Model of spontaneous hippocampal epilepsy in the anesthetized rat: electrographic, [K+]0, and [Ca2+]0 response patterns.

These experiments present a model of spontaneous epileptiform activity that can be produced acutely in the urethane-anesthetized rat. Extracellular potential changes were recorded in CA1 or the dentate gyrus along with measurements of extracellular potassium ([K+]0) and calcium ([Ca2+]0) throughout 90 min of continuous stimulation to the contralateral CA3 region and for up to 4 h afterwards. During the continuous stimulation, both brain regions showed a cyclic pattern of electrographic seizures. Immediately upon stopping the stimulation, spontaneous epileptiform activity continued for up to 90 min in both CA1 and dentate gyrus. A quiescent period without electrographic activity was followed by the return of spontaneous epileptiform activity an average of 2 h after the end of stimulation. The excitability of the system was depressed after the continuous stimulation and gradually recovered during the quiescent period before the onset of the spontaneous epileptiform activity. [K+]0 increased during, not before, each seizure (both during the continuous stimulation and during the delayed spontaneous epileptiform activity) and remained elevated as long as neuronal discharges occurred. [Ca2+]0 transiently decreased with the onset of electrographic activity and never decreased before the appearance of epileptiform discharges.