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Background and Aim: Human blood group system variations may impact the individual's health and hearing status. It was found that individuals with O-positive blood are more prone to noise-induced hearing loss, and they exhibit reduced amplitude in otoacoustic emissions, elevated Acoustic Reflex Threshold (ART), and a slightly higher resonance frequency of the middle ear. Hence, a study was needed to observe if the same trend is followed for those with Rh-ve blood groups. Methods: A cross-sectional group post-test-only design with a non-random convenient sample was applied. This study was conducted with forty adult female participants with a pure tone threshold range of less than or equal to 15 dBHL and ages ranging from 18 to 25 years. In each blood group (A-, B-, O-, AB-), 10 participants were recruited. All participants underwent immittance evaluation, pure tone audiometry, and extended highfrequency audiometry. Results: On analyzing the data, participants with the O negative blood group showed significantly elevated ART in both ipsilateral and contralateral ears. Also, there was no significant difference for pure tone thresholds for the frequencies 250 Hz to 16 kHz and tympanometry findings. Conclusion: This study indicates that the elevated ARTs in O negative blood group people could be attributed to relatively increased stiffness in the middle ear and fewer outer hair cells compared with other blood groups. [ABSTRACT FROM AUTHOR]

Cochlear outer hair cells (OHCs) play a fundamental role in the hearing sensitivity and frequency selectivity of mammalian hearing and are especially vulnerable to noise-induced damage. The OHCs depend on Ca2+ homeostasis, which is a balance between Ca2+ influx and extrusion, as well as Ca2+ buffering by proteins and organelles. Alterations in OHC Ca2+ homeostasis is not only an immediate response to noise, but also associated with impaired auditory function. However, there is little known about the contribution of Ca2+ buffering proteins and organelles to the vulnerability of OHCs to noise. In this study, we used a knockout (KO) mouse model where oncomodulin (Ocm), the major Ca2+ binding protein preferentially expressed in OHCs, is deleted. We show that Ocm KO mice were more susceptible to noise induced hearing loss compared to wildtype (WT) mice. Following noise exposure (106 dB SPL, 2 h), Ocm KO mice had higher threshold shifts and increased OHC loss and TUNEL staining, compared to age-matched WT mice. Mitochondrial morphology was significantly altered in Ocm KO OHCs compared to WT OHCs. Before noise exposure, Ocm KO OHCs showed decreased mitochondrial abundance, volume, and branching compared to WT OHCs, as measured by immunocytochemical staining of outer mitochondrial membrane protein, TOM20. Following noise exposure, mitochondrial proteins were barely visible in Ocm KO OHCs. Using a mammalian cell culture model of prolonged cytosolic Ca2+ overload, we show that OCM has protective effects against changes in mitochondrial morphology and apoptosis. These experiments suggest that disruption of Ca2+ buffering leads to an increase in noise vulnerability and mitochondrial-associated changes in OHCs. [ABSTRACT FROM AUTHOR]

Signal transducer and activator of transcription 3 (Stat3) plays a role in various cellular processes such as differentiation, inflammation, cell survival and microtubule dynamics, depending on the cell type and the activated signaling pathway. Stat3 is highly expressed in the hair cells and supporting cells of the cochlea and is essential for the differentiation of mouse hair cells in the early embryonic stage. However, it is unclear how Stat3 contributes to the correct function of cells in the organ of Corti postnatally. To investigate this, an inducible Cre/loxp system was used to knock out Stat3 in either the outer hair cells or the supporting cells. The results showed that the absence of Stat3 in either the outer hair cells or the supporting cells resulted in hearing loss without altering the morphology of the organ of Corti. Molecular analysis of the outer hair cells revealed an inflammatory process with increased cytokine production and upregulation of the NF-kB pathway. However, the absence of Stat3 in the supporting cells resulted in reduced microtubule stability. In conclusion, Stat3 is a critical protein for the sensory epithelium of the cochlea and hearing and functions in a cell and function-specific manner. [ABSTRACT FROM AUTHOR]

Background: Outer hair cells are specialized sensory cells of the mammalian cochlea that contribute to cochlear amplification. Otoacoustic emissions have great potential to detect cochlear impairment, especially in nonlinear mechanical functions of the outer hair cells (OHCs). Objective: To assess the hearing in normal ear by determining cochlear function, as evaluated by TEOAE and DBOAE in patient with unilateral sensory hearing loss with sudden onset. Patients and Methods: This case control study included study group, which included patients with history of SSNHL with normal ear and control group that included similar number of matched subjects included in the same period with bilateral normal hearing. Every participant was subjected to full audiological history taking, otoscopic examination, pure tone audiometer, immittancemetry and otoacoustic emissions. Results: There was a statistically significant difference among the two groups concerning TEOAE of the left ear frequency in Freq 1.0 NF, Freq 1.0 TE NF, Freq 1.5 NF, Freq 2.0 NF, and Freq 2.0 TE NF, among DBOAE of the right ear in F 1641 DP NF, F2 2016 NF, F 2484 DP NF, F2 3000 NF, F 3281 DP NF, F 4922 DP NF, F 6516 DP NF, F1 609 DP, and F 609 DP NF and among DBOAE of the left ear, F1 4922 DP, F 4922 DP NF, F2 2016 NF, F 1641 DP NF, F2 1500 NF, and F2 750 NF. Conclusion: The study supported the use of otoacoustic emissions as a noninvasive and sensitive tool for assessing cochlear health, particularly in cases of sudden hearing loss. [ABSTRACT FROM AUTHOR]

Background: Patients with diabetes mellitus with hearing loss were analyzed for the effect of diabetes mellitus on the outer hair cells. Materials and Methods: Thirty patients with diabetes mellitus who visited to ENT and endocrinology outpatient clinics were analyzed for the effect of diabetes mellitus on hearing, between March 1st, 2021, and August 31st, 2022, in this prospective study. Statistical Analysis: On measurement of Mean and Standard Deviation- Pure tone average shows high hearing threshold in higher frequencies with increase in HbA1c levels (P = 0.001). With increase in HbA1C amplitude of recorded waves for OAE in 29 diabetics were significantly lower (P = 0.001) which attributed to disorder in the hair cells of the cochlea Categorical data were presented as percentages and Chi-square test was used to derive comparisons. For all statistical testing, P = 0.05 was considered significant. The incidence of hearing loss was analyzed from the data of otoacoustic emissions (OAE). All the clinic demographic factors were studied and correlations of hearing loss in diabetics were made to various positive risk factors. Results: In the present study, only 3.3% of subjects exhibited OAE. With an increase in glycosylated hemoglobin (P = 0.001), the distortion product OAE (DPOAE) amplitude decreased. Majority, i.e., 12 (41.3%) had reduced amplitude of DPOAE at 6 kHz, followed by 9 (31.2%) at 4 kHz, 5 (17.2%) at 2 kHz, and 3 (10.3%) at 8 kHz. Males predominated, i.e., 21 (72.4%) in comparison to the females 9 (27.5%). Conclusions: Diabetes has been associated with hearing impairment secondary to alterations in the organ of Corti and the stria vascularis. Hearing deficit is also attributed to the combined effect of hyperglycemia and oxidative stress leading to cochlear microangiopathy and auditory neuropathy. The quality of life improves in diabetics with control of the glycemic index. [ABSTRACT FROM AUTHOR]

The mouse auditory organ cochlea contains two types of sound receptors: inner hair cells (IHCs) and outer hair cells (OHCs). Tbx2 is expressed in IHCs but repressed in OHCs, and neonatal OHCs that misexpress Tbx2 transdifferentiate into IHC-like cells. However, the extent of this switch from OHCs to IHC-like cells and the underlying molecular mechanism remain poorly understood. Furthermore, whether Tbx2 can transform fully mature adult OHCs into IHC-like cells is unknown. Here, our single-cell transcriptomic analysis revealed that in neonatal OHCs misexpressing Tbx2, 85.6% of IHC genes, including Slc17a8, are upregulated, but only 38.6% of OHC genes, including Ikzf2 and Slc26a5, are downregulated. This suggests that Tbx2 cannot fully reprogram neonatal OHCs into IHCs. Moreover, Tbx2 also failed to completely reprogram cochlear progenitors into IHCs. Lastly, restoring Ikzf2 expression alleviated the abnormalities detected in Tbx2+ OHCs, which supports the notion that Ikzf2 repression by Tbx2 contributes to the transdifferentiation of OHCs into IHC-like cells. Our study evaluates the effects of ectopic Tbx2 expression on OHC lineage development at distinct stages of either male or female mice and provides molecular insights into how Tbx2 disrupts the gene expression profile of OHCs. This research also lays the groundwork for future studies on OHC regeneration. [ABSTRACT FROM AUTHOR]

