The development of the interictal spike during kindling in the rat.

An attempt was made to determine the location of the generator(s) of interictal discharge in the kindled rat preparation. Animals were kindled by stimulation of hippocampal area CA3, fornix/fimbria, perforant path, amygdala or lateral olfactory tract. The development of interictal discharge was monitored in the intact preparation, and hippocampal slices were subsequently taken from both kindled and control animals. Contrary to our initial hypothesis, the hippocampus did not appear to generate interictal discharge (as determined by onset time) even when the animal was kindled in the hippocampus or one of its input pathways. Also, hippocampal slices taken from kindled animals did not appear to be significantly more prone to either evoked or spontaneous epileptiform responses, compared to control slices, in medium containing high K+ concentrations. Among the structures from which recordings were taken, the amygdala and/or pyriform cortex appeared to show the earliest onset spikes regardless of the site of stimulation. It is proposed that the generator of interictal discharge in kindled animals may reside in the pyriform lobe.