Lj. Herberg et Ic. Rose, KINDLED EPILEPTIC SEIZURES, POSTICTAL REFRACTORINESS, STATUS EPILEPTICUS, AND ELECTRICAL SELF-STIMULATION, Neuroscience and biobehavioral reviews, 18(3), 1994, pp. 411-420
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.