Signal transducer and activator of transcription 3 (Stat3) plays a role in various cellular processes such as differentiation, inflammation, cell survival and microtubule dynamics, depending on the cell type and the activated signaling pathway. Stat3 is highly expressed in the hair cells and supporting cells of the cochlea and is essential for the differentiation of mouse hair cells in the early embryonic stage. However, it is unclear how Stat3 contributes to the correct function of cells in the organ of Corti postnatally. To investigate this, an inducible Cre/loxp system was used to knock out Stat3 in either the outer hair cells or the supporting cells. The results showed that the absence of Stat3 in either the outer hair cells or the supporting cells resulted in hearing loss without altering the morphology of the organ of Corti. Molecular analysis of the outer hair cells revealed an inflammatory process with increased cytokine production and upregulation of the NF-kB pathway. However, the absence of Stat3 in the supporting cells resulted in reduced microtubule stability. In conclusion, Stat3 is a critical protein for the sensory epithelium of the cochlea and hearing and functions in a cell and function-specific manner.

Cochlear outer hair cells (OHCs) play a fundamental role in the hearing sensitivity and frequency selectivity of mammalian hearing and are especially vulnerable to noise-induced damage. The OHCs depend on Ca2+ homeostasis, which is a balance between Ca2+ influx and extrusion, as well as Ca2+ buffering by proteins and organelles. Alterations in OHC Ca2+ homeostasis is not only an immediate response to noise, but also associated with impaired auditory function. However, there is little known about the contribution of Ca2+ buffering proteins and organelles to the vulnerability of OHCs to noise. In this study, we used a knockout (KO) mouse model where oncomodulin (Ocm), the major Ca2+ binding protein preferentially expressed in OHCs, is deleted. We show that Ocm KO mice were more susceptible to noise induced hearing loss compared to wildtype (WT) mice. Following noise exposure (106 dB SPL, 2 h), Ocm KO mice had higher threshold shifts and increased OHC loss and TUNEL staining, compared to age-matched WT mice. Mitochondrial morphology was significantly altered in Ocm KO OHCs compared to WT OHCs. Before noise exposure, Ocm KO OHCs showed decreased mitochondrial abundance, volume, and branching compared to WT OHCs, as measured by immunocytochemical staining of outer mitochondrial membrane protein, TOM20. Following noise exposure, mitochondrial proteins were barely visible in Ocm KO OHCs. Using a mammalian cell culture model of prolonged cytosolic Ca2+ overload, we show that OCM has protective effects against changes in mitochondrial morphology and apoptosis. These experiments suggest that disruption of Ca2+ buffering leads to an increase in noise vulnerability and mitochondrial-associated changes in OHCs.

Aim: Prestin molecule and transporter fructose GLUT5 in the lateral walls of outer hair cells are essential. This study aimed to investigate epigenetic alterations in the GLUT5 gene. Materials and methods: The animals were divided into three groups randomly. No injection was received in the first group (n=3). Groups 2(n=3) and 3(n=6) were injected with intramuscular saline and sodium salicylate, respectively. Electrophysiological measurements were performed at 1st, 2nd, and 8th hours to evaluate the acute effect and in 2 weeks to evaluate the chronic effect. Methylation of CpG dinucleotides in the promoter can lead to dysregulated and repressed gene expression. Genomic DNA was isolated from bone tissues, treated with bisulfite, and analyzed using methylation specific PCR (polymerase chain reaction) (MSP). Epigenetic alterations in the GLUT5 gene were investigated by using the MSP method. Results: There was a significant decrease in electrophysiological measurements at all frequencies in the acute effect (p<0.01), whereas there was no significant difference in the chronic effect for Group 3 (p>0.05). However, methylation of GLUT5 was observed to be increased during acute administration, followed by a decreasing trend to normal during the chronic period. Conclusion: Our findings show that methylation of GLUT5 may decrease GLUT5 expression in lateral walls of outer hair cells, thereby changing prestin-bound fructose transport in cell membranes due to reduced GLUT5 expression. [ABSTRACT FROM AUTHOR]

Background: The cochlear sympathetic system plays a key role in auditory function and susceptibility to noise-induced hearing loss (NIHL). The formation of reactive oxygen species (ROS) is a well-documented process in NIHL. In this study, we aimed at investigating the effects of a superior cervical ganglionectomy (SCGx) on NIHL in Sprague-Dawley rats. Methods: We explored the effects of unilateral and bilateral Superior Cervical Ganglion (SCG) ablation in the eight-ten weeks old Sprague-Dawley rats of both sexes on NIHL. Auditory function was evaluated by auditory brainstem response (ABR) testing and Distortion product otoacoustic emissions (DPOAEs). Outer hair cells (OHCs) counts and the expression of α2A-adrenergic receptor (AR) in the rat cochlea using immunofluorescence analysis. Cells culture and treatment, CCK-8 assay, Flow cytometry staining and analysis, and western blotting were to explore the mechanisms of SCG fibers may have a protective role in NIHL. Results: We found that neither bilateral nor unilateral SCGx protected the cochlea against noise exposure. In HEI-OC1 cells, H2O2-induced oxidative damage and cell death were inhibited by the application of norepinephrine (NE). NE may prevent ROS-induced oxidative stress in OHCs and NIHL through the α2A-AR. Conclusion: These results demonstrated that sympathetic innervation mildly affected cochlear susceptibility to acoustic trauma by reducing oxidative damage in OHCs through the α2A-AR. NE may be a potential therapeutic strategy for NIHL prevention. [ABSTRACT FROM AUTHOR]

Outer hair cells (OHCs) of the organ of Corti (OoC), acting as bidirectional cellular mechanoelectrical transducers, generate, receive, and exchange forces with other major elements of the cochlear partition, including the sensory inner hair cells (IHCs). Force exchange is mediated via a supporting cell scaffold, including Deiters' (DC) and outer pillar cells (OPC), to enable the sensitivity and exquisite frequency selectivity of the mammalian cochlea and to transmit its responses to the auditory nerve. To selectively activate DCs and OPCs in male and female mice, we conditionally expressed in them a hyperpolarizing halorhodopsin (HOP), a light-gated inward chloride ion pump, and measured extracellular receptor potentials (ERPs) and their DC component (ERPDCs) from the cortilymph, which fills the OoC fluid spaces, and compared the responses with similar potentials from HOP-/- littermates. The compound action potentials (CAP) of the auditory nerve were measured as an indication of IHC activity and transmission of cochlear responses to the CNS. HOP light-activated hyperpolarization of DCs and OPCs suppressed cochlear amplification through changing the timing of its feedback, altered basilar membrane (BM) responses to tones at all measured levels and frequencies, and reduced IHC excitation. HOP activation findings reported here complement recent studies that revealed channelrhodopsin activation depolarized DCs and OPCs and effectively bypassed, rather than blocked, the control of OHC mechanical and electrical responses to sound and their contribution to timed and directed electromechanical feedback to the mammalian cochlea. Moreover, our findings identify DCs and OPCs as potential targets for the treatment of noise-induced hearing loss. [ABSTRACT FROM AUTHOR]

Cardiac cells generate and amplify force in the context of cardiac load, yet the membranous sheath enclosing the muscle fibers-the sarcolemma-does not experience displacement. That the sarcolemma sustains beat-to-beat pressure changes without experiencing significant distortion is a muscle-contraction paradox. Here, we report that an elastic element-the motor protein prestin (Slc26a5)-serves to amplify actin-myosin force generation in mouse and human cardiac myocytes, accounting partly for the nonlinear capacitance of cardiomyocytes. The functional significance of prestin is underpinned by significant alterations of cardiac contractility in Prestin-knockout mice. Prestin was previously considered exclusive to the inner ear's outer hair cells; however, our results show that prestin serves a broader cellular motor function.

