Hair cell ribbon synapses

Hearing and balance rely on the faithful synaptic coding of mechanical input by the auditory and vestibular hair cells of the inner ear. Mechanical deflection of their stereocilia causes the opening of mechanosensitive channels, resulting in hair cell depolarization, which controls the release of glutamate at ribbon-type synapses. Hair cells have a compact shape with strong polarity. Mechanoelectrical transduction and active membrane turnover associated with stereociliar renewal dominate the apical compartment. Transmitter release occurs at several active zones along the basolateral membrane. The astonishing capability of the hair cell ribbon synapse for temporally precise and reliable sensory coding has been the subject of intense investigation over the past few years. This research has been facilitated by the excellent experimental accessibility of the hair cell. For the same reason, the hair cell serves as an important model for studying presynaptic Ca(2+) signaling and stimulus-secretion coupling. In addition to common principles, hair cell synapses differ in their anatomical and functional properties among species, among the auditory and vestibular organs, and among hair cell positions within the organ. Here, we briefly review synaptic morphology and connectivity and then focus on stimulus-secretion coupling at hair cell synapses.

Loss of Baiap2l2 destabilizes the transducing stereocilia of cochlear hair cells and leads to deafness

KEY POINTS

Mechanoelectrical transduction at auditory hair cells requires highly specialized stereociliary bundles that project from their apical surface, forming a characteristic graded 'staircase' structure. The morphogenesis and maintenance of these stereociliary bundles is a tightly regulated process requiring the involvement of several actin-binding proteins, many of which are still unidentified. We identify a new stereociliary protein, the I-BAR protein BAIAP2L2, which localizes to the tips of the shorter transducing stereocilia in both inner and outer hair cells (IHCs and OHCs). We find that Baiap2l2 deficient mice lose their second and third rows of stereocilia, their mechanoelectrical transducer current, and develop progressive hearing loss, becoming deaf by 8 months of age. We demonstrate that BAIAP2L2 localization to stereocilia tips is dependent on the motor protein MYO15A and its cargo EPS8. We propose that BAIAP2L2 is a new key protein required for the maintenance of the transducing stereocilia in mature cochlear hair cells.

ABSTRACT

The transduction of sound waves into electrical signals depends upon mechanosensitive stereociliary bundles that project from the apical surface of hair cells within the cochlea. The height and width of these actin-based stereocilia is tightly regulated throughout life to establish and maintain their characteristic staircase-like structure, which is essential for normal mechanoelectrical transduction. Here, we show that BAIAP2L2, a member of the I-BAR protein family, is a newly identified hair bundle protein that is localized to the tips of the shorter rows of transducing stereocilia in mouse cochlear hair cells. BAIAP2L2 was detected by immunohistochemistry from postnatal day 2.5 (P2.5) throughout adulthood. In Baiap2l2 deficient mice, outer hair cells (OHCs), but not inner hair cells (IHCs), began to lose their third row of stereocilia and showed a reduction in the size of the mechanoelectrical transducer current from just after P9. Over the following post-hearing weeks, the ordered staircase structure of the bundle progressively deteriorates, such that, by 8 months of age, both OHCs and IHCs of Baiap2l2 deficient mice have lost most of the second and third rows of stereocilia and become deaf. We also found that BAIAP2L2 interacts with other key stereociliary proteins involved in normal hair bundle morphogenesis, such as CDC42, RAC1, EPS8 and ESPNL. Furthermore, we show that BAIAP2L2 localization to the stereocilia tips depends on the motor protein MYO15A and its cargo EPS8. We propose that BAIAP2L2 is key to maintenance of the normal actin structure of the transducing stereocilia in mature mouse cochlear hair cells.

