Experimental design for Experiment 1 (a), characterization of nicotine-induced psychomotor effects, and Experiment 2 (b), consequences of social defeat on the psychomotor effects of nicotine. (a) Four groups of mice were daily injected with saline, 0.1, 0.4, or 1.0 mg/kg (s.c.) of nicotine for 13 days, during which 5 locomotor test days were carried out. Additional saline and nicotine challenges were scheduled after short- and long-term withdrawal from intermittent nicotine treatment. (b) One group of mice underwent 10 days of episodic stress (and its corresponding control group), and another group underwent 10 days of continuous social stress (with its respective control group). After termination of chronic stress, mice were tested for locomotor activity after saline and nicotine (0.1 mg/kg, s.c.) challenges, shortly after stress (~1 day) or after ~10 days. Locomotor activity was also tested after a methamphetamine challenge (1.0 mg/kg, i.p.), on day 22.