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The Mouse Round-window Approach for Ototoxic Agent Delivery: A Rapid and Reliable Technique for Inducing Cochlear Cell Degeneration
Published on: November 26, 2015
Ultrastructural cochlear changes following acoustic hyperstimulation and ototoxicity
Abstract:
Using guinea pigs and chinchillas as experimental animals, modes and patterns of sensory cell damage by acoustic hyperstimulation and kanamycin intoxication were compared. In general, outer hair cells were more vulnerable to both acoustic trauma and ototoxicity (particularly in the basal turn) than inner hair cells. However, in kanamycin ototoxicity, the inner hair cells were more vulnerable in the apical coil. Nerve endings and nerve fibers generally were resistant to both acoustic trauma and kanamycin intoxication, and their degeneration appears to be secondary to the sensory cell degeneration. A large number of unmyelinated nerve fibers were seen in both the organ of Corti and the osseous spiral lamina even three months after the organ of Corti had been completely degenerated by ototoxicity. The total number of unmyelinated and myelinated nerve fibers in the osseous spiral lamina far exceeded the scanty surviving ganglion cells in Rosenthal's canal, indicating the possibility of regeneration of these fibers following kanamycin intoxication. The remaining few ganglion cells were mainly type II or type III cells, and a majority of the type I ganglion cells appeared to be degenerated. Signs of strial damage were observed in both acoustic trauma and ototoxicity, but their pattern did not correlate well with that of sensory cell degeneration.
Insights
Outer hair cells are generally more vulnerable to acoustic trauma and kanamycin ototoxicity. However, kanamycin uniquely damages inner hair cells in the apical cochlea, suggesting potential nerve fiber regeneration.
Area of Science:
- Ototoxicity and Auditory Neuroscience
- Comparative Animal Studies
Background:
- Acoustic trauma and kanamycin intoxication are significant causes of hearing loss.
- Understanding the differential vulnerability of cochlear sensory cells and neural structures is crucial for developing therapeutic strategies.
Purpose of the Study:
- To compare the patterns of sensory cell damage induced by acoustic hyperstimulation and kanamycin intoxication in guinea pigs and chinchillas.
- To investigate the effects on nerve fibers and ganglion cells following these insults.
Main Methods:
- Experimental animals (guinea pigs, chinchillas) were subjected to acoustic hyperstimulation and kanamycin intoxication.
- Histological analysis was performed to assess damage to outer hair cells, inner hair cells, nerve endings, nerve fibers, and stria vascularis.
Main Results:
- Outer hair cells were more susceptible to both acoustic trauma and kanamycin, particularly in the basal cochlear turn.
- Kanamycin uniquely caused greater inner hair cell vulnerability in the apical turn.
- Nerve fibers showed resistance, with degeneration appearing secondary to sensory cell loss; evidence suggests potential regeneration after kanamycin exposure.
- Strial damage occurred but did not consistently correlate with sensory cell degeneration patterns.
Conclusions:
- Differential vulnerability of cochlear structures exists between acoustic trauma and kanamycin ototoxicity.
- Kanamycin-induced ototoxicity may offer a window for nerve fiber regeneration despite significant sensory cell loss.
- Further research into the mechanisms of nerve fiber regeneration in the cochlea is warranted.
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