Two-phase endolymphatic hydrops: a new dynamic guinea pig model

cAMP-Epac1 signaling is activated in DDAVP-induced endolymphatic hydrops of guinea pigs

OBJECTIVE

To explore whether Cyclic Adenosine Monophosphate (cAMP)-Epac1 signaling is activated in 1-Desamino-8-D-arginine-Vasopressin-induced Endolymphatic Hydrops (DDAVP-induced EH) and to provide new insight for further in-depth study of DDAVP-induced EH.

METHODS

Eighteen healthy, red-eyed guinea pigs (36 ears) weighing 200-350 g were randomly divided into three groups: the control group, which received intraperitoneal injection of sterile saline (same volume as that in the other two groups) for 7 consecutive days; the DDAVP-7d group, which received intraperitoneal injection of 10 mg/mL/kg DDAVP for 7 consecutive days; and the DDAVP-14d group, which received intraperitoneal injection of 10 μg/mL/kg DDAVP for 14 consecutive days. After successful modeling, all animals were sacrificed, and cochlea tissues were collected to detect the mRNA and protein expression of the exchange protein directly activated by cAMP-1 and 2 (Epac1, Epac2), and Repressor Activator Protein-1 (Rap1) by Reverse Transcription (RT)-PCR and western blotting, respectively.

RESULTS

Compared to the control group, the relative mRNA expression of Epac1, Epac2, Rap1A, and Rap1B in the cochlea tissue of the DDAVP-7d group was significantly higher (p <  0.05), while no significant difference in Rap1 GTPase activating protein (Rap1gap) mRNA expression was found between the two groups. The relative mRNA expression of Epac1, Rap1A, Rap1B, and Rap1gap in the cochlea tissue of the DDAVP-14d group was significantly higher than that of the control group (p <  0.05), while no significant difference in Epac2 mRNA expression was found between the DDAVP-14d and control groups. Comparison between the DDAVP-14d and DDAVP-7d groups showed that the DDAVP-14d group had significantly lower Epac2 and Rap1A (p <  0.05) and higher Rap1gap (p < 0.05) mRNA expression in the cochlea tissue than that of the DDAVP-7d group, while no significant differences in Epac1 and Rap1B mRNA expression were found between the two groups. Western blotting showed that Epac1 protein expression in the cochlea tissue was the highest in the DDAVP-14d group, followed by that in the DDAVP-7d group, and was the lowest in the control group, showing significant differences between groups (p <  0.05); Rap1 protein expression in the cochlea tissue was the highest in the DDAVP-7d group, followed by the DDAVP-14d group, and was the lowest in the control group, showing significant differences between groups (p <  0.05); no significant differences in Epac2 protein expression in the cochlea tissue were found among the three groups.

CONCLUSION

DDAVP upregulated Epac1 protein expression in the guinea pig cochlea, leading to activation of the inner ear cAMP-Epac1 signaling pathway. This may be an important mechanism by which DDAVP regulates endolymphatic metabolism to induce EH and affect inner ear function. OXFORD CENTRE FOR EVIDENCE-BASED MEDICINE 2011 LEVELS OF EVIDENCE: Level 5.

Aldosterone inhibits Dot1l expression in guinea pig cochlea

BACKGROUND

Aldosterone relieves transcriptional repression of epithelial sodium channel (ENaC) by inhibiting Dot1a and Af9 expression and their interaction with ENaC promoter in various tissues. Expressions of ENaC and Af9 in inner ear have been identified. However, it is not known how Dot1l is regulated by aldosterone in inner ear.

METHODS

Twenty-eight adult guinea pigs were randomly divided into the control group and treatment group. Aldosterone 1 mg/kg/d was injected intraperitoneally in the treatment group and saline in the control group for 7 days. Animals were killed 1 month later following auditory brainstem response examination. Histomorphology of cochlea was detected with hematoxylin-eosin staining, and Dot1l expression was examined with immunohistochemistry and Western blot.

RESULTS

There was no significant difference in ABR thresholds before and after injection of aldosterone or saline in either group. Endolymphatic hydrops was found in 75% of animals in the treatment group. Dot1l was found in both groups in the stria vascularis, Reissner's membrane, spiral limbus, organ of Corti and spiral ligament. Dot1l expression in the treatment group was decreased by aldosterone.

CONCLUSIONS

Dot1l in guinea pig cochlea is inhibited by aldosterone with induction of endolymphatic hydrops. Dot1l may be closely related to endolymph regulation by aldosterone and to pathogenesis of Meniere's disease.

Anatomical variation of inner ear may be a predisposing factor for unilateral Ménière's disease rather than for ipsilateral delayed endolymphatic hydrops

Objective

Radiological anatomical variations, measured by magnetic resonance imaging (MRI), were evaluated in patients with ipsilateral delayed endolymphatic hydrops (DEH) and unilateral Ménière’s disease (MD). The role of anatomical variations in different subtypes of hydropic ear disease was investigated.

Methods

Twenty-eight patients with ipsilateral DEH, 76 patients with unilateral MD, and 59 control subjects were enrolled. The radiological indices included the distance between the vertical part of the posterior semicircular canal and the posterior fossa (MRI-PP distance) and the visibility of vestibular aqueduct (MRI-VA). These variations among patients with DEH, MD, and control subjects were compared. The correlation between radiological anatomical variations and clinical features or audio-vestibular findings was also examined.

