In vitro positron emission tomography (PET): use of positron emission tracers in functional imaging in living brain slices

Positron-emitting radionuclides have short half-lives and high radiation energies compared with radioisotopes generally used in biomedical research. We examined the possibility of applying positron emitter-labeled compounds to functional imaging in brain slices kept viable in an oxygenated buffer solution. Brain slices (300 μm thick) containing the striatum were incubated with positron emitter-labeled tracers for 30-45 min. The slices were then rinsed and placed on the bottom of a Plexiglas chamber filled with oxygenated Krebs-Ringer solution. The bottom of the chamber consisted of a thin polypropylene film to allow good penetration of β⁺ particles from the brain slices. The chamber was placed on a storage phosphor screen, which has a higher sensitivity and a wider dynamic range than X-ray films. After an exposure period of 15-60 min, the screen was scanned by the analyzer and radioactivity images of brain slices were obtained within 20 min. We succeeded in obtaining quantitative images of (1) [¹⁸F]fluoro-deoxyglucose uptake, (2) dopamine D₂ receptor binding, (3) dopa-decarboxylase activity, and (4) release of [ ¹¹ C]dopamine preloaded as l-[¹¹C]DOPA in the brain slice preparation. These results demonstrate that positron emitter-labeled tracers in combination with storage phosphor screens are useful for functional imaging of living brain slices as a novel neuroscience technique.