Dopamine transporter (DAT) mRNA from selected brain regions of individual male Fischer rats was quantitated utilizing a sensitive solution hybridization assay in which the levels of RNase-protected 32P-labeled mRNA:cRNA hybrids were measured. DAT mRNA was detected in whole brain regions known to contain abundant DAT mRNA (mean picogram of DAT mRNA/microgram of total RNA +/- SEM): substantia nigra, 7.17 +/- 0.47; ventral tegmentum, 4.71 +/- 0.38. In regions known to contain low levels of DAT mRNA, these levels were detected: central grey, 0.39 +/- 0.06; hypothalamus, 0.14 +/- 0.03. In addition, DAT mRNA was detected in areas where it had not previously been identified: amygdala, 0.19 +/- 0.03; caudate-putamen, 0.15 +/- 0.03; nucleus accumbens, 0.13 +/- 0.01; pons/medulla, 0.12 +/- 0.02; globus pallidus, 0.09 +/- 0.04; pituitary 0.07 +/- 0.01; frontal cortex, 0.05 +/- 0.01. No DAT mRNA was detected in 150 micrograms of rat liver RNA. As cocaine binds to and inhibits the activity of the dopamine transporter, we sought to determine if there were differences in dopamine transporter mRNA levels between saline- and cocaine-injected rats or rats withdrawn from a chronic "binge" pattern (15 mg/kg per dose i.p.; three doses at 1 h intervals each day) cocaine injection. Using trichloroacetic acid precipitation of mRNA:cRNA hybrids from RNA extracted from whole brain regions, we found no significant differences in the substantia nigra or the ventral tegmentum following subacute (3 days) binge, chronic (14 days) binge or 10 days withdrawal from a chronic binge pattern cocaine or saline administration.