Oridonin employs interleukin 1 receptor type 2 to treat noise-induced hearing loss by blocking inner ear inflammation.

NOD-like receptor protein 3 (NLRP3) inflammasomes trigger the inflammatory cascades and participate in various inflammatory diseases, including noise-induced hearing loss (NIHL) caused by oxidative stress. Recently, the anti-inflammatory traditional medicine oridonin (Ori) has been reported to provide hearing protection in mice after noise exposure by blocking the NLRP3-never in mitosis gene A-related kinase 7 (NEK7)-inflammasome complex assembly. Using RNA sequencing analysis, we further elucidated that interleukin 1 receptor type 2 (IL1R2) may be another crucial factor regulated by Ori to protect NIHL. We observed that IL1R2 expression was localized in spiral ganglion neurons, inner and outer hair cells, in Ori-treated mouse cochleae. Additionally, we confirmed that ectopic overexpression of IL1R2 in the inner ears of healthy mice using an adeno-associated virus delivery system significantly reduced noise-induced ribbon synapse lesions and hearing loss by blocking the "cytokine storm" in the inner ear. This study provides a novel theoretical foundation for guiding the clinical treatment of NIHL.

The Diagnostic Value of 1.5T Versus 3.0T Magnetic Resonance Imaging Intratympanic Gadolinium Inner Ear Enhancement in Patients with Meniere's Disease.

BACKGROUND: A comparative study of 1.5T and 3.0T magnetic resonance imaging inner ear gadolinium enhancement was carried out to further explore the practicality and universality of 1.5T magnetic resonance imaging in the diagnosis of inner ear labyrinthine hydrops positive imaging. METHODS: This dual case-control study was conducted on 25 patients with Meniere's disease (experimental group), diagnosed by People's Hospital of Ordos Dongsheng District between April 2017 and April 2019 and 51 patients with Meniere's disease (control group), diagnosed by People's Hospital Affiliated to Fujian University of Traditional Chinese Medicine between March 2010 and February 2011 and published on Chinese Medical Journal in 2011. Both groups were injected with gadolinium diluent into bilateral tympanic chambers through the tympanic membrane, and 3 dimensional-Fluid Attenuated Inversion Recovery (FLAIR) magnetic resonance imaging scanning of the inner ear was performed 24 hours later. The results of the 2 groups were observed, calculated, and statistically processed. RESULTS: The positive rate of membranous labyrinthine hydrops was 96% (24/25) in the experimental group and 96.1% (49/51) in the control group. The results are very close. CONCLUSION: In clinical diagnoses of Meniere's disease, 1.5T magnetic resonance imaging and 3.0T magnetic resonance imaging have the same value and significance.

Otopathologic and Computed Tomography Correlation of Internal Auditory Canal Diverticula in Otosclerosis.

INTRODUCTION: Internal auditory canal (IAC) diverticula, also known as IAC cavitary lesions or anterior cupping of the IAC, observed in otopathologic specimens and high-resolution computed tomography (CT) scans of the temporal bone are thought to be related to otosclerosis. Herein, we examined the usefulness of CT scans in identifying diverticula and determined whether IAC diverticula are associated with otosclerosis on otopathology. METHODS: One hundred five consecutive specimens were identified from the National Temporal Bone Hearing and Balance Pathology Resource Registry. Inclusion criteria included the availability of histologic slides and postmortem specimen CT scans. Exclusion criteria included cases with severe postmortem changes or lesions causing bony destruction of the IAC. RESULTS: Ninety-seven specimens met criteria for study. Of these, 42% of the specimens were from male patients, and the average age of death was 77 years (SD = 18 yr). IAC diverticula were found in 48 specimens, of which 46% were identified in the CT scans. The mean area of the IAC diverticula was 0.34 mm 2 . The sensitivity and specificity of detecting IAC diverticula based on CT were 77% and 63%, respectively. Overall, 27% of specimens had otosclerosis. Histologic IAC diverticula were more common in specimens with otosclerosis than those without (37.5% versus 16%; p = 0.019). Cases with otosclerosis had a greater mean histologic diverticula area compared with nonotosclerosis cases (0.69 mm 2 versus 0.14 mm 2 ; p = 0.001). CONCLUSION: IAC diverticula are commonly found in otopathologic specimens with varied etiologies, but larger diverticula are more likely to be associated with otosclerosis. The sensitivity and specificity of CT scans to detect IAC diverticula are limited.

