Responses Of Hair Cells Research Articles

Early Development of Hearing in Zebrafish

The zebrafish (Danio rerio) has become a valuable vertebrate model for human hearing and balance disorders because it combines powerful genetics, excellent embryology, and exceptional in vivo visualization in one organism. In this study, we investigated auditory function of zebrafish at early developmental stages using the microphonic potential method. This is the first study to report ontogeny of response of hair cells in any fish during the first week post fertilization. The right ear of each zebrafish embedded in agarose was linearly stimulated with a glass probe that was driven by a calibrated piezoelectric actuator. Using beveled micropipettes filled with standard fish saline, extracellular microphonic potentials were recorded from hair cells in the inner ear of zebrafish embryos or larvae in response to 20, 50, 100, and 200-Hz stimulation. Saccular hair cells expressing green fluorescent protein of the transgenic zebrafish from 2 to 7days post fertilization (dpf) were visualized and quantified using confocal microscopy. The otic vesicles' areas, otoliths' areas, and saccular hair cell count and density increased linearly with age and standard body length. Microphonic responses increased monotonically with stimulus intensity, stimulus frequency, and age of zebrafish. Microphonic threshold at 200Hz gradually decreased with zebrafish age. The increases in microphonic response and sensitivity correlate with the increases in number and density of hair cells in the saccule. These results enhance our knowledge of early development of auditory function in zebrafish and provide the control data that can be used to evaluate hearing of young zebrafish morphants or mutants.

Will the Rod Bend or Break? Analyzing the Structural Resilience of Cellular Organelles

Will the Rod Bend or Break? Analyzing the Structural Resilience of Cellular Organelles

Intraoperative Round Window Recordings to Acoustic Stimuli From Cochlear Implant Patients

Acoustically evoked neural and hair cell potentials can be measured from the round window (RW) intraoperatively in the general population of cochlear implant recipients. Cochlear implant performance varies greatly among patients. Improved methods to assess and monitor functional hair cell and neural substrate before and during implantation could potentially aid in enhanced nontraumatic intracochlear electrode placement and subsequent improved outcomes. Subjects (1-80 yr) undergoing cochlear implantation were included. A monopolar probe was placed at the RW after surgical access was obtained. The cochlear microphonic (CM), summating potential (SP), compound action potential (CAP), and auditory nerve neurophonic (ANN) were recorded in response to tone bursts at frequencies of 0.25 to 4 kHz at various levels. Measurable hair cell/neural potentials were detected to 1 or more frequencies in 23 of 25 subjects. The greatest proportion and magnitude of cochlear responses were to low frequencies (<1,000 Hz). At these low frequencies, the ANN, when present, contributed to the ongoing response at the stimulus frequency. In many subjects, the ANN was small or absent, whereas hair cell responses remained. In cochlear implant recipients, acoustically evoked cochlear potentials are detectable even if hearing is extremely limited. Sensitive measures of cochlear and neural status can characterize the state of hair cell and neural function before implantation. Whether this information correlates with speech performance outcomes or can help in tailoring electrode type, placement or audiometric fitting, can be determined in future studies.

Loss of Slc4a1b Chloride/Bicarbonate Exchanger Function Protects Mechanosensory Hair Cells from Aminoglycoside Damage in the Zebrafish Mutant persephone

