Effects Of Dexmetomidine On Visceral Pain In Rats:the Role Of α₂ Adrenergic Receptors In Locus Coeruleus

Objective:To evaluate the effet of dexmedetomidine on visceral pain in rats and the role of?₂ adrenergic receptors in locus coeruleus（LC）.Methods:Thirty-two healthy adult male Sprague-Dawley rats,weighing 250-300 g,were divided into 4 groups（n=8 each）using a random number table method:control group（group c）,visceral pain group（group VP）,dexmedetomidine group（group DEX）and?₂-adrenergic receptor antagonist atipamezole group（group AP）.?₂-adrenergic receptor antagonist atipamezole522?g/kg was intramuscularly injected in group AP,and the equal volume of normal saline was given instead in C,VP and DEX groups.At 10 min after intramuscular injection,dexmedetomidine 10?g/kg was injected via the tail vein in DEX and AP groups,and the equal volume of normal saline was given instead in C and VP groups.VP,DEX and AP groups received intraperitoneal injection of 0.9%acetic acid 10 ml/kg to make the visceral pain model at 15 min after injection via the tail vein.The cumulative visceral pain score was recorded within 60 min after acetic acid injection.The number of c-fos positive cells in LC was detected by immunohistochemistry,and the content of norepinephrine（NA）in the spinal cord were detectedd by enzyme-linked immunosorbent assay at 2 h after acetic acid injectionResults:Compared with group C,the cumulative visceral pain scores,the number of c-fos positive cells in LC and content of NA in the spinal cord were significantly increased in VP,DEX and AP groups（P<0.05）.Compared with group VP,the cumulative visceral pain scores,the number of c-fos positive cells in LC and content of NA in the spinal cord were significantly decreased in DEX and AP groups（P<0.05）.Compared with group DEX,the cumulative visceral pain scores,the number of c-fos positive cells in LC and content of NA in the spinal cord were significantly increased in group AP（P<0.05）.Conclusion:Dexmedetomidine can alleviate visceral pain in rats,and the mechanism is partially related to activating?₂ adrenergic receptors in LC.