Effects of lidocaine on salicylate-induced discharge of auditory neurons in the inferior colliculus of the guinea pig

Abstract

The effects of lidocaine (a local anesthetic known to relieve tinnitus) in a guinea pig animal model of tinnitus in which spontaneous discharge of inferior colliculus (IC) neurons was augmented by intravenous application of salicylate (200 mg/kg) were studied by extracellular recording. The salicylate induced discharge was inhibited by intravenous injection of lidocaine at a concentration (lmg/kg) used clinically for treating tinnitus. IC neurons could be divided into two groups according to the difference in sensitivity to lidocaine, weakly sensitive neurons and highly sensitive neurons. In weakly sensitive neurons, the lidocaine effect lasted for less than five min, and the inhibiton of the discharge of neurons was increased as the latency of response to the sound stimulus became longer. It was considered that lidocaine inhibited the propagation of action potentials by blocking Na+ channels. In highly sensitive neurons, on the other hand, the activity of neurons was almost completely inhibited for longer than 30 min and it might involved different mechanisms. Furthermore, the inhibitory action of lidocaine was stronger in IC neurons discharging at higher frequencies, suggesting a use dependent blocking action of Na+ channels, by lidocaine.