Sensory innervation of the dorsal portion of the lumbar intervertebral discs in rats

Study Design. The levels of dorsal root ganglions (DRGs) innervating the dorsal portion of the lumbar intervertebral discs from L1-L2 to L4-L5 were investigated in rats by the retrograde transport method. The pathways and functions of nerve fibers supplying the dorsal portion of the discs were investigated by denervation and immunohistochemistry. Objectives. To investigate the sensory innervation of the dorsal portion of the lumbar intervertebral discs in rats. Summary of Background Data. The dorsal portion of the L5-L6 disc has been reported to be innervated multi-segmentally, and anesthetic blockade of the paravertebral sympathetic trunks and the L2 spinal nerve can relieve discogenic low back pain. However, sensory innervation of the dorsal portion of the lumbar discs at other levels has not been clarified. Methods. A retrograde transport of Fluoro-Gold was used. We studied a nonsympathectomy group (n = 44) and a sympathectomy group (n = 50) in which paravertebral sympathetic trunks were resected from L1 to L5 levels. Using a ventral approach, Fluoro-Gold crystals were inserted into the dorsal portion of the L1-L2, L2-L3, L3-L4, and L4-L5 discs. Seven days after surgery, Fluoro-Gold-labeled neurons were counted in the bilateral dorsal root ganglions from T10 to L6. Results. Fluoro-Gold-labeled neurons were distributed in dorsal root ganglions from T11 to L5 levels in the nonsympathectomy group. However, in the sympathectomy group the number of labeled neurons was less than that of the nonsympathectomy group in T11. T12, and T13 dorsal root ganglions of the L1-L2 disc group, in T12, T13, and L1 dorsal root ganglions of the L2-L3 disc group, in T12, T13, L1, and L2 dorsal root ganglions of the L3-L4 disc group, and in T12, T13, L1, and L2 dorsal root ganglions of the L4-L5 disc group. Conclusion. The dorsal portion of the lumbar discs from L1-L2 to L4-L5 is multisegmentally innervated by the T11 through L5 dorsal root ganglions. Sensory fibers from the upper dorsal root ganglions innervate the dorsal portion of the discs via the paravertebral sympathetic trunks, although those from the lower dorsal root ganglions innervate via the sinuvertebral nerves. Furthermore, sensory nerve fibers enter the paravertebral sympathetic trunks through the corresponding ramus communicans and reach the dorsal root ganglions via each ramus communicans at the L2 and/or more cranial levels.