EFFECTS OF LIDOCAINE ON HIPPOCAMPAL PYRAMIDAL CELLS - DEPRESSION OF REPETITIVE FIRING

THE effects of lidocaine on repetitive firing of the CA1 pyramidal cel ls were studied in the hippocampal slice preparation using conventiona l intracellular recording technique. The cells were activated by injec ting depolarizing current through the recording microelectrode. Lidoca ine (50 muM) diminished the repetitive firing and progressively reduce d the maximal rate of rise of the successive action potentials. The fi ring produced by low currents was little affected but that produced by high currents was substantially depressed. The maximal rate-of rise o f successive action potentials produced by a train of short depolarizi ng pulses was also progressively reduced, especially at high frequency (100 Hz) of activation. These findings suggest that, in the hippocamp al pyramidal cells, lidocaine causes a use-dependent depression of the Na+ current. This action may be responsible for the anticonvulsant ef fects of lidocaine since it occurred at a clinically relevant concentr ation.