Striatal μ-opioid receptor availability predicts cold pressor pain threshold in healthy human subjects

Previous PET studies in healthy humans have shown that brain μ-opioid receptor activation during experimental pain is associated with reductions in the sensory and affective ratings of the individual pain experience. The aim of this study was to find out whether brain μ-opioid receptor binding at the resting state, in absence of painful stimulation, can be a long-term predictor of experimental pain sensitivity. We measured μ-opioid receptor binding potential (BPND) with μ-opioid receptor selective radiotracer [11C]carfentanil and positron emission tomography (PET) in 12 healthy male subjects. Later, we recruited these subjects to participate in a separate psychophysical testing session to measure cold pressor pain threshold, cold pressor pain tolerance and tactile sensitivity with von Frey monofilaments. We used both voxel-by-voxel and region-of-interest image analyses to examine the potential associations between μ-opioid receptor BPND and psychophysical measures. The results show that striatal μ-opioid receptor BPND predicts cold pressor pain threshold, but not cold pressor pain tolerance or tactile sensitivity. This finding suggests that striatal μ-opioid receptor density is involved in setting individual pain threshold.

► Imaging of [11C]carfentanil binding allows determining brain μ-opioid receptor availability. ► Striatal μ-opioid receptor availability predicted cold pressor pain threshold in healthy males. ► μ-Opioid receptor availability failed to correlate with cold pain tolerance or tactile threshold. ► Striatal μ-opioid receptor availability is involved in setting individual pain threshold.