Innervation of the sacroiliac joint in rats by calcitonin gene‐related peptide‐immunoreactive nerve fibers and dorsal root ganglion neurons

Abstract

The sacroiliac joint (SIJ) can be a source of low back pain. Calcitonin gene‐related peptide (CGRP) has been reported to play a significant role in nociceptive processing. However, the occurrence of CGRP‐immunoreactive (CGRP‐ir) sensory nerve fibers in the SIJ has not been fully defined. The present study investigated CGRP‐ir nerve fibers supplying the SIJ. CGRP‐ir nerve fibers in the vicinity of the SIJ cartilage and CGRP‐ir neurons in the bilateral dorsal root ganglia (DRG) were examined immunohistochemically by administering anti‐CGRP antiserum to rats. The SIJ was decalcified and cut into sections, and the CGRP‐ir fibers around the SIJ cartilage were counted under microscopy. In another group, fluoro‐gold (F‐G), a neural tracer, was injected into the SIJ from the dorsal or ventral side with dorsal or ventral denervation. The number of F‐G‐labeled CGRP‐ir neurons was counted in individual DRG. CGRP‐ir fibers were observed more frequently in the tissues adjacent to the cranial part of the SIJ surface. In the case of dorsal denervation (ventral nerve supply), the CGRP‐ir neurons composed 18.2% of the F‐G‐labeled neurons. In the case of ventral denervation (dorsal nerve supply), the CGRP‐ir neurons composed 40.9% of the F‐G‐labeled neurons. There was a statistically significant difference in the number of CGRP‐ir neurons between the ventral and dorsal nerve supplies to the SIJ. The cranial part of the dorsal side could be the part most associated with pain in the SIJ. Clin. Anat. 20:82–88, 2007.