Basal opioid receptor binding is associated with differences in sensory perception in healthy human subjects: a [18F]diprenorphine PET study.

The endogenous opioid system is involved in many body functions including pain processing and analgesia. To determine the role of basal opioid receptor availability in the brain in pain perception, twenty-three healthy subjects underwent positron emission tomography (PET) utilizing the subtype-nonselective opioid antagonist [(18)F]diprenorphine, quantitative sensory testing (QST) and the cold pressor test. Binding potentials (BPs) were calculated using a non-invasive reference tissue model and statistical parametric mapping was applied for t-statistical analysis on a voxelwise basis. We found that cold pain-sensitive subjects present a significantly lower BP in regions including the bilateral insular cortex and the left orbitofrontal cortex. In addition, correlation analysis revealed an inverse correlation between opioid BP in the bilateral motor and premotor region and perceptual wind-up. These findings indicate that interindividual differences in pain perception are partially accounted for by basal opioid receptor availability. A secondary aim of this study was to investigate the contribution of basal opioid receptor availability to the perception of non-nociceptive stimuli. The following negative correlations between regional opioid BP and scores of QST parameters were found: BP in the right premotor cortex and scores of alternating cold and warm stimuli, BP in the left midcingular cortex and scores of cold detection threshold, BP in the left insula and scores of mechanical detection threshold. These results suggest that the opioid receptor system is involved in the perception not only of pain but also of non-painful somatosensory stimuli.