Anxiety and otovestibular disorders: linking behavioral phenotypes in men and mice

Vertigoheel improves central vestibular compensation after unilateral peripheral vestibulopathy in rats

The aim of this study was to assess the effect of Vertigoheel on central vestibular compensation and cognitive deficits in rats subjected to peripheral vestibular loss. Young adult male Long Evans rats were subjected to bilateral vestibular insults through irreversible sequential ototoxic destructions of the vestibular sensory organs. Vestibular syndrome characteristics were monitored at several time points over days and weeks following the sequential insults, using a combination of behavioral assessment paradigms allowing appreciation of patterns of change in static and dynamic deficits, together with spatial navigation, learning, and memory processes. Vertigoheel administered intraperitoneally significantly improved maximum body velocity and not moving time relative to its vehicle control on days 2 and 3 and on day 2, respectively, after unilateral vestibular lesion (UVL). It also significantly improved postural control relative to its vehicle 1 day after UVL. Conversely, Vertigoheel did not display any significant effect vs. vehicle on the severity of the syndrome, nor on the time course of other examined parameters, such as distance moved, mean body velocity, meander, and rearing. Spatial cognition testing using Y- and T-maze and eight-radial arm maze did not show any statistically significant difference between Vertigoheel and vehicle groups. However, Vertigoheel potentially enhanced the speed of learning in sham animals. Evaluating Vertigoheel's effect on thigmotaxis during the open-field video tracking test revealed no significant difference between Vertigoheel and its vehicle control groups suggesting that Vertigoheel does not seem to induce sedative or anxiolytic effects that could negatively affect vestibular and memory function. Present observations reveal that Vertigoheel improves central vestibular compensation following the unilateral peripheral vestibular loss as demonstrated by improvement of specific symptoms.

Effects of acquired vestibular pathology on the organization of mouse exploratory behavior

Rodent open field behavior is highly organized and occurs spontaneously in novel environments. This organization is disrupted in mice with vestibular pathology, suggesting vestibular signals provide important contributions to this behavior. A caveat to this interpretation is that previous studies have investigated open field behavior in adult mice with congenital vestibular dysfunction, and the observed deficits may have resulted from developmental changes instead of the lack of vestibular signals. To determine which aspects of open field behavior depend specifically on vestibular signals, mouse movement organization was examined under dark and light conditions at two time points, 1 and 2 months, after bilateral chemical labyrinthectomy. Our results show that acquired vestibular damage selectively disrupted the organization of open field behavior. Access to visual environmental cues attenuated, but did not eliminate, these significant group differences. Improvement in movement organization from the first to the second testing session was limited to progression path circuity. These observations provide evidence for the role of the vestibular system in maintaining spatial orientation and establishes a foundation to investigate neuroplasticity in brain systems that process self-movement information.

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.

Electrical Stimulation Normalizes c-Fos Expression in the Deep Cerebellar Nuclei of Depressive-like Rats: Implication of Antidepressant Activity

The electrical stimulation of specific brain targets has been shown to induce striking antidepressant effects. Despite that recent data have indicated that cerebellum is involved in emotional regulation, the mechanisms by which stimulation improved mood-related behaviors in the cerebellum remained largely obscure. Here, we investigated the stimulation effects of the ventromedial prefrontal cortex (vmPFC), nucleus accumbens (NAc), and lateral habenular nucleus on the c-Fos neuronal activity in various deep cerebellar and vestibular nuclei using the unpredictable chronic mild stress (CMS) animal model of depression. Our results showed that stressed animals had increased number of c-Fos cells in the cerebellar dentate and fastigial nuclei, as well as in the spinal vestibular nucleus. To examine the stimulation effects, we found that vmPFC stimulation significantly decreased the c-Fos activity within the cerebellar fastigial nucleus as compared to the CMS sham. Similarly, there was also a reduction of c-Fos expression in the magnocellular part of the medial vestibular nucleus in vmPFC- and NAc core-stimulated animals when compared to the CMS sham. Correlational analyses showed that the anxiety measure of home-cage emergence escape latency was positively correlated with the c-Fos neuronal activity of the cerebellar fastigial and magnocellular and parvicellular parts of the interposed nuclei in CMS vmPFC-stimulated animals. Interestingly, there was a strong correlation among activation in these cerebellar nuclei, indicating that the antidepressant-like behaviors were possibly mediated by the vmPFC stimulation-induced remodeling within the forebrain-cerebellar neurocircuitry.

