Possible explanation for interictal-ictal transition: evolution of epileptiform activity in hippocampal slice by chloride depletion.

In thin hippocampal slices, paroxysmal epileptiform discharge was generated in high potassium medium. Removal of chloride from the high potassium medium caused explosive potentiation of the paroxysmal discharge and emergence of clonic relapsing discharges. Evolution of the paroxysm to regenerative seizure was attributed to the reduction of inhibitory postsynaptic potentials.