The Effects of Lidocaine on Inhibition in the Cerebral Cortex

Following intravenous injection of lidocaine, 10 mg/kg, into cats anesthetized with pentobarbital: 1) the mean threshold stimulus for direct cortical inhibition increased 30—50 per cent; 2) GABA-induced inhibition was not blocked; 3) the discharge rate of L-glutamate-activated neurons decreased. After local application of lidocaine from multibarrel micropipettes: 1) neither inhibition evoked by surface stimulation nor that induced by GABA was reduced; 2) the spike amplitude and rate of L-glutamate-evoked discharges were eventually depressed. It is concluded that the elevated thresholds for direct inhibition of cortical neurons that follow intravenous injection of lidocaine are more likely to result from conduction block along inhibitory fibers than from specific blockade of inhibitory synapses on the cortical neurons.