Effects of dexmedetomidine on expression of spinal matrix metalloproteinase-9 in a rat model of neuropathic pain

Objective To evaluate the effects of dexmedetomidine on the expression of spinal matrix metalloproteinase-9 (MMP-9) in a rat model of neuropathic pain (NP).Methods Eighty-one adult male SpragueDawley rats,weighing 190-230 g,were randomly divided into 3 groups (n =27 each) using a random number table:sham operation group (group S); group NP; dexmedetomidine group (group Dex).The animals were anesthetized with intraperitoneal 10％ chloral hydrate 350 mg/kg.The right sciatic nerve was exposed and 4 loose ligatures were placed on the sciatic nerve at 1 mm intervals with 4-0 silk thread in NP and Dex groups.In group Dex,dexmedetomidine 50 μg/kg was injected intraperitoneally once a day starting from the end of operation until the animals were sacrificed.The equal volume of normal saline was given instead of dexmedetomidine in S and NP groups.Paw withdrawal threshold to von Frey filament stimulation (MWT) and paw withdrawal latency to thermal stimulation (TWL) were measured at 1 day before operation (To,baseline) and 5,9 and 16 days after operation (T1-3).Nine animals were sacrificed after measurement of pain threshold at T1-3 and their lumbar segments (L4,5) of the spinal cord were removed for detection of MMP-9 expression (by immuno-histochemistry) and tumor necrosis factor-alpha (TNF-α) content (by ELISA).Results Compared with group S,MWT was significantly decreased,TWL was shortened,and the levels of MMP-9 and TNF-α were increased at T1-3 in NP and Dex groups.Compared with NP group,MWT was significantly increased,TWL was prolonged,and the levels of MMP-9 and TNF-α were decreased at T1-3 in Dex group.Conclusion Dexmedetomidine can inhibit up-regulation of MMP-9 expression,and decrease inflammatory responses,thus attenuating NP in rats. Key words: Dexmedetomidine ;  Neuralgia ;  Spinal cord ;  Matrix metalloproteinase 9