Excitatory Amino Acids: Receptor Differentiation by Selective Antagonists and Role in Synaptic Excitation

By the use of selective antagonists, excitatory amino acid receptors in the mammalian and amphibian spinal cords have been differentiated into at least two major types. One type is activated selectively by N-methyl-D2+-aspartate (NMDA) and blocked by a range of organic antagonists and also by Mg . Another type is activated by kainate and is relatively insensitive to NMDA antagonists. A correlation has been observed between NMDA-blocking activity and the ability of such antagonists to depress spinal synaptic excitation. The specificity of action of these antagonists suggests that NMDA receptors are probably transmitter receptors which mediate the effects of an excitatory amino acid transmitter. The identity of such a transmitter is discussed.