Figure 1. The time course of effects on percentage maximum possible effect in the tail flick test (left) and the colorectal distension test (right) during intrathecal infusion of morphine (Mor) at the rate of 1 [micro sign]g [middle dot] kg-1[middle dot] h-1(n = 6), 6 [micro sign]g [middle dot] kg-1[middle dot] h-1(n = 7), or 10 [micro sign]g [middle dot] kg-1[middle dot] h-1(n = 7) or of saline (Sal)(n = 7) for 6 days. Data are presented as the mean +/− SD. *Significantly different from Sal.