Age-related hearing loss is difficult to study in humans because multiple genetic and environmental risk factors may contribute to pathology and cochlear function declines in older adults. These pathologies, including degeneration of the stria vascularis, are hypothesized to affect outer hair cells responsible for active cochlear amplification of low-level sounds. Otoacoustic emission (OAE) measures are used to quantify the energy added to the traveling wave in cochlear amplification, which typically weakens with increased pure-tone thresholds and for older individuals. Thus, the current study evaluated two OAE measures for individuals with different components of age-related hearing loss. We examined two retrospective adult lifespan datasets (18 to 89+ years of age) from independent sites (Medical University of South Carolina and Boys Town National Research Hospital), which included demographics, noise history questionnaires, distortion-product otoacoustic emissions (DPOAE), and cochlear reflectance (CR). Metabolic and sensory estimates of age-related hearing loss were derived from the audiograms in each dataset, and then tested for associations with DPOAE and CR. The results showed that metabolic estimates increased for older participants and were associated with lower overall DPOAE and CR magnitudes across frequency (i.e., lower fitted intercepts). Sensory estimates were significantly higher for males, who reported more positive noise histories compared to females and were associated with steeper negative across-frequency slopes for DPOAEs. Although significant associations were observed between OAE configurations, DPOAEs appeared uniquely sensitive to metabolic estimates. The current findings suggest that distortion-based measures may provide greater sensitivity than reflection-based measures to the components of age-related hearing loss. [ABSTRACT FROM AUTHOR]

Auditory frequency coding is place‐specific, which depends on the mechanical coupling of the basilar membrane‐outer hair cell (OHC)‐tectorial membrane network. Prestin‐based OHC electromotility improves cochlear frequency selectivity and sensitivity. Cochlear amplification determines the frequency coding wherein discrete sound frequencies find a 'best' place along the cochlear length. Loss of OHC is the leading cause of age‐related hearing loss (ARHL) and is the most common cause of sensorineural hearing loss and compromised speech perception. Lipid interaction with Prestin impacts OHC function. It has been established that high‐fat diet (HFD) is associated with ARHL. To determine whether genetic background and metabolism preserve cochlear frequency place coding, we examined the effect of HFD in C57BL/6J (B6) and CBA/CaJ (CBA) on ARHL.We found a significant rescuing effect on ARHL in aged B6 HFD cohort. Prestin levels and cell sizes were better maintained in the experimental B6‐HFD group. We also found that distortion product otoacoustic emission (DPOAE) group delay measurement was preserved, which suggested stable frequency place coding. In contrast, the response to HFD in the CBA cohort was modest with no appreciable benefit to hearing threshold. Notably, group delay was shortened with age along with the control. In addition, the frequency dependent OHC nonlinear capacitance gradient was most pronounced at young age but decreased with age. Cochlear RNA‐seq analysis revealed differential TRPV1 expression and lipid homeostasis. Activation of TRPV1 and downregulation of arachidonic acid led to downregulation of inflammatory response in B6 HFD, which protects the cochlea from ARHL. The genetic background and metabolic state‐derived changes in OHC morphology and function collectively contribute to a redefined cochlear frequency place coding and improved age‐related pitch perception. [ABSTRACT FROM AUTHOR]

There is evidence of ototoxicity from antiretrovirals (ARVs), and ARV therapy in pregnant/nursing mothers can expose offspring to these compounds. The current work modelled whether exposure to ARVs in utero and during nursing altered the functioning of the auditory system in offspring mice. The females of seven breeding pairs of C57BL6/J mice were given daily doses of ARVs lamivudine and tenofovir disoproxil fumarate by oral gavage during gestation and nursing. Three breeder females were given equivalent volumes of water as controls. At wean age (3 weeks after birth), the offspring mice were tested with auditory brainstem responses (ABRs). At the conclusion of the experiment, the offspring mice's cochleae were examined for hair cell counts. Ten breeder female C57BL6/J mice and 69 offspring mice. The offspring mice exposed to ARVs during development showed higher ABR thresholds than the control offspring. No differences were found in supra-threshold ABRs. There was no evidence of missing hair cells. Hearing impairment may be a possible consequence of exposure to ARVs during gestation and development. Because the threshold differences were not large, if they are occurring in humans, it is unlikely they would be identified in any hearing screening tests. [ABSTRACT FROM AUTHOR]

Objectives: This study aimed to determine the prognostic value of otoacoustic emissions (OAEs) in idiopathic sudden sensorineural hearing loss patients. Methods: The study included 30 subjects with unilateral idiopathic sudden sensorineural hearing loss (ISSNHL). Each patient was evaluated four times: at baseline and after one week, one month, and three months of treatment. During each visit, each patient was subjected to full audiological history, otoscopic examination, basic audiological evaluations, and transiently evoked and distortion product otoacoustic emission (TEOAEs & DEOAEs). Results: The hearing thresholds (frequency range 250–8000 Hz) and word recognition scores of patients with detectable TEOAEs and DPOAEs improved significantly, whereas no significant improvements were observed in those with no response. Conclusion: Hearing improvement is better in patients with detectable TEOAEs and DPOAEs. As a result, TEOAEs and DPOAEs are recommended as routine tests in all SSNHL patients to predict outcomes and monitor treatment as TEOAEs and DPOAEs reflect the cochlear OHCs activity.

Objective: To investigate the electrophysiology of the cochlear summating potential (SP) in patients with Meniere's disease (MD). Although long considered a purely hair cell potential, recent studies show a neural contribution to the SP. Patients with MD have an enhanced SP compared to those without the disease. Consequently, this study was to determine if the enhancement of the SP was in whole or part due to neural dysfunction. Design: Study participants included 41 adults with MD and 53 subjects with auditory neuropathy spectrum disorder (ANSD), undergoing surgery where the round window was accessible. ANSD is a condition with known neural dysfunction, and thus represents a control group for the study. The ANSD subjects and 17 of the MD subjects were undergoing cochlear implantation (CI) surgery; the remaining MD subjects were undergoing either endolymphatic sac decompression or labyrinthectomy to alleviate the symptoms of MD. Electrocochleography was recorded from the round window using high intensity (90 dB nHL) tone bursts. The SP and compound action potential (CAP) were measured to high frequencies (> = 2 kHz) and the SP, cochlear microphonic (CM) and auditory nerve neurophonic (ANN) to low frequencies. Linear mixed models were used to assess differences between MD and ANSD subjects. Results: Across frequencies, the MD subjects had smaller alternating current (AC) response than the ANSD subjects (F = 31.61,534, p < 0.001), but the SP magnitudes were larger (F = 94.31,534, p < 0.001). For frequencies less than 4 kHz the SP magnitude in the MD group was significantly correlated with the magnitude of the CM (p's < 0.001) but not in the ANSD group (p's > 0.05). Finally, the relative proportions of both ANN and CAP were greater in MD compared to ANSD subjects. The shapes of the waveforms in the MD subjects showed the presence of multiple components contributing to the SP, including outer and inner hair cells and neural activity. Conclusion: The results support the view that the increased negative polarity SP in MD subjects is due to a change in the operating point of hair cells rather than a loss of neural contribution. The steady-state SP to tones in human subjects is a mixture of different sources with different polarities. [ABSTRACT FROM AUTHOR]

Noise-induced hearing loss (NIHL) results from prolonged exposure to intense noise, causing damage to sensory outer hair cells (OHCs) and spiral ganglion neurons (SGNs). The blood labyrinth barrier (BLB) hinders systemic drug delivery to the inner ear. This study applied a retro-auricular round window membrane (RWM) method to bypass the BLB, enabling the transport of macromolecular proteins into the inner ear. Pigment epithelium-derived factor (PEDF), which has anti-inflammatory and neuroprotective properties, is conjugated to a prestin-targeting peptide 2 (PrTP2) using N-succinimidyl-3-maleimidopropionate (SMP) to form PrTP2-SMP/PEDF. This compound specifically targeted Prestin and accumulated around OHCs for sustained release, effectively reducing OHC and SGN loss. Functional and structural tests, including auditory brainstem response (ABR), confocal microscopy, and scanning electron microscopy (SEM), revealed significant hearing restoration and cellular protection. Additionally, the results of enzyme-linked immunosorbent assay (ELISA), Annexin V and propidium iodide (PI) staining and immunoblotting show that noise exposure may induce pyroptosis in the cochlea by activating the NOD-like receptor protein 3 (NLRP3)-apoptosis-associated speck-like protein containing a CARD (ASC) - cysteinyl aspartate specific proteinase (Caspase-1) pathway and PrTP2-SMP/PEDF alleviates the inflammatory response by inhibiting pyroptosis. Toxicity analysis indicates no adverse effects, suggesting that PrTP2-SMP/PEDF has a promising therapeutic prospective for NIHL., (© 2025 Wiley‐VCH GmbH.)

