P-EP029. Variability in seizure phenotypes in individual epilepsy rat model contributes to the propagation of the seizure

Introduction. Among 16 possible types of ictal onset and offset based on seizure dynamics, the saddle node/homoclinic (SN/SH), which is characterized by ictal Direct Current shift (ictal DC), seems to be predominant across species. We predicted that individuals with epilepsy may express different types of seizures, and thus, which may show different propagation patterns during the ictal period. We tested these hypotheses in an experimental model of temporal lobe epilepsy. Method. We enrolled 10 male Sprague-Dawley rats treated with pilocarpine (380 mg/kg, i.p.), which developed spontaneous epileptic seizures. Electroencephalogram (EEG) was obtained with a Microdrive with bandpass filter (0.1 Hz-) and sampling rate 2 kHz. Each seizure was classified based upon the type of onset (SN, SNIC, SupH, or SubH) and offset (SH, SNIC SupH, or FLC). We evaluated i) seizure duration, ii) the amplitude of ictal DC, iii) the number of brain regions involved during seizure propagation using gamma (γ: 30-50 Hz) power. Results. In line with our hypotheses, we confirmed that each animal expresses different types of seizures during the day and across days. The most common form of seizure is characterized by ictal DC at onset. The spatiotemporal extension of seizures is variable from seizure to the next but follows simple rules. For seizures with ictal DC, we find that their duration and the size of propagation area are inversely proportional to the amplitude of the ictal DC. For all types of seizures, their duration and the size of the propagation area are proportional to the time from seizure onset and the occurrence of maximum gamma power in the seizure-onset zone. Conclusion. The most frequent form of seizures with ictal DC (SN onset) is characterized by faster propagation to surrounding regions, and a duration that is inversely proportional to the amplitude of ictal DC.