Pilocarpine-induced status epilepticus in mice: A comparison of spectral analysis of electroencephalogram and behavioral grading using the Racine scale

Pilocarpine-induced status epilepticus (SE) is a widely used seizure model in mice, and the Racine scale has been used to index seizure intensity. The goal of this study was to analyze electroencephalogram (EEG) quantitatively using fast Fourier transformation (FFT) and statistically evaluate the correlation of electrographic seizures with convulsive behaviors. Simultaneous EEG and video recordings in male mice in a mixed genetic background were conducted and pilocarpine was administered intraperitoneally to induce seizures. The videos were graded using the Racine scale and the root-mean-square (RMS) power analysis of EEG was performed with Sirenia Seizure Pro software. We found that the RMS power was very weakly correlated with convulsive behavior induced by pilocarpine. Convulsive behaviors appeared long before electrographic seizures and showed a strong negative correlation with theta frequency activity and a moderate positive correlation with gamma frequency activity. Racine scores showed moderate correlations with RMS power across multiple frequency bands during the transition from first electrographic seizure to SE. However, there was no correlation between Racine scores and RMS power during the SE phase except a weak correlation with RMS power in the theta frequency. Our analysis reveals limitations of the Racine scale as a primary index of seizure intensity in status epilepticus, and demonstrates a need for quantitative analysis of EEG for an accurate assessment of seizure onset and severity.