Increased Innervation of the Intervertebral Disc Is Associated with Glial Cell Growth

Introduction: In health, the intervertebral disc is generally avascular and sparsely innervated. Those few nerves and blood vessels present are generally restricted to the outer areas of the annulus fibrosus where they lie predominantly between concentric layers of matrix (called lamellae). During disc degeneration, however, many more nerves are seen within the annulus, often in association with an increased vasculature. In addition, these nerves penetrate further into the disc, towards the inner annulus and nucleus pulposus (1-3). Such new nerve growth into degenerate discs, particularly nerves immunopositive for GAP-43 entering into deeper regions of the disc, has been associated with discogenic low back pain (3). We are currently investigating the mechanisms that regulate the capacity of nerves to penetrate the intervertebral disc. One aspect of this study has been to determine the presence of nerve support cells within discs and here we show that cells that are immunopositive for the glial cell marker, GFAP, are commonly seen in association with nerves.