Results

(1) MRI-PP distance in the affected side of unilateral MD was shorter than that in ipsilateral DEH (Z =  − 2.481, p = 0.013) and control subjects (Z =  − 2.983, p = 0.003), while the difference of MRI-PP distance between the affected side of ipsilateral DEH and control subjects was not statistically significant (Z =  − 0.859, p = 0.391). (2) There was no significant interaural difference of MRI-PP distance in patients with unilateral MD (Z =  − 0.041, p = 0.968) and ipsilateral DEH (t =  − 0.107, p = 0.915) respectively. (3) No significant interaural difference of MRI-VA visibility was observed in patients with unilateral MD (χ² = 0.742, p = 0.389) and ipsilateral DEH (χ² = 0.327, p = 0.567) respectively. (4) No correlation was found between these anatomical variables and clinical features or audio-vestibular findings in patients with unilateral MD and ipsilateral DEH respectively (p > 0.05).

Conclusions

Anatomical variations of inner ear may be a predisposing factor in the pathogenesis of unilateral MD rather than ipsilateral DEH.

Key Points

• Patients with ipsilateral delayed endolymphatic hydrops showed normal distance between the vertical part of the posterior semicircular canal and the posterior fossa.

• Compared to patients with ipsilateral delayed endolymphatic hydrops and control subjects, patients with unilateral Ménière’s disease exhibited shorter distance between the vertical part of the posterior semicircular canal and the posterior fossa.

• Anatomical variations of inner ear may be a predisposing factor in the pathogenesis of unilateral Ménière’s disease rather than ipsilateral delayed endolymphatic hydrops.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00330-021-08430-7.

Vestibular Aqueduct Size Correlates With the Degree of Cochlear Hydrops in Patients With and Without Menière's Disease

OBJECTIVE

To correlate the CT imaging findings of the visibility and size of the vestibular aqueduct (VA) with the degree of the cochlear hydrops determined in MRI late imaging of the hydrops. Study Design: Retrospective study. Setting: Tertiary referral center. Patients: A total of 127 patients (62 women, 65 men, average age 55.6 yrs): 86 of these were diagnosed with Menière's disease (American Academy of Otolaryngology-Head and Neck Surgery [AAO-HNS] criteria; 67 unilateral, 19 bilateral).

INTERVENTIONS

Temporal bone CT and hydrops MRI were performed in all patients.

MAIN OUTCOME MEASURES

Visibility/width of the VA in temporal bone CT and grade of cochlear hydrops evaluated by MRI.

RESULTS

The width of the VA is significantly smaller in patients diagnosed with Menière's disease (30% non-visible VA), compared with the patients who did not fulfill the diagnostic criteria of Menière's disease (12% non-visible VA) (double sided Spearman correlation, p < 0.001). In all ears of patients diagnosed with Menière's disease the width of the VA was significantly correlated with the degree of the cochlear hydrops (in cases of non-visible VA 65% [34/52] ears presented with hydrops grade 3 or 4; 13% [7/52] ears presented with hydrops grade 1 or 2 and 21% [11/52] ears showed no hydrops) (Spearman correlation p = 0.001/p < 0.01). This is also true for all ears that can be summarized as hydrophic ear disease (symptomatic ears that present with a hydrops in MRI).

CONCLUSIONS

The results of our study could confirm the importance of the VA in the pathogenesis of the endolymphatic hydrops in vivo.

High-quality imaging of endolymphatic hydrops acquired in 7 minutes using sensitive hT2W-3D-FLAIR reconstructed with magnitude and zero-filled interpolation

Background

It is still challenging to detect endolymphatic hydrops (EH) in patients with Meniere’s disease (MD) using MRI. The aim of the present study was to optimize a sensitive technique generating strong contrast enhancement from minimum gadolinium–diethylenetriamine pentaacetic acid (Gd–DTPA) while reliably detecting EH in the inner ear, including the apex.

Materials and methods

All imaging was performed using a 3.0 T MR system 24 h after intratympanic injection of low-dose Gd–DTPA. Heavily T2-weighted 3-dimensional fluid-attenuated inversion recovery reconstructed with magnitude and zero-filled interpolation (hT₂W–FLAIR–ZFI) was optimized and validated in phantom studies and compared with medium inversion time inversion recovery imaging with magnitude reconstruction (MIIRMR). The following parameters were used in hT₂W–FLAIR–ZFI: repetition time 14,000 ms, echo time 663 ms, inversion time 2900 ms, flip angle 120°, echo train length 271, and field of view 166 × 196 mm².

Results

MRI obtained using hT₂W–FLAIR–MZFI yielded high-quality images with sharper and smoother borders between the endolymph and perilymph and a higher signal intensity ratio and more homogenous perilymph enhancement than those generated with MIIRMR (p < 0.01). There were predominantly grade II EHs in the cochleae and grade III EHs in the vestibule in definite MD. EH was detected in the apex of 11/16 ipsilateral ears, 3/16 contralateral ears in unilateral definite MD and 3/6 ears in bilateral MD.

Conclusions

The novel hT₂W–FLAIR–MZFI technique is sensitive and demonstrates strong and homogenous enhancement by minimum Gd–DTPA in the inner ear, including the apex, and yields high-quality images with sharp borders between the endolymph and perilymph.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00405-021-06912-4.

Interpreting pendred syndrome as a foetal hydrops: Clinical and animal model evidence

BACKGROUND

Menière disease (MD) and SLC26A4 related deafness (Pendred syndrome (PS) or DFNB4) are two different inner ear disorders which present with fluctuating and progressive hearing loss, which could be a direct consequence of endolymphatic hydrops.

