Electroencephalographic characterization of spike-wave discharges in cortex and thalamus in WAG/Rij rats

Purpose: The waveform of spontaneous spike-wave discharges (SWD) in the electroencephalogram ( EEG) was delineated in the WAG/Rij rat model of absence epilepsy according to the definitions of clinical electroencephalography. We defined four elements in SWD based on the schema of Weir ( 1965): Spike 1 and 2, Positive Transient ( PT), and Wave. The EEG patterns of generalized type I and local type II SWD in cortical and thalamic areas were analyzed. Methods: EEGs were recorded in freely moving rats epidurally from different cortical regions and with deep electrodes from the specific and reticular thalamic nuclei. Grand average SWD waveforms were computed to assess spatiotemporal patterns of seizures. Results: SWD I in the frontal cortex comprised of a large Spike 2 + Wave, and in the thalamus PT + Wave. Small transient spikes were associated with SWD I in the anterior-middle part of the cortex. SWD II were found in the occipital cortex as a sequence of ( occasional) Spike 1 + PT + Wave. Conclusions: The EEG structure of SWD in WAG/Rij rats was comparable with that of epileptic patients, suggesting face validity of the WAG/Rij model. Fast transients spikes are an integrative part of SWD I. Time-amplitude linkage between cortical and thalamic counterparts of SWD I suggests a complex spatiotemporal organization of SWD I. The thalamus sustained SWD I, but not SWD II.