Comparison of the reinforcing and activating effects of drugs of abuse in C57BL/6J mice. (a) Bar graph summarizing the development of CPP to morphine, heroin, ethanol, nicotine, methamphetamine, cocaine or saline injections (i.p.). The number of drug conditioning sessions is indicated in parentheses. The level of significance was measured using ANOVA following the Newman-Keuls post-hoc test for drug versus saline; *P < 0.05; **P < 0.01 (n = 6 to 12). (b) Graph summarizing locomotor activation in response to drug treatment measured as increased ambulation in an activity cage during 4 h (n = 5). (c,d) Analysis of correlations between drug-induced changes in gene expression and behavioral effects of drugs in mice (Additional file 9). Scatter plots present the most significant correlation between the behavioral effects (y-axis) and the level of drug-induced transcription (x-axis). Correlation with locomotor activation was computed using data for each particular time point.