Quantification of NT mRNA in situ hybridization autoradiograms after an acute injection of saline, cocaine, amphetamine, or haloperidol in D3+/+, D3+/− and D3−/− mice. Films were analyzed with a computer-assisted image analysis system and results expressed as nCi/mg tissue; bars represent mean+SEM (n = 4–7 mice per group). NT gene expression in the striatum is shown here at the caudal level. Results were analyzed by ANOVA followed by Tukey test. Significant main effects of treatment (vs. saline-treated mice) are indicated by + (p<0.05), and ++ (p<0.01). **p<0.01, vs. saline-treated mice of the same genotype.