OBJECTIVE: Adenosine is an endogenous modulator of synaptic functions in the 
central nervous system. The effects of adenosine are mediated by at least four 
adenosine receptor subtypes. Decreased density of adenosine A1 receptors, which 
is a major subtype adenosine receptor in the hippocampus, has been reported in 
vitro in Alzheimer's disease. We evaluated adenosine A1 receptor in the brain of 
elderly normal subjects and patients with Alzheimer's disease (n = 8 and 6, 
respectively), using positron emission tomography (PET) and 8- 
dicyclopropylmethyl-1-[(11)C]methyl-3-propylxanthine ([(11)C]MPDX).
METHODS: A 60-min PET scan with [(11)C]MPDX was performed. The patients with 
Alzheimer's disease also underwent PET with [(18)F]fluorodeoxyglucose (FDG). The 
binding potential of [11C]MPDX was quantitatively calculated in the regions of 
interest (ROIs) placed on the frontal, medial frontal, temporal, medial 
temporal, parietal, and occipital cortices, striatum, thalamus, cerebellum, and 
pons. Statistical parametric mapping (SPM2) was used for analysis of [(11)C]MPDX 
and FDG-PET.
RESULTS: In the ROI-based analysis, the binding potential of [(11)C]MPDX in 
patients with Alzheimer's disease was significantly lower in the temporal and 
medial temporal cortices and thalamus than that in elderly normal subjects (P = 
0.038, 0.028, and 0.039, respectively). SPM analysis also showed significant 
decreased binding potential in the temporal and medial temporal cortices and 
thalamus in patients with Alzheimer's disease. FDG uptake was significantly 
decreased in the temporoparietal cortex and posterior cingulate gyrus.
CONCLUSIONS: Decreased binding of [(11)C]MPDX in patients with Alzheimer's 
disease was detected in temporal and medial temporal cortices and thalamus. This 
pattern possibly differed from the hypometabolism pattern of FDG. [(11)C]MPDX 
PET is valuable for the detection of degeneration in the temporal and medial 
temporal cortices and corticothalamic transmission, and may provide a different 
diagnostic tool from FDG-PET in brain disorders such as Alzheimer's disease.