Ethnic disparities in pain processing among healthy adults: -opioid receptor binding potential as a putative mechanism

Although ethnic differences in pain perception are well documented, the underlying mechanism for these outcomes has not been established. µ-opioid receptor (MOR) function might contribute to this disparity, given that MORs play a key role in pain sensitivity and modulation. However, no study has characterized ethnic differences in MOR physiology. This study sought to address this knowledge gap by examining differences in µ-selective agonist binding potential (BP_ND; [¹¹C]-Carfentanil) between 27 non-Hispanic black (NHB) and 27 demographically similar, non-Hispanic white participants. Participants completed questionnaires and two 90-minute high-resolution research tomograph positron emission tomography (PET) imaging sessions. During PET imaging, a capsaicin or control cream was applied to individuals' arms, and pain ratings were collected. Bonferroni-corrected PET volumes of interest analyses revealed significantly greater [¹¹C]-Carfentanil BP_NDamong NHB participants in bilateral ventral striatum ([left]: F_1,52= 16.38, P < 0.001; [right]: F_1,52= 21.76, P < 0.001), bilateral dorsolateral prefrontal cortex ([left] F_1,52= 17.3, P < 0.001; [right]: F_1,52= 14.17, P < 0.001), bilateral subgenual anterior cingulate cortex ([left]: F_1,52= 10.4, P = 0.002; [right]: F_1,52= 12.91, P = 0.001), and right insula (F_1,52= 11.0, P = 0.002). However, there were no significant main effects of condition or ethnicity × condition interaction effects across models, likely attributable to individual variability in the direction of change within groups. BP_NDvalues were significantly correlated with pain ratings collected during the capsaicin condition (r range = 0.34-0.46, P range = 0.01-0.001). Results suggest that NHB individuals might have generally greater unoccupied MOR density than non-Hispanic white peers. Findings have implications for physiological differences underlying ethnicity-related pain disparities. If replicated, these results further emphasize the need for tailored treatments in historically underserved populations.