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

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Abstract
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 be‐tween 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.