CGRP-immunoreactive nerve fibers projecting to lumbar facet joints through the paravertebral sympathetic trunk in rats.

We previously reported that the L5-6 facet joint is innervated from DRGs from L1 to L5 and the paravertebral sympathetic ganglia from T12 to L6 in rats. In the present study, to determine the sensory pathway from L5-6 facet joint, we placed the fluorescent carbocyanine dye, DiI, in the L5-6 facet joint, and examined the paravertebral sympathetic trunks and ganglia bilaterally. We found some DiI-labeled nerve fibers exhibiting calcitonin gene-related peptide (CGRP)-immunoreactivity, and some DiI-labeled neurons surrounded by CGRP-immunoreactive varicose fibers in the ganglia. The results suggest that a sensory pathway from the L5-6 facet joint to L1 and/or L2 DRGs is present in the paravertebral sympathetic trunk, and that sensory nerve fibers may connect with sympathetic postganglionic neurons projecting to lumbar facet joints.