increase in the amount per unit of blood of glutamic acid (2-aminopentanedioic acid), a non-essential alpha-amino used in the biosynthesis of proteins; its anion form, glutamate, is the major excitatory neurotransmitter in the mammalian central nervous system and also serves as the metabolic precursor of gamma-aminobutyric acid (GABA), an inhibitory neurotransmitter