Intrinsic Resistance of the Hippocampal CA2 Subfield to Neuroinflammation After Status Epilepticus

Abstract

ObjectiveTo determine the spatiotemporal patterns of pro-inflammatory (IL-1beta) and anti-inflammatory (IL-10) cytokines in hippocampal subfields, focusing on the CA2 region, using a pilocarpine-induced status epilepticus (SE) model. MethodsStatus epilepticus was induced in adult male Wistar rats with pilocarpine. Animals were divided into control, 1-day post-SE and 7-day post-SE groups (n = 5, 3 and 3). Hippocampi were processed for immunohistochemistry using antibodies against IL-1beta, IL-10, NeuN (mature neurons), and PCP4 (CA2 marker). Microglial activation states (M1/M2) were inferred from cytokine profiles: sustained IL-1beta expression indicated a pro-inflammatory milieu (M1), whereas declining IL-1beta in the presence of IL-10 suggested an anti-inflammatory or reparative state (M2). ResultsThe CA2 region exhibited IL-1beta immunoreactivity at 1 day post-SE, which decreased by day 7, while CA3 maintained elevated IL-1beta levels. Anti-IL-10 immunostaining was prominent across hippocampal subregions in the control group and 1-day SE group but was absent by day 7 in all regions. NeuN staining revealed limited neuronal death in CA2 at 1 day post-SE, with substantial loss across CA1, CA3, and CA4 by day 7. SignificanceThe CA2 subfield appears relatively protected from sustained inflammation and neuronal loss, likely owing to unique microglial responses and structural features such as perineuronal nets. These findings highlight microglial polarization as a potential determinant of subfield vulnerability in temporal lobe epilepsy and support further investigation of glial-targeted therapies.