Role of acetyl-L-carnitine in the brain: revealed by Bioradiography

To elucidate the role of acetyl-L-carnitine in the brain, we used a novel method, 'Bioradiography,' in which the dynamic process could be followed in living slices by use of positron-emitter labeled compounds and imaging plates. We studied the incorporation of 2-[F-18]fluoro-2-deoxy-D-glucose ([F-18]FDG) into rat brain slices incubated in oxygenated Krebs-Ringer solution. Under the glucose-free condition, [F-18]FDG uptake rate decreased with time and plateaued within 350 min in the cerebral cortex and cerebellum, and the addition of I or 5 mM acetyl-L-carnitine did not alter the [F-18]FDG uptake rate. When a glutaminase inhibitor, 0.5 mM 6-diazo-5-oxo-L-norleucine (DON), was added under the normal glucose condition, [F-18]FDG uptake rate decreased. Acetyl-L-carnitine (I mM), which decreased [F-18]FDG uptake rate, reversed this DON-induced decrease in [F-18]FDG uptake rate in the cerebral cortex. These results suggest that acetyl-L-carnitine can be used for the production of releasable glutamate rather than as an energy source in the brain. (C) 2003 Elsevier Science (USA). All rights reserved.