Localization of trapping of 6-[F-18]fluoro-L-m-tyrosine, an aromatic L-amino acid decarboxylase tracer for PET

The purpose of this study was to address four major questions regarding 6-F MT, a noncatecholic PET tracer for AAAD: 1) Where is the specific uptake of 6-FMT? 2) Why does it accumulate where and to the degree that it does? 3) How does its uptake differ from that of fluoroDOPA globally? and 4) Does it s regional uptake differ significantly from that of fluoroDOPA? High-resolu tion PET scans were obtained in three rhesus monkeys using 6-FMT and in two of them using fluoroDOPA. Anatomic distribution was analyzed visually and quantitative uptake of 6-FMT was compared with published regional decarboxy lase activity and monoamine neurotransmitter concentrations. In addition to high uptake in the dopamine-rich striatal nuclei, there was specific uptak e of 6-FMT in brain regions which have little dopaminergic innervation but which have other amines in significant concentration. 6-FMT uptake correlat ed best with regional AAAD activity (r = 0.97). It correlated slightly less well with the sum of catecholamine and indolamine neurotransmitter concent rations, but does not correlate with dopamine concentration. The uptake of 6-FMT is greater than that of fluoroDOPA, with only slight differences in t heir regional distributions. Radiolabeled analogs of DOPA are often implici tly or explicitly regarded as tracers for presynaptic dopaminergic function . However, localization of these tracers more broadly includes many regions with relatively high concentrations of norepinephrine and serotonin. This may be especially important in diseases or experimental states in which dop aminergic neurons are selectively reduced, and may allow for the study of n ondopaminergic neuronal systems in vivo with this tracer. (C) 1999 Wiley-Li ss, Inc.