An improved procedure for integrated behavioral z-scoring illustrated with modified Hole Board behavior of male inbred laboratory mice

BACKGROUND

Guilloux et al. introduced: integrated behavioral z-scoring, a method for behavioral phenotyping of mice. Using this method multiple ethological variables can be combined to show an overall description of a certain behavioral dimension or motivational system. However, a problem may occur when the control group used for the calculation has a standard deviation of zero or when no control group is present to act as a reference group.

NEW METHOD

In order to solve these problems, an improved procedure is suggested: taking the pooled data as reference. For this purpose a behavioral study with male mice from three inbred strains was carried out. The integrated behavioral z-scoring methodology was applied, thereby taking five different reference group options. The outcome regarding statistical significance and practical importance was compared.

RESULTS

Significant effects and effect sizes were influenced by the choice of the reference group. In some cases it was impossible to use a certain population and condition, because one or more behavioral variables in question had a standard deviation of zero. Based on the improved method, male mice from the three inbred strains differed regarding activity and anxiety.

COMPARISON WITH EXISTING METHOD

Taking the method described by Guilloux et al. as basis, the present procedure improved the generalizability to all types of experimental designs in animal behavioral research.

CONCLUSIONS

To solve the aforementioned problems and to avoid getting the diagnosis of data manipulation, the pooled data (combining the data from all experimental groups in a study) as reference option is recommended.

New mouse model for inducing and evaluating unilateral vestibular deafferentation syndrome

BACKGROUND

Unilateral vestibular deafferentation syndrome (uVDS) holds a particular place in the vestibular pathology domain. Due to its suddenness, the violence of its symptoms that often result in emergency hospitalization, and its associated original neurophysiological properties, this syndrome is a major source of questioning for the otoneurology community. Also, its putative pathogenic causes remain to be determined. There is currently a strong medical need for the development of targeted and effective countermeasures to improve the therapeutic management of uVDS.

NEW METHODS

The present study reports the development of a new mouse model for inducing and evaluating uVDS. Both the method for generating controlled excitotoxic-type peripheral vestibular damages, through transtympanic administration of the glutamate receptors agonist kainate (TTK), and the procedure for evaluating the ensuing clinical signs are detailed.

COMPARISON WITH EXISTING METHODS

Through extensive analysis of the clinical symptoms characteristics, this new animal model provides the opportunity to better follow the temporal evolution of various uVDS specific symptoms, while better appreciating the different phases that composed this syndrome.

RESULTS

The uVDS evoked in the TTK mouse model displays two main phases distinguishable by their kinetics and amplitudes. Several parameters of the altered vestibular behaviour mimic those observed in the human syndrome.

CONCLUSION

This new murine model brings concrete information about how uVDS develops and how it affects global behaviour. In addition, it opens new opportunity to decipher the etiopathological substrate of this pathology by authorizing the use of genetically modified mouse models.

The Severity of Vestibular Dysfunction in Deafness as a Determinant of Comorbid Hyperactivity or Anxiety

