D-1 type of dopamine autoreceptors are not involved in the regulation of dopamine synthesis in the striatum.

To clarify if dopamine (DA) synthesis is regulated by D-1 DA receptors located on dopaminergic nerve terminals in the striatum, we investigated effects of D-1 DA receptor agonist and antagonist on striatal 3,4-dihydroxyphenylalanine (DOPA) accumulation induced by gamma-butyrolactone in mice treated with an amino acid decarboxylase inhibitor. SKF 38393, a D-1 agonist, did not affect DOPA accumulation, whereas apomorphine that stimulates both D-1 and D-2 receptors inhibited the accumulation. SCH 23390, a D-1 antagonist, did not antagonize apomorphine-induced inhibition of DOPA accumulation, while YM-09151-2, a D-2 antagonist, reversed it. These results suggest that D-1 type of DA autoreceptors is not involved in the inhibition of in vivo DA synthesis.