Endolymphatic hydrops induced by chronic administration of vasopressin

The clinical manifestation and treatment of Meniere's Disease from the viewpoint of the water homeostasis of the inner ear

Endolymphatic hydrops, a pathological feature of Ménière's disease, has been experimentally and clinically confirmed to be influenced by the blood circulation of vasopressin (VP). VP is a well-known hormonal regulator of water homeostasis. In addition, VP is influenced by various environmental changes, dehydration, fluctuation of atmospheric pressure, pregnancy, and other factors. Furthermore, VP is a key regulator of the hypothalamic-pituitary-adrenal (HPA) axis. The HPA axis is a major neuroendocrine system that controls reactions to emotional and physical stresses, as well as the sleep/wake cycle (circadian rhythm). Therefore, VP is susceptible to change via the HPA axis. This review considers possible mechanisms of the formation of endolymphatic hydrops from the perspective of the vasopressin-aquaporin 2 system.

Efficacy of a Serotonin-Norepinephrine Reuptake Inhibitor as a Treatment for Meniere Disease: A Randomized Clinical Trial

Importance

Meniere disease accounts for up to 15% of new vestibular diagnoses,; however, the optimal treatment has yet to be identified. A conservative treatment that would reduce or stop the vertigo episodes has not been identified.

Objective

To determine the efficacy of a serotonin-norepinephrine reuptake inhibitor, venlafaxine, compared to placebo in treating patients with Meniere disease.

Design, Setting, and Participants

This was a randomized, double-blind, placebo-controlled, crossover pilot study spanning 22 weeks of follow-up. The clinical trial took place at a single-center tertiary referral center in Charleston, South Carolina. Participants were eligible if they were 18 years or older, had definite Meniere disease criteria as defined by Barany criteria, had at least 2 episodes in the last month, had not received intratympanic gentamycin, skull base surgery, or radiation therapy to the head or neck, not currently taking diuretics for Meniere disease, not currently taking oral steroids, and not currently taking serotonin-modulating medication. Patients were enrolled between February 2020 and September 2023.

Interventions

Patients received either 1 venlafaxine tablet, 37.5 mg, taken daily by mouth for 8 weeks or 1 placebo tablet taken daily by mouth for 8 weeks. Group 1 received placebo during phase 1 of the trial and venlafaxine in phase 2 of the trial. Group 2 received venlafaxine during phase 1 of the trial and placebo in phase 2 of the trial.

Main Outcomes and Measures

The main outcomes included the number of episodes and scores on the following scales: Dizziness Handicap Inventory, Neuropsychological Vertigo Inventory, Meniere Disease Patient-Oriented Symptom Index, 20-Item Short Form Health Survey, Penn State Worry Questionnaire, Cognitive Failure Questionnaire.

Results

A total of 182 patients were screened, and 40 participants with Meniere disease enrolled in the trial. The mean (SD) age of participants was 56.6 (14.3) years, and 22 (55%) were female. Participants had a mean (SD) of 13.8 (10.1) episodes per phase at baseline, 5.4 (4.4) episodes (Δ8.4) during the venlafaxine phase, and 5.0 (4.6) episodes (Δ8.8) during the placebo phase. No significant difference was identified between venlafaxine and placebo groups in the number of episodes or quality-of-life metrics.

Conclusions and Relevance

This randomized clinical trial failed to identify a difference between venlafaxine and placebo in number of episodes and other quality-of-life metrics. Future studies may benefit from different dosing regimens, larger cohorts, and longer lengths of therapy.

Trial Registration

ClinicalTrials.gov Identifier: NCT04218123.

Immunohistochemical localisation of aquaporin 2 and vasopressin type 2 receptor in the human endolymphatic sac

OBJECTIVE

This study aimed to determine the distribution and subcellular localisation of aquaporin 2 and vasopressin type 2 receptor in the human endolymphatic sac.

METHODS

Ten samples of human endolymphatic sac were collected during acoustic neurinoma removal using the translabyrinthine approach. Immunohistochemistry and immunofluorescence were performed using aquaporin 2 and vasopressin type 2 receptor monoclonal antibodies.

RESULTS

Confocal microscopy demonstrated that vasopressin type 2 receptor labelling was expressed in both the apical and basolateral plasma membranes, and in the cytoplasm of the endolymphatic sac epithelium, whereas aquaporin 2 was strongly expressed at the basolateral site of the endolymphatic sac epithelium, in both the intraosseous and extraosseous parts of the endolymphatic sac.

CONCLUSION

Both aquaporin 2 and vasopressin type 2 receptor were detected in the epithelial cells of the human endolymphatic sac, suggesting that this channel may be involved in inner-ear fluid homeostasis. However, strong basolateral expression of aquaporin 2 in endolymphatic sac epithelium suggested that the function of aquaporin 2 may differ between the endolymphatic sac and kidney.

Live Imaging of the Dehydration Effect of Isosorbide on the Normal and Hydropic Guinea Pig Cochleae Using Optical Coherence Tomography

OBJECTIVE

To investigate the isosorbide-induced dehydration effect on the endolymphatic space by intratympanic administration of isosorbide.

BACKGROUND

Isosorbide, an osmotic diuretic, is used orally as a typical conservative therapy for Menière's disease (MD) in Japan. The dehydration effect occurs 6 hours after isosorbide ingestion. Intratympanic administration of isosorbide resolves endolymphatic hydrops faster than oral ingestion. In addition, the dehydration effect has never been shown directly. Therefore, we investigated the dehydration effect of intratympanic administration of isosorbide on endolymphatic hydrops using optical coherence tomography.