Introduction: Dentists and dental professionals report a high prevalence of noise-induced hearing loss (NIHL) and related symptoms. Chronic exposure to high-frequency dental instrument sounds, which can damage the outer hair cells (OHCs) of the cochlea, is strongly linked to their NIHL. Similarly, dental students in teaching clinics often report symptoms associated with NIHL. In this study, we measured plasma levels of prestin and otolin-1, two biomarkers associated with inner ear health, in first-year (D1) and third-year (D3) dental students. D1 students were selected for their relatively short exposure to dental clinics, while D3 students represented a group with substantial cumulative exposure. First-year (M1) medical students, who have no exposure to dental instruments, served as the negative controls, while dental faculty, many of whom are diagnosed with NIHL or self-report hearing problems, served as the positive controls., Methods: Thirty-one students (D1=11, D3=8, M1=12) and 10 dental faculty volunteered for the study. Participating students completed an online survey about their hearing health, exposure to excessive sounds within and outside school, and use of hearing protection. Sound levels of medical Osteopathic Manipulative Medicine (OMM) and dental Simulation (SIM) labs while in session were recorded with a calibrated sound meter. Plasma levels of prestin and otolin-1 were quantitated using commercial ELISA kits., Results: The sound level of in-session OMM lab was significantly higher (72.64 ± 1.69 dBA) than SIM lab (65.37 ± 3.97 dBA). Both medical and dental students experienced similar exposure to outside school noises; however, dental students had significantly longer exposure to high-frequency dental instrument sounds in the SIM lab (12.3 hours/week; 74.93-80.51 dBA). Plasma prestin levels were lowest in D3 students (559.88 ± 24.91 ng/ml), followed by D1 students (576.27 ± 71.44 ng/ml). Negative control M1 students had higher levels (675.73 ± 90.23 ng/ml), while the positive control dental faculty group exhibited the highest prestin levels (727.71 ± 128.65 ng/ml). Prestin levels in D3 students were significantly lower than those in M1 students, and the dental faculty group had significantly higher prestin levels than both D1 and D3 students. No differences in otolin-1 levels were observed among the groups., Conclusions: Our finding that D3 students, with greater experience using dental instruments in the SIM lab, exhibited the lowest plasma prestin levels may indicate a protective mechanism by the OHCs, downregulating its expression to reduce the risk of NIHL. This is in line with the findings in the dental faculty, who self-reported NIHL or hearing problems and exhibited the highest prestin levels. The lack of changes in plasma otolin-1 levels across groups, combined with students self-reporting excellent hearing health, may offer alternate view of subclinical inner ear damage among dental students. Future studies incorporating audiometry and otoacoustic emission tests along with the inner ear biomarkers may provide better understanding of NIHL in dental students., Competing Interests: Human subjects: Consent for treatment and open access publication was obtained or waived by all participants in this study. LECOM Institutional Review Board issued approval 31-028. Prior to enrollment, all participants received information about the research protocol and voluntarily completed the Informed Consent form. The study was reviewed and approved by the LECOM Institutional Review Board (Protocol Number: 31-028) in accordance with U.S. federal regulations for human research, and the 1964 Helsinki declaration. Animal subjects: All authors have confirmed that this study did not involve animal subjects or tissue. Conflicts of interest: In compliance with the ICMJE uniform disclosure form, all authors declare the following: Payment/services info: All authors have declared that no financial support was received from any organization for the submitted work. Financial relationships: All authors have declared that they have no financial relationships at present or within the previous three years with any organizations that might have an interest in the submitted work. Other relationships: All authors have declared that there are no other relationships or activities that could appear to have influenced the submitted work., (Copyright © 2024, Lee et al.)

ObjectiveTo investigate the electrophysiology of the cochlear summating potential (SP) in patients with Meniere’s disease (MD). Although long considered a purely hair cell potential, recent studies show a neural contribution to the SP. Patients with MD have an enhanced SP compared to those without the disease. Consequently, this study was to determine if the enhancement of the SP was in whole or part due to neural dysfunction.DesignStudy participants included 41 adults with MD and 53 subjects with auditory neuropathy spectrum disorder (ANSD), undergoing surgery where the round window was accessible. ANSD is a condition with known neural dysfunction, and thus represents a control group for the study. The ANSD subjects and 17 of the MD subjects were undergoing cochlear implantation (CI) surgery; the remaining MD subjects were undergoing either endolymphatic sac decompression or labyrinthectomy to alleviate the symptoms of MD. Electrocochleography was recorded from the round window using high intensity (90 dB nHL) tone bursts. The SP and compound action potential (CAP) were measured to high frequencies (> = 2 kHz) and the SP, cochlear microphonic (CM) and auditory nerve neurophonic (ANN) to low frequencies. Linear mixed models were used to assess differences between MD and ANSD subjects.ResultsAcross frequencies, the MD subjects had smaller alternating current (AC) response than the ANSD subjects (F = 31.61,534, p < 0.001), but the SP magnitudes were larger (F = 94.31,534, p < 0.001). For frequencies less than 4 kHz the SP magnitude in the MD group was significantly correlated with the magnitude of the CM (p’s < 0.001) but not in the ANSD group (p’s > 0.05). Finally, the relative proportions of both ANN and CAP were greater in MD compared to ANSD subjects. The shapes of the waveforms in the MD subjects showed the presence of multiple components contributing to the SP, including outer and inner hair cells and neural activity.ConclusionThe results support the view that the increased negative polarity SP in MD subjects is due to a change in the operating point of hair cells rather than a loss of neural contribution. The steady-state SP to tones in human subjects is a mixture of different sources with different polarities.

After a damaging insult, hair cells can spontaneously regenerate from cochlear supporting cells within the first week of life. While the regenerated cells express several markers of immature hair cells and have stereocilia bundles, their capacity to differentiate into inner or outer hair cells, and ability to form new synaptic connections has not been well-described. In addition, while multiple supporting cell subtypes have been implicated as the source of the regenerated hair cells, it is unclear if certain subtypes have a greater propensity to form one hair cell type over another. To investigate this, we used two CreER mouse models to fate-map either the supporting cells located near the inner hair cells (inner phalangeal and border cells) or outer hair cells (Deiters', inner pillar, and outer pillar cells) along with immunostaining for markers that specify the two hair cell types. We found that supporting cells fate-mapped by both CreER lines responded early to hair cell damage by expressing Atoh1, and are capable of producing regenerated hair cells that express terminal differentiation markers of both inner and outer hair cells. The majority of regenerated hair cells were innervated by neuronal fibers and contained synapses. Unexpectedly, we also found that the majority of the laterally positioned regenerated hair cells aberrantly expressed both the outer hair cell gene, oncomodulin, and the inner hair cell gene, vesicular glutamate transporter 3 (VGlut3). While this work demonstrates that regenerated cells can express markers of both inner and outer hair cells after damage, VGlut3 expression appears to lack the tight control present during embryogenesis, which leads to its inappropriate expression in regenerated cells. [ABSTRACT FROM AUTHOR]

Objective: The present study aimed to perform a morphological and morphometric analysis of cochlear structures of C57BL/6J mice receiving oral melatonin for a 12-month period. Methods: 32 male C57BL/6J were divided into control and melatonin groups. Control received saline and ethanol solution and melatonin group, 50 μL of 10 mg of melatonin/kg/day orally for a 12-month period. After de experiment the animals were sacrificed into a 40% concentration of CO2 chamber, and the blades were morphological and morphometrically analyzed. Results: The melatonin group revealed a higher median density of viable cells (45 ± 10.28 cells/100 μm2, 31–73, vs. 32 ± 7.47 cells/100 μm2, 25–48). The median area of stria vascularis was 55.0 ± 12.27 cells/100 μm2 (38–80) in the control, and 59.0 ± 16.13 cells/100 μm2 (40–134) in the melatonin group. The morphometric analysis of the spiral ligament reveals a higher median of total viable neurons in the melatonin (41 ± 7.47 cells/100 μm2, 27–60) than in the control group (31 ± 5.68 cells/100 μm2, 21–44). Conclusion: Although melatonin is a potent antioxidant, it does not completely neutralize the occurrence of presbycusis; however, it may delay the onset of this condition. Level of evidence: 3.

