Evidence for two pharmacologically distinct populations of glutamate-activated first order interneurons in a vertebrate spinal cord.

The Atlantic stingray, Dasyatis sabina, is being employed as a simple vertebrate model for studying spinal cord circuitry. Current investigations are aimed at determining the role of excitatory amino acids in the production of spinal reflexes. It is generally believed that primary afferents in vertebrates release a transmitter, probably glutamate, onto first order interneurons which act on non-N-methyl-D-aspartate (NMDA) receptors (Davies and Watkins, 1983). In this communication we sought to test this hypothesis by assessing the pharmacological profile of glutamate-activated first order interneurons in the stingray spinal cord in vivo. Glutamate has been shown to be a mixed agonist on mammalian spinal neurons, capable of activating both NMDA and non-NMDA receptors (Mayer and Westbrook, 1985). By using the selective NMDA antagonist DL-2-amino-5-phosphonovaleric acid (APV) (Davies et al, 1981), and the nonselective excitatory amino acid antagonist kynurenate (Perkins and Stone, 1982) we are able to determine if glutamate is acting primarily on NMDA or non-NMDA receptors.