Mechanosensory hair cell death is a leading cause of hearing and balance disorders in the human population. Hair cells are remarkably sensitive to environmental insults such as excessive noise and exposure to some otherwise therapeutic drugs. However, individual responses to damaging agents can vary, in part due to genetic differences. We previously carried out a forward genetic screen using the zebrafish lateral line system to identify mutations that alter the response of larval hair cells to the antibiotic neomycin, one of a class of aminoglycoside compounds that cause hair cell death in humans. The persephone mutation confers resistance to aminoglycosides. 5 dpf homozygous persephone mutants are indistinguishable from wild-type siblings, but differ in their retention of lateral line hair cells upon exposure to neomycin. The mutation in persephone maps to the chloride/bicarbonate exchanger slc4a1b and introduces a single Ser-to-Phe substitution in zSlc4a1b. This mutation prevents delivery of the exchanger to the cell surface and abolishes the ability of the protein to import chloride across the plasma membrane. Loss of function of zSlc4a1b reduces hair cell death caused by exposure to the aminoglycosides neomycin, kanamycin, and gentamicin, and the chemotherapeutic drug cisplatin. Pharmacological block of anion transport with the disulfonic stilbene derivatives DIDS and SITS, or exposure to exogenous bicarbonate, also protects hair cells against damage. Both persephone mutant and DIDS-treated wild-type larvae show reduced uptake of labeled aminoglycosides. persephone mutants also show reduced FM1-43 uptake, indicating a potential impact on mechanotransduction-coupled activity in the mutant. We propose that tight regulation of the ionic environment of sensory hair cells, mediated by zSlc4a1b activity, is critical for their sensitivity to aminoglcyoside antibiotics.

Ototoxin-induced cellular damage in neuromasts disrupts lateral line function in larval zebrafish

The ototoxicity of a number of marketed drugs is well documented, and there is an absence of convenient techniques to identify and eliminate this unwanted effect at a pre-clinical stage. We have assessed the validity of the larval zebrafish, or more specifically its lateral line neuromast hair cells, as a microplate-scale in vivo surrogate model of mammalian inner ear hair cell responses to ototoxin exposure. Here we describe an investigation of the pathological and functional consequences of hair cell loss in lateral line neuromasts of larval zebrafish after exposure to a range of well known human and non-human mammalian ototoxins. Using a previously described histological assay, we show that hair cell damage occurs in a concentration-dependent fashion following exposure to representatives from a range of drug classes, including the aminoglycoside antibiotics, salicylates and platinum-based chemotherapeutics, as well as a heavy metal. Furthermore, we detail the optimisation of a semi-automated method to analyse the stereotypical startle response in larval zebrafish, and use this to assess the impact of hair cell damage on hearing function in these animals. Functional assessment revealed robust and significant attenuation of the innate startle, rheotactic and avoidance responses of 5 day old zebrafish larvae after treatment with a number of compounds previously shown to induce hair cell damage and loss. Interestingly, a startle reflex (albeit reduced) was still present even after the apparent complete loss of lateral line hair cell fluorescence, suggesting some involvement of the inner ear as well as the lateral line neuromast hair cells in this reflex response. Collectively, these data provide evidence to support the use of the zebrafish as a pre-clinical indicator of drug-induced histological and functional ototoxicity.

Effects of cross-modal selective attention on the sensory periphery: Cochlear sensitivity is altered by selective attention

There is increasing evidence that alterations in the focus of attention result in changes in neural responding at the most peripheral levels of the auditory system. To date, however, those studies have not ruled out differences in task demands or overall arousal in explaining differences in responding across intermodal attentional conditions. The present study sought to compare changes in the response of cochlear outer hair cells, employing distortion product otoacoustic emissions (DPOAEs), under different, balanced conditions of intermodal attention. DPOAEs were measured while the participants counted infrequent, brief exemplars of the DPOAE primary tones (auditory attending), and while counting visual targets, which were instances of Gabor gradient phase shifts (visual attending). Corroborating an earlier study from our laboratory, the results show that DPOAEs recorded in the auditory-ignoring condition were significantly higher in overall amplitude, compared with DPOAEs recorded while participants attended to the eliciting primaries; a finding in apparent contradiction with more central measures of intermodal attention. Also consistent with our previous findings, DPOAE rapid adaptation, believed to be mediated by the medial olivocochlear efferents (MOC), was unaffected by changes in intermodal attention. The present findings indicate that manipulations in the conditions of attention, through the corticofugal pathway, and its last relay to cochlear outer hair cells (OHCs), the MOC, alter cochlear sensitivity to sound. These data also suggest that the MOC influence on OHC sensitivity is composed of two independent processes, one of which is under attentional control.

