Morphine-induced co-regulation of gene transcription. (a) Clusters of genes co-expressed with (1) Hspa1b, (2) Tsc22d3 (Dsip1), and (3) Olig2 after morphine treatment (SAL, control group; MOR, acute [ACU] and chronic [CHR] morphine groups). Colored rectangles represent expression levels of the gene indicated by the probe set on the left and gene symbol on the right. Intensity of the color is proportional to the fold change as indicated on the bar below the cluster image. (b) Network graphs of transcripts co-regulated with (1) Hspa1b, (2) Tsc22d3 (Dsip1), and (3) Olig2 were generated using the gene-to-gene correlation tool in WebQTL (Hippocampus Consortium M430v2 Dec05 PDNN). Correlation coefficients for each pair of transcripts are indicated beside the line. The Hspa1b gene was represented by three different probe sets on the microarray. (c) Confirmation of morphine induced regulation of expression of three selected genes by quantitative real-time reverse transcription polymerase chain reaction (qPCR). Results are presented as fold change over control group with standard error (n = 6 to 9). Significant main effects from multivariate analysis of variance for morphine treatment (***P < 0.001) and interaction ($$P < 0.01) are indicated. Difference between morphine-treated and control groups was analyzed using Bonferroni post hoc test (#P < 0.05).