In Alzheimer's disease, extracellular deposits of amyloid β1–42 (Aβ1–42) may induce activation of microglial cells by releasing proinflammatory factors that contribute to the neurodegeneration process. Since the activation of cytosolic phospholipase A2α (cPLA2α) has been reported in inflammatory conditions, its role in primary rat microglial cell activated by aggregated Aβ1–42 was elucidated. The results of the present study show that activation of microglia by 5 μM aggregated Aβ1–42 (as evident by the amoeboid morphology and increased CD68 immunofluorescence reactivity) caused an immediate activation of cPLA2α, measured by its phosphorylated form and its specific activity, followed by a gradual elevation of its expression and activity during 24 h. Inhibition of cPLA2α expression and activity by the presence of 1 μM specific antisense resulted in a significant decrease in NADPH oxidase activity that releases superoxides, PGE2 formation, iNOS expression, and NO production, indicating a major role for cPLA2α in the regulation of these inflammatory processes. NADPH oxidase activity, which is under cPLA2α regulation, was found to upregulate cPLA2α and COX-2 protein expression through the redox-sensitive NFκB activation as evident by its phosphorylation on Ser-536, resulting in increased PGE2 formation. The secreted PGE2 induced the synthesis of iNOS and the production of NO through the PKA-CREB pathway. Taken together, our results suggest that the response of cPLA2α to aggregated Aβ1–42 is probably a key player in the oxidative stress present in AD, regulating potent oxidative agents: the production of superoxides by NADPH oxidase and NO formation by iNOS. © 2009 Wiley-Liss, Inc.