Effect of human auditory efferent feedback on cochlear gain and compression

The mammalian auditory system includes a brainstem-mediated efferent pathway from the superior olivary complex by way of the medial olivocochlear system, which reduces the cochlear response to sound (Warr and Guinan, 1979; Liberman et al., 1996). The human medial olivocochlear response has an onset delay of between 25 and 40 ms and rise and decay constants in the region of 280 and 160 ms, respectively (Backus and Guinan, 2006). Physiological studies with nonhuman mammals indicate that onset and decay characteristics of efferent activation are dependent on the temporal and level characteristics of the auditory stimulus (Bacon and Smith, 1991; Guinan and Stankovic, 1996). This study uses a novel psychoacoustical masking technique using a precursor sound to obtain a measure of the efferent effect in humans. This technique avoids confounds currently associated with other psychoacoustical measures. Both temporal and level dependency of the efferent effect was measured, providing a comprehensive measure of the effect of human auditory efferents on cochlear gain and compression. Results indicate that a precursor (>20 dB SPL) induced efferent activation, resulting in a decrease in both maximum gain and maximum compression, with linearization of the compressive function for input sound levels between 50 and 70 dB SPL. Estimated gain decreased as precursor level increased, and increased as the silent interval between the precursor and combined masker-signal stimulus increased, consistent with a decay of the efferent effect. Human auditory efferent activation linearizes the cochlear response for mid-level sounds while reducing maximum gain.

[Audiological profile of patients with SARS-Co-V-2 PCR-positive cases]

COVID-19 is a new pandemic caused by a novel coronavirus, SARS-CoV-2. COVID-19 has spread throughout China and received worldwide attention. On 11 February 2020, World Health Organization (WHO) officially declared COVID-19. The clinical symptoms of COVID-19 patients may vary, more often include symptoms affected by upper and lower respiratory tract damage. In ENT practice it is used to mention rhinitis, sore throat, anosmia/hyposmia. The effect of COVID-19 is an interesting issue in audiology. There were 78 patients who were confirmed positive for COVID-19 PCR-positive cases and 30 normal non-infected subjects in our study. The patients were divided into two groups according to severity their clinical symptoms from asymptomatic COVID-19 PCR-positive cases to severe form. All patients underwent audiological evaluation included tympanometry, acoustic threshold and transient evoked otoacoustic emission (TEOAE). Although hearing sensitivity was normal among some participants, it was statistically proved that TEOAEs could pick up subtle deterioration in the outer hair cells functions and impact on the cochlear.

The expression of nicotinic receptor alpha7 during cochlear development

Nicotinic acetylcholine receptor alpha7 expression was examined in the developing and adult auditory system using mice that were modified through homologous recombination to coexpress either GFP (alpha7GFP) or Cre (alpha7Cre), respectively. The expression of alpha7GFP is first detected at embryonic (E) day E13.5 in cells of the spiral prominence. By E14.5, sensory regions including the putative outer hair cells and Deiters' cells express alpha7GFP as do solitary efferent fibers. This pattern diminishes after E16.5 in a basal to apex progression, as Hensen's cells and cells of the spiral ligament acquire alpha7GFP expression. At birth and thereafter alpha7GFP also identifies a subset of spiral ganglion cells whose processes terminate on inner hair cells. Efferent fibers identified by peripherin or calcitonin gene-related protein do not coexpress alpha7GFP. In addition to cochlear structures, there is strong expression of alpha7GFP by cells of the central auditory pathways including the ventral posterior cochlear nucleus, lateral lemniscus, central inferior colliculus, and the medial geniculate nucleus. Our findings suggest that alpha7 expression by both neuronal and non-neuronal cells has the potential to impact multiple auditory functions through mechanisms that are not traditionally attributed to this receptor.

Fate-mapping analysis of cochlear cells expressing Atoh1 mRNA via a new Atoh13*HA-P2A-Cre knockin mouse strain

BACKGROUND

Atoh1 is recognized to be essential for cochlear hair cell (HC) development. However, Atoh1 temporal and spatial expression patterns remain widely debated. Here, we aimed to obtain evidence to resolve the controversies regarding Atoh1 expression by generating a new knockin mouse strain: Atoh1^3*HA-P2A-Cre .

RESULTS

Fate-mapping analysis of Atoh1^{3*HA-P2A-Cre/+} ; Rosa26-CAG-LSL-tdTomato (Ai9)/+ mice enabled us to concurrently characterize the temporal expression of Atoh1 protein (through HA-tag immunostaining) and visualize the cells expressing Atoh1 mRNA (as tdTomato+ cells). Our findings show that whereas Atoh1 mRNA expression is rapidly turned on in early cochlear progenitors, Atoh1 protein is only detected in differentiating HCs or progenitors just committed to the HC fate. Cre activity is also stronger in Atoh1^{3*HA-P2A-Cre/+} than in previous mouse models, because almost all cochlear HCs and nearby supporting cells here are tdTomato+. Furthermore, tdTomato, but not HA, is expressed in middle and apical spiral ganglion neurons.

