Picrotoxin-induced generalised convulsive seizure in rat: changes in regional distribution and frequency of the power of electroencephalogram rhythms

Objectives: It is unknown how generalised discharges in primary generalised epilepsy (PGE) develop from background brain electrical activity or how widespread these discharged are throughout the brain. Here we address this by determining which neural structures and rhythms lead to and participate in generalised discharges in the picrotoxin rat model of PGE. Methods: Rats with chronically implanted electrodes were infused with picrotoxin until a seizure occurred. This process we refer to as acute epileptogenesis. The electroencephalogram (EEG) was recorded and spectral analysis applied off-line to determine changes in the spectral power of contributing frequencies in 13 brain regions. Results: Two types of generalised discharge occurred, spindles and seizure, which were present in all brain regions studied. None of the frequencies (1–100 Hz) were significantly increased in background EEG before either spindles or seizure. Within the generalised discharges, power changes revealed significant increases in 6–8 Hz, most powerful in ventrolateral thalamus and neocortex. Gamma frequencies were increased significantly in neocortical structures during spindles with further increases in most structures at seizure onset. 1 Hz was significantly increased in parietal cortex during spindles with differential increases at seizure onset. Conclusions: We conclude that gamma, 1 and 6–8 Hz frequencies do not appear to contribute to picrotoxin epileptogenesis but do play a role in generalised seizures. The distribution of these frequencies during discharges suggests that the spindles are thalamocortical events and that the seizure is a cortical event with downstream effects on other brain regions.