Symposium on the Role of the Vestibular Organs in Space Exploration (1970) / Chapter Skim
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PATTERNS OF COCHLEAR HAIR-CELL LOSS IN GUINEA PIGS AFTER INTENSE STIMULA TION BY SINUSOIDAL SOUND
PATTERNS OF COCHLEAR HAIR-CELL LOSS IN GUINEA PIGS AFTER INTENSE STIMULA TION BY SINUSOIDAL SOUND
Pages 285-298
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From page 285... ...
STOCKWELL, AND LYNN B POCHE University of Illinais HANS ENGSTROM University of Uppsala SUMMARY Guinea pigs were individually exposed to intense sinusoidal sound stimulation of various frequencies and varying also in intensity and duration.
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From page 286... ...
It is quite feasible to chart all the hair cells, each in its proper position in relation to the rest, and to note their condition (i.e., intact, damaged, or replaced by a phalangeal scar)
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From page 287... ...
After exposure, the animals were maintained for 4 to 7 weeks to allow time for degeneration of any hair cells damaged by the exposure stimuli. At the end of the survival period, they were anesthetized with pentobarbital sodium and decapitated, and rapid dissection of the ears was carried out as previously described by Engstrrim, Ades, and Andersson (ref.
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From page 288... ...
Thus, when the hair cells have been swept away either by the sound exposure or by clumsy dissection, the spiral lamina remains intact. Therefore, it was usually sufficient to scale the distance along the missing portion to make a fairly accurate estimate of the number of hair cells that were involved.
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From page 289... ...
The small arrow above each curve indicates the position of maximum stimulation for the exposure frequency. Blackened areas indicate damage to all four hair cell rows; .
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From page 290... ...
The small arrow above each curve indicates the position of maximum stimulation for the exposure frequency. Blackened areas indicate damage to all four hair cell rows; .
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From page 291... ...
IHC loss was most severe in the middle regions, and OHC loss was spread rather evenly in the apical half of the organ of Corti. In contrast with their mean curve, the individual damage curves for these ears, shown in figure 7, display much more localized hair-cell loss occurring in a series of sharp peaks.
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From page 292... ...
Nine of ten ears exposed at 1000 Hz showed areas of maximum damage that occupied positions between 8.75 and 12.75 mm from the base. Among 12 ears exposed at 500 Hz, only five showed an area of total damage; all of these areas were well below the point of maximum stimulation for 500 Hz.
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From page 293... ...
Besides the localized areas of total damage characteristic of high frequencies, these ears display damage limited largely to OHC near the apex, which is characteristic of low frequency exposures. The prominence of multiple damage peaks seen in these ears exposed to a pure tone stimulus provides further argument against a simple correspondence between stimulation and damage patterns.
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From page 294... ...
The other major problem that concerns investigators of hearing loss arises as a result of the expectations of place theory; each frequency is presumed to cause maximum stimulation at a specific site on the organ of Corti. Hair cells that receive maximum stimulation by a particular frequency should be the first ones to be damaged when the intensity is raised: however, the greatest hearing loss usually occurs one-half
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From page 295... ...
Since high frequencies produce maximum displacement amplitudes nearer the base, it follows that high frequencies produce greater acceleration, and therefore greater stress, in the region of maximum amplitude than do lower frequencies. High frequencies should cause more hair-cell damage than low frequencies by the mechanism of mechanical stress.
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From page 296... ...
On the other hand, lower frequencies at the same SPL developed less mechanical stress, so this factor was relatively less important as a cause of hair-cell damage: hence, most IHC survived lowfrequency exposure, while OHC were damaged in greater numbers. This fact and the fact that OHC damage increased between 1 and 4 hours suggest that OHC are more sensitive to gradually accumulating effects of stimulation, and that this factor was a more important mechanism of damage at lower frequencies.
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From page 297... ...
The nerve supply in the normal human cochlea appears macroscopically to be evenly distributed throughout all coils except in the most basal few millimeters of the basal coil. Figure Dl shows the nerve supply in the basal coil in a case of noise exposure, and figure D2 shows the cochlea from a woman 86 years of age.
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From page 298... ...
298 THE ROLE OF THE VESTIBULAR ORGANS IN SPACE EXPLORATION FIGURE D2. -- Basal coil of the left cochlea from a woman aged 86 years, with no known excessive noise exposure.
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