cVEMP correlated with imbalance in a mouse model of vestibular disorder

BACKGROUND@#Cervical vestibular evoked myogenic potential (cVEMP) testing is a strong tool that enables objective determination of balance functions in humans. However, it remains unknown whether cVEMP correctly expresses vestibular disorder in mice.@*OBJECTIVE@#In this study, correlations of cVEMP with scores for balance-related behavior tests including rotarod, beam, and air-righting reflex tests were determined in ICR mice with vestibular disorder induced by 3,3'-iminodipropiontrile (IDPN) as a mouse model of vestibular disorder.@*METHODS@#Male ICR mice at 4 weeks of age were orally administered IDPN in saline (28 mmol/kg body weight) once. Rotarod, beam crossing, and air-righting reflex tests were performed before and 3-4 days after oral exposure one time to IDPN to determine balance functions. The saccule and utricles were labeled with fluorescein phalloidin. cVEMP measurements were performed for mice in the control and IDPN groups. Finally, the correlations between the scores of behavior tests and the amplitude or latency of cVEMP were determined with Spearman's rank correlation coefficient. Two-tailed Student's t test and Welch's t test were used to determine a significant difference between the two groups. A difference with p < 0.05 was considered to indicate statistical significance.@*RESULTS@#After oral administration of IDPN at 28 mmol/kg, scores of the rotarod, beam, and air-righting reflex tests in the IDPN group were significantly lower than those in the control group. The numbers of hair cells in the saccule, utricle, and cupula were decreased in the IDPN group. cVEMP in the IDPN group was significantly decreased in amplitude and increased in latency compared to those in the control group. cVEMP amplitude had significant correlations with the numbers of hair cells as well as scores for all of the behavior tests in mice.@*CONCLUSIONS@#This study demonstrated impaired cVEMP and correlations of cVEMP with imbalance determined by behavior tests in a mouse model of vestibular disorder.

Role of peripheral vestibular receptors in the control of blood pressure following hypotension

Hypotension is one of the potential causes of dizziness. In this review, we summarize the studies published in recent years about the electrophysiological and pharmacological mechanisms of hypotension-induced dizziness and the role of the vestibular system in the control of blood pressure in response to hypotension. It is postulated that ischemic excitation of the peripheral vestibular hair cells as a result of a reduction in blood flow to the inner ear following hypotension leads to excitation of the central vestibular nuclei, which in turn may produce dizziness after hypotension. In addition, excitation of the vestibular nuclei following hypotension elicits the vestibulosympathetic reflex, and the reflex then regulates blood pressure by a dual-control (neurogenic and humoral control) mechanism. In fact, recent studies have shown that peripheral vestibular receptors play a role in the control of blood pressure through neural reflex pathways. This review illustrates the dual-control mechanism of peripheral vestibular receptors in the regulation of blood pressure following hypotension.

Internacionalização, ciência e saúde: a medicina regenerativa global e os mercados paralelos / Internationalization, science and health: global regenerative medicine and the parallel markets

A medicina regenerativa implica em uma mudança de paradigma, a regeneração do organismo ao nível celular ou tecidual – um assunto contemporâneo controverso e de difícil estandardização. O artigo apresenta um resumo das tendências científicas, econômicas, sociais e de regulamentação global nessa área, analisadas em relação a dilemas teóricos relevantes em antropologia médica e sociologia da ciência e da saúde. Em especial, aqueles que tratam da construção de um ‘aparato coletivo de sentido’ para as novas entidades biológicas e ontológicas, a formação da cidadania biológica e a governança pela incerteza. Apresentam-se, também, evidências empíricas sobre um fenômeno chave para a governança e a regulamentação, qual seja a instalação de uma nova demanda transnacional em pesquisa e saúde através de mercados paralelos de óvulos e de terapias celulares em experimentação. Utilizam-se dados qualitativos coletados para uma pesquisa mais abrangente, resenhas jornalísticas e entrevistas com lideranças internacionais. Conclui-se com uma reflexão sobre a importância da governança internacional em ensaios clínicos e dos caminhos a serem explorados, visando uma harmonização da diversidade de práticas normativas.

