Objective:This study aims to investigate the mechanism and potential effects of two exposures to 100 dB sound pressure level（SPL） broadband white noise, with a 14-days interval, on the myelin sheath of the cochlear auditory nerve in mice. The research provides experimental evidence for understanding the pathophysiological processes of noise-induced hearing loss and hidden hearing loss. Methods:Fifteen 6-week-old male C57BL/6J mice with normal hearing thresholds were randomly divided into three groups: a control group（no noise exposure）, a single noise exposure group, and a double noise exposure group. The single noise exposure group was exposed to 100 dB SPL white noise for 2 hours, and ABR thresholds were measured 1 day（P1） and 14 days（P14） after the exposure. The double noise exposure group was exposed to the same conditions of 100 dB SPL white noise for 2 hours, followed by a second identical exposure 14 days later. ABR thresholds were measured 1 day（P15） and 14 days（P28） after the second exposure. The cochleae of all three groups were then collected for immunofluorescence observation of the basilar membrane and transmission electron microscopy to observe changes in the structure of the auditory nerve myelin sheath. Results:In the single noise exposure group, ABR thresholds at all frequencies were significantly elevated compared to the control group at P1. There were no significant changes in ABR thresholds at any frequency at P14. In the double noise exposure group, ABR thresholds at all frequencies were significantly elevated compared to the control group at P15 and P28（P<0.001）. After the first noise exposure, immunofluorescence observation revealed no significant weakening of the auditory nerve myelin sheath signal; transmission electron microscopy showed no significant changes in myelin sheath morphology. However, after the second noise exposure, immunofluorescence observation revealed a weakening of the myelin sheath signal, and transmission electron microscopy showed thinning of the myelin sheath, disruption of the lamellar structure, and separation from the axon, indicating demyelination. Conclusion:Two exposures to 100 dB SPL broadband white noise can lead to damage to the auditory nerve myelin sheath in mice, whereas a single exposure does not cause significant changes.
Animals ; Male ; Myelin Sheath/pathology* ; Mice ; Cochlear Nerve/pathology* ; Mice, Inbred C57BL ; Noise/adverse effects* ; Hearing Loss, Noise-Induced/physiopathology* ; Cochlea ; Evoked Potentials, Auditory, Brain Stem

Objective:To investigate the impact of Waardenburg syndrome（WS） -associated Sox10 p.S100Rfs*9 mutation on inner ear function and its mechanism in noise-induced hearing impairment. Methods:A mice model carrying the Sox10 p.S100Rfs*9 mutation was established using CRISPR-Cas9 gene editing technology. Auditory phenotypes were assessed under baseline conditions and after noise exposure（96 dB SPL, 2 hours）. Auditory brainstem response（ABR） tests were performed to evaluate hearing function, combined with immunofluorescence staining of cochlear basilar membrane whole-mounts to observe hair cells and ribbon synapses. Transcriptome sequencing was conducted to analyze molecular mechanisms. Results:Sox10 p.S100Rfs*9 heterozygous mice exhibited normal hearing thresholds with characteristic ventral pigmentation abnormalities under baseline conditions. Following noise exposure, mutant mice showed significantly higher ABR thresholds at 24 000 Hz compared to wild-type controls（[60.00±6.12]vs[48.13±4.28]dB SPL, P<0.000 1）, and a significant reduction in ribbon synapses（CtBP2-positive puncta） in the basal turn（[55.0±2.3]vs[64.8±3.3]per inner hair cell, P=0.006 6）, while hair cell morphology and number remained intact. Transcriptome analysis revealed altered expression of genes involved in immune regulation, membrane structures, ion channels, and neuroactive ligand-receptor interactions. Conclusion:The Sox10 p.S100Rfs*9 mutation does not alter baseline hearing function but significantly increases inner ear susceptibility to noise damage, primarily manifested as enhanced ribbon synapse vulnerability, especially in high-frequency regions. This gene-environment interaction reveals that Sox10 haploinsufficiency may compromise noise tolerance by affecting synaptic stability and inner ear protective mechanisms. These findings provide new perspectives on the phenotypic heterogeneity in WS patients and theoretical basis for individualized noise protection strategies for patients carrying SOX10 mutations.
Animals ; SOXE Transcription Factors/genetics* ; Waardenburg Syndrome/physiopathology* ; Mice ; Hearing Loss, Noise-Induced/genetics* ; Evoked Potentials, Auditory, Brain Stem ; Mutation ; Noise ; Disease Models, Animal ; Ear, Inner/physiopathology*

Hearing Loss, Noise-Induced ; physiopathology ; Humans

OBJECTIVETo investigate the application of auditory brainstem response (ABR) and 40 Hz auditory event related potential (40 Hz AERP) to the diagnosis of occupational noise-induced hearing impairment and to provide the evidence for diagnosis of occupational deafness.