The function and molecular identity of inward rectifier channels in vestibular hair cells of the mouse inner ear

Inner ear hair cells respond to mechanical stimuli with graded receptor potentials. These graded responses are modulated by a host of voltage-dependent currents that flow across the basolateral membrane. Here, we examine the molecular identity and the function of a class of voltage-dependent ion channels that carries the potassium-selective inward rectifier current known as I(K1). I(K1) has been identified in vestibular hair cells of various species, but its molecular composition and functional contributions remain obscure. We used quantitative RT-PCR to show that the inward rectifier gene, Kir2.1, is highly expressed in mouse utricle between embryonic day 15 and adulthood. We confirmed Kir2.1 protein expression in hair cells by immunolocalization. To examine the molecular composition of I(K1), we recorded voltage-dependent currents from type II hair cells in response to 50-ms steps from -124 to -54 in 10-mV increments. Wild-type cells had rapidly activating inward currents with reversal potentials close to the K(+) equilibrium potential and a whole-cell conductance of 4.8 ± 1.5 nS (n = 46). In utricle hair cells from Kir2.1-deficient (Kir2.1(-/-)) mice, I(K1) was absent at all stages examined. To identify the functional contribution of Kir2.1, we recorded membrane responses in current-clamp mode. Hair cells from Kir2.1(-/-) mice had significantly (P < 0.001) more depolarized resting potentials and larger, slower membrane responses than those of wild-type cells. These data suggest that Kir2.1 is required for I(K1) in type II utricle hair cells and contributes to hyperpolarized resting potentials and fast, small amplitude receptor potentials in response to current inputs, such as those evoked by hair bundle deflections.

The ethylene pathway contributes to root hair elongation induced by the beneficial bacteria Phyllobacterium brassicacearum STM196

In Arabidopsis roots, some epidermal cells differentiate into root hair cells. Auxin regulates root hair positioning, while ethylene controls cell elongation. Phyllobacterium brassicacearum STM196, a beneficial strain of plant growth promoting rhizobacteria (PGPR) isolated from the roots of field-grown oilseed rape, stimulates root hair elongation in Arabidopsis thaliana seedlings. We investigated the role of ethylene in the response of root hair cells to STM196 inoculation. While we could not detect a significant increase in ethylene biosynthesis, we could detect a slight activation of the ethylene signalling pathway. Consistent with this, an exhaustive survey of the root hair elongation response of mutants and transgenic lines affected in the ethylene pathway showed contrasting root hair sensitivities to STM196. We propose that local ethylene emission contributes to STM196-induceed root hair elongation.

Cognitive task demands modulate the sensitivity of the human cochlea.

Recent studies lead to the conclusion that focused attention, through the activity of corticofugal and medial olivocochlear (MOC) efferent pathways, modulates activity at the most peripheral aspects of the auditory system within the cochlea. In two experiments, we investigated the effects of different intermodal attention manipulations on the response of outer hair cells (OHCs), and the control exerted by the MOC efferent system. The effect of the MOCs on OHC activity was characterized by measuring the amplitude and rapid adaptation time course of distortion product otoacoustic emissions (DPOAEs). In the first, DPOAE recordings were compared while participants were reading a book and counting the occurrence of the letter “a” (auditory-ignoring) and while counting either short- or long-duration eliciting tones (auditory-attending). In the second, DPOAEs were recorded while subjects watched muted movies with subtitles (auditory-ignoring/visual distraction) and were compared with DPOAEs recorded while subjects counted the same tones (auditory-attending) as in Experiment 1. In both Experiments 1 and 2, the absolute level of the averaged DPOAEs recorded during the auditory-ignoring condition was statistically higher than that recorded in the auditory-attending condition. Efferent-induced rapid adaptation was evident in all DPOAE contours, under all attention conditions, suggesting that two medial efferent processes act independently to determine rapid adaptation, which is unaffected by attention, and the overall DPOAE level, which is significantly affected by changes in the focus of attention.

