120) Physiological relevance of a rodent model of degenerative disc disease

The American Pain Society estimates that 45% of the U.S. population seeks medical help for chronic pain at some point in their lives. Those affected include the 15% of Americans with persistent back pain. There are many potential sources including degenerative disc disease (DDD), which is one of the primary causes of chronic low back pain (LBP). Natural age related degeneration of lumbar intervertebral discs (IVDs) is common, but abnormal degeneration can occur, often resulting in pain, instability, and biomechanical movement disadvantages. IVDs are articular joints between vertebra and they act to distribute loads placed on the spine through hydrostatic pressures. The disc is composed of the exterior annulus fibrosus surrounded by ligaments and the central nucleus pulposus. The presence of nerve fibres and nerve endings in the lumbar IVDs and in the adjacent longitudinal ligaments has been demonstrated by many authors. In healthy discs, innervation is mostly limited to the posterior and anterior longitudinal ligaments and the superficial layers of the annulus fibrosus. Human IVDs are supplied by a variety of nerve fiber types including Cand A-delta fibers (substance P and CGRP), A-beta fibers (myelin basic protein) and sympathetic fibers entering from the sympathetic nerve truck. Specialized sensory nerve endings have also been described (i.e. pacinian corpuscles and golgi tendon organs). The goal of this study is to assess if the rat is of potential use to develop a relevant, rodent model of DDD-related LBP. Lumbar IVD innervation will be assessed in rats by immunohistochemistry to examine total innervation and fiber type(s). Preliminary results suggest that IVD innervation in rat and human are similar. Supported by grants from the Canadian Institute for Health Research (LSS) and the American Pain Society (MM).