Neuronal responses to vestibular stimulation in the guinea pig hypothalamic paraventricular nucleus

Tympanostomy tube placement for intractable Meniere's disease in the elderly

BACKGROUND

The treatment of refractory elderly Meniere's disease is a challenge.

AIM

To investigate the efficacy of tympanostomy tube placement in elderly patients with Meniere's disease.

METHODS

31 patients over 60 years old with Meniere's disease who had failed medical treatment and underwent tympanostomy tube placement. Vertigo control, hearing level, tinnitus, and ear fullness were recorded and analyzed preoperatively and postoperatively.

RESULTS

All patients completed a 6-month follow-up. At 6 months postoperatively,complete control, substantial control and limited control of vertigo were achieved in 10 (32%), 13 (42%), and 6 (19%) patients respectively. Two patients (6%) reported no substantial improvement. Twelve patients completed a 2-year follow-up. At 2 years postoperatively, complete control, substantial control and limited control of vertigo were achieved in 3 (25%), 5 (42%), and 1 (8%) patients respectively. Three (25%) patients showed no significant improvement in vertigo. The majority of patients reported significant improvement in the functional level scale, the Dizziness Handicap Inventory scores, and ear fullness at 6 months and 2 years postoperatively.

CONCLUSIONS AND SIGNIFICANCE

Tympanostomy tube placement may reduce vertigo attacks and improved the quality of life in elderly patients with Meniere's disease.

Thyroid Axis and Vestibular Physiopathology: From Animal Model to Pathology

A recent work of our group has shown the significant effects of thyroxine treatment on the restoration of postural balance function in a rodent model of acute peripheral vestibulopathy. Based on these findings, we attempt to shed light in this review on the interaction between the hypothalamic-pituitary-thyroid axis and the vestibular system in normal and pathological situations. Pubmed database and relevant websites were searched from inception through to 4 February 2023. All studies relevant to each subsection of this review have been included. After describing the role of thyroid hormones in the development of the inner ear, we investigated the possible link between the thyroid axis and the vestibular system in normal and pathological conditions. The mechanisms and cellular sites of action of thyroid hormones on animal models of vestibulopathy are postulated and therapeutic options are proposed. In view of their pleiotropic action, thyroid hormones represent a target of choice to promote vestibular compensation at different levels. However, very few studies have investigated the relationship between thyroid hormones and the vestibular system. It seems then important to more extensively investigate the link between the endocrine system and the vestibule in order to better understand the vestibular physiopathology and to find new therapeutic leads.

Anxiolytic effects of vestibular stimulation: an update

The vestibular system inhibits both HPA and SAM axis and contributes to the management of anxiety. Both direct and indirect pathways exist in the inhibition of the HPA and SAM axis. In this review article, the authors describe various pathways through which the vestibular system can regulate the HPA and SAM axis activity. Lastly, the authors highlight the need of starting translational research work in this field. Rocking is soothing and this is a universal fact that babies in the swing will calm down and sleep. These soothing effects of vestibular stimulation may be due to the inhibition of cortical and subcortical structures. Vestibular stimulation may be able to manage anxiety through its connections with multiple brain areas. There is a need to undertake translational research in this area to establish strong scientific evidence and recommend implementation of the vestibular stimulation in the management of anxiety.

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.

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.

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.

Stress and the vestibular system

In this chapter we review the existing literature regarding the interactions between stress and the mechanisms that maintain balance. Evidence suggests that the interplay between neuro-endocrine and psychological factors may have a significant role in balance function. For example, in healthy individuals vestibular stimulation has been shown to trigger the stress response as indicated by increased blood cortisol levels, whereas in patients with vestibular pathology factors such as resilience and anxiety may be the key focus of interactions with stress. Critically, factors such as anxiety are known to influence clinical outcomes, despite our mechanistic understanding of these processes remaining in their infancy.

Inner Ear Arginine Vasopressin-Vasopressin Receptor 2-Aquaporin 2 Signaling Pathway Is Involved in the Induction of Motion Sickness

