Morphine-induced changes in gene expression correlated with the behavioral response. Transcriptional and behavioral responses to morphine were compared across the four inbred strains of mice with specific opioid-related phenotype (C57BL/6J, DBA/2J, 129P3/J, and SWR/J). Behavioral data were gathered as described in the Materials and methods section. The results were obtained by using Pearson correlation (Additional data file 5). Correlation between each opioid-related trait and transcriptional response to acute morphine is presented on the left panel along with chronic morphine on the right panel. Positive correlations between changes in gene expression and behavioral response are highlighted by red color (+), and negative ones are highlighted by the blue color (-).