Naxagolide (MK-458; L 647,339; (+)-PHNO) is a dopamine D2/D3-receptor agonist, which was studied for the treatment of patients with Parkinson's disease, but further study was discontinued. In addition, was discovered, that Naxagolide C-11 ([(11)C]-(+)-PHNO) was a potential radiotracer for imaging the high-affinity state of dopamine D2 receptors with positron emission tomography (PET) in human subjects. This radiotracer is a suitable for imaging the agonist binding sites (denoted D(2HIGH) and D(3)) of these receptors. PET studies in nonhuman primates documented that, in vivo, [(11)C]-(+)-PHNO displays a relative selectivity for D(3) compared with D(2HIGH) receptor sites and that the [(11)C]-(+)-PHNO signal is enriched in D(3) contribution compared with conventional ligands such as [(11)C] raclopride. Recently was published article reflects the relationship between social attachment and dopamine D2/3 receptor availability in the brains of healthy humans using [11C]-(+)-PHNO.