Video-EEG for safety pharmacology seizure liability assessment in rabbits

Linking brain activity with behavior during video-electroencephalographic (video-EEG) recordings provides a better insight into epileptic phenomena than behavioral observations alone. Detection of non-convulsive seizures (often with subtle behavioral manifestations but clear EEG signatures) or non-brain-derived convulsive-like behavior, makes the technique superior in seizure liability assessment in preclinical safety. The present study was motivated by a need for confirmation of seizurogenic effect of a compound, which was labelled as pro-convulsive in a standard tolerability study with clinical observations in rabbits. Considering contradicting results from extensive experiments performed during development and no proof other than visual observation, the study was recreated with use of the video-EEG methodology. Prior to the exact experiment, the newly-build recording setup for rabbits was validated. Epileptic activity elicited by a single, subcutaneous injection of pentylenetetrazol (PTZ), which dose-dependently evoked both convulsive and non-convulsive seizures and induced a wide range of seizure-related behaviors, was assessed. Female New Zealand White rabbits were implanted with telemetry devices (implant M01, DSI a division of Harvard Bioscience, Inc., USA). After post-surgical recovery, animals were habituated to recording cages equipped with two video cameras allowing front and side views. On a test day, 1-h baseline recordings of EEG, temperature, activity and video signals were performed, after which rabbits received either PTZ (20, 40 or 60 mg/kg) or vehicle (saline) and were recorded for 24 consecutive hours. Synchronized EEG and video signals were analyzed offline by custom-made software, which automatically detected suspicious EEG epochs and linked them with the video fragments for closer inspection. Vice versa, abnormal behavior during the test could be immediately linked to the EEG signal to assess contribution from the central nervous system to the observed behavior. PTZ dose-dependently evoked both types of epileptic phenomena, non-convulsive seizures in the form of spike complexes after the low dose, and convulsions after the middle and high dose. The video-EEG set up allowed reliable, simultaneous recordings of brain activity and behavior of the rabbits and characterization of epileptic activity evoked by a reference compound.