Attention-deficit/hyperactivity disorder (ADHD) and anxiety-related disorders occur at rates 2-3 times higher in deaf compared with hearing children. Potential explanations for these elevated rates and the heterogeneity of behavioral disorders associated with deafness have usually focused on socio-environmental rather than biological effects. Children with the 22q11.2 deletion or duplication syndromes often display hearing loss and behavioral disorders, including ADHD and anxiety-related disorders. Here, we show that mouse mutants with either a gain or loss of function of the T-Box transcription factor gene, Tbx1, which lies within the 22q11.2 region and is responsible for most of the syndromic defects, exhibit inner ear defects and hyperactivity. Furthermore, we show that (1) inner ear dysfunction due to the tissue-specific loss of Tbx1 or Slc12a2, which encodes a sodium-potassium-chloride cotransporter and is also necessary for inner ear function, causes hyperactivity; (2) vestibular rather than auditory failure causes hyperactivity; and (3) the severity rather than the age of onset of vestibular dysfunction differentiates whether hyperactivity or anxiety co-occurs with inner ear dysfunction. Together, these findings highlight a biological link between inner ear dysfunction and behavioral disorders and how sensory abnormalities can contribute to the etiology of disorders traditionally considered of cerebral origin.SIGNIFICANCE STATEMENT This study examines the biological rather than socio-environmental reasons why hyperactivity and anxiety disorders occur at higher rates in deaf individuals. Using conditional genetic approaches in mice, the authors show that (1) inner ear dysfunction due to either Tbx1 or Slc12a2 mutations cause hyperactivity; (2) it is vestibular dysfunction, which frequently co-occurs with deafness but often remains undiagnosed, rather than auditory dysfunction that causes hyperactivity and anxiety-related symptoms; and (3) the severity of vestibular dysfunction can predict whether hyperactivity or anxiety coexist with inner ear dysfunction. These findings suggest a need to evaluate vestibular function in hearing impaired individuals, especially those who exhibit hyperactive and anxiety-related symptoms.

Effects of light regime and substrain on behavioral profiles of male C57BL/6 mice in three tests of unconditioned anxiety

Substrains of the C57BL/6 inbred mouse are widely used in genetic, behavioral and physiological research, as well as models for human disease. Throughout, the choice of the respective substrain can have a large influence on experimental results. Likewise, the conditions under which experiments are performed, such as the light regime, can significantly affect the outcome of an experiment, especially when aiming at experimental behavior. Here, two commonly used mouse substrains, C57BL/6JOlaHsd and C57BL/6NCrl, were housed under either a conventional or a reverse light regime and were tested in either the light phase or the dark phase, respectively. All animals were exposed to three unconditioned anxiety-related behavior set-ups: the modified Hole Board test, the light-dark box and the elevated plus maze. Significant substrain and light regime effects were found in all three behavioral tests, with some of the latter being substrain and test specific. This signifies the importance of the choice of substrain used in for example, a mouse knockout experiment studying behavior, also in relation to light regime under which the animals are tested.

The role of GABAB receptors in the vestibular oculomotor system in mice

Systemic administration of a gamma-amino butyric acid type B (GABAB) receptor agonist, baclofen, affects various physiological and psychological processes. To date, the effects on oculomotor system have been well characterized in primates, however those in mice have not been explored. In this study, we investigated the effects of baclofen focusing on vestibular-related eye movements. Two rotational paradigms, i.e. sinusoidal rotation and counter rotation were employed to stimulate semicircular canals and otolith organs in the inner ear. Experimental conditions (dosage, routes and onset of recording) were determined based on the prior studies exploring the behavioral effects of baclofen in mice. With an increase in dosage, both canal and otolith induced ocular responses were gradually affected. There was a clear distinction in the drug sensitivity showing that eye movements derived from direct vestibulo-ocular reflex pathways were relatively unaltered, while the responses through higher-order neural networks in the vestibular system were substantially decreased. These findings were consistent with those observed in primates suggesting a well-conserved role of GABAB receptors in the oculomotor system across frontal-eyed and lateral-eyed animals. We showed here a previously unrecognized effect of baclofen on the vestibular oculomotor function in mice. When interpreting general animal performance under the drug, the potential contribution of altered balance system should be taken into consideration.

Vestibular Stimulation for Stress Management in Students

INTRODUCTION

Although several methods are developed to alleviate stress among college students, logistic limitations in adopting them have limited their utility.

AIM

Hence, we aimed to test a very practical approach to alleviate stress among college students by achieving vestibular stimulation using swings.

