithelium of the endolymphatic sac (ES) of guinea pigs and its relation to the development of endolymphatic hydrops (EH) following locally mounted secondary immune reaction. In the duration between 12 h and day 1, ET-1-like activity completely disappeared from the epithelium of the ES and was associated with the accumulation of inflammatory cells in the ES and a rapid development of EH. On day 7, ET-1-like activity recovered as a consequence of the decrease of inflammatory cells and reduction of EH. These findings suggest that ET-1 may play an important role as one of the regulators maintaining the fluid balance.

Osmolar changes and neural activity in frog vestibular organs

The effects of hypotonic and hypertonic solutions (the normal value was 240 mOsm) on posterior canal resting and evoked discharge were studied in isolated labyrinth preparations. Hypotonic solutions (60-180 mOsm) were obtained by reducing the perilymphatic NaCl content. Hypertonic solutions (300-420 mOsm) were obtained by adding to normal perilymphatic solutions suitable amounts of NaCl, glucose, sucrose, glycerol, mannitol and urea. The results demonstrated that any kind of receptor activity was inhibited by hypotonic solutions. On the contrary, hypertonic solutions produced different effects on resting and evoked activity. The resting discharge was, with the exception of urea, constantly increased whereas the evoked responses were constantly decreased by all the hypertonic solutions tested. The possible effects of media with changed osmolarity in Meniere's patients is also discussed.

Degenerative changes in the organ of Corti and lateral cochlear wall in experimental endolymphatic hydrops and human Menière's disease

The pathogenesis of sensorineural hearing loss in Menière's disease and experimental endolymphatic hydrops is not fully understood. At the light microscopic level, there is poor correlation between the histopathology and loss of sensitivity and speech discrimination. The results of electron microscopic investigation of histopathology and alterations in immunoreactivity in the organ of Corti and lateral cochlear wall in the hydropic guinea pig are presented. Loss of outer and inner hair cells and spiral ganglion cells, particularly in the apical turn was evident by light microscopy. By electron microscopy, further evidence of degeneration was detected in the cuticular plate of outer hair cells, neural endings of both inner and outer hair cells, myelinated dendritic fibers, spiral ganglion cells, and types I and II fibrocytes of the lateral cochlear wall. There was a marked decrease in immunoreactivity for a variety of enzymes, calcium binding proteins, structural proteins, and integral membrane proteins of gap junctions, particularly among type I and type II fibrocytes of the lateral cochlear wall. The evidence suggests that dysfunction and degeneration of hair cells, afferent neurons and fibrocytes of the lateral cochlear wall are involved in the pathogenesis of hearing loss in endolymphatic hydrops.

Lipocortin I immunolocalization in normal and hydropic guinea pig ears

Annexins are a family of eight highly conserved proteins that bind phospholipids in the presence of calcium. One of these proteins, lipocortin I, has restricted distribution in adult and developing tissues, suggesting regulatory function. Among the protean roles theorized are regulation of inflammation by influencing eicosanoid production, participation in endo- and exocytosis, and control of membrane permeability. Such processes could have important roles in the inner ear; therefore, we investigated the patterns of lipocortin I expression in the normal guinea pig ear. Lipocortin I appeared at high levels in nonsensory, endolymph-facing tissues. Perilymph-facing cells had little lipocortin I activity. Lipocortin I was minimally expressed, or is absent, in sensory cells of the cochlea and vestibular systems. In the kidney, changes in quantity and distribution of lipocortin I have been seen during recovery from acute tubular necrosis. In an attempt to gain insight into the role of lipocortin I, the authors investigated its response to an experimental insult. Surgically created endolymphatic hydrops was chosen as an insult involving the endolymph-producing epithelia that richly express lipocortin I. Comparing unilaterally created hydrops, for up to 3 weeks' duration, to contralateral control ears demonstrated no quantitative or distribution changes in lipocortin I.

Changes in immunostaining of cochleas with experimentally induced endolymphatic hydrops

Cochleas with experimentally induced endolymphatic hydrops were immunostained for Na+,K(+)-ATPase, intracellular Ca(++)-ATPase, carbonic anhydrase, aldehyde dehydrogenase, calcium-binding proteins, vimentin, and the gap junction protein, connexin 26. No changes in immunostaining of hydropic ears were observed 1 week after blockage of the endolymphatic duct. Two weeks to 1 month after the operation, immunostaining of type I fibrocytes in the spiral ligament, which are positive for all but Na+,K(+)-ATPase, was slightly decreased on the operated side. These changes became more pronounced 3 months after the operation. However, staining for Na+,K(+)-ATPase of the stria vascularis and of type II fibrocytes of the spiral ligament was not reduced until 6 months postoperative. The reduction of enzymes and other cell constituents that may be involved in ion balance of cochlear fluids indicates that cells in the spiral ligament play an important role in cochlear homeostasis and that they merit further study in animal and human otopathology.

Endolymph calcium increases with time after surgical induction of hydrops in guinea-pigs

The ionized Ca2+ concentration in cochlear endolymph is normally extremely low. Previous studies have shown that endolymph Ca2+ levels become elevated when measured at long intervals after endolymphatic hydrops is surgically induced. The present study was designed to investigate how rapidly endolymph Ca2+ increases following endolymphatic duct ablation. Hydropic animals were tested at either 4 days, 4 weeks, 8 weeks or 16 weeks after surgery. In each animal endolymph Ca2+ and endocochlear potentials were measured in all four cochlear turns using double-barreled Ca(2+)-sensitive electrodes. Cochlear sensitivity was assessed using compound action potential thresholds. Our results confirm that hydropic animals show an elevation of endolymph Ca2+ and a reduction of EP which is initially small, but becomes more pronounced at longer times after surgery. At 16 weeks endolymph Ca2+ was increased by an average factor of 20 in the basal turn and 7.5 in the fourth turn. These findings suggest that endolymph Ca2+ changes may not be the primary factor responsible for hydrops generation, but probably contribute to cochlear dysfunction in later phases of hydrops. For some experimental groups, the elevation of AP threshold was more closely correlated with endolymph Ca2+ level than it was with endolymph volume. Endolymph Ca2+ changes must therefore be considered in order to account for dysfunction in the hydropic cochlea.