title: Altered traveling wave propagation and reduced endocochlear potential associated with cochlear dysplasia in the BETA2/NeuroD1 null mouse.
abstract: The BETA2/NeuroD1 null mouse has cochlear dysplasia. Its cochlear duct is shorter than normal, there is a lack of spiral ganglion neurons, and there is hair cell disorganization. We measured vertical movements of the tectorial membrane at acoustic frequencies in excised cochleae in response to mechanical stimulation of the stapes using laser doppler vibrometry. While tuning curve sharpness was similar between wild-type, heterozygotes, and null mice in the base, null mutants had broader tuning in the apex. At both the base and the apex, null mice had less phase lag accumulation with increasing stimulus frequency than wild-type or heterozygote mice. In vivo studies demonstrated that the null mouse lacked distortion product otoacoustic emissions, and the cochlear microphonic and endocochlear potential were found to be severely reduced. Electrically evoked otoacoustic emissions could be elicited, although the amplitudes were lower than those of wild-type mice. Cochlear cross-sections revealed an incomplete partition malformation, with fenestrations within the modiolus that connected the cochlear turns. Outer hair cells from null mice demonstrated the normal pattern of prestin expression within their lateral walls and normal FM 1-43 dye entry. Overall, these data demonstrate that while tonotopicity can exist with cochlear dysplasia, traveling wave propagation is abnormally fast. Additionally, the presence of electrically evoked otoacoustic emissions suggests that outer hair cell reverse transduction is present, although the acoustic response is shaped by the alterations in cochlear mechanics.
authors: The Bobby R. Alford Department of Otolaryngology--Head and Neck Surgery, Baylor College of Medicine, One Baylor Plaza, NA102, Houston, TX 77030, USA.
authors: Anping
authors: A
authors: Xia
authors: Ann Marie B
authors: AM
authors: Visosky
authors: Jang-Hyeon
authors: JH
authors: Cho
authors: Ming-Jer
authors: MJ
authors: Tsai
authors: Fred A
authors: FA
authors: Pereira
authors: John S
authors: JS
authors: Oghalai
mesh_terms: D000818:Animals; D051792:Basic Helix-Loop-Helix Proteins / Q000235:genetics / Q000502:physiology*; D001696:Biomechanical Phenomena; D003051:Cochlea / Q000002:abnormalities* / Q000473:pathology / Q000502:physiology; D003055:Cochlear Microphonic Potentials; D016057:Evoked Potentials, Auditory, Brain Stem; D005260:Female; D008297:Male; D051379:Mice; D008822:Mice, Transgenic; D017084:Otoacoustic Emissions, Spontaneous
chemical_list: D051792:Basic Helix-Loop-Helix Proteins; C501008:Neurod1 protein, mouse
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