Metabotropic glutamate receptor: A new possible therapeutic target for cochlear synaptopathy.

Objectives: Cochlear synaptopathy is a common cause of auditory disorders in which glutamate over-activation occurs. Modulating glutamatergic pathways has been proposed to down-regulate post-synaptic excitation. Materials and Methods: 12-guinea pigs as sham and test groups were exposed to a 4-kHz noise at 104 dB SPL, for 2 hr. Pre-exposure intra-tympanic injection with LY354740 and normal saline 9% was applied in the test and sham groups. The amplitude growth of ABR-wave-I and wave-III latency shift with noise were considered in pre- and post-exposure times. The synapses were observed by transmission electron-microscopy. Results: ABR thresholds recovered 1-week post-exposure in both groups. The reduction of wave-I amplitude at 4, 6, and 8 kHz were statistically different between pre- and 1- day post-exposure and recovered mostly in the sham group. The amount of latency shift in masked ABR was different between pre- and all post-exposure, and the response could not be detected at higher than 50 dB SL noise. However, the response detectability increased to 60 dB SL noise, and the significance of differences between pre- and post-exposure persisted only at the high level of noise in the test group. In electron-microscopy of sham samples, the size of the ribbon was larger, spherical with an irregularity, and hollow. The post-synaptic density was thicker and missed its flat orientation. Conclusion: The higher slope of the ABR-wave I amplitude, the more tolerance of noise in masked ABR, concomitant with the histological finding that revealed less synaptic damage, confirmed the therapeutic effect of LY354740 in cochlear synaptopathy.

The Effect of Otic Melanocyte Destruction on Auditory and Vestibular Function: a Study on Vitiligo Patients.

The hallmark of vitiligo is the disappearance of melanocytes from the skin. As a result, of melanocytes presence in the auditory and vestibular apparatus, the involvement of these systems in vitiligo which targets the melanocytes of the whole body is possible; suggesting that vitiligo is a systemic disease rather than a purely cutaneous problem. A total of 21 patients with vitiligo were enrolled in this study. A group of 20 healthy subjects served as a control group. Pure tone audiometry (PTA), auditory brainstem responses (ABR) and vestibular evoked myogenic potentials (VEMP) were carried out in all participants. High frequency sensory neural hearing loss was seen in 8 (38.09%) patients. ABR analysis revealed 10 (47.61%) had an abnormal increase in latency of wave III, and 6 (28.57%) had an abnormal prolongation of IPL I-III, however, regarding our VEMP findings, there were no recorded responses on left ear of 1 (4.76%) patient and latency of p13 was prolonged in 5(23.80%) patients. There was no correlation between ages, duration of disease, and any of the recorded parameters (P>0.05). In the present survey, we highlighted the auditory and vestibular involvement in vitiligo patients.

Effects of Fish Oil Supplementation during the Suckling Period on Auditory Neural Conduction in n-3 Fatty Acid-Deficient Rat Pups.

INTRODUCTION: Omega-3 fatty acid, particularly in the form of fish oil, has a structural and biological role in various systems of the body. The auditory and nervous systems are both influenced by omega-3 fatty acids, with omega-3 deficiency having devastating effects on both systems. Numerous studies have attempted to investigate this further. This study aimed to evaluate neural conduction in n-3 fatty acid-deficient rat pups following supplementation with fish oil during the suckling period. MATERIALS AND METHODS: In this interventional and experimental study, omega-3 fatty acids from fish oil (FO) were fed to rat pups of n-3 polyunsaturated fatty acid (PUFA)-deficient dams. Changes in auditory neural conduction were compared with those of control and n-3 PUFA-deficient groups using auditory brainstem response (ABR). The parameters of interest were P1, P3, and P4 absolute latency, P1-P3, P1-P4, and P3-P4 interpeak latency (IPL), and P4/P1 amplitude ratio. The rat pups were given oral FO, 5 ml/g weight for 17 days, between the age of 5 and 21 days. RESULTS: No significant group differences were observed in P1 and P3 absolute latency (P>0.05), but there was a significant difference in P4 (P≤0.05). The n-3 PUFA-deficient + vehicle group had the most prolonged (the worst) P1-P4 IPL and P3-P4 IPL compared with control and n-3 PUFA-deficient + FO groups. There was no significant difference in P1-P4 IPL and P3-P4 IPL between the n-3 PUFA-deficient + FO group and the control group (P>0.05). There was a significant effect of diet on P1-P4 IPL and P3-P4 IPL between groups (P≤0.05). CONCLUSION: The results of present study showed the effect of omega-3 deficiency on auditory neural structure during pregnancy and the lactation period. Additionally, we observed reduced reduction in devastating effects on neural conduction in n-3 fatty acid-deficient rat pups following the supplementation of FO during the suckling period.

