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Abstract 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.
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Abstract Introduction Tinnitus is the perception of sound in the absence of external sound stimulation. There is a general agreement that it is a direct consequence of irreversible and permanent cochlear damage. Objectives The present work is designed to study the distortion product otoacoustic emissions (DPOAEs) in tinnitus patients with normal hearing in comparison with normal hearing control and to study any possible correlation between DPOAEs recording and patients' complaints. Methods The present study included 80 subjects divided into 2 groups: Control group: consisted of 30 normal-hearing adults not complaining of tinnitus and Study group: consisted of 50 normal-hearing adults complaining of tinnitus. The methodology includes full audiological history, otoscopic examination, basic audiological evaluation, DPOAEs including both DP-gram and DPOAEs input/output functions. Results Basic audiological evaluation showed within normal hearing sensitivity in both groups, however, with significant higher hearing thresholds in tinnitus patients at all frequency ranges. The Tinnitus Handicap Inventory Questionnaire showed mean scores of 35.2 ± 16.9 in the study group. The DP-gram showed higher amplitudes in the control group when compared with tinnitus patients. The DPOAEs input-output functions at different frequencies (1, 2, 4 and 6kHz) also showed higher amplitudes at all frequencies and different input levels. The slope of the I/O function tends to be steeper in tinnitus cases. Conclusion Patients with tinnitus might have neural dysfunction at either the level of the cochlea, as shown in reduced DPOAE levels, and changes in the normal DP-I/O function recorded in the present work.
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RESUMO Objetivo avaliar o efeito da variação da intensidade de estimulação sobre as respostas das emissões otoacústicas produto de distorção em indivíduos com perda auditiva neurossensorial, utilizando um protocolo de gradiente de fase das emissões. Métodos estudo observacional transversal. Participaram 38 indivíduos com diagnóstico de perda auditiva neurossensorial de grau leve, moderado ou severo. Foram realizadas anamnese, meatoscopia, audiometria tonal liminar, logoaudiometria, imitanciometria, emissões otoacústicas produto de distorção e emissões otoacústicas residuais. As emissões otoacústicas residuais foram coletadas com o equipamento Echodia, modelo Elios®. O protocolo utilizado permite a variação dos parâmetros frequência e intensidade e as respostas são analisadas por meio do teste do Gradiente de Fase. As respostas registradas nas emissões residuais foram consideradas como "presente", "ausente" e "artefato", considerando a variação da fase em função de f1. Resultados Foram incluídas 72 orelhas. Houve diferença estatisticamente significativa nas frequências de 1300 Hz e 2000 Hz, ao comparar os resultados das emissões residuais. Ao correlacionar o resultado da audiometria e a intensidade de estimulação que evocou a emissão residual, houve correlação positiva para as frequências de 1000 Hz e 4000Hz. O "artefato" foi registrado, principalmente, nas frequências mais agudas: 56,2% em 3000 Hz e 58,2% em 4000 Hz. A emissão otoacústica residual presente foi registrada em 18,6% em 1000 Hz, 13,4% em 2000 Hz, 6,3% em 3000 Hz e 7,5% em 4000 Hz. Conclusão o aumento da intensidade de estimulação no exame de emissões pode auxiliar no estudo das células ciliadas residuais, desde que seja utilizado um protocolo capaz de diferenciar respostas fisiológicas de artefatos.
ABSTRACT Purpose To study the effect of stimulation intensity variation on the responses of distortion products in subjects with sensorineural hearing loss using a new protocol to register the otoacoustic emissions. Methods This is a cross-sectional observational study. The following procedures were performed: anamnesis, otoscopy, pure tone audiometry, speech audiometry, tympanometry, distortion product and residual otoacoustic emissions. The residual DPOAE were collected with the Echodia equipment, Elios®. The protocol that was developed allows the variation of frequency and intensity parameters and the responses are analyzed by phase gradient test. Responses recorded in residual otoacoustic emissions were considered "present", "absent" or "artifact". Results The total included ears was 72. On residual otoacoustic emissions test, at a frequency of 1300Hz and 2000Hz, there was statistically significant difference. By analyzing the average found in the audiometry and the results of residual emissions, only the frequency of 1300Hz showed a statistically significant association in all groups. By correlating the results of the audiometry and the stimulation intensity used to evoke the residual emission, there was positive correlation for the frequencies of 1000Hz and 4000Hz. The "artifact" was mostly recorded in the higher frequencies: 56.2% in 3000Hz and 58.2% in 4000 Hz. Residual EOAPD present was recorded as 18.6% at 1000Hz, 13.4% at 2000Hz, 6.3% at 3000Hz and 7.5% at 4000Hz. Conclusion The increased stimulation intensity in the otoacoustic emissions test can aid in the study of residual outer hair cells, as long as a protocol is used to check the correctness of the responses.
