Table of Contents:
Rationale: Epilepsy is a common neurological disorder with an incidence of 50.4 per 100 000 per year. Up to 80 % of mesial temporal lobe epilepsy (mTLE) patients are resistant to pharmacological treatment. Many of them do not qualify for resective brain surgery. For these patients, an alternative treatment is deep brain stimulation (DBS). In epilepsy, different protocols for DBS have been tested but until now, the mechanisms of DBS are not fully understood and the best protocol remains to be evaluated.
MicroRNAs (miRNAs) are small, single stranded RNAs, which regulate protein synthesis on messengerRNA (mRNA) level. Various miRNAs have been found to be regulated in epilepsy, and regulation of miRNAs after DBS has been shown in Parkinson´s disease patients.
We compared different targets and frequencies of DBS in a rat model of mTLE to identify stimulation paradigms that inhibit epileptogenesis or lead to seizure reduction in manifest epilepsy. We then investigated miRNA regulation after DBS with the most effective paradigm.
Methods: We used a rat perforant pathway stimulation (PPS) model of mTLE (Norwood et al., 2010). Stimulation electrodes were implanted into the PP and recording electrodes were implanted into the dentate gyrus (DG). After one week of recovery, the perforant pathway was stimulated on two consecutive days for 30 min and on the third day for 8 h. The animals developed epilepsy within 12 to 34 days after stimulation.
We investigated DBS of four different targets: the PP, the fimbria fornix formation (FF), the DG and the ventral hippocampal commissure (VHC). Stimulation was applied for one or two weeks starting one day after the final PPS to investiagate an antiepileptogenic effect or starting after the first spontaneouse seizure occurred to test a disease modifying effect. Three different stimulation paradigms were used: 130 Hz and 0.1 V, 5 Hz and 2 V or 1 Hz and 1 V, respectively.
We analyzed miRNA expression in the hippocampus immediately after DBS and after 97 days of continuous video EEG monitoring. Therefore, miRNA-sequencing was performed and compared to control rats that were not treated with DBS.
Results: No DBS paradigm decreased seizure frequency in animals that already had developed epilepsy. Two-week DBS of the VHC with 1 Hz and 1 V significantly prolonged the latency period in the PPS model from 19 (±11) to 56 (±23) days. Expression of 8 miRNAs were significantly altered immediately after DBS. Five miRNAs were significantly altered in the control group after 97 days but showed no changes in the DBS-treated group.
1. None of the tested paradigms acted anticonvulsive.
2. LFS of the VHC had an antiepileptogenic effect.
3. Antiepileptogenic VHC-stimulation led to an acute expression change of 8 miRNAs and inhibited PPS-induced long-term changes of 5 miRNAs, namely miRNA-129-5p, miRNA-379-3p, miRNA-410-3p, miRNA-431 and miRNA-433-3p. These miRNAs are candidates for an in vivo manipulation to inhibit epileptogenesis.