Immunohistochemical demonstration of sensory nerve fibers and endings in lumbar intervertebral discs of the rat

Although it is accepted that the intervertebral disc has a sensory component, it has not been previously shown by any specific method. Immunoreactivity of the physiologically active neuropeptide, calcitonin gene-related peptide (CGRP), was used as a specific marker of sensory nerve fibers and their endings in the intervertebral disc of the rat. In this study, positive fiber immunoreactivity was taken as an indication that those fibers were of sensory, and not sympathetic, origin. Immunoreactivity was found in the outer annulus fibrosus of all intervertebral discs studied. The CGRP-like immunoreactivity was also found in structures that resembled nerve endings. To the authors’ knowledge, this is the first report presenting detailed positive evidence of sensory fibers and their endings in the lumbar intervertebral disc of any mammalian species.