Effect of dexmedetomidine on expression of c-fos protein in dorsal root ganglion neurons in a rat model of neuropathic pain

Objective To evaluate the effect of dexmedetomidine on the expression of c-fos protein in the dorsal root ganglion neurons in a rat model of neuropathic pain (NP).Methods Seventy-two adult male SpragueDawley rats,weighing 180-240 g,were randomly divided into 3 groups (n =24 each) using a random number table:sham operation group (group S),group NP,and 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 50μg/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.The mechanical paw withdrawal threshold (MWT) and thermal paw withdrawal latency (TWL) were measured at 1 day before ligation (T0,baseline) and 3,7 and 14 days after ligation (T1-3).Eight animals were sacrificed after measurement of pain threshold at T13 and the dorsal root ganglions of the lumbar segments (L44) were removed for detection of c-fos expression (by immuno-histochemistry).Results Compared with group S,MWT was significantly decreased,TWL was shortened,and the expression of c-fos protein was up-regulated at T1-3 in NP and Dex groups.Compared with NP group,MWT was significantly increased,TWL was prolonged,and the expression of c-fos protein was down-regulated at T1-3 in Dex group.Conclusion Dexmedetomidine can inhibit upregulation of c-fos protein expression,thus attenuating NP in rats. Key words: Dexmedetomidine ;  Neuralgia ;  Ganglia, spinal ;  Proto-oncogene proteins c-fos