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

Abstract

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-[ 18F]fluoro-2-deoxy- d-glucose ([ 18F]FDG) into rat brain slices incubated in oxygenated Krebs–Ringer solution. Under the glucose-free condition, [ 18F]FDG uptake rate decreased with time and plateaued within 350 min in the cerebral cortex and cerebellum, and the addition of 1 or 5 mM acetyl- l-carnitine did not alter the [ 18F]FDG uptake rate. When a glutaminase inhibitor, 0.5 mM 6-diazo-5-oxo- l-norleucine (DON), was added under the normal glucose condition, [ 18F]FDG uptake rate decreased. Acetyl- l-carnitine (1 mM), which decreased [ 18F]FDG uptake rate, reversed this DON-induced decrease in [ 18F]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.