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Humans , Auditory Threshold , Otoacoustic Emissions, Spontaneous/physiology , Hair Cells, Auditory , Hearing Loss, Sensorineural/diagnosis , Cross-Sectional StudiesABSTRACT
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.
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Animals , Humans , Mice , Cochlea/metabolism , Hair Cells, Auditory, Outer/metabolism , Hearing , Mammals/metabolism , Mice, Knockout , Molecular Motor Proteins/metabolismABSTRACT
RESUMO Objetivo Estimar a magnitude da associação entre a exposição a agrotóxicos e o risco de alteração da função coclear de estudantes expostos a agrotóxicos. Método Neste estudo, foram avaliados indivíduos entre 8-30 anos, de ambos os gêneros, residentes em área de intensa utilização de agrotóxicos no município de Nova Friburgo, Estado do Rio de Janeiro. Cada participante do estudo respondeu a um questionário para aferir o grau de exposição a agrotóxicos. Para avaliação da função coclear, foram realizados os exames de audiometria, emissões otoacústicas evocadas por estímulo transiente (EOAET) e por produto de distorção (EOAPD). Resultados As respostas das EOAET foram, em média, menores nas altas frequências, especialmente 2,0 e 4,0 kHz, e, nestas frequências, também menores entre os indivíduos mais expostos. Padrão similar foi observado para as respostas das EOAPD. Para estas, o menor nível de resposta foi observado na frequência de 6 kHz, no grupo com maior escore de exposição. A proporção de falhas observadas em mais de uma frequência nas EOAET, na OD, no grupo de maior exposição, foi significativamente superior àquela observada no grupo menos exposto. No teste das EOAPD, o percentual de falhas também foi superior no grupo de maior exposição, quando comparado ao de menor exposição. Conclusão Os resultados sugerem que a exposição a agrotóxicos pode contribuir significativamente para alterações da função coclear de indivíduos com limiares audiométricos ainda preservados.
ABSTRACT Purpose To estimate the degree of association between exposure to pesticides and the risk of alteration in cochlear function in students exposed to pesticides. Methods This study evaluated individuals aged 8 to 30, of both genders, residing in an area of heavy pesticide use in the town of Nova Friburgo, Rio de Janeiro State. Each study participant answered a questionnaire to assess their degree of pesticide exposure. To evaluate cochlear function, audiometry exams were performed, including transient evoked otoacoustic emissions (TEOAEs) and distortion product otoacoustic emissions (DPOAEs). Results The TEOAE responses were on average lower at higher frequencies, especially at 2.0 and 4.0 kHz, and lower at these frequencies among the most exposed individuals. A similar pattern was observed for DPOAE responses. The lowest response level in the DPOAE tests was observed at the frequency of 6 kHz in the group with the highest exposure score. The proportion of failures observed at more than one frequency in the TEOAE tests on the right ear was significantly higher in the highest exposure group when compared to the lowest exposure group. In the DPOAE test, the rate of failure was also greater in the group with highest exposure when compared to that of lowest exposure. Conclusion The results suggest that exposure to pesticides can significantly contribute to alterations in cochlear function in individuals with preserved audiometric thresholds.
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Humans , Male , Female , Child , Adolescent , Adult , Young Adult , Pesticides/toxicity , Students/statistics & numerical data , Cochlea/drug effects , Auditory Threshold , Brazil , Cross-Sectional Studies , Surveys and Questionnaires , Otoacoustic Emissions, Spontaneous , Cochlea/physiopathologyABSTRACT
Abstract In this paper a new solution to micromechanical model of the cochlea developed by Neely and Kim is presented using Lagrange's equation. This solution has the advantage over previous methodologies to provide a mathematical model for the displacement exercised on the outer hair cells in the organ of Corti that only depends of the mechanical characteristics in the system and the value of the excitation frequency in the inner ear. For the evaluation of this new model the parameters developed by Ku are used and is considers that the amplitude of the excitation frequency is normalized. The model developed is satisfactorily compared with the impedance method and its numerical solution proposed by Neely and Kim, the state space analysis developed by Elliot, Ku and Lineton and the physiological measurements taken from Békésy.
