Sensorimotor Rehabilitation Promotes Vestibular Compensation in a Rodent Model of Acute Peripheral Vestibulopathy by Promoting Microgliogenesis in the Deafferented Vestibular Nuclei

Clinical characteristics of patients with dizziness/vertigo showing a dissociation between caloric and video head impulse test results

ObjectiveTo explore the clinical characteristics of patients with dizziness/vertigo who showed a dissociation between the results of the caloric test and video head impulse test (vHIT).MethodsA total of 327 patients who complained of dizziness/vertigo were continuously included. All patients underwent both the horizontal vHIT (h-vHIT) and caloric tests. Of the 327 patients, 69 patients showed a dissociation between the results of the two tests, 4 patients were excluded because the interval between the two tests exceeded 7 days. Finally, 65 patients were included in the analysis.ResultsAmong the 65 patients, 55 (84.6%) patients showed a positive caloric test (+) with a negative h-vHIT (-), and 10 (15.4%) patients showed a negative caloric test (-) with a positive h-vHIT (+). Peripheral and central lesions were identified in 50 (90.9%) and 5 (9.1%) patients, respectively, in the caloric test (+)/h-vHIT (-) group; and central lesions were found in 6 (60%) patients in caloric test (-)/h-vHIT (+) group. The etiologies were unilateral peripheral vestibular dysfunction (n = 25), Meniere's disease (MD, n = 10), sudden hearing loss with vertigo (SHLV, n = 7), benign paroxysmal positional vertigo (n = 5), vestibular neuritis (n = 2), autoimmune inner ear disease (n = 1), vestibular migraine (VM, n = 3), multiple sclerosis (n = 1), and multiple system atrophy (n = 1) in the caloric test (+)/h-vHIT (-) group, which were SHLV (n = 3), MD (n = 1), VM (n = 1), episodic ataxia type 2 (n = 1), cerebellopontine angle tumor (N = 1), Parkinson's disease (n = 1), Persistent postural perceptual dizziness (n = 1), and posterior circulation ischemia (n = 1) in the caloric test (-)/h-vHIT (+) group.ConclusionDissociation between the results of caloric test and h-vHIT is not uncommon. A positive caloric test with a negative h-vHIT occurred more frequently, and these patients mostly had peripheral vestibular lesions; while a negative caloric test with a positive h-vHIT was unusual, these patients had both peripheral and central lesions.

Pro-histaminergic drug restores balance, promotes microgliogenesis and modulates neuroinflammation after vestibular injury

Vestibular compensation is a neurobiological process that allows the recovery of impaired vestibular functions after unilateral vestibular damage. Among the post-injury plasticity mechanisms expressed in the vestibular nuclei (VN) that promote the restoration of balance function, neurogliogenesis and excitability changes appear to be in the forefront. At the central level, the vestibular syndrome expression results from an electrophysiological imbalance between intact and deafferented VNs, known to activate the central histaminergic system. In this study, we aimed to investigate the impact of pharmacological modulation of the central histaminergic system on balance function recovery and its underlying post-injury mechanisms in deafferented VN. For this purpose, we used a histamine analog, betahistine dihydrochloride (BD), which increases histamine synthesis and release in the VN through its histamine H3 autoreceptor antagonistic properties. BD treatment was tested in 3 animal groups: a UVN BD group subjected to unilateral vestibular neurectomy (UVN) treated orally during 10 days (50mg/kg/day), a UVN placebo group (control), and a SHAM group. We show for the first time, in a UVN rodent model, the effects of BD on the reduction of the vestibular syndrome and highlight new targets and impact of this drug at the cellular level. Indeed, the results show that treatment with BD significantly attenuates the number of astrocytes and microglia which are key components of neuroinflammation. BD also prioritizes the differentiation of neoformed cells towards a microglia phenotype. These results, which need to be confirmed and further investigated by identifying the histaminergic receptors responsible for this effect, may lead to new therapeutic targets in vestibular pathology.

