l-DOPA and Its Receptor GPR143: Implications for Pathogenesis and Therapy in Parkinson's Disease.

l-3,4-Dihydroxyphenylalanine (l-DOPA) is the most effective therapeutic agent for Parkinson's disease (PD). l-DOPA is traditionally believed to be an inert amino acid that exerts actions and effectiveness in PD through its conversion to dopamine. In contrast to this generally accepted idea, l-DOPA is proposed to be a neurotransmitter. Recently, GPR143 (OA1), the gene product of ocular albinism 1 was identified as a receptor candidate for l-DOPA. GPR143 is widely expressed in the central and peripheral nervous system. GPR143 immunoreactivity was colocalized with phosphorylated α-synuclein in Lewy bodies in PD brains. GPR143 may contribute to the therapeutic effectiveness of l-DOPA and might be related to pathogenesis of PD.