CONCLUSION

Collectively, our findings indicate that Atoh1^3*HA-P2A-Cre can serve as a powerful genetic model in the developmental biology field. This article is protected by copyright. All rights reserved.

Clinical profile and management of revision cochlear implant surgeries

OBJECTIVES

To discuss our experience with managing cochlear implant cases that required revision surgery.

METHODS

A retrospective case series study including data from 922 cochlear implant patients at an academic tertiary center was evaluated retrospectively. All patients who underwent revision cochlear implant (CI) surgery between January 2011 and July 2017 were included. The following data were collected: patient demographic data, details on the first implant, reasons for the revision, duration from initial implantation to revision, type of device, and management.

RESULTS

Out of 922 CI patients, 37 (4%) underwent revision surgery, comprising 33 children and 4 adults. The most common reason for revision surgery, at 28/37 cases (75.6%), was device failure. Surgical and medical aetiologies were responsible for 9/37 (24.3%) revisions. The mean duration from the initial implantation to the revision surgery was 29 months.

CONCLUSION

Revision CI surgery is not uncommon after initial implantation. Cochlear implant programs must implement long-term follow-up processes for CI users. Whenever a patient's rehabilitated performance regresses, the cause should be investigated to determine whether subsequent reimplantation is necessary.

Cochlear implantation in children with anomalous cochleovestibular anatomy

Our aim was to determine the influence of inner-ear anomalies on surgical difficulty and postoperative audiologic outcomes among pediatric cochlear implant (CI) recipients at our institution. We reviewed medical and audiologic records from 78 consecutive pediatric CI cases between 1985 and June 2009. Thirty patients had high-resolution temporal bone computed tomography imaging available for retrospective interpretation. Seven of these 30 patients (23%) had cochleovestibular dysplasia. Fifty percent of patients with severe dysplasia had a cerebrospinal fluid gusher intraoperatively, compared with 13% of patients with no dysplasia. Of patients with available audiologic outcome data, 17 of 26 patients with normal/mild/moderate dysplasia were able to complete CNC testing, whereas neither of the 2 patients with severe dysplasia could complete the open set test. Our experience suggests that surgical difficulty and audiologic outcomes in pediatric CI recipients may be affected by the presence and severity of a cochleovestibular anomaly.

Bottom-up and shotgun proteomics to identify a comprehensive cochlear proteome

Proteomics is a commonly used approach that can provide insights into complex biological systems. The cochlear sensory epithelium contains receptors that transduce the mechanical energy of sound into an electro-chemical energy processed by the peripheral and central nervous systems. Several proteomic techniques have been developed to study the cochlear inner ear, such as two-dimensional difference gel electrophoresis (2D-DIGE), antibody microarray, and mass spectrometry (MS). MS is the most comprehensive and versatile tool in proteomics and in conjunction with separation methods can provide an in-depth proteome of biological samples. Separation methods combined with MS has the ability to enrich protein samples, detect low molecular weight and hydrophobic proteins, and identify low abundant proteins by reducing the proteome dynamic range. Different digestion strategies can be applied to whole lysate or to fractionated protein lysate to enhance peptide and protein sequence coverage. Utilization of different separation techniques, including strong cation exchange (SCX), reversed-phase (RP), and gel-eluted liquid fraction entrapment electrophoresis (GELFrEE) can be applied to reduce sample complexity prior to MS analysis for protein identification.

Improved Environment-Aware-Based Noise Reduction System for Cochlear Implant Users Based on a Knowledge Transfer Approach: Development and Usability Study

BACKGROUND

Cochlear implant technology is a well-known approach to help deaf individuals hear speech again and can improve speech intelligibility in quiet conditions; however, it still has room for improvement in noisy conditions. More recently, it has been proven that deep learning-based noise reduction, such as noise classification and deep denoising autoencoder (NC+DDAE), can benefit the intelligibility performance of patients with cochlear implants compared to classical noise reduction algorithms.

OBJECTIVE

Following the successful implementation of the NC+DDAE model in our previous study, this study aimed to propose an advanced noise reduction system using knowledge transfer technology, called NC+DDAE_T; examine the proposed NC+DDAE_T noise reduction system using objective evaluations and subjective listening tests; and investigate which layer substitution of the knowledge transfer technology in the NC+DDAE_T noise reduction system provides the best outcome.

