Fig. 6. Experiment IIIB: Effects of chronic ibudilast treatment on morphine antinociception in morphine-tolerant rats. Morphine-tolerant rats were treated with a continuation treatment of morphine and ibudilast, and acute antinociception was measured using the tail-flick (  A ) and hot plate (  B ) tests. This response is compared with the ibudilast-induced antinociception in rats undergoing ibudilast continuation treatment. Morphine was administered subcutaneously; ibudilast was administered intraperitoneally. The mean of the maximum possible effect (MPE%) ± SEM is plotted after 30 min of administration. * Statistically significant difference (  P < 0.05) as compared with the vehicle control. # Statistically significant difference (  P < 0.05) as compared with the morphine-treated, morphine-tolerant group (  black bar ). n = 7 per group. BID = twice daily.