METHODS

We used eight Hartley guinea pigs, divided into normal and hydrops groups. In the hydrops group, the animals underwent endolymphatic sac obliteration to create endolymphatic hydrops. We obtained midmodiolar section images of the cochleae using optical coherence tomography. Then, 50 to 70% isosorbide was sequentially administered intratympanically for 5 minutes, and the apical turn of the cochlea was observed. The relative midmodiolar cross-sectional area of the scala media was calculated for quantitative assessment of the endolymphatic space.

RESULTS

In the normal group, 50% isosorbide had a slight but significant dehydration effect on the scala media; at 55 to 70%, Reissner's membrane became flat. In the hydrops group, 50% isosorbide slightly reduced endolymphatic hydrops; 65% flattened Reissner's membrane, and 70% slightly concaved it toward the basilar membrane.

CONCLUSION

The results suggest that we could select the concentration of isosorbide according to the stage or severity of MD and relief from acute attack. Intratympanic administration of isosorbide may be a promising treatment for patients with MD.

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.

Vestibular Disorders and Hormonal Dysregulations: State of the Art and Clinical Perspectives

The interaction between endocrine and vestibular systems remains poorly documented so far, despite numerous observations in humans and animals revealing direct links between the two systems. For example, dizziness or vestibular instabilities often accompany the menstrual cycle and are highly associated with the pre-menopause period, while sex hormones, together with their specific receptors, are expressed at key places of the vestibular sensory network. Similarly, other hormones may be associated with vestibular disorders either as causal/inductive factors or as correlates of the pathology. This review was carried out according to the PRISMA method, covering the last two decades and using the MEDLINE and COCHRANE databases in order to identify studies associating the terms vestibular system and/or vestibular pathologies and hormones. Our literature search identified 646 articles, 67 of which referred directly to vestibular dysfunction associated with hormonal variations. While we noted specific hormonal profiles depending on the pathology considered, very few clinical studies attempted to establish a direct link between the expression of the vestibular syndrome and the level of circulating hormones. This review also proposes different approaches to shed new light on the link between hormones and vestibular disorders, and to improve both the diagnosis and the therapeutic management of dizzy patients.

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.

Smoking Is Positively Related and Alcohol Consumption Is Negatively Related to an Increased Risk of Meniere's Disease

A few prior researchers presumed the impacts of smoking and alcohol on the risk of Meniere’s disease (MD). This study investigated the relationship between smoking, alcohol consumption, and obesity with Meniere’s disease in an adult population. The ≥40-year-old population in the Korean National Health Insurance Service-Health Screening Cohort 2002−2019 was analyzed. A total of 15,208 patients with MD were matched with 499,658 comparison participants. The current smoking, alcohol consumption, and past medical histories were collected. Body mass index (BMI) was grouped into underweight, normal, overweight, obese I, and obese II. The odds of histories of smoking and alcohol consumption and the BMI group for MD were analyzed using conditional logistic regression analysis. These associations were further analyzed in subgroups of age, sex, smoking, alcohol consumption, and BMI. In the overall adult population, smoking and alcohol consumption did not show an association with MD. Being underweight was linked with lower odds for MD (adjusted OR [aOR] = 0.80, 95% CI = 0.68−0.93, p = 0.004). In the male group, smoking was positively associated with MD (aOR = 1.08, 95% CI = 1.00−1.17, p = 0.043), while alcohol consumption was negatively related to MD (aOR = 0.87, 95% CI = 0.81−0.94, p < 0.001). Being underweight was related to a lower risk of MD. In adult men, smoking was predicted to increase, while alcohol consumption was predicted to decrease the risk of MD.

Hormones and Vestibular Disorders: The Quest for Biomarkers

The vestibular system exerts control over various functions through neural pathways that are not yet fully mapped. Functional dysregulations or tissue lesions at different levels of the peripheral and the central vestibular networks can alter these different functions, causing a wide variety of symptoms, ranging from posturo-locomotor alterations to psychiatric syndromes such as PPPD, including the deregulation of the main biological functions. These different symptoms differ by their expression kinetics (they each appear and regress with their own kinetics) by the targets affected (muscles, organs, and brain areas) and by the sensitivity specific to each individual. Vestibular pathologies thus cover a mosaic of distinct effects, and they involve various effectors—which constitute the many markers of their different types and stages. It is therefore crucial, to predict the onset of a vertigo syndrome, to follow its temporal course, or to monitor the impact of therapeutic approaches, and to have specific and reliable biomarkers. Hormonal variations are among the possible sources of biomarkers for neurotology. We know that specific hormonal profiles can promote the appearance of vestibular disorders. We also know that the expression of vertigo syndrome is accompanied by measurable hormonal variations. The link between endocrine deregulation and vestibular alterations therefore no longer needs to be proven. However, there are still few data on their precise correlations with the vertigo syndrome. This study was undertaken with the aim to deliver an extensive review of the hormonal alterations linked to vestibular disorders. A review of the literature covering the last two decades was carried out using the MEDLINE and COCHRANE databases in order to identify studies associating the terms vestibular system or vestibular pathologies and hormones. Bibliographic data provides several outcomes in terms of therapeutic innovation in the diagnosis and therapeutic follow-up of vestibular pathologies.

The Effect of Endolymphatic Hydrops and Mannitol Dehydration Treatment on Guinea Pigs

Background

Endolymphatic hydrops (EH) is considered as the pathological correlate of Menière’s disease (MD) and cause of hearing loss. The mechanism of EH, remaining unrevealed, poses challenges for formalized clinical trials.

Objective

This study aims to investigate the development of hearing loss, as well as the effect of dehydration treatment on EH animal models.

