Positron emission tomography with appropriate tracers provides unique opportunity to study
neurotransmitter systems in the living human brain. PET with [18F] 6-fluoro-L-dopa (FD) provides an index of the integrity of nigrostriatal pathway, and striatal FD uptake correlates linearly with the density of nigral neurons. PET allows us to assess the progression of the nigral lesions in
Parkinson's disease (PD). A 68-year-old normal female volunteer was scanned by FD-PET. Subsequently, she developed
parkinsonism 3.7 years after the scan. A repeated FD-PET scan revealed a significant reduction of FD uptake by 20% over the 5.2 year interval. The results suggest a relatively short presymptomatic period with fast initial losses of nigral neurons in PD. FD-PET has been used to determine the viability of fetal graft implanted in the striatum for the treatment of PD. PET imaging of
dopamine D1 and D2 receptors may be useful for the differential diagnosis of PD and
striatonigral degeneration. PET reveals significant reduction of
dopamine D1 and D2 receptor binding in the putamen of patients with SND, while D1 and D2 receptor binding is normal or slightly upregulated in PD. We found
hypersensitivity of
muscarinic cholinergic receptors in the frontal cortex of patients with PD by using PET. The result suggests a loss of ascending
cholinergic system in the frontal cortex in PD, which may cause the frontal lobe dysfunction in PD. Recently,
acetylcholine analogs labelled with positron emitter have been developed for measurement of brain
acetylcholinesterase activity in vivo. These tracers may be useful for the assessment of ascending
cholinergic system in
Alzheimer's disease and PD.