The efficacy of early rehabilitation in enhancing vestibular compensation in mice with unilateral vestibular neurectomy by promoting cellular proliferation and glial reaction

Acute peripheral vestibular dysfunction is associated with a variety of postural and balance disturbances. Vestibular rehabilitation training (VRT) is widely acknowledged as an effective intervention for promoting vestibular compensation. Nevertheless, the broader implementation of early VRT is hindered by an incomplete understanding of its neurobiological mechanisms. Building upon prior research, the present study investigates the effects of early VRT on postural behavior and the cellular mechanisms within the medial vestibular nucleus (MVN) following unilateral vestibular neurectomy (UVN) in a murine model. Through the use of progressive motorized running wheel training, we assessed vestibular syndrome, motor function behaviors, and plasticity events, including cell proliferation and gliogenesis within the MVN. Our findings suggest that VRT facilitates the recovery of postural motor deficits during vestibular compensation, likely mediated by cell proliferation and glial responses, particularly the proliferation of microglia, in the MVN. Furthermore, we demonstrate that ultra-early rehabilitation training yields greater benefits for the long-term recovery of dynamic deficits following UVN. These results carry significant implications for the clinical implementation of early VRT in patients experiencing acute peripheral vestibular dysfunction.

Plastic Events of the Vestibular Nucleus: the Initiation of Central Vestibular Compensation

Vestibular compensation is a physiological response of the vestibular organs within the inner ear. This adaptation manifests during consistent exposure to acceleration or deceleration, with the vestibular organs incrementally adjusting to such changes. The molecular underpinnings of vestibular compensation remain to be fully elucidated, yet emerging studies implicate associations with neuroplasticity and signal transduction pathways. Throughout the compensation process, the vestibular sensory neurons maintain signal transmission to the central equilibrium system, facilitating adaptability through alterations in synaptic transmission and neuronal excitability. Notable molecular candidates implicated in this process include variations in ion channels and neurotransmitter profiles, as well as neuronal and synaptic plasticity, metabolic processes, and electrophysiological modifications. This study consolidates the current understanding of the molecular events in vestibular compensation, augments the existing research landscape, and evaluates contemporary therapeutic strategies. Furthermore, this review posits potential avenues for future research that could enhance our comprehension of vestibular compensation mechanisms.

Repeated balance exercise promotes cholinergic neuroprotection of the pedunculopontine nucleus in a progressive model of Parkinson's disease

Vestibular rehabilitation (VR) is a therapeutic approach that minimizes the impacts of balance alterations by enhancing the central vestibular compensation mechanism. The present study investigates the effect of repeated balance exercises on the central vestibular compensation mechanism in a reserpine-induced progressive model of parkinsonism in aged rats. Male Wistar rats were assigned to three cohort experiments: Exp 1: repeated balance exercises (narrow beam test) - performed every 48 h during 20 days; Exp 2: balance exercises performed on the 0th and 8th days; Exp 3: balance exercises performed only on the 0th and 20th days. For each experiment, the animals were divided into two groups (n = 7 per group): CTL (vehicle) and RES (reserpine 0.1 mg/kg). The animals received 4 (exp. 2) or 10 (exp 1 and 3) s.c. injections (0.1 mg/kg), one every 48 h. The cohorts were evaluated using catalepsy and open field tests (0th, 8th and 20th days). After completion of behavioral tests, the brains were analyzed for immunohistochemistry for tyrosine hydroxylase (TH) and choline acetyltransferase (ChAT). The RES group presented motor deficits in the catalepsy and open field tests on day 20, but not on day 8. There was no decrease in the number of TH neurons and terminals in the substantia nigra pars compacta (SNpc), ventral tegmental area (VTA) and dorsal striatum (DS) for animals from Exp. 2. However, a decrease was observed in the SNpc, VTA and striatum of animals from Exp 1 and Exp 3. In the balance beam test, the animals in the RES group showed a longer crossing time from day 8 to day 14 (Exp 1), on the 8th day (Exp 2) and on the 20th day (Exp. 3). This finding was correlated with a decrease in the number of ChAT immunoreactive cells in the pedunculopontine tegmental nucleus (PPN) for the animals that performed the dynamic balance test only once (Exp. 2 and 3), but no reduction was observed in the animals that performed the test repeatedly (Epx. 1). Thus, it was possible to verify that repeated exposure of the animals to balance assessment tasks potentiated the performance of the central vestibular compensation mechanism in the animal model of parkinsonism.

Application of clinical indicators in evaluating vestibular compensation efficacy in benign recurrent vestibular vertigo patients with short-term personalized vestibular rehabilitation

BACKGROUND

Short-term personalized vestibular rehabilitation (ST-PVR) can establish stable vestibular compensation. However, there is a lack of a clear definition for clinical indicators that can dynamically reflect the progress of vestibular rehabilitation (VR).

