Epileptiform activity in combined slices of the hippocampus, subiculum and entorhinal cortex during perfusion with low magnesium medium.

Reduction of [Mg2+]o induced spontaneous epileptiform activity consisting of 40-100-ms bursts of population spikes in hippocampal slices. This activity disappeared from area CA1 when the connections to area CA3 were cut, but persisted in isolated minislices of area CA3. Spontaneous activity was also observed in the dentate gyrus, provided that the connections to the subiculum and entorhinal cortex (EC) were intact. In the parasubiculum and EC longer lasting epileptiform events were observed which resembled seizure-like behaviour. The epileptiform activity was completely suppressed by 2-aminophosphonovalerate (30 microM) suggesting that N-methyl-D-aspartate receptors for excitatory amino acid transmitters participate in the generation of this activity. These findings show that the EC possesses properties which permit the generation of seizure-like activity in contrast to the hippocampus where the activity resembled recurrent interictal events.