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.