Methods

In this study, different severity EH animal models were created. The laser Doppler vibrometer (LDV) and auditory brainstem responses (ABR) were used to study the effects of EH and the dehydration effects of mannitol. The LDV was used to measure the vibration of the round window membrane (RWM) reflecting the changes in inner ear impedance. ABR was used to evaluate the hearing changes. Furthermore, tissue section and scanning electron microscopy (SEM) observations were used to analyze the anatomical change to the cochlea and outer hair cells.

Results

The RWM vibrations decreased with the severity of EH, indicating an increase in the cochlear impedance. The dehydration therapy lowered the impedance to restore acoustic transduction in EH 10- and 20-day animal models. Simultaneously, the ABR thresholds increased in EH models and were restored after dehydration. Moreover, a difference in the hearing was found between ABR and LDV results in severe EH animal models, and the dehydration therapy was less effective, indicating a sensorineural hearing loss (SNHL).

Conclusion

Endolymphatic hydrops causes hearing loss by increasing the cochlear impedance in all tested groups, and mannitol dehydration is an effective therapy to restore hearing. However, SNHL occurs for the EH 30-day animal models, limiting the effectiveness of dehydration. Our results suggest the use of dehydrating agents in the early stage of EH.

A Perspective for Ménière’s Disease: In Silico Investigations of Dexamethasone as a Direct Modulator of AQP2

Ménière’s disease is a chronic illness characterized by intermittent episodes of vertigo associated with fluctuating sensorineural hearing loss, tinnitus and aural pressure. This pathology strongly correlates with a dilatation of the fluid compartment of the endolymph, so-called hydrops. Dexamethasone is one of the therapeutic approaches recommended when conventional antivertigo treatments have failed. Several mechanisms of actions have been hypothesized for the mode of action of dexamethasone, such as the anti-inflammatory effect or as a regulator of inner ear water homeostasis. However, none of them have been experimentally confirmed so far. Aquaporins (AQPs) are transmembrane water channels and are hence central in the regulation of transcellular water fluxes. In the present study, we investigated the hypothesis that dexamethasone could impact water fluxes in the inner ear by targeting AQP2. We addressed this question through molecular dynamics simulations approaches and managed to demonstrate a direct interaction between AQP2 and dexamethasone and its significant impact on the channel water permeability. Through compartmentalization of sodium and potassium ions, a significant effect of Na+ upon AQP2 water permeability was highlighted as well. The molecular mechanisms involved in dexamethasone binding and in its regulatory action upon AQP2 function are described.

Pathogenesis and Etiology of Ménière Disease: A Scoping Review of a Century of Evidence

Importance

Ménière disease is a rare chronic benign disorder of the inner ear with a natural history of multiple clinical phenotypes of variable severity and a tendency to burnout with time. Although multiple treatment modalities have been shown to improve the disease process-some adversely affecting cochleovestibular function-it remains uncertain whether one, several separate, or a combination of pathophysiologic mechanisms affect the disease process. A scoping review of the evidence underlying proposed pathophysiologic mechanisms of Ménière disease is needed to determine which processes are most likely to be etiopathogenic factors.

Observations

Of the 4602 relevant articles found through Embase, Ovid, and PubMed, 444 met inclusion criteria. The most common reported causes of Ménière disease were autoimmune or immune-mediated, genetic, or structural dysfunction of the inner ear. During the study period from inception to March 2021, etiologic theories shifted from structural dysfunction to autoimmune and genetic causes of Ménière disease.

Conclusions and Relevance

This scoping review found that Ménière disease is a multifactorial disease with lifelong comorbidities and loss of quality-associated life-years whose most commonly reported causes were structural dysfunction, immunologic damage, and genetic susceptibility. Recent studies have examined how autoinflammatory processes and vestibular migraine may be associated with Ménière disease. Large heterogeneity among studies may be explained by historical differences in the clinical understanding of the disease, as well as evolving intervention methodologies and practitioner expertise. Ménière disease is a multifactorial disease with lifelong comorbidities and loss of quality-associated life-years; therefore, future studies of reliable biomarkers of endolymphatic hydrops and real-time imaging are warranted to improve understanding and treatment.

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.

Endolymphatic Sac Drainage Surgery and Plasma Stress Hormone Vasopressin Levels in Meniere's Disease

Meniere's disease is a common inner ear disorder accompanied by vertigo attacks and fluctuating hearing loss that some believe is due to a stressful lifestyle. To elucidate the scientific relationship in neuro-endocrinology between Meniere's disease and stress, we examined the surgical results of endolymphatic sac drainage surgery and changes in stress-induced plasma arginine-vasopressin levels. We enrolled 100 intractable Meniere's patients and examined surgical results and plasma vasopressin levels. Fifty-four chronic otitis media patients who underwent tympano-mastoidectomy formed a control group. We assessed surgical results during a 2-year follow-up period, including vertigo and hearing loss. We examined plasma vasopressin levels just before surgery and 1 week, 1 year, and 2 years after surgery. In patients with intractable Meniere's disease, plasma vasopressin levels were significantly reduced 1 week after surgery compared to the decrease observed in chronic otitis media patients after tympano-mastoidectomy. In intractable Meniere's disease, long-lasting low plasma vasopressin levels after surgery were associated with significantly good surgical results. In recurrent Meniere's disease, a gradual plasma vasopressin level elevation was observed after surgery, followed by recurrent vertigo attacks and sensorineural hearing loss. It is suggested that long-lasting high levels of plasma vasopressin could have adverse effects on inner ear water metabolism and the subsequent Meniere's disease symptoms. Effective treatments for Meniere's disease might be best based on the maintenance of low plasma vasopressin levels.