OBJECTIVE

To explore the clinical indicators suitable for evaluating the effectiveness of ST-PVR in treating benign recurrent vertigo (BRV).

METHODS

In total, 50 patients diagnosed with BRV were enrolled. All patients received the ST-PVR treatment program. At 2 and 4 weeks after rehabilitation, subjective scales, including the visual analogue scale (VAS), dizziness handicap inventory scale (DHI), activities-specific balance confidence scale (ABC) and generalized anxiety disorder (GAD-7) were assessed. Objective vestibular function tests were performed. VR grading was determined.

RESULTS

At 2 weeks after rehabilitation, significant enhancements were observed in VAS, DHI, ABC, GAD-7, UW, vHIT results, and VR grading scores (p < 0.05). The sensory organization test (SOT) results demonstrated statistically significant improvements at 2 weeks and 4 weeks after rehabilitation (p < 0.05).

CONCLUSION AND SIGNIFICANCE

Both subjective scales and partial examination results in objective assessment can serve as indicators to dynamically monitor the compensatory process of vestibular function in patients with BRV. The VR efficacy grading score, which incorporates the above indicators, allows for quantification of the changes that occur during the vestibular rehabilitation process.

Increased functional connectivity between default mode network and visual network potentially correlates with duration of residual dizziness in patients with benign paroxysmal positional vertigo

Objective

To assess changes in static and dynamic functional network connectivity (sFNC and dFNC) and explore their correlations with clinical features in benign paroxysmal positional vertigo (BPPV) patients with residual dizziness (RD) after successful canalith repositioning maneuvers (CRM) using resting-state fMRI.

Methods

We studied resting-state fMRI data from 39 BPPV patients with RD compared to 38 BPPV patients without RD after successful CRM. Independent component analysis and methods of sliding window and k-means clustering were adopted to investigate the changes in dFNC and sFNC between the two groups. Additionally, temporal features and meta-states were compared between the two groups. Furthermore, the associations between fMRI results and clinical characteristics were analyzed using Pearson's partial correlation analysis.

Results

Compared with BPPV patients without RD, patients with RD had longer duration of BPPV and higher scores of dizziness handicap inventory (DHI) before successful CRM. BPPV patients with RD displayed no obvious abnormal sFNC compared to patients without RD. In the dFNC analysis, patients with RD showed increased FNC between default mode network (DMN) and visual network (VN) in state 4, the FNC between DMN and VN was positively correlated with the duration of RD. Furthermore, we found increased mean dwell time (MDT) and fractional windows (FW) in state 1 but decreased MDT and FW in state 3 in BPPV patients with RD. The FW of state 1 was positively correlated with DHI score before CRM, the MDT and FW of state 3 were negatively correlated with the duration of BPPV before CRM in patients with RD. Additionally, compared with patients without RD, patients with RD showed decreased number of states and state span.

Conclusion

The occurrence of RD might be associated with increased FNC between DMN and VN, and the increased FNC between DMN and VN might potentially correlate with the duration of RD symptoms. In addition, we found BPPV patients with RD showed altered global meta-states and temporal features. These findings are helpful for us to better understand the underlying neural mechanisms of RD and potentially contribute to intervention development for BPPV patients with RD.

The Vestibular Nuclei: A Cerebral Reservoir of Stem Cells Involved in Balance Function in Normal and Pathological Conditions

In this review, we explore the intriguing realm of neurogenesis in the vestibular nuclei-a critical brainstem region governing balance and spatial orientation. We retrace almost 20 years of research into vestibular neurogenesis, from its discovery in the feline model in 2007 to the recent discovery of a vestibular neural stem cell niche. We explore the reasons why neurogenesis is important in the vestibular nuclei and the triggers for activating the vestibular neurogenic niche. We develop the symbiotic relationship between neurogenesis and gliogenesis to promote vestibular compensation. Finally, we examine the potential impact of reactive neurogenesis on vestibular compensation, highlighting its role in restoring balance through various mechanisms.

