Changes in neuroactive substances in a rat model of neuropathic pain and the role of hyperexcitability in neurons of spinal cord-dorsal colum-thalamus pathway

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The aim of this study was to examine the change in mRNA expression of inhibitory amino acid (GABAA and glycine) receptor subunits and neuropeptides in DRG of an experimental rat model of neuropathic pain. Rats received tight ligations of left L5 spinal nerves under deep anesthesia. After confirmation of the presence of neuropathic pain behaviors at 7th postoperative days, L4,5 DRG and spinal cord were dissected out for in situ hybridization and immunohistochemistry. L5 DRG neurons showed the down-regulated expression ofmRNAs of gamma2-GABAA receptor and beta1-glycine receptor subunits. Immunohistochemistry with calcitonin gene-related peptide antibody revealed that increased immunostaining in laminae III-IV of L4-5 spinal cord These data suggest that depressed inhibitory effect of amino acid and increased excitatory effect ofneuropeptide on dorsal horn neurons may contribute to the pathomechanisms of neuropathic pain.