Fig. 3. Conditioned place preference persists over a 3-week period of abstinence from nicotine or ethanol. (A) Following 4 weeks of daily 20 min exposure to 30 µmol l^–1 nicotine (black bars) fish showed a significantly greater change in place preference for the treatment side compared with control water-treated fish (grey bars; paired t-test ^*P<0.05). The change in preference exhibited by nicotine-treated fish was significantly greater than the change in preference exhibited by control, water-treated fish 24 h, 7 or 21 days after last drug exposure (two-sample t-test, P<0.05): control, water-treated fish showed no significant change in preference. The place preference for the treatment side after 21 days of abstinence was significantly less than the preference after 24 h of abstinence (two-sample t-test, ^**P<0.05). (B) 4 weeks of daily 20 min exposure to 175 mmol l^–1 ethanol (black bars) induced a significant change in preference compared with control, water treatment (grey bars; ^*P<0.05, two-sample t-test). This preference persisted over 3 weeks of abstinence.