It has been identified that arginine vasopressin (AVP), vasopressin receptor 2(V2R), and the aquaporin 2 (AQP2) signaling pathway in the inner ear play important roles in hearing and balance functions through regulating the endolymph equilibrium; however, the contributions of this signaling pathway to the development of motion sickness are unclear. The present study was designed to investigate whether the activation of the AVP-V2R-AQP2 signaling pathway in the inner ear is involved in the induction of motion sickness and whether mozavaptan, a V2R antagonist, could reduce motion sickness. We found that both rotatory stimulus and intraperitoneal AVP injection induced conditioned taste aversion (a confirmed behavioral index for motion sickness) in rats and activated the AVP-V2R-AQP2 signaling pathway with a responsive V2R downregulation in the inner ears, and AVP perfusion in cultured epithelial cells from rat endolymphatic sacs induced similar changes in this pathway signaling. Vestibular training, V2R antagonist mozavaptan, or PKA inhibitor H89 blunted these changes in the V2R-AQP2 pathway signaling while reducing rotatory stimulus- or DDAVP (a V2R agonist)-induced motion sickness in rats and dogs. Therefore, our results suggest that activation of the inner ear AVP-V2R-AQP2 signaling pathway is potentially involved in the development of motion sickness; thus, mozavaptan targeting AVP V2Rs in the inner ear may provide us with a new application option to reduce motion sickness. SIGNIFICANCE STATEMENT: Motion sickness affects many people traveling or working. In the present study our results showed that activation of the inner ear arginine vasopressin-vaspopressin receptor 2 (V2R)-aquaporin 2 signaling pathway was potentially involved in the development of motion sickness and that blocking V2R with mozavaptan, a V2R antagonist, was much more effective in reducing motion sickness in both rat and dog; therefore, we demonstrated a new mechanism to underlie motion sickness and a new candidate drug to reduce motion sickness.

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.

AVP modulation of the vestibular nucleus via V1b receptors potentially contributes to the development of motion sickness in rat

BACKGROUND

Arginine vasopressin (AVP) is considered to be an etiologic hormone in motion sickness (MS). The present study was designed to investigate whether individual differences in AVP expression in the paraventricular nucleus (PVN) and in modulation on the vestibular nucleus (VN) are involved in MS. Systemic application or microinjection of AVP into rat VN and rotatory stimulus were used to induce conditioned taste aversion (CTA) to 0.15 % saccharin sodium solution as a model of MS.

RESULTS

Intra-VN use of SSR149415, an antagonist of V1b receptors (V1bRs), blunted CTA. AVP inhibited Ca(2+) influxes through L-type Ca(2+) channels and NMDA receptor channels in cultured VN neurones, but antagonised by SSR149415. More AVP and V1bRs were expressed respectively in the PVN and VN after rotatory stimulus, especially in rats susceptible to MS. In the VN, AVP content was low, the AVP mRNA was less expressed, a few AVP-positive fibres were sparsely distributed, and fewer AVP/synaptophysin-positive terminals were identified. Almost no fluoro-ruby-labelled AVP-positive neurones in the PVN were found with retrograde tracing from the VN. SNP analysis of the reported 9 sites of the AVP gene showed significant difference between the groups susceptible and insusceptible to MS at the site rs105235842 in the allele frequencies and genotypes. However, there was not any difference between these two groups in the SNP of the reported 38 sites of V1bR gene.

CONCLUSIONS

AVP, through its modulatory, possibly humoral action on the VN neurones via the mediation of V1bR, may contribute to the development of motion sickness in rats; AVP gene polymorphisms may contribute to the individual difference in the responsive expression of AVP in the PVN; and higher expressions of AVP in the PVN and V1bRs in the VN may contribute to the development of motion sickness in rats after vestibular stimulation.

Interactions between Stress and Vestibular Compensation - A Review

Elevated levels of stress and anxiety often accompany vestibular dysfunction, while conversely complaints of dizziness and loss of balance are common in patients with panic and other anxiety disorders. The interactions between stress and vestibular function have been investigated both in animal models and in clinical studies. Evidence from animal studies indicates that vestibular symptoms are effective in activating the stress axis, and that the acute stress response is important in promoting compensatory synaptic and neuronal plasticity in the vestibular system and cerebellum. The role of stress in human vestibular disorders is complex, and definitive evidence is lacking. This article reviews the evidence from animal and clinical studies with a focus on the effects of stress on the central vestibular pathways and their role in the pathogenesis and management of human vestibular disorders.

Plasma vasopressin and V2 receptor in the endolymphatic sac in patients with delayed endolymphatic hydrops

OBJECTIVE

There are some kinds of sicknesses provoked by inadequate adaptation to physical and/or psychogenic stress in daily life. Delayed endolymphatic hydrops (DEH) is an inner ear disease like Ménière's disease (MD) characterized by episodic vertigo in the setting of preexisting unilateral deafness that especially occurs in civilized people with a stressful lifestyle. Its otopathologic finding was demonstrated to be inner ear endolymphatic hydrops through a temporal bone study in 1976, as in the case with MD in 1938. To elucidate the relationship between stress and the inner ear, we examined the plasma antidiuretic stress hormone vasopressin (pAVP) and its type 2 receptor (V2R) expression in the endolymphatic sac in patients with DEH.

STUDY DESIGN

A prospective molecular biological study.

