Seizure patterns in kindling and cortical stimulation models of experimental epilepsy

A large number of animal models has been proposed for the evaluation of the anticonvulsant effect of antiepileptic drugs. Various seizure patterns are produced and differences are frequently observed in anticonvulsant effect estimates obtained for the same drug in different models. The incidence of seizures and the threshold for the induction are usually the only measures used for the determination of the anticonvulsant effect. However, behavioural components expressed during seizures induced by different means are likely to differ considerably. The aim of this study was to provide a detailed behavioural description of ictal and post-ictal components in two models of electrically induced seizure activity: kindling and cortical stimulation model (CSM). Seizure activity was induced in two groups of 6 Wistar-derived rats. Ictal and post-ictal behaviours were recorded on video tape and quantified using a computer supported frame-by-frame encoding of the behavioural components. We encoded the duration and rate of occurrence of the following behavioural items: whisker movements, eye closure, myoclonic jerk, facial gasping, forelimb clonus, forelimb tonus, hindlimb tonus, immobility and chewing. It appears that both models are, in many respects, qualitatively similar. However, the models differ quantitatively. Behavioural expression of seizure activity differs in the following respects: (1) the total duration of the seizure induced by cortical stimulation is shorter than by kindling; (2) seizure activity in the CSM occurs mainly during stimulation, while in amygdala kindling, it occurs thereafter; and (3) seizures evoked in the CSM comprise relatively less violent behavioural items than in the amygdala kindling. The evaluation of the ictal and post-ictal behavioural components suggests that behavioural analysis could assist in the detection of differences in the mechanisms of action of antiepileptic drugs. In addition, observational measures can also be used to assess animal distress inflicted by different experimental procedures.