MATERIALS AND METHODS

In this study 60 male and female participants were randomly assigned into vestibular stimulation or control groups. Depression, anxiety, stress scores, sleep quality, heart rate, blood pressure, Autonomic functions, respiratory, haematological, cognitive function, Quality of life were recorded before and after 1(st), 7(th), 14(th), 21(st), 28(th) days of vestibular stimulation.

RESULTS

STAI S and STAI T scores were significantly improved on day 28(th) following vestibular stimulation. Diastolic and mean arterial blood pressure were significantly decreased and remained within normal limits in vestibular group on day 28(th) following vestibular stimulation. Postural fall in blood pressure was significantly improved on day 14 onwards, following vestibular stimulation. Respiratory rate was significantly improved on day 7 onwards, following vestibular stimulation. PSQI sleep disturbance, PSQI sleep latency, PSQI total score and bleeding time was significantly improved following vestibular stimulation.

CONCLUSION

Our study supports the adoption of vestibular stimulation for stress management. Hence, placement of swings in college campuses must be considered, which may be a simple approach to alleviate stress among college students.

Quality-of-life for individuals with a vestibular impairment following an acquired brain injury (ABI); the clients' perspective

PRIMARY OBJECTIVE

To investigate how a vestibular deficit following an acquired brain injury (ABI) affects an individuals' quality-of-life.

RESEARCH DESIGN

A qualitative exploratory design.

PARTICIPANTS

Nine community dwelling individuals who experienced significant symptoms and limitations as a result of their vestibular deficits.

METHODS

The individuals participated in face-to-face interviews with open ended questions. Data was analysed initially using a case study research approach, exploring the experience for each individual and then cross-case analysis to determine common themes for the group with the assistance of nVivo 10 qualitative analysis software.

RESULTS

Thematic analysis determined four main themes arising from the interviews; (1) validation, (2) definitive diagnosis is more difficult amongst an array of ABI symptoms, (3) vestibular adaptation is more difficult in the presence of an ABI and (4) emotional and social.

CONCLUSION

Individuals who suffer a brain injury and experience vestibular symptoms as part of their overall presentation are not diagnosed in a timely manner, with individuals, their families, associates and even health professionals feeling uncertain of the legitimacy of their reported symptoms. It is important that all patients who experience an acquired brain injury are screened for vestibular impairment and, if necessary, receive vestibular rehabilitation including explanation and education.

Visuo-vestibular contributions to anxiety and fear

The interactive roles of the visual and vestibular systems allow for postural control within boundaries of perceived safety. In specific circumstances, visual vestibular and postural interactions act as a cue that trigger fear, similarly to what occurs in motion sickness. Unusual patterns of visuo-vestibular interaction that emerge without warning can elicit fear, which can then become associated to a certain stimuli or situation, creating a CS-US association, (i.e., phobia), or can emerge without warning but also without becoming associated to a particular concomitant event (i.e., panic). Depending on the individual sensitivity to visuo-vestibular unusual patterns and its impact in postural control, individuals will be more or less vulnerable to develop these disorders. As such, the mechanism we here propose is also sufficient to explain the lack of certain fears albeit exposure. Following this rationale, a new subcategory of anxiety disorders, named visuo-vestibular fears can be considered. This model brings important implications for developmental and evolutionary psychological science, and invites to place visuo-vestibular fears in a particular subtype or specification within the DSM-5 diagnostic criteria.

Modulation of human vestibular reflexes with increased postural threat

Anxiety and arousal have been shown to facilitate human vestibulo-ocular reflexes, presumably through direct neural connections between the vestibular nuclei and emotional processing areas of the brain. However, the effects of anxiety, fear and arousal on balance-relevant vestibular reflexes are currently unknown. The purpose of this study was to manipulate standing height to determine whether anxiety and fear can modulate the direct relationship between vestibular signals and balance reflexes during stance. Stochastic vestibular stimulation (SVS; 2-25 Hz) was used to evoke ground reaction forces (GRF) while subjects stood in both LOW and HIGH surface height conditions. Two separate experiments were conducted to investigate the SVS-GRF relationship, in terms of coupling (coherence and cumulant density) and gain, in the medio-lateral (ML) and antero-posterior (AP) directions. The short- and medium-latency cumulant density peaks were both significantly increased in the ML and AP directions when standing in HIGH, compared to LOW, conditions. Likewise, coherence was statistically greater between 4.3 Hz and 6.7 Hz in the ML, and between 5.5 and 17.7 Hz in the AP direction. When standing in the HIGH condition, the gain of the SVS-GRF relationship was increased 81% in the ML direction, and 231% in the AP direction. The significant increases in coupling and gain observed in both experiments demonstrate that vestibular-evoked balance responses are augmented in states of height-induced postural threat. These data support the possibility that fear or anxiety-mediated changes to balance control are affected by altered central processing of vestibular information.

