AN IN-VIVO MICRODIALYSIS STUDY OF STRIATAL 6-[F-18]FLUORO-L-M-TYROSINE METABOLISM

In vivo brain microdialysis was used to monitor 6-[F-18]fluoro-L-m-tyr osine (FMT) uptake and metabolism in the striatum of conscious freely moving rats for 3 hours after FMT injection (25 mg/kg, iv). Microdialy sate collected 20 to 120 min post-dose, contained FMT at a concentrati on (0.2 to 0.3 nM) approximately ten-fold below that of its metabolite [F-18]fluoro-3-hydroxyphenylacetic acid (FPAC; 3.2 to 3.3 nM). D-amph etamine (2.5 mg/kg, i.p.) injected 120 min after significantly increas ed microdialysate FPAC (3.27 +/- 0.31 nM to 4.51 +/- 0.45 nM) in contr ol but not reserpinized rats. Taken together these data demonstrate FM T is heavily metabolized following its entry into the striatum yieldin g FPAC which appears to be stored, at least in part, in reserpine sens itive cytoplasmic vesicles. Presynaptic retention of FPAC may contribu te to the preferential accumulation of FMT positron emission tomograph y (PET) signaling in dopaminergic brain areas.