EEG Patterns of High dose Pilocarpine-Induced Status Epilepticus in Rats

B a c k g r o u n d : We studied EEG changes during pilocarpine-induced status epilepticus(SE), a widely used model whose EEG characteristics have not been fully described previously. M e t h o d s : Male Sprague-Dawley rats weighing 250-350 grams were used as subjects. SE was induced 5-7 days after placement of chronic epidural electrodes, using 360-380 mg/Kg pilocarpine IP. Rats were observed with continuous EEG recording following pilocarpine injection until end of the SE episode. R e s u l t s : SE occurred in 10/12 rats studied. SE began with a series of discrete seizures 11.1±3.93 minutes after pilocarpine injection. 5.2±2.71 seizures occurred over 10.9±4.62 minutes, until the EEG converted to a waxing and waning pattern, during which the amplitude and frequency of epileptiform activity increased. After 1.4±1.82 minutes, a pattern of continuous high amplitude rapid spiking was established. Continuous spiking continued for 3.4±0.48 hours with a very gradual decline in amplitude and frequency, until periodic epileptiform discharges(PEDs) began to occur. The EEG consisted primarily of PEDs for another 7.4±3.09 hours, until electrographic generalized seizures began to occur. These continued for 5.8±4.82 hours until death. Duration of SE was 17.0±5.88 hours. Flat periods were a prominent feature during all EEG patterns in this model. C o n c l u s i o n : EEG features distinctive in pilocarpine SE(but not unique to it) include flat periods during all patterns and resumption of continuous spiking episodes after the onset of PEDs. The sequence of discrete seizures to waxing and waning to continuous spiking to PEDs was identical to that which has been described in humans and other animal models.