TEMPORARY LATENCY SHIFTS IN AUDITORY-EVOKED POTENTIALS BY INJECTION OF LIDOCAINE IN THE RAT

Temporary latency shifts in auditory evoked potentials by intravenous injection of lidocaine were investigated in albino rats. Auditory brai nstem responses (ABR) were recorded with 4000Hz short tone bursts. The re was no significant difference of latencies in wave P1 of the ABR be tween drug-administered group (6 mg/kg body weight of lidocaine) and c ontrol group (0.6 ml/kg of 0.9% saline). As for waves P2. P3 and P4 of ABR, the latencies of the waves were significantly prolonged after th e lidocaine injection (p < 0.05. U-test). The prolongation of latency of wave P4 was the most prominent in the fast waves and dependent on t he dose of lidocaine. The latencies of the slow positive wave of the e voked potentials on the inferior colliculus (wave 8) with clicks and t he slow positive wave (wave P) and the negative wave following ABR (wa ve NA) with 4000Hz short tone bursts were also studied. The latencies of waves S. P and NA showed significant temporal prolongation (p < 0.0 5, U-test) after lidocaine injection. The present study revealed that a relatively small dose of lidocaine can cause temporary prolongation of latencies of auditory evoked potentials not only in the fast compon ents but also in the slow components including wave NA which is a larg e slow negative wave following the ABR. The effects are considered to be caused by the action of lidocaine which reduces the excitabilities on the auditory nervous system.