Abstracts

Rationale: Inflammatory mechanisms are involved in the pathogenesis of mesial temporal lobe epilepsy (mTLE). Cytokines modulate cerebral tissue remodelling and neuronal excitability after an epileptogenic insult. This offers the opportunity to influence and possibly prevent epileptogenesis. However, the time course of cytokine release in the epileptogenic zone has to be quantified in order to allow for precise timing of therapeutic interventions. Microdialysis allows measuring cytokine release at multiple time points in the same subject. To this end, we sought to quantify hippocampal levels of six cytokines (IL-1߬ IL-6, IL-10, CCL-2, CCL-3, and CCL-5) during the course of epileptogenesis in an animal model of mTLE with hippocampal sclerosis (mTLE-HS). Methods: Electrodes were implanted bilaterally in the perforant pathway (stimulation) and the dentate gyrus (recording) in 20 male Sprague Dawley rats. A microdialysis guide cannula was implanted into the right hippocampus. After 8 d, mTLE-HS was in induced in 6 rats by electrical perforant pathway stimulation (PPS; d1+2: 30 min, d3: 8h). Six control rats were implanted identically, but received no PPS. The 8 remaining rats were excluded due to loss of electrodes or death during anesthesia. Rats were continuously video-EEG-monitored. Hippocampal microdialysis was performed using a high-cut-off (100 kD) microdialysis probe at baseline (7d after implantation=1d before PPS), d1 after PPS, d8, d15, and 4 weeks after the first seizure (epilepsy group) or 4 weeks after d15 microdialysis (control group), respectively. Concentrations of IL-1߬ IL-6, IL-10, CCL-2, CCL-3, and CCL-5 were quantified using a magnetic bead-based multi-analyte panel (Magpix?(R), Milliplex?(R)). Results are presented descriptively as mean SD. Results: Mean duration of the epileptogenic period in stimulated animals was 21.7 days (range: 5-61). Consistent elevations at all time points were seen for IL-1 and IL-10. IL-10 release was at maximum on d1 (24.4 13.2 pg/ml in epileptic animals vs. 7.7 9.8 pg/ml in controls). IL-1ߠrelease had a maximum at d8 (2.0 1.9 pg/ml in epileptic animals vs. 0.4 1.1 pg/ml in controls) (Fig. 1, Fig. 2). We found no systematic changes in IL-6, CCL-2, CCL-3, or CCL-5. Conclusions: Longitudinal cerebral cytokine microdialysis monitoring is possible over several weeks in freely moving rats. IL-10 has anti-inflammatory effects and is considered anticonvulsant. Hence, hippocampal IL-10 release might be a compensatory mechanism to diminish deleterious inflammatory effects. Pro-epileptogenic effects of IL-1ߠwere described earlier, and IL-1ߠcan directly increase neuronal excitability. Antagonization of IL-1ߠin the early stages after an epileptogenic insult is a candidate approach for therapeutic intervention studies in experimental epilepsy. Our data allow calculation of animal numbers to power larger confirmatory studies (e.g. extrapolating mean and variance from our results, 13 animals per group were required to show a significant difference in IL-10 at d1 with a power of 80%). Funding: This work was supported by the Rhoen-Klinkum AG, Germany.