Ionic interaction of [11C]-N,alpha-dimethylbenzylamine (DMBA) in rodent brain

The [S] enantiomer of [11C]-N,alpha-dimethylbenzylamine (DMBA) was synthesized by N-methylation of [S]-alpha-methylbenzylamine, and its biodistribution in mice was measured. [11C]-[S]-DMBA was rapidly distributed into the brain, heart and lungs, and considerable long-term retention in the brain was observed. The radioactive metabolites in the plasma were analyzed by liquid chromatography. Kinetic analysis using unmetabolized [11C]DMBA in the plasma as the input function was performed employing a simplified two-compartment model. The estimated distribution volumes (DV) of [11C]DMBA in the brain and heart were 6.05 and 3.95, respectively. The right striatum of the rat brain was lesioned with ibotenic acid 2 weeks before the tracer experiment. Both in vitro and in vivo autoragiographic studies were performed, and revealed significant reduction of the radioactivity levels in the lesioned striatum. On the other hand, the regional cerebral blood flow, as measured by [14C]iodoantipyrine, was not significantly altered in the lesioned striatum. These results indicate that the ionic binding component for DMBA exists mainly in neural cells rather than in glial cells. [11C]DMBA might be a useful radiotracer for detection of neural cell loss in the brain.