SH-SY5Y cells grown on glass coverslips were pretreated with 200 μM morphine (Mor) for 1 h, and then treated with 4 μM DOX for 16 h. After treatment, cells were immunostained and visualized as described in the Materials and methods section. The images are representative of three independent experiments yielding similar results. Green, NF-κB p65; dark blue, nucleus; white, NF-κB p65 in the nucleus. Values are means±S.E.M. for three independent experiments (##P<0.01 compared with control; **P<0.01 compared with DOX).