gms | German Medical Science

Experimental data and case reports of patients suffering from epilepsy treated with STN stimulation (HFS) suggest an anticonvulsive effect. An anticonvulsive effect of acute high frequency stimulation (HFS) into an ongoing absence seizure has been reported in the generalised absence epileptic rat from Strasbourg (GAERS). In the present study the influence of two chronic stimulation paradigms on seizure activity in a rat model of absence epilepsy was investigated.

Bilateral chronic intermittent or continuous STN HFS was conducted to rats of the WAG/Rij strain (n=12/n=10), suffering from well- defined absence seizures. Bipolar, concentric deep brain electrodes and screw-skull electrodes were implanted by stereotaxy. A stimulation frequency of 130 Hz with an single-impulse duration of 60 µs, with current strength 20% below the motor threshold was given as train of 30 sec. every 5 min. for one hour in the intermittent stimulation group and continuously for 10 minutes in the continuous stimulation group. The procedure was repeated after one week (intermittent stimulation) or three days (continuous stimulation). Effects were evaluated by cumulated seizure duration (CSD) and seizure frequency (SF) in the EEG during a baseline period (B1 and B2 à 1h/10min) during stimulation (S1 and S2 1h/10min) and immediately after stimulation (P1 and P2 à 1h/10min). For statistical analysis, the non-parametric Friedman-Test followed by the Wilcoxon-Test was performed.

After the first stimulation period, the chronic intermittent bilateral HFS of the STN resulted in a decrease of cumulated seizure duration (B1: 119 sec; S1: 61 sec.; P1: 38 sec.) and in a further reduction also during baseline measurement on the second experimental day one week later (B2: 20 sec; S2: 13 sec.; P2: 3 sec.). This reduction in CSD and SF was statistically significant (CSD: B1 vs B2 p=0,006, B1 vs. P1 p=0,008; SF: B1 vs B2 p=0,006, B1 vs. P1 p=0,013). The continuous stimulation design revealed no anticonvulsive effect.

This study provides evidence for the anticonvulsive properties of chronic intermittent bilateral HFS of the STN in absence epilepsy. Ineffectiveness of chronic-continuous stimulation suggest dependency of anticonvulsive effects on stimulation paradigms. In addition, a long-term anticonvulsive effect lasting at least for one week was assessed and was boosted by the second stimulation.