The effects of lidocaine on Basilar membrane vibration (BMV) and compound action potentials (CAP) of the cochlea were studied in young guinea pigs in order to determine the site of action of lidocaine in the cochlea. The BMV 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 the local administration of lidocaine into the scala tympani, the BMV and CAP amplitude both decreased significantly at around the characteristic frequency (CF) of the measuring point (P<0.05); the average change was 4 dB in BMV velocity and 40dB in CAP threshold. In contrast, no such change was observed after an intravenous injection of lidocaine.
Since the BMV reflects the motility of the outer hair cells, the present results suggest that lidocaine acts not only on the cochlear nerve, but also on the outer hair cells when it is administered into the cochlea.