Analysis Tools
hearing/vestibular/ear
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• outer hair cells, but not inner hair cells, exhibit severe degeneration in the cochlea
• loss of outer hair cells shows a tonotopic gradient, which starts from the cochlear base and progresses to the apex
• marker analysis indicates that death of outer hair cells is not due to apoptosis but rather necroptosis
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• outer hair cells show greater sensitivity to hypotonic stress than wild-type cells, with an immediate change in cell shape of a 11% decrease in length and 15% increase in width compared to 4% length decrease and 5% width increase in wild-type cells, an 18% increase in volume compared to 6% increase in wild-type, and some cells bursting
• outer hair cells exposed to a milder hypotonic stress by reducing the extracellular osmolarity show a 10% decrease in length and 16% increase in wight compared to wild-type cells which are resistant to this hypotonic stress
• while wild-type outer hair cells show increased intracellular calcium concentration in response to a hypo-osmotic stimulus, mutant outer hair cells do no show a change in intracellular calcium concentration
• outer hair cells exhibit unchanged K+ currents compared to wild-type cells which show increased outward K+ currents
• hypo-osmolarity-induced currents are absent in outer hair cells
• however, mechano-transduction currents are normal
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• auditory brainstem response (ABR) elicited by click stimuli is undetectable in adult mice, even at 90 dB sound pressure level
• the thresholds of ABR to pure tones of different frequencies (6, 12, 18, 24, and 30 kHz) are elevated to over 90 dB sound pressure level
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• distortion product otoacoustic emission thresholds are severely impaired, indicating impaired outer hair cell function
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• hearing loss is moderate at P16 but progresses significantly at P2 1and P28 and is profound by P35 at all frequencies tested
• however, vestibular function is not impaired
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nervous system
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• outer hair cells, but not inner hair cells, exhibit severe degeneration in the cochlea
• loss of outer hair cells shows a tonotopic gradient, which starts from the cochlear base and progresses to the apex
• marker analysis indicates that death of outer hair cells is not due to apoptosis but rather necroptosis
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• however, mechano-transduction currents are normal
• outer hair cells show greater sensitivity to hypotonic stress than wild-type cells, with an immediate change in cell shape of a 11% decrease in length and 15% increase in width compared to 4% length decrease and 5% width increase in wild-type cells, an 18% increase in volume compared to 6% increase in wild-type, and some cells bursting
• outer hair cells exposed to a milder hypotonic stress by reducing the extracellular osmolarity show a 10% decrease in length and 16% increase in wight compared to wild-type cells which are resistant to this hypotonic stress
• while wild-type outer hair cells show increased intracellular calcium concentration in response to a hypo-osmotic stimulus, mutant outer hair cells do no show a change in intracellular calcium concentration
• outer hair cells exhibit unchanged K+ currents compared to wild-type cells which show increased outward K+ currents
• hypo-osmolarity-induced currents are absent in outer hair cells
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