A revised Racine's scale for PTZ-induced seizures in rats

Behavioral scoring is commonly used to access seizure intensity in different seizure models. Racine's scale, originally developed for the amygdala-kindling model, is also frequently used as an intensity measurement in other experimental seizure or epilepsy models. The aim of the present study is to assess the validity of Racine's scale as an adequate seizure intensity measurement for the Pentylenetetrazole (PTZ) model. Male adult Wistar rats received systemic injections of PTZ starting with an initial dose of 20 mg/kg added up by 10 mg/kg every 15 min until the occurrence of a 5minute lasting convulsive seizure. Simultaneous EEG and video recordings were made. The PTZ-induced seizures gradually increased in intensity. Eleven behavioral categories were identified and statistically analyzed. Six different seizure intensity categories were found to differ from each other based on differences in onset latencies, the pattern of occurrence during high or low doses of PTZ and the EEG pattern. These categories were quite different from those of Racine's scale. We suggest that Racine's scale is not adequate for the assessment of the seizure intensity of PTZ-induced seizures and that an alternative scale with the six proposed behavioral seizure categories is a more adequate description of PTZ-induced seizures.