Fig. 1.

The acquisition and maintenance of chronic nicotine self-administration. Nicotine (30 μg/kg, i.v.) or saline was available 23 h/d for 12 d. Nicotine rats had significantly more active than inactive lever presses (repeated measure ANOVA, F_{1, 30} = 105.2, p < 0.001), and more active presses than saline rats (F_{1, 30} = 97.1, p < 0.001). Active and inactive presses were similar in saline rats (F_{1, 30} = 1.69, p > 0.05). All data are expressed as mean ± SEM.