Fig. 5. Experiment IIIA: Effects of acute ibudilast treatment on morphine antinociception in morphine-tolerant rats in the hot plate test. Morphine-naive rats were given subcutaneous morphine or vehicle, and morphine-tolerant rats were given morphine and/or two different doses of intraperitoneal ibudilast or control. (  A ) The mean of the maximum possible effect (MPE%) ± SEM is plotted for two doses of ibudilast after 30 min of administration. (  B ) Mean hot plate latencies (in seconds) ± SEM are plotted for 30 and 120 min after administration of treatments shown. * Statistically significant difference (  P < 0.05) as compared with the vehicle control. # Statistically significant difference (  P < 0.05) as compared with the morphine-tolerant group that was given morphine acutely. § Statistically significant differences (  P < 0.05) between selected groups. n = 7 per group.