Differential effects of MK-801, a N-methyl-D-aspartate non-competitive antagonist, on the dorsal horn neuron hyperactivity and hyperexcitability in neuropathic rats.

N-methyl-D-aspartate (NMDA) involvement in altered spinal neuron activity following peripheral nerve injury has been investigated in rats with chronic constriction of the sciatic nerve. Extracellular single neuron recordings were performed, in anesthetized, paralyzed rats, from the sciatic spinal cord segments (lumbar, L5-L6) ipsilateral to the constriction, and the effect of iontophoresized MK-801, an NMDA receptor non-competitive antagonist, was tested on baseline hyperactivity and hyperresponsiveness to noxious stimulation. The results show that baseline activity was unaffected whereas the noxious evoked responses were significantly modified, there being amplitude reduction and after-discharges suppression. The different role of NMDA in the abnormal pain states related to the abnormal neuronal activities is discussed.