Excitatory Amino Acids and Their Antagonists

Definition There are more than 100 known excitatory amino acids (EAAs) and the large majority of them are non-proteinforming amino acids initially purified from algae or fungi (Lubec and Rosenthal 1990). The endogenous EAAs Glutamate (Glu) and Aspartate act in the nervous system as excitatory neurotransmitters; they are released from neurons and they induce neuronal excitation via ionotropic and metabotropic Glu receptors (iGluRs and mGluRs). Related endogenous molecules like N-acetylaspartylglutamate (NAAG) could also belong to the group of EAAs, but they have no demonstrated neurotransmitter properties. EAAs are usually grouped to distinguish them from AAs like GABA, Glycine, or Taurine exerting inhibitory effects on neuronal cells. Excitatory neurotransmission is present in central and peripheral nervous system, and in the periphery EAAs contribute to the regulation of gastrointestinal motility, pain sensation, as well as respiratory and cardiovascular functions. In nonneuronal cells, Glu receptors and transporters exert a role in the control of proliferation, immune response, and bone tissue dynamic (Gill and Pulido 2005).