Dipeptide antagonists of amino acid-induced and synaptic excitation in the frog spinal cord

The dipeptide gamma-D-glutamylglycine (gamma DGG) antagonizes amino acid-induced depolarization and synaptic excitation in the isolated hemisected spinal cord of the frog. In general, the effects of this compound resembled those of the structurally similar D-alpha-aminosuberate (D alpha AS) in being more effective against N-methyl-D-aspartate (NMDA)-induced responses than against responses induced by other excitatory amino acids. However gamma DGG appeared to be more effective than D alpha AS in depressing kainate-induced responses. Similar, though weaker, effects were produced by the L isomer of the dipeptide (gamma LGG), a natural brain constituent.