Interictal spikes and experimental seizures - reciprocal facilitatory and suppressive relationships

Experimental epileptic foci were produced by topical application of Penicillin, Tubocurarine or Picrotoxin on the pericruciate cortex of cats. The frequency of interictal spikes changed once seizures began to be recorded. Between seizures spikes occurred at a lower rate than before the first seizures and in some preparations ceased completely. Diphenylhydantoin sodium, Diazepam or Thiopental in small doses prevented the seizures but led to a return or intensification of the interictal spiking rate. The same effect was obtained after application of GABA on the area of the epileptic focus. In another series of experiments, triggering of the interictal spikes by electrical stimulation of the thalamus (VPL) could precipitate seizures in certain conditions but suppress seizures in other conditions. The suppressive effect was obtained only when using stimuli effective in triggering interictal spikes and only at certain rates of stimulation. These results suggest reciprocal facilitatory and suppressive relationships between interictal spikes and seizures. These relationships could explain why seizures tend to occur only at certain optimal rates of the interictal spikes.