Biomarkers for Inner Ear Disorders: Scoping Review on the Role of Biomarkers in Hearing and Balance Disorders

The diagnostics of inner ear diseases are primarily functional, but there is a growing interest in inner ear biomarkers. The present scoping review aimed to elucidate gaps in the literature regarding the definition, classification system, and an overview of the potential uses of inner ear biomarkers. Relevant biomarkers were categorized, and their possible benefits were evaluated. The databases OVID Medline, EMBASE, EBSCO COINAHL, CA PLUS, WOS BIOSIS, WOS Core Collection, Proquest Dissertations, Theses Global, PROSPERO, Cochrane Library, and BASE were searched using the keywords “biomarker” and “inner ear”. Of the initially identified 1502 studies, 34 met the inclusion criteria. The identified biomarkers were classified into diagnostic, prognostic, therapeutic, and pathognomonic; many were detected only in the inner ear or temporal bone. The inner-ear-specific biomarkers detected in peripheral blood included otolin-1, prestin, and matrilin-1. Various serum antibodies correlated with inner ear diseases (e.g., anti-type II collagen, antinuclear antibodies, antibodies against cytomegalovirus). Further studies are advised to elucidate the clinical significance and diagnostic or prognostic usage of peripheral biomarkers for inner ear disorders, filling in the literature gaps with biomarkers pertinent to the otology clinical practice and integrating functional and molecular biomarkers. These may be the building blocks toward a well-structured guideline for diagnosing and managing some audio-vestibular disorders.

Live imaging and functional changes of the inner ear in an animal model of Meniere's disease

The symptoms of Meniere's disease (MD) are generally considered to be related to endolymphatic hydrops (EH). There are many recent reports supporting the possibility that vasopressin (VP) is closely linked to the formation of EH in Meniere's disease. Based on this, we developed a clinically relevant animal model of Meniere's disease in which a VP type 2 receptor agonist was administered after electrocauterization of the endolymphatic sac. We report live imaging of the internal structure, and functional changes of the inner ear after electrocauterization of the endolymphatic sac and administration of a VP type 2 receptor agonist. In this model, the development of EH was visualized in vivo using optical coherence tomography, there was no rupture of Reissner's membrane, and low-tone hearing loss and vertiginous attacks were observed. This study suggested that acute attacks are caused by the abrupt development of EH. This is the first report of live imaging of the development of EH induced by the administration of a VP type 2 receptor agonist.

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.

Solute carrier family 4 member 1 might participate in the pathogenesis of Meniere's disease in a murine endolymphatic hydrop model

Background: To date, the pathogenesis of Meniere's disease (MD) remains unclear. Previous research found that the SLC4A1 gene significantly down-regulated. Aims: This study sought to understand the effect of SLC4A1 on the pathogenesis of MD. ELH C57 mice models were induced by intraperitoneal injection of AVP. Material and methods: The mRNA expression levels of SLC4A1, SLC4A10 and SLC26A4 were monitored by real-time quantitative PCR, the protein expression levels of SLC4A1 were monitored by immunoblotting and immunofluorescence before and after the ELH. DIDS is an inhibitor of SLC4A1. The expression levels of SLC4A1 were also monitored in the AVP + DIDS group. Results: We successfully established the model of ELH after applied AVP. The results of HE staining showed displacement of Reissner's membrane with bulge to scala vestibule in ears of the AVP group. Cochlea/ELS SLC4A1 protein and SLC4A1, SLC4A10, SLC26A4 mRNA expressions were reduced significantly in C57 mice of the AVP group. The SLC4A1 protein expression levels and SLC4A1, SLC4A10, SLC26A4 mRNA expression levels declined more obvious in the cochlea and ELS in C57 mice of the AVP + DIDS group. Conclusions and significance: SLC4A1 was a protective factor in the pathogenesis of MD, but the mechanisms were unknown.

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.

Dizziness in peri- and postmenopausal women is associated with anxiety: a cross-sectional study

Background

Although dizziness is one of the most common symptoms of menopause, the underlying mechanism is not precisely known. Therefore, this study aimed to investigate the prevalence of, and the factors associated with, dizziness in peri- and postmenopausal women.

Methods

We conducted a cross-sectional study in which we analyzed the first-visit records of 471 Japanese women aged 40 to 65 years who enrolled in a health and nutrition education program at a menopause clinic. The prevalence of dizziness was estimated according to the participants’ responses to the Menopausal Health-Related Quality of Life Questionnaire. The background characteristics of age, menopause status, body composition, cardiovascular parameters, basal metabolism, and physical fitness; other menopausal symptoms, including vasomotor, insomnia, depression, and anxiety symptoms; and lifestyle characteristics were assessed for their associations with dizziness.

Results

The percentage of women who suffered from dizziness once a week or more frequently was 35.7%. Compared to the women without dizziness, those with the symptom were younger; had a higher body weight, body mass index, body fat percentage, muscle mass, and waist-to-hip ratio; had higher systolic pressure; were slower in reaction time; had higher physical and psychological symptom scores of menopause; exercised less regularly; and consumed less alcohol. A multivariate logistic regression analysis revealed that the anxiety symptom, which was evaluated by the Hospital Anxiety and Depression Scale, was the sole factor that was independently associated with dizziness (adjusted odds ratio 1.14; 95% confidence interval 1.08–1.20).

Conclusions

Dizziness is highly prevalent in Japanese peri- and postmenopausal women and it is associated with anxiety. The treatment of anxiety in this population might improve the symptom.

