Parkinson's disease (PD) is associated with slowness, especially of sequential movements, and is pathologically characterised by degeneration of dopaminergic neurons, particularly targeting nigro-striatal projections. In turn, nigrostriatal dopamine has been suggested to be critical for the execution of sequential movements. The objective of this study was to investigate in vivo with [11C]raclopride PET changes in regional brain levels of dopamine in healthy volunteers and PD patients during the execution of paced, stereotyped sequential finger movements. Striatal [11C]raclopride binding reflects dopamine D2 receptor availability and is influenced by synaptic levels of endogenous dopamine. During execution of a prelearned sequence of finger movements a significant reduction in binding potential (BP) of [11C]raclopride was seen in both caudate and putamen in healthy volunteers compared to a resting baseline, consistent with release of endogenous dopamine. PD patients also showed attenuated [11C]raclopride BP reductions during the same motor paradigm in striatal areas less affected by the disease process. These findings confirm that striatal dopamine release is a component of movement sequencing and show that dopamine release can be detected in early Parkinson's disease during a behavioural manipulation.

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