Takahisa Watabe

Auditory resting-state functional connectivity in tinnitus and modulation with transcranial direct current stimulation

Abstract Conclusions: The functional connectivity (FC) between the right and left auditory cortex is weak in tinnitus patients. Transcranial direct current stimulation (tDCS) over the auditory cortex has potential as a tool to modulate auditory-based FC. Objective: This study investigated the effects of applying tDCS in tinnitus patients, and searched for modulation of brain networks in resting-state functional magnetic resonance imaging (rs-fMRI) through an analysis of FC with the stimulated brain region. Subjects and methods: Nine male patients with chronic tinnitus and 10 male volunteers with normal hearing were enrolled. The subjects were evaluated with rs-fMRI immediately before and after tDCS. The tinnitus patients filled out the self-evaluation questionnaires designed to measure tinnitus conditions before tDCS treatment and 1 week afterwards. Results: The FC between the right and left auditory cortex was significantly weaker in tinnitus patients than in controls. After tDCS treatment, in the tinnitus group, the primary auditory cortex showed a reduction in the amount of statistically significant connectivity with the somatosensory area and motor area, but maintained strong significant connectivity (p < 0.005) with the auditory area and insular cortex. In contrast, in the control group, there remained strong significant connectivity between the primary auditory cortex and the somatosensory area, motor area, insular cortex, and auditory area.

Expression and Function of Sox21 During Mouse Cochlea Development

The development of the inner ear is an orchestrated process of morphogenesis with spatiotemporally controlled generations of individual cell types. Recent studies have revealed that the Sox gene family, a family of evolutionarily conserved HMG-type transcriptional factors, is differentially expressed in each cell type of the mammalian inner ear and plays critical roles in cell-fate determination during development. In this study, we examined the expression pattern of Sox21 in the developing and adult murine cochlea. Sox21 was expressed throughout the sensory epithelium in the early otocyst stage but became restricted to supporting cells during adulthood. Interestingly, the expression in adults was restricted to the inner phalangeal, inner border, and Deiters’ cells: all of these cells are in direct contact with hair cells. Evaluations of the auditory brainstem-response revealed that Sox21−/− mice suffered mild hearing impairments, with an increase in hair cells that miss their appropriate planar cell polarity. Taken together with the previously reported critical roles of SoxB1 families in the morphogenesis of inner ear sensory and neuronal cells, our results suggest that Sox21, a counteracting partner of the SoxB1 family, controls fine-tuned cell fate decisions. Also, the characteristic expression pattern may be useful for labelling a particular subset of supporting cells.

Moderate hearing loss associated with a novel KCNQ4 non-truncating mutation located near the N-terminus of the pore helix

Genetic mutation is one of the causative factors for idiopathic progressive hearing loss. A patient with late-onset, moderate, and high-frequency hearing loss was found to have a novel, heterozygous KCNQ4 mutation, c.806_808delCCT, which led to a p.Ser260del located between S5 and the pore helix (PH). Molecular modeling analysis suggested that the p.Ser269del mutation could cause structural distortion and change in the electrostatic surface potential of the KCNQ4 channel protein, which may impede K+ transport. The present study supports the idea that a non-truncating mutation around the N-terminus of PH may be related to moderate hearing loss.

A psychometric validation of the Japanese versions of new questionnaires on tinnitus (THI-12, TRS, TRSw, TSS, and TSSw)

Abstract Conclusion: The Japanese version of the Tinnitus Handicap Inventory-12 (THI-12), Tinnitus Rating Scale (TRS), TRS 1-week version (TRSw), Tinnitus Severity Scale (TSS), and TSS 1-week version (TSSw), which were developed in this study, showed high reliability and validity, suggesting their usefulness in clinical practice. Based on the THI severity grades, we propose that the severity grades of THI-12 (draft) are categorized into four groups: 0–4 points, 5–9 points, 10–14 points, and 15–24 points. Objectives: We developed Japanese versions of new questionnaires for evaluating the level of psychological distress and difficulty in activities of daily living due to tinnitus, and performed their psychometric validation to determine the reliability and validity. The THI-12 is an assessment consisting of 12 items, each of which is rated on a 3-point scale that was created by reducing the number of questions from the 25 items of the THI. The TRS, TRSw, TSS, and TSSw, which were self-evaluation questionnaires of tinnitus on an 11-grade integer Likert scale from 0 to10 points, were used as additional instruments to assess tinnitus severity and distress. Methods: The subjects were healthy adults, and patients with subjective tinnitus who were examined at the Otolaryngology Department of Keio University Hospital, Osaka City University Hospital, or Nagoya City University Hospital with a chief complaint of tinnitus between September 2010 and January 2011. In all, 38 healthy adult subjects and 113 patients with subjective tinnitus were included. We examined the reproducibility and the internal consistency for reliability. We also examined the relationship with the available scales (THI and Hospital Anxiety and Depression Scale, HADS) and group divergence for validity. Results: The psychometric validation showed high reliability and validity of the THI-12, TRS, TRSw, TSS, and TSSw.

