Study design: An investigation of c-fos activation pattern in spinal neurons of intact adult rats after acute bouts of treadmill locomotion. Objectives: To map spinal neurons that are involved in quadrupedal treadmill stepping of intact adult rats by using c-fos as a marker. Settings: Los Angeles, CA, USA. Methods: Spinal cord sections of rats that were not stepped (n ¼ 4) were used to map the FOSpositive ( þ ) neurons under basal conditions. The stepped group (n ¼ 16) was placed on a treadmill to step quadrupedally for varying durations to induce c-fos activity. Spinal cord sections of thoracic and lumbar segments of Stp and Nstp rats were processed using a c-fos antibody, choline acetyl transferase and heat shock protein 27 for identifying motoneurons. Results: Stepping induced a greater number of FOS þ neurons than was observed in rats that did not step on the treadmill. There was a rostrocaudal and a dorsoventral gradient of FOS labeled neurons. The number of FOS þ neurons increased with the duration of treadmill stepping. Significant increases in FOS þ neurons were in the most medial parts of laminae IV, V, and VII. FOS þ motoneurons increased with treadmill stepping, particularly in large motoneurons (X700 mm 2 ). Conclusion: These data suggest that FOS can be used to identify activity-dependent neuronal pathways in the spinal cord that are associated with treadmill stepping, specifically in lamina VII and in alpha motoneurons. Sponsorship: NIH NS16333, NS40917, and the Christopher Reeve Paralysis Foundation (CRPF VEC 2002).

Object Appropriate animal models of disc degeneration are critical for the study of proposed interventions as well as to further delineate the degenerative process. The purpose of this study was to characterize a porcine model for disc degeneration confirmed on magnetic resonance (MR) imaging studies and histological analysis. Methods Twelve miniature pigs were used (weight 48–65 kg) to study degeneration in the lumbar spine. Under fluoroscopic guidance, the disc was percutaneously punctured with a 3.2-mm-diameter trephine to a 5-mm depth into the annulus fibrosus. Control and experimental levels were randomized among 6 levels in the lumbar spine. The unlesioned spinal levels were used as controls and were compared with lesioned levels. Magnetic resonance imaging grading and disc height were serially recorded preoperatively, and at 5, 8, 19, 32, and 39 weeks postoperatively. The animals were killed in groups of 3 at 7, 18, 32, and 41 weeks postinjury, and the discs were examined histopathologically. Results Consistent, sequential, and progressive degeneration of the annular injury was observed on MR imaging and histopathological studies from the time of injury to the final time point. The disc height and the disc height index also sequentially decreased from the time of the injury in a consistent manner. The uninjured control levels did not show any progressive degeneration and maintained their normal state. Conclusions Based on MR imaging and histopathological findings, the authors demonstrated and characterized a reliable model of sequential disc degeneration in miniature pigs with percutaneous injury to the annulus fibrosus. In the early stages, as soon as 5 weeks after injury, significant disc degeneration was seen on MR imaging grading with decreases in disc height. This degeneration did not improve by the final time point of 39 weeks.