Validation of a neocortical slice preparation for the study of epileptiform activity.

A simple slice chamber was designed to achieve easy manipulations of temperature, ionic composition and drug concentrations. Spontaneous and evoked extracellular potentials could be recorded with glass microelectrodes from 500 micron thick slices of rat frontal neocortex. In the absence of magnesium ions in the superfusing medium or in the presence of convulsant agents, epileptiform activity was seen. The amplitude of this activity was greatest in layer II/III, each burst consisting of a long-lasting negative potential on the decay phase of which were superimposed many afterpotentials. There were multiple foci from which spontaneous epileptiform bursts spread to other ipsi- and contralateral parts of the cortex via both the grey and white matter. Although such bursts were observed between 23 and 37 degrees C, optimal recording of discrete epileptiform activity was achieved at 29 +/- 1 degrees C. Decreasing extracellular calcium or increasing extracellular concentrations of potassium enhanced burst discharges. Proconvulsant agents initiated both interictal and ictal epileptiform events. This, together with the reduction of epileptiform activity by standard anticonvulsant drugs such as carbamazepine and phenobarbitone suggested that this in vitro model may be useful for studying the pharmacology of epileptogenesis and for developing new therapeutic strategies for epilepsy.