Regenerative medicine involves a paradigm change due to organism regeneration at cellular and tissue level – a controversial contemporary issue and difficult to regulate. This article presents a summary of the main scientific, economic, social and regulatory global trends, analyzed according to relevant theoretical dilemmas in medical anthropology and in the sociology of science and health. This is especially true of the construction of a ‘collective frame of reference’ on the new biological and ontological entities, the shaping of biological citizenship, and governance through uncertainty. Empirical evidence is also presented on a key aspect in regulation and governance, namely the emergence of a new transnational demand in health research through the establishment of parallel markets for ova and experimental cellular therapies. Qualitative data collected for a broader research paper is analyzed, as well as journal reviews and information gathered during interviews with international leaders. The paper concludes with a discussion on the importance on international governance of clinical trials and on further exploration, towards a multilevel harmonization of a diversity of normative practices.

Effect of hydrogen peroxide on electric current of large-conductance calcium-activated potassium channel in isolated outer hair cells of old guinea pig cochlea / 生理学报

The present study was aimed to investigate the effect of hydrogen peroxide (H₂O₂, oxygen free radical donator) on the current of large-conductance calcium-activated potassium channels (BK(Ca) channels) in isolated outer hair cells of old guinea pig cochlea, and to explore the underlying mechanism. Outer hair cells of old guinea pig cochlea were acutely enzyme-isolated, and currents were recorded by whole-cell patch clamp. The results showed that, rapid activation and non-deactivation electric currents with a string of large amplitude were recorded. Activation voltage of the current was above -40 - -30 mV. The amplitude of current was increased continuously with the rising of membrane potential. The current showed characteristics of outward rectification without "rundown" phenomenon. IbTX (100 nmol/L) could completely block the activity of channel, which confirmed BK(Ca) channel's current. BK(Ca) current amplitude and peak current density increased with the increment of H₂O₂ concentration (1, 2, 4 μmol/L), showing concentration-dependent activation by H₂O₂. Our results suggest that oxygen free radical/BK(Ca) pathway may be able to adjust the balance of intracellular calcium in outer hair cells.

The Protective Effect of Epigallocatechin-3-Gallate Against Gentamicin Vestibular Ototoxicity in Type I Vestibular Hair Cell of Guinea Pig / 대한이비인후과학회지

BACKGROUND AND OBJECTIVES: Gentamicin (GM) is well known for its vestibulotoxicity. There have been many reports about vestibulotoxicity, however, its mechanism is still unclear. So far, it is known that GM affects the voltage-dependent K+ current and nitric oxide (NO) production. Epigallocatechin-3-gallate (EGCG) is the major component of green tea and is known to have anti-oxidative and anti-toxic effect. This study was undertaken to investigate the protective effect of EGCG against gentamicin on vestibular hair cell (VHC). MATERIALS AND METHOD: White guinea pigs (200-250 g) were rapidly decapitated and the temporal bones were immediately removed. Under a dissecting microscope, the crista ampullaris was obtained. The dissociated VHCs were transferred into a recording chamber mounted onto an inverted microscope. Whole-cell membrane currents and potentials were recorded using standard patch-clamp techniques. In addition, measurements of NO production were obtained using the NO-sensitive dye, 4,5-diamino-fluorescein diacetate (DAF-2DA). RESULTS: Type I VHCs Voltage-dependent K+ current was activated from low depolarizing stimulation. As the stimulation increased, higher current was detected. Voltage-dependent K+ current in type I VHCs was decreased when GM (200 microM) was administrated and GM effects of K+ current inhibition was significantly blocked by EGCG. Extracellular GM-induced an increase in DAF-2DA fluorescence, which thus indicates NO production in VHCs. Also, the GMinduced NO production was inhibited by EGCG. CONCLUSION: GM inhibits voltage-dependent K+ current by releasing NO in isolated type I VHCs. EGCG blocks this inhibitory effects, suggesting a protective role on GM vestibulotoxicity.