Resumen En este trabajo se presenta una nueva solución utilizando la ecuación de Lagrange al modelo micromecánico de la cóclea desarrollado por Neely y Kim. Esta solución tiene la ventaja respecto a las ya existentes de proporcionar un modelo matemático del desplazamiento ejercido a los cilios en el órgano de Corti que sólo depende de las características mecánicas del sistema y del valor de la frecuencia de excitación en el oído interno. Para su evaluación se utilizan los parámetros desarrollados por Ku y se considera que la amplitud de la frecuencia de excitación está normalizada. El modelo desarrollado se compara satisfactoriamente con el método de impedancias y su solución numérica propuesta por Neely y Kim, el método de análisis de espacio estado desarrollado por Elliot, Ku y Lineton y con las mediciones fisiológicas realizadas por Békésy.
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The main objective of this study is to describe the role and function of prestin on cochlear amplification based on the relationship of electromotility and prestin in the outer hair cells (OHCs). After the finding of cochlear active process or amplification, OHCs have been received a lot of attention as a source of the cochlear amplification. In response to acoustic signals, the OHCs produce the receptor potentials resulting in changes in the length of the OHCs called electromotility. The electromotility originates within the lateral wall of the OHCs and relates to the unique structures of the OHCs. The OHC electromotility depends on particles of the lateral plasma membrane due to an area motor in the lateral plasma membrane. Recently, it has been reported that the electromotility requires a voltage-dependent membrane based motor protein, prestin. Prestin means fast in Italian. The presence of prestin is essential for cochlear amplification and electromotility. Prestin is a member of solute carrier 26 anion transporter family. Prestin is associated with the unique structure of the lateral wall of the OHCs. Prestin forms motor complexes with other proteins and lipids of the lateral wall sensing the transmembrane potential and generating force by changing its surface area. Recently, prestin knockout mice have been used to prove the presence of prestin. Prestin is required for electromotility of the OHCs and for cochlear amplification in normal hearing because targeted depletion of prestin in mice leads to loss of OHC electromotility and loss of hearing sensitivity up to 60 dB. In addition, recent studies have shown that the loss of cochlear amplification after intense noise exposure can result from damage to prestin and prestin involves in the process of aminoglycoside-induced apoptosis in OHCs. These show that prestin plays an important role in transducing apoptosis signals in response to antibiotics. Therefore, the presence of prestin is mandatory for cochlear active process and amplification in normal hearing.
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Animals , Humans , Mice , Acoustics , Anti-Bacterial Agents , Apoptosis , Cell Membrane , Hair , Hearing , Hearing Loss, Noise-Induced , Membrane Potentials , Membranes , Mice, Knockout , Noise , ProteinsABSTRACT
BACKGROUND AND OBJECTIVES: Aminoglycoside antibiotics are widely used for the treatment of infection caused by Gram-negative bacilli, but prolonged exposure to it can cause permanent hearing loss since are reported to interrupt the function of medial olivocochlear bundle. This study was designed to explore the effects of several aminoglycoside antibiotics on acetylcholine, the neurotransmitter of medial olivocochlear bundle, and how it affects potassium currents of the guinea pig outer hair cells. MATERIALS AND METHOD: Using extracted outer hair cells from Guinea pigs, potassium currents induced by acetylcholine were recorded using the whole-cell patch clamp technique. The effects of different aminoglycoside antibiotics on the potassium current were also studied. RESULTS: Acetylcholine increased the potassium currents of outer hair cells. All of aminoglycoside antibiotics tested such as neomycin, streptomycin, gentamicin, and amikacin decreased the acetylcholine-induced potassium current. CONCLUSION: These experimental results suggest that aminoglycoside antibiotics have effects on the membrane potential of outer hair cells regulated by acetylcholine, which is thought to be one of the mechanisms of aminoglycoside ototoxicity.
