Upregulation of putaminal dopamine D-2 receptors in early Parkinson's disease: A comparative PET study with [C-11]raclopride and [C-11]N-methylspiperone

Dopamine D-2 receptor function was assessed in a PET study with 2 dopamine D-2 receptor PET ligands, [C-11]raclopride (RAG) and [C-11]N-methylspiperon e (NMSP), in early Parkinson's disease. Methods: Seven patients with early Parkinson's disease and 5 healthy volunteers were studied. Each underwent P ET both with reversible [C-11]RAC and with irreversible [C-11]NMSP. Results : Upregulation of dopamine D-2 receptors in the putamen contralateral to th e predominant symptoms of Parkinson's disease was confirmed using both [C-1 1]RAC and [C-11]NMSP. Uptake of [C-11]RAC in the contralateral putamen was 105% of uptake in the opposite putamen (P = 0.020). For [C-11]NMSP, uptake in the contralateral putamen was 105% of uptake in the ipsilateral putamen (P = 0.011). No significant differences between Parkinson's disease patient s and healthy volunteers were detected in any of the studied brain regions using either [C-11]RAC or [C-11]NMSP. No significant differences between [C -11]RAC and [C-11]NMSP uptake were detected in the striatum, whereas in the extrastriatal regions, [C-11]NMSP showed significantly higher uptake than [C-11]RAC both in healthy volunteers and in Parkinson's disease patients. C onclusion: This study confirms an increase in dopamine D-2 receptors in the putamen contralateral to the predominant symptoms, compared with the ipsil ateral putamen, in early Parkinson's disease. This increase was seen both w ith reversible ligand [C-11]RAC and with irreversible ligand [C-11]NMSP and thus does not seem a consequence of depleted endogenous dopamine.