Levels of amino acids in 52 discrete areas of postmortem brain of adult and aged humans.

In a series of studies we have analyzed the regional distribution of the free amino acid pool in 52 discrete areas of postmortem brain of adult and aged humans. Here we show the distribution of eleven amino acids: alanine, methionine, valine, leucine, isoleucine, glutamine, asparagine, lysine, arginine, ornithine, and histidine. As found previously for other amino acids, the distribution of these amino acids was seen to be heterogeneous, the level of the area of highest level being 3.4 to 10.7 times that of the area of the lowest level. On average we found a five- or six-fold difference in concentration between the highest and lowest level areas in the brain samples from adult and old respectively. The distribution patterns were found to be different for each amino acid; they were not similar even in the same class (amides, branched chain, basic amino acids), and they were different from those recently found in rat brain. Only a few changes, mostly increases, were found in the aged brain, such as increases in alanine and valine levels in cortical areas. In studies of changes in cerebral amino acid levels, the great regional heterogeneity of distribution has to be taken into account since changes in whole brain values may not reflect regional changes. The functional significance and the control of this regional heterogeneity are under investigation.