In phase 1, mice received repeated saline or morphine administration. Mechanical and thermal sensitivities were measured on day 5. In phase 2, after OIH had fully developed, mice were treated with CaMKIIα siRNA or scrambled siRNA (2μg, twice/day for 3 days.). Mechanical and thermal sensitivities were tested daily. Established OIH was reversed by CaMKIIα siRNA. Data are expressed in Mean ± SEM. *** p<0.001, compared with the saline treated group; ††† p < 0.001, compared with the morphine treated group; n = 5 for each group. Arrows indicated saline, CaMKIIα or scrambled siRNA administration.