The action of quinolinate in the rat spinal cord in vitro

The responses of dorsal horn neurones to the excitatory amino acids quisqualate, kainate, N-methyl-D-aspartate (NMDA), and quinolinate have been examined in an in vitro preparation of the rat spinal cord. The antagonism of these responses by iontophoretically applied D-(-)-2-amino-5-phosphonovalerate (DAPV), kynurenate, and acridinate was tested, and the results were compared with data obtained from the spinal cord in vivo. The pattern of antagonism was similar in both preparations, although the potencies of agonists and antagonists were found to be significantly greater in vitro. The antagonism of amino acid induced firing of neurones was also recorded during the application of DAPV and kynurenate in the bathing medium. Dose-response curves and IC50 values were determined for these antagonists against all four agonists. The responses to quinolinate were antagonized differently from those to NMDA, quisqualate, or kainate, suggesting that quinolinate does not act specifically through the NMDA receptor as it does in other regions, nor does it appear to act via two or more of the three archetypal amino acid receptors. These findings suggest that a fourth amino acid receptor responsible for quinolinate's action in the spinal cord may exist.