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  • Acoustic trauma  (2)
  • Circadian oscillator  (1)
  • Cochlear nucleus  (1)
  • 1
    Electronic Resource
    Electronic Resource
    Discharge patterns in the cochlear nucleus of the chinchilla following noise induced asymptotic threshold shift (1978)
    Springer
    Experimental brain research 32 (1978), S. 301-320 
    Details
    ISSN: 1432-1106
    Keywords: Cochlear nucleus ; Noise induced deafness ; Cochleagrams ; Tuning curves ; Spontaneous activity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Chinchillas were exposed to an 86 dB SPL octave band of noise centered at 4.0 kHz for 3.5–5 days. The noise elevated the hearing thresholds between 4.0 and 16.0 kHz to between 60 and 75 dB SPL. Measurements from single neurons in the cochlear nucleus revealed abnormalities in the response properties of neurons with characteristic frequencies (CF) above 2.0 kHz. Units above 2.0 kHz had elevated thresholds (between 50 and 90 dB SPL) and broad tuning curves due to a greater loss in sensitivity near CF than at lower frequencies. The tuning curve Q10dB values for high frequency neurons were generally less than 3.0 and approached the Q10dB values for basilar membrane displacement. Spontaneous activity rates in units above 2.0 kHz were also low. In a few units, the threshold for single tone inhibition was significantly lower than that for excitation; the best inhibitory frequencies were always below 2.0 kHz. Two-tone inhibition was present in both low and high threshold neurons, but its strength was not assessed. Cochleagrams obtained 12 hours postexposure revealed discrete hair cell lesions in the basal third of the cochlea. The locations of the lesions were consistent with the frequencies of maximum hearing loss. The behavioral thresholds and the thresholds at CF of the most sensitive units were within 10–15 dB of each other. The results indicate that intense sounds reduce the sensitivity, frequency selectivity and spontaneous activity of units in the cochlear nucleus. The findings are similar to those obtained in auditory nerve fibers with ototoxic drugs and hypoxia.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00238704
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  • 2
    Electronic Resource
    Electronic Resource
    Cyclic GMP-activated channels of the chick pineal gland: Effects of divalent cations, pH, and cyclic AMP (1993)
    Springer
    Journal of comparative physiology 172 (1993), S. 271-279 
    Details
    ISSN: 1432-1351
    Keywords: Cyclic GMP ; Cyclic AMP ; Pineal ; Circadian oscillator ; Phototransduction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Chick pineal cells maintained in dissociated cell culture express an intrinsic photosensitive circadian oscillator, but the mechanisms of phototransduction in avian pinealocytes are not fully understood. In this study, we have used inside-out patches to examine the characteristics of cyclic GMP-activated channels of chick pinealocytes in more detail, concentrating on the effects of factors known to modulate the secretion of melatonin and/or the function of circadian pacemakers. In most patches, the predominant conductance state was 19 pS in symmetrical 145 mM NaCl. But in some patches, a second cyclic GMP-activated channel with a unitary conductance of 29 pS was also present. The current flowing through cyclic GMP-activated channels was not affected by application of salines containing 1 μM Ca2+ to the cytoplasmic face of the patch membrane. By contrast, application of 1 mM Ca2+ caused a partial reduction in cyclic GMP-activated current at all membrane potentials. Application of 1–5 mM Mg2+ ions caused a virtually complete blockade of current at positive membrane potentials, but caused only a small decrease in current at negative membrane potentials. No obvious differences in the gating of cyclic GMP-activated channels were observed in pH 8.2, 7.4 or 6.2 salines. Application of salines containing 100 μM, 500 μM, or 1 mM cyclic AMP did not cause activation of the channels, but 5 mM cyclic AMP evoked a low level of channel activity. Application of 5 mM but not 100 μM cyclic AMP decreased the probability of channel activation caused by 20–100 μM cyclic GMP and also increased the percentage of openings to an 11 pS subconductance state. Thus, cyclic AMP acts as a weak partial agonist. Nevertheless, the gating of these channels does not seem to be controlled directly by physiologically relevant changes in intracellular Ca2+, pH, or cyclic AMP.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00216609
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  • 3
    Electronic Resource
    Electronic Resource
    Auditory nerve activity and cochlear morphology after noise exposure (1979)
    Springer
    European archives of oto-rhino-laryngology and head & neck 224 (1979), S. 111-116 
    Details
    ISSN: 1434-4726
    Keywords: Auditory nerve fiber ; Acoustic trauma ; Hair cells
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Four chinchillas were exposed for 5 days to an octave band of noise centered at 4 kHz and having an SPL of 86 dB. After a recovery period of approximately 6 months, behavioral audiograms were obtained and auditory nerve fiber activity was recorded. The animals were killed and the cochleas embedded in plastic to obtain a surface preparation and 1 μ radial sections of the organ of Corti. Behavioral threshold shifts ranged from 5 to 20 dB at frequencies between 4 and 11 kHz. Auditory nerve fiber thresholds were elevated up to 70 dB for units with characteristic frequencies between 4 and 14 kHz. Units with higher and lower characteristic frequencies had normal thresholds. Cochleagrams showed narrow lesions of inner and/or outer hair cells over approximately a 1 mm distance. A comparison of the three realms of data revealed the following: (1) The greatest threshold shifts from the noise exposure were seen in the single nerve fiber thresholds while the smallest shifts were seen in the behavioral thresholds, (2) the greatest behavioral and neural threshold shifts and greatest cochlear damage occurred 1 octave above the center frequency of the noise exposure, and (3) based on the frequency-place map of the chinchilla cochlea, the range of fibers with elevated thresholds exceeded the extent of the OHC lesion. A number of anatomical changes were seen that effectively increased the extent of the damage found in the chochleagram. These changes included: distortions in the surface topography of the organ of Corti affecting the orientation of IHC; missing pillar cells in the presence of normal OHC and/or IHC and protrusion of the IHC cuticular plate into the subtectorial space.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00455233
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  • 4
    Electronic Resource
    Electronic Resource
    Ultrastructural changes to the cochlea resulting from impulse noise (1981)
    Springer
    European archives of oto-rhino-laryngology and head & neck 230 (1981), S. 273-278 
    Details
    ISSN: 1434-4726
    Keywords: Acoustic trauma ; Cochlear pathology ; Hair cell ; Stereocilia
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Following impulse noise trauma to chinchillas, observation of plastic-embedded surface preparations of the organ of Corti showed no consistent relationship between cochlear hair cell loss and permanent hearing loss (Hamernik et al. 1980). In some animals there was a loss of hearing when hair cells were present. The cochleas from that experiment were examined with transmission electron microscopy to determine at the ultrastructural level if there was damage to the sensory cells that would explain the change in threshold sensitivity. Ultrastructural changes in cochlear hair cells include an increase in lysosomes, multivesicular bodies, vacuolization of subsurface cisternae, and proliferation of Hensen bodies. These changes are observed in all experimental animals. Alterations to the ultrastructure of the stereocilia vary from animal to animal and on the outer hair cells, the changes include loosening of the stereocilia membranes, loss of stiffness, fusion of the stereocilia and disintegration of the rootlets. These changes are observed only in animals that have a permanent threshold shift after noise trauma.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00456329
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    Paper (German National Licenses)
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