The purpose of this study was to evaluate the dorsal root ganglion (DR:kG) neurons which innervate the glenohumeral joint (GHJ) and subacromial bursa (SAB) in the rat contracture model. The contracture models were made by tying the humerus and scapula using 2-0 Fiber wire. First, contracture model was confirmed using X-ray 8 weeks after the operation. Abduction and total arc of the rotation were statistically significantly decreased in the contracture group. Two kinds of neurotracers such as fluoro-gold (FG) and dioctadecyl-tetramethyl-indocarbocyanine-perchlorate (DiI) were used to detect GHJ and SAB separately 8 weeks after the first operation. FGs were injected into the GHJ and DiI were injected into the SAB. Seven days after, DRGs were harvested between C1 and T1. Immunohistochemistry using calcitonin gene-related peptide was performed and the percentage of FG labeled CGRP-immunoreactive (ir) neurons in the total number of FG-labeled neurons and the percentage of DiI-labeled, CGRP-ir neurons in the total number of DiI-labeled neurons were evaluated. CGRP-ir DRG neurons were found to be 26.6% in the sham group and 54.4% in the contracture group of the total FG-labeled neurons. DiI-labeled, CGRP-ir DRG neurons were found to be 33.5% in the sham group and 51.7% in the contracture group of the total DiI-labeled neurons. The percentage of the CGRP-ir DRG neurons was significantly higher in the contracture group both in GHJ and SAB. These data demonstrated that the painful conditioned in shoulder contracture may be induced by the higher rate of existence of CGRP expression in DRG neurons.
