ANTINOCICEPTION INDUCED BY INUS)-2-CARBOXYPIPERAZIN-4-YL)-PROPYL-1-PHOSPHONIC ACID (CPP), AN N-METHYL-D-ASPARTATE (NMDA) COMPETITIVE ANTAGONIST, PLUS 6,7-DINITROQUINOXALINE-2,3-DIONE (DNQX), A NON-NMDA ANTAGONIST, DIFFERS FROM THAT INDUCED BY MK-801 PLUS DNQX

Excitatory amino acid receptors have been implicated in mediating pain . (+/-)-2-Carboxypiperazin-4-yl)-propyl-1-phosphonic acid (CPP), a com petitive N-methyl-D-aspartate (NMDA) antagonist and MK-801, a phencycl idine (PCP) ligand and non-competitive NMDA antagonist, were injected intrathecally in mice alone or in combination with 6,7-dinitroquinoxal ine-2,3-dione (DNQX), a non-NMDA antagonist. When tested in the formal in model of pain, antinociception following CPP plus DNQX was greater than that after MK-801 plus DNQX in both the acute and tonic phases. T hese dissimilarities are not consistent with activity of CPP and MK-80 1 at the same sites in the spinal cord.