Figure 2.

Escape latencies recorded during trials of the training sessions on days 1–4 prior to drug treatments and in a post-treatment assessment of memory retention on day 14 (n = 5, mice selected from those treated with saline alone (ie, vehicle) on day 5) in mice tested in an MWM (A). Values are shown as mean ± SEM (n = 74). Alterations in the mean time spent in the target quadrant during 120 seconds on day 5 (B). On day 5, 24 hours after the final training session (day 4), the mice (n = 67 out of 74 mice shown in Fig. 2A) were randomly divided into five treatment groups: saline (n = 15), 15 mg/kg morphine (n = 15), 15 mg/kg naloxone (n = 15), 15 mg/kg morphine plus 15 mg/kg naloxone (n = 15), and 1 mg/kg scopolamine (n = 7). Thirty minutes after these injections, the mice were exposed to the maze for the probe trial. Values are shown as mean ± SEM (n = 7–15). *P < 0.05, compared with saline (post hoc Bonferroni–Dunn test).