After a damaging insult, hair cells can spontaneously regenerate from cochlear supporting cells within the first week of life. While the regenerated cells express several markers of immature hair cells and have stereocilia bundles, their capacity to differentiate into inner or outer hair cells, and ability to form new synaptic connections has not been well-described. In addition, while multiple supporting cell subtypes have been implicated as the source of the regenerated hair cells, it is unclear if certain subtypes have a greater propensity to form one hair cell type over another. To investigate this, we used two CreER mouse models to fate-map either the supporting cells located near the inner hair cells (inner phalangeal and border cells) or outer hair cells (Deiters’, inner pillar, and outer pillar cells) along with immunostaining for markers that specify the two hair cell types. We found that supporting cells fate-mapped by both CreER lines responded early to hair cell damage by expressing Atoh1, and are capable of producing regenerated hair cells that express terminal differentiation markers of both inner and outer hair cells. The majority of regenerated hair cells were innervated by neuronal fibers and contained synapses. Unexpectedly, we also found that the majority of the laterally positioned regenerated hair cells aberrantly expressed both the outer hair cell gene, oncomodulin, and the inner hair cell gene, vesicular glutamate transporter 3 (VGlut3). While this work demonstrates that regenerated cells can express markers of both inner and outer hair cells after damage, VGlut3 expression appears to lack the tight control present during embryogenesis, which leads to its inappropriate expression in regenerated cells.

• Nicotinic receptor currents of neonatal inner and outer hair cells were investigated. • There were differences in amplitude, voltage-sensitivity and reversal potential. • There was some indication that activation and desensitization kinetics were slower in IHCs. • These differences might indicate the presence of different auxiliary subunits of the receptor. In the developing cochlea, just before the onset of hearing on postnatal day 12, the medial olivocochlear efferent axons in synaptic contact with the inner hair cells (IHCs) start withdrawing and new efferent synaptic connections are formed on the outer hair cells (OHCs), thereby progressing towards the adult pattern of medial olivocochlear efferent innervation. The synapses are inhibitory, calcium influx through the α9α10 nicotinic acetylcholine receptors (nAChRs) driving opening of calcium-dependent potassium channels. The nAChRs appear to function similarly in IHCs and OHCs, although with probable kinetic differences. Our aim was to assess their functional similarity in the neonatal mouse cochlea by making whole-cell recordings from both hair cell types between postnatal day 7 and 10 when nAChRs are expressed. ACh was applied to voltage-clamped hair cells by pressure-ejection from a pipette. The cells were dialysed with a Cs+-based solution designed to eliminate calcium-dependent potassium currents. There were differences in amplitude, voltage-sensitivity and reversal potential of the nAChR currents between IHCs and OHCs. There was also some indication that IHC nAChRs have slower activation and desensitization kinetics, although the relatively slow ACh application limited interpretation of this result. These differences, particularly concerning the reversal potential, might indicate the presence of different auxiliary protein subunits of the α9α10 receptor in neonatal IHCs and OHCs. [ABSTRACT FROM AUTHOR]

• Ocm and Slc26a5 do not influence the expression of each other • Ocmtm1e homozygotes show progressive high-frequency hearing loss • Slc26a5tm1Cre homozygotes show stable raised thresholds at all frequencies • Slc26a5tm1Cre heterozygotes have raised thresholds at high frequencies • Ocmtm1e homozygotes have scattered hair cell loss even when ABR thresholds are normal The genes Ocm (encoding oncomodulin) and Slc26a5 (encoding prestin) are expressed strongly in outer hair cells and both are involved in deafness in mice. However, it is not clear if they influence the expression of each other. In this study, we characterise the auditory phenotype resulting from two new mouse alleles, Ocmtm1e and Slc26a5tm1Cre. Each mutation leads to absence of detectable mRNA transcribed from the mutant allele, but there was no evidence that oncomodulin regulates expression of prestin or vice versa. The two mutants show distinctive patterns of auditory dysfunction. Ocmtm1e homozygotes have normal auditory brainstem response thresholds at 4 weeks old followed by progressive hearing loss starting at high frequencies, while heterozygotes show largely normal thresholds until 6 months of age, when signs of worse thresholds are detected. In contrast, Slc26a5tm1Cre homozygotes have stable but raised thresholds across all frequencies tested, 3 to 42 kHz, at least from 4 to 8 weeks old, while heterozygotes have raised thresholds at high frequencies. Distortion product otoacoustic emissions and cochlear microphonics show deficits similar to auditory brainstem responses in both mutants, suggesting that the origin of hearing impairment is in the outer hair cells. Endocochlear potentials are normal in the two mutants. Scanning electron microscopy revealed normal development of hair cells in Ocmtm1e homozygotes but scattered outer hair cell loss even at 4 weeks old when thresholds appeared normal, indicating that there is not a direct relationship between numbers of outer hair cells present and auditory thresholds. [ABSTRACT FROM AUTHOR]

Allergic rhinitis (AR) is a type I hypersensitivity reaction of the nasal mucosa, primarily mediated by IgE, with a complex etiology, determined by genetic and environmental interactions. Several mechanisms by which AR affect middle ear and cause conductive hearing loss have been well described. There is paucity of data regarding involvement of inner ear in AR patients leading to sensorineural hearing loss. However, endolymphatic sac and outer hair cells have been hypothesized to be the seat of immunoreactivity. To study the audiological profile in AR and effect of AR on inner ear functions. 100 cases of AR patients (55 males, 45 females, mean age group 21–30 years) and 100 controls (65 males, 35 females, mean age group 41–50 years) were enrolled in study. All underwent thorough clinical ear, nose and throat examination, diagnostic nasal endoscopy and otoendoscopy, followed by audiological assessment including pure tone audiometry, tympanometry and oto-acoustic emission test. Hearing results of both the groups were compared and analysed statistically. Thirty two patients among case group had sensorineural hearing loss, pronounced at 4000 and 8000 Hz frequencies. 18 patients showed conductive hearing loss in the form of type B or type C tympanogram. 32 patients of AR patients showed unusual oto-acoustic emission test. We found higher prevalence of high frequency sensorineural hearing loss in pure tone audiometry and abnormal OAEs in patients having upper airway allergy. The likely seat of damage appears to be the inner ear as evidenced by recordings of OAE in allergic patients. [ABSTRACT FROM AUTHOR]

Cochlear sensitivity, essential for communication and exploiting the acoustic environment, results from sensory-motor outer hair cells (OHCs) operating in a structural scaffold of supporting cells and extracellular cortilymph within the organ of Corti (OoC). Cochlear sensitivity control is hypothesized to involve interaction between the OHCs and OoC supporting cells (e.g., Deiters' cells [DCs] and outer pillar cells [OPCs]), but this has never been established in vivo. Here, we conditionally expressed channelrhodopsins (ChR2) specifically in male and female mouse DCs and OPCs. Illumination of the OoC activated the nonselective ChR2 cation conductance and depolarized DCs when measured in vivo and in isolated OoC. Measurements of sound-induced cochlear mechanical and electrical responses revealed that OoC illumination suppressed the normal functions of OoC supporting cells transiently and reversibly. OoC illumination blocked normally occurring continuous minor adjustments of tone-evoked basilar membrane displacements over their entire dynamic range and OHC voltage responses to tones at levels and frequencies subject to cochlear amplification. OoC illumination altered the OHC mechanoelectrical transduction conductance operating point, which reversed the asymmetry of OHC voltage responses to high level tones. OoC illumination accelerated recovery from temporary loud sound-induced acoustic desensitization. We concluded that DCs and OPCs are involved in both the control of cochlear responses (which are essential for normal hearing) and the recovery from temporary acoustic desensitization. This is the first direct in vivo evidence for the interdependency of the structural, mechanical, and electrochemical arrangements of OHCs and OoC supporting cells that together provide fine control of cochlear responses. [ABSTRACT FROM AUTHOR]