Analysis on outer hair cells hazards from occupational exposure to low frequency electric and magnetic fields and magnetic fields and its related factors / 临床耳鼻咽喉头颈外科杂志

OBJECTIVE@#To explore the function of outer hair cells and its influencing factors in the workers of occupational exposure to low frequency electric and magnetic fields.@*METHOD@#502 high-strength LF EMFs-exposed workers were taken as the study subjects. The field intensity indicator and noise analyzer were employed for the examination of the electromagnetic energy intensity and noise value at the working sites. Self-administered questionnaires were adopted. Universal hearing screening by distortion product otoacoustic emission (DPOAE) and pure tone audiometry (PTA) were done. 100 workers who had abnormal POAE were taken as the observation group and 100 workers who had normal DPOAE were taken as the control group. The workers need be confirmed with ABR testing when the pure tone threshold of two consecutive frequencies were above 20 dB HL or DPOAE detection in any frequency did not pass. Multiple factor analysis with logistic regression was performed for the risk factors.@*RESULT@#The average electric power density in job locations was 21-38 KV/m, which was higher than national standard (< 5 kv/m). Average noise-level in job locations was 52-65 dBHL, which was within the standard (< 85 dB(A). Questionnaire presented that low frequency electric and magnetic fields might increase the incidence of headache, insomnia and tinnitus in the observed group. The incidence of abnormal DPOAE was higher in the subjects of the observed group (P < 0.01). At 676, 933, 3616, 5 130, 7253 Hz, the DPOAE amplitudes of the observed group workers were significantly lower than the control group. Multivariate analysis showed that the risk factors of abnormal DPOAE included exposure of EMF, length of service, daily exposure time, conservatory measures might be protective factors.@*CONCLUSION@#The changes of DPOAE indicated that the exposure to low frequency electric and magnetic fields had a subtle, discreet and localized impairing effects on outer hair cells. Exposure of low frequency electric and magnetic fields, length of service, daily exposure time might be risk factors, conservatory measures might be protective factors.

Development of Multichannel Vestibular Prosthesis for Treatment of Bilateral Vestibular Deficiency / 대한이비인후과학회지

Bilateral loss of vestibular sensation from injuries of vestibular hair cells causes individuals suffering poor vision during head movement, postural instability, chronic disequilibrium, and cognitive distraction. A vestibular prosthesis analogous to cochlear implants but designed to modulate vestibular nerve activity during head movement should improve quality of life for these chronically dizzy individuals. An implantable prosthesis that partly restores normal activity on branches of the vestibular nerve should improve quality of life for individuals disabled by this disorder. There have been many efforts to develop and restore 3-dimensional angular vestibule-ocular reflex and the Johns Hopkins vestibular neuro-engineering laboratory has been developing a head-mounted multichannel vestibular prosthesis that restores sufficient semicircular canal function to partially recreate a normal 3-dimensional angular vestibulo-ocular reflex. In this review, their results are described.

Effect of JNK signal transduction pathway in intense noise-induced apoptosis of vestibular hair cells in guinea pigs / 中华劳动卫生职业病杂志

