• Kazuyo Yamauchi, Gen Inoue, Takana Koshi, Masaomi Yamashita, Toshinori Ito, Munetaka Suzuki, Yawara Eguchi, Sumihisa Orita, Masashi Takaso, Koichi Nakagawa, Yasuchika Aoki, Nobuyasu Ochiai, Shunji Kishida, Mitsuharu Endo, Toshihide Yamashita, Kazuhisa Takahashi, and Seiji Ohtori.
• Department of Orthopaedic Surgery, Graduate School of Medicine, Chiba University, Chiba, Japan. kazuyo@sb3.so-net.ne.jp
• Spine. 2009 Oct 1;34(21):2263-9.

Study DesignWe investigated the mechanism of discogenic low back pain using an in vitro model.ObjectiveTo evaluate the axonal growth and induction of a painful neuropeptide, substance P (SP), using rat dorsal root ganglion (DRG) neurons and degenerated human disc cells in vitro.Summary Of Background DataDegeneration of the lumbar intervertebral disc is a cause of low back pain. The pathologic mechanism is thought to be sensory nerve ingrowth into the inner layers of the degenerated intervertebral disc; however, the precise patho-mechanism has not been clarified.MethodsThe nucleus pulposus (NP) and annulus fibrosus (AF) of human intervertebral discs were harvested from patients with discogenic low back pain. Extracted medium from human degenerative intervertebral discs was cultured with neurons of rat DRGs. We evaluated the promotion of axonal growth and SP induction of DRG neurons in extracted medium from the NP and AF using immunocytochemistry.ResultsThe average length of growing axons in the NP and AF was significantly longer than that in the control (P < 0.005). That in the NP was significantly longer than that in the AF. The average length of growing axons in the NP was significantly shortened after anti-nerve growth factor (NGF)beta treatment (P < 0.005); however, that in the AF was not (P > 0.05). The percentage of SP-immunoreactive cells with growing axons was significantly higher only in the NP group compared with the control and AF groups (P < 0.005), and anti-NGFbeta treatment decreased the expression of SP in the NP group (P < 0.05).ConclusionExtracted medium from the NP and AF promoted axonal growth. Furthermore, NGF from the NP promoted axonal growth and induced SP. These in vitro results may suggest that NGF from the NP promotes the growth of sensory nerve fibers innervating the degenerated intervertebral disc and may induce SP related with pain transmission.

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