In mammals, the piezoelectric protein, Prestin, endows the outer hair cells (OHCs) with electromotility (eM), which confers the capacity to change cellular length in response to alterations in membrane potential. Together with basilar membrane resonance and possible stereociliary motility, Prestin-based OHC eM lays the foundation for enhancing cochlear sensitivity and frequency selectivity. However, it remains debatable whether Prestin contributes to ultrahigh-frequency hearing due to the intrinsic nature of the cell's low-pass features. The low-pass property of mouse OHC eM is based on the finding that eM magnitude dissipates within the frequency bandwidth of human speech. In this study, we examined the role of Prestin in sensing broad-range frequencies (4–80 kHz) in mice that use ultrasonic hearing and vocalization (to >100 kHz) for social communication. The audiometric measurements in mice showed that ablation of Prestin did not abolish hearing at frequencies >40 kHz. Acoustic associative behavior tests confirmed that Prestin-knockout mice can learn ultrahigh-frequency sound-coupled tasks, similar to control mice. Ex vivo cochlear Ca2+ imaging experiments demonstrated that without Prestin, the OHCs still exhibit ultrahigh-frequency transduction, which in contrast, can be abolished by a universal cation channel blocker, Gadolinium. In vivo salicylate treatment disrupts hearing at frequencies <40 kHz but not ultrahigh-frequency hearing. By pharmacogenetic manipulation, we showed that specific ablation of the OHCs largely abolished hearing at frequencies >40 kHz. These findings demonstrate that cochlear OHCs are the target cells that support ultrahigh-frequency transduction, which does not require Prestin. [ABSTRACT FROM AUTHOR]

The short- and long-term effects of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection on the medial olivocochlear reflex and outer hair cells in the cochlea remain largely unclear. The aim of this study was to investigate the efferent auditory system effects in adult patients with COVID-19. The study included 18–50 years old 44 volunteers: 26 individuals (52 ears) with COVID-19 in the study group and 18 healthy individuals (36 ears) in the control group. Otolaryngological examination, immitancemetric evaluation, distortion product otoacoustic emission (DPOAE), contralateral acoustic stimulation with DPOAE, audiometric evaluation, and high frequency audiometric evaluation were performed in all individuals participating in the study. In our study, patients with COVID-19 had significantly lower DPOAE results with or without broadband noise at only 6 kHz frequency and contralateral suppression results at all frequencies compared to healthy individuals. A statistically significant difference was found between the study and control groups according to whether the participants had a response in the high frequency audiometry at 12 and 16 kHz frequencies. COVID-19 affects many systems in the body. As a result of the findings obtained in the present study, it is shown that the auditory efferent system may also be affected. [ABSTRACT FROM AUTHOR]

Cochlear outer hair cells (OHCs) are essential for hearing. A short, OHC‐specific enhancer is necessary but not yet available for gene therapeutic applications in OHC damage. Such damage is a major cause of deafness. Prestin is a motor protein exclusively expressed in OHCs. We hypothesized that the cis‐regulatory DNA fragment deletion of Slc26a5 would affect its expression. We tested this hypothesis by conducting CRISPR/Cas9‐mediated large DNA fragment deletion of mouse Slc26a5 intron regions. First, starting from a ~13 kbp fragment, step‐by‐step, we narrowed down the sequence to a 1.4 kbp segment. By deleting either a 13 kbp or 1.4 kbp fragment, we observed delayed Prestin expression. Second, we showed that 1.4 kbp was an OHC‐specific enhancer because enhanced green fluorescent protein (EGFP) was highly and specifically expressed in OHCs in a transgenic mouse where EGFP was driven by the 1.4 kbp segment. More importantly, specific EGFP was also driven by its homologous 398 bp fragment in human Slc26a5. This suggests that the enhancer is likely to be evolutionarily conserved across different species. [ABSTRACT FROM AUTHOR]

Age-related hearing loss is a multifactorial condition with effects of aging and environmental exposures that contribute to cochlear pathologies. Metabolic hearing loss involves declines in the endocochlear potential, which broadly reduce cochlear amplification of low-level sounds. Sensory hearing loss involves damage to outer hair cells that may eliminate amplification, especially for high-frequency sounds. A novel approach was developed to estimate the extent of metabolic and sensory components (in dB) for an individual, by combining hearing loss profiles to optimally approximate their hearing thresholds (audiogram). This approach was validated using estimates of metabolic and sensory hearing loss from retrospective datasets including gerbils, cross-sectional and longitudinal audiograms from older adults, a measure of speech recognition in noise, and histopathology case reports. Simulation results showed that well-approximated audiograms can produce accurate metabolic and sensory estimates. Estimates of metabolic and sensory components of age-related hearing loss differentiated gerbils with known strial and/or sensory pathologies based on age and exposures. For older adults, metabolic estimates consistently increased with age and were associated with poorer speech recognition in noise, while sensory estimates were related to sex and noise exposure differences. Histopathology case reports (with audiograms) that described strial and outer hair cell pathology in temporal bones from older donors showed significant differences in metabolic and sensory estimates, respectively. The results support the view that audiograms include information that can be used to estimate the metabolic and sensory components of age-related hearing loss. [ABSTRACT FROM AUTHOR]

Here, we developed a safe and highly effective nanocarrier using β-cyclodextrin (β-CD) and oligoarginine peptide (Arg8)-modified dendrimer-entrapped gold nanoparticles (Au@CD-PAMAM-Arg8), with a diameter of 5 nm, for improved delivery of dexamethasone (Dex) to the inner ear. The properties and in vivo distribution of the Au@CD-PAMAM-Arg8 were assessed in vitro, and a streptomycin (SM) ototoxicity model was used in vivo. Flow cytometry analysis of HEIOC1 cells treated with Au@CD-PAMAM-Arg8 and Au @CD-PAMAM at different time intervals indicated that cell uptake efficiency of the drug delivery carrier Au@CD-PAMAM-Arg8 was higher than that of Au @CD-PAMAM. Au@CD-PAMAM-Arg8 carrying Dex (Au@CD-PAMAM-Arg8/Dex) were mainly distributed in hair cells, the spiral ganglion, lateral wall, and nerve fibers and had stronger protective effects on the inner ear than Dex administration alone. In vivo tracer tests revealed that tympanic injection was significantly more effective than posterior ear injection, muscle injection, and tail vein injection, whereas clinical retro-auricular injection could not increase the efficiency of drug delivery into the ear. Electrocochleography results showed that Au@CD-PAMAM-Arg8/Dex significantly improved hearing in C57/BL6 mice after SM exposure. These findings indicate that Au@CD-PAMAM-Arg8 may be the useful drug carriers for the treatment of inner ear diseases.

Deficiency of otoferlin causes profound prelingual deafness in humans and animal models. Here, we closely analyzed developmental deficits and degenerative mechanisms in Otof knock-out (Otof–/–) mice over the course of 48 weeks. We found otoferlin to be required for proper synapse development in the immature rodent cochlea: In absence of otoferlin, synaptic pruning was delayed, and postsynaptic boutons appeared enlarged at 2 weeks of age. At postnatal day 14 (P14), we found on average ∼15 synapses per inner hair cell (IHC) in Otof–/– cochleae as well as in wild-type controls. Further on, the number of synapses in Otof–/– IHCs was reduced to ∼7 at 8 weeks of age and to ∼6 at 48 weeks of age. In the same period, the number of spiral ganglion neurons (SGNs) declined in Otof–/– animals. Importantly, we found an age-progressive loss of IHCs to an overall number of 75% of wildtype IHCs. The IHC loss more prominently but not exclusively affected the basal aspects of the cochlea. For outer hair cells (OHCs), we observed slightly accelerated age-dependent degeneration from base to apex. This was associated with a progressive decay in DPOAE amplitudes for high frequency stimuli, which could first be observed at the age of 24 weeks in Otof–/– mice. Our data will help to plan and predict the outcome of a gene therapy applied at various ages of DFNB9 patients.

