Suppression of hippocampal epileptic seizures in the kainate rat by Poisson distributed stimulation.

Purpose: Hippocampal deep brain stimulation (DBS) is an experimental therapy for patients with pharmacoresistant temporal lobe epilepsy (TLE). Despite the successful clinical application of DBS, the optimal stimulation parameters are undetermined. We evaluate the efficacy of a new form of DBS, using continuous stimuli with Poisson distributed intervals (Poisson distributed stimulation, PDS) in the kainate (KA) rat model, a validated model for human TLE.

Methods: Status epilepticus was elicited by injection of KA (i.p.). After development of spontaneous seizures, rats were implanted with hippocampal DBS- and depth electroencephalography (EEG) electrodes. After baseline EEG monitoring, one group of rats (n = 13) was treated with PDS and a second (n = 11) received regular high frequency stimulation (HFS) at 130 Hz. Stimulation intensity was 100 μA below the threshold for induction of epileptiform EEG activity.

Results: Stimulation intensity was significantly lower for PDS (156 ± 20 μA) than HFS (207 ± 23 μA; p < 0.02). Seven (54%) of 13 rats treated with PDS and 5 (45%) of 11 rats treated with HFS experienced a significant reduction in seizure frequency. In PDS-improved rats, seizure frequency was reduced to 33% (p < 0.01) of baseline value and in HFS-improved rats to 50% (p < 0.01). After termination of PDS, seizure rate returned to baseline value.

Discussion: Continuous hippocampal PDS significantly reduces the number of spontaneous seizures. Compared to regular HFS, there is a slightly larger number of improved rats and a larger efficacy at a considerably lower stimulus intensity. The first two observations leave room for optimization, whereas a lower intensity is beneficial for battery life.