FIG. 4.

Tracers for presynaptic dopaminergic function. The vesicular monoamine transporter 2 (VMAT2) is responsible for packaging monoamine transmitters into synaptic vesicles. 6-¹⁸F-fluoro-L-dopa is a radioactive analog of levodopa that is decarboxylated into 6-¹⁸F-fluoro-L-dopamine, which is subsequently stored in synaptic vesicles but then undergoes slow egress and enzymatic degradation. Once dopamine is release from the synapse, it is taken up by the dopamine transporter (DaT), which can be labeled using a variety of ¹¹C and ¹⁸F (for PET) and ¹³¹I or ^99mTc (for SPECT) tracers. For each tracer, the left panel shows a healthy control subject, whereas the right shows a patient with mild Parkinson’s disease. In the latter, there is asymmetric reduction of tracer uptake, maximally affecting the posterior striatum. From Chandran & Stoessl, in Jankovic & Tolosa, Parkinson’s Disease and Movement Disorders, Wolters Kluwer, 2015.