Change in endolymphatic hydrops 2 years after endolymphatic sac surgery evaluated by MRI

OBJECTIVE

This study was performed to determine whether endolymphatic sac surgery improves vestibular and cochlear endolymphatic hydrops 2 years after sac surgery and to elucidate the relationship between the degree of improvement of endolymphatic hydrops and the changes in vertigo symptoms, the hearing level, and the summating potential/action potential ratio (-SP/AP ratio) by electrocochleography (ECochG) in patients with Ménière's disease (MD).

METHODS

Twenty-one patients with unilateral MD who underwent sac surgery were included in this study. All patients underwent gadolinium-enhanced magnetic resonance imaging (Gd-MRI) before and 2 years after sac surgery. We evaluated the difference in vestibular and cochlear endolymphatic hydrops between before and after surgery in both ears and compared these findings with the frequency of vertigo attacks, hearing level, and ECochG findings.

RESULTS

In affected ears, the presence of vestibular endolymphatic hydrops and the frequency of vertigo attacks significantly decreased after surgery. However, affected ears showed no significant improvement in the presence of cochlear endolymphatic hydrops or the -SP/AP ratio by ECochG; there was also no significant improvement or deterioration in the hearing level.

CONCLUSION

The present findings suggest that sac surgery reduces vestibular endolymphatic hydrops and prevents aggravation of cochlear endolymphatic hydrops, and these changes lead to a reduction of vertigo attacks and suppress the progression of hearing impairment associated with vertigo attacks.

Vestibular Function Change in a Vasopressin-Induced Hydrops Model

HYPOTHESIS

A vasopressin-induced endoymphatic hydrops model can represent an acute vertiginous attack in Menière's disease (MD).

BACKGROUND

Previous animal models are not appropriate to evaluate the efficacy of new treatments for hydrops because they cannot represent an acute attack of MD. Recently, a new dynamic model was introduced for acute hydrops exacerbation using the vasopressin type 2 receptor agonist, desmopressin (1-deamino-8-D-Arginine vasopressin, VP); however, resulting changes in vestibular function have not been investigated.

METHODS

A total of 37 guinea pigs were used. Two to 4 weeks after surgical ablation of endolymphatic sacs in 33 guinea pigs, acute exacerbation of hydrops was induced by a single VP injection in 18 animals (group A). Next, two VP injections at 1 hour interval were administered to investigate the effect of multiple VP doses on vestibular function in the other 15 animals (group B). In the remaining four animals, VP was injected without surgery for the control group (control). Bidirectional sinusoidal harmonic acceleration (SHA) tests of vestibular function were performed. "Type I response" was defined as when the maximum slow-phase velocity (SPV) during left rotation (toward the operated ear) was lower than that during right rotation (toward the normal ear). In contrast, "Type II response" was defined as when maximum SPV at the left rotation was higher than that at the right rotation. Vestibular symmetry scores were analyzed at baseline and after each of two VP injections given 1 hour apart.

RESULTS

Vestibular symmetry scores increased at 1 hour after VP injection in all 18 animals in group A (p < 0.001). Two hours after VP injection, symmetry score decreased to the initial score. Two different types of vestibular response were observed after VP. However, the symmetry scores between type I and II responses were not significantly different (p = 0.173). In all 15 animals of Group B, vestibular asymmetry was sustained over 3 hours when two VP injections were given 1 hour apart. In three of Group B, the type of vestibular response changed from type II response to type I response after the 2nd VP injection; however, no animal demonstrated a shift from type I to type II response.

CONCLUSION

VP can transiently induce an acute exacerbation of hydrops and asymmetric vestibular dysfunction in guinea pigs. This model could help in studying new treatments for acute hydrops and in explaining the mechanism of bidirectional nystagmus in MD.

Ménière’s Disease Pathophysiology: Endolymphatic Sac Immunohistochemical Study of Aquaporin-2, V2R Vasopressin Receptor, NKCC2, and TRPV4

Objectives

Endolymphatic sac (ELS) pathophysiology in Ménière’s disease (MD) remains poorly understood. We identified from the literature a group of proteins expressed on the ELS and involved in endolymph volume regulation: aquaporin-2 (AQP2), vasopressin receptor V2R, sodium potassium chloride cotransporter 2 (NKCC2), and transient receptor potential cation channel V4 (TRPV4). Our objective was to determine whether their ELS expression was altered in MD, to better understand the pathophysiology of endolymphatic hydrops.

Study Design

Prospective case-control study.

Setting

Tertiary care center.

Subjects

Twenty-four patients with definite MD undergoing endolymphatic duct blockage surgery were recruited, as well as 23 controls with no history of MD undergoing surgery for vestibular schwannoma (VS).

Methods

ELS biopsies and blood samples for plasma arginine vasopressin (AVP) were obtained. Immunohistochemistry for AQP2, V2R, NKCC2, and TRPV4 was performed. Slides were scanned digitally for highly sensitive pixel density analysis by specialized software (VIS; Visiopharm).

Results

Global scores generated by the software represent total and relative protein expression density of 3 staining intensity levels, exclusively on ELS epithelium. AQP2 expression density was significantly elevated in MD compared to VS ( P = .003). There was no significant difference in plasma AVP, V2R, NKCC2, and TRPV4 expression.

Conclusion

This original study evaluates simultaneous in situ expression of AQP2, V2R, NKCC2, and TRPV4 on the human ELS in MD, with a control group. Our results show only AQP2 upregulation on the ELS of patients with MD. We suggest a constitutively increased expression of AQP2 in MD, independent of its regulatory axis (AVP-V2R). Acquired regulator sequence mutations could support this model.