OBJECTIVE

To present similarities between both pathologies and explore how the concept of hydrops may be applied to PS/DFNB4.

METHODS

Review of the literature on MD, PS/DFNB4 and mouse model of PS/DFNB4.

RESULTS

MD and PS/DFNB4 share a number of similarities such as fluctuating and progressive hearing loss, acute episodes with vertigo and tinnitus, MRI and histological evidence of endolymphatic hydrops (although with different underlying mechanisms). MD is usually diagnosed during the fourth decade of life whereas PS/DFNB4 is congenital. The PS/DFNB4 mouse models have shown that biallelic slc26a4 mutations lead to Na+ and water retention in the endolymph during the perinatal period, which in turn induces degeneration of the stria vascularis and hearing loss. Crossing clinical/imagery characteristics and animal models, evidence seems to support the hypothesis of PS being a foetal hydrops.

CONCLUSIONS

When understanding PS/DFNB4 as a developmental hydrops, treatments used in MD could be repositioned to PS.

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.

Experimental Animal Models for Meniere's Disease: A Mini-Review

Several novel animal models that represent the pathophysiological process of endolymphatic hydrops (ELH) of Meniere's disease (MD) have been developed. Animal models are important to identify and characterize the pathophysiology of ELH and to corroborate molecular and genetic findings in humans. This review of the current animal models will be useful in understanding the pathophysiology of and developing proper treatments for MD. Surgical animal models will be replaced by medication-induced animal models. Study models previously developed in guinea pigs will be developed in several smaller animals for ease of conducting molecular analysis. In this review, we provided updated resources including our previous studies regarding the current and desirable animal models for MD.

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.

Cannula-based drug delivery to the guinea pig round window causes a lasting hearing loss that may be temporarily mitigated by BDNF

Sustained local delivery of drugs to the inner ear may be required for future regenerative and protective strategies. The round window is surgically accessible and a promising delivery route. To be viable, a delivery system should not cause hearing loss. This study determined the effect on hearing of placing a drug-delivery microcatheter on to the round window, and delivering either artificial perilymph (AP) or brain-derived neurotrophic factor (BDNF) via this catheter with a mini-osmotic pump. Auditory brainstem responses (ABRs) were monitored for 4 months after surgery, while the AP or BDNF was administered for the first month. The presence of the microcatheter - whether dry or when delivering AP or BDNF for 4 weeks - was associated with an increase in ABR thresholds of up to 15 dB, 16 weeks after implantation. This threshold shift was, in part, delayed by the delivery of BDNF. We conclude that the chronic presence of a microcatheter in the round window niche causes hearing loss, and that this is exacerbated by delivery of AP, and ameliorated temporarily by delivery of BDNF.

Effect of aldosterone on cochlear Af9 expression and hearing in guinea pig

CONCLUSIONS

Af9 protein in cochlea may be closely related to endolymph regulation by aldosterone and thus may be involved in pathogenesis of endolymphatic hydrops (EH).

OBJECTIVES

EH is the pathological characteristic of Ménière's disease (MD). Aldosterone could induce EH, but its relationship with MD is still controversial. The aim of the present study is to investigate the Af9 protein expression in guinea pig cochlea and regulation of Af9 expression and cochlear function by aldosterone. The role of Af9 in pathogenesis of EH is discussed.

METHODS

Thirty guinea pigs were randomly divided into two groups. The treatment group was intraperitoneally injected with aldosterone 0.1 mg/kg/d for 5 days, while the control group was done with saline. Hearing and histomorphology of cochlea were examined. In addition, expression of Af9 protein was studied.

RESULTS

The hearing threshold of the treatment group was increased. EH was induced in 73% of guinea pigs in the treatment group, and no EH was found in the control group. Af9 protein was found in spiral limbus, stria vascularis, Reissner's membrane, organ of Corti and spiral ganglion in both groups. Af9 expression in cochlea decreased significantly at protein level after treatment by aldosterone.

Secondary Endolymphatic Hydrops

HYPOTHESIS

A review of the most recent literature will provide clinicians with an update of secondary endolymphatic hydrops, aiding in diagnosis and treatment of affected patients.

BACKGROUND

Secondary endolymphatic hydrops is a pathologic finding of the inner ear resulting in episodic vertigo and intermittent hearing loss. It is a finding for which extensive research is being performed.

METHODS

A review of the most recent literature on secondary endolymphatic hydrops was performed using PubMed literature search.

RESULTS

Recent investigation of secondary endolymphatic hydrops has brought attention to traumatic and inflammatory insults as causes for secondary endolymphatic hydrops. Such etiologies, including postsurgical effects of cochlear implantation and endolymphatic sac ablation; otosclerosis and its operative intervention(s); acoustic and mechanical trauma; medications; and systemic inflammatory processes, have been determined as causes of secondary lymphatic hydrops. Histopathological slides for many of the etiologies of secondary endolymphatic hydrops are presented.

CONCLUSION

Through an understanding of the pathophysiology and etiologies of secondary endolymphatic hydrops, clinicians will gain a better understanding of this complex disease process, which will aid in treatment of patients with this disease process.

