INTERACTION OF NEUROMELANIN AND IRON IN SUBSTANTIA-NIGRA AND OTHER AREAS OF HUMAN BRAIN

Nine areas of the brain were studied by electron paramagnetic resonanc e spectroscopy and total reflection X-ray fluorescence spectroscopy to measure paramagnetic metal ions, free radicals (neuromelanin), and to tal metal content. We also determined the extent of accumulation of me tal ions by melanins incubated in homogenates of a region of the brain (putamen). The electron paramagnetic resonance spectra of metal ions varied considerably among areas of the brain. There was no correlation between total content of particular metal ions (iron was especially p ertinent) and the observed electron paramagnetic resonance spectra, ex cept that the substantia nigra appeared more consistently to have a pr ominent g = 4 electron paramagnetic resonance signal characteristic of ferric iron in a rhombic state. Only the substantia nigra, and to a l esser extent the locus coeruleus, had a free radical signal consistent with that of neuromelanin. This signal was much more prominent in the unprocessed substantia nigra but when metal ions were removed (reduci ng the amount of suppression of the electron paramagnetic resonance si gnal of neuromelanin due to dipole-dipole broadening from nearby metal ions), the electron paramagnetic resonance spectrum of neuromelanin o f the locus coeruleus increased much more than that of the substantia nigra. This suggests that the structure of the pigment may differ in t hese two regions. Incubating synthetic melanins with homogenates of pu tamen resulted in accumulation of metal ions on the melanins with the concentrations of the three metal ions, relative to their values in th e putamen, increasing by factors of 20-30, 3-4, and 25-30, for iron, c opper, and zinc, respectively. This suggests that the metal content of isolated neuromelanin may include metal ions which became bound to th e neuromelanin during the isolation procedure. Copyright (C) 1996 IBRO . Published by Elsevier Science Ltd.