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  • 1
    ISSN: 1432-1351
    Keywords: Hair cell ; Stimulus transduction ; Cytoskeleton ; Apical membrane ; Electroreception
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The receptor cells of the ampullary electroreceptor organs of Ictalurus nebulosus bear microvilli on the apical membrane. Whereas microvilli in mechanoreceptive hair cells and in chemoreceptor cells have a transduction function, the function of these membrane specializations in electroreceptor cells is not fully understood. To study the role of the microvilli of the electroreceptor cells, the ampullary electroreceptor organs were apically exposed to the microfilament-disrupting agents cytochalasin B and D. Electrophysiological measurements showed that cytochalasin caused a high decrease in sensitivity and a slight decrease in spontaneous activity. Exposure to cytochalasin B resulted in a striking disorganization of the microvilli on the apical membrane of the electroreceptor cells. The most plausible explanation for the results is that treatment with cytochalasin mainly affects the actin filaments of the microvilli causing an increase of the resistance of the apical membrane. A high apical resistance results in a decrease of the voltage over the basal membrane, which in turn reduces the sensitivity. The conclusion is that intact apical microvilli are necessary for proper functioning of ampullary electroreceptor organs. Alterations in microvillar properties, like surface area and ion channel conductancy might play a considerable role in the regulation of the sensitivity.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Journal of comparative physiology 176 (1995), S. 103-109 
    ISSN: 1432-1351
    Keywords: Electroreception ; Stimulus transduction ; Signal filtering ; Hair cell ; Microvilli ; Cytochalasin B ; Electrical model
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Ampullary electroreceptor organs of catfish show a band-pass-filter characteristic on sinusoidal electric stimulation. The structures and processes which are responsible for the frequency characteristics are not fully understood. To investigate the role of the apical membrane and its microvilli in signal filtering, the ampullary organs were apically exposed to the actin filament disrupting agent cytochalasin B. Electrophysiological data showed that cytochalasin B treatment reduced the absolute sensitivity to about 20% over the whole frequency range. The decrease in sensitivity at 20 Hz, however, was less than at other frequencies. The phase lags at 14 and 20 Hz became less negative, indicating a relatively better transduction at high frequencies. Calculations with an electric equivalent circuit of an electroreceptor cell indicated that a reduction in apical surface area in combination with a reduction of the number or the conductivity of apical ion channels can explain such effects. We conclude that, although only the basal membrane is thought to be involved in stimulus transduction, the apical membrane contributes considerably to the frequency characteristics of ampullary electroreceptor organs.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1432-0878
    Keywords: Hair cell ; Synapses ; Freeze-fracture ; Organ of Corti ; Guinea pig
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Afferent and efferent synapses of hair cells in the organ of Corti of the guinea pig have been examined in freeze-fracture replicas. Afferent synapse In the inner hair cells, intramembranous particles 10 nm in diameter are aggregated on the ridge on the P-face of the presynaptic membrane directly beneath the synaptic rod. In the outer hair cells, in which the synaptic rod is located in the presynaptic cytoplasm underneath the presynaptic membrane, small aggregations of intramembranous particles 10 nm in diameter can be found on the P-face of the presynaptic membrane corresponding to the site of the presynaptic dense projection. Intramembranous particles 10 nm in diameter are also densely aggregated on the P-face of the postsynaptic membrane of the outer hair cells. Efferent synapse of the outer hair cells Large intramembranous particles 13 nm in diameter are distributed in clusters composed of four to ten particles on the P-face of the presynaptic membrane. In the P-face of the postsynaptic membrane, disc-like aggregations of intramembranous particles 9 nm in diameter are found. The subsynaptic cistern covers the cytoplasmic surface of the postsynaptic membrane of the efferent synapse; it may cover more than one postsynaptic membrane when several efferent synapses are in close proximity to one another.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1432-0878
    Keywords: Key words: Keratan sulphate ; Elastin ; Extracellular linkages ; Stereocilia ; Hair cell ; Cochlea ; Guinea pig
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract. The stereociliary bundles of hair cells contain cross-linking extracellular filaments which have been suggested to play a role in mechanoelectrical transduction. To investigate the composition of these filaments, antibodies to the extracellular matrix molecules elastin and keratan sulphate have been used for light- and electron-microscopic immunocytochemistry of the guinea-pig organ of Corti. With the antibody to elastin, no immunoreactivity was found in hair bundles. This implies either that the epitope recognised by this antibody is not present in the links or that it is obscured. The antibody to keratan sulphate labelled the stereociliary bundles of both inner and outer hair cells but not supporting cells. The tips of the tallest stereocilia, especially on outer hair cells, the tips of the shorter stereocilia where the tip links attach to the stereociliary membrane, and the attachments of the lateral links, were labelled. This suggests that the links contain keratan sulphate proteoglycans, molecules which in other tissues are known to maintain structural integrity and fibrillar spacing, and to influence the microenvironment of the cell surface.