In Vivo Visualization of Endolymphatic Hydrops in Guinea Pigs: Magnetic Resonance Imaging Evaluation at 4.7 Tesla

In order to find out whether it is possible to visualize experimental endolymphatic hydrops in the cochlea with magnetic resonance imaging (MRI) at 4.7 T, we used 11 guinea pigs. Five normal guinea pigs were used as controls. Early manifestation of endolymphatic hydrops was evaluated in endolymphatic sac (ES)-intact animals (n = 6), and advanced manifestation in ES-damaged animals (n = 5) by means of MRI with gadolinium-diethylenetriaminepentaacetate-bismethylamide (Gd-DTPA-BMA) contrast agent. Hearing was tested with electrocochleography. The surface area of 3 partitions of the cochlea was used to quantify endolymphatic hydrops. The fine structure of the 3 partitions of the cochlea was visualized with MRI in all animals, as Gd-DTPA-BMA appeared mainly in the scala tympani and scala vestibuli. As early as 5 days after endolymphatic sac surgery, endolymphatic hydrops started to appear as visualized by MRI and also verified with histology. Severe damage to the inner ear barrier with Gd-DTPA-BMA leakage into the scala media was detected with MRI in 1 ES-damaged animal that had a 60-dB hearing loss. To conclude, endolymphatic hydrops can be visualized with high-resolution MRI by means of Gd-DTPA-BMA, and it is possible to quantify the extent of endolymphatic hydrops. Damage to the inner ear barrier or possible rupture of membranes can be shown with the assistance of Gd-DTPA-BMA.

Evaluation of the usefulness of three-dimensional optical coherence tomography in a guinea pig model of endolymphatic hydrops induced by surgical obliteration of the endolymphatic duct

Optical coherence tomography (OCT) has advanced significantly over the past two decades and is currently used extensively to monitor the internal structures of organs, particularly in ophthalmology and dermatology. We used ethylenediamine tetra-acetic acid (EDTA) to decalcify the bony walls of the cochlea and investigated the inner structures by deep penetration of light into the cochlear tissue using OCT on a guinea pig model of endolymphatic hydrops (EH), induced by surgical obliteration of the endolymphatic duct. The structural and functional changes associated with EH were identified using OCT and auditory brainstem response tests, respectively. We also evaluated structural alterations in the cochlea using three-dimensional reconstruction of the OCT images, which clearly showed physical changes in the cochlear structures. Furthermore, we found significant anatomical variations in the EH model and conducted graphical analysis by strial atrophy for comparison. The physical changes included damage to and flattening of the organ of Corti—evidence of Reissner's membrane distention—and thinning of the lateral wall. These results indicate that observation of EDTA-decalcified cochlea using OCT is significant in examination of gradual changes in the cochlear structures that are otherwise not depicted by hematoxylin and eosin staining.

Long-term administration of vasopressin can cause Ménière's disease in mice

CONCLUSION

A new murine model of Ménière's disease has been developed, based on long-term administration of vasopressin. Induction of vestibular dysfunction in the present animal model can cause additional stress, by reducing inner ear blood flow. Latanoprost, a selective agonist for the FP prostanoid receptor, may become a new remedy for Ménière's disease.

OBJECTIVE

The purpose of this study was to develop a more suitable animal model, with a closer resemblance to the pathophysiological process in Ménière's disease.

METHODS

Adult CBA/J or ICR mice were treated by subcutaneous injection of vasopressin for 5 days up to 8 weeks. Morphological analyses were performed of the cochlea, vestibular end organs and endolymphatic sac. The effect of latanoprost on the development of endolymphatic hydrops was also examined.

RESULTS

All experimental animals showed mild to moderate endolymphatic hydrops, increasing in severity as the vasopressin treatment was prolonged. Animals treated with vasopressin for 8 weeks showed severe endolymphatic hydrops with partial loss of outer hair cells and spiral ganglion cells. These animals also had a reversible vestibular dysfunction following intratympanic injection of epinephrine. Latanoprost inhibited the development of endolymphatic hydrops caused by vasopressin.

Inner ear symptoms and disease: pathophysiological understanding and therapeutic options

In recent years, huge advances have taken place in understanding of inner ear pathophysiology causing sensorineural hearing loss, tinnitus, and vertigo. Advances in understanding comprise biochemical and physiological research of stimulus perception and conduction, inner ear homeostasis, and hereditary diseases with underlying genetics. This review describes and tabulates the various causes of inner ear disease and defines inner ear and non-inner ear causes of hearing loss, tinnitus, and vertigo. The aim of this review was to comprehensively breakdown this field of otorhinolaryngology for specialists and non-specialists and to discuss current therapeutic options in distinct diseases and promising research for future therapies, especially pharmaceutic, genetic, or stem cell therapy.

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.

The effect of systemic administration of desmopressin on cochlear function in guinea pigs

CONCLUSIONS

Systemic desmopressin (dDAVP) administration in guinea pigs for up to 2 weeks induced only minor or no significant changes in cochlear sensitivity, suggesting that other factors may be required to induce the cochlear dysfunction that is usually associated with endolymphatic hydrops.

OBJECTIVES

To investigate the effects of chronic systemic administration of dDAVP, a synthetic analog of vasopressin, on cochlear sensitivity in guinea pigs.

METHODS

dDAVP was administered subcutaneously via a mini-osmotic pump, at a rate of 0.2 ng/kg/min (low-dose group) or 2.0 ng/kg/min (high-dose group) for up to 2 weeks. Cochlear responses (compound action potentials) and distortion product otoacoustic emissions (DPOAEs) were measured. Example specimens were scanned using X-ray micro-tomography (micro-CT).

