Role of the tectorial membrane revealed by otoacoustic emissions recorded from wild - type and transgenic

Role of the tectorial membrane revealed by otoacoustic emissions recorded from wild-type and transgenic Tecta ENT/ENT mice ABSTRACT Distortion product otoacoustic emissions (DPOAE) were recorded from wild-type mice and mutant Tecta ENT/ENT mice with detached tectorial membranes (TM), under combined ketamine/xylaxine anaesthesia. In Tecta ENT/ENT mice DPOAEs could be detected above the noise floor only when the levels of the primary tones exceeded 65 dB SPL. DPOAE amplitude decreased with increasing frequency of the primaries in Tecta ENT/ENT mice. This was attributed to hair cell excitation via viscous coupling to the surrounding fluid, and not by interaction with the TM as in the wild-type mice. Local minima and corresponding phase transitions in the DPOAE growth functions occurred at higher DPOAE levels in wild-type than in Tecta ENT/ENT mice. In less sensitive Tecta ENT/ENT mice the position of the local minima varied non-systematically with frequency or no minima were observed. A bell-like dependence of the DPOAE amplitude on the ratio of the primaries was recorded in both wild-type and Tecta ENT/ENT mice. However, the pattern of this dependence was different in the wild-type and Tecta ENT/ENT mice; an indication that the bell-like shape of the DPOAE was produced by a combination of different mechanisms. A non-linear low frequency resonance, revealed by non-monotonicity of the phase behaviour, was seen in the wild-type but not in Tecta ENT/ENT mice.