Search for PET probes for imaging the globus pallidus studied with rat brain ex vivo autoradiography

We have evaluated the feasibility of using four positron emission tomography (PET) tracers for imaging the globus pallidus by ex vivo autoradiography in rats. The tracers investigated were [C-11]KF18446, [C-11]SCH23390 and [C-11]raclopride for mapping adenosine A(2A), dopamine D-1 and dopamine D-2 receptors, respectively, and [F-18]FDG. The highest uptake by the globus pallidus was found for [C-11]SCH23390, followed by [F-18]FDG, [C-11]KF18446 and [C-11]raclopride. The receptor-specific uptake by the globus pallidus was observed in [C-11]KF18446 and [C-11]SCH23390, but not in [C-11]raclopride. Uptake ratios of globus pallidus to the striatum for [F-18]FDG and [C-11]KF18446 were approximately 0.6, which was twice as large as that for [C-11]SCH23390. In a rat model of degeneration of striatopallidal gamma -aminobutyric acid-ergic-enkephalin neurons induced by intrastriatal injection of quinolinic acid, the uptake of [C-11]KF18446 by the striatum and globus pallidus was remarkably reduced. To prove the visualization of the globus pallidus by PET with [F-18]FDG and [C-11]ECF18446, PET-MRI registration technique and advances in PET technologies providing high-resolution PET scanner will be required. The metabolic activity of the globus pallidus could then be measured by PET with [18F]FDG, and [C-11]KF18446 may be a candidate tracer for imaging the pallidal terminals projecting from the striatum.