METHODSPure tone audiometry, ABR and 40 Hz AERP were performed in 54 workers occupationally exposed to noise. The thresholds of higher frequency band, 3 kHz and 4 kHz were compared with the threshold of ABR. The thresholds of auditory frequency ban and 0.5 kHz were compared with the threshold of 40 Hz AERP.

RESULTSA better correlation was found between thresholds of ABR and higher frequency pure tone audiometry. There was a significant difference of thresholds between 40 kHz AERP and pure tone audiometry. The correction values of thresholds between 40 kHz AERP and pure tone audiometry in the light noise-induced hearing impairment group and the moderate noise-induced hearing impairment group were (16.43 ± 1.08) and (11.80 ± 1.12) dBn HL, respectively.

CONCLUSIONIn diagnosis of occupational noise-induced hearing impairment, the threshold of ABR can be used to estimate the hearing threshold of pure noise higher frequency. Because there is the significant difference of the thresholds between pure tone audiometry and 40 Hz AERP, the response threshold can not be served as the audiometry threshold, and the behavioral hearing thresholds can only be obtained by adjusting the response threshold with respective correction value.

Adult ; Audiometry, Evoked Response ; Audiometry, Pure-Tone ; Auditory Threshold ; Evoked Potentials, Auditory ; Evoked Potentials, Auditory, Brain Stem ; Hearing Loss, Noise-Induced ; diagnosis ; physiopathology ; Humans ; Male ; Middle Aged ; Noise, Occupational ; Young Adult

OBJECTIVE: To observe the changes of free radicals in the cochlea of guinea pigs after noise exposure directly using electron spin resonance (ESR) technology. METHOD: Forty-two guinea pigs as experimental group were given (125 +/- 1) dB SPL noise exposure for 2 hours, and then investigated auditory function immediately, at 2, 6, 12, 24, 48 and 72 hour. After ABR examinations, 21 animals decollated and extracted cochlea immediately and then placed the cochleas to liquid nitrogen for deep freezing and measuring free radicals using ESR technology. Another 21 animals observed hair cells morphology by AgNO3 staining. Meantime, 6 animals without noise exposure were served as negative control group. RESULT: A few free radicals were detected in the cochlea at control group and the relative value of free radicals were (21.68 +/- 1.27) dB SPL. After noise exposure, the relative value of free radicals increased obviously and achieved to the max of (147.01 +/- 4.95) dB SPL at 2 h and gradually decreased near the normal level. CONCLUSION Free radicals in the cochlea increase evidently and have a concentration-time rule after acute acoustic trauma. The ESR method can be used to examine the content of free radicals in cochlea for its direct, objective and sensitive characters.
Animals ; Cochlea ; chemistry ; Electron Spin Resonance Spectroscopy ; Free Radicals ; analysis ; Guinea Pigs ; Hearing Loss, Noise-Induced ; physiopathology

Adult ; Audiometry, Pure-Tone ; Case-Control Studies ; Evoked Potentials, Auditory, Brain Stem ; Hearing Loss, Noise-Induced ; diagnosis ; physiopathology ; Humans ; Male ; Middle Aged ; Noise, Occupational

OBJECTIVETo evaluate the pathological status of the vestibular system associated with noise-induced inner ear impairment.

METHODSTotally 68 patients with noise-induced hearing loss (NIHL) who presented with vestibular symptoms including vertigo, dizziness, and chronic disequilibrium were screened. All patients underwent a series of conventional vestibular function tests and vestibular autorotation test and the results were retrospectively reviewed and evaluated.