Association Between Incomplete Partition Type III and Abnormal Hypothalamic Morphology: Further Imaging Evidence.

PURPOSE: Incomplete partition III (IP-III), characterized by congenital mixed or sensorineural hearing loss, is a rare genetic disease transmitted through X-linked mode of inheritance. Inner ear findings of IP-III have been well described and allow an immediate diagnosis to be made. Recently, an association between IP-III and distinct hypothalamic malformations has been reported in some of the patients with IP-III. The purpose of this study was to investigate the morphologic abnormalities of the hypothalamus in IP-III. MATERIALS AND METHODS: Magnetic resonance imaging studies of 8 subjects, including 1 set of brothers, who were diagnosed with IP-III based on their clinical and inner ear imaging findings, were analyzed. RESULTS: Of the 8 subjects, 7 demonstrated some degree of morphologic abnormality of the hypothalamus. Of these, 2 showed asymmetrical thickening, 1 showed symmetrical thickening, and 4 showed mass-like enlargement of the hypothalamus. Six of 7 subjects with hypothalamic abnormalities showed asymmetry in caudal extension of the abnormalities, which was more discernible on coronal oblique T2-weighted images. Clinically, none of the subjects had endocrinologic or neurologic symptoms. CONCLUSIONS: This retrospective analysis presents further magnetic resonance imaging evidence on the association between the rare IP-III malformations and the presence of hypothalamic morphologic abnormalities.

Structural changes in the inner ear over time studied in the experimentally deafened guinea pig.

Today a cochlear implant (CI) may significantly restore auditory function, even for people with a profound hearing loss. Because the efficacy of a CI is believed to depend mainly on the remaining population of spiral ganglion neurons (SGNs), it is important to understand the timeline of the degenerative process of the auditory neurons following deafness. Guinea pigs were transtympanically deafened with neomycin, verified by recording auditory brainstem responses (ABRs), and then sacrificed at different time points. Loss of SGNs as well as changes in cell body and nuclear volume were estimated. To study the effect of delayed treatment, a group of animals that had been deaf for 12 weeks was implanted with a stimulus electrode mimicking a CI, after which they received a 4-week treatment with glial cell-derived neurotrophic factor (GDNF). The electrical responsiveness of the SGNs was measured by recording electrically evoked ABRs. There was a rapid degeneration during the first 7 weeks, shown as a significant reduction of the SGN population. The degenerative process then slowed, and there was no difference in the amount of remaining neurons between weeks 7 and 18. © 2016 The Authors Journal of Neuroscience Research Published by Wiley Periodicals, Inc.

Auditory Brainstem Response Latency in Noise as a Marker of Cochlear Synaptopathy.

Evidence from animal and human studies suggests that moderate acoustic exposure, causing only transient threshold elevation, can nonetheless cause "hidden hearing loss" that interferes with coding of suprathreshold sound. Such noise exposure destroys synaptic connections between cochlear hair cells and auditory nerve fibers; however, there is no clinical test of this synaptopathy in humans. In animals, synaptopathy reduces the amplitude of auditory brainstem response (ABR) wave-I. Unfortunately, ABR wave-I is difficult to measure in humans, limiting its clinical use. Here, using analogous measurements in humans and mice, we show that the effect of masking noise on the latency of the more robust ABR wave-V mirrors changes in ABR wave-I amplitude. Furthermore, in our human cohort, the effect of noise on wave-V latency predicts perceptual temporal sensitivity. Our results suggest that measures of the effects of noise on ABR wave-V latency can be used to diagnose cochlear synaptopathy in humans. SIGNIFICANCE STATEMENT: Although there are suspicions that cochlear synaptopathy affects humans with normal hearing thresholds, no one has yet reported a clinical measure that is a reliable marker of such loss. By combining human and animal data, we demonstrate that the latency of auditory brainstem response wave-V in noise reflects auditory nerve loss. This is the first study of human listeners with normal hearing thresholds that links individual differences observed in behavior and auditory brainstem response timing to cochlear synaptopathy. These results can guide development of a clinical test to reveal this previously unknown form of noise-induced hearing loss in humans.