METHODS

The knowledge transfer technology was adopted to reduce the number of parameters of the NC+DDAE_T compared with the NC+DDAE. We investigated which layer should be substituted using short-time objective intelligibility and perceptual evaluation of speech quality scores as well as t-distributed stochastic neighbor embedding to visualize the features in each model layer. Moreover, we enrolled 10 cochlear implant users for listening tests to evaluate the benefits of the newly developed NC+DDAE_T.

RESULTS

The experimental results showed that substituting the middle layer (ie, the second layer in this study) of the noise-independent DDAE (NI-DDAE) model achieved the best performance gain regarding short-time objective intelligibility and perceptual evaluation of speech quality scores. Therefore, the parameters of layer 3 in the NI-DDAE were chosen to be replaced, thereby establishing the NC+DDAE_T. Both objective and listening test results showed that the proposed NC+DDAE_T noise reduction system achieved similar performances compared with the previous NC+DDAE in several noisy test conditions. However, the proposed NC+DDAE_T only required a quarter of the number of parameters compared to the NC+DDAE.

CONCLUSIONS

This study demonstrated that knowledge transfer technology can help reduce the number of parameters in an NC+DDAE while keeping similar performance rates. This suggests that the proposed NC+DDAE_T model may reduce the implementation costs of this noise reduction system and provide more benefits for cochlear implant users.

Cochlear Nerve Canal Stenosis: Association With MYH14 and MYH9 Genes

The bony cochlear nerve canal transmits the cochlear nerve as it passes from the fundus of the internal auditory canal to the cochlea. Stenosis of the cochlear nerve canal, defined as a diameter less than 1.0 mm in transverse diameter, is associated with inner ear anomalies and severe to profound congenital hearing loss. We describe an 11-month-old infant with nonsyndromic congenital sensorineural hearing loss with cochlear nerve canal stenosis. Next-generation sequencing revealed heterozygous mutations in MYH9 and MYH14, encoding for the inner ear proteins myosin heavy chain IIA and IIC. The patient's hearing was rehabilitated with bilateral cochlear implantation.

Cochlear-Vestibular Impairment due to West Nile Virus Infection

OBJECTIVES

West Nile virus (WNV) has been spreading over the last 20 years. Human infection is asymptomatic in most cases. When the disease becomes clinically manifest, it may involve a range of issues, from a mild infection with flu-like symptoms to a neuroinvasive disease. Albeit rarely, WNV-associated sensorineural hearing loss (SNHL) has also been reported. Here we describe two new cases of SNHL and balance impairment caused by WNV infection.

METHODS

The patients were investigated with repeated audiometric tests and, for the first time, videonystagmography was also used.

RESULTS

Unlike findings in the few other published cases, an improvement in audiometric thresholds and vestibular function was documented in both of our patients.

CONCLUSIONS

In the light of our findings, a prospective study would be warranted on a large series of patients with WNV infection in order: (i) to better define the epidemiology of the related cochlear-vestibular involvement; and (ii) to elucidate the virus-related changes to peripheral and central auditory and vestibular functions.

Unidirectional and stage-dependent roles of Notch1 in Wnt-responsive Lgr5+ cells during mouse inner ear development

Wnt and Notch signaling play crucial roles in the determination of the prosensory domain and in the differentiation of hair cells (HCs) and supporting cells during mouse inner ear development; however, the relationship between the two signaling pathways in the mouse cochlea remains largely unknown. Here, we investigated the interactions between Notch and Wnt signaling on the basis of the bidirectional regulation of Notch1 specifically in Wnt-responsive Lgr5⁺ progenitors during different cochlear development stages. We found that the downregulation of Notch1 in Lgr5⁺ cells from embryonic day (E) 14.5 to E18.5 can drive the quiescent Lgr5⁺ cells to re-enter the cell cycle and differentiate into extra HCs, whereas the upregulation of Notch1 expression did not affect the proliferation or differentiation of otic progenitor cells. No effect was observed on the upregulation or downregulation of Notch1 in Lgr5⁺ cells from E10.5 to E14.5. We concluded that the roles of Notch1 in Wnt-responsive Lgr5⁺ cells are unidirectional and stage dependent and Notch1 serves as a negative regulator for Lgr5⁺ progenitor activation during cochlear differentiation. Our findings improved the understanding of the interactions between Notch and Wnt signaling in cochlear development.

