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Time course effect of a challenge injection of methylphenidate (2.5 mg/kg) on Day 1 (left panel) and Day 3 (right panel) in rats treated previously with saline (n=8) or nicotine (0.8 mg/kg; n=8). Data are expressed as the mean (±SEM) distance traveled (cm) during each 5-min time interval. Asterisks indicate a significant difference from saline-treated rats during the corresponding time interval (*p<.01).
