Abstracts

Rationale: The most common pathological finding associated with temporal lobe epilepsy is hippocampal sclerosis (HS). According to the International League Against Epilepsy, HS is described as a pattern of neuronal loss in the hippocampal subfields CA1, CA3, CA4 and dentate gyrus. It is supposed that an inflammatory process occurs contributing with onset of hippocampal changes, mediated by pro and anti-inflammatory cytokines. The pro-inflammatory are the most prominent in the tissue, causing high neuronal excitability and thus, excitotoxicity. Some cytokines are considered pro-inflammatory, for instance interleukins IL-1β, IL-2, IL-7, are considered anti-inflammatory as IL-1, IL-4, IL-10. Our hypothesis is based in the most affected hippocampal areas in HS, the CA2 region is the one with the lowest signs of active pro-inflammatory cytokines, raising the hypothesis that this area is protected from inflammation and HS.

Methods: To test our hypothesis, we decided to verify the hippocampal subfields from 11 adult rats, 6 of them previously submitted to status epilepticus (SE), being 3 rats with 1-day survival and 3 with 7-day survival. The last ones were sacrificed without undergoing SE (Control group). In order to induce SE, we applied pilocarpine epilepsy experimental model. We used all rats that reached grade 3 on the Racine scale (1972), indicating SE onset. To verify neuronal death and pro/anti-inflammatory cytokines expression, specific antibodies were used in the immunohistochemical process. Anti-NeuN to show mature neurons, anti-IL-1β to verify pro- inflammatory patterns and anti-IL-10 for anti-inflammatory. To be able to delimit CA2 area, we used anti- PCP4 antibody.

Results: The Immunohistochemistry revealed an inflammatory pattern (IL-1β) present in the 1-day CA2 SE group. In the 7-day group, we also detected pattern of positive CA2/CA3 immunoreactivity (IL-1β), being more prominent in the CA3 area. We did not observe inflammatory cytokines (IL-1β) in the control group, nevertheless for anti- inflammatory pattern (IL-10) all the control group hippocampal areas were marked. Anti-IL-10 immunostaining was observed in the 1-day CA2, CA3, CA4 and the GD SE group. However, anti-IL-10 labeling was absent in the 7-day SE group. In the 1-day Anti-NeuN SE group, staining revealed a little CA2/CA3 neuronal death evidences CA2/CA3 and dense SE 7-day CA1, CA2 and CA3 neuronal death.

Conclusions: The higher immunoreactivity for the inflammatory cytokine IL-1β observed in CA3, as well as the lower expression of this cytokine in the 7-day CA2 group, may be related to possible migration of inflammation over time driven by neuroprotective factors in CA2, such as perineuronal net and other anti-inflammatory citokynes. Regarding anti-inflammatory features, IL-10 does not seem to be the main CA2 neuroprotective cytokine, as we observed a discrete pattern of immunoreactivity in CA1, CA3 and GD in the 1-day group. The immunoreactivity absence in all CA areas for IL-10 7-day group leads us the hypothesis that other anti-inflammatory cytokines may be involved in neuroprotection of ca2, competing with each other.

Funding: Federal University of Pará - Proap/CAPES