Inhibition of connexin 43 induces hearing loss in postnatal mice

BACKGROUND

Connexin 43 (Cx43) is the most ubiquitously expressed member of the family of connexins, constituting gap junctions and mediating cell communication, still its role in hearing loss has been little studied.

METHODS

Immunohistochemistry was used to detect the expression pattern of Cx43. Spiral ganglia neurons (SGNs) and Corti co-culture were utilized to assay the re-innervation of hair cells by newborn SGNs. Gap19 was utilized to inhibit Cx43 hemichannels. Auditory brainstem responses (ABR) and endocochlear potential (E.P.) were measured to confirm the hearing loss.

RESULTS

The expression of Cx43 in P14 mice was higher than in P0 and P28 (adult) mice, the earlier time point coinciding with the early inner ear development. Additionally, the growth and synapse generation of fibers were inhibited after Gap 19 treatment of the co-cultures of the Corti and SGNs from newborn mice. Furthermore, the inhibition of Cx43 could increase the ABR threshold and decrease E.P. level in postnatal mice, whereas such an effect was not observed in adult mice.

CONCLUSION

The function of Cx43 is critical during the early development of mouse cochlea but is dispensable in adult mice.

Application of a new computer-assisted robotic visualization system in cochlear implantation-Proof of concept

BACKGROUND

Over the last decades conventional cochlear implant (CI) surgery has remained essentially unchanged. Nevertheless, alternative implantation techniques to further improve patient outcomes such as endaural implantation or robot-assisted surgery have been proposed in recent years. However, none of these have gained acceptance in clinical routine, thus confirming a demand for new developments.

METHODS

Cochlear implant surgery was performed in two mastoid bones obtained from body donors using a novel hands-free exoscope. Advantages and disadvantages of the system were evaluated.

RESULTS

In all cases, implantation of the electrode was feasible. The system allowed for hands-free movement and adjustment of the exoscope by the head-mounted display. Network connectivity of the system leaves room for improvement.

CONCLUSION

The RoboticScope is an innovative tool and can be used supportively in conventional CI surgery in the experimental setting. Although operating the device requires a certain learning curve, the usability is intuitive for every ear surgeon.

Multiple actions of neurturin correlate with spatiotemporal patterns of Ret expression in developing chick cranial ganglion neurons

The neurotrophic effects of neurturin (NRTN) on chick cranial ganglia were evaluated at various embryonic stages in vitro and related to its receptor expression. NRTN promoted the outgrowth and survival of ciliary ganglion neurons at early embryonic (E) stages (E6-E12), trigeminal ganglion neurons at midstages (E9-E16), and vestibular ganglion neurons at late stages (E12-E16). NRTN had no positive effects on cochlear ganglion neurons throughout development. In accordance with the time and order of onset in NRTN responsiveness, Ret protein was first detected in ciliary ganglia at E6, subsequently in trigeminal ganglia at E9, and in vestibular ganglia at E12. Ret was absent in E16 ciliary ganglia as well as in cochlear ganglia at all developmental stages that were tested. Exogenous application of retinoic acid induced NRTN responsiveness and Ret protein expression from E9 vestibular ganglion neurons, suggesting that retinoic acid can regulate Ret protein expression in peripheral sensory neurons in vitro. Ret was confined to the neuron cell body, whereas GFRalpha was localized predominantly in peripheral and central neurite processes. No noticeable change in GFRalpha expression was seen in any cranial ganglia throughout the developmental stages that were tested (E6-E16). These results demonstrate that NRTN exerts neurotrophic effects on different cranial ganglia at different developmental stages and that the onset and offset of NRTN responsiveness are regulated mainly by the spatiotemporal patterns of Ret, but not of GFRalpha receptors. The results also substantiate the recently emerging view that NRTN may be an essential target-derived neurotrophic factor for parasympathetic neurons during development.

