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Upregulation of Putaminal Dopamine D₂ Receptors in Early Parkinson's Disease: A Comparative PET Study with [¹¹C]Raclopride and [¹¹C]N-Methylspiperone

Department of Neurology, University of Turku, Turku, Finland
Radiopharmaceutical Chemistry Laboratory, Turku PET Centre, Turku, Finland

Correspondence: For correspondence or reprints contact: Juha O. Rinne, MD, PhD, Department of Neurology, University of Turku, FIN-20520 Turku, Finland.

ABSTRACT

Dopamine D₂ receptor function was assessed in a PET study with 2 dopamine D₂ receptor PET ligands, [¹¹C]raclopride (RAC) and [¹¹C]N-methylspiperone (NMSP), in early Parkinson's disease. Methods: Seven patients with early Parkinson's disease and 5 healthy volunteers were studied. Each underwent PET both with reversible [¹¹C]RAC and with irreversible [¹¹C]NMSP. Results: Upregulation of dopamine D₂ receptors in the putamen contralateral to the predominant symptoms of Parkinson's disease was confirmed using both [¹¹C]RAC and [¹¹C]NMSP. Uptake of [¹¹C]RAC in the contralateral putamen was 105% of uptake in the opposite putamen (P = 0.020). For [¹¹C]NMSP, uptake in the contralateral putamen was 105% of uptake in the ipsilateral putamen (P = 0.011). No significant differences between Parkinson's disease patients and healthy volunteers were detected in any of the studied brain regions using either [¹¹C]RAC or [¹¹C]NMSP. No significant differences between [¹¹C]RAC and [¹¹C]NMSP uptake were detected in the striatum, whereas in the extrastriatal regions, [¹¹C]NMSP showed significantly higher uptake than [¹¹C]RAC both in healthy volunteers and in Parkinson's disease patients. Conclusion: This study confirms an increase in dopamine D₂ receptors in the putamen contralateral to the predominant symptoms, compared with the ipsilateral putamen, in early Parkinson's disease. This increase was seen both with reversible ligand [¹¹C]RAC and with irreversible ligand [¹¹C]NMSP and thus does not seem a consequence of depleted endogenous dopamine.

Key Words: Parkinson's disease • dopamine D₂ receptor • raclopride • N-methylspiperone • PET

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