Abstracts

Rationale: Long-lasting (neuro)inflammation is induced after epileptogenic injuries in animal models of epilepsy. This process contributes to experimental seizures generation most likely because of lack of activation of efficient resolution mechanisms in the brain. Resolution of inflammation is a highly coordinated process chiefly controlled by endogenous pro-resolving lipids or peptides. To prevent tissue dysfunction, it is instrumental to switch-off inflammation within times and modalities compatible with tissue repair and homeostasis activation. Our hypothesis is that brain inflammation after epileptogenic injuries is inefficiently controlled by pro-resolving mediators, i.e Chemerin and LipoxinA4 (LXA4) and their cognate receptors ChemR23 and LXA4 Receptor (ALXR), thus potentially contributing to epilepsy development. Using mouse models of epileptogenesis, we studied the expression of key pro-resolving molecules after chemically or electrically induced status epilepticus in mice (SE). This study will set the basis for limiting the pathologic consequences of the inflammatory response by boosting resolution pathways with ad hoc pharmacological interventions. Methods: Adult male naïve mice were exposed to SE induced by intra-amygdala kainic acid, amygdala electrical stimulation or systemic pilocarpine, then killed 24 h and 1 week later (at the onset of epilepsy). SE-exposed and naïve mice were paraformaldehyde perfused for immunohistochemical (IHC) analysis of cellular expression of ChemR23 and ALXR in forebrain. We analyzed also microglia and astrocyte activation (MAC-1 and GFAP), neuroinflammation (IL-1beta) and neurodegeneration by NISSL staining. Acute seizure susceptibility to intrahippocampal kainate (7 ng/0.5µl) was tested in ChemR23 knock-out (KO) mice vs their wild-type (WT) controls using EEG analysis. Results: In sham hippocampi, ChemR23 and ALXR specific IHC signal was confined to scattered pyramidal and hilar interneurons. In all SE models, ChemR23 and ALXR expression was induced during epileptogenesis in phenotypically identified activated microglia and astrocytes, respectively. A more prominent receptor expression was observed in the pilocarpine model. Acute seizures susceptibility was not modified in ChemR23 KO vs WT mice as assessed by measuring their onset time (11.6±2.5 min, n=7-12), number (8.0±0.9) and duration (5.0±0.6 min). CA3 pyramidal cell loss was also unaltered. Conclusions: In physiological conditions, ChemR23 and ALXR are expressed by neurons while they are significantly induced after SE in activated glial cells, thus indicating seizure-mediated up-regulation. Co-localization of these pro-resolving receptors with inflammatory mediators expressed after SE is under evaluation. The similar sensitivity of ChemR23 KO and WT mice to acute seizures will permit to test the development of epilepsy in mice exposed to SE. This set of evidence is required to determine the best experimental protocol for pharmacological intervention with drugs mimicking pro-resolving lipid mediators.