Histaminergic System and Vestibular Function in Normal and Pathological Conditions

Most neurotransmitter systems are represented in the central and peripheral vestibular system and are thereby involved both in normal vestibular signal processing and the pathophysiology of vestibular disorders. However, there is a special relationship between the vestibular system and the histaminergic system. The purpose of this review is to document how the histaminergic system interferes with normal and pathological vestibular function. In particular, we will discuss neurobiological mechanisms such as neuroinflammation that involve histamine to modulate and allow restoration of balance function in the situation of a vestibular insult. These adaptive mechanisms represent targets of histaminergic pharmacological compounds capable of restoring vestibular function in pathological situations. The clinical use of drugs targeting the histaminergic system in various vestibular disorders is critically discussed.

Advanced Dynamic Weight Bearing as an Observer-independent Measure of Hyperacute Hypersensitivity in Mice

Background

Standard methods assessing pain in rodents are often observer dependent, potentially resulting in biased outcomes. Advanced dynamic weight bearing (ADWB) offers an observer-independent approach that can provide objective, reliable data in preclinical pain research.

Aims

The aim of this study was to characterize the use of ADWB in assessing murine responses to allyl isothiocyanate (AITC)-induced hyperacute hypersensitivity and identify best practices for use of the device.

Methods

Male C57BL/6J mice received intraplantar injections of saline or 0.1% AITC solution and were assessed using the ADWB system; simultaneous observer-dependent durations of paw licking and biting were measured. ADWB data were analyzed using the proprietary software from Bioseb and correlated to observer-dependent results, with parameters assessed to optimize data collected.

Results

ADWB detected pain-directed changes in weight and surface area distribution in AITC-treated mice, with paw weight and surface area placement correlating to paw licking and biting. Optimization of adjustable threshold parameters allowed for reduced coefficients of variability and increased duration of validated data.

Conclusions

The ADWB assay provides an efficient and unbiased measure of chemical-induced hyperacute hypersensitivity in mice. ADWB detection parameters influence amount of validated data and variability, a consideration for data analysis in future studies.

[Animal models of balance pathologies: New tools to study peripheral vestibulopathies]

The different types of peripheral vestibulopathies (PVs) or peripheral vestibular disorders (PVDs) are essentially diagnosed on the basis of their clinical expression. The heterogeneity of vestibular symptoms makes it difficult to stratify patients for therapeutic management. Animal models of PVs are a good mean to search for clinical evaluation criteria allowing to objectively analyze the kinetics of expression of the vertigo syndrome and to evaluate the benefits of therapeutic strategies, whether they are pharmacological or rehabilitative. The question of the predictability of these animal models is therefore crucial for the identification of behavioral and biological biomarkers that could then be used in the human clinic. In this review, we propose an overview of the different animal models of PVs, and discuss their relevance for the understanding of the underlying pathophysiological mechanisms and the development of new and more targeted therapeutic approaches.

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.

Oxytocin Disturbs Vestibular Compensation and Modifies Behavioral Strategies in a Rodent Model of Acute Vestibulopathy

Unilateral inner ear injury is followed by behavioral recovery due to central vestibular compensation. The therapeutic effect of oxytocin (OT) on vestibular compensation was investigated by behavioral testing in a rat model of unilateral vestibular neurectomy (UVN). Animals in the oxytocin group (UVN-OT) exhibited delayed vestibular compensation on the qualitative scale of vestibular deficits and aggravated static postural deficits (bearing surface) compared to animals in the NaCl group (UVN-NaCl). Surprisingly, oxytocin-treated animals adopt a different postural strategy than untreated animals. Instead of shifting their weight to the ipsilesional paws (left front and hind paws), they shift their weight to the front paws (right and left) without modification along the lateral axis. Furthermore, some locomotor strategies of the animals to compensate for the vestibular loss are also altered by oxytocin treatment. UVN-OT animals do not induce an increase in the distance traveled, their mean velocity is lower than that in the control group, and the ipsilesional body rotations do not increase from 7 to 30 days after UVN. This study reveals that oxytocin treatment hinders the restoration of some postural and locomotor deficits while improving others following vestibular lesions. The mechanisms of the action of oxytocin that support these behavioral changes remain to be elucidated.

What Predictability for Animal Models of Peripheral Vestibular Disorders?

