Fig. 1.

Four day, but not six h morphine pellet administration leads to opioid dependence as determined by abstinence withdrawal. Mice were implanted with a placebo [6 h (n=3) or 4 days (n=4)] or morphine [6 h (n=6) or 4 days (n=5)] pellet. The pellets were removed after 6 h or 4 days and mice were observed for signs of opiate withdrawal that was determined by counting the number (± SEM) of jumps (A), rearing (B) and forepaw tremors (C) over the next two h following pellet removal. The 6 h and 4 day placebo groups were pooled. *** P<0.001 vs placebo pellet, ### P<0.001 vs 6 h morphine pellet.