<p><b>OBJECTIVE</b>To investigate the mechanism of intense noise-induced apoptosis of vestibular hair cells in guinea pigs and the effect of phosphorylated c-Jun N-terminal kinase (JNK) signal transduction pathway in intense noise-induced apoptosis of vestibular hair cells.</p><p><b>METHODS</b>Thirty-two guinea pigs were randomly and equally divided into 1, 5, and 15 d experimental groups and control group. The guinea pigs in the experimental groups were exposed to 4 kHz narrow-band noise at 120 dB SPL for 4 h and then subjected to measurement of auditory brainstem response at 1, 5, or 15 d after noise exposure. In each group, four guinea pigs were used to prepare paraffin sections of vestibular hair cells, and the rest for extraction of total protein from vestibular hair cells. The apoptosis of vestibular hair cells was detected by terminal deoxynucleotidyl transferase (TdT)-mediated d-UTP nick-end labeling (TUNEL). The expression levels of p-JNK and pc-Jun were measured by immunohistochemistry and Western blot.</p><p><b>RESULTS</b>TUNEL-positive cells were found in the vestibular hair cells in the experimental groups, most in the 1 d experimental group and least in the 15 d experimental group, but no positive cells were found in the control group. The immunohistochemical results showed that p-JNK and pc-Jun were detected in the cell nuclei in the experimental groups, but no p-JNK- and pc-Jun-positive cells were found in the control group. The Western blot showed that p-JNK and pc-Jun were increased and activated quickly at 1d after noise exposure, reached the peak levels at 5 d after noise exposure, and were then decreased gradually, but they were still at relatively high levels at 15 d after noise exposure.</p><p><b>CONCLUSION</b>Intense noise can cause injury to vestibular hair cells by inducing cell apoptosis, and p-JNK marks the activation of JNK signal transduction pathway, suggesting that JNK signal transduction pathway plays an important role in intense noise-induced apoptosis of vestibular hair cells in guinea pigs.</p>

Vestibular symptoms in factory workers subjected to noise for a long period

Noise can cause permanent or temporary hearing loss. High levels of noise may stimulate the vestibular system and thereby cause disturbances in the balancing mechanism. To determine the effect of long-term exposure to occupational noise on the vestibular system. A dizziness questionnaire was administered to 20 factory workers who were exposed to occupational noise for more than 10 years. The results were compared with 2 control groups. The control group 1 consisted of 20 people who had similar physical activity during work but were not exposed to high level of noise. Control group 2 consisted of 20 students never exposed to hazardous noise. There was significant difference between the experimental group and the 2 control groups in terms of frequency of vestibular symptoms. However, most of the symptoms were subtle in nature. Tinnitus was significantly [p<0.05] more frequent in the experimental group than the 2 control groups. Long-term exposure to noise may cause vestibular symptoms before clinically detectable hearing loss. The symptoms are subtle for which they are mostly neglected; the symptoms do not affect the functional ability of workers

Temporary and permanent level shifts in distortion product otoacoustic emissions following noise exposure in an animal model

Noise-induced hearing loss [NIHL] is one of the most common occupational illnesses. Most of the studies on NIHL were conducted at high noise levels that people are rarely exposed to but in industries. The function of the outer hair cells [OHCs] is impaired after exposure to industrial noise. Distortion product otoacoustic emissions [DPOAEs] are useful in examination of noise-induced level shifts. To assess the function of OHCs by DPOAE temporary and permanent level shifts [TLSdp and PLSdp] in rabbits exposed to white noise at realistic levels typically found in industrial settings over a broad range of frequencies. 12 albino rabbits were divided into two groups: the experimental group rabbits which were exposed to 95 dB SPL white noise at 500-8000 Hz for 8 hrs/day for 5 consecutive days, and the control group rabbits with no exposure to noise. The function of OHCs was examined by DPOAE level [Ldp] in different occasions. The study groups were compared for DPOAE temporary and permanent level shifts [TLSdp and PLSdp] to assess the effect of noise on OHCs function. Noise-induced DPOAE levels [Ldp] were decreased up to 20.65 dB [on day 8] and 18.93 dB [on day 11] at 5888.50 Hz [p=0.081]. TLSdp and PLSdp were significantly decreased up to 17.99 dB and 16.27 dB, respectively in the experimental group. The most and least Ldp were significantly different [p<0.05]; they occurred at 5888.50 and 588.00 Hz, respectively. There were significant differences between temporary and permanent threshold shift at various frequencies [p<0.05]. These differences were mainly related to 5888.50 Hz compared to other frequencies in each ear [p<0.05]. DPOAEs are an attractive tool for obtaining information about small temporary or permanent threshold shifts, even when the pure tone audiogram is normal