Time-controllable Nkcc1 knockdown replicates reversible hearing loss in postnatal mice

Identification of the causal effects of specific proteins on recurrent and partially reversible hearing loss has been difficult because of the lack of an animal model that provides reversible gene knockdown. We have developed the transgenic mouse line Actin-tTS::Nkcc1tetO/tetO for manipulatable expression of the cochlear K+ circulation protein, NKCC1. Nkcc1 transcription was blocked by the binding of a tetracycline-dependent transcriptional silencer to the tetracycline operator sequences inserted upstream of the Nkcc1 translation initiation site. Administration of the tetracycline derivative doxycycline reversibly regulated Nkcc1 knockdown. Progeny from pregnant/lactating mothers fed doxycycline-free chow from embryonic day 0 showed strong suppression of Nkcc1 expression (~90% downregulation) and Nkcc1 null phenotypes at postnatal day 35 (P35). P35 transgenic mice from mothers fed doxycycline-free chow starting at P0 (delivery) showed weaker suppression of Nkcc1 expression (~70% downregulation) and less hearing loss with mild cochlear structural changes. Treatment of these mice at P35 with doxycycline for 2 weeks reactivated Nkcc1 transcription to control levels and improved hearing level at high frequency; i.e., these doxycycline-treated mice exhibited partially reversible hearing loss. Thus, development of the Actin-tTS::Nkcc1tetO/tetO transgenic mouse line provides a mouse model for the study of variable hearing loss through reversible knockdown of Nkcc1.

Auditory Related Resting State fMRI Functional Connectivity in Tinnitus Patients: Tinnitus Diagnosis Performance

OBJECTIVE The purpose of the present study was to investigate functional connectivity in tinnitus patients with and without hearing loss, and design the tinnitus diagnosis performance by resting state functional magnetic resonance imaging (rs-fMRI). SUBJECTS AND METHODS Nineteen volunteers with normal hearing without tinnitus, 18 tinnitus patients with hearing loss, and 11 tinnitus patients without hearing loss were enrolled in this study. The subjects were evaluated with rs-fMRI, and region of interests (ROIs) based correlation analyses were performed using the CONN toolbox version 16 and SPM version 8. The correlation coefficients from individual level results were converted into beta values. RESULTS With a beta threshold of more than 0.2, 91% of all possible connections between auditory-related ROIs (Heschls gyrus, planum temporale, planum polare, operculum, insular cortex, superior temporal gyrus) in the control group remained intact, whereas 83 and 66% of such connections were present in the hearing loss and the normal-hearing tinnitus group. However, between non-auditory-related ROIs, the rates of intact connections at a beta threshold of more than 0.2 were 17% in the control group, and 16 and 15% in the tinnitus groups. When resting state fMRI positive is defined as less than 9% of all possible connections between auditory-related ROIs with a beta threshold of more than 0.7, the sensitivity and specificity of tinnitus diagnosis is 86 and 74%, respectively. CONCLUSIONS The associations between auditory-related networks are weakened in tinnitus patients, even if they have normal hearing. It is possible that rs-fMRI can be a tool for objective examination of tinnitus, by focusing the auditory-related areas.

Hearing Loss Controlled by Optogenetic Stimulation of Nonexcitable Nonglial Cells in the Cochlea of the Inner Ear.

Light-gated ion channels and transporters have been applied to a broad array of excitable cells including neurons, cardiac myocytes, skeletal muscle cells and pancreatic β-cells in an organism to clarify their physiological and pathological roles. Nonetheless, among nonexcitable cells, only glial cells have been studied in vivo by this approach. Here, by optogenetic stimulation of a different nonexcitable cell type in the cochlea of the inner ear, we induce and control hearing loss. To our knowledge, deafness animal models using optogenetics have not yet been established. Analysis of transgenic mice expressing channelrhodopsin-2 (ChR2) induced by an oligodendrocyte-specific promoter identified this channel in nonglial cells—melanocytes—of an epithelial-like tissue in the cochlea. The membrane potential of these cells underlies a highly positive potential in a K+-rich extracellular solution, endolymph; this electrical property is essential for hearing. Illumination of the cochlea to activate ChR2 and depolarize the melanocytes significantly impaired hearing within a few minutes, accompanied by a reduction in the endolymphatic potential. After cessation of the illumination, the hearing thresholds and potential returned to baseline during several minutes. These responses were replicable multiple times. ChR2 was also expressed in cochlear glial cells surrounding the neuronal components, but slight neural activation caused by the optical stimulation was unlikely to be involved in the hearing impairment. The acute-onset, reversible and repeatable phenotype, which is inaccessible to conventional gene-targeting and pharmacological approaches, seems to at least partially resemble the symptom in a population of patients with sensorineural hearing loss. Taken together, this mouse line may not only broaden applications of optogenetics but also contribute to the progress of translational research on deafness.