PET demonstrates different behaviour of striatal dopamine D-1 and D-2 receptors in early Parkinson's disease.

Striatal dopamine D-1 receptor binding was investigated in vivo with positron emission tomography (PET) in five patients with early Parkinson's disease using [11C]-SCH 23390. All patients had predominantly unilateral symptoms and showed a significant reduction in the accumulation of [18F]-6-F-DOPA in the striatum contralateral to the symptoms. None of the patients had received any antiparkinsonian medication. The striatal and cerebellar radioactivity was measured and corresponding striatum/cerebellum ratios were counted. The mean striatum/cerebellum ratio of [11C]-SCH 23390 binding was symmetric between the hemispheres. By contrast, the striatum/cerebellum ratio of [11C]raclopride binding, labelling dopamine D-2 receptors, was increased significantly in the hemisphere contralateral to the symptoms as compared with the opposite hemisphere. Thus, the present results show that the behaviour of striatal D-1 and D-2 receptors is different in early Parkinson's disease.