Comparative morphology of the two type's hair cells from saccule and utricle under inverted phase contrast microscope / 临床耳鼻咽喉头颈外科杂志

OBJECTIVE@#To explore more reliable standards for identifying vestibular hair cells of saccule and utricle prepared in studies with patch clamp technique under inverted phase contrast microscope.@*METHOD@#The length and width of two type's hair cell's were measured besides the length of cilia, and all datas were analyzed statistically.@*RESULT@#The width and length of cilia of two types hair cells in saccule and utricle from guinea pig were similar. The length of type I was longer than that of type II, so the ratio between length and width was larger and the ratio of the length between cilia and cell body was small.@*CONCLUSION@#Two type's hair cells of saccule and utricle from guinea pig may be distinguished through the ratio of cell body's length and width even the ratio of the length between cilia and cell body, besides the standards before.

Isolation of Voltage Dependent Calcium Current in Chick Inner Hair Cell / 대한이비인후과학회지

BACKGROUND AND OBJECTIVES: Voltage dependent calcium channel (VDCC) mediates calcium ion influx and controls neurotransmitter release in excitable cells. Hair cells in vertebrates cochlea are known to express L-type VDCC. The purpose of this study was to measure calcium current from hair cells to investigate basic activity and characteristics of VDCC. MATERIALS AND METHOD: We measured calcium current in hair cells of the chicken's auditory organ, the basilar papilla analogous to the mammalian cochlea, in whose L-type, dihydropyridinesensitive calcium channels predominate and in vestibular hair cells from cristae. Calcium currentthrough VDCC was isolated in voltage-clamp recording using Cesium, Tetraethylammonium, 4- aminopyridine and apamin to block the much larger potassium currents. Various concentrations of internal calcium buffer, ethylene glycol tetraacetic acid (EGTA) or 1,2-bis (o-aminophenoxy) ethane-N,N,N',N'-tetraacetic acid (BAPTA) were used. RESULTS: The higher the buffer concentration, the larger the current size were ; they were significantly larger in 10 mM of calcium buffer concentration (ANOVA, p< 0.05). There was no difference in calcium current between cochlear and vestibular hair cells. CONCLUSION: We could successfully isolate stable inward calcium current from chick hair cells. This experiment can be used as a basic method to understand neurotransmission process between hair cells and afferent neurons.

Antioxidant and Anti-Apoptotic Effect of Melatonin on the Vestibular Hair Cells of Rat Utricles

OBJECTIVES: Aminoglycosides are commonly used antibiotic agents, and they are known to generate free oxygen radicals within the inner ear and to cause vestibulo-cochlear toxicity and permanent damage to the sensory hair cells and neurons. Melatonin, a pineal secretory product, has the properties of being a powerful direct and indirect antioxidant. The aim of the present study was to prove the antioxidant effect of melatonin against gentamicin-induced ototoxicty. METHODS: The utricular maculae of Sprague-Dawley rats were prepared from postnatal day 2-4, and these maculae were were divided into 6 groups as follows: 1) control, 2) melatonin only, 3) gentamicin only, and 4), 5), and 6) gentamicin plus melatonin (10, 50, and 100 micrometer, respectively). To count the number of hair cells, 5 utricles from each group were stained with phalloidin-FITC on the 1st, 4th, and 7th days after drug administration. Reactive oxygen species (ROS) was assessed by using the fluorescent probe hydrofluorescent diacetate acetyl ester. The caspase-3 activity was also examined with using the fluorescent caspase-3 substrate and performing Western blotting. RESULTS: The result of this study showed that gentamicin induced the loss of utricular hair cells, and this loss of hair cells was significantly attenuated by co-administration of melatonin. Melatonin reduced ROS production and caspase-3 activation in the gentamicin treated utricular hair cells. CONCLUSION: Our findings conclusively reveal that melatonin has protective effects against gentamicin-induced hair cell loss in the utricles of rat by inhibiting both ROS production and caspase-3 activity.

