SELECTIVE ANTINOCICEPTIVE EFFECT OF EXCITATORY AMINO-ACID ANTAGONISTSIN INTACT AND ACUTE SPINAL RATS

Results of neurophysiologic and behavioral studies suggest that excita tory amino acid (EAA) antagonists may provide a new class of analgesic agents, which might be selective for neuropathic pain states that are resistant to opiate treatment. Most of these paradigms involve animal models of peripheral injury. The present study evaluated the antinoci ceptive effect of spinally [intrathecally (IT)] administered EAA antag onists after central injury, produced by spinal transection. Intrathec al injection of the AMPA/kainate receptor antagonist 6-cyano-7-nitroqu inoxaline-2,3-dione produced dose-dependent antinociception on the the rmal tail withdrawal [tail-flick (TF)] reflex test in Intact rats, whi ch was significantly potentiated after spinal transection. In contrast , IT injection of the NMDA antagonist, 2-amino-5-phosphonopentanoic ac id (AP5) did not affect the TF in intact rats, but significantly block ed this response in spinal rats. However, some of the spinal rats did not recover the reflex, suggesting a possible toxic action of AP5.