Figure 1.

Time-dependent increases in drug CPP after withdrawal from low but not high doses of morphine. Data are the mean ± SEM of preference score in seconds (time in the morphine-paired chamber minus time in the saline-paired chamber) during the CPP preference tests performed 1, 7, or 14 d after withdrawal from morphine. A, Between-subjects assessment using 12 groups of rats (n = 9–10 per group); each group was tested at a single withdrawal day. B, Within-subjects assessment using four groups of rats (n = 9–10 per group) that were repeatedly tested after 1, 7, and 14 d of withdrawal from morphine. p < 0.05, different from withdrawal days 1 (*) and 7 (#) within each morphine training dose.