Analysis Tools
hearing/vestibular/ear
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• at P2, mutant TMs are less darkly stained with Toluidine blue and less compact than wild-type TMs
• at P25, detached TMs do not stain with antisera directed against beta-tectorin and otogelin
• at P23, detached TMs contain randomly organized collagen fibrils, with small dense particles arrayed along some of the collagen fibrils
• at P23, detached TMs lack a fine, filament-based striated sheet matrix
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• at P23, detached TMs lack a fine, filament-based striated sheet matrix
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• at P23-P67, all homozygotes display TMs that are completely detached from both the spiral limbus and the organ of Corti and are associated with Reissner's membrane
• however, the organ of Corti and structure and orientation of hair bundles of IHCs and OHCs remain normal
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• at P32-P56, homozygotes display significantly reduced otoconial membranes
• however, the cupulae of the semicircular canal organs appear normal
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• at P32-P56, only a few, abnormally large, scattered otoconia are detected
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• mutant OHCs operate in an insensitive region of their receptor-potential transfer function and are unable to provide optimum feedback to the basilar membrane
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• only 10% of the OHC transducer channels are open at rest in freestanding hair bundles in the mutant cochlea
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• in the basal turn of the cochlea, basal membrane responses are tuned but are 30-40 dB less sensitive
• however, estimated CFs of the basal turn are not signifcantly different from those in wild-type mice
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• the cochlear microphonic cannot be recorded for frequencies below ~2 kHz
• the mutant cochlear microphonic is always asymmetrical, whereas that of wild-type mice is symmetrical for low-level tones and at the onset of high-level tones
• however, homozygotes display normal endocochlear potentials relative to wild-type mice
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• compound action potential detection threshold audiograms indicate that homozygotes are 80 dB less sensitive than wild-type mice at frequencies between 15 and 20 kHz
• this differences is reduced at higher frequencies as thresholds for mutant mice decrease with increasing frequency at ~6 dB/octave
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• at 6-8 weeks, 2f1-f2 emissions recorded from homozygotes are high-pass filtered i.e. DPOAE amplitude decreases with decreasing frequency of the primary tones
• local amplitude minima and corresponding phase transitions in DPOAE growth functions occur at lower DPOAE levels in homozygotes relative to wild-type mice
• in less-sensitive homozygotes, the position of local amplitude minima varies nonsystematically with frequency or no minima were observed
• mutant DPOAE's band-pass characteristics are highly abnormal with steeper low- and high-ratio cut-offs relative to wild-type DPOAEs
• a nonlinear low-frequency resonance, revealed by nonmonotonicity of the phase behavior, is detected in wild-type but not in homozygous mutant mice
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• homozygotes fail to exhibit detectable DPOAEs using primary tones with sound levels up to 60 dB SPL
(J:77634)
• at 6-8 weeks, 17 of 28 homozygotes display detectable DPOAEs above the noise floor only when levels of the primary tones are >65 dB SPL
(J:117747)
• in the remaning 11 homozygotes, the highest levels of primaries used (75/85 dB SPL) fail to evoke DPOAEs above the noise floor
(J:117747)
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nervous system
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• mutant OHCs operate in an insensitive region of their receptor-potential transfer function and are unable to provide optimum feedback to the basilar membrane
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• the cochlear microphonic cannot be recorded for frequencies below ~2 kHz
• the mutant cochlear microphonic is always asymmetrical, whereas that of wild-type mice is symmetrical for low-level tones and at the onset of high-level tones
• however, homozygotes display normal endocochlear potentials relative to wild-type mice
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• only 10% of the OHC transducer channels are open at rest in freestanding hair bundles in the mutant cochlea
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• compound action potential detection threshold audiograms indicate that homozygotes are 80 dB less sensitive than wild-type mice at frequencies between 15 and 20 kHz
• this differences is reduced at higher frequencies as thresholds for mutant mice decrease with increasing frequency at ~6 dB/octave
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behavior/neurological
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• homozygotes are behaviorally normal, and do not circle or head-bob
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