A new method for in vivo measurement of brain monoamine oxidase activity.
The radiotracers, C-14-N-methylphenylethylamine (MPEA) and N-methylphenylethanolamine (MPEOA) both rapidly entered mouse brain after their intravenous injection and were metabolized by brain monoamine oxidase (MAO) to C-14-methylamine and corresponding aldehydes. The labelled metabolite was trapped in the brain. Measurement of radioactivity showed that the amount of the metabolite produced in the brain from C-14-MPEA was proportional to the MAO activity remaining after combined treatment with a specific MAO-A inhibitor, clorgyline and a MAO-B inhibitor, 1-deprenyl, but not by treatment with either inhibitor alone. The rate of production of the labelled metabolite produced from C-14-MPEOA was highly sensitive to the extent of inhibition of MAO-B activity (with phenylethylamine as substrate) by pretreatment with 1-deprenyl, but was relatively insensitive to inhibitor clorgyline. This selectivity suggests that MPEOA is a specific substrate of MAO-B in mouse brain in vivo. The above results indicate that C-14-labelled N-methylphenylethylamine and N-methylphenylethanolamine derivatives can be used for measurement of brain MAO activity and that C-14-MPEOA is a specific substrate for mouse brain MAO-B. The value and possible applications of this method for measurement of MAO-B in brain under different physiological conditions are discussed.
D015078:2-Hydroxyphenethylamine / Q000031:analogs & derivatives / Q000378:metabolism; D000818:Animals; D001921:Brain / Q000201:enzymology*; D003010:Clorgyline / Q000494:pharmacology; D007527:Isoenzymes / Q000037:antagonists & inhibitors / Q000378:metabolism*; D008297:Male; D008744:Methylamines / Q000096:biosynthesis; D051379:Mice; D008809:Mice, Inbred C3H; D008995:Monoamine Oxidase / Q000378:metabolism*; D008996:Monoamine Oxidase Inhibitors; D012642:Selegiline / Q000494:pharmacology; D013379:Substrate Specificity
D007527:Isoenzymes; D008744:Methylamines; D008996:Monoamine Oxidase Inhibitors; D012642:Selegiline; C027140:N-methylphenylethanolamine; D015078:2-Hydroxyphenethylamine; C027451:methylamine; D008995:Monoamine Oxidase; D003010:Clorgyline