Baseline preference and conditioned place preference (CPP).

<p>Figure <b><i>a)</i></b> Amount of time spent by naïve zebrafish in the white or brown compartment of the CPP tank during 5 min in a drug-free pretest. <b><i>b)</i></b> CPP establishment at different nicotine concentrations 0 (control), 15, 30 and 50 mg/L. CPP score was calculated as % of time spent in the drug-paired side after drug exposure (test) minus % of time spent on the drug-paired side before drug exposure (pretest) over a 300 s time period. <b><i>c)</i></b> Shows 15 mg/L nicotine-CPP scores for nicotine-paired, nicotine-unpaired and saline control groups at different time points after a 5 min interval of habituation. <b><i>d)</i></b> Shows the percentage of time spent in the white compartment during pretest and test sessions for individual zebrafish from the 3 groups. Data are presented as mean ± SEM. 0 mg/L (control) n = 15; nicotine-unpaired n = 12; nicotine-paired: 15 mg/L n = 21, 30 mg/L n = 12, and 50 mg/L n = 12. ** <i>p</i><0.01, ***<i>p</i><0.001 nicotine-paired <i>vs</i>. control and ## <i>p</i><0.01, ### <i>p</i><0.001 nicotine-paired <i>vs</i> nicotine-unpaired.