Figure 4. Effect of intrathecal (IT) morphine on punctate mechanical hyperalgesia caused by an incision. A, Withdrawal threshold in saline-treated rats on the day of surgery. B, Withdrawal threshold after incision in rats treated with 5 micro gram of IT morphine on the day of surgery. C and D, Summary of withdrawal thresholds 30 min after administration of saline or IT morphine on the day of surgery and 1 day after surgery. *P < 0.05 vs. 0 min by Friedman and Dunnett's test. (dagger)P < 0.05 vs. saline by Kruskal-Wallis and Dunnett's test. The box and whisker plots are described in Figure 2.