High Frequency Oscillations during the First Week after Status Epilepticus: A Predictor for Subsequent Development of Spontaneous Seizures.
Abstract number :
1.003
Submission category :
Year :
2001
Submission ID :
152
Source :
www.aesnet.org
Presentation date :
12/1/2001 12:00:00 AM
Published date :
Dec 1, 2001, 06:00 AM
Authors :
A. Bragin, PhD, Neurology, UCLA, Los Angeles, CA; C. Wilson, PhD, Neurology, UCLA, Los Angeles, CA; J. Engel, Jr., MD PhD, Neurology, UCLA, Los Angeles, CA
RATIONALE: After a head trauma or fever with status, some individuals later develop epilepsy but most do not. Animal models of chronic epilepsy also display large individual variability in the probability that an initial precipitating event will lead to spontaneous seizures. In previous studies we found that 46% of rats did not develop spontaneous seizures after unilateral intrahippocampal kainic acid (KA) injection. In the remainder, recurrent spontaneous seizures developed within 2-6 months. These two groups of rats showed no significant difference in the severity of the behavioral components of the status epilepticus they underwent during the first 4 hours following KA injection. The goal of the present study was to record continuously before, during and after KA injection and during the silent period to identify the electrographic features which are correlated with the early or late occurrence of recurrent chronic seizures
METHODS: A guide cannula for KA injection was implanted in the right CA3 area of the posterior hippocampus of 6 adult Sprague-Dawley rats. Recording microelectrodes were implanted bilaterally in the dentate gyrus (DG), entorhinal cortex (EC) and piriform cortex. Baseline activity was recorded one week before KA. Recording continued for 4 hours after injection and then 8 hrs a day for the next 4-6 months. During this period rats were also observed 16-24 hr/day with video monitoring in order to detect behavioral seizures
RESULTS: Epileptiform bursts started within one minute from the DG adjacent to KA injection and within 2-3 minutes spread to all other brain areas. Spectral power during status increased in the wide band frequency range. Increase power in 250-500 Hz band was due to bursts of population spikes in microelectrodes located in cellular layers. The persistence of spontaneous 250-500 Hz oscillations (fast ripples, FR) after status correlated with the duration of the silent period prior to spontaneous seizures. One rat did not have FR after termination of the KA-induced status and did not have SZ within the next six months. In four rats FR reoccurred within a period of 11-21 days and their spontaneous seizures started within 1-4 months after status. In one rat FR did not disappear after status and this rat started to have spontaneous seizures within 2 weeks
CONCLUSIONS: These results suggest a possible role for mechanism underlying FR in epileptogenesis during the silent period. FR may represent activity from pathologically interconnected neuron clusters that generate hypersynchronous bursts of population spikes that eventually form an epileptic network generating seizure activity. The occurrence of FR after status epilepticus whether immediate or delayed, may thus be a predictive factor for the eventual occurrence of spontaneous seizures
Support: NIH grants NS 02808 and NS 33310.