A Scoping New Revolution for Tinnitus Management: A Neuromonics Narrative Review

With a prevalence ranging from 16-21%, tinnitus is an irking neurological disorder, manifesting as the perception of a roar of cacophony without an external acoustic stimulus. Although tinnitus is a non-life-threatening symptom, tinnitus's negative repercussions, such as personality disturbances and social withdrawal, are daunting concerns despite a gamut of conventional and emerging treatment options. Tinnitus management is still a critical challenge that provides opportunities for clinicians, ENT (Ear/eye, nose and throat) physicians, and other specialists such as audiologists, psychiatrists, and psychologists. Among the new treatment modalities, Neuromonics tinnitus treatment (NTT) draws special attention in tinnitus management due to its mounting success rate. Nonetheless, unlike in developed countries like Australia, the United States, and the United Kingdom, the scanty awareness of NTT among Indian ENT specialists is a titanic setback for care providers. Because of this backdrop, this review emphasized the current perspectives on tinnitus management and the underlying principles and clinical efficacy of NTT. The challenges for tinnitus management can be met and reduced by suppressing tinnitus through motivation, counseling, cochlear implant, and psychotherapy.

Sensory cells determine afferent terminal morphology in cross-innervated electroreceptor organs: implications for hair cells

Type I and type II hair cells of the vestibular system are innervated by afferents that form calyceal and bouton terminals, respectively. These cannot be experimentally cross-innervated in the inner ear to determine how they influence each other. However, analogous organs are accessible for transplantation and cross-innervation in the brown ghost electric fish. These fish possess three types of electroreceptor organs. Of these, the sensory receptors of the type I tuberous organ are S-100- and parvalbumin-positive with a calbindin-positive afferent that forms a large calyx around the organ. Neither the sensory receptors nor the afferents of the ampullary organs label with these antibodies, and the afferent branches form a single large bouton beneath each receptor cell. In controls, when cut ampullary afferents reinnervate transplanted ampullary organs, they have characteristic calbindin-negative terminals with large boutons. When type I tuberous afferents reinnervate ampullary organs, receptor cells remain S-100- and parvalbumin-negative, and the tuberous afferents still express calbindin. The nerve terminals, however, make large ampullary-like boutons on the receptor cells. These results suggest that (1) afferent terminal morphology is dictated by the receptor organ; (2) expression of calbindin by the afferent is not suppressed by innervation of the incorrect end organ; (3) ampullary organs generate ampullary receptor cells although innervated by tuberous afferents; and (4) ampullary receptor cells can be trophically supported by tuberous afferents.

Case report: Bilateral sudden deafness in acute middle cerebellar peduncle infarction: central or peripheral?

Background

The middle cerebellar peduncle (MCP) is the most common site associated with hearing impairment in acute ischaemic stroke. Narrowing or occlusion of the vertebrobasilar artery due to atherosclerosis is thought to be the main pathogenesis of MCP infarction. Most previous reports of MCP infarction have not been clear whether the patient's hearing impairment is localized to the center or periphery.

Case presentation

We report 44-year-old man with vertigo, tinnitus, and bilateral sudden sensorineural hearing loss (SSNHL) as the first symptoms. Pure Tone Audiogram revealed complete hearing loss in both ears. Acute bilateral MCP infarction was diagnosed by repeated brain magnetic resonance imaging (MRI). The brainstem auditory evoked potential (BAEP) and the electrocochleography were normal. The otoacoustic emissions showed binaural cochlear dysfunctions. After the antiplatelet, lipid-lowering, steroids and hyperbaric oxygen therapy, the pure-tone average (PTA) showed a clear improvement with 67 decibels (dB) on the right and 73 dB on the left at the 3-month follow-up.

Conclusion

Vertebrobasilar diseases due to atherosclerosis should be routinely considered in middle-aged and elderly patients with vascular risk factors and bilateral hearing loss. Bilateral SSNHL can be a prodrome of acute MCP infarction and it can be peripheral. Brain MRI, brain magnetic resonance angiogram (MRA), brain and neck computed tomography angiography (CTA), BAEP, otoacoustic emissions, and Pure Tone Audiogram help to localize and qualify the diagnosis. Bilateral SSNHL localized to the periphery usually improves better and has a good prognosis. Early detection of hearing loss and intervention can help patients recover.

Research progress in delineating the pathological mechanisms of GJB2-related hearing loss

Hearing loss is the most common congenital sensory impairment. Mutations or deficiencies of the GJB2 gene are the most common genetic cause of congenital non-syndromic deafness. Pathological changes such as decreased potential in the cochlea, active cochlear amplification disorders, cochlear developmental disorders and macrophage activation have been observed in various GJB2 transgenic mouse models. In the past, researchers generally believed that the pathological mechanisms underlying GJB2-related hearing loss comprised a K⁺ circulation defect and abnormal ATP-Ca²⁺ signals. However, recent studies have shown that K⁺ circulation is rarely associated with the pathological process of GJB2-related hearing loss, while cochlear developmental disorders and oxidative stress play an important, even critical, role in the occurrence of GJB2-related hearing loss. Nevertheless, these research has not been systematically summarized. In this review, we summarize the pathological mechanisms of GJB2-related hearing loss, including aspects of K⁺ circulation, developmental disorders of the organ of Corti, nutrition delivery, oxidative stress and ATP-Ca²⁺ signals. Clarifying the pathological mechanism of GJB2-related hearing loss can help develop new prevention and treatment strategies.

