Heterogeneous distribution of functionally important amino acids in brain areas of adult and aging humans.

The regional distribution of seven amino acids thought to have inhibitory neurotransmitter or neurotransmitter precursor function--GABA, glycine, taurine, serine, threonine, phenylalanine, and tyrosine--was determined in 52 discrete areas from brain of adult and old humans. Significant heterogeneity was found, with 3- to 16-fold differences in levels in the various regions analyzed. The patterns of distribution were somewhat different from those in the adult or old rat brain. Relatively few changes were seen in old brain. Heterogeneity in distribution has to be taken into account in assessing physiological changes in amino acid levels and metabolism.