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BACKGROUND: Valproic acid has been reported to decrease apoptosis, promote neuronal differentiation of brain-derived neural stem cells, and inhibit glial differentiation of brain-derived neural stem cells.OBJECTIVE: To investigate the effects of valproic acid on proliferation of endogenous neural sterm cells in a rat model of spinal cord injury.DESIGN, TIME AND SETTING: A randomized, controlled, neuropathological study was performed at Key Laboratory of Trauma, Buming, and Combined Injury, Research Institute of Surgery, Daping Hospital, the Third Military Medical University of Chinese PLA between November 2005 and February 2007.MATERIALS: A total of 45 adult, Wistar rats were randomly divided into sham surgery (n=5), injury(n=20), and valproic acid (n=20) groups. Valproic acid was provided by Sigma, USA.METHODS: Injury was induced to the T10 segment in the injury and valproic acid groups using the metal weight-dropping method. The spinal cord was exposed without contusion in the sham surgery group. Rats in the valproic acid group were intraperitoneally injected with 150 mg/kg valproic acid every 12 hours (twice in total).MAIN OUTCOME MEASURES: Nestin expression (5 mm from injured center) was detected using immunohistochemistry at 1, 3 days, 1, 4, and 8 weeks post-injury.RESULTS: Low expression of nestin was observed in the cytoplasm, but rarely in the white matter of the spinal cord in the sham surgery group. In the injury group, nestin expression was observed in the ependyma and pia mater one day after injury, and expression reached a peak at 1 week (P