Ototoxic effects of streptomycin in vestibular organotypic cultures / 中华耳鼻咽喉头颈外科杂志

<p><b>OBJECTIVE</b>To investigate the ototoxic effects of streptomycin in vestibular organotypic cultures.</p><p><b>METHODS</b>F344 rats with age at postnatal day three or four were used for this study. The maculae of saccule and utricle were routinely dissected out and cultured with serum-free medium containing various dose of streptomycin for 24 hours. The ciliary turf of vestibular hair cells was stained with fluorescent phalloidin, and its nucleus was stained with to pro-3 DNA probe. The vestibular hair cells were quantitatively counted and photographed under confocal fluorescent microscope.</p><p><b>RESULTS</b>Morphological feature of vestibular hair cells were good in normal control cultures. However, the density of hair cells was decreased in evidence with increase of streptomycin sulfate concentrations. Twenty-four hours after streptomycin cultures, 0.25 mmol/L streptomycin caused a 10% hair cell missing, 50% hair cell loss from 1 mmol/L streptomycin treatment, and more than 75% hair cells gone post-3 mmol/L streptomycin cultures. After streptomycin treatment, the nuclear shrinkage and fragmentation were found in vestibular hair cells, whereas the vestibular supporting cells were normal.</p><p><b>CONCLUSION</b>Streptomycin induced-vestibular hair cells lesion was in a dose dependent manner with nuclear shrinkage and fragmentation. This may suggest that streptomycin leads vestibular hair cell die through apoptosis.</p>

Preventive and Therapeutic Effects of Low Level Laser Irradiation on Gentamicin-Induced Vestibulotoxicity in Rat Utricles / 대한이비인후과학회지

BACKGROUND AND OBJECTIVES: The purpose of this study was to investigate the effects of low level laser for the prevention and treatment of aminoglycoside-induced vestibular ototoxicity. MATERIALS AND METHOD: An organotypic culture of 2 to 4 days old rat utricular maculae was established. Rats were divided into 6 groups according to the treadtment of the utricles: G (gentamicintreated), L (laser-irradiated), LG (laser-irradiated and gentamicin-treated), GL (gentamicin-treated and laser-irradiated), LGL (gentamicin-treated during laser-irradiated) and C (control). After organotypic culture, the utricles of 6 groups were examined by confocal laser scanning electron microscope and scanning electron microscope. The results of each group were compared with each other by statistical methods. RESULTS: The number of vestibular hair cells of the group G was smaller compared to that of the group C. The group L had no difference compared with the group C. The groups LG and GL showed more vestibular hair cells compared with the group G. The group LG showed more vestibular hair cells than the group GL. The group LGL showed most vestibular hair cells compared to that of the groups G, LG, and GL. CONCLUSION: The most effective treatment of aminoglycosideinduced vestibular otoxicity is the irradiation of low level laser before and after the insult of the aminoglycoside. Further clinical studies using low level laser were needed to prevent aminoglycoside-induced ototoxicity and to promote the regeneration of vestibular hair cells.

Co-location of ACh-sensitive BK channels and L-type calcium channels in type II vestibular hair cells of guinea pig / 中华耳鼻咽喉头颈外科杂志