Evaluation of distortion and transient evoked otoacoustic emission in tinnitus patients with normal hearing.

INTRODUCTION: Tinnitus is a perception of sound without external source. The exact etiology of tinnitus is not fully understood, although some researchers believe that the condition usually starts in the cochlea. The aim of this study was to determine the potential contribution of outer hair cell dysfunction to chronic tinnitus, by application of Distortion-Product Evoked Otoacoustic Emission (DPOAE) and Transient Evoked Otoacoustic Emission (TEOAE) and also to determine the relationship between tinnitus loudness and the amplitude of these two potentials. MATERIALS AND METHODS: This study was conducted on 20 tinnitus patients aged 20-45 years and 20 age- and gender-matched control subjects. DPOAE and TEOAE were performed on each subject. RESULTS: The difference in the amplitudes of TEOAE between the two groups was not significantly different (P=0.08), but the amplitude of DPOAE in patients with tinnitus was significantly lower than the corresponding value in the control subjects (P=0.01). There was no correlation between tinnitus loudness and the amplitudes of neither DPOAE nor TEOAE. CONCLUSION: Abnormal findings in the DPOAE of tinnitus sufferers suggest some form of cochlear dysfunction in these patients. As there was no correlation between the amplitude of the recorded potentials and tinnitus loudness, factors other than cochlear dysfunction may also influence the loudness of tinnitus.

Saccular function in otosclerosis patients: bone conducted-vestibular evoked myogenic potential analysis.

Vestibular involvements have long been observed in otosclerotic patients. Among vestibular structures saccule has the closest anatomical proximity to the sclerotic foci, so it is the most prone vestibular structure to be affected during the otosclerosis process. The aim of this study was to investigate the saccular function in patients suffering from otosclerosis, by means of Vestibular Evoked Myogenic Potential (VEMP). The material consisted of 30 otosclerosis patients and 20 control subjects. All participants underwent audiometric and VEMP testing. Analysis of tests results revealed that the mean values of Air-Conducted Pure Tone Average (AC-PTA) and Bone-Conducted Pure Tone Average (BC-PTA) in patients were 45.28 ± 15.57 and 19.68 ± 10.91, respectively and calculated 4 frequencies Air Bone Gap (ABG) was 25.64 ± 9.95. The VEMP response was absent in 14 (28.57%) otosclerotic ears. A statistically significant increase in latency of the p13 was found in the affected ears (P=0.004), differences in n23 latency did not reach a statistically significant level (P=0.112). Disparities in amplitude of p13-n23 in between two study groups was statistically meaningful (P=0.009), indicating that the patients with otosclerosis had lower amplitudes. This study tends to suggest that due to the direct biotoxic effect of the materials released from the otosclerosis foci on saccular receptors, there might be a possibility of vestibular dysfunction in otosclerotic patients.

Translation, validity, and reliability of a persian version of the iowa tinnitus handicap questionnaire.

INTRODUCTION: Tinnitus is a common otologic symptom that can seriously affect a patient's quality of life. The purpose of the present study was to translate and validate the Iowa Tinnitus Handicap Questionnaire (THQ) into the Persian language, and to make it applicable as a tool for determining the effects of tinnitus on a patient's life. MATERIALS AND METHODS: The main version of the THQ was translated into the Persian language. The agreed Persian version was administered to 150 tinnitus patients. The validity of the Persian THQ was evaluated and internal reliability was confirmed using Cronbach's α-coefficient. Finally, the effect of independent variables such as age, mean patient threshold, gender, and duration of tinnitus were considered in order to determine the psychometric properties of tinnitus. RESULTS: After an exact translation process, the Persian THQ was found to exhibit face validity. In terms of content validity, content validity index in total questionnaire was 0.93. Further, in structural validity measurements, intermediate correlation with annoyance from tinnitus (r=0.49), low correlation with duration of tinnitus (r=0.34) and high correlation with the Tinnitus Handicap Inventory (THI) questionnaire (r=0.84) were demonstrated. Additionally, a negligible effect of gender and age was noted on degree of tinnitus handicap (P= 0.754, P= 0.573, respectively). In the internal reliability assessment for Factors 1, 2, 3, and the whole questionnaire, Cronbach`s α-coefficient was 0.95, 0.92, 0.25 and 0.88, respectively. CONCLUSION: The Persian version of the Iowa THQ demonstrates high validity and reliability and can be used for the determination of tinnitus handicap and for following-up in the intervention process in Persian tinnitus patients.