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Animals , Acetylcholine , Amikacin , Aminoglycosides , Anti-Bacterial Agents , Gentamicins , Guinea Pigs , Hair , Hearing Loss , Membrane Potentials , Neomycin , Neurotransmitter Agents , Potassium , StreptomycinABSTRACT
Objective To investigate the influence of long-term sound conditioning on the physiology of outer hair cells.Methods Twenty healthy guinea pigs were exposed to a broadband noise for 14 days consecutively at the level 90 dB(A),8 h/day.The DP-gram and input/output(I/O)function(1~8 kHz)were measured at pre-conditioning,fourteen days conditioning,seven days post-conditioning and fourteen days post-conditioning,respectively.Results The results of DP-gram measurements demonstrated that long-term sound conditioning could enhance the DPOAE amplitudes within low frequencies(1~3 kHz,especially 5.0 dB at 2 kHz and 7.5 dB at 3 kHz,P
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BACKGROUND AND OBJECTIVES: It has been known that the motility of the outer hair cell controls the physiological characteristics of the organ of Corti. Motility can be divided into two different types: fast and slow motility. Slow motility can be induced by high concentration of KCl and increase of intracellular Ca2+ concentration. In this study, authors aimed to define the effect of acetylcholine, one of the efferent neurotransmitters, on the slow motility of the outer hair cells of guinea pig. MATERIALS AND METHOD: Outer hair cells were isolated from guinea pigs by enzymatic and mechanical dissociation. The length of the hair cells was recorded by CCD camera equipped on an inverted microscope. Slow motility was induced by 10 (micro)M of ionomycin and 150 mM of KCl. Carbamylcholine (1 mM), a non-hydrolyzable derivative of acetylcholine, was used to observe the effect of acetylcholine and choline chloride (1 mM) was used as control. RESULTS: The length of outer hair cell was decreased after adding 150 mM of KCl and increased after adding 10 (micro)M of ionomycin. Stimulation of carbamylcholine (1 mM) did not induce the length change of the outer hair cells. Preincubation of 1 mM of carbamylcholine also did not affect the length change induced by ionomycin or KCl in outer hair cells. CONCLUSION: We could suggest that carbamylcholine does not have an effect on the slow motility of outer hair cell induced by the change of osmotic pressure which was elicited by high potassium, or intracellular Ca2+ increase.
Subject(s)
Animals , Acetylcholine , Calcium , Carbachol , Choline , Guinea Pigs , Hair , Ionomycin , Neurons, Efferent , Neurotransmitter Agents , Organ of Corti , Osmotic Pressure , Potassium Chloride , PotassiumABSTRACT
BACKGROUND AND OBJECTIVES: Auditory signal can be amplified by the organ of Corti and be detected in the auditory cortex. Outer hair cells (OHCs) play a pivotal role in this amplification process. The signal transduction mechanism of OHC relys on the precise control of intracellular calcium ([Ca2+]i). Membrane depolarization, induced by electrical stimulation or extracellular high concentration of KCl solution, increases [Ca2+]i through the opening of voltage-gated Ca2+ channel or the release from intracellular Ca2+ store which is stimulated by second messenger system. Efferent stimulation seems to inhibit the electromotility of OHC and modify the amplification process. Acetylcholine is the most promising neurotransmitter released from efferent synapse. In this study, we aimed to observe the effect of carbamylcholine (a non-hydrolyzable, non-selective cholinergic agonist) on the change of [Ca2+]i, and the modification of depolarization-induced [Ca2+]i increase in isolated OHCs of the guinea pig cochlea using the fluorescent indicator fluo-3. MATERIALS AND METHOD: Outer hair cells were isolated from the guinea pig cochlea and incubated in HBSS containing 5 M fluo-3 for 30 min. The [Ca2+]i was measured under inverted microscope equipped with epifluorescence system. The images were analysed and [Ca2+]i was calculated using Fmax, Fmin and Kd obtained from in vivo and in vitro calibration. RESULTS: [Ca2+]i increased by extracellular carbamylcholine application (1mM) in OHCs. KCl solution could induce [Ca2+]i increase when used more than 25mM and the responses were concentration-dependent. Preincubation of carbamylcholine, however, did not modify the depolarization-induced [Ca2+]i increase. CONCLUSION: Through these results, we speculate that the acetylcholine, released from the efferent synapse, can induce local increase of [Ca2+]i, but acetylcholine can not regulate the depolarization-induced [Ca2+]i in isolated OHCs of the guinea pig cochlea.