Arginine Vasopressin-Aquaporin-2 Pathway-Mediated Dehydration Effects of Electroacupuncture in Guinea Pig Model of AVP-Induced Eendolymphatic Hydrops

OBJECTIVE

To investigate the effects of electroacupuncture (EA) on endolymphatic hydrops (EH) and the regulation of arginine vasopressin (AVP)-aquaporin-2 (AQP2) pathway in guinea pigs.

METHODS

EH was induced in male guinea pigs by an intraperitoneal injection of AVP. For the treatment, EA was delivered to Baihui (GV 20) and Tinggong (SI 19) acupoints, once per day for 10 consecutive days. In histomorphological studies, cochlear hydrops degree was evaluated by hematoxylin-eosin (HE) staining, and then the ratio of scala media (SM) area to SM + scala vestibuli (SV) area (R value) was calculated. In mechanical studies, a comparison of plasma AVP (p-AVP) concentrations, cyclic adenosine monophosphate (cAMP) levels, vasopressin type 2 receptor (V2R) and AQP2 mRNA expressions in the cochlea were compared among groups.

RESULTS

EA significantly reduced cochlear hydrops in guinea pigs (P=0.001). EA significantly attenuated the AVPinduced up-regulation of p-AVP concentrations (P=0.006), cochlear cAMP levels (P=0.003) and AQP2 mRNA expression (P=0.016), and up-regulated the expression of V2R mRNA (P=0.004) in the cochlea.

CONCLUSIONS

The dehydrating effect of EA might be associated with its inhibition of AVP-AQP2 pathway activation.

Longitudinal up-regulation of endolymphatic hydrops in patients with Meniere's disease during medical treatment

Objective/Hypothesis

Meniere's disease (MD) is a common inner ear disease characterized by repeated episodic vertigo, fluctuating sensorineural hearing loss, and tinnitus. Its pathology is defined as endolymphatic hydrops (EH) in the inner ear and EH has been hypothesized to correlate with the clinical symptoms of MD. We presented the dynamics of in vivo EH in MD patients during medical treatments.

Study Design

Prospective, single-arm repeated measures.

Methods

Eleven MD patients were enrolled. All subjects prospectively underwent gadolinium-enhanced inner ear magnetic resonance (MR) imaging and neuro-otological testing before and after medical treatment. The volume of EH was quantitatively evaluated by processing MR images. All MD patients were administered continuous medication and followed up for more than 12 months.

Results

The frequency of vertigo episodes decreased in all patients and vestibular function decreased to 13-91% of the pre-treatment level. The volume ratio of post-treatment EH-to-pre-treatment EH ranged from 1.01-3.22. The total volume of pre-treatment EH was significantly correlated with cochlear symptom disease duration and the affected ear's hearing level.

Conclusion

EH in MD patients developed longitudinally with deterioration of inner ear function during medical treatment. The natural course of MD may progress with development of EH at least for a certain period.

Level of Evidence

2b.

Computer-aided detection and quantification of endolymphatic hydrops within the mouse cochlea in vivo using optical coherence tomography

Diseases that cause hearing loss and/or vertigo in humans such as Meniere’s disease are often studied using animal models. The volume of endolymph within the inner ear varies with these diseases. Here, we used a mouse model of increased endolymph volume, endolymphatic hydrops, to develop a computer-aided objective approach to measure endolymph volume from images collected <italic<in vivo</italic< using optical coherence tomography. The displacement of Reissner’s membrane from its normal position was measured in cochlear cross sections. We validated our computer-aided measurements with manual measurements and with trained observer labels. This approach allows for computer-aided detection of endolymphatic hydrops in mice, with test performance showing sensitivity of 91% and specificity of 87% using a running average of five measurements. These findings indicate that this approach is accurate and reliable for classifying endolymphatic hydrops and quantifying endolymph volume.

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.

Claudin expression in the rat endolymphatic duct and sac - first insights into regulation of the paracellular barrier by vasopressin

Hearing and balance functions of the inner ear rely on the homeostasis of the endolymphatic fluid. When disturbed, pathologic endolymphatic hydrops evolves as observed in Menière’s disease. The molecular basis of inner ear fluid regulation across the endolymphatic epithelium is largely unknown. In this study we identified the specific expression of the tight junction (TJ) molecules Claudin 3, 4, 6, 7, 8, 10, and 16 in epithelial preparations of the rat inner ear endolymphatic duct (ED) and endolymphatic sac (ES) by high-throughput qPCR and immunofluorescence confocal microscopy. Further we showed that Claudin 4 in the ES is a target of arginine-vasopressin (AVP), a hormone elevated in Menière’s disease. Moreover, our transmission-electron microscopy (TEM) analysis revealed that the TJs of the ED were shallow and shorter compared to the TJ of the ES indicating facilitation of a paracellular fluid transport across the ED epithelium. The significant differences in the subcellular localization of the barrier-forming protein Claudin 3 between the ED and ES epithelium further support the TEM observations. Our results indicate a high relevance of Claudin 3 and Claudin 4 as important paracellular barrier molecules in the ED and ES epithelium with potential involvement in the pathophysiology of Menière’s disease.

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

OBJECTIVE

The correlation between the isosorbide-induced decompression effect on the endolymphatic space and plasma osmolality (p-OSM) or plasma arginine vasopressin (p-AVP) was investigated on comparing two different dosages of isosorbide (2.8 and 1.4 g/kg) to elucidate why the decompression effect is delayed with a large dose of isosorbide.

