Figure 2.

Human brain opioid receptor PET images in coronal (upper row) and axial (lower row) planes. Modified and reproduced with permission from Peciña et al. [19]. From left to right, we see (A) the µOR agonist [¹¹C]carfentanil, binding most abundantly in the caudate nucleus, anterior cingulate cortex, thalamus, and pituitary gland; (B) the δOR antagonist N1′-([¹¹C]methyl)natrindole, which has diffuse binding throughout neocortex; (C) the κOR antagonist [¹¹C]LY2795050, which has high binding in the insular cortex, lateral frontal cortex and amygdala; (D) the NOP antagonist [¹¹C]NOP-1A, which binds abundantly throughout the brain. Binding sites of µ-, κ- and NOP-OR ligands are expressed as binding potential relative to the cerebellum (BP_ND), whereas binding of the δ-ligand (which has no non-binding reference region) is expressed as net influx (K_i,) in units of perfusion (mL cm⁻³ min⁻¹). The color scale in the lower right indicates (for A, C, and D) BP_ND ranging from 0 to 2, or (B) K_i ranging from 0–0.1 mL cm⁻³ min⁻¹