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Hair cell damage produced by acoustic trauma in the chick cochlea
Insights
Acoustic damage to chick cochleae shows hair cell injury location depends on sound intensity, not age. Higher intensities create distinct damage patterns along the basilar papilla, affecting auditory development.
Area of Science:
- Ototoxicology
- Auditory Neuroscience
- Developmental Biology
Background:
- Acoustic trauma can cause permanent hearing loss by damaging sensory hair cells in the cochlea.
- Understanding how noise exposure affects developing auditory systems is crucial for preventing hearing impairment.
Purpose of the Study:
- To investigate the effects of pure-tone acoustic overstimulation on hair cell damage in the developing chick basilar papilla.
- To determine the influence of stimulus intensity and developmental age on the location and extent of cochlear hair cell damage.
Main Methods:
- Chicks were exposed to pure-tone acoustic stimuli at various intensities and ages post-hatching.
- Scanning electron microscopy was used to evaluate hair cell damage, including stereocilia injury and cell loss, in the basilar papilla.
- Damage patterns were analyzed for tonotopic distribution, correlation with stimulus intensity, and age-dependent changes.
Main Results:
- Hair cell damage was tonotopically organized by frequency along the basilar papilla.
- Two distinct damage sites were observed, with their locations correlating to stimulus intensity.
- Low intensities caused damage along the superior edge; increased intensities led to additional damage along the inferior edge, forming wedge-shaped and crescent-shaped lesions.
- Damage site locations did not change with age, but extent and position varied with stimulus intensity and middle ear development.
Conclusions:
- Developmental changes in hair cell damage location and extent are primarily driven by the effective stimulus intensity reaching the cochlea.
- Age-related differences in damage are linked to stimulus intensity and maturational changes in the middle ear, rather than altered cochlear frequency coding.
Abstract:
Examination of pure-tone acoustic damage in the chick basilar papilla revealed that the location and extent of hair cell damage was a function of both the stimulus intensity and the age at which the chicks were exposed. Scanning electron microscopic evaluation of noise-exposed cochleae at post-hatching days 1, 10 and 30 permitted the identification of discrete regions of damage, including hair cells with stereocilia injuries as well as those lost from the epithelium. The hair cell damage was tonotopically distributed along the cochlea according to frequency. However, for each exposure frequency two distinct sites of damage were often produced, and their locations were correlated with stimulus intensity. At low intensities, a longitudinal strip of hair cell damage ran along the superior edge of the basilar papilla. As exposure intensity increased, a second damage site developed along the inferior edge of the basilar papilla, distal to the longitudinal strip. This second type of damage initially took the form of a series of laterally-oriented wedges, but at higher intensities, the wedges coalesced to form a large crescent-shaped patch of damage. The location of the damage sites for each frequency did not shift with age. However, there were differences in the extent and position of the damage which could be correlated with stimulus intensity and with changes in middle ear admittance during development [(1983) Development of Auditory and Vestibular Systems, pp. 3-25. Editor: R. Romand. Academic Press, New York]. These results suggest that developmental changes in the location and extent of hair cell damage depend on the effective stimulus intensity reaching the cochlea, rather than on alterations in the frequency coding of the hair cells.