Rearing in enriched environment increases parvalbumin-positive small neurons in the amygdala and decreases anxiety-like behavior of male rats

BACKGROUND

Early life experiences including physical exercise, sensory stimulation, and social interaction can modulate development of the inhibitory neuronal network and modify various behaviors. In particular, alteration of parvalbumin-expressing neurons, a gamma-aminobutyric acid (GABA)ergic neuronal subpopulation, has been suggested to be associated with psychiatric disorders. Here we investigated whether rearing in enriched environment could modify the expression of parvalbumin-positive neurons in the basolateral amygdala and anxiety-like behavior.

RESULTS

Three-week-old male rats were divided into two groups: those reared in an enriched environment (EE rats) and those reared in standard cages (SE rats). After 5 weeks of rearing, the EE rats showed decreased anxiety-like behavior in an open field than the SE rats. Under another anxiogenic situation, in a beam walking test, the EE rats more quickly traversed an elevated narrow beam. Anxiety-like behavior in the open field was significantly and negatively correlated with walking time in the beam-walking test. Immunohistochemical tests revealed that the number of parvalbumin-positive neurons significantly increased in the basolateral amygdala of the EE rats than that of the SE rats, while the number of calbindin-D28k-positive neurons did not change. These parvalbumin-positive neurons had small, rounded soma and co-expressed the glutamate decarboxylase (GAD67). Furthermore, the number of parvalbumin-positive small cells in the basolateral amygdala tended to positively correlate with emergence in the center arena of the open field and negatively correlated with walking time in the beam walking test.

CONCLUSION

Rearing in the enriched environment augmented the number of parvalbumin-containing specific inhibitory neuron in the basolateral amygdala, but not that of calbindin-containing neuronal phenotype. Furthermore, the number of parvalbumin-positive small neurons in the basolateral amygdala was negatively correlated with walking time in the beam walking test and tended to be positively correlated with activity in the center arena in the open field test. The results suggest that rearing in the enriched environment augmented parvalbumin-positive specific neurons in the basolateral amygdala, which induced behavioral plasticity that was reflected by a decrease in anxiety-like behavior in anxiogenic situations.

Potential translational targets revealed by linking mouse grooming behavioral phenotypes to gene expression using public databases

Rodent self-grooming is an important, evolutionarily conserved behavior, highly sensitive to pharmacological and genetic manipulations. Mice with aberrant grooming phenotypes are currently used to model various human disorders. Therefore, it is critical to understand the biology of grooming behavior, and to assess its translational validity to humans. The present in-silico study used publicly available gene expression and behavioral data obtained from several inbred mouse strains in the open-field, light-dark box, elevated plus- and elevated zero-maze tests. As grooming duration differed between strains, our analysis revealed several candidate genes with significant correlations between gene expression in the brain and grooming duration. The Allen Brain Atlas, STRING, GoMiner and Mouse Genome Informatics databases were used to functionally map and analyze these candidate mouse genes against their human orthologs, assessing the strain ranking of their expression and the regional distribution of expression in the mouse brain. This allowed us to identify an interconnected network of candidate genes (which have expression levels that correlate with grooming behavior), display altered patterns of expression in key brain areas related to grooming, and underlie important functions in the brain. Collectively, our results demonstrate the utility of large-scale, high-throughput data-mining and in-silico modeling for linking genomic and behavioral data, as well as their potential to identify novel neural targets for complex neurobehavioral phenotypes, including grooming.

