PET DEMONSTRATES DIFFERENT BEHAVIOR OF STRIATAL DOPAMINE D-1 AND D-2 RECEPTORS IN EARLY PARKINSONS-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 [C-11]-SCH 23390. All patients had predominantly unilateral symptoms and showed a significant reduction in the accumulation of [F-18]-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 [C-11]-SCH 23390 binding was symmetric between the hemispheres. By contrast, the striatum/cerebellum ratio of [C-11]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.