Early Development of Hearing in Zebrafish

Event Abstract Back to Event Early Development of Hearing in Zebrafish Zhongmin Lu1* and Alexandra A. DeSmidt1 1 University of Miami, Department of Biology, United States The zebrafish (Danio rerio) has become a valuable model for biomedical research because it combines powerful genetics, excellent embryology, and exceptional in vivo visualization in one organism. The zebrafish has the simplest vertebrate inner ear having sensory hair cells that are structurally, genetically, and functionally similar to those in other vertebrates including humans. In this study, we report auditory function of zebrafish at early developmental stages using the microphonic potential method. This is the first study to report ontogeny of response of hair cells in any fish during the first week post fertilization. The right ear of each zebrafish embryo/larva embedded in agarose was linearly stimulated with a glass probe that was driven by a calibrated piezoelectric actuator. Extracellular microphonic potentials at 20, 50, 100, and 200 Hz were recorded from hair cells in the inner ear using beveled micropipettes filled with a standard fish saline. Inner ear hair cells of the transgenic fish with hair cells expressing green fluorescent protein were visualized and counted using confocal microscopy. The results of this study showed that microphonic responses increase monotonically with stimulus intensity, stimulus frequency, and age of zebrafish larvae. Microphonic threshold at 200 Hz gradually decreased with zebrafish age. The increases in microphonic amplitude and sensitivity correlate well with the increase in total number of hair cells in the saccule. These results enhance our knowledge of early ontogeny of hearing in zebrafish and provide the control data of auditory function that can be used to evaluate auditory function of young zebrafish morphants or mutants. Acknowledgements This work was supported by the National Institute of Deafness and Other Communicative Disorders of the National Institutes of Health (R21DC009879), University of Miami Provost Research Award, and College of Arts and Sciences Gabelli Fellowship. Keywords: auditory, development, fish, Hair cell, Inner ear, Otic vesicle, Otolith organ, Saccule Conference: Tenth International Congress of Neuroethology, College Park. Maryland USA, United States, 5 Aug - 10 Aug, 2012. Presentation Type: Poster Presentation (see alternatives below as well) Topic: Sensory: Audition Citation: Lu Z and DeSmidt AA (2012). Early Development of Hearing in Zebrafish. Conference Abstract: Tenth International Congress of Neuroethology. doi: 10.3389/conf.fnbeh.2012.27.00277 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 30 Apr 2012; Published Online: 07 Jul 2012. * Correspondence: Prof. Zhongmin Lu, University of Miami, Department of Biology, Coral Gables, FL, United States, zlu@miami.edu Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Zhongmin Lu Alexandra A DeSmidt Google Zhongmin Lu Alexandra A DeSmidt Google Scholar Zhongmin Lu Alexandra A DeSmidt PubMed Zhongmin Lu Alexandra A DeSmidt Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Ototoxin-induced cellular damage in neuromasts disrupts lateral line function in larval zebrafish

The ototoxicity of a number of marketed drugs is well documented, and there is an absence of convenient techniques to identify and eliminate this unwanted effect at a pre-clinical stage. We have assessed the validity of the larval zebrafish, or more specifically its lateral line neuromast hair cells, as a microplate-scale in vivo surrogate model of mammalian inner ear hair cell responses to ototoxin exposure. Here we describe an investigation of the pathological and functional consequences of hair cell loss in lateral line neuromasts of larval zebrafish after exposure to a range of well known human and non-human mammalian ototoxins. Using a previously described histological assay, we show that hair cell damage occurs in a concentration-dependent fashion following exposure to representatives from a range of drug classes, including the aminoglycoside antibiotics, salicylates and platinum-based chemotherapeutics, as well as a heavy metal. Furthermore, we detail the optimisation of a semi-automated method to analyse the stereotypical startle response in larval zebrafish, and use this to assess the impact of hair cell damage on hearing function in these animals. Functional assessment revealed robust and significant attenuation of the innate startle, rheotactic and avoidance responses of 5 day old zebrafish larvae after treatment with a number of compounds previously shown to induce hair cell damage and loss. Interestingly, a startle reflex (albeit reduced) was still present even after the apparent complete loss of lateral line hair cell fluorescence, suggesting some involvement of the inner ear as well as the lateral line neuromast hair cells in this reflex response. Collectively, these data provide evidence to support the use of the zebrafish as a pre-clinical indicator of drug-induced histological and functional ototoxicity.

