Cerebral cortical cultures were either co-incubated or pretreated (8, 16, or 24 h) with 100 μM of acetaminophen (APAP) and exposed to 5 μM menadione for 4 h. Apoptosis was measured by ELISA quantitation of nucleosome fragmentation. The number of control cells i.e. viable cells not exposed to any treatment was defined as 100%. Data are mean ± SD from 3 separate experiments. ***p < 0.001 vs. control. #p < 0.001 vs. menadione alone.