Neural Activity During Audiovisual Speech Processing: Protocol For a Functional Neuroimaging Study

BACKGROUND

Functional near-infrared spectroscopy (fNIRS) studies have demonstrated associations between hearing outcomes after cochlear implantation and plastic brain changes. However, inconsistent results make it difficult to draw conclusions. A major problem is that many variables need to be controlled. To gain further understanding, a careful preparation and planning of such a functional neuroimaging task is key.

OBJECTIVE

Using fNIRS, our main objective is to develop a well-controlled audiovisual speech comprehension task to study brain activation in individuals with normal hearing and hearing impairment (including cochlear implant users). The task should be deductible from clinically established tests, induce maximal cortical activation, use optimal coverage of relevant brain regions, and be reproducible by other research groups.

METHODS

The protocol will consist of a 5-minute resting state and 2 stimulation periods that are 12 minutes each. During the stimulation periods, 13-second video recordings of the clinically established Oldenburg Sentence Test (OLSA) will be presented. Stimuli will be presented in 4 different modalities: (1) speech in quiet, (2) speech in noise, (3) visual only (ie, lipreading), and (4) audiovisual speech. Each stimulus type will be repeated 10 times in a counterbalanced block design. Interactive question windows will monitor speech comprehension during the task. After the measurement, we will perform a 3D scan to digitize optode positions and verify the covered anatomical locations.

RESULTS

This paper reports the study protocol. Enrollment for the study started in August 2021. We expect to publish our first results by the end of 2022.

CONCLUSIONS

The proposed audiovisual speech comprehension task will help elucidate neural correlates to speech understanding. The comprehensive study will have the potential to provide additional information beyond the conventional clinical standards about the underlying plastic brain changes of a hearing-impaired person. It will facilitate more precise indication criteria for cochlear implantation and better planning of rehabilitation.

INTERNATIONAL REGISTERED REPORT IDENTIFIER (IRRID)

DERR1-10.2196/38407.

Hearing Impairment and Neuroimaging Results in Mitochondrial Diseases

Mitochondrial diseases (MDs) are heterogeneous genetic disorders characterized by mitochondrial DNA (mtDNA) defects, involving tissues highly dependent on oxidative metabolism: the inner ear, brain, eye, skeletal muscle, and heart. We describe adult patients with genetically defined MDs, characterizing hearing function and neuroimaging results. We enrolled 34 patients (mean age: 50.02 ± 15 years, range: 18-75 years; 20 females and 14 males) classified in four groups: MELAS, MIDD, PEO, and Encephalopathy/Polyneuropathy. Audiological evaluations included psychoacoustical tests (pure-tone and speech audiometry), electrophysiological tests (Auditory Brainstem Responses, ABRs), and Impedenzometry. Neuroimaging evaluations considered global MRI abnormalities or structural brain changes. In total, 19/34 patients carried the m.3243A > G mutation (6 affected by MELAS, 12 affected by MIDD, and 1 affected by PEO); 11 had an mtDNA deletion (all affected by PEO); 3 had nuclear genes associated with MDs (POLG1 and OPA1); and 1 patient had an mtDNA deletion without an identified nuclear gene defect (affected by PEO). Sensory neural, bilateral, and symmetrical hearing loss was present in 25 patients (73.5%) to different degrees: 9 mild, 9 moderate, 5 severe, and 2 profound. The severe/profound and mild hearing losses were associated with pantonal and high-frequency audiograms, respectively. Instead, moderate hearing losses were associated with both high-frequency (five cases) and pantonal (five cases) audiogram shapes. In addition, 21/25 patients showed a cochlear site of lesion (84%), and 4/25 (16%) showed a retrocochlear site. We found global MRI abnormalities or structural brain changes in 26/30 subjects (86.6%): 21 had white matter abnormalities, 15 had cortical atrophy, 10 had subcortical atrophy, 8 had basal nuclei involvement or cerebellar atrophy, 4 had stroke-like lesions or laminar necrosis, and 1 had cysts or vacuolated lesions. We concluded that genetic alterations are associated with different clinical presentations for both auditory function and neuroradiological findings. There is no fixed relationship between genotype and phenotype for the clinical conditions analyzed.