RESULTSSixty-eight (14.5%) patients with NIHL were identified among 469 patients with vertigo, dizziness, or imbalance. A pure tone hearing threshold of patients with vertigo and NIHL at 4000 Hz were between 30 dB HL and 80 dB HL with an average threshold of (46.7 +/- 17.6) dB HL in left ear and (37.3 +/- 16.7) dB HL in right ear. Patients with symmetrical hearing loss at 4000 Hz accounted for 41.7% and those with asymmetrical loss accounted for 58.3%. Vestibular pathologies included benign positional paroxysmal vertigo (45.7%), unilateral decreased caloric responses (20.0%), bilateral decreased caloric responses (26.7%), abnormal vestibulo-spinal reflex function (28.6%), vestibular function response hyperactivity (3.0%), and abnormal vestibulo-ocular reflex presentation at high frequencies (97.0%).

CONCLUSIONSLoud acoustic stimulation not only damages the cochlea but also causes clear functional impairment to the vestibular end organs. Although the vestibular pathology is not correlated with the severity of the hearing loss, it correlates with the subjective symptoms of the vestibular system.

Adult ; Aged ; Aged, 80 and over ; Female ; Hearing Loss, Noise-Induced ; pathology ; physiopathology ; Humans ; Male ; Middle Aged ; Noise ; Retrospective Studies ; Vestibular Function Tests ; Vestibule, Labyrinth ; pathology ; physiopathology ; Young Adult

OBJECTIVE: To observe the changes of auditory electrophysiology and inner ear pathology in rat cochlea after the noise exposure, and to offer the experimental data for exploring the mechanism of noise-damaged cochlea. METHOD: The rats in the study group were exposed to a intense narrow band noise centered at 4 kHz at the leave of 120 dB (SPL) for 4 h. The exposed cochleae were collected at various intervals (1 or 21 days) after the noise exposure. Auditory function was monitored by measuring thresholds of auditory brain stem responses (ABR). The morphological changes in rat cochlear hair cell (HC) were examined by HC nuclei stained with Propidium iodide (PI), a fluorescent dye specifically labelling the nuclear DNA and scanning electron microscopy (SEM). The number of spiral ganglion cells was calculated using pathologic technique. RESULT: The thresholds of ABR in the study group were significantly greater than that in the normal control group (P < 0.01). Examined at 1 day after the noise exposure, normal, apoptosis, necrotic and missing out hair cell (OHC) could be distinguished with PI staining, whereas the apoptosis OHC were not found at 21 days. Significant OHC loss was found in as compared to the normal control group (P < 0.01). There was not significant difference in the calculation of spiral ganglion cells (P > 0.05). SEM revealed the injured stereocilia of OHC (disarrangement, collapse) and OHC loss in the study group, which was more severe in OHC3 than the other two rows of OHC. CONCLUSION The intense noise used in our study could injure the rat cochlea and bring permanent threshold shift (PTS). Under this condition, the death modes of HC in the cochlea include apoptosis and necrosis in the fore part, whereas necrotic is the major mode in the evening of exposure. The injured stereocilia of OHC and OHC loss could remain the most consistent correlate of PTS.
Animals ; Apoptosis ; Auditory Threshold ; Cochlea ; pathology ; physiopathology ; Evoked Potentials, Auditory, Brain Stem ; Hearing ; Hearing Loss, Noise-Induced ; pathology ; physiopathology ; Necrosis ; Noise ; adverse effects ; Rats ; Rats, Sprague-Dawley