Besides Huntington's disease, does brain-type creatine kinase play a role in other forms of hearing impairment resulting from a common pathological cause?

Hearing impairment following cochlear damage due to noise trauma, ototoxicity caused by aminoglycoside antibiotics, or age-related cochlear degeneration was linked to a common pathogenesis involving the formation of reactive oxygen species (ROS). Cochleae are more vulnerable to oxidative stress than other organs because of the high metabolic demands of their mechanosensory hair cells in response to sound stimulation. We recently showed that patients and mice with Huntington's disease (HD) have hearing impairment and that the dysregulated phosphocreatine (PCr)-creatine kinase (CK) system may account for this auditory dysfunction. Given the importance of noninvasive biomarkers and the easy access of hearing tests, the symptom of hearing loss in HD patients may serve as a useful clinical indicator of disease onset and progression of HD. We also showed that dietary creatine supplementation rescued the impaired PCr-CK system and improved the expression of cochlear brain-type creatine kinase (CKB) in HD mice, thereby restoring their hearing. Because creatine is an antioxidant, we postulated that creatine might enhance expression of CKB by reducing oxidative stress. In addition to HD-related hearing impairment, inferior CKB expression and/or an impaired PCr-CK system may also play an important role in other hearing impairments caused by elevated levels of ROS. Most importantly, dietary supplements may be beneficial to patients with these hearing deficiencies.

From High-Tech to Biotech Using Stem Cell and Gene Therapy to Treat Hearing Loss

From High-Tech to Biotech Using Stem Cell and Gene Therapy to Treat Hearing Loss

Motile responses of cochlear outer hair cells stimulated with an alternating electrical field

The goal of the present study was to evaluate and characterize the motile responses of guinea pig OHCs, stimulated at frequencies varying from 50 Hz to 4 kHz, using high-definition, high-speed video recording and fully automatic image analysis software. Cells stimulated in continuous, burst and sweeping modes with an external alternating electrical field showed robust fast and slow motility, which were dependent on frequency, mode and intensity of stimulation. In response to continuous stimulation, electromotile amplitude ranged from 0.3% to 3.2% of total cell length, whereas cell length usually decreased in amounts varying from 0.1% to 4.3%. Electromotile amplitude in OHCs stimulated with square wave’s sweeps was near constant up to 200 Hz, progressively decreased between 200 Hz and 2 kHz, and then remained constant up to 4 kHz. In continuous and burst modes electromotility followed cycle-by-cycle the electrical stimulus, but it required 1–2 s to fully develop and reach maximal amplitude. Instead, slow cell length changes started about 0.6 s after the beginning and continuously developed up to 3 s after the end of electrical stimulation. Incubation of OHCs with 10 mM salicylate affected electromotility but not slow motility, whereas incubation with 3 mM gadolinium affected both. Thus, combination of external electrical stimulation, high-speed video recording and advanced image analysis software provides information about OHC motile responses at acoustic frequencies with an unprecedented detail, opening new areas of research in the field of OHC mechanics.

Caprin-1 is a target of the deafness gene Pou4f3 and is recruited to stress granules in cochlear hair cells in response to ototoxic damage.