The two types of spiral ganglion neurons (SGNs), types I and II, innervate inner hair cells and outer hair cells, respectively, within the mammalian cochlea and send another process back to cochlear nuclei in the hindbrain. Studying these two neuronal types has been made easier with the identification of unique molecular markers. One of these markers, peripherin, was shown using antibodies to be present in all SGNs initially but becomes specific to type II SGNs during maturation. We used mice with fluorescently labeled peripherin (Prph-eGFP) to examine peripherin expression in SGNs during development and in aged mice. Using these mice, we confirm the initial expression of Prph-eGFP in both types I and II neurons and eventual restriction to only type II perikarya shortly after birth. However, while Prph-eGFP is uniquely expressed within type II cell bodies by P8, both types I and II peripheral and central processes continue to express Prph-eGFP for some time before becoming downregulated. Only at P30 was there selective type II Prph-eGFP expression in central but not peripheral processes. By 9 months, only the type II cell bodies and more distal central processes retain Prph-eGFP expression. Our results show that Prph-eGFP is a reliable marker for type II SGN cell bodies beyond P8; however, it is not generally a suitable marker for type II processes, except for central processes beyond P30. How the changes in Prph-eGFP expression relate to subsequent protein expression remains to be explored.

Noise exposure is the most important external factor causing acquired hearing loss in humans, and it is strongly associated with the production of reactive oxygen species (ROS) in the cochlea. Several studies reported that the administration of various compounds with antioxidant effects can treat oxidative stress-induced hearing loss. However, traditional systemic drug administration to the human inner ear is problematic and has not been successful in a clinical setting. Thus, there is an urgent need to develop rescue treatment for patients with acute acoustic injuries. Hydrogen gas has antioxidant effects, rapid distribution, and distributes systemically after inhalation.The purpose of this study was to determine the protective efficacy of a single dose of molecular hydrogen (H2) on cochlear structures. Guinea pigs were divided into six groups and sacrificed immediately after or at 1 or 2 weeks. The animals were exposed to broadband noise for 2 h directly followed by 1-h inhalation of 2% H2 or room air. Electrophysiological hearing thresholds using frequency-specific auditory brainstem response (ABR) were measured prior to noise exposure and before sacrifice. ABR thresholds were significantly lower in H2-treated animals at 2 weeks after exposure, with significant preservation of outer hair cells in the entire cochlea. Quantification of synaptophysin immunoreactivity revealed that H2 inhalation protected the cochlear inner hair cell synaptic structures containing synaptophysin. The inflammatory response was greater in the stria vascularis, showing increased Iba1 due to H2 inhalation.Repeated administration of H2 inhalation may further improve the therapeutic effect. This animal model does not reproduce conditions in humans, highlighting the need for additional real-life studies in humans.

Deficiency of otoferlin causes profound prelingual deafness in humans and animal models. Here, we closely analyzed developmental deficits and degenerative mechanisms in Otof knock-out (Otof –/–) mice over the course of 48 weeks. We found otoferlin to be required for proper synapse development in the immature rodent cochlea: In absence of otoferlin, synaptic pruning was delayed, and postsynaptic boutons appeared enlarged at 2 weeks of age. At postnatal day 14 (P14), we found on average ∼15 synapses per inner hair cell (IHC) in Otof –/– cochleae as well as in wild-type controls. Further on, the number of synapses in Otof –/– IHCs was reduced to ∼7 at 8 weeks of age and to ∼6 at 48 weeks of age. In the same period, the number of spiral ganglion neurons (SGNs) declined in Otof –/– animals. Importantly, we found an age-progressive loss of IHCs to an overall number of 75% of wildtype IHCs. The IHC loss more prominently but not exclusively affected the basal aspects of the cochlea. For outer hair cells (OHCs), we observed slightly accelerated age-dependent degeneration from base to apex. This was associated with a progressive decay in DPOAE amplitudes for high frequency stimuli, which could first be observed at the age of 24 weeks in Otof –/– mice. Our data will help to plan and predict the outcome of a gene therapy applied at various ages of DFNB9 patients. [ABSTRACT FROM AUTHOR]

Background Understanding the functional differences between crossed and uncrossed medial olivocochlear (MOC) neurons has been of interest to researchers for decades. Previous reports revealed conflicting results about which MOC pathway, crossed or uncrossed, is stronger in humans. Both crossed and uncrossed MOC neurons synapse at the base of the outer hair cells (OHCs) in each ear. OHCs generate the cochlear microphonic, which is a major contributor to the cochlear response (CR) Purpose The current study investigated the effects of eliciting the crossed and uncrossed MOC reflex (MOCR) on CR in humans with three levels of noise. Research Design Normal-hearing, young adults (n=16) participated in this study. The CR was recorded using 500 Hz tone-burst stimuli presented at 80 dB nHL. To examine the crossed and uncrossed MOCR, CR was recorded without and with continuous ipsilateral or contralateral broadband noise (BBN) at three levels (40, 50, and 60 dB SPL). Data Analysis Analysis of the CR was completed using the amplitude of the response extracted using fast Fourier transform. Statistical analysis was completed using repeated measures analysis of variance and post-hoc analysis. Results Compared with baseline, the presentation of BBN, specifically contralaterally, resulted in CR enhancement with no significant difference as a function of the three BBN levels. Greater enhancement of the CR amplitude was observed with contralateral than ipsilateral BBN elicitor. Conclusions The current findings suggest that a contralateral elicitor of the uncrossed MOC pathway results in a larger CR amplitude enhancement compared with an ipsilateral elicitor of the crossed MOC pathway, regardless of the elicitor level. Eliciting the MOCR appears to modulate the OHCs function. Furthermore, assessing the MOCR with the 500 Hz CR with BBN elicitors at moderate levels should separate its effects (i.e., increase response amplitude) from those associated with the middle ear muscle reflex (i.e., reduce response amplitude). [ABSTRACT FROM AUTHOR]

The two types of spiral ganglion neurons (SGNs), types I and II, innervate inner hair cells and outer hair cells, respectively, within the mammalian cochlea and send another process back to cochlear nuclei in the hindbrain. Studying these two neuronal types has been made easier with the identification of unique molecular markers. One of these markers, peripherin, was shown using antibodies to be present in all SGNs initially but becomes specific to type II SGNs during maturation. We used mice with fluorescently labeled peripherin (Prph- eGFP) to examine peripherin expression in SGNs during development and in aged mice. Using these mice, we confirm the initial expression of Prph- eGFP in both types I and II neurons and eventual restriction to only type II perikarya shortly after birth. However, while Prph- eGFP is uniquely expressed within type II cell bodies by P8, both types I and II peripheral and central processes continue to express Prph- eGFP for some time before becoming downregulated. Only at P30 was there selective type II Prph- eGFP expression in central but not peripheral processes. By 9 months, only the type II cell bodies and more distal central processes retain Prph- eGFP expression. Our results show that Prph- eGFP is a reliable marker for type II SGN cell bodies beyond P8; however, it is not generally a suitable marker for type II processes, except for central processes beyond P30. How the changes in Prph- eGFP expression relate to subsequent protein expression remains to be explored. [ABSTRACT FROM AUTHOR]

