Prolonged depth electrode implantation in the limbic system increases the severity of status epilepticus in rats

Chronically implanted intracranial depth electrodes are widely used for studying electroencephalographic activities in deep cerebral locations and for electrical stimulation of such locations. We have previously reported that prolonged implantation of an electrode in the basolateral amygdala (BLA) of rats facilitates subsequent kindling from this site, indicating a pro-kindling or pro-epileptogenic effect. To further characterize this phenomenon, we analyzed data from experiments in which we induced a self-sustaining status epilepticus (SSSE) by BLA stimulation following different periods of post-surgical delay. In a total of 183 Sprague-Dawley rats, three groups with different periods of postsurgical delay to onset of electrical stimulation were compared: group 1 (16 days on average), group 2 (28 days) and group 3 (48 days). Three types of SSSE were observed after BLA stimulation: type 1 (nonconvulsive), type 2 (nonconvulsive occasionally interrupted by generalized convulsive activity), and type 3 (generalized convulsive). While groups 1 and 2 did not differ in the frequency of these SSSE types, the group with the longest interval between electrode implantation and stimulation (group 3) showed significantly more severe SSSE than the two other groups. The data indicate that intracranial electrode implantation may increase the sensitivity of the implanted area to seizure induction, extending previous findings in the kindling model. Potential mechanisms of these findings include the functional consequences of local microhemorrhages and blood-brain barrier destruction.