Analysis of Vestibular Evoked Myogenic Potentials and Electrocochleography in Noise Induced Hearing Loss.

OBJECTIVE: Our objective was to analyze the electrocochleography (ECoG) and cervical vestibular evoked myogenic potential (cVEMP) results of patients with noise-induced hearing loss (NIHL). MATERIALS AND METHODS: The study included 20 patients with NIHL. Pure-tone audiometry, tympanic membrane ECoG, and cVEMP were performed on all patients. The patients were divided into two groups based on averaged thresholds at 4, 6, and 8 kHz; whereby, group 1 comprised patients who had a threshold higher than 68.3 dB HL, whereas group 2 comprised patients with a threshold lower than 68.3 dB HL. RESULTS: Group 2 had a significantly higher number of patients with abnormal cVEMP values (63% versus 28%) (p=0.028). There was no significant difference in the incidence of ECoG abnormality between the groups (p>0.05), but there was a significant difference in the incidence of recognizable ECoG potentials between the groups (p<0.05). When only patients with vertigo/dizziness were considered, the group with vertigo and a lower degree of hearing loss (group 2) showed a higher incidence of abnormal cVEMP (p<0.05). CONCLUSION: Although the anatomical proximity of the sacculus to the cochlea leads to the consideration of a common involvement of these structures in NIHL, our results did not support the idea of a common and proportional involvement of the vestibular and auditory systems. Our study shows that saccular involvement is disproportionate to auditory involvement in NIHL.

MRI Inner Ear Imaging and Tone Burst Electrocochleography in the Diagnosis of Ménière's Disease.

OBJECTIVE: To compare the sensitivity of gadolinium MRI inner imaging with tone burst electrocochleography (EcochG) for diagnosing endolymphatic hydrops. STUDY DESIGN: A prospective study on patients who were to have an MRI scan to exclude retrocochlear pathology. SETTING: Tertiary care center. PATIENTS: One hundred and two patients: 57 patients with Possible, Probable, or Definite Ménière's Disease, 25 with asymmetrical hearing loss, 18 with sudden sensorineural hearing loss, and 2 with unilateral tinnitus had additional MRI inner ear imaging and click and tone burst stimulus EcochG testing. INTERVENTION: Diagnostic. MAIN OUTCOME MEASURE: To compare the sensitivity of the two techniques. RESULTS: In 30 patients with symptom-based Definite Ménière's Disease, tone burst EcochG was positive in 25 (83%) and the click EcochG was positive in 9/30 (30%), and gadolinium MRI imaging diagnosed hydrops in 14 (47%). A positive result for either MRI imaging or tone burst EcochG was seen in 26 patients (87%). In 14 subjects with symptom-based Probable Ménière's Disease, 10 (71%) had either a positive EcochG or MRI. In 13 with Possible Ménière's Disease, four (31%) had a positive EcochG or MRI. CONCLUSION: This study confirms the greatly enhanced diagnostic sensitivity of tone burst EcochG over click response in diagnosing endolymphatic hydrops in Ménière's disease. Even though adequate MRI imaging was achieved in 90%, tone burst EcochG was a more sensitive test.

[Pneumococcal meningitis with accompanying severe hearing loss: 3D-FLAIR imaging of the inner ear and treatment].