Noise exposure is the most important external factor causing acquired hearing loss in humans, and it is strongly associated with the production of reactive oxygen species (ROS) in the cochlea. Several studies reported that the administration of various compounds with antioxidant effects can treat oxidative stress-induced hearing loss. However, traditional systemic drug administration to the human inner ear is problematic and has not been successful in a clinical setting. Thus, there is an urgent need to develop rescue treatment for patients with acute acoustic injuries. Hydrogen gas has antioxidant effects, rapid distribution, and distributes systemically after inhalation.The purpose of this study was to determine the protective efficacy of a single dose of molecular hydrogen (H2) on cochlear structures. Guinea pigs were divided into six groups and sacrificed immediately after or at 1 or 2 weeks. The animals were exposed to broadband noise for 2 h directly followed by 1-h inhalation of 2% H2 or room air. Electrophysiological hearing thresholds using frequency-specific auditory brainstem response (ABR) were measured prior to noise exposure and before sacrifice. ABR thresholds were significantly lower in H2-treated animals at 2 weeks after exposure, with significant preservation of outer hair cells in the entire cochlea. Quantification of synaptophysin immunoreactivity revealed that H2 inhalation protected the cochlear inner hair cell synaptic structures containing synaptophysin. The inflammatory response was greater in the stria vascularis, showing increased Iba1 due to H2 inhalation.Repeated administration of H2 inhalation may further improve the therapeutic effect. This animal model does not reproduce conditions in humans, highlighting the need for additional real-life studies in humans. [ABSTRACT FROM AUTHOR]

2-Hyroxypropyl-beta-cyclodextrin (HPβCD) is being used to treat Niemann-Pick C1, a fatal neurodegenerative disease caused by abnormal cholesterol metabolism. HPβCD slows disease progression, but unfortunately causes severe, rapid onset hearing loss by destroying the outer hair cells (OHC). HPβCD-induced damage is believed to be related to the expression of prestin in OHCs. Because prestin is postnatally upregulated from the cochlear base toward the apex, we hypothesized that HPβCD ototoxicity would spread from the high-frequency base toward the low-frequency apex of the cochlea. Consistent with this hypothesis, cochlear hearing impairments and OHC loss rapidly spread from the high-frequency base toward the low-frequency apex of the cochlea when HPβCD administration shifted from postnatal day 3 (P3) to P28. HPβCD-induced histopathologies were initially confined to the OHCs, but between 4- and 6-weeks post-treatment, there was an unexpected, rapid and massive expansion of the lesion to include most inner hair cells (IHC), pillar cells (PC), peripheral auditory nerve fibers, and spiral ganglion neurons at location where OHCs were missing. The magnitude and spatial extent of HPβCD-induced OHC death was tightly correlated with the postnatal day when HPβCD was administered which coincided with the spatiotemporal upregulation of prestin in OHCs. A second, massive wave of degeneration involving IHCs, PC, auditory nerve fibers and spiral ganglion neurons abruptly emerged 4–6 weeks post-HPβCD treatment. This secondary wave of degeneration combined with the initial OHC loss results in a profound, irreversible hearing loss.

Sound evokes sub-nanoscale vibration within the sensory epithelium. The epithelium contains not only immotile cells but also contractile outer hair cells (OHCs) that actively shrink and elongate synchronously with the sound. However, the in vivo motion of OHCs has remained undetermined. The aim of this work is to perform high-resolution and -accuracy vibrometry in live guinea pigs with an SC-introduced spectral-domain optical coherence tomography system (SD-OCT). In this study, to reveal the effective contribution of SC source in the recording of the low reflective materials with the short total acquisition time, we compare the performances of the SC-introduced SD-OCT (SCSD-OCT) to that of the conventional SD-OCT. As inanimate comparison objects, we record a mirror, a piezo actuator, and glass windows. For the measurements in biological materials, we use in/ex vivo guinea pig cochleae. Our study achieved the optimization of a SD-OCT system for high-resolution in vivo vibrometry in the cochlear sensory epithelium, termed the organ of Corti, in mammalian cochlea. By introducing a supercontinuum (SC) light source and reducing the total acquisition time, we improve the axial resolution and overcome the difficulty in recording the low reflective material in the presence of biological noise. The high power of the SC source enables the system to achieve a spatial resolution of 1.72 ± 0.00 μm on a mirror and reducing the total acquisition time contributes to the high spatial accuracy of sub-nanoscale vibrometry. Our findings reveal the vibrations at the apical/basal region of OHCs and the extracellular matrix, basilar membrane. [ABSTRACT FROM AUTHOR]

Cochlear outer hair cells (OHCs) are known to uniquely participate in auditory processing through their electromotility, and like inner hair cells, are also capable of releasing vesicular glutamate onto spiral ganglion (SG) neurons: in this case, onto the sparse Type II SG neurons. However, unlike glutamate signaling at the inner hair cell-Type I SG neuron synapse, which is robust across a wide spectrum of sound intensities, glutamate signaling at the OHC-Type II SG neuron synapse is weaker and has been hypothesized to occur only at intense, possibly damaging sound levels. Here, we tested the ability of the OHC-Type II SG pathway to signal to the brain in response to moderate, nondamaging sound (80 dB SPL) as well as to intense sound (115 dB SPL). First, we determined the VGluTs associated with OHC signaling and then confirmed the loss of glutamatergic synaptic transmission from OHCs to Type II SG neurons in KO mice using dendritic patch-clamp recordings. Next, we generated genetic mouse lines in which vesicular glutamate release occurs selectively from OHCs, and then assessed c-Fos expression in the cochlear nucleus in response to sound. From these analyses, we show, for the first time, that glutamatergic signaling at the OHC-Type II SG neuron synapse is capable of activating cochlear nucleus neurons, even at moderate sound levels.SIGNIFICANCE STATEMENT Evidence suggests that cochlear outer hair cells (OHCs) release glutamate onto Type II spiral ganglion neurons only when exposed to loud sound, and that Type II neurons are activated by tissue damage. Knowing whether moderate level sound, without tissue damage, activates this pathway has functional implications for this fundamental auditory pathway. We first determined that OHCs rely largely on VGluT3 for synaptic glutamate release. We then used a genetically modified mouse line in which OHCs, but not inner hair cells, release vesicular glutamate to demonstrate that moderate sound exposure activates cochlear nucleus neurons via the OHC-Type II spiral ganglion pathway. Together, these data indicate that glutamate signaling at the OHC-Type II afferent synapse participates in auditory function at moderate sound levels. [ABSTRACT FROM AUTHOR]

Light sheet fluorescence microscopy (LSFM) provides a rapid and complete three‐dimensional image of the cochlea. The method retains anatomical relationships—on a micrometer scale—between internal structures such as hair cells, basilar membrane (BM), and modiolus with external surface structures such as the round and oval windows. Immunolabeled hair cells were used to visualize the spiraling BM in the intact cochlea without time intensive dissections or additional histological processing; yet material prepared for LSFM could be rehydrated, the BM dissected out and reimaged at higher resolution with the confocal microscope. In immersion‐fixed material, details of the cochlear vasculature were seen throughout the cochlea. Hair cell counts (both inner and outer) as well as frequency maps of the BM were comparable to those obtained by other methods, but with the added dimension of depth. The material provided measures of angular, linear, and vector distance between characteristic frequency regions along the BM. Thus, LSFM provides a unique ability to rapidly image the entire cochlea in a manner applicable to model and interpret physiological results. Furthermore, the three‐dimensional organization of the cochlea can be studied at the organ and cellular level with LSFM, and this same material can be taken to the confocal microscope for detailed analysis at the subcellular level. [ABSTRACT FROM AUTHOR]

Purpose: The blood group can have an effect on the auditory system, and it is suggested that it could be an indicator of noise-induced hearing loss. There could be changes in the immittance findings, too, in adults having different blood groups. The present study attempted to determine if there are any differences in tympanometric results (admittance, peak pressure, gradient, resonance frequency, and ear canal volume) and acoustic reflex thresholds (ART) at 500, 1000, 2000 and 4000 Hz between individuals with different blood groups (A positive, B positive, O positive and AB positive). Methods: Eighty normal hearing adults between the age of 18 and 27 years were considered for the study. They were divided into 20 participants, each with blood groups A, B, AB, and O. The immittance findings were recorded from all the participants of the study. Results: The results showed that the resonance frequency was slightly higher in blood group O compared to other blood groups. Also, the acoustic reflex thresholds were slightly elevated at all frequencies (ipsilateral and contralateral) for individuals with blood group O. Conclusions: The results of the study suggest possible reduced outer hair cells in persons with blood group O. This could have resulted in elevated acoustic reflex thresholds. [ABSTRACT FROM AUTHOR]