Evaluation of [14C]phenylacetate as a prototype tracer for the measurement of glial metabolism in the rat brain

[C-14]Phenylacetate was designed as a prototype tracer for the measurement of glial metabolism, and its potency in comparison with that of [C-14]acetate was evaluated in this study. Normal rats were intravenously injected with [C-14]phenylacetate or [C-14]acetate, and radioactivity concentrations were measured in the plasma, cerebral cortex, cerebellum and peripheral tissues by dissection method. In addition, [C-14]phenylacetate uptake in the rat brain was compared by autoradiography with that of [C-14]acetate following the injection of fluorocitrate, a selective glial toxin, into the brain. [C-14]Phenylacetate was rapidly taken up into the brain and was retained at high levels up to 20 min postadministration. The levels of [C-14]phenylacetate in the cerebral cortex were about threefold higher than those of [C-14]acetate at 1 min postinjection. Microinjection of fluorocitrate into the right striatum resulted in a significant decrease of the uptake of both [C-14]phenylacetate and [C-14]acetate into the right striatum. Radiochemical analysis confirmed the rapid hydrolysis of [C-14] phenylacetate in the rat brain, with less than 20% of radioactivity representing unmetabolized [C-14] phenylacetate at 1 min postinjection. These results suggest that [C-14]phenylacetate is rapidly taken up into the brain and is hydrolyzed and converted to [C-14]acetate. [C-14] Phenylacetate may have the potential to serve as a tracer for the measurement of glial metabolism in an intact brain. (c) 2006 Elsevier Inc. All rights reserved.