Inhibition of chronic morphine-induced CGRP up-regulation by the co-administration of various inhibitors. Western blot analyses revealed that a 7-day treatment with morphine (M, 15 μg) increases CGRP levels in the DRG. This effect was blocked by the co-delivery of PD98059 (MEK inhibitor, PD, 10 μg), SB203580 (p38 inhibitor, SB, 10 μg) or KN93 (CaMKII inhibitor, KN, 15 nmol). Data are expressed as mean ± SEM of 4 animals. *p < 0.01 vs saline (NS) group. #p < 0.01 vs morphine group.