Dopamine receptor properties in Parkinson's disease and Huntington's chorea evaluated by positron emission tomography using 11C-N-methyl-spiperone.

Dopaminergic receptor properties in the striatum of patients with Parkinson's disease (PD) and Huntington's chorea (HD) were studied by positron emission tomography (PET), using 11C-N-methyl-spiperone as a dopamine D2 receptor ligand. The time-dependent regional radioactive uptake in the caudate nucleus and the putamen was measured and fitted to a 3-compartment pharmacokinetic model. The rate constant k3 for specific binding to the receptor compartment in the striatum was determined in relation to the binding in regions with a low density of specific binding sites, such as the cerebellum and the frontal cortex . k3, which is a measure of the receptor density, was reduced in one patient with HD but less affected in PD in comparison with healthy controls. The pattern of k3 values calculated from the 6 PD patients is discussed in relation to any side-to-side differences in dopamine receptor densities in hemiparkinsonism and to possible "hypersensitivity" of dopamine receptors in the early stage of the disease and down-regulation in more advanced disease.