Effects of applied currents on epileptiform bursts in vitro

In this study, results show that applied electric currents can be effective to control the neuronal bursting that characterizes epileptic activity. Recordings from the CA1 region of rat hippocampus treated with penicillin show that local inhibition of epileptiform bursts is possible by short anodic current pulses (50 ms duration) applied extracellularly. Inhibition was evidenced by a large reduction (greater than 90%) in the amplitude of field potential. Data collected from 20 slices with moderate field potentials (50-80% of maximum) showed that current needed for complete inhibition was on the order of 42 +/- 3 microA. Intracellular recordings in CA1 cells (n = 13) showed that the decrease in field potential amplitude was accompanied by suppression of intracellular neuronal firing caused by somatic hyperpolarization as measured by transmembrane potentials. The resulting hyperpolarization was on the order of 13 mv below resting potential for weakly epileptiform responses (less than 50% of maximum response), and 50 mv below resting potential for strongly epileptiform activity (greater than 50% of maximum response). These results reveal the existence of a stimulation window within which inhibition of neuronal elements can be achieved without simultaneous excitation.