Fig. 2. The anti-interleukin (IL)-10 antibody and p38 mitogen-activated protein kinase (MAPK) inhibitor SB203580 partially reverses the potentiating effect of amitriptyline on the antinociceptive effect of morphine in chronic morphine-infused rats. (  A ) Time-course of tail-flick latencies of rats received continuous intrathecal infusion of saline (CONT), amitriptyline (CONT+AMI), SB203580 (CONT+SB), morphine alone (MO), morphine plus amitriptyline (MO+AMI), morphine plus amitriptyline plus SB203580 (MO+AMI+SB), or daily intrathecal injection of neutralization anti-IL-10 antibody (CONT/Anti-IL-10 Ab), or morphine plus amitriptyline plus Anti-IL-10 antibody (MO+AMI/Anti-IL-10 Ab) for 5 days (n = 6 of each groups). ***  P < 0.001 as compared with saline-infused group; ###  P < 0.001 as compared with morphine-infused group; +++  P < 0.001 as compared to the amitriptyline/morphine coinfused group. (  B ) On day 5, dose-response curves for morphine were constructed in rats from different drug infusion groups described above. The dose-response effect was presented as the percentage of the maximal possible antinociceptive effect (% of MPE). All data points are presented as the mean ± SEM (n = 12) of each group.