High Potassium-Induced Epileptiform Bursting In Rat Hippocampal Slices

Abstract

Hippocampal slices from adult Wistar rats were used to assess the presence and frequency of epileptiform bursting (EB) induced by high potassium levels in the bathing medium. In vitro hippocampal slices were stabilized initially in 3.5 mM K* artificial cerebrospinal fluid for one hour. All slices were checked for evoked responses in region CA1. The bath K* was then increased to 8.0 mM. Spontaneous epileptiform bursting was checked and recorded from regions CA1 and CA3. A branching logic design was used to define bursting, nombursting and non'respor1sive slices. At the end of the 6-7 in experiment, all slices were checked, again, for evoked responses in CA1. Of '76 slices, 70 were responsive at the beginning and 68 al: the end. Exposure to 8.0 mM Kl' produced BB in both regions CA1 (38/68) and CA3 (35/68). Average time to first EB in CA3 was 23 min. Bursting frequencies in CA1 and CA3 were highly correlated (r3=0.95, df=62). These results suggest that BB in region CA1 is as reliable as that in CA3. Consequently, in screening large numbers of slices for E3, recording from CA}. is sufficient.