A 66-year-old man was admitted to our hospital because of unconsciousness. He was diagnosed with pneumococcal meningitis and treated with a combination of antibiotics (meropenem hydrate), dexamethasone, and intravenous immunoglobulin. Although he gradually regained consciousness, he started showing signs of hearing disturbance. Measurement of auditory brainstem response revealed severe sensorineural hearing loss. The patient then underwent three-dimensional fluid-attenuated inversion recovery magnetic resonance imaging, which revealed increased signals in the cochlea and the vestibuum, and their enhancement after gadolinium administration. This enhancement was still observed on images of the inner ear acquired on the 52nd hospital day. These findings suggested that the change of content in the lymph and the damage to the blood-labyrinth barrier was caused and aggravated by an immune response. Recent studies have shown that an MyD88-dependent immune response contributes to hearing loss in an experimental mouse model of pneumococcal meningitis. The patient was administered steroid pulse and hyperbaric oxygen therapies for improving the hearing deficit, but these therapies were discontinued because of the aggravation of hepatitis B and diabetes mellitus, which he had developed previously.

Usher proteins in inner ear structure and function.

Usher syndrome (USH) is a neurosensory disorder affecting both hearing and vision in humans. Linkage studies of families of USH patients, studies in animals, and characterization of purified proteins have provided insight into the molecular mechanisms of hearing. To date, 11 USH proteins have been identified, and evidence suggests that all of them are crucial for the function of the mechanosensory cells of the inner ear, the hair cells. Most USH proteins are localized to the stereocilia of the hair cells, where mechano-electrical transduction (MET) of sound-induced vibrations occurs. Therefore, elucidation of the functions of USH proteins in the stereocilia is a prerequisite to understanding the exact mechanisms of MET.

[Otosclerosis- <> or the loss of the natural variant of inertness (<> of the labyrinth capsule)].

The author suggests an original hypothesis of otosclerosis based on the analyses of the literature publications for many years and his personal clinical observations. The normal labyrinth capsule is considered to be bradytrophic, i.e. inert and showing an extremely low level of metabolic processes. The disturbance of bradytrophicity under the action of individual factors and/or especially their combination make it involved in the maintenance of calcium homeostasis in the body. The validity of this conjecture is confirmed by the results of histological investigations, viz. the appearance of diquide or xplasma-like, bone in the labyrinth of the patients suffering otosclerosis. Such bone resorption is known to occur in other parts of the bony skeletontoo and should be regarded as a normal physiological process contributing to the replenishment of blood calcium deficiency.The subsequent reorganization (remodeling) of any part of the bony skeleton is physiologically neutral. In the labyrinth capsule,with its small size and delicate structure, such reorganization induces the otosclerotic process responsible for dysfunction of the membranaceous labyrinth. The surgical treatment of the patients presenting with otosclerosis should be supplemented by conservative treatment intended to slow down the otosclerotic reorganization and to restore bradytrophicity of the labyrinth capsule.

Nutrient-enhanced diet reduces noise-induced damage to the inner ear and hearing loss.

Oxidative stress has been implicated broadly as a cause of cell death and neural degeneration in multiple disease conditions; however, the evidence for successful intervention with dietary antioxidant manipulations has been mixed. In this study, we investigated the potential for protection of cells in the inner ear using a dietary supplement with multiple antioxidant components, which were selected for their potential interactive effectiveness. Protection against permanent threshold shift (PTS) was observed in CBA/J mice maintained on a diet supplemented with a combination of ß-carotene, vitamins C and E, and magnesium when compared with PTS in control mice maintained on a nutritionally complete control diet. Although hair cell survival was not enhanced, noise-induced loss of type II fibrocytes in the lateral wall was significantly reduced (P < 0.05), and there was a trend toward less noise-induced loss in strial cell density in animals maintained on the supplemented diet. Taken together, our data suggest that prenoise oral treatment with the high-nutrient diet can protect cells in the inner ear and reduce PTS in mice. The demonstration of functional and morphologic preservation of cells in the inner ear with oral administration of this antioxidant supplemented diet supports the possibility of translation to human patients and suggests an opportunity to evaluate antioxidant protection in mouse models of oxidative stress-related disease and pathology.

