Oltipraz increased the expression of HO-1 in the spinal cords of PINP rats. a The spinal expression of HO-1 was significantly increased in PINP rats (**P < 0.01 compared with the vehicle group, n = 6 in each group). Moreover, oltipraz treatment further increased the spinal expression of HO-1 in PINP rats, which was reversed by the preadministration of trigonelline (*P < 0.05, ***P < 0.001 compared with the vehicle group, ##P < 0.01, ###P < 0.001 compared with the oltipraz-treated group). b HO-1 (green) was localized in neurons (as indicated by NeuN, a neuronal marker, red)