RESULTS

Compared with the control group, the low-dose dDAVP group showed a significant threshold increase in response to a 2 kHz tone-burst after 2 weeks of treatment, and also a decrease in the amplitude of the DPOAE after 1 week of treatment. However, individual results were variable and the high-dose dDAVP group showed no significant change compared to the control group. In the micro-CT images, two of four ears in the low-dose group showed mild hydrops, but no hydrops was found in the three ears sampled from the high-dose group.

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.

Endolymphatic hydrops: pathophysiology and experimental models

It is well established that endolymphatic hydrops plays a role in Ménière disease, even though the precise role is not fully understood and the presence of hydrops in the ear does not always result in symptoms of the disease. It nevertheless follows that a scientific understanding of how hydrops arises, how it affects the function of the ear, and how it can be manipulated or reversed could contribute to the development of effective treatments for the disease. Measurements in animal models in which endolymphatic hydrops has been induced have given numerous insights into the relationships between hydrops and other pathologic and electrophysiological changes, and how these changes influence the function of the ear. The prominent role of the endolymphatic sac in endolymph volume regulation, and the cascade of histopathological and electrophysiological changes that are associated with chronic endolymphatic hydrops, have now been established. An increasing number of models are now available that allow specific aspects of the interrelationships to be studied. The yclical nature of Ménière symptoms gives hope that treatments can be developed to maintain the ear in permanent state of remission, possibly by controlling endolymphatic hydrops, thereby avoiding the rogressive damage and secondary pathologic changes that may also contribute to the patient's symptoms.

Psychological assessment of patients with Menière's disease

The objective of this study was to evaluate daily stressors, coping, personality, physical and mental health, and quality of life in Menière patients. 110 consecutive patients with definite Menière's disease were assessed using the Dutch Daily Hassles List, Coping Inventory for Stressful Situations (CISS), Symptoms Checklist 90 (SCL-90), NEO Five Factor Inventory (NEO-FFI), General Health Questionnaire (GHQ-12), and the Short Form Health Survey 36 (SF-36). Duration and subjective severity of symptoms were scored using a self-report questionnaire. It was shown that Menière patients had more daily stressors, used certain coping strategies less often, and had more psychopathology (e.g. anxiety and depression), and a worse quality of life compared to healthy reference groups. No abnormalities in personality were found. Patients with more severe symptoms had more psychopathology and a worse quality of life than patients with mild symptoms. The psychological profile of Menière patients seems comparable to patients with other chronic diseases. The outcomes should be used to intensify psychological support in patients with this disabling disease.

Effect of inner ear blood flow changes in Ménière's model mice

CONCLUSIONS

The endolymphatic sac (ES) is important for inner ear fluid homeostasis. A dysfunctional ES can cause vertigo attacks following additional stress such as a sudden change in endolymphatic volume and/or pressure, or restricted inner ear blood flow.

OBJECTIVE

The purpose of this study was to elucidate the mechanism of vertigo attacks in Ménière's disease.

MATERIALS AND METHODS

Adult CBA/J mice were given an intratympanic injection of lipopolysaccharide and an intraperitoneal injection of aldosterone. These 'model' animals had epinephrine or sodium nitroprusside (SNP) instilled into the middle ear cavity. Cochleae, vestibules, and endolymphatic sacs were studied morphologically by light microscopy.

RESULTS

The injection of epinephrine into the model animals reduced the endolymphatic hydrops in the cochlea, but also produced mild hydrops in the vestibule, which was never observed in untreated (control) animals. The ES did not react to epinephrine in the normal way. Injection of SNP did not cause any changes.

Stress as a Trigger of Attacks in Menière's Disease. A Case-Crossover Study

BACKGROUND

Menière's disease is defined as the presence of recurrent, spontaneous episodic vertigo, hearing loss (HL), aural fullness, and tinnitus. The occurrence of attacks is unpredictable. The etiology is still unknown, but the disease has a pathologic correlate in hydropic distension of the endolymphatic system. Earlier studies have shown increased incidence of stress on the same day as vertigo attacks, but it has not been determined whether stress occurring on the day of the vertiginous episode came before or after the onset of the vertigo.

METHODS

A case-crossover study including 46 patients with active Menière's disease.

MAIN OUTCOME MEASURE

Relative risks with 95% confidence intervals (CI).

FINDINGS

During the study period, 153 Menière's attacks were reported. Twenty-four (52%) of the 46 patients reported attacks. Twelve of the 153 (8%) attacks occurred within 3 hours after exposure to emotional stress. The relative risk of having an attack was 5.10 (95% CI 2.37-10.98) during 3 hours after being exposed to emotional stress. Twenty-nine percent of the patients with attacks had at least one attack after exposure to emotional stress. For mental stress, the relative risk was 4.16 (95% CI 1.46-11.83) and the hazard period 1 hour, but only five attacks were exposed. No excess risk was found after physical stress.

INTERPRETATION

Being exposed to emotional stress increases the risk of getting an attack of Menière's disease during the next hour, and the hazard period is possibly extended up to 3 hours.

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.

What's new in ion transports in the cochlea?

Recent advances in the field of the physiology of inner ear fluids permitted the characterization of the molecular mechanisms involved in critical processes such as the absorption of K(+) through cochlear sensory hair cells (mechanoelectrical transduction) or the secretion of K(+) by marginal cells of the stria vascularis. In addition, new pathways for ion circulations were evidenced. Mutations of transporters involved in some of these pathways, especially in K(+) recycling through gap junction systems, and in local pH regulation, are among the most frequent etiologies of genetic deafness in humans.