The different clinical entities grouped under the term peripheral vestibulopathies (PVs) or peripheral vestibular disorders (PVDs) are distinguished mainly based on their symptoms/clinical expression. Today, there are very few commonly accepted functional and biological biomarkers that can confirm or refute whether a vestibular disorder belongs to a precise classification. Consequently, there is currently a severe lack of reliable and commonly accepted clinical endpoints, either to precisely follow the course of the vertigo syndrome of vestibular origin or to assess the benefits of therapeutic approaches, whether they are pharmacological or re-educational. Animal models of PV are a good means to identify biomarkers that could subsequently be exploited in human clinical practice. The question of their predictability is therefore crucial. Ten years ago, we had already raised this question. We revisit this concept today in order to take into account the animal models of peripheral vestibular pathology that have emerged over the last decade, and the new technological approaches available for the behavioral assessment of vestibular syndrome in animals and its progression over time. The questions we address in this review are the following: are animal models of PV predictive of the different types and stages of vestibular pathologies, and if so, to what extent? Are the benefits of the pharmacological or reeducational therapeutic approaches achieved on these different models of PV (in particular the effects of attenuation of the acute vertigo, or acceleration of central compensation) predictive of those expected in the vertiginous patient, and if so, to what extent?

Vestibular Nuclei: A New Neural Stem Cell Niche?

We previously reported adult reactive neurogliogenesis in the deafferented vestibular nuclei following unilateral vestibular neurectomy (UVN) in the feline and the rodent model. Recently, we demonstrated that UVN induced a significant increase in a population of cells colocalizing the transcription factor sex determining region Y-box 2 (SOX2) and the glial fibrillary acidic protein (GFAP) three days after the lesion in the deafferented medial vestibular nucleus. These two markers expressed on the same cell population could indicate the presence of lesion-reactive multipotent neural stem cells in the vestibular nuclei. The aim of our study was to provide insight into the potential neurogenic niche status of the vestibular nuclei in physiological conditions by using specific markers of stem cells (Nestin, SOX2, GFAP), cell proliferation (BrdU) and neuronal differentiation (NeuN). The present study confirmed the presence of quiescent and activated adult neural stem cells generating some new neurons in the vestibular nuclei of control rats. These unique features provide evidence that the vestibular nuclei represent a novel NSC site for the generation of neurons and/or glia in the adult rodent under physiological conditions.

Frontiers in Neurogenesis

One of the most intriguing dogmas in neurosciences-the empirical lack of brain neuronal regeneration in adulthood onwards to late life-began to be debunked initially by research groups focused on understanding postnatal (early days/weeks of murine and guinea pigs) neurodevelopmental and neuroplastic events [...].

Effects of Diet and Lifestyle on Audio-Vestibular Dysfunction in the Elderly: A Literature Review

BACKGROUND

The world's age-related health concerns continue to rise. Audio-vestibular disorders, such as hearing loss, tinnitus, and vertigo, are common complaints in the elderly and are associated with social and public health burdens. Various preventative measures can ease their impact, including healthy food consumption, nutritional supplementation, and lifestyle modification. We aim to provide a comprehensive summary of current possible strategies for preventing the age-related audio-vestibular dysfunction.

METHODS

A PubMed, Embase, and Cochrane review databases search was conducted to identify the relationship between diet, lifestyle, and audio-vestibular dysfunction. "Diet", "nutritional supplement", "lifestyle", "exercise", "physical activity", "tinnitus", "vertigo" and "age-related hearing loss" were used as keywords.

RESULTS

Audio-vestibular dysfunction develops and progresses as a result of age-related inflammation and oxidative stress. Diets with anti-inflammatory and antioxidant effects have been proposed to alleviate this illness. A high-fat diet may induce oxidative stress and low protein intake is associated with hearing discomfort in the elderly. Increased carbohydrate and sugar intake positively correlate with the incidence of audio-vestibular dysfunction, whereas a Mediterranean-style diet can protect against the disease. Antioxidants in the form of vitamins A, C, and E; physical activity; good sleep quality; smoking cessation; moderate alcohol consumption; and avoiding noise exposure are also beneficial.

CONCLUSIONS

Adequate diet or nutritional interventions with lifestyle modification may protect against developing audio-vestibular dysfunction in elderly individuals.

