augh DA, Cftneyt O, Kallakuri S, Chen C. 2001. Effect of nucleus pulposus on the neural activity of dorsal root ganglion. Spine 26.940-4. Turk DC, Gatchel RI. 2002. Psychological approaches to pain management. 2nd ed. New York: Guilford. van Den Berg WB. 1999. The role of cytokines and growth factors in