<p><b>OBJECTIVE</b>To explore the mechanisms of the influx of calcium ions during the activation of ACh-sensitive BK channel (big conductance, calcium-dependent potassium channel) in type II vestibular hair cells of guinea pigs.</p><p><b>METHODS</b>Type II vestibular hair cells were isolated by collagenase type IA. Under the whole-cell patch mode, the sensitivity of ACh-sensitive BK current to the calcium channels blockers was investigated, the pharmacological property of L-type calcium channel activator-sensitive current and ACh-sensitive BK current was compared.</p><p><b>RESULTS</b>Following application of ACh, type II vestibular hair cells displayed a sustained outward potassium current, with a reversal potential of (-70.5 +/- 10.6) mV (x +/- s, n = 10). At the holding potential of -50 mV, the current amplitude of ACh-sensitive potassium current activated by 100 micromol/L ACh was (267 +/- 106) pA (n = 11). ACh-sensitive potassium current was potently sensitive to the BK current blocker, IBTX (iberiotoxin, 200 nmol/L). Apamin, the well-known small conductance, calcium-dependent potassium current blocker, failed to inhibit the amplitude of ACh-sensitive potassium current at a dose of 1 micromol/L. ACh-sensitive BK current was sensitive to NiCl2 and potently inhibited by CdCl2. NiCl2 and CdCl2 showed a dose-dependent blocking effect with a half inhibition-maximal response of (135.5 +/- 18.5) micromol/L (n = 7) and (23.4 +/- 2.6) micromol/L (n = 7). The L-type calcium channel activator, (-) -Bay-K 8644 (10 micromol /L), mimicked the role of ACh and activated the IBTX-sensitive outward current.</p><p><b>CONCLUSION</b>ACh-sensitive BK and L-type calcium channels are co-located in type II vestibular hair cells of guinea pigs.</p>

Properties of cholinergic receptor-mediated ion channels on type I vestibular hair cells of guinea pigs / 生理学报

To confirm the existence of cholinergic receptors on type I vestibular hair cells (VHCs I) of guinea pigs and to study the properties of the cholinergic receptor-mediated ion channels on VHCs I, electrophysiological responses of isolated VHCs I to external ACh were examined by means of whole-cell patch-clamp recordings. The results showed that 7.5% (21/279) VHCs I were found to be sensitive to ACh (10-1000 μmol/L). ACh generated an outward current in a steady, slow, dose-dependent [EC(50) was (63.78±2.31) μmol/L] and voltage-independent manner. In standard extracellular solution, ACh at the concentration of 100 μmol/L triggered a calcium-dependent current of (170±15) pA at holding potential of -50 mV, and the current amplitude could be depressed by extracellularly added calcium-dependent potassium channel antagonist TEA. The time interval for the next complete activation of ACh-sensitive current was no less than 1 min. The ion channels did not shut off even when they were exposed to ACh for an extended period of time (8 min). The results suggest that dose-dependent, calcium-dependent and voltage-independent cholinergic receptors were located on a few of the VHCs I investibular epithelium of guinea pigs. The cholinergic receptors did not show desensitization to ACh. This work reveals the existence of efferent neurotransmitter receptors on VHCs I and helps in understanding the function of vestibular efferent nervous system, and may provide some useful information on guiding the clinical rehabilitative treatment of vertigo.

Polarity specific segregation of the primary vestibular afferent fibers in mice

One of the striking features of the vestibular hair cells is the polarized arrangement of their stereocilia and their consequent characteristic of best activation/deactivation directions. Furthermore each of the vestibular end organs is characterized by a distinct organization of these polarized cells. Specifically, all the hair cells in the crista of an individual canal have the same polarity, and the macula are each divided in halves along the striola where the polarities of the hair cells show mirror image symmetry. We utilized the technique of post-fixation transganglionic neuronal tracing with immunofluorescent lipid soluble dyes in new born and 8 day old mice to investigate whether these polarity characteristics influence the pattern of connections between the end organs and their central targets: the vestibular nuclei and cerebellum. We found the cerebellar projection originates preferentially from the medial and superomedial half of the utricular and saccular macula, respectively, while the vestibular projection originates primarily from their lateral and superolateral half respectively. This indicates that striola defines almost mutually exclusive central projections, as well as opposing hair cell polarities. It is suggested that, this macular organization provides an inhibitory side loop through the cerebellum to produce synergetic tuning effects in the vestibular nuclei. In the canals, the entire crista projects to the vestibular nuclei, but the projection to the vestibulocerebellum originates preferentially from the medial half of each of the cristae. The reason for this pattern is not clear, but it may compensate for unequal activation of crista hair cells

