In vivo studies on striatal dopamine D-1 and D-2 site binding in L-dopa-treated Parkinson's disease patients with and without dyskinesias

Dyskinesias are usually seen in Parkinson's disease (PD) patients after several years of L-dopa therapy. Their presence has been attributed to supersensitivity of striatal D-1 and D-2 receptors. We have used PET to assess striatal D-2 receptor binding in untreated PD patients and striatal D-1 and D-2 binding in L-dopa-treated PD patients. Untreated patients showed a 14% increase in mean D-2 receptor binding in the putamen contralateral to the more affected limbs (p < 0.02). Treated patients were segregated into subgroups according to the presence or absence of dyskinesias. There were no differences in mean caudate and putamen D-1 and D-2 binding between dyskinetic and nondyskinetic patients, matched for duration of clinical disease. Both dyskinetic and nondyskinetic PD subgroups showed a similar 16% reduction of mean caudate D-2 binding (p < 0.01) with normal D-2 binding in putamen. Mean caudate and putamen D-1 binding potentials of bath subgroups were reduced by 10% compared with those of controls, though this trend did not reach significance. Putamen D-1 binding, however, showed a negative correlation with duration of disease and L-dopa treatment (p < 0.03). These findings suggest that, while exposure of PD patients to L-dopa may be associated with reductions in caudate D-2 and caudate and putamen D-1 receptor, dyskinesias are unlikely to result from alterations in striatal dopamine receptor binding.