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Title: Brain region binding of the D2/3 agonist [11C]‐(+)‐PHNO and the D2/3 antagonist [11C] raclopride in healthy humans
Authors: Graff-Guerrero, Ariel
Willeit, Matthaeus
Ginovart, Nathalie
Mamo, David
Mizrahi, Romina
Rusjan, Pablo
Vitcu, Irina
Seeman, Philip
Wilson, Alan A.
Kapur, Shitij
Keywords: Tomography, Emission
Globus pallidus
Substantia nigra
Issue Date: 2008
Publisher: John Wiley & Sons, Inc.
Citation: Graff‐Guerrero, A., Willeit, M., Ginovart, N., Mamo, D., Mizrahi, R., Rusjan, P., ... & Kapur, S. (2008). Brain region binding of the D2/3 agonist [11C]‐(+)‐PHNO and the D2/3 antagonist [11C] raclopride in healthy humans. Human Brain Mapping, 29(4), 400-410.
Abstract: The D2 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. [11C]-(+)-PHNO is a PET D2agonist radioligand and therefore provides a preferential measure of the D2high receptors. In contrast, [11C]raclopride is an antagonist radioligand and thus binds with equal affinity to the D2 high- and low-affinity states. The aim was to compare the brain uptake, distribution and binding characteristics between [11C]-(+)-PHNO and [11C]raclopride in volunteers using a within-subject design. Both radioligands accumulated in brain areas rich in D2/D3-receptors. However, [11C]-(+)-PHNO showed preferential uptake in the ventral striatum and globus pallidus, while [11C]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 [11C]raclopride, equal in the ventral-striatum (3.4 vs. 3.3), and higher in the globus pallidus for [11C]-(+)-PHNO (1.8 vs. 3.3). Moreover [11C]-(+)-PHNO kinetics in the globus pallidus showed a slower washout than other regions. One explanation for the preferential binding of [11C]-(+)-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 D3-over-D2 with [11C]-(+)-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.
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