The aim of the present study was to investigate the role of glutamate receptors in the damage of spiral ganglion neurons (SGNs) induced by acute acoustic noise. This investigation included in vivo and in vitro studies. In vivo, kynurenic acid (KYNA), a broad-spectrum antagonist of glutamate receptors, was applied to the round window of guinea pigs, and its protective effect was observed. The animals were divided into three groups: control (saline, 0.9%, 10 microL), saline (0.9%, 10 microL) + noise and KYNA (5 mmol/L, 10 microL) + noise. Saline and KYNA were applied to the round window membrane with a microsyringe. The animals were exposed to 110 dB SPL of white noise for 1 h. Hearing thresholds for auditory brainstem responses (ABRs) and compound action potentials (CAPs) in all animals were measured before and after treatment. The amplitudes of III waveform of ABR and N1 waveform of CAP and the latency of N1 waveform at different stimulation levels (intensity-amplitude and intensity-latency functions) were also measured. The cochleas were then dissected for transmission electron microscopy (TEM) after final electrophysiological measurement. In vitro, the SGNs of the normal guinea pigs were isolated and glutamate (100 micromol/L or 1 000 micromol/L) was added into the medium. The morphology of the SGNs was examined by light microscopy. In vivo results showed that the hearing function and morphology of the inner ear including hair cells and SGNs in the control group were normal. Compared with that in the control group the thresholds for ABR and CAP (click and tone burst) in saline + noise group were elevated significantly. The input-output functions showed that the amplitudes of III waveform of ABR and N1 waveform of CAP decreased and the latency of N1 waveform increased obviously. There was significant difference in the amplitude and latency between saline + noise group and KYNA + noise group (P<0.05). TEM indicated obvious swelling and vacuoles at the terminate of dendrites of SGNs in NS + noise group. On the contrary, the afferent dendrites in KYNA + noise group showed normal appearance without swelling and vacuoles. In vitro experiment showed that the isolated SGNs of guinea pigs obviously swelled and even died after application of 100 micromol/L or 1 000 micromol/L glutamate. These results suggest that noise exposure causes hearing impairment, damage of hair cells and hair cell/afferent synapse and death of SGNs. The antagonist of glutamate receptors provides protective effects against hearing loss and SGN damage. It is inferred that excessive release of glutamate from the inner hair cells induced by noise may be responsible for these damages. Glutamate receptors are involved in the degeneration and death of SGNs.
Action Potentials ; physiology ; Animals ; Evoked Potentials, Auditory, Brain Stem ; physiology ; Excitatory Amino Acid Antagonists ; pharmacology ; Guinea Pigs ; Hearing Loss, Noise-Induced ; metabolism ; pathology ; physiopathology ; Kynurenic Acid ; pharmacology ; Male ; Neurons ; pathology ; Noise ; adverse effects ; Random Allocation ; Receptors, Glutamate ; metabolism ; Spiral Ganglion ; pathology

OBJECTIVETo study the preventive effects of vitamin E on short-term noise-induced hearing loss (NIHL).

METHODSForty-eight male pigmented guinea pigs were randomly divided into 6 groups, 8 animals in each group. The animals of group 1, 2, 3, 4 were exposed to the noise (4 kHz octave band noise, 100 dB SPL), 8 hours per day for 3 days consecutively and received normal saline, corn oil, 10 mg/kg vitamin E, 50 mg/kg vitamin E respectively daily by intraperitoneal injection from 3 days before the noise exposure, through the 3 noise exposure days to 3 days after the noise exposure. The animals of group 5 and group 6 days were not exposed to the noise but received normal saline and 50 mg/kg vitamin E injection respectively at the same time as that of group 1, 2, 3, 4. The preventive effects of vitamin E on NIHL were determined by comparing the threshold shifts of auditory brainstem responses (ABR) immediately, on the second day and on the 8th day after the exposure.

RESULTSThe ABR threshold shifts immediately, on the second day and on the 8th day after the exposure for group 3 at 2, 4 and 8 kHz were (15.9 +/- 6.8), (39.4 +/- 4.8), (42.5 +/- 6.3), (0.3 +/- 2.5), (19.1 +/- 7.9), (21.9 +/- 6.4), (0.3 +/- 1.6), (10.9 +/- 8.6), (12.2 +/- 8.1) dB, respectively, which were significantly lower than those for group 1 [(30.9 +/- 11.3), (47.8 +/- 8.8), (49.7 +/- 6.9), (10.0 +/- 3.5), (29.1 +/- 6.5), (29.1 +/- 7.6), (4.7 +/- 3.6), (20.3 +/- 6.5), (17.5 +/- 9.0) dB, respectively] (P < 0.05). The ABR threshold shifts immediately, on the second day and on the 8th day after the exposure for group 4 at 2, 4 and 8 kHz were respectively (14.4 +/- 5.3), (36.6 +/- 4.4), (43.1 +/- 2.9), (0.3 +/- 2.5), (16.9 +/- 4.6), (19.4 +/- 3.2), (0.0 +/- 3.7), (7.5 +/- 4.2), (9.1 +/- 4.2) dB, which were significantly lower than those for group 1 (P < 0.05).

CONCLUSIONVitamin E has some preventive effects on the NIHL.

Animals ; Antioxidants ; administration & dosage ; pharmacology ; Auditory Threshold ; Dose-Response Relationship, Drug ; Evoked Potentials, Auditory, Brain Stem ; Guinea Pigs ; Hearing Loss, Noise-Induced ; physiopathology ; prevention & control ; Male ; Random Allocation ; Vitamin E ; administration & dosage ; pharmacology