METHODS

Between 1998 and 2007, we enrolled 20 patients with ipsilateral DEH to examine their pAVP during remission from vertigo attacks. Plasma vasopressin was also examined in 87 patients with unilateral MD and 30 control patients with chronic otitis media. Using the real-time polymerase chain reaction method with tissue samples obtained during surgery, we examined V2R mRNA expression in the endolymphatic sac in 6 patients with ipsilateral DEH, 9 patients with unilateral MD, and 6 control patients with acoustic neuroma.

RESULTS

Plasma vasopressin (1.5 times versus controls; unpaired t test, p = 0.140) and V2R mRNA expression in the endolymphatic sac (35.8 times versus controls; unpaired t test, p = 0.002) were higher in patients with DEH compared with those with acoustic neuroma. There were no significant differences in pAVP or V2R expression in the endolymphatic sac between DEH and MD. Patients with DEH showed a significantly negative correlation between pAVP and V2R (Pearson test, r = -0.92, p = 0.009) as in those with MD (Pearson test, r = -0.68, p = 0.043).

CONCLUSION

Civilized people are frequently exposed to stress in their daily life, and pAVP can easily become elevated at any time. Therefore, a negative feedback system between pAVP and V2R in the endolymphatic sac may function for inner ear fluid homeostasis against stress-induced increases in pAVP. For the pathogenesis of endolymphatic hydrops resulting in vertigo attacks in patients with DEH as well as MD, pAVP may represent a matter of consequence, but V2R overexpression in the endolymphatic sac could be much more essential as a basis for these diseases.

Stress axis plasticity during vestibular compensation in the adult cat

The postural, ocular motor, perceptive and neurovegetative syndromes resulting from unilateral vestibular neurectomy (UVN) symptoms could generate a stress and thereby activate the hypothalamo-pituitary-adrenal (HPA) axis. This study was aimed at determining whether UVN causes changes in the activity of the HPA axis, and if so, evaluating the time course of changes associated with UVN syndrome. At the cellular level, corticotropin-releasing factor (CRF) and arginine vasopressin (AVP) immunoreactivity (Ir) were analyzed and quantified in the paraventricular nucleus (PVN) and the vestibular nuclei (VN) complex of cats killed early (1 and 7 days) or late (30 and 90 days) after UVN. Dopamine-beta-hydroxylase (DbetaH), the enzyme synthesizing noradrenaline was examined in the locus coeruleus (LC) in these same cats. At the behavioral level, the time course of recovery of the postural and locomotor functions was quantified at the same postoperative delays in another group of UVN cats. Results showed a significant bilateral increase in the number of both AVP-Ir and CRF-Ir neurons in the PVN and an increase of DbetaH-Ir neurons in the LC at 1, 7 and 30 days after UVN. This increased number of neurons was no longer observed at 90 days. Conversely, a significant bilateral decrease of CRF-Ir neurons was observed in the VN at these same postlesion times, with a similar return to control values at 90 days. Our behavioral observations showed strong posturo-locomotor functional deficits early after UVN (1 and 7 days), which had recovered partially at 30 days and completely by 90 days postlesion. We demonstrate a long-lasting activation of the HPA axis, which likely reflects a chronic stress, experienced by the animals, which corresponds to the time course of full vestibular compensation, and which is no longer present when the animals are completely free of posturo-locomotor symptoms at 90 days.

Vestibular modulation of plasma vasopressin levels in rats

Recent studies, which have shown an increase of plasma vasopressin (VP) in experimental motion sickness and the efficacy of VP antagonists for motion sickness, suggest an important role of VP in the development of vestibulo-autonomic responses. We have recently found evidence of the co-existence of vasopressinergic neurons with the stress-sensitive chemokinergic neuronal system in the hypothalamo-pituitary pathway in rats, which uses cytokine-induced neutrophil chemoattractant (CINC) as an effector molecule. In this study, to elucidate possible roles of VP and CINC in the vestibulo-autonomic responses, we simultaneously measured plasma VP and CINC concentrations after electrical or caloric vestibular stimulation in urethane-anesthetized rats. Electrical vestibular stimulation with more than 200 microA increased the plasma levels of VP in a current intensity-dependent manner, and stimulation with 500 microA increased the plasma VP levels to 350% of the normal control group, which received no stimulation. Caloric vestibular stimulation with cold water increased the plasma VP levels to 262% of the control group, which received caloric stimulation with water at 37 degrees C, and stimulation with warm water tended to increase the plasma VP levels. Plasma CINC levels were neither affected by electrical nor caloric vestibular stimulation. These findings indicate that vestibular stimulation increased plasma levels of VP but not CINC, and this vestibular-induced activation of VP neurons may be involved in a mechanism of vestibulo-autonomic responses.