A new metabolically trapped agent by brain monoamine oxidase: N-methyl labeled (14C) N-methylphenylethylamine (14C-MPEA).

A new type of metabolically trapped agent for measuring regional brain function was designed and evaluated. N-methylphenylethylamine (14C-MPEA) was synthesized with trifluoroacetylphenylethylamine and 14C-methyl iodide. A high concentration of 14C-MPEA accumulated in mouse brain 1 min after injection, and radioactivities in the brain remained for a long period. By radiochemical analysis, it was found 14C-MPEA was metabolized in the brain to 14C-methylamine. 14C-methylamine was trapped by the blood-brain barrier because of its cationic charge at physiological pH. When the mouse was pretreated with a MAO inhibitor (pargyline hydrochloride 100 mg/kg IP) the radioactivity was rapidly excreted from the brain with a half-life of about 45 min. These results indicate that 11C-MPEA has potential for the measurement of brain MAO activity.