Vestibular Evoked Myogenic Potential Produced by Bone-Conducted Stimuli: A Study on its Basics and Clinical Applications in Patients with Conductive and Sensorineural Hearing Loss and a Group with Vestibular Schawannoma.

INTRODUCTION: Vestibular evoked myogenic potential (VEMP) has recently been broadly studied in vestibular disorders. As it is evoked by loud sound stimulation, even mild conductive hearing loss may affect VEMP results. Bone-conducted (BC) stimulus is an alternative stimulation for evoking this response. This study aims to assess the characteristics of BC-VEMP in different groups of patients. MATERIALS AND METHODS: We performed a cross sectional analysis on 20 healthy volunteers with normal pure-tone audiometry as a control group; and on a group of patients consisted of 20 participants with conductive hearing loss, five with bilateral sensorineural hearing loss and four with vestibular schawannoma. AC and BC-VEMP were performed in all participants. RESULTS: In control group the VEMP responses to both kinds of stimuli had an acceptable morphology and consisted of p13 and n23 waves. Latency value of these main components in each type of stimulus was not significantly different (P>0.05). However, the mean amplitude was larger in BC modality than AC stimulation (P=0.025). In the group with conductive hearing loss, the VEMP response was absent in fifteen (46.87%) of the 32 ears using the AC method, whereas all (100%) displayed positive elicitability of VEMP by BC method. Normal VEMP responses in both stimuli were evoked in all patients with sensorineural hearing loss. In patients with unilateral vestibular schwannomas (VS), 2 (50.00%) had neither AC-VEMP nor BC-VEMP. CONCLUSION: Auditory stimuli delivered by bone conduction can evoke VEMP response. These responses are of vestibular origin and can be used in vestibular evaluation of patients with conductive hearing loss.

Temporal processing evaluation in tinnitus patients: results on analysis of gap in noise and duration pattern test.

INTRODUCTION: Tinnitus is a perception of sound without external source. For complete assessment of tinnitus, central auditory processing abilities should be considered in addition to the routine psychological evaluation of tinnitus characteristics. Temporal processing is one of the important auditory skills that are necessary for complex higher level auditory processing. MATERIALS AND METHODS: 20 tinnitus patients and 20 healthy volunteers without tinnitus, all with normal auditory thresholds (≤ 20 dBnHL), were enrolled in present study. Pure Tone Audiometry (PTA), Tinnitus evaluation, Gap in Noise (GIN) test and Duration Pattern Test (DPT) were applied to all participants. RESULT: Analysis of GIN test revealed statistically significant increases in an approximate threshold value of gap detection in the patients group, both in right and left sides (P=0.007 and P=0.011, respectively). Comparison of percentage of correct responses in between two groups was also statistically meaningful in right and left ears (P=0.019 and P=0.026, respectively). The comparison of different parameters of DPT in two study groups revealed no significant differences in percentage of correct responses between two groups (P>0.05). CONCLUSION: GIN test results identified auditory temporal resolution difficulties in patients with tinnitus, meaning that in spite of normal auditory thresholds there may be some possibility of abnormality in central auditory processing functions.

Audiological manifestations in vitiligo patients.

INTRODUCTION: The hallmark of vitiligo is the disappearance of melanocytes from the skin due to an as yet unidentified mechanism. The presence of melanocytes in the auditory apparatus suggests that this system could possibly be affected by vitiligo, which targets the melanocytes of the whole body and not just the skin. The purpose of this study was to assess the incidence of auditory alterations in patients with vitiligo. MATERIALS AND METHODS: A total of 21 patients diagnosed with vitiligo were enrolled in this study. A group of 20 healthy subjects served as a control group. Pure tone audiometry (PTA) and measurements of auditory brain stem responses (ABR) were carried out in all participants. RESULTS: High frequency sensory neural hearing loss was detected in 8 patients (38.09%). Analysis of ABR revealed that 10 patients (47.61%) had an abnormal increase in the latency of Wave III and 6 (28.57%) had an abnormal prolongation of the inter peak latency between Wave I and III. There was no correlation between age, duration of disease, and any of the recorded parameters. CONCLUSION: This study highlights the involvement of the auditory system in patients with vitiligo, suggesting that vitiligo is a systemic disease rather than a purely cutaneous problem.