The POU4 family of transcription factors are required for survival of specific cell types in different sensory systems. Pou4f3 is essential for the survival of auditory sensory hair cells and several mutations in human POU4F3 cause hearing loss. Thus, genes regulated by Pou4f3 are likely to be essential for hair cell survival. We performed a subtractive hybridisation screen in an inner-ear-derived cell line to find genes with differential expression in response to changes in Pou4f3 levels. The screen identified the stress-granule-associated protein Caprin-1 as being downregulated by Pou4f3. We demonstrated that this regulation occurs through the direct interaction of Pou4f3 with binding sites in the Caprin-1 5' flanking sequence, and describe the expression pattern of Caprin-1 mRNA and protein in the cochlea. Moreover, we found Caprin-1-containing stress granules are induced in cochlear hair cells following aminoglycoside-induced damage. This is the first report of stress granule formation in mammalian hair cells and suggests that the formation of Caprin-1-containing stress granules is a key damage response to a clinically relevant ototoxic agent. Our results have implications for the understanding of aminoglycoside-induced hearing loss and provide further evidence that stress granule formation is a fundamental cellular stress response.

Origin of Inner Ear Hair Cells: Morphological and Functional Differentiation from Ciliary Cells into Hair Cells in Zebrafish Inner Ear

Auditory and vestibular functions in vertebrates depend on the transduction of sound vibration or head acceleration into electrical responses in inner ear hair cells. Mechanoelectrical transduction occurs at the tip of stereocilia, which are polarized to form an orientational arrangement that determines directional sensitivity. It remains to be clarified when and how premature hair cells acquire their specialized structure and function in living animals. The developmental origin of inner ear hair cells has been studied in vivo in zebrafish embryos. Tether cells, a small number of ciliated cells associated with an "ear stone" (or otolith) in the embryonic zebrafish inner ear, are believed to be precocious hair cells. However, whether or not tether cells acquire hair bundles and mechanosensitivity remains unknown. In the present study, we investigated the morphological and functional development of tether cells. Immunohistochemical examination revealed that stereocilia appeared on the tether cell apex in a polarized arrangement at 22 h postfertilization (hpf). Labeling with FM1-43, a marker of functional mechanotransduction channels, and the in vivo electrophysiological recording of mechanotransducer responses in the developing inner ear demonstrated that tether cells acquired direction-selective mechanosensitivity at 23 hpf. These results revealed that tether cells begin to function as hair cells within an hour after the appearance of a polarized array of stereociliary bundles. Thus, the ciliary cells morphologically and functionally differentiate into the first sensory hair cells in the inner ear of the zebrafish.

Linking LIMK1 deficiency to hyperacusis and progressive hearing loss in individuals with Williams syndrome

Williams syndrome (a.k.a. Williams-Beuren Syndrome) is a multisystem disorder caused by the hemizygous deletion of a 1.6-Mb region at 7q11.23 encompassing about 26 genes, including that encoding LIM kinase 1 (LIMK1). Individuals with Williams Syndrome manifest hyperacusis and progressive hearing loss, and hyperacusis early onset suggests that it could be associated with one of the deleted genes. Based on our results about the critical role of LIM kinases in the regulation of the motile response of cochlear outer hair cells and cochlear amplification, we propose here that a reduced expression of LIMK1 in outer hair cells would be the major underlying cause of the hyperacusis and progressive hearing loss observed in patients with Williams Syndrome. Moreover, we propose a novel model of gain-control for cochlear amplification based on the LIMK-mediated regulation of slow motility of cochlear outer hair cells.

