Seizures in the intrahippocampal kainic acid epilepsy model: characterization using long-term video-EEG monitoring in the rat

Intrahippocampal injection of kainic acid (KA) in rats evokes a status epilepticus (SE) and leads to spontaneous seizures. However to date, precise electroencephalographic (EEG) and clinical characterization of spontaneous seizures in this epilepsy model using long-term video-EEG monitoring has not been performed. Rats were implanted with bipolar hippocampal depth electrodes and a cannula for the injection of KA (0.4 mu g/0.2 mu l) in the right hippocampus. Video-EEG monitoring was used to determine habitual parameters of spontaneous seizures such as seizure frequency, severity, progression and day-night rhythms. Spontaneous seizures were detected in all rats with 13 out of 15 animals displaying seizures during the first eight weeks after SE. A considerable fraction (35%) of the spontaneous seizures did not generalize secondarily. Seizure frequency was quite variable and the majority of the KA-treated animals had less than one seizure per day. A circadian rhythm was observed in all rats that showed sufficient seizures per day. This study shows that the characteristics of spontaneous seizures in the intrahippocampal KA model display many similarities to other SE models and human temporal lobe epilepsy.