Fig. 1. Experiment I: Effects of ibudilast on acute morphine antinociception in the tail-flick (  A ) and hot plate (  B ) tests. Rats (n = 7 per group) were given the same subcutaneous dose of morphine (2.5 mg/kg) or vehicle with or without three different doses of intraperitoneal ibudilast or vehicle. The mean of the maximum possible effect (MPE%) ± SEM is plotted after 30 min of administration. For the ibudilast groups: * Statistically significant difference (  P < 0.05) as compared with the group that was given vehicle only. For the morphine groups: # Statistically significant difference (  P < 0.05) as compared with the group that was given morphine without ibudilast. § Statistically significant difference (  P < 0.05) as compared with the group that was given the same dose of ibudilast without morphine.