Figure 1. Time course of effects on %MPE in tail flick test (left panel) and colorectal distension test (right panel) after intrathecal challenge test with morphine (Mor) 5 [micro sign]g in rats that received intrathecal infusion of Mor 1 [micro sign]g [middle dot] kg^-1[middle dot] h^-1(n = 6), Mor 6 [micro sign]g [middle dot] kg^-1[middle dot] h^-1(n = 7), Mor 10 [micro sign]g [middle dot] kg^-1[middle dot] h^-1(n = 6), or saline (Sal)(n = 7) for 6 days. In Sal infusion group, %MPEs in the TF and CD tests increased to 100% for 30 min with a return to baseline values at 180 min. %MPEs in the TF and CD showed significant differences (P < 0.01) between groups with Mor 6 or Mor 10 and Sal groups from 10 min to 120 min, and also showed significant differences (P < 0.01) between Mor 1 and Sal groups from 60 min to 120 min but not from 10 min to 30 min. In Mor 10 infusion group, %MPE in the TF test was almost completely inhibited to less than 20 %MPE, but %MPE in the CD test demonstrated 40% at peak. Data are presented as mean +/− SD. *Significantly different from Sal.