Functional IsK/KvLQT1 potassium channel in a new corticosteroid-sensitive cell line derived from the inner ear

Endolymph, a high K(+)/low Na(+) fluid, participates in mechanoelectrical transduction in inner ear. Molecular mechanisms controlling endolymph ion homeostasis remain elusive, hampered by the lack of appropriate cellular models. We established an inner ear cell line by targeted oncogenesis. The expression of SV40 T antigen was driven by the proximal promoter of the human mineralocorticoid receptor (MR) gene, a receptor expressed in the inner ear. The EC5v cell line, microdissected from the semicircular canal, grew as a monolayer of immortalized epithelial cells forming domes. EC5v cells exhibited on filters of high transepithelial resistance and promoted K(+) secretion and Na(+) absorption. Functional MR and the 11beta-hydroxysteroid dehydrogenase type 2, a key enzyme responsible for MR selectivity were identified. Expression of the epithelial sodium channel and serum glucocorticoid-regulated kinase 1 was shown to be up-regulated by aldosterone, indicating that EC5v represents a novel corticosteroid-sensitive cell line. Ionic measurements and (86)Rb transport assays revealed an apical secretion of K(+) at least in part through the I(sK)/KvLQT1 potassium channel under standard culture conditions. However, when cells were exposed to high apically K(+)/low Na(+) fluid, mimicking endolymph exposure, I(sK)/KvLQT1 actually functioned as a strict apical to basolateral K(+) channel inhibited by clofilium. Quantitative reverse transcriptase-PCR further demonstrated that expression of KvLQT1 but not of I(sK) was down-regulated by high K(+) concentration. This first vestibular cellular model thus constitutes a valuable system to further investigate the molecular mechanisms controlling ionic transports in the inner ear and the pathophysiological consequences of their dysfunctions in vertigo and hearing loss.

Triple Semicircular Canal Occlusion in Guinea Pigs with Endolymphatic Hydrops

HYPOTHESIS

Triple semicircular canal occlusion will eliminate rotatory stimulation to the vestibular peripheral system (as it blocks endolymphatic fluid movement) and therefore release rotatory vertigo attack. This surgery is safe in ears with endolymphatic hydrops.

BACKGROUND

Semicircular canal occlusion has been used as an alternative treatment of intractable benign paroxysmal positional vertigo with varied success. Triple semicircular canal occlusion in animal models blocks the responses of the semicircular canals to rotation and spares cochleae and the otolithic apparatus. This result suggests that triple semicircular canal occlusion is a prospective method in vertigo management for patients with Ménière's disease. However, the effectiveness and safety of triple semicircular canal occlusion has not been fully evaluated in ears with endolymphatic hydrops.

METHODS

Endolymphatic hydrops was established in 20 guinea pigs by endolymphatic sac obliteration. Triple semicircular canal occlusion was performed in 12 of them 120 days after endolymphatic hydrops surgery, whereas 8 others were killed for morphologic observation to confirm endolymphatic hydrops. Auditory and vestibular functions were monitored from the time before endolymphatic hydrops until 1 month after triple semicircular canal occlusion. Endolymphatic hydrops and canal occlusion were confirmed by morphologic observation.

RESULTS

Successful establishment of endolymphatic hydrops was indicated by mild elevation of the auditory brainstem response threshold and tentative asymmetry in nystagmus. Endolymphatic hydrops was confirmed by cochlear morphology in all eight animals that were killed 120 days after endolymphatic hydrops surgery. After triple semicircular canal occlusion, all 12 animals showed spontaneous nystagmus with a slow component toward the side that had been operated on, head tilt, rotated walking, and tentative asymmetry in rotatory nystagmus. The static symptoms disappeared within 1 month after triple semicircular canal occlusion. Caloric nystagmus was only slightly reduced after endolymphatic hydrops as compared with the contralateral ears but could not be elicited at all after triple semicircular canal occlusion. No significant elevation in auditory brainstem response threshold was found after triple semicircular canal occlusion. The canal occlusion and endolymphatic hydrops were confirmed in all surgical ears.

CONCLUSION

Triple semicircular canal occlusion is effective for eliminating the response of semicircular canals to rotation and caloric stimulation and is safe in ears with endolymphatic hydrops. Also, the static compensation to the disequilibrium is quick and complete. These results suggest that triple semicircular canal occlusion should be an option for controlling rotatory vertigo in Ménière's disease.

Analysis of Cortisol and Other Stress-Related Hormones in Patients with M??ni??re??s Disease

OBJECTIVE

To evaluate cortisol and catecholamine levels in patients with Ménière's disease.

STUDY DESIGN

Prospective, controlled study.

SETTING

Tertiary referral center.

PATIENTS

Thirty patients with Ménière's disease and 18 healthy controls.

MAIN OUTCOME MEASURES

Serum and saliva cortisol, serum cortisol after the dexamethasone suppression test, urine free cortisol, and urine catecholamines.