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.

Performance in anxiety and spatial memory tests following bilateral vestibular loss in the rat and effects of anxiolytic and anxiogenic drugs

Vestibular dysfunction in humans is associated with anxiety and cognitive disorders. However, various animal studies of the effects of vestibular loss have yielded conflicting results, from reduced anxiety to increased anxiety, depending on the particular model of vestibular dysfunction and the anxiety test used. In this study we revisited the question of whether rats with surgical bilateral vestibular deafferentation (BVD) exhibit changes in anxiety-related behaviour by testing them in the open field maze (OFM), elevated plus maze (EPM) and elevated T maze (ETM) in the presence of a non-sedating anxiolytic drug, buspirone, or an anxiogenic drug, FG-7142. We also tested the animals in a spatial T maze (STM) in order to evaluate their cognitive function under the same set of conditions. We found that BVD animals exhibited increased locomotor activity (P≤0.003), reduced supported and unsupported rearing (P≤0.02 and P≤0.000, respectively) and reduced thigmotaxis (P≤0.000) in the OFM, which for the most part the drugs did not modify. By contrast, there were no significant differences between BVD and sham control animals in the EPM and the BVD animals exhibited a marginally longer escape latency in the ETM (P≤0.03), with no change in avoidance latency. In the STM, the BVD animals demonstrated a large and significant decrease in accuracy compared to the sham control animals (P≤0.000), which was not affected by drug treatment. These results have replicated previous findings regarding increased locomotor activity, reduced rearing and thigmotaxis in the OFM, and impaired performance in the STM. However, they failed to replicate some previous results obtained using the EPM and ETM. Overall, they do not support the hypothesis that BVD animals exhibit increased anxiety-like behaviour and suggest that the cognitive deficits may be independent of the emotional effects of vestibular loss.

Influence of anxiety in spatial memory impairments related to the loss of vestibular function in rat

It is now well established that vestibular information plays an important role in spatial memory processes. Although vestibular lesions induce anxiety in humans, this finding remains controversial in rodents. However, it is possible that anxiety-related behavior is associated with spatial memory impairments after vestibular lesions. We aimed to evaluate anxiety-like behavior and the effect of an anxiolytic treatment during a complex spatial memory task in a rat model of compensated bilateral vestibular lesions. Adult rats were divided into four groups, with or without vestibular lesions and, treated or untreated by diazepam. The vestibular lesion was performed by transtympanic injection of arsanilate and compared to transtympanic saline injection. Diazepam or saline was administered 1h before each test or learning session. Vestibular-lesioned rats exhibited anxiety-like behavior which was decreased with diazepam. Spatial memory performance was similar in control-treated and untreated groups, suggesting no effect on memory at the dose of diazepam used. Spatial memory performances were not modified by anxiolytic drug treatment in vestibular-lesioned rats compared to vestibular-lesioned rats without drug treatment. We conclude that bilateral vestibular lesions in rats induced anxiety-like behavior which was unrelated to spatial memory impairment and was probably specifically related to the loss of vestibular information.

Targeting ASIC3 for pain, anxiety, and insulin resistance

The acid-sensing ion channel 3 (ASIC3) is a pH sensor that responds to mild extracellular acidification and is predominantly expressed in nociceptors. There is much interest in targeting ASIC3 to relieve pain associated with tissue acidosis, and selective drugs targeting ASIC3 have been used to relieve acid-evoked pain in animal models and human studies. There is accumulating evidence that ASIC3 is widely expressed in many neuronal and non-neuronal cells, such as neurons in the brain and adipose cells, albeit to a lesser extent than in nociceptors. Asic3-knockout mice have reduced anxiety levels and enhanced insulin sensitivity, suggesting that antagonizing ASIC3 has additional benefits. This view is tempered by recent studies suggesting that Asic3-knockout mice may experience cardiovascular disturbances. Due to the development of ASIC3 antagonists as analgesics, we review here the additional benefits, safety, risks, and strategy associated with antagonizing ASIC3 function.

