The therapeutic effect of dexmedetomidine on rat diabetic neuropathy pain and the mechanism

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Diabetic neuropathy pain (DNP) is a common chronic complication of diabetes characterized by spontaneous pain, hyperalgesia and allodynia. Dexmedetomidine is a selective α₂ adrenergic agonist that relieves sympathetic nervous tension and reduces the release of glutamate. Thus, it is possible that dexmedetomidine may relieve DNP as well. In this study, we examined the effect of dexmedetomidine on DNP in the presence or absence of the α₂ adrenergic antagonist yohimbine in rats utilizing a streptozotocin (STZ)-induced diabetes as a model of DNP. To examine DNP, we examined behavior using the mechanical withdrawal threshold (MWT) and thermal withdrawal latency (TWL) tests, and microglia and astrocyte activation was examined by immunofluorescence staining. The levels of pro-inflammatory cytokine TNF-α and IL-1β in the spinal cord were measured by ELISA. Cell apoptosis in spinal cord was examined by TUNEL assay. Glutamate production in caudal lumbar was measured by high performance liquid chromatograpy (HPLC). We found that STZ-treated rats had decreased pain threshold, elevated activation of microglia but not astrocytes, increased level of pro-inflammatory cytokines, increased apoptosis and glutamate production compared to control animals, and these effects were ameliorated by dexmedetomidine treatment. Pretreatment of yohimbine abolished almost all of the protective effects of dexmedetomidine except for glutamate production. In conclusion: our data confirmed that dexmedetomidine can relieve hyperalgesia in diabetic neuropathy pain, and protect spinal cord cells from apoptotic death. The mechanism may be related to dexmedetomidine-mediated inhibition of microglia activation, reduction of inflammatory reaction in the spinal cord, and suppression of glutamate production.