In vivo and in vitro imaging of I₂ imidazoline receptors in the monkey brain

Abstract

I₂ imidazoline receptors (I₂Rs) are associated with depression, Alzheimer's disease, and Huntington's disease. However, in vivo imaging of I₂Rs in the monkey brain has not been reported until now. We performed in vitro and in vivo imaging of (I₂Rs) in the monkey brain using ¹¹C-labeled 2-(3-fluoro-4-tolyl)-4,5-dihydro-1H-imidazole ([¹¹C]FTIMD) which has high and selective affinity of I₂Rs. In an auto-radiography (ARG) study, the distribution pattern of [¹¹C]FTIMD in the monkey brain was similar to that of [³H]idazoxan binging to I₂Rs in the human brain, which was previously described. The specific binding of [¹¹C]FTIMD accounted for >97% of total binding in brain regions existing I₂ Rs. In positron emission tomography (PET) studies, the radioactivity was accumulated in brain regions existing I₂Rs ligand BU224, the accumulated radioactivity was decreased to approximately 66%-75% of the baseline measurement at 15-45 min after injection of [¹¹C]FTIMD. These results suggest that [¹¹C]FTIMD shows the specific-binging to I₂Rs in the monkey brain as depicted by PET and ARG. We performed the first in vivo imaging of I₂Rs using [¹¹C]FTIMD in the monkey brain.