Figure 1.

The effects of morphine on spontaneous alternation behavior (A) and the total number of arm entries (B) in mice tested in a Y-maze. Mice (n = 48) were randomly divided into six treatment conditions (n = 8/group): saline, 15 mg/kg morphine, 30 mg/kg morphine, 15 mg/kg morphine plus 15 mg/kg naloxone, 30 mg/kg morphine plus 15 mg/kg naloxone, and 15 mg/kg naloxone. Thirty minutes after these injections, the mice were placed in a Y-maze. Values are shown as means ± SEM (n = 8/group). *P < 0.05, compared with saline-treated mice. *P < 0.05, compared with saline-treated mice. ^†P < 0.05, compared with 15 mg/kg morphine-treated mice. ^‡P < 0.05, compared with 30 mg/kg morphine-treated mice. (C) Relationship between the total number of arm entries and Y-maze alterations (correlation coefficient = −0.42, P > 0.05; n = 48).