RESULTS

The serum and saliva cortisol levels were higher in Ménière's patients compared with their control group: 440 +/- 127 (n = 28) versus 366 +/- 90 (nmol/L) (n = 18) and 17.2 +/- 6.1 (n = 18) versus 11.6 +/- 4.6 (nmol/L) (n = 9), respectively. Both differences were significant (p < 0.05). There were no dissimilarities in urine cortisol or urine catecholamines for either group. Twenty-eight Ménière's patients were divided into two subgroups, namely, high- and low-cortisol groups, using a serum cortisol level cutoff point of 465 nmol/L (median). The total Ménière's disease time and the duration of tinnitus tended to be longer in the high-cortisol group (p = 0.07, two-tailed). The total Ménière's disease time was 13.5 +/- 9.9 years in the high-cortisol group and 7.1 +/- 7.4 years in the low-cortisol group (n = 14 for both). The subgroups were matched for age, gender, and unilaterally or bilaterally affected ears.

CONCLUSION

Patients with Ménière's disease have higher serum cortisol levels. It is suggested that these higher cortisol levels are rather the result than the cause of this chronic disease, because patients affected longer seem to have higher cortisol levels. The exact impact of these higher cortisol levels on the inner ear and endolymph homeostasis is yet unknown.

Le sac endolymphatique : ses fonctions au sein de l’oreille interne

The endolymphatic sac is a non-sensory organ of the inner ear. It is connected to the endolymphatic compartment that is filled with endolymph, a potassium-rich fluid that bathes the apical side of inner ear sensory cells. The main functions ascribed to the endolymphatic sac are the regulation of the volume and pressure of endolymph, the immune response of the inner ear, and the elimination of endolymphatic waste products by phagocytosis. Functional alteration of these functions, leading to deficient endolymph homeostasis and/or altered inner ear immune response, may participate to the pathophysiology of Ménière's disease, an inner ear pathology that causes episodes of vertigo, sensorineural hearing loss and tinnitus, and is characterized by an increase in volume of the cochleo-vestibular endolymph (endolymphatic hydrops).

Three-dimensional Fourier transformation constructive interference in steady state magnetic resonance imaging of the inner ear in patients with unilateral and bilateral Menière's disease

OBJECTIVE

In this study, three-dimensional Fourier transformation constructive interference in steady state (3DFT-CISS) magnetic resonance imaging was used to quantify the distance between the vertical part of the posterior semicircular canal and the posterior fossa as a measure of the endolymphatic sac and duct in patients with Menière's disease. Differences in this distance between affected and unaffected ears, as well as differences between unilaterally and bilaterally affected patients, were studied and compared with a control group. Also, possible correlations between the measured distance and the duration and severity of symptoms, patient age, and average hearing loss were investigated in the group of patients with Menière's disease.

STUDY DESIGN

Retrospective clinical study.

SETTING

Tertiary referral center (University Hospital) as part of a large, diagnostic research project on Menière's disease.

PATIENTS

Of the 111 patients with Menière's disease initially included, 90 patients underwent 3DFT-CISS MRI. Eighty-six of these patients were analyzed in this MRI study. Fifty-six patients had unilateral Menière's disease, and 30 patients had bilateral Menière's disease (116 affected and 56 unaffected ears). Sixty-two ears in patients without Menière's disease were studied as controls.

INTERVENTION

The distance between the vertical part of the posterior semicircular canal and the posterior fossa was determined by 3DFT-CISS MRI.

MAIN OUTCOME MEASURES

Contiguous axial 3DFT-CISS MRI slices of 0.7 to 1.0 mm were made by a radiologist according to a strict protocol. Measurements of the distance between the vertical part of the posterior semicircular canal and the posterior fossa were taken by two professionals-a radiologist and an otolaryngologist-using a ruler and the original scan.

RESULTS

A significantly smaller distance (2.9 mm) between the vertical part of the posterior semicircular canal and the posterior fossa as visualized on MRI scans was found in the ears of patients with Menière's disease than in the ears of patients in the control group (3.8 mm, p < 0.001). In both uni- and bilaterally affected patients (n = 56 and n = 30, respectively), no significant difference between ears was found (p = 0.44 and p = 0.19, respectively). In bilaterally affected patients, however, this distance (3.2 mm) was significantly greater than the distance in unilaterally affected patients (2.7 mm, p = 0.004). There was no relationship between the MRI-visualized distance between the vertical part of the posterior semicircular canal and the posterior fossa and the duration of disease, average hearing loss, or severity of symptoms in uni- and bilaterally affected patients.

CONCLUSION

The difference in MRI-visualized distances between the vertical part of the posterior semicircular canal and the posterior fossa of uni- and bilaterally affected patients strongly suggests that unilateral and bilateral hearing loss are two different entities in patients with Menière's disease. The size of the endolymphatic sac seems not to be the only factor in the pathogenesis of Menière's disease. That the MRI-visualized distance between the vertical part of the posterior semicircular canal and the posterior fossa does not have any relationship to the duration of the disease or to patient age indicates that this distance is a congenital feature.

Sensory cell damage in two-phase endolymphatic hydrops: a morphologic evaluation of a new experimental model by low-voltage scanning techniques

HYPOTHESIS

The aim of this study was to create a more dynamic animal model of Ménière's disease combining multiple causes, such as the role of endocrine factors and endolymphatic sac dysfunction, that may mimic the fluctuant characteristics of Ménière's disease.

BACKGROUND

Endolymphatic hydrops remains to be considered a pathologic substrate in the etiology of Ménière's disease. The classic guinea pig model of inducing hydrops by total destruction of the endolymphatic sac is a nonphysiologic rigid model of Ménière's disease.

METHODS

The authors developed the two-phase endolymphatic hydrops model by inducing hydrops by mild chronic endolymphatic sac dysfunction, in combination with increased endolymph production by aldosterone. Sensory cell damage was evaluated by low-voltage field emission scanning microscopy.

