Abnormal hyperexcitability of hippocampal slices from kindled rats is transient

The anatomic substrates and mechanisms responsible for the development and permanence of kindling remain to be determined. One region believed to play an important role in kindling development is the hippocampus. Epileptiform activity (K+-induced spontaneous bursting) was recently shown to be enhanced in hippocampal slices from kindled rats studied 1 day after kindling from the lateral entorhinal cortex (LEC). Identical results one month after kindling raised the possibility that hippocampal excitability might be permanently increased in kindled animals. One goal of the present study was to confirm this finding, and also to extend it in terms of both the anatomic extent and the duration of this excitability increase. Stimulus train-induced bursting (STIB) is an in vitro model of hippocampal epileptogenesis. Parallels between STIB and kindling suggested STIB might prove useful for studying mechanisms underlying kindling. To strengthen the relation of STIB to kindling, we examined whether slices from kindled animals would behave as if they had undergone STIB during kindling. K+-induced bursting and STIB were studied in hippocampal slices from control and kindled rats one day and about 3 months after completion of kindling from the right LEC. Both K+-induced bursting and STIB development were enhanced one day after kindling. The enhancement of K+-induced bursting was present in both temporal and septal slices from both the ipsilateral and the contralateral hippocampus. Neither of these proepileptic changes was detected 3 months after kindling.(ABSTRACT TRUNCATED AT 250 WORDS)