Evaluation of the effect of dexamethasone in experimentally induced endolymphatic hydrops in guinea pigs.

PURPOSE: The aim of this study was to investigate the audiological and histopathologic effects of dexamethasone in the treatment of experimentally induced endolymphatic hydrops. MATERIALS AND METHODS: Thirty mature, male guinea pigs weighing 400 +/- 50 g were operated on to induce experimental endolymphatic hydrops in their right ear. Left ear served as control. Subjects were separated into control and dexamethasone groups, with the latter receiving dexamethasone 5 mg/(kg d) intraperitoneally for 10 days. Electrocochleography and auditory brainstem response were applied to all subjects at preoperation, on the second postoperative day and also on the 15th postoperative day in animals that lived for a long time. The histopathologic examination of the inner ear in all animals was done at the end of the study. RESULTS: The summating potential and the ratio of the summating potential to the action potential measured on the second postoperative day were found to be increased in both groups, but more significantly in the control one. When the left and right ears were compared, significant difference was found in the control group; however, no significant difference was found between the ears in the dexamethasone group. Histopathologic examination revealed varying degrees of hydrops in the control group, but showed only normal findings or minor changes in the dexamethasone group. CONCLUSIONS: Dexamethasone can prevent the audiological and histopathologic findings of experimentally induced endolymphatic hydrops. However, these results must be supported by clinical and experimental studies designed with a large number of subjects.

Effects of antioxidants on the aging inner ear.

Age-related cochlear structural changes include the degeneration of sensory, neural cells and the stria vascularis. The hypothesis that cellular degeneration results from exposure to oxidative products of respiration was tested by supplementing aged dogs with a diet high in antioxidants and mitochondrial metabolites and by genetically modifying the expression level of the antioxidant, manganese superoxide dismutase (SOD2) in mice. Aged dogs received either a high antioxidant diet or a normal, control diet for the last 3 years of their life. Cellular measures were compared among the two aged groups (10-15 years) and young dogs. Both aged groups had cellular degeneration relative to young dogs, but the animals fed the antioxidant diet showed less degeneration at the base and apex than the control-diet group. Transgenic mice, heterozygous null for SOD2, produce only half as much enzyme as a normal mouse. These mice showed no increase in the amount of hearing loss relative to the background strain. A diet containing antioxidants reduced the magnitude of cochlear degeneration. Genetic reduction of one antioxidant, however, did not increase the magnitude of hearing loss in aging mice. A reduction in one enzyme seems to be compensated while the addition of a complex of factors is effective.

Optimization of ribonucleic acid detection from archival Guinea pig temporal bone specimens.