MATERIALS AND METHODS

Two experiments were performed using 80 guinea pigs. Experiment 1 was designed to morphologically investigate the sequential influence of the oral intake of 1.4- and 2.8-g/kg doses of isosorbide on the endolymphatic volume. The animals used were 50 guinea pigs (control: 10, experimental: 40). All animals underwent surgical obliteration of the endolymphatic sac of the left ear. One month after the surgery, control animals were sacrificed 3 hours after the intake of distilled water, and experimental animals were sacrificed 3 and 6 hours after the isosorbide intake. All of the left temporal bone served for the quantitative assessment of changes in the endolymphatic space, and the cross-sectional area of the scala media was measured from the mid-modiolar sections of the cochlea.Experiment 2 was designed to investigate changes in p-OSM and p-AVP levels 3 hours after the oral intake of isosorbide. Animals used were 15 guinea pigs (control: 5, experimental: 10). The control group received the oral administration of distilled water (4 ml/kg), and the experimental animals were subdivided into two groups consisting of 10 animals each by the dosage of isosorbide (1.4 or 2.8 g/kg). All animals were sacrificed for the measurement of p-OSM and p-AVP concentrations 3 hours after the intake of water or 70% isosorbide solution.

RESULTS

Morphologically, an isosorbide-induced decompression effect was noted in animals with both 1.4- and 2.8-g/kg doses of isosorbide. According to the regression analysis, however, the volumetric decrease of the endolymphatic space was more evident in cases with the small dose (1.4 g/kg) 3 hours after the intake (analysis of covariance [ANCOVA], p < 0.001). Six hours after, the decompression effect was significantly greater in cases with the large dose (2.8 g/kg) (ANCOVA, p < 0.001).Isosorbide intake caused a rise in p-OSM levels dose-dependently. The Cochran-Cox test revealed that the differences in the mean values among control and isosorbide groups were significant (p < 0.01). Regarding the p-AVP level, a significant increase was evident in cases with the large dose (2.8 g/kg) (p < 0.01, Cochran-Cox test), and not in cases with the small dose (1.4 g/kg).

CONCLUSION

An isosorbide-induced decompression effect of the endolymphatic space was evident in spite of two different dosages of isosorbide (2.8 and 1.4 g/kg). Three hours after the isosorbide intake, however, the decompression effect was more marked in the group with the small dose (1.4 g/kg). Since significant rises in p-OSM and p-AVP were evident in the group with the large dose, this early rise of p-AVP due to dehydration seems to be the major reason for the delayed decompression effect in cases with a large isosorbide intake.

Preceding profound deafness and co-factors promote development of endolymphatic hydrops in preliminary patients with delayed endolymphatic hydrops

CONCLUSION

Profound deafness (PD) is unlikely to be the only cause of endolymphatic hydrops (EH) in patients with delayed endolymphatic hydrops (DEH). Further studies in large patient cohorts are required to determine the etiologic co-factors involved in the development of EH in patients with PD and DEH.

OBJECTIVES

DEH usually occurs in patients with sustained unilateral PD who then develop episodic vertigo or fluctuating hearing loss. The latency can vary markedly between PD and development of DEH, but the factors affecting inner ear homeostasis and causing EH during this latency period remain unclear. The study aimed to assess the differences in EH and functional status of the inner ear between patients with PD only and those with DEH.

METHOD

Two PD and 10 DEH patients who had developed PD in early childhood were enrolled. Gadolinium-enhanced magnetic resonance imaging of the inner ear was performed in all patients to assess the degree of EH in the vestibule and cochlea.

RESULTS

There was no evidence of EH in the affected ears of patients with PD alone. DEH patients, however, showed significant EH in either the cochlea or vestibule, suggesting that EH development and DEH onset were strongly correlated.

Endolymph movement visualized with light sheet fluorescence microscopy in an acute hydrops model

There are a variety of techniques available to investigate endolymph dynamics, primarily seeking to understand the cause of endolymphatic hydrops. Here we have taken the novel approach of injecting, via a glass micropipette, fluorescein isothiocyanate-dextran (FITC-dex) and artificial endolymph into scala media of anaesthetized guinea pigs, with subsequent imaging of the inner ear using Light Sheet Fluorescence Microscopy (LSFM) as a means to obtain highly resolved 3D visualization of fluid movements. Our results demonstrate endolymph movement into the utricle, semicircular canals and endolymphatic duct and sac when more than 2.5 μl of fluid had been injected into scala media, with no apparent movement of fluid into the perilymphatic compartments. There was no movement of endolymph into these compartments when less than 2.5 μl was injected. The remarkable uptake of the FITC-dex into the endolymphatic duct, including an absorption into the periductal channels surrounding the endolymphatic duct, highlights the functional role this structure plays in endolymph volume regulation.

A Two-Year Randomized Trial of Interventions to Decrease Stress Hormone Vasopressin Production in Patients with Meniere's Disease-A Pilot Study

Meniere's disease, a common inner ear condition, has an incidence of 15-50 per 100,000. Because mental/physical stress and subsequent increase in the stress hormone vasopressin supposedly trigger Meniere's disease, we set a pilot study to seek new therapeutic interventions, namely management of vasopressin secretion, to treat this disease. We enrolled 297 definite Meniere's patients from 2010 to 2012 in a randomized-controlled and open-label trial, assigning Group-I (control) traditional oral medication, Group-II abundant water intake, Group-III tympanic ventilation tubes and Group-IV sleeping in darkness. Two hundred sixty-three patients completed the planned 2-year-follow-up, which included assessment of vertigo, hearing, plasma vasopressin concentrations and changes in stress/psychological factors. At 2 years, vertigo was completely controlled in 54.3% of patients in Group-I, 81.4% in Group-II, 84.1% in Group-III, and 80.0% in Group-IV (statistically I < II = III = IV). Hearing was improved in 7.1% of patients in Group-I, 35.7% in Group-II, 34.9% in Group-III, and 31.7% in Group-IV (statistically I < II = III = IV). Plasma vasopressin concentrations decreased more in Groups-II, -III, and -IV than in Groups-I (statistically I < II = III = IV), although patients' stress/psychological factors had not changed. Physicians have focused on stress management for Meniere's disease. However, avoidance of stress is unrealistic for patients who live in demanding social environments. Our findings in this pilot study suggest that interventions to decrease vasopressin secretion by abundant water intake, tympanic ventilation tubes and sleeping in darkness is feasible in treating Meniere's disease, even though these therapies did not alter reported mental/physical stress levels.