Subject(s)
Animals , Acetylcholine , Auditory Cortex , Calcium , Calibration , Carbachol , Cochlea , Electric Stimulation , Guinea Pigs , Guinea , Hair , Membrane Potentials , Membranes , Neurotransmitter Agents , Organ of Corti , Second Messenger Systems , Signal Transduction , SynapsesABSTRACT
Objective To observe the effect of tetraethylplyrazine(TMP) on outward K~+ channel of outer hair cells in guinea pig cochlea.Methods 60 guinea pigs were divided into 6 groups randomly in the experiment.Auditory brainstem response was used to monitor the change of ABR thresholds and patch clamp techniques to observe the effect of TMP on outward K~+ channel.Results TMP decreased the elevated ABR threshold caused by streptomycin. The TMP increased the amplitudes of calcium sensitive potassium channels (I_ K(Ca) ) and delayed outward potassium channels (IK) of outer hair cells of guinea pig cochlea.Conclusion The study indicates that TMP may act as a protective agent against ototoxicity of streptomycin. The amplitudes of I_ K(Ca) and IK of outer hair cells are increased by the TMP,suggesting the possible mechanisms of reducing ototoxicity.
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Objective To study the changes of cell motility of outer hair cells in the cochlear of guinea pigs under treatment of sodium nitroprusside(SNP). Methods By using the whole cell patch clamp recording technique in normal external and internal cell solution, the cell motility of outer hair cells under stimulation of voltage was observed in different concentration of SNP. Results Sodium nitroprusside apparently inhibited outer hair cells' motility when SNP concentration was higher than 100 ?Mol/L ( P
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AIM To examined the effect of bFGF on the calcium influx in outer hair cells (OHCs) and its antagonistical effects with streptomycin. The aim of the study is to explore the mechanism of acute ototoxicity of streptomycin and antagonism of bFGF. METHODSE The OHCs of guinea pig were isolated using an enzyme machine methods and loaded with 10 ?mol?L -1 Fluo 3/AM for 30 min at 37℃,then cultured 60 min at room temperature. Individual Fluo 3 loaded OHCs were examined with a confocal microscope (ACAS Ultima, USA) using a 20? objective lens and linear scan mean. The fluorescent images, collected every 5 sec for 300 s, were stored in a computer. The fluorescent intensity of the images were analyzed by the software cooperated with the confocal microscope, and a function curve showing the change trend of fluorescent intensity with time was obtained. RESULTS The OHCs [Ca 2+ ] i hold steady within the process of normal extracellular liquid perfusion. OHCs [Ca 2+ ] i increased when perfused 100 mmol?L -1 high potassium media(10/11) and normal media containing 1 nmol?L -1 bFGF(9/9), but the OHCs [Ca 2+ ] i don't changes in high potassium free calcium media(7/7) and free calcium media containing 1 nmol?L -1 bFGF(8/8). After treated by 1 mmol?L -1 streptomycin, the OHCs [Ca 2+ ] i increased 0/12, 4/8 respectively when perfused high potassium media and bFGF media. And after treated by 1 nmol?L -1 bFGF, high potassium media make OHCs [Ca 2+ ] i increased more obviously and keeping longer time. After treated by 1 mmol?L -1 streptomycin, respectively, 0 1,1 and 10 nmol?L -1 bFGF make 4/11,6/9 and 12/12 OHCs [Ca 2+ ] i increasing when perfused high potassium media. CONCLUSION High potassium media and bFGF perfusion can result in increasing of OHCs [Ca 2+ ] i ,and OHCs [Ca 2+ ] i increase rooted in the calicum influx, there is synergic effects between high potassium and bFGF. The streptomycin can block the process of calcium influx induced by high potassium media and the block effects can be antagonized by bFGF, and the antagonistical effects have bFGF concentration dependence.
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Aim To observe the effect of kanamycin on the change of Ca2+ concentration in outer hair cells caused by acetylcholine to explore the relationship between kanamycin ototoxicity and the cochlear efferent nervous system.Methods After the guinea pigs were killed by decapitation,the OHCs were isolated in artificial perilymph and divided into three groups:control group,acetylcholine(ACh) group and kanamycin + ACh group.OHCs were loaded with Fluo-3/AM for 30 min and then the change of Ca2+ fluorescence intensity was observed.Results Ca2+ fluorescent intensity in OHCs remained basically unchanged in control group,increased 3.06 times(n=6) in ACh Group,and increased 1.75 times(n=6) in kanamycin +ACh Group.Conclusions Kanamycin can obviously inhibit the increasing of Ca2+ concentration in OHCs caused by ACh.