Ontogeny of auditory saccular sensitivity in the plainfin midshipman fish, Porichthys notatus

The auditory system of the plainfin midshipman fish, Porichthys notatus, is an important sensory receiver system used to encode intraspecific social communication signals in adults, but the response properties and function of this receiver system in pre-adult stages are less known. In this study we examined the response properties of auditory-evoked potentials from the midshipman saccule, the main organ of hearing in this species, to determine whether the frequency response and auditory threshold of saccular hair cells to behaviorally relevant single tone stimuli change during ontogeny. Saccular potentials were recorded from three relative sizes of midshipman fish: small juveniles [1.9-3.1 cm standard length (SL), large juveniles (6.8-8.0 cm SL) and non-reproductive adults (9.0-22.6 cm SL)]. The auditory evoked potentials were recorded from the rostral, middle and caudal regions of the saccule while single tone stimuli (75-1,025 Hz) were presented via an underwater speaker. We show that the frequency response and auditory threshold of the midshipman saccule is established early in development and retained throughout ontogeny. We also show that saccular sensitivity to frequencies greater than 385 Hz increases with age/size and that the midshipman saccule of small and large juveniles, like that of non-reproductive adults, is best suited to detect low frequency sounds (<105 Hz) in their natural acoustic environment.

The Association of Lead Exposure and Impairment of Brainstem Auditory-evoked Response and Cochlea Function

PP-31-156 Background/Aims: On the basis of some researches, the heavy metals (including lead, mercury, and tin) may be toxic on hearing in human beings and animals. Complex exposures to lead and noise were the 2 common sources of occupational exposures in the factories. The aim of the study was to investigate the effect of occupational lead on the auditory system. Methods: We measured the auditory brainstem-evoked response and cochlea function with distortion product otoacoustic emissions (DPOAEs) that are preneural responses of the outer hair cells of the inner ear in 12 adult lead-workers and 12 age- and sex- matched persons who were not exposed to lead and noise. Results: The results showed that the auditory brainstem-evoked response latency of wave I, II, III, and III–V significantly increased in the group of lead-workers (blood lead: 36.13 ± 4.52 μg/dL), as compared with the group without lead exposure (blood lead: 4.09 ± 1.41 μg/dL). The latency of wave I, II, III, V, and interpeak latency I–III were correlated to blood lead levels. Mean DPOAEs of the lead workers were significantly different from the reference group at DP frequencies of 812, 1000, 1281, 1593, 2031, 2562, and 3187 Hz. However, the DPOAEs for the lead workers were within the normal ranges of the reference group only at 4031 Hz. Although there was a tendency for the lead workers to have diminished DPOAEs, no consistent correlation of DPOAEs with lead level was found. The prevalence of normal DPOAEs in the lead workers was up to 79%. Conclusion: We concluded that lead should be otoneural toxic, especially, in the workers exposed to lead and noise both. The hearing conservation program should enhance more for the worker exposing to both ototoxic agents.

Responses of pigeon vestibular hair cells to cholinergic agonists and antagonists

Acetylcholine (ACh) is the major neurotransmitter released from vestibular efferent terminals onto hair cells and afferents. Previous studies indicate that the two classes of acetylcholine receptors, nicotinic (nAChRs) and muscarinic receptors (mAChRs), are expressed by vestibular hair cells (VHCs). To identify if both classes of receptors are present in VHCs, whole cell, voltage-clamp- and current-clamp-patch recordings were performed on isolated pigeon vestibular type I and type II HCs during the application of the cholinergic agonists, acetylcholine and carbachol, and the cholinergic antagonists, d-tubocurarine and atropine. By applying in different combinations, these compounds were used to selectively activate either nAChRs or mAChRs. The effects of nAChR and mAChR activation on HC currents and zero electrode current potential (Vz) were monitored. It was found that presumed mAChR activation decreased both inward and outward currents in both type I and type II HCs, resulting in either a depolarization or hyperpolarization. Conversely, nAChR activation mainly increased both inward and outward currents in type II HCs, resulting in a hyperpolarization of their Vz. nAChR activation also increased outward currents in type I HCs resulting in either a depolarization or hyperpolarization of their Vz. The decrease of inward and outward currents and the depolarization of the Vz in type I pigeon HCs by activation of mAChRs represents a new finding. Ion channel candidates in pigeon vestibular HCs that might underlie the modulation of the macroscopic ionic currents and Vz by different AChR activation are discussed.