Immunohistochemical demonstration of increased prostaglandin F_2α levels in the rat hippocampus following kainic acid-induced seizures

Prostaglandin (PG) F_2α is one of the major prostanoids biosynthesized by cyclooxygenases (COXs) from arachidonic acid. Although it has been reported that there is a selective surge in PGF_2α production in the hippocampus during kainic acid (KA)-induced seizure activity, the precise intra-hippocampal distribution of PGF_2α has not been elucidated due to the paucity of effective histological techniques for detecting PGs in tissues. We investigated the tissue distribution of PGF_2α in the rat hippocampus 30min after KA injection by developing fixation and immunohistological-staining methods. To detect PGF_2α directly on histological sections, we used systemic perfusion fixation with water-soluble carbodiimide fixative, followed by immersion of the brains in Zamboni's fixative. We then performed immunofluorescence staining with anti-PGF_2α antibody, with negative control experiments used to confirm the staining specificity. Definitive immunolabeling for PGF_2α was evident most markedly in pyramidal cells of the hippocampal cornu Ammonis (CA) 3 sector and neurons of the hilus in KA-treated rats. Immunolabeling for PGF_2α was also evident in granule cells of the dentate gyrus. Double immunfluorescence staining revealed that PGF_2α-immunopositive neurons expressed cytosolic phospholipases A₂, COX-2, and FP receptor. These results suggest that the major source of PGF_2α production immediately after KA injection was neurons of the hippocampal CA3 sector, hilus and dentate gyrus. These neurons exert PGF_2α-mediated functions via FP receptors in an autocrine/paracrine manner and may play pathophysiological roles in the acute phase (30min) of excitotoxicity.