Striatal dopamine D1 and D2 receptors in burning mouth syndrome

Animal studies have indicated that the nigrostriatal dopaminergic system is involved in central pain modulation. In a recent positron emission tomography (PET) study, we demonstrated presynaptic dysfunction of the nigrostriatal dopaminergic pathway in burning mouth syndrome, which is a chronic pain state. The objective of the present study was to examine striatal dopamine D1 and D2 receptors in these patients. We used C-11-NNC 756 and C-11-raclopride to study D1 and D2 receptor binding in a PET study in ten burning mouth patients and 11 healthy controls. Patients underwent a structured psychiatric evaluation and an electrophysiological test for the excitability of the blink reflex. The striatal uptake of C-11-NNC 756 did not differ between patients and controls. In a voxel-level analysis, the uptake of C-11-raclopride was statistically significantly higher in the left putamen in burning mouth patients (corrected P-value 0.038 at cluster-level). In the region of interest analysis, the D1/D2 ratio was 7.7% lower in the right putamen (0.64 +/- 0.04 vs. 0.69 +/- 0.04, P = 0.01) and 6.4 % lower in the left putamen (0.65 +/- 0.05 vs. 0.70 +/- 0.05, P = 0.05) when compared to controls. Increased 11C-raclopride uptake and the subsequent decrease in the D1/D2 ratio may indicate a decline in endogenous dopamine levels in the putamen in burning mouth patients. (C) 2002 International Association for the Study of Pain. Published by Elsevier Science B.V. All rights reserved.