Dopamine receptor interactions: some implications for the treatment of Parkinson's disease.

Since the discovery that L-DOPA could alleviate the symptoms of Parkinson's disease, it has been assumed that the striatum is the site of action of the dopamine formed from L-DOPA. However, for the past 15 years, evidence has accumulated to suggest that dopamine is also released by the dendrites of dopamine neurons in the substantia nigra and D1 dopamine receptors in this region of the brain appear to play an important role in the actions of L-DOPA. Activation of D1 receptors in the substantia nigra may, in part, explain some of the synergistic effects of D1 and D2 agonists in animal models for Parkinson's disease. These effects are discussed in light of recent studies suggesting that dopamine, acting on D1 and D2 dopamine receptor subtypes, activates distinct efferent pathways from the striatum. Clinical studies suggest that these findings may have important implications for the treatment of Parkinson's disease.