The D-1 antagonist SCH 23390 stimulates while the D-1 agonist SKF 38393 fails to affect dopamine release in the dorsal caudate of freely moving rats.

SCH 23390, from doses of 0.012 mg/kg s.c., dose dependently stimulated the release of dopamine (DA) and the output of its metabolites, dihydroxyphenylacetic acid and homovanillic acid, in the dorsal caudate of freely moving rats implanted with transcerebral dialysis fibers. SKF 38393 failed to modify DA release and metabolism at doses of 5, 10 and 25 mg/kg s.c. but at 25 mg/kg s.c. it abolished the effect of 0.025 mg/kg of SCH 23390. Administration of gamma-butyrolactone (700 mg/kg s.c.), which blocks the firing of DA neurons, prevented the effect of 0.050 mg/kg s.c. SCH 23390. The results indicate that D-1 receptors control the release of DA, probably through stimulation of the firing of DA neurons.