TRIAL REGISTRATION

ClinicalTrials.gov NCT01099046.

Vasopressin induces endolymphatic hydrops in mouse inner ear, as evaluated with repeated 9.4 T MRI

From histopathological specimens, endolymphatic hydrops has been demonstrated in association with inner ear disorders. Recent studies have observed findings suggestive of hydrops using MRI in humans. Previous studies suggest that vasopressin may play a critical role in endolymph homeostasis and may be involved in the development of Ménière's disease. In this study we evaluate the effect of vasopressin administration in vivo in longitudinal studies using two mouse strains. High resolution MRI at 9.4 T in combination with intraperitoneally delivered Gadolinium contrast, was performed before and after chronic subcutaneous administration of vasopressin via mini-osmotic pumps in the same mouse. A development of endolymphatic hydrops over time could be demonstrated in C57BL6 mice (5 mice, 2 and 4 weeks of administration) as well as in CBA/J mice (4 mice, 2 weeks of administration; 6 mice, 3 and 4 weeks of administration). In most C57BL6 mice hydrops developed first after more than 2 weeks while CBA/J mice had an earlier response. These results may suggest an in vivo model for studying endolymphatic hydrops and corroborates the future use of MRI as a tool in the diagnosis and treatment of inner ear diseases, such as Ménière's disease. MRI may also be developed as a critical tool in evaluating inner ear homeostasis in genetically modified mice, to augment the understanding of human disease.

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.

The physiological and pathophysiological functions of renal and extrarenal vasopressin V2 receptors

The arginine vasopressin (AVP) type 2 receptor (V2R) is unique among AVP receptor subtypes in signaling through cAMP. Its key function is in the kidneys, facilitating the urine concentrating mechanism through the AVP/V2 type receptor/aquaporin 2 system in the medullary and cortical collecting ducts. Recent clinical and research observations strongly support the existence of an extrarenal V2R. The clinical importance of the extrarenal V2R spans widely from stimulation of coagulation factor in the endothelium to as yet untested potential therapeutic targets. These include V2R-regulated membranous fluid turnover in the inner ear, V2R-regulated mitogensis and apoptosis in certain tumor tissues, and numerous other cell types where the physiological role of V2Rs still requires further research. Here, we review current evidence on the physiological and pathophysiological functions of renal and extrarenal V2Rs. These functions of V2R are important, not only in rare diseases with loss or gain of function of V2R but also in relation to the recent use of nonpeptide V2R antagonists to treat hyponatremia and possibly retard the growth of cysts and development of renal failure in autosomal dominant polycystic kidney disease. The main functions of V2R in principal cells of the collecting duct are water, salt, and urea transport by modifying the trafficking of aquaporin 2, epithelial Na(+) channels, and urea transporters and vasodilation and stimulation of coagulation factor properties, mainly seen with pharmacological doses of 1-desamino-8-D-AVP. The AVPR2 gene is located on the X chromosome, in a region with high probability of escape from inactivation; this may lead to phenotypic sex differences, with females expressing higher levels of transcript than males.

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.

Progression of endolymphatic hydrops in Ménière's disease as evaluated by magnetic resonance imaging

OBJECTIVE

To evaluate the presence and the degree of endolymphatic hydrops (EHs) in patients with unilateral Ménière's disease (MD), as a function of duration of the disease, estimated using a 3-dimensional fluid-attenuated inversion recovery sequence in a 3-Tesla magnetic resonance imaging unit, after intratympanic gadolinium administration.

PATIENTS

A total of 32 patients (21 male and 11 female subjects, aged 25-78 yr; median, 56 yr) participated in the investigation. The duration of the disease ranged from 2 months to 10 years (median, 3 yr), with a prevalence of vertigo spells in the last 6 months ranging from 0.5 to 8 per month (median, 2.5).

INTERVENTION

A 0.6-ml solution of gadobutrol (1 mmol/ml) diluted 1:7 in saline was injected in the affected ear through the inferior-posterior quadrant of the tympanic membrane, using a 22-gauge spinal needle. The patient was kept with the head rotated 45 degrees contralaterally for 30 minutes after each injection. Twenty-four hours later, a 3-dimensional fluid-attenuated inversion recovery magnetic resonance imaging was performed.

MAIN OUTCOME MEASURE

Perilymphatic enhancement was evaluated in different portions of the labyrinth as a function of MD duration.

RESULTS

Reduced or absence of enhancement of the vestibule occurred precociously and occurred in all subjects at long term. The prevalence of enhancement abnormalities in the cochlea and the semicircular canals was directly proportional to MD duration. At long term, the vestibule and the cochlea showed a more severe hydropic involvement compared with semicircular canals. A statistical significant correlation between enhancement abnormalities and MD duration was observed for most inner ear sites.

CONCLUSION

The increased prevalence and severity of EH with the duration of MD indicates that hydrops is a progressive degenerative phenomenon. The frequent abnormality in the vestibule and, secondarily, in the cochlea is in line with some histopathologic investigations. It remains to be clarified whether hydropic changes are related to specific signs and symptoms of MD.