Cellular substrates for epileptiform activity induced by repeated tetanic stimulation in hippocampal slices

Using intact and transected hippocampal slices, we investigated the relationship between CA3 and CA1 subfields in the generation of stimulus train-induced bursting. In intact slices, spontaneous bursts in CA3 always preceded those in CA1, whereas after-discharge bursts in CA3 followed those in CA1 when it was possible to distinguish differences in the burst onset. After transection between CA3 and CA1, neither spontaneous nor triggered bursts could be induced or maintained in isolated CA1, where only small after-discharge bursts with higher bursting frequency were observed. Some of the mechanisms underlying the generation of these stimulus train-induced bursts are discussed.