Eicosanoid formation in the rat cerebral cortex

Despite the extensive literature on brain eicosanoids, no information is available on the cellular source of individual compounds in the mature organ and the relative contribution of different cell types to the total synthetic product. To address this problem, neurons and glia were isolated from the cerebral cortex of the adult rat by a process comprising, in order, trypsinization, selective sieving, differential centrifugation, and density gradient centrifugation. Enrichment of cells in the appropriate fractions was verified by morphological, immunocytochemical, and biochemical criteria. Both neuron- and glia-rich fractions retained synthetic activity throughout the period of incubation (max. 60 min). Among the eicosanoids examined, prostaglandin (PG) E₂ was the predominant compound, followed by leukotriene (LT) E₄ and thromboxane (TX) B₂, whereas LTC₄ occurred in minimal amounts. Although the rank order of eicosanoids did not vary with the cell type, absolute values of PGE₂ and TXB₂ were greater with neurons. PGE₂ synthesis was increased by supplementation of the medium with arachidonic acid (2.6 μM), whereas indomethacin (5.6 μM) had the opposite effect. Conversely, LT synthesis was not altered by arachidonic acid and was only marginally reduced by the 5-lipoxygenase inhibitor, U-60,257 (10 μM). Several agonists (12-O-tetradecanoyl-phorbol-13-acetate, TPA; Ca ionophore A23187; plateletactivating factor; endotoxin; recombinant IL-1) were tested on both neuron- and glia-rich fractions but none of them had an effect. We conclude that freshly isolated neurons and glia are viable insofar as the basal rate of eicosanoid synthesis is concerned. No qualitative difference was noted between the two cell types in the spectrum of products formed and the spectrum itself accorded with early data on the biosynthetic activity of the intact tissue in vivo. Our isolation procedure appears useful for the analysis of the cellular source of eicosanoids under resting conditions, although it cannot be applied to the study of the site and mode of action of activators.