HYPOTHESIS: The choice of ribonucleic acid (RNA) isolation protocol coupled with modifications to RNA extraction and detection procedures may result in a more reliable method to detect gene expression in archived temporal bones. BACKGROUND: A large number of archival temporal bones exist. Retrospective analysis of these specimens using techniques of RNA extraction will greatly enrich our understanding of the pathophysiology of specific otologic diseases. However, archival human temporal bones are aged and embedded in paraffin or celloidin, rendering isolation and manipulation of nucleic acid in preserved specimens difficult, especially as it pertains to RNA degradation. Despite some reports of moderate success in the recent past, RNA isolation and gene expression using polymerase chain reaction (PCR) analysis continues to be challenging and unreliable. Archival guinea pig temporal bone specimens were used to develop and optimize a protocol for RNA extraction and gene expression analysis using PCR and quantitative PCR methods. The genes amplified comprise housekeeping genes and genes associated with the glutamate pathway. METHODS: Archival celloidin-embedded guinea pig temporal bones were collected from the senior author's collection of experimental hydropic inner ear specimens. RNA from this tissue was extracted using the protocol described previously in 16animals and using a modified trizol extraction technique in 10 animals. Gene expression analysis was performed on the extracted RNA. Analysis included two housekeeping genes, GAPDH and 18S, as well as three mediators of the glutamate pathway, glutamate aspartate transporter, glutamate synthetase, and inducible nitric oxide synthase. RESULTS: Compared with the standard extraction protocol, the trizol-based extraction technique showed greater reliability and reproducibility of RNA detection. The housekeeping gene GAPDH or 18S was detected in 7 of 36 attempts with the standard protocol versus 9 of 9 using the modified extraction method (P < 0.001). The gene of interest, glutamate aspartate transporter, was detected in 3 of 26 attempts with the standard protocol versus 12 of 13 attempts using the modified extraction method (P < 0.001). Quantification of messenger RNA levels was then achieved using quantitative PCR methods. CONCLUSION: Improved reliability for detection of gene expression and demonstration of reproducibility were accomplished by modification of RNA extraction technique and standard reverse transcriptase PCR protocol. In addition, we also showed that gene expression from archival material can be quantified by real-time PCR.

[Influence of hyperbaric oxygen on the view of chicken's inner ear damage after exposure to wide-band noise]. / Wplyw tlenu hiperbarycznego na obraz zniszczen komórek rzesatych ucha wewnetrznego kurczat poddanych ekspozycji na halas szerokopasmowy.

The aim of the study was to assess the influence of hyperbaric oxygen on regeneration processes which take place in the inner ear (basilar papilla - BP) of chicken after exposure to wide-band noise at the level 120 dB for 48 hours. We found, that hyperbaric oxygen applied once a day after exposure to the noise restricted he extensiveness and decreased the dynamics of hair cells injury. Quantative and qualitive differences in histological changes which take place in chick basilar papilla after exposure to hyperbaric oxygen and glucocorticoids may prove the presence of different their effectory points of acting.

NF-kappaB mediated glucocorticoid response in the inner ear after acoustic trauma.

The inner ear of humans and experimental animals demonstrate an abundance of glucocorticoid receptors (GR). Glucocorticoids (GC) are widely used to treat different hearing disorders; yet the mechanisms of GC action on the inner ear are unknown. We demonstrate how GR can directly modulate hearing sensitivity in response to a moderate acoustic trauma that results in a hearing loss (10-30 dB). The GC agonist (dexamethasone) and the drugs (metyrapone + RU 486) showed opposing effects on hearing threshold shifts. GC agonist (dexamethasone) decreased the hearing threshold whereas pre-treatment with a GC synthesis inhibitor (metyrapone) in combination with a GR antagonist (RU 486) exacerbated auditory threshold shifts (25-60 dB) after acoustic trauma with statistically significant increase in GR mRNA and GR protein compared with the vehicle and acoustic trauma group. Acoustic trauma caused a significant increase in the nuclear transport of NF-kappaB, whereas pre-treatment with the drugs (metyrapone and RU 486) blocked NF-kappaB nuclear transport into spiral ganglion nuclei. An NF-kappaB inhibitor, pyrrolidine dithiocarbamate ammonium blocked the trauma-induced translocation of NF-kappaB and resulted in a hearing loss (45-60) dB. These results indicate that several factors define the responsiveness of the inner ear to GC, including the availability of ligand or receptor, and the nuclear translocation of GR and NF-kappaB. These findings will further our understanding of individual GC responsiveness to steroid treatment, and will help improve the development of pharmaceuticals to selectively target GR in the inner ear for individuals with increased sensitivity to acoustic trauma.

The use of zebrafish for assessing ototoxic and otoprotective agents.

