High-frequency cortical activity associated with postischemic epileptiform discharges in an in vivo rat focal stroke model.

OBJECT The postischemic brain has greater susceptibility to epileptogenic activity than physiologically healthy tissue. Epileptiform discharges are thought to exacerbate postischemic brain function. The aim of this study was to develop an in vivo focal stroke model in rats to characterize epileptiform activity. METHODS The authors developed a parasagittal 8-channel intracortical microelectrode array to obtain recordings of cortical oscillations of local field potentials following partial middle and anterior cerebral artery occlusion. All experiments were done in urethane-anesthetized Sprague-Dawley rats. RESULTS Theta runs (TRs), ranging in duration from 5 seconds to 5 minutes, were observed in 62% of animals within 1 hour of occlusion. High-frequency oscillations (HFOs) in the high gamma range (80-120 Hz) were observed 5-15 seconds before each TR and terminated at the onset of the discharge. Periodic epileptiform discharges (PEDs) were detected in 54% of rats following ischemia. The PEDs consisted of an early negative slow wave, a high-amplitude positive spike, and a short negative slow wave. Transient HFOs in the low gamma range (30-70 Hz) occurred during the first negative wave and the rising phase of the positive spike of the PED. CONCLUSIONS These recordings provide the first intracortical evidence of a high-frequency component that could be an important element for diagnosis and intervention in postischemic epileptogenic activity. The early onset also suggests that HFOs could serve as a reliable method of detecting small epileptiform events and could be used as a consideration in deciding whether antiepileptic medications are appropriate as part of a patient's poststroke care.