Behavioral Characterization of Pentylenetetrazole-induced Seizures: Moving Beyond the Racine Scale

Detailed behavioral characterization of seizures is essential in animal models of epilepsy. Although various protocols exist for inducing seizures, the Racine scale remains the most widely adopted method for its quantification. Initially developed to score the progressive recruitment of behaviors during electrical kindling of limbic structures, the scale has since become the standard for classifying seizures across models with varying etiologies. However, careful examination of behavior following pentylenetetrazole (PTZ) administration, a commonly used seizure model, reveals that the Racine scale cannot capture the full spectrum of behavioral alterations induced by this GABAergic antagonist. After a single subcutaneous high-dose PTZ injection, mice first exhibit non-convulsive behaviors such as hypotonia, reduced ambulation, behavioral arrest, and tremors. These are succeeded by ictal behaviors, including spasms, myoclonic jerks, and limbic seizures, though only the latter is quantified by the Racine scale. To overcome these limitations, a refined approach is employed that combines video tagging with animal tracking to distinguish spasms and myoclonus as distinct behavioral expressions from limbic seizures. These early behaviors may facilitate the recruitment of limbic structures, eventually triggering limbic seizures. The method is straightforward to implement and enables a more comprehensive assessment of PTZ-induced acute seizures. Its utility is further evident in the PTZ kindling protocol, in which repeated low doses of PTZ result in temporal changes in spasms, myoclonus, and limbic seizure severity. This approach holds potential for improving reproducibility in seizure and epilepsy research.