Association of striatal dopamine D2/D3 receptor binding potential with pain but not tactile sensitivity or placebo analgesia

Striatal dopamine D2/D3 receptors have been suggested to play a role in pain sensitivity and placebo effect. We studied whether the association of dopamine D2/D3 receptor binding potential (BP) with sensory thresholds is specific to the modality of pain, and whether striatal dopamine D2/D3 receptor BP predicts the magnitude of placebo analgesia. Pain and tactile thresholds, and placebo analgesia were assessed in eight healthy human male subjects who had previously participated in a dopamine D2/D3 receptor positron emission tomography study with [11C]raclopride. The results show that the cutaneous heat pain threshold was inversely correlated with dopamine D2/D3 receptor BP in the right putamen, but responses to tactile stimulation did not correlate with striatal dopamine D2/D3 receptor BP. Placebo-induced elevation of the heat pain threshold did not correlate with striatal dopamine D2/D3 receptor BP. These results suggest that the influence of striatal dopamine D2/D3 receptors on sensory thresholds is selective for the modality of pain. Moreover, striatal dopamine D2/D3 receptor BP appears not to predict individual's analgesic response to placebo.