BACKGROUND: The changes of calcitonin gene-related peptide (CGRP) expression are closely associated with peripheral nerve injury, whereas it should be further investigated whether the damage of central nerve can lead to the changes of CGRP expression, and whether it is associated with the neural regeneration and repair.OBJECTIVE: To observe the changing law of CGRP expression in the anterior and posterior horns of spinal cord following brachial plexus injury.DESIGN: A randomized controlled trial.SETTINGS: Department of Anatomy, Yunyang Medical College; Department of Anatomy, Basic Medical College, Sun Yat-sen University.MATERIALS: Sixty-five adult male SD rats of clean degree, weighing 180 - 220 g, provided by the experimental animal center of the Basic Medical College, Sun Yat-sen University, were randomly divided into control group (n =5) and experimental group (n =60), and the latter was subdivided into three damage groups: avulsion of anterior root group (n =20), disjunction of posterior root group (n =20) and transection of spinal cord group (n =20). Diaminobenzidine (DAB) chromogen, rabbit anti-CGRP polyclonal antibody were the products of Sigma Company; Leica image analytical apparatus was produced by QUIN Company (Germany); Histotome by Sigma Company.METHODS: The experiments were carried out in the Department of Anatomy, Basic Medical College, Sun Yat-sen University from September 2004 to March 2005. Three kinds of models of brachial plexus injury were established: In the avulsion of anterior root group, right C7 anterior root was avulsed, and the distal nerve residual root was transected. In the disjunction of posterior root group, right C7 anterior root was avulsed and right C5 - T1 posterior horns were cut to block the sensory afferent pathway. In the transection of spinal cord group, right C7 anterior root was avulsed and C5-6 segments of right spinal cord were semi-transected to block the cortical descending pathway. In the control group, C5 - T1 vertebral plates were prayed open, and then the skin was sutured. The C7 segments of spinal cord were removed on the 1st, 3rd, 7th and 14th days postoperatively respectively, and the CGRP expressions in the anterior and posterior horns of spinal cord were determined and analyzed using immunohistochemical method and image analysis.MAIN OUTCOME MEASURES: ① Number of CGRP immuno-positive motor neurons in the anterior horn of spinal cord; ② Total area of CGRP immuno-positive fibers in the posterior horn of spinal cord.RESULTS: All the 65 rats were involved in the analysis of results. ① Number of CGRP immuno-positive motor neurons in the anterior horn of spinal cord: CGRP immuno-positive motor neurons could be observed in the anterior horns of C7 spinal cord in the control group and damage groups, the neurons had big cell body with stained cytoplasm, appeared as brown granules, and mainly distributed in the ventral lateral anterior horn of spinal cord. On the 1st day postoperatively, the number of CGRP positive neurons was obviously higher in the in the avulsion of anterior root group than in the control group (P ＜ 0.01), whereas obviously lower in the disjunction of posterior root group than in the control group (P ＜ 0.01), and there was no obvious difference between the transection of spinal cord group and the control group (P ＞ 0.05). On the 7th day, the numbers of CGRP positive neurons in the damage groups were obviously higher than that in the control group (P ＜ 0.01), also obviously different from those on the 1st day in the same group respectively (P ＜ 0.01). On the 14th day, the number of CGRP positive neurons in the disjunction of posterior root group was decreased, but there was no obvious difference as compared with that in the control group, whereas those in the avulsion of anterior root group and transection of spinal cord group were still obviously higher than that in the control group (P ＜ 0.01). The number of CGRP positive neurons was the most in the avulsion of anterior root group, followed by the transection of spinal cord group, and the least in the disjunction of posterior root group, and there were significant differences among them (P ＜ 0.01). ② Total area of CGRP immuno-positive fibers in the posterior horn of spinal cord: Dense CGRP immuno-positive nerve fibers distributed in the layers Ⅰ and Ⅱ of the C7 posterior horn of spinal cord in the control group. On the 1st day postoperatively, the total areas of CGRP positive fibers in the avulsion of anterior root group and transection of spinal cord group were obviously larger than that in the control group (P ＜ 0.01), whereas there was no obvious difference between the disjunction of posterior root group and control group. On the 7th day, the CGRP expression in the posterior horn of spinal cord decreased to the lowest level in the disjunction of posterior root group, whereas there were no obvious differences in the avulsion of anterior root group and transection of spinal cord group as compared with that in the control group (P ＞ 0.05). On the 14th day, the area continued to decrease in the avulsion of anterior root group and transection of spinal cord group, and it was obviously lower in the transection of spinal cord group than in the control group (P ＜ 0.01), and it was slightly increased in the disjunction of posterior root group as compared with that on 7th day, but still obviously lower than that in the control group (P ＜ 0.01).CONCLUSION: The expression and role of CGRP are in discrepancy in the anterior and posterior horns of spinal cord after brachial plexus injury. The CGRP in anterior horn of spinal cord are derived from the cell body of motor neurons, and may be involved in the repairing mechanism of nerve injury regeneration;Whereas those in the posterior horn are mainly derived from posterior root ganglion, and may be associated with the conduction of noxious stimulations.