A noncoding point mutation of Zeb1 causes multiple developmental malformations and obesity in Twirler mice

Heterozygous Twirler (Tw) mice develop obesity and circling behavior associated with malformations of the inner ear, whereas homozygous Tw mice have cleft palate and die shortly after birth. Zeb1 is a zinc finger protein that contributes to mesenchymal cell fate by repression of genes whose expression defines epithelial cell identity. This developmental pathway is disrupted in inner ears of Tw/Tw mice. The purpose of our study was to comprehensively characterize the Twirler phenotype and to identify the causative mutation. The Tw/+ inner ear phenotype includes irregularities of the semicircular canals, abnormal utricular otoconia, a shortened cochlear duct, and hearing loss, whereas Tw/Tw ears are severely malformed with barely recognizable anatomy. Tw/+ mice have obesity associated with insulin-resistance and have lymphoid organ hypoplasia. We identified a noncoding nucleotide substitution, c.58+181G>A, in the first intron of the Tw allele of Zeb1 (Zeb1^Tw). A knockin mouse model of c.58+181G>A recapitulated the Tw phenotype, whereas a wild-type knockin control did not, confirming the mutation as pathogenic. c.58+181G>A does not affect splicing but disrupts a predicted site for Myb protein binding, which we confirmed in vitro. In comparison, homozygosity for a targeted deletion of exon 1 of mouse Zeb1, Zeb1^ΔEx1, is associated with a subtle abnormality of the lateral semicircular canal that is different than those in Tw mice. Expression analyses of E13.5 Twirler and Zeb1^ΔEx1 ears confirm that Zeb1^ΔEx1 is a null allele, whereas Zeb1^Tw RNA is expressed at increased levels in comparison to wild-type Zeb1. We conclude that a noncoding point mutation of Zeb1 acts via a gain-of-function to disrupt regulation of Zeb1^Tw expression, epithelial-mesenchymal cell fate or interactions, and structural development of the inner ear in Twirler mice. This is a novel mechanism underlying disorders of hearing or balance.

Twirler (Tw) mice have a combination of abnormalities that includes cleft palate, malformations of the inner ear, hearing loss, vestibular dysfunction, obesity, and lymphoid hypoplasia. In this study, we show that the underlying mutation affects the Zeb1 gene. Zeb1 was already known to encode a protein normally expressed in mesenchymal cells, where it represses expression of genes that are uniquely expressed in epithelial cells. The Tw mutation is a rare example of a single-nucleotide substitution in a region of a gene that does not encode protein, promoter, or splice sites, so we engineered a mouse model with the mutation that confirmed its causative role. The Tw mutation disrupts a consensus DNA binding site sequence for the Myb family of regulatory proteins. We conclude that this mutation leads to abnormal expression of Zeb1, structural malformations of the inner ear, and a loss of hearing and balance function. A similar mechanism may underlie other features of Twirler, such as obesity and cleft palate.

An observed relationship between vestibular function and auditory thresholds in aircraft-maintenance workers

OBJECTIVE

We sought to examine the vestibular function and whether an association exists between vestibular function and hearing thresholds in a group of military aircraft-maintenance workers with exposures to high levels of noise and organic solvents, relative to two different comparison groups.

METHODS

Vestibular function (using functional reach) and hearing (with pure-tone audiometry) were assessed in 601 exposed personnel, compared with two unexposed groups (500 technical trade and 391 nontrade).

RESULTS

Linear regression model showed that functional reach was slightly better for the comparison groups than the exposed group, with only one group being statistically significant, and there was a significant association between vestibular function and auditory thresholds at 500 and 1000 Hz.

CONCLUSION

This study has demonstrated a relationship between low-frequency hearing loss, vestibular dysfunction, anxiety, and depression in an occupational population.

Mechanisms of vestibular compensation: recent advances

PURPOSE OF REVIEW

This article reviews recent studies that have provided experimental evidence for mechanisms of neural and synaptic plasticity in the brain during vestibular compensation, the behavioural recovery that takes place following peripheral vestibular lesions.

