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Objective To evaluate the relationship betweenα2 adrenergic receptors and expression of Nav1. 8 in dorsal root ganglion (DRG) neurons, and to illuminate the mechanism of dexmedetomidine-induced reduction of acute visceral pain in rats. Methods Thirty-two clean-grade healthy adult male Spra-gue-Dawley rats, aged 6-8 weeks, weighing 180-220 g, were divided into 4 groups ( n=8 each) using a random number table method: control group ( group C ) , acute visceral pain group ( group VP ) , dexmedetomidine group (group D), and dexmedetomidine plus atipamezole group (group DA). In VP, D and DA groups, 10-3 mmol∕L capsaicin 1. 3 ml was injected into the rectum at a dose of 10-3 mmol∕L to establish the acute visceral pain model, while the equal volume of normal saline was given instead in group C. Atipamezole 1 mg∕kg was subcutaneously injected through the back of the neck at 20 min before establishing the model in group DA. Dexmedetomidine 10μg∕kg was injected through the tail vein at 15 min before establishing the model in D and DA groups, while the equal volume of normal saline was given instead at the correspording time points in C and VP groups. The visceral pain behavior score was recorded at 1 h after establishing the model. The animals were then sacrificed, and DRGs of the lumbar segment (L3-6) were removed for determination of the number of Nav1. 8 positive DRG neurons (by immunohisto-chemistry) and expression of Nav1. 8 mRNA (by quantitative real-time polymerase chain reaction). Results Compared with group C, the visceral behavior scores and the number of Nav 1. 8 positive DRG neurons were significantly increased, and the expression of Nav 1. 8 mRNA was up-regulated in VP, D and DA groups (P<0. 05). Compared with group VP, the visceral behavior score and the number of Nav1. 8 positive DRG neurons were significantly decreased, and the expression of Nav 1. 8 mRNA was down-regulated in D and DA groups (P<0. 05). Compared with group D, the visceral behavior scores and the number of Nav1. 8 positive DRG neurons were significantly increased, and the expression of Nav1. 8 mRNA was up-regulated in group DA ( P<0. 05) . Conclusion The mechanism by which dexmedetomidine reduces acute visceral pain is related to activatingα2 adrenergic receptors and to down-regulating the expression of Nav1. 8 in DRG neu-rons of rats.
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Objective To investigate the effect of dexmedetomidine pretreatment on inflammatory visceral pain in rats. Methods Forty healthy male Wistar rats, weighing 200-300 g, aged 6-8 weeks, were divided into 5 groups ( n=8 each) using a random number table method: control group ( group C) , visceral pain group ( group VP ) , dexmedetomidine 1 μg∕kg group ( group Dex1 ) , dexmedetomidine 5μg∕kg group ( group Dex2) and dexmedetomidine 10μg∕kg group ( group Dex3) . The model of inflammato-ry visceral pain was established by intraperitoneally injecting 0. 9% acetic acid 10 ml∕kg in VP, Dex1, Dex2 and Dex3 groups, and the equal volume of normal saline was given instead in group C. At 15 min be-fore intraperitoneal injection, dexmedetomidine 1, 5 and 10μg∕kg were injected via the tail vein in Dex1, Dex2 and Dex3 groups, respectively, and the equal volume of normal saline was given instead in C and VP groups. Behavioral changes of rats were observed within 60 min after the model was established, and viscer-al pain index ( VPI) was calculated. Blood samples were collected from the hearts at 180 min after establis-hing the model for determination of tumor necrosis factor-alpha ( TNF-α) concentrations in serum. The ani-mals were then sacrificed, and colons were obtained for examination of pathological changes with a light mi-croscope. Results Compared with group C, the VPI and serum TNF-α concentrations were significantly increased in VP and Dex1-2 groups, and the serum TNF-αconcentrations were significantly increased ( P<0. 05), and no significant change was found in VPI in group Dex3 (P>0. 05). Compared with group VP, the VPI and serum TNF-α concentrations were significantly decreased (P<0. 05), and the pathological changes of colon tissues were significantly attenuated in group Dex1-3. Compared with group Dex1, the VPI and serum TNF-α concentrations were significantly decreased ( P<0. 01) , and the pathological changes of colon tissues were significantly attenuated in Dex2-3 groups. Compared with group Dex2, the VPI and ser-um TNF-α concentrations were significantly decreased (P<0. 01), and the pathological changes of colon tissues were significantly attenuated in group Dex3. Conclusion Dexmedetomidine pretreatment can miti-gate inflammatory visceral pain in rats.
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Objective To evaluate the effect of intrathecal dexmedetomidine on expression of sub-stance P (SP) and c-fos in the spinal dorsal horns of rats with visceral pain. Methods Thirty-two clean-grade 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 (C group), visceral pain group (VP group), dexmedetomidine group (D group) and dexmedetomidine plus atipamezole group (DA group). VP, D and DA groups received intraperitoneal injection of 0. 9% acetic acid 10 ml∕kg to establish the model of visceral pain, while group C received the equal volume of normal saline instead. At 10 min before the model was es-tablished, dexmedetomidine 20 μl (1μg∕kg) and dexmedetomidine 1μg∕kg plus atipamezole 1μg∕kg (20μl) were intrathecally injected in D and DA groups, respectively, and the equal volume of normal saline 20μl was given instead in C and VP groups. Visceral pain index ( VPI) was recorded at 1 h after intraperito-neal injection, and then rats were sacrificed, and the dorsal horns of the spinal cord ( L4-6 ) were removed for determination of the expression of SP and c-fos by immunohistochemistry. Results Compared with group C, VPI was significantly increased, and the expression of SP and c-fos was up-regulated in VP, D and DA groups (P<0. 05). Compared with group VP, VPI was significantly decreased, and the expression of SP and c-fos was down-regulated in D and DA groups (P<0. 05). Compared with group D, VPI was signifi-cantly increased, and the expression of SP and c-fos was up-regulated in group DA ( P<0. 05) . Conclusion Intrathecal dexmedetomidine reduces the visceral pain through inhibiting the expression of SP and c-fos in the spinal dorsal horns, which is related to the α2-adrenergic receptor in spinal dorsal horns of rats.
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Objective To evaluate the effect of dexmedetomidine on visceral pain in rats and the role of α2 adrenergic receptors in locus coeruleus (LC).Methods Thirty-two healthy adult male SpragueDawley 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 α2-adrenergic receptor antagonist atipamezole group (group AP).α2-adrenergic receptor antagonist atipamezole 522 μg/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 μg/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 detected by enzyme-linked immunosorbent assay at 2 h after acetic acid injection.Results 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 α2 adrenergic receptors in LC.