Brain region binding of the D2/3 agonist [11C]-(+)-PHNO and the D2/3 antagonist [11C]raclopride in healthy humans

Hum Brain Mapp. 2008 Apr;29(4):400-10. doi: 10.1002/hbm.20392.


The D(2) receptors exist in either the high- or low-affinity state with respect to agonists, and while agonists bind preferentially to the high-affinity state, antagonists do not distinguish between the two states. [(11)C]-(+)-PHNO is a PET D(2) agonist radioligand and therefore provides a preferential measure of the D(2) (high) receptors. In contrast, [(11)C]raclopride is an antagonist radioligand and thus binds with equal affinity to the D(2) high- and low-affinity states. The aim was to compare the brain uptake, distribution and binding characteristics between [(11)C]-(+)-PHNO and [(11)C]raclopride in volunteers using a within-subject design. Both radioligands accumulated in brain areas rich in D(2)/D(3)-receptors. However, [(11)C]-(+)-PHNO showed preferential uptake in the ventral striatum and globus pallidus, while [(11)C]raclopride showed preferential uptake in the dorsal striatum. Mean binding potentials were higher in the putamen (4.3 vs. 2.8) and caudate (3.4 vs 2.1) for [(11)C]raclopride, equal in the ventral-striatum (3.4 vs. 3.3), and higher in the globus pallidus for [(11)C]-(+)-PHNO (1.8 vs. 3.3). Moreover [(11)C]-(+)-PHNO kinetics in the globus pallidus showed a slower washout than other regions. One explanation for the preferential binding of [(11)C]-(+)-PHNO in the globus pallidus and ventral-striatum could be the presence of a greater proportion of high- vs. low-affinity receptors in these areas. Alternatively, the observed distribution could also be explained by a preferential binding of D(3)-over-D(2) with [(11)C]-(+)-PHNO. This differential binding of agonist vs. antagonist radioligand, especially in the critically important region of the limbic striatum/pallidum, offers new avenues to investigate the role of the dopamine system in health and disease.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Binding, Competitive / drug effects
  • Binding, Competitive / physiology
  • Brain Mapping / methods
  • Carbon Radioisotopes
  • Corpus Striatum / diagnostic imaging
  • Corpus Striatum / metabolism*
  • Dopamine / metabolism*
  • Dopamine Agonists / metabolism
  • Dopamine Agonists / pharmacokinetics
  • Dopamine Antagonists / metabolism
  • Dopamine Antagonists / pharmacokinetics
  • Dopamine D2 Receptor Antagonists*
  • Female
  • Globus Pallidus / diagnostic imaging
  • Globus Pallidus / metabolism
  • Humans
  • Male
  • Neostriatum / diagnostic imaging
  • Neostriatum / metabolism
  • Oxazines / metabolism
  • Oxazines / pharmacokinetics*
  • Positron-Emission Tomography / methods
  • Raclopride / metabolism
  • Raclopride / pharmacokinetics*
  • Receptors, Dopamine D2 / agonists*
  • Receptors, Dopamine D2 / metabolism
  • Substantia Nigra / diagnostic imaging
  • Substantia Nigra / metabolism
  • Time Factors
  • Tissue Distribution


  • Carbon Radioisotopes
  • Dopamine Agonists
  • Dopamine Antagonists
  • Dopamine D2 Receptor Antagonists
  • Oxazines
  • Receptors, Dopamine D2
  • naxagolide
  • Raclopride
  • Dopamine