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

Study Design. The vertebral levels of dorsal root ganglia innervating the d orsal portion of the L5-L6 intervertebral disc were investigated in rats us ing a retrograde transport method. The pathways and functions of nerve fibe rs supplying the dorsal portion of the disc were determined by denervation and immunohistochemistry. Objectives. The dorsal portion of the lumbar intervertebral disc has been r eported to be innervated segmentally, hut anesthetic block of the paraverte bral sympathetic trunks and the L2 spinal nerve can relieve discogenic low back pain. In the current study, the sensory innervation of the dorsal port ion of the L5-L6 intervertebral disc was investigated, because the disc ana tomically corresponds to the L4-L5 disc in humans, and the dorsal portion o f the human L4-L5 disc is frequently subject to injury that causes low back pain. Methods. A retrograde transport of Fluoro-Gold (F-G; Fluorochrome, Denver, CO) was used. Subjects included nontreated control (n = 32) and sympathecto mized rats in which paravertebral sympathetic trunks were removed from L2 t o L3 (n = 9). In a ventral approach, Fluoro-Gold crystals were placed on th e dorsal portion of the L5-L6 disc, and labeled neurons in the bilateral do rsal root ganglia from T10 to L6 were counted. Results. Fluoro-Gold crystals did not leak from the dorsal portion of the L 5-L6 disc in 14 of the 32 nontreated rats and in 5 of the 9 sympathectomize d rats. These rats were used for analysis. Fluro-Gold-labeled neurons were found in dorsal root ganglia from T13 to L6 in the 14 control rats but only from L2 to L6 in the 5 sympathectomized rats. Conclusion. The dorsal portion of the L5-L6 disc of rats was shown to be mu ltisegmentally innervated by the T13 to L6 dorsal root ganglia. The sensory fibers from T13, L1, and L2 dorsal root ganglia were shown to innervate th e dorsal portion of the L5-L6 disc th rough the paravertebral sympathetic t runks. In contrast, those from the L3-L6 dorsal root ganglia may innervate the dorsal portion of the L5-L6 disc through the sinuvertebral nerves.