Low Mg2+ induced epileptiform activity in the subiculum before and after disconnection from rat hippocampal and entorhinal cortex slices.

The subiculum is an area within the hippocampal complex which participates strongly in ictaform activity generated in the entorhinal cortex (EC). To study the properties of epileptiform activity with intra- and extracellular recording techniques in the subiculum, combined slices containing the EC, subiculum and hippocampus were prepared with and without surgical disconnection of the subiculum from the EC and area CA1. For induction of epileptiform activity extracellular magnesium was lowered. After acute disconnection of the subiculum from the cornu ammonis and the EC, seizure like events similar to those in the more intact preparation did develop. These were characterized by slow negative field potential shifts and, in intracellular recordings by sustained depolarization shifts lasting for 10-43 s. This activity could develop into late recurrent discharges of 1-2 s. These data indicate that the subiculum may be an important zone for epileptogenesis in temporal lobe epilepsy.