TH expression and activity. (a–i) In situ hybridization for TH mRNA; dark-field (a–c and g–i) and bright-field (d–f) microscopy. (a and d) Wild-type male mice express TH mRNA in the arcuate nucleus. TH mRNA is increased in Drd2–/– mice (b and e) and appears to be decreased, though clearly still evident, in Prlr–/– mice (c and f). Note comparable levels of TH mRNA in the ventral tegmental area and substantia nigra among the three genotypes: wild type (g), Drd2–/– (h), and Prlr–/– (i). Two or three mice per group were evaluated. (j) Hypothalamic and (k) striatal content of DOPA after NSD 1015 treatment. Striatal DOPA is significantly increased, and hypothalamic DOPA shows a similar trend in Drd2–/– mice, consistent with increased TH activity in dopamine neuronal terminals. DOPA levels did not differ between Prlr–/– and wild-type mice in either brain area. Scale bar represents 250 μm. Comparison was by ANOVA and Fisher post hoc test. *P < 0.05 compared with both other groups; n = 4–7.