KINDLED EPILEPTIC SEIZURES, POSTICTAL REFRACTORINESS, STATUS EPILEPTICUS, AND ELECTRICAL SELF-STIMULATION

A single stimulus applied once daily to the limbic system commonly lea ds to convulsive seizures yet seizures are relatively infrequent durin g intracranial self-stimulation (ICSS), a procedure that involves many hundreds of similar stimuli. The present study examined the possible role of electrode site, interstimulus interval, afterdischarge and rei nforcement thresholds and postictal refractoriness in accounting for t his paradox. Electrode location was an overriding factor: seizures wer e never seen with hypothalamic implants posterior to the level of the ventromedial nucleus but were elicited by the majority of more rostral reward sites. Frequent repeated stimulation by ICSS did not in itself prevent subsequent kindling or reverse the effects of earlier kindlin g; on the contrary, seizures induced by ICSS showed a progressive incr ease in severity similar to the progression produced by conventional k indling. Individual convulsive seizures, as in previous studies, confe rred transient protection against further seizures whether from ICSS o r from kindling. More prolonged protection occasionally developed afte r repeated convulsive seizures: protection was accompanied by continuo us EEG slow-waves corresponding in presentation to clinical petit mal status. Prolonged resistance to seizures has also been reported after tonic-clonic status epilepticus causing temporal lobe damage. The rela tive infrequency of seizures during ICSS ordinarily appears to depend on the siting of the electrodes, on distinct short- and long-term post ictal refractory states, and on the rat learning to restrict stimulus input to subseizural levels.