Effect of intrathecal dexmedetomidine on expression of substance P and c-fos in spinal dorsal horns of rats with visceral pain

Abstract

Objective To evaluate the effect of intrathecal dexmedetomidine on expression of substance 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 established, dexmedetomidine 20 μl (1 μg/kg) and dexmedetomidine 1 μg/kg plus atipamezole 1 μg/kg (20 μl) were intrathecally injected in D and DA groups, respectively, and the equal volume of normal saline 20 μl was given instead in C and VP groups.Visceral pain index (VPI) was recorded at 1 h after intraperitoneal 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 significantly 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. Key words: Dexmedetomidine; Injections, spinal; Viscera; Pain; Substance P; Proto-oncogene proteins c-fos