The effect of H(2)O(2) on DNA binding activity of activator protein-1 (AP-1) was studied by electrophoretic mobility shift assay (EMSA) in cortical primary cultures of trisomy-16 mice and their diploid littermates. Exposure to 10 microM H(2)O(2) for 15 min elicited a greater and earlier occurring increase of AP-1 DNA binding in neuronal primary cultures of trisomy-16 mice than of diploid mice. When astrocyte-rich primary cultures were exposed to 10 microM H(2)O(2) a two-fold increase of AP-1 DNA binding activity was found in trisomy-16 and diploid mice. Supershift EMSA analysis revealed that c-jun was a component of AP-1 in neuronal and glial cultures of diploid and trisomic mice. A 15-min exposure to 10 microM H(2)O(2) increased c-jun mRNA in cortical neuronal cultures by six-fold, compared with a two-fold increase in cultured astrocytes. The results documented that H(2)O(2)-elicited activation of AP-1 DNA binding in trisomy-16 primary cultures is transcriptionally regulated. Since oxidative stress also activates various stress-inducible protein kinases that may phosphorylate AP-1 dimers, the increase of AP-1 DNA binding may, in part, be triggered by phosphorylation.