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

Graff-Guerrero, Ariel
Willeit, Matthaeus
Mamo, David
Mizrahi, Romina
Rusjan, Pablo
Vitcu, Irina
Seeman, Philip
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Published in Human brain mapping. 2008, vol. 29, no. 4, p. 400-10
Abstract 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.
Keywords AdultBinding, Competitive/drug effects/physiologyBrain Mapping/methodsCarbon RadioisotopesCorpus Striatum/diagnostic imaging/metabolismDopamine/metabolismDopamine Agonists/metabolism/pharmacokineticsDopamine Antagonists/metabolism/pharmacokineticsDopamine D2 Receptor AntagonistsFemaleGlobus Pallidus/diagnostic imaging/metabolismHumansMaleNeostriatum/diagnostic imaging/metabolismOxazines/metabolism/pharmacokineticsPositron-Emission Tomography/methodsRaclopride/metabolism/pharmacokineticsReceptors, Dopamine D2/agonists/metabolismSubstantia Nigra/diagnostic imaging/metabolismTime FactorsTissue Distribution
PMID: 17497628
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GRAFF-GUERRERO, Ariel et al. Brain region binding of the D2/3 agonist [11C]-(+)-PHNO and the D2/3 antagonist [11C]raclopride in healthy humans. In: Human brain mapping, 2008, vol. 29, n° 4, p. 400-10. doi: 10.1002/hbm.20392 https://archive-ouverte.unige.ch/unige:93444

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Deposited on : 2017-04-11

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