Effects of lidocaine on basilar membrane vibration in guinea pig

The effects of lidocaine on basilar membrane (BM) vibration and compound action potential (CAP) were studied in young guinea pigs in order to elucidate the acting site of lidocaine in the cochlea The BM vibration was measured with a laser doppler vibrometer through an opening made on the bony wall of the scala tympani at the basal turn. Ten minutes after local administration of lidocaine into the scala tympani, the velocity of BM vibration and CAP amplitude decreased significantly at around the characteristic frequency (CF) of the stimulus sound (p <0.05). The maximum decrease was 4 dB in the velocity of BM vibration and 40 dB in the CAP amplitude. In contrast, such change was not observed after intravenous injection of lidocaine. The present results suggest that lidocaine acts not only on the outer hair cells but also on the cochlear nerve when it is administered into the scala tympani.