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Annals of biomedical engineering 26 (1998), S. 157-165 
    ISSN: 1573-9686
    Keywords: Shell model ; Cochlear mechanics ; Biological membrane characteristics ; Elastic properties ; Hair cell ; Ear ; Hearing
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract We propose a mathematical model for analyses of the elastic properties of the wall of the outer hair cell (OHC) in the inner ear. The model reflects the properties of the major components of the OHC wall: the subsurface cisternae, the cortical lattice, the plasma membrane, and the radial pillars. The wall is treated as a composite consisting of three elastic cylindrical shells. Two inner shells, isotropic and orthotropic, are adjacent to each other, and the outermost isotropic shell is connected to the combined inner shell by elastic springs. We derive Flügge-type equations for the composite wall and apply the model to the interpretation of the experiments with axial loading and with inflation of the OHC. We derive expressions for the axial stiffness and the wall strains measured in these experiments in terms of the elastic properties of the wall components. We also consider a conceivable experiment with torsion of the OHC and obtain relations between the torque (the axial reaction) and the angle of torsion. These solutions provide necessary information for the future determination of the OHC elastic properties. © 1998 Biomedical Engineering Society. PAC98: 4364Ld, 8745Bp, 8722-q, 8710+e
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Microscopy Research and Technique 31 (1995), S. 317-325 
    ISSN: 1059-910X
    Keywords: Cytochemistry ; Quantification ; EFTEM ; Teleost ; Tectum opticum ; Hair cell ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Natural Sciences in General
    Notes: Four different methods for calcium precipitation are compared in the optic tectum and the inner ear of the cichlid fish, Oreochromis mossambicus. Several parameters are investigated concerning their influences on the reaction product. Three procedures (bichromate, fluoride, and oxalate-pyroantimonate) produce fine-grained deposits, often flocculent in the latter method. The fourth method (potassium-pyroantimonate) generates predominantly coarse-grained reaction product. The calcium content of the deposits is always proven with energy-filtering transmission electron microscopy (EFTEM). In both tissues fine-grained reaction product is found in endoplasmic reticulum and synaptic vesicles, and in addition in some mitochondria and at the cytoskeleton. The coarse-grained deposits of the potassium-pyroantimonate method have a more unspecific distribution. This is the only method which produces extracellular deposits in the inner ear, whereas in the optic tectum extracellular precipitates are always present except with the oxalate-pyroantimonate procedure. Two factors have an influence on the reaction product: the duration of fixation and the type of resin. The prolongation of the fixation time up to 24 hours leads to an increase of the reaction product, which also becomes coarse-grained. These observations are corroborated by quantification with image analysis. Furthermore the use of an epoxy resin compared to acrylic resins decreases the amount of reaction product produced. We show that the application of several methods is meaningful in order to understand the calcium properties of the investigated tissue, but it is necessary to optimize a certain method for a given tissue. © 1995 Wiley-Liss, Inc.
    Additional Material: 4 Ill.
