High frequency radial movements of the reticular lamina induced by outer hair cell motility.

Recently, it was shown in cochlear explants from the guinea pig cochlea that electrokinetic motile responses of outer hair cells can induce radial and transverse motion of the reticular lamina. Here we demonstrate, that the radial component of these motions can be measured up to high frequencies (15 kHz). Cochlear explants were taken from guinea pig inner ears and exposed to a sinusoidal electric field. A double photodiode was used as a linear position detector with high spatial and temporal resolution to detect radial movements in the plane of the reticular lamina. The organ of Corti of the second, third and fourth cochlear turns was stimulated with frequencies of the electrical field between 0.5 Hz and 20 kHz. Sinusoidal movements of up to 15 kHz were recorded. At higher frequencies the signal-to-noise ratio became too small. The largest responses were measured at the three rows of outer hair cells. If the strength of the electrical field was 2 kV/m, into which the cochlear explants were placed, the amplitudes of outer hair cell movements were around 1 micron at 1 Hz and 10 nm at 10 kHz. Uncoupling of the outer hair cells from the tunnel of Corti and from the inner hair cells decreased the oscillations of inner hair cells but did not affect outer hair cells. The movements showed frequency dependent amplitudes like a complex low-pass filter but no best frequency was observed.