RECENT FINDINGS

First, experimental evidence from animal studies indicates that an unbalanced vestibular commissural system is a fundamental cause of the syndrome of oculomotor and postural deficits after unilateral labyrinthectomy. Second, recent studies suggest the involvement of both GABAergic and glycinergic commissural neurons. In addition gliosis and reactive neurogenesis in the ipsilesional vestibular nuclei appear to be involved in compensation. Third, evidence from cerebellar-deficient mutant mice demonstrates an important role for cerebellum-dependent motor learning in the longer term. Factors such as stress steroids and neuromodulators such as histamine influence these plasticity mechanisms and may thus contribute to the development of compensation in patients.

SUMMARY

Vestibular compensation involves multiple, parallel plastic processes at various sites in the brain. Experimental evidence suggests that adaptive changes in the sensitivity of ipsilesional vestibular neurons to the inhibitory neurotransmitters GABA and glycine, changes in the electrophysiological excitability of vestibular neurons, changes in the inhibitory control of the brainstem vestibular networks by the cerebellum, gliosis and neurogenesis in the ipsilesional vestibular nuclei, and activity-dependent reorganization of the synaptic connectivity of the vestibular pathways are mechanisms involved in compensation.

Hybridizing behavioral models: a possible solution to some problems in neurophenotyping research?

The use of batteries of single-domain tests for neurophenotyping research is a common strategy to achieve higher data density and explore different behavioral domains. This approach, however, is accompanied by several methodological challenges, briefly discussed here. As an alternative, this paper advocates the wider use of extensive "hybrid" protocols that assess multiple domains in parallel, or logically/logistically combine experimental paradigms, in a way that disproportionately maximizes the number of tested phenotypes per experimental manipulation. Several examples of this approach are given in this paper, demonstrating the potential to reduce time, cost and subject requirements for the experiments. Offering behavioral analyses that are lacking in the standard single-domain tests, such "hybrid" models enable innovative modeling of neuropsychiatric disorders by more thorough and broader investigation of complex phenotypical characteristics.

Effects of bilateral vestibular deafferentation on anxiety-related behaviours in Wistar rats

Despite frequent reports that patients with vestibular dysfunction exhibit an unusually high incidence of anxiety disorders, few studies have investigated the emotional effects of vestibular damage in animals. In this study we investigated the effects of a permanent surgical bilateral vestibular deafferentation (BVD) on the performance of rats in a series of anxiety tests at 3 weeks (3-W), 3 months (3-M) and 5 months (5-M) following the lesion. We used the elevated plus maze (EPM), elevated T maze (ETM), hyponeophagia and social interaction tests. Contrary to expectation, we found that, at 3 and 5M post-op, BVD rats spent more rather than less time on the open arms of the EPM compared to sham controls, and they displayed a lack of learned inhibitory avoidance in the ETM. Compared to sham controls, BVD rats showed no significant difference over the 3 time points in their latencies to eat in a novel situation; however, they did engage in social interaction to a significantly lesser extent. Finally, blood corticosterone levels were not significantly different between BVD and sham rats at 6 months post-op. These results suggest that BVD causes changes in the performance of rats in the EPM and ETM that might reflect emotional changes, or could be due to the cognitive impairment and hyperactivity caused by BVD.

The regular and light-dark Suok tests of anxiety and sensorimotor integration: utility for behavioral characterization in laboratory rodents

Animal behavioral models are crucial for neurobiological research, allowing for the thorough investigation of brain pathogenesis to be performed. In both animals and humans, anxiety has long been linked to vestibular disorders. However, although there are many tests of anxiety and vestibular deficits, there are few protocols that address the interplay between these two domains. The Suok test and its light-dark modification presented here appear to be suitable for testing this pathogenetic link in laboratory rodents. This protocol adds a new dimension to previously used tests by assessing animal anxiety and balancing simultaneously, resulting in efficient, high-throughput screens for testing psychotropic drugs, phenotyping genetically modified animals, and modeling clusters of human disorders related to stress/anxiety and balancing.