All Phenotypes Grid1<tm1Jnz> MGI Mouse

cochlear outer hair cell degeneration ( J:121999 )

• at 8 weeks, homozygotes show variable and scattered OHC loss in the basal-most region of the cochlea

• OHC loss is restricted to cochlear frequency regions well above that where the threshold shift is observed

• however, no loss of IHCs or cochlear neurons is observed, and all other structures of the cochlear duct, including the stria vascularis, appear unaffected

type IV spiral ligament fibrocyte degeneration ( J:121999 )

• at 8 weeks, homozygotes show a consistent and significant loss of type IV fibrocytes in the spiral ligament throughout most of the basal turn

• all cell nuclei are absent in this region of the spiral ligament, and only the fibrous network is observed

decreased endocochlear potential ( J:121999 )

• at 6 to 8 weeks, homozygotes show a significant reduction of 20 to 25 mV in the endolymphatic potential, as measured in the basal turn at roughly the 45-kHz place

abnormal auditory brainstem response ( J:121999 )

• at 6 to 8 weeks, suprathreshold ABR amplitudes are significantly reduced at frequencies of >16 kHz

• however, no significant changes in response waveforms are observed

increased or absent threshold for auditory brainstem response ( J:121999 )

• at 6 to 8 weeks, homozygotes display ABR threshold elevatations by 20-45 dB for frequencies of >16 kHz

• however, at lower frequencies (<16 kHz), ABR threshold elevations are non-significant (<10 dB)

abnormal distortion product otoacoustic emission ( J:121999 )

• at 6 to 8 weeks, homozygotes display significant DPOAE threshold elevatations for frequencies of >16 kHz

• in addition, suprathreshold DPOAE amplitudes are significantly reduced at frequencies of >16 kHz

• however, at lower frequencies (<16 kHz), DPOAE threshold elevations are non-significant, and no significant changes in response waveforms are observed

absent distortion product otoacoustic emissions ( J:121999 )

• at 6 to 8 weeks, some mutant ears show no DPOAEs at the highest test sound levels (80 dB SPL)

increased susceptibility to noise-induced hearing loss ( J:121999 )

• at 12 hrs after a 2-hr exposure to an octave noise band (8 to 16 kHz) at 89 dB SPL, 6-8-wk-old homozygotes display significantly higher temporary threshold shifts in both ABR and DPOAE than wild-type mice

• however, the efferent innervation of hair cells and the classic efferent inhibition of OHCs remain unaffected

impaired hearing ( J:121999 )

• at 6 to 8 weeks, homozygots display significant high-frequency hearing loss

• however, hippocampal and vestibular sensory-end organ morphology and function remain normal at 2 months of age

decreased body weight ( J:121999 )

• at 4 months of age, the weights of male and female homozygotes are ~89% and ~87% of those of wild-type males and females, respectively

• however, no significant weight differences in either sex are observed at 2 months or earlier