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  • 7
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal of Electron Microscopy Technique 15 (1990), S. 261-279 
    ISSN: 0741-0581
    Keywords: Cochlea ; Hair cell ; Cytoskeleton ; Immunocytochemistry ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Natural Sciences in General
    Notes: The organization of microtubules in hair cells of the guinea-pig cochlea has been investigated using transmission electron microscopy and correlated with the location of tubulin-associated immunofluorescence in surface preparations of the organ of Corti. Results from both techniques reveal consistent distributions of microtubules in inner and outer hair cells.In the inner hair cells, microtubules are most concentrated in the apex. Reconstruction from serial sections shows three main groups: firstly, in channels through the cuticular plate and in a discontinuous belt around its upper perimeter; secondly, forming a ring inside a rim extending down from the lower perimeter of the plate; and thirdly, in a meshwork underlying the main body of the plate. In the cell body, microtubules line the inner face of the subsurface cistern and extend longitudinally through a tubulo-vesicular track between the apex and base.In outer hair cells, the pattern of microtubules associated with the cuticular plate is similar, although there are fewer present than in inner hair cells. In outer hair cells from the apex of the cochlea, microtubules occur around an infracuticular protrusion of cuticular plate material. In the cell body, many more microtubules occur in the region below the nucleus compared with inner hair cells.The possible functions of microtubules in hair cells are discussed by comparison with those found in other systems. These include morphogenesis and maintenance of cell shape; intracellular transport, e.g., of neurotransmitter vesicles; providing a possible substrate for motility; mechanical support of structures associated with sensory transduction.
    Additional Material: 15 Ill.
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  • 8
    Publication Date: 2022-05-25
    Description: © The Author(s), 2018. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Cell Reports 25 (2018): 1281–1291, doi:10.1016/j.celrep.2018.10.005.
    Description: Morphogenesis and mechanoelectrical transduction of the hair cell mechanoreceptor depend on the correct assembly of Usher syndrome (USH) proteins into highly organized macromolecular complexes. Defects in these proteins lead to deafness and vestibular areflexia in USH patients. Mutations in a non-USH protein, glutaredoxin domain-containing cysteine-rich 1 (GRXCR1), cause non-syndromic sensorineural deafness. To understand the deglutathionylating enzyme function of GRXCR1 in deafness, we generated two grxcr1 zebrafish mutant alleles. We found that hair bundles are thinner in homozygous grxcr1 mutants, similar to the USH1 mutants ush1c (Harmonin) and ush1ga (Sans). In vitro assays showed that glutathionylation promotes the interaction between Ush1c and Ush1ga and that Grxcr1 regulates mechanoreceptor development by preventing physical interaction between these proteins without affecting the assembly of another USH1 protein complex, the Ush1c- Cadherin23-Myosin7aa tripartite complex. By elucidating the molecular mechanism through which Grxcr1 functions, we also identify a mechanism that dynamically regulates the formation of Usher protein complexes.
    Description: This work was supported by grants from the NIH (DC004186, OD011195, and HD22486).
    Keywords: Grxcr1 ; Usher syndrome ; Hair cell ; Stereocilia ; Glutathionylation ; Harmonin ; Sans
    Repository Name: Woods Hole Open Access Server
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  • 9
    Publication Date: 2022-05-25
    Description: Author Posting. © The Company of Biologists, 2019. This article is posted here by permission of Company of Biologists for personal use, not for redistribution. The definitive version was published in Journal of Experimental Biology 222(2) (2019): jeb190587, doi:10.1242/jeb.190587.
    Description: A longstanding question in aquatic animal sensory physiology is the impact of self-generated movement on lateral line sensitivity. One hypothesis is that efferent modulation of the sensory hair cells cancels self-generated noise and allows fish to sample their surroundings while swimming. In this study, microwire electrodes were chronically implanted into the anterior lateral line nerve of oyster toadfish and neural activity was monitored during forward movement. Fish were allowed to freely swim or were moved by a tethered sled. In all cases, neural activity increased during movement with no evidence of efferent modulation. The anterior lateral line of moving fish responded to a vibrating sphere or the tail oscillations of a robotic fish, indicating that the lateral line also remains sensitive to outside stimulus during self-generated movement. The results suggest that during normal swim speeds, lateral line neuromasts are not saturated and retain the ability to detect external stimuli without efferent modulation.
    Description: Funding was provided by National Science Foundation grants IOS 1354745 and DBI 1359230 and 1659604.
    Description: 2020-01-25
    Keywords: Efferent ; Hair cell ; Self-generated movement ; Modulation
    Repository Name: Woods Hole Open Access Server
    Type: Article
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