MK-801 reduces non-noxious stimulus-evoked Fos-like immunoreactivity in the spinal cord of rats with chronic constriction nerve injury.

We investigated the role of N-methyl-D-aspartate (NMDA) receptors on non-noxious stimulus-induced pain by examining the effect of MK-801, a non-competitive NMDA receptor antagonist, on Fos-like immunoreactivity (FLI) in the spinal dorsal horn by non-noxious stimulation to rats with chronic constriction injury (CCI) of the sciatic nerve. In CCI rats that did not receive the non-noxious stimulus, FLI was significantly increased in laminae V/VI of the dorsal horn at the 7th and 14th days after surgery relative to sham rats. When CCI rats received non-noxious stimuli, rubbing the plantar of the hind paw, FLI in laminae I/II at the 14th day was significantly increased relative to CCI rats that did not receive the stimulation. In sham rats, the same stimulus significantly decreased FLI in laminae III/IV and V/VI at the 7th and 14th day. When MK-801 was administered intraperitoneally prior to non-noxious stimulation in CCI rats at the 14th day after surgery, the stimulus-induced FLI in laminae I/II in CCI rats was significantly reduced. This study indicates that NMDA receptor is involved in upregulating FLI in response to non-noxious stimulation of CCI rats.