Microglial Dynamics Modulate Vestibular Compensation in a Rodent Model of Vestibulopathy and Condition the Expression of Plasticity Mechanisms in the Deafferented Vestibular Nuclei

Unilateral vestibular loss (UVL) induces a vestibular syndrome composed of posturo-locomotor, oculomotor, vegetative, and perceptivo-cognitive symptoms. With time, these functional deficits progressively disappear due to a phenomenon called vestibular compensation, known to be supported by the expression in the deafferented vestibular nuclei (VNs) of various adaptative plasticity mechanisms. UVL is known to induce a neuroinflammatory response within the VNs, thought to be caused by the structural alteration of primary vestibular afferents. The acute inflammatory response, expressed in the deafferented VNs was recently proven to be crucial for the expression of the endogenous plasticity supporting functional recovery. Neuroinflammation is supported by reactive microglial cells, known to have various phenotypes with adverse effects on brain tissue. Here, we used markers of pro-inflammatory and anti-inflammatory phenotypes of reactive microglia to study microglial dynamics following a unilateral vestibular neurectomy (UVN) in the adult rat. In addition, to highlight the role of acute inflammation in vestibular compensation and its underlying mechanisms, we enhanced the inflammatory state of the deafferented VNs using systemic injections of lipopolysaccharide (LPS) during the acute phase after a UVN. We observed that the UVN induced the expression of both M1 proinflammatory and M2 anti-inflammatory microglial phenotypes in the deafferented VNs. The acute LPS treatment exacerbated the inflammatory reaction and increased the M1 phenotype while decreasing M2 expression. These effects were associated with impaired postlesional plasticity in the deafferented VNs and exacerbated functional deficits. These results highlight the importance of a homeostatic inflammatory level in the expression of the adaptative plasticity mechanisms underlying vestibular compensation. Understanding the rules that govern neuroinflammation would provide therapeutic leads in neuropathologies associated with these processes.

In vivo neuroplasticity in vestibular animal models

An acute unilateral vestibulopathy leads to symptoms of vestibular tone imbalance, which gradually decrease over days to weeks due to central vestibular compensation. Animal models of acute peripheral vestibular lesions are optimally suited to investigate the mechanisms underlying this lesion-induced adaptive neuroplasticity. Previous studies applied ex vivo histochemical techniques or local in vivo electrophysiological recordings mostly in the vestibular nucleus complex to delineate the mechanisms involved. Recently, the use of imaging methods, such as positron emission tomography (PET) or magnetic resonance imaging (MRI), in vestibular animal models have opened a complementary perspective by depicting whole-brain structure and network changes of neuronal activity over time and in correlation to behaviour. Here, we review recent multimodal imaging studies in vestibular animal models with a focus on PET-based measurements of glucose metabolism, glial activation and synaptic plasticity. [18F]-FDG-PET studies indicate dynamic alterations of regional glucose metabolism in brainstem-cerebellar, thalamic, cortical sensory and motor, as well as limbic areas starting early after unilateral labyrinthectomy (UL) in the rat. Sequential whole-brain analysis of the metabolic connectome during vestibular compensation shows a significant increase of connections mostly in the contralesional hemisphere after UL, which reaches a maximum at day 3 and thereby parallels the course of vestibular recovery. Glial activation in the ipsilesional vestibular nerve and nucleus peak between days 7 and 15 after UL. Synaptic density in brainstem-cerebellar circuits decreases until 8 weeks after UL, while it increases in frontal, motor and sensory cortical areas. We finally report how pharmacological compounds modulate the functional and structural plasticity mechanisms during vestibular compensation.

L-Thyroxine Improves Vestibular Compensation in a Rat Model of Acute Peripheral Vestibulopathy: Cellular and Behavioral Aspects

Unilateral vestibular lesions induce a vestibular syndrome, which recovers over time due to vestibular compensation. The therapeutic effect of L-Thyroxine (L-T4) on vestibular compensation was investigated by behavioral testing and immunohistochemical analysis in a rat model of unilateral vestibular neurectomy (UVN). We demonstrated that a short-term L-T4 treatment reduced the vestibular syndrome and significantly promoted vestibular compensation. Thyroid hormone receptors (TRα and TRβ) and type II iodothyronine deiodinase (DIO2) were present in the vestibular nuclei (VN), supporting a local action of L-T4. We confirmed the T4-induced metabolic effects by demonstrating an increase in the number of cytochrome oxidase-labeled neurons in the VN three days after the lesion. L-T4 treatment modulated glial reaction by decreasing both microglia and oligodendrocytes in the deafferented VN three days after UVN and increased cell proliferation. Survival of newly generated cells in the deafferented vestibular nuclei was not affected, but microglial rather than neuronal differentiation was favored by L-T4 treatment.