Zebrafish and other fish exhibit hair cells in the lateral-line neuromasts which are structurally and functionally similar to mammalian inner ear hair cells. To facilitate drug screening for ototoxic or otoprotective agents, we report a straightforward, quantitative in vivo assay to determine potential ototoxicity of drug candidates and to screen otoprotective agents in zebrafish larva. In this study, a fluorescent vital dye, DASPEI (2-(4-(dimethylamino)styryl)-N-ethylpyridinium iodide), was used to stain zebrafish hair cells in vivo and morphometric analysis was performed to quantify fluorescence intensity and convert images to numerical endpoints. Various therapeutics, including gentamicin, cisplatin, vinblastine sulfate, quinine, and neomycin, which cause ototoxicity in humans, also resulted in hair cell loss in zebrafish. In addition, protection against cisplatin-induced ototoxicity was observed in zebrafish larva co-treated with cisplatin and different antioxidants including, glutathione (GSH), allopurinol (ALO), N-acetyl l-cysteine (l-NAC), 2-oxothiazolidine-4-carboxylate (OTC) and d-methionine (d-MET). Our data indicate that results of ototoxicity and otoprotection in zebrafish correlated with results in humans, supporting use of zebrafish for preliminary drug screening.

Identification and characterization of choline transporter-like protein 2, an inner ear glycoprotein of 68 and 72 kDa that is the target of antibody-induced hearing loss.

The Kresge Hearing Research Institute-3 (KHRI-3) antibody binds to a guinea pig inner ear supporting cell antigen (IESCA) and causes hearing loss. To gain insight into the mechanism of antibody-induced hearing loss, we used antibody immunoaffinity purification to isolate the IESCA, which was then sequenced by mass spectroscopy, revealing 10 guinea pig peptides identical to sequences in human choline transporter-like protein 2 (CTL2). Full-length CTL2 cDNA sequenced from guinea pig inner ear has 85.9% identity with the human cDNA. Consistent with its expression on the surface of supporting cells in the inner ear, CTL2 contains 10 predicted membrane-spanning regions with multiple N-glycosylation sites. The 68 and 72 kDa molecular forms of inner ear CTL2 are distinguished by sialic acid modification of the carbohydrate. The KHRI-3 antibody binds to an N-linked carbohydrate on CTL2 and presumably damages the organ of Corti by blocking the transporter function of this molecule. CTL2 mRNA and protein are abundantly expressed in human inner ear. Sera from patients with autoimmune hearing loss bind to guinea pig inner ear with the same pattern as CTL2 antibodies. Thus, CTL2 is a possible target of autoimmune hearing loss in humans.

Mice lacking the B1 subunit of H+ -ATPase have normal hearing.

Acid-base homeostasis of endolymph is thought to be essential for normal inner ear function. This assumption was supported by clinical data from individuals affected by autosomal recessive distal renal tubular acidosis with sensorineural hearing loss. This recessive syndrome was recently demonstrated to be due to mutations in the gene encoding the B1 subunit of H(+)-ATPase (ATP6B1). To examine the potential roles of H(+)-ATPase B1 subunit in inner ear development and function, we defined its spatial and temporal expression patterns in the developing mouse inner ear and examined the morphologic and physiologic effects of loss of its function. Standard in situ hybridization was used for the expression study with routine morphologic and physiologic assessments of hearing and balance in H(+)-ATPase B1 subunit (Atp6b1) null mutant mice. Atp6b1 mRNA was first detected at embryonic day 11.5 (E11.5) in the endolymphatic duct epithelia. From E16.5 onward, Atp6b1 was also observed in the presumptive interdental cell layer of the spiral limbus in the cochlea. Auditory brainstem response tests revealed normal hearing in mice lacking Atp6b1. The inner ears of these mice develop normally and show no overt morphological abnormalities. Our data demonstrate that Atp6b1 is not critical for normal inner ear development or normal inner ear function in mice and suggest that other proton-transporting mechanisms or pH buffering systems must allow the mouse inner ear to compensate for lack of normal Atp6b1 activity.