A Promotive Effect of Low-Level Laser on Hair Cell Regeneration Following Gentamicin Induced Ototoxicity in Postnatal Organotypic Culture of Rat Utricles / 대한이비인후과학회지

BACKGROUND AND OBJECTIVES: In normal postnatal mammalian inner ear sensory epithelium, regeneration of hair cells is a very rare event, but there is hair cell regeneration with partial restoration of the vestibular sensory epithelium following ototoxic damage. In this study, the effects of low-level laser on hair cell regeneration following gentamicin exposure in postnatal organotypic culture of rat utricles were investigated. MATERIALS AND METHOD: A long term organotypic culture of 2 to 7 day old rat utricular maculae was established to study aminoglycoside-induced vestibular hair cell renewal. The utricles were exposed to 1 mM of gentamicin for 48 hr and allowed to recover in a culture medium only or in a medium with daily irradiation of low-level laser, whereas the control group was not exposed to gentamicin. Whole-mount utricles were stained with FM1-43, which are known to be an efficient marker, to identify live hair cells in cultured tissues. RESULTS: Loss of hair cells was nearly stopped from 2 days after exposure to gentamicin ; a peak of regeneration was reached after 18 days and sustained for two weeks in the medium with the irradiation of low-level laser. CONCLUSION: These results suggest that low-level laser promotes spontaneous hair cell regeneration following gentamicin damage in utricular explants.

Cation ions modulate the ACh-sensitive current in type II vestibular hair cells of guinea pigs / 生理学报

Molecular biological studies and electrophysiological data have demonstrated that acetylcholine (ACh) is the principal cochlear and vestibular efferent neurotransmitter among mammalians. However, the functional roles of ACh in type II vestibular hair cells among mammalians are still unclear, with the exception of the well-known alpha9-containing nicotinic ACh receptor (alpha9-nAChR) in cochlear hair cells and frog saccular hair cells. In this study, the properties of the ACh-sensitive current were investigated by whole-cell patch clamp technique in isolated type II vestibular hair cells of guinea pigs. The direct effect of extracellular ACh was to induce a hyperpolarization effect in type II vestibular hair cells. Type II vestibular hair cells displayed a sustained outward current in response to the perfusion of ACh. It took about 60 s for the ACh-sensitive current to get a complete re-activation. The reversal potential of the ACh-sensitive current was (-66 +/- 8) mV, which indicated that potassium ion was the main carrier of this current. The blocking effect by the submillimolar concentration of tetraethylammonium (TEA) further indicated that extracellular ACh stimulated the calcium-dependent potassium current. Following replacement of the compartment of NaCl in the normal external solution with TrisCl, LiCl or saccharose respectively, the amplitude of the ACh-sensitive current was not affected. Blocking of the release of intracellular Ca(2+) stores by intracellular application of heparin failed to inhibit the ACh-sensitive current. Therefore, extracellular Na(+)and the inositol 1,4,5-trisphosphate (IP(3))-dependent intracellular Ca(2+)release were not involved in the activation of the ACh-sensitive current. However, the ACh-sensitive current was strongly affected by the concentration of the extracellular K(+), extracellular Ca(2+) and intracellular Mg(2+). The amplitude of the ACh- sensitive current was strongly inhibited by high concentration of extracellular K(+). In the Ca(2+)-free external solution, ACh only activated a very small current; however, the ACh-sensitive current demonstrated a Ca(2+)-dependent inhibition effect in high concentration of Ca(2+)solution. In addition, the ACh-sensitive current was inhibited by increasing of the concentration of intracellular Mg(2+). In conclusion, the present results demonstrate that ACh plays an important role in the vestibular efferent system. The fact that Na(+) is not involved in the ACh-sensitive current will not favor the well-known profile of alpha9-nAChR, which is reported to display a small but important permeability to Na(+). It is also suggested that, in vivo, the amplitude of the ACh-induced hyperpolarization may strongly depend on the concentration of extracellular Ca(2+)and intracellular Mg(2+).