INVIVO BINDING OF [C-11] TETRABENAZINE TO VESICULAR MONOAMINE TRANSPORTERS IN MOUSE-BRAIN

The time course of regional mouse brain distribution of radioactivity after i.v. injection of a tracer dose of [C-11]tetrabenazine ([C-11]TBZ) has been determined. Radiotracer uptake into brain is rapid, with 3.2% injected dose in the brain at 2 min. Egress from the brain is also very rapid, with only 0.21% of the injected dose still present in brain at 60 min. Radiotracer washout is slowest from the striatum and hypothalamus, consistent with binding to the higher numbers of vesicular monoamine transporters in those brain regions. The rank order of radioligand binding at 10 min after injection is striatum > hypothalamus > hippocampus > cortex = cerebellum, similar to that found using in vitro assays of the vesicular monoamine transporters. Maximum ratios of striatum/cerebellum and hypothalamus/cerebellum were 2.85 +/- 0.52 and 1.69 +/- 0.25, respectively, at 10 min after injection. Co-injection of unlabeled tetrabenazine (10 mg/kg) or pretreatment with reserpine (1 mg/kg i.p., 24 h prior) was used to demonstrate specific binding of radioligand in striatum, hypothalamus, cortex, hippocampus and cerebellum. Distribution of [C-11]TBZ was unaffected by pretreatment with the neuronal dopamine uptake inhibitor GBR 12935 (20 mg/kg i.p., 30 min prior). [C-11]Tetrabenazine is thus a promising new radioligand for the in vivo study of monoaminergic neurons using Positron Emission Tomography.