Ninjinyoeito Has a Protective Effect on the Auditory Nerve and Suppresses the Progression of Age-Related Hearing Loss in Mice

Currently, there are limited reports available regarding the treatment and prevention of progressive age-related hearing loss. This is because age-related hearing loss is not a critical disease with direct fatalities and has several well-established countermeasures such as hearing aids and cochlear implants. This study evaluated the efficacy of Ninjinyoeito (NYT) in the treatment of age-related hearing loss. C57BL/6J mice were divided into three groups: baseline group, untreated group, and NYT-treated group, with the latter receiving NYT treatment for 2 months. The mice were fed with NYT extract mixed with 4% mouse normal chow. Hearing loss was confirmed by a reduction in intact cell density of the auditory nerve from the age of 5–7 months. The suppression of hearing loss with aging and decrease in the intact cell density of the auditory nerve were significant in mice fed with NYT for 2 months. NYT has been reported to improve blood flow and enhance mitochondrial activity and may exert its protective effects on spiral neurons through these mechanisms. There was no decrease in the size of the stria vascularis from the age of 5–7 months in C57BL/6J mice. The present model failed to reveal the effect of NYT on atrophy of the stria vascularis of the cochlear duct. In conclusion, NYT appears to have a protective effect on the auditory nerve and suppress the progression of age-related hearing loss by reducing age-related auditory nerve degeneration.

Stereotactic radiosurgery does not appear to impact cochlear implant performance in patients with neurofibromatosis type II

INTRODUCTION

Neurofibromatosis Type 2 (NF2) is a genetic condition associated with the presence of bilateral vestibular schwannoma and progressive sensorineural hearing loss. Treatment options include observation, stereotactic radiosurgery (SRS) or surgical resection. Historically, retrocochlear pathology was a contraindication to cochlear implantation (CI). However it is now recognized as viable, in an attempt to restore hearing and improve communication.Thus, the aim of this study was to contrast auditory function in CI recipients with NF2 whose tumors were either observed versus initially treated with SRS.

METHODS

A local review of hearing outcomes in 2 CI patients (3 ears total) with NF2 was undertaken and then pooled with the existing medical literature. Comparative post-implant outcome data, including pure-tone average and aided speech perception measurements was analyzed and compared between 8 subjects whose tumors were observed and 11 subjects who received pre-implantation SRS.

RESULTS

Mean tumor size in the observation cohort was 0.81cm (.13cm to 1.50cm), and 2.34cm in the SRS group (0.10cm to 3.7cm). The mean reported duration of deafness was 22 months as compared to 71 months in the SRS cohort. Both groups demonstrated similar pre-implant candidacy criteria, average age and open-set speech recognition. Although disparate outcome measurements were utilized across studies, an analysis of post-implant open-set speech perception found no significant differences between groups.

CONCLUSION

Despite a small sample size and highly variable post implantation testing methods, patients who undergo SRS for NF2 associated Schwannoma prior to CI have similar hearing performance and benefit by having already completed definitive tumor management.

The Blood-Labyrinth Barrier: Non-Invasive Delivery Strategies for Inner Ear Drug Delivery

The inner ear is a relatively isolated organ, protected by the blood-labyrinth barrier (BLB). This barrier creates a unique lymphatic fluid environment within the inner ear, maintaining a stable physiological state essential for the mechano-electrical transduction process in the inner ear hair cells while simultaneously restricting most drugs from entering the lymphatic fluid. Under pathological conditions, dysfunction of the stria vascularis and disruption in barrier structure can lead to temporary or permanent hearing impairment. This review describes the structure and function of the BLB, along with recent advancements in modeling and protective studies related to the BLB. The review emphasizes some newly developed non-invasive inner ear drug delivery strategies, including ultrasound therapy assisted by microbubbles, inner ear-targeting peptides, sound therapy, and the route of administration of the cerebrospinal fluid conduit. We argue that some intrinsic properties of the BLB can be strategically utilized for effective inner ear drug delivery.