Seizure clustering is a common and significant phenomenon in patients with
epilepsy. The clustering of spontaneous recurrent
seizures (SRSs) in animal models of
epilepsy, including mouse
pilocarpine models, has been reported. However, most studies have analyzed
seizures for a short duration after the induction of
status epilepticus (SE). In this study, we investigated the detailed characteristics of seizure clustering in the chronic stage of a mouse
pilocarpine-induced
epilepsy model for an extended duration by continuous 24/7 video-EEG monitoring. A seizure cluster was defined as the occurrence of one or more
seizures per day for at least three consecutive days and at least five
seizures during the cluster period. We analyzed the cluster duration, seizure-free period, cluster interval, and numbers of
seizures within and outside the seizure clusters. The video-EEG monitoring began 84.5±33.7 days after the induction of SE and continued for 53.7±20.4 days. Every mouse displayed seizure clusters, and 97.0% of the
seizures occurred within a cluster period. The seizure clusters were followed by long seizure-free periods of 16.3±6.8 days, showing a cyclic pattern. The SRSs also occurred in a grouped pattern within a day. We demonstrate that almost all
seizures occur in clusters with a cyclic pattern in the chronic stage of a mouse
pilocarpine-induced
epilepsy model. The seizure-free periods between clusters were long. These findings should be considered when performing in vivo studies using this animal model. Furthermore, this model might be appropriate for studying the unrevealed mechanism of ictogenesis.