Synaptically evoked spreading cortical depression in short-term high-frequency electrical stimulation of the rat brain

Properties of the cortical spreading depression (SD) were studied at different parameters of the electrical stimulation (ES) of the rat brain. The ES consists of 10 pulses with the frequency from 10 to 200 Hz. Thus, the seizure activity, usually complicating SD, did not appear. With an increase of the ES frequency SD thresholds decreased from 30-40 to 5-10 V. Suprathreshold ES significantly broadened the SD focus. Secondary synaptic SD foci were regularly triggered in the stimulating and contralateral hemisphere as well. Long-term changes in the cortical excitability following the high-frequency ES resulted in a decrease of SD latencies and thresholds. These changes have shown the active role of synaptic events in SD triggering.