RESULTS

This study describes a wide spectrum of morphologic effects of the outer hair cells in radial gradients, in which most effects were observed in the third to second row of outer hair cells, and longitudinal gradients in which the most severe effects were observed in the apical turns. Most affected were the ears that underwent distal endolymphatic sac dissection followed by the administration of aldosterone. Damaging effects proceeded from degeneration and absence of short stereocilia of outer hair cells and even some inner hair cells in the apical turns, to stereociliary disarrangement and atrophy, followed by degeneration and absence of outer hair cells, which were replaced by supporting cells.

CONCLUSION

The two-phase endolymphatic hydrops model seems to represent a functional model that may mimic the fluctuant characteristics of Ménière's disease and emphasizes the influence of multiple and coexisting hydrops-inducing influences.

Perilymphatic and Endolymphatic Pressure in the Guinea Pig After Distal Dissection of the Endolymphatic Sac

HYPOTHESIS

The study was designed to investigate whether endolymphatic pressure exceeds perilymphatic pressure in an endolymphatic hydrops model with a partially functioning endolymphatic sac.

BACKGROUND

Previous investigations of perilymphatic and endolymphatic pressure measurements during endolymphatic hydrops were done in a classic endolymphatic hydrops model, with a surgically blocked endolymphatic duct and sac. This model, in contrast to the clinical situation of Meniere's patients, totally lacks the functional contribution of the endolymphatic sac.

METHODS

In the guinea pig, a partially functioning endolymphatic sac was created via dissection of the distal portion of the sac from the sigmoid sinus. Three (n = 5) and 6 months (n = 3) later, perilymphatic and endolymphatic pressures were measured consecutively using a WPI 900A micropressure system.

RESULTS

It was observed that damage to the distal part of the endolymphatic sac caused endolymphatic hydrops in 58% of the cases. The hydrostatic pressure in hydropic ears did not differ from that of control ears. There was no pressure difference between the perilymphatic and endolymphatic compartments in ears with endolymphatic hydrops. The endocochlear potential in ears with hydrops was statistically significantly decreased (p < 0.002).

CONCLUSION

In a hydrops model developed to be more comparable to the histopathologic appearance of Meniere's disease in the inner ear, no hydrostatic pressure difference was measured between the perilymphatic and endolymphatic spaces. The only functional difference from control ears we found was a decreased endocochlear potential.

Ultrastructure of the endolymphatic sac in two-phase endolymphatic hydrops in the guinea pig

Two-phase endolymphatic hydrops is a subtle experimental model for Meniere's disease. Chronic dysfunction of the endolymphatic sac, induced by dissection of the most distal part without causing damage to the intermediate part, is combined with increased endolymph production induced by administration of aldosterone which stimulates the N/K-ATPase in the stria vascularis. A transmission electron microscopic study was performed on the endolymphatic sacs of four groups of guinea pig cochleas: controls: non-operated aldosterone-treated cochleas; operated (dissection of the endolymphatic sac) cochleas; operated and aldosterone-treated cochleas. Light and electron microscopy showed a normal morphology in the controls. Aldosterone treatment had no visible effect. Dissected ears revealed severe deviations. The epithelium of the intermediate sac was low, showed dilated lateral intercellular spaces indicating elevated fluid transport and displayed serious degenerative processes. Distally, the endolymphatic sac was completely blocked by newly formed bone. Additional aldosterone treatment had no cumulative effect on the dissected ears.

Expression of mRNAs encoding hormone receptors in the endolymphatic sac of the rat

The endolymphatic sac (ES) is believed to absorb the endolymphatic fluid produced by the stria vascularis and vestibular dark cells. Recent studies have implied that the function of the ES may be controlled by circulating hormones, suggesting that hormone receptors should exist there. In the present study, the expression of genes encoding receptors for aldosterone, atrial natriuretic peptide (ANP) and vasopressin in the ES was examined by reverse transcription-polymerase chain reaction (RT-PCR). Next, the cellular localization of the expression of these genes was investigated by in situ hybridization. RT-PCR indicated that aldosterone. ANP-A and vasopressin V1a receptor genes were expressed in the ES. In contrast, neither ANP-B nor vasopressin V2 receptor gene expression was detected. In situ hybridization experiments demonstrated aldosterone receptor gene expression in epithelial cells of the intermediate potion of the ES, while expression of ANP-A or V1a receptor genes was not detected. The present results suggested that aldosterone may play a specific role in the function of the ES. However, we could not conclude that ANP and vasopressin play physiological roles in the ES because receptors for these hormones were detected only by highly sensitive PCR.

Perilymphatic pressure dynamics following posture change in patients with Menière's disease and in normal hearing subjects

The hydrostatic pressure of the inner ear depends on the cerebrospinal fluid pressure through the cochlear aqueduct. The time-course of inner ear pressure change following rapid change in cerebrospinal fluid pressure is related to the aqueduct patency. In this study the patency of the cochlear aqueduct in 27 patients with Menière's disease (28 affected ears, 16 non-affected ears) and in 12 normal hearing subjects (18 control ears) was assessed non-invasively by means of the MMS-10 Tympanic Displacement Analyser. Following a rapid change in body position, changes in intracranial cerebrospinal fluid pressure were found to influence perilymphatic pressure within 1 min. No significant differences were found among affected ears, non-affected ears and control ears.