Inner hair cell stereocilia displacement in response to focal stimulation of the basilar membrane in the ex vivo gerbil cochlea

• Published in: Hearing research Vol. 412; p. 108372
• Main Authors: Zosuls, Aleksandrs, Rupprecht, Laura C., Mountain, David. C.
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 01.12.2021
• Subjects: Animals; Basilar membrane; Basilar Membrane - physiology; Cochlea - physiology; Cochlear mechanics; Distortion product otoacoustic emissions; Gerbillinae; Hair cell stereocilia; Hair Cells, Auditory, Inner; Reticular lamina; Stereocilia; Traveling wave; Traveling wave; Hair cell stereocilia; Basilar membrane; Distortion product otoacoustic emissions; Cochlear mechanics; Reticular lamina
• ISSN: 0378-5955; 1878-5891
• DOI: 10.1016/j.heares.2021.108372

•Measurements of inner hair cell stereocilia radial displacement•Traveling waves are present at the inner hair cell stereocilia.•Traveling waves propagate forward and backward along the cochlear partition.•Longitudinal coupling is significant in the row of inner hair cells.•Local stimulation of the basilar membrane to mimic otoacoustic emissions The inner hair cells in the mammalian cochlea transduce mechanical signals to electrical signals that provide input to the auditory nerve. The spatial-temporal displacement of the inner hair cell stereocilia (IHCsc) relative to basilar membrane (BM) displacement is central to characterizing the transduction process. This study specifically focuses on measuring displacement of the stereocilia hair bundles in the radial dimensions where they are most sensitive. To simplify the mechanical response of the cochlear partition, a mechanical probe was used to drive the BM. Optical imaging was used to measure radial displacement of the inner hair cell stereocilia local to the probe in ex vivo gerbil cochleae. The mechanical probe displaced the BM in the transverse direction using sinusoidal stimuli with frequencies ranging from 10 Hz to 42.5 kHz. IHCsc displacement measurements were made in the radial dimension as a function of their longitudinal location along the length of the BM. The results were used to quantify the frequency response, longitudinal space coupling, traveling wave velocity, and wavelength of the radial displacement of the stereocilia. The measurements were centered at two best frequency locations along the BM: Proximal to the round window (first turn), and in the second turn. At both locations, frequency tuning was seen that was consistent with published place maps. At both locations, traveling waves were observed simultaneously propagating basal and apical from the probe. The velocity of the traveling waves at the center frequency (CF) of the location was higher in the first turn than in the second. As the stimulus frequency increased and approached CF for a location, the traveling wavelength decreased. Differential motion of the BM and IHCsc was observed in the second turn as the stimulus frequency increased toward CF. The longitudinal coupling measured in this study was longer than observed in previous studies. In summary the results suggest that the shape of the wave patterns present on the BM are not sufficient to characterize the displacement of the IHCsc.