BACKGROUND: Ginkgo biloba leaf extract exhibits neuroprotective effects in spinal cord injury. However,the mechanisms of action remain unclear.OBJECTIVE: To investigate inducible nitric oxide synthase (iNOS) and Bcl-2/Bax expression in the injured spinal cord, and to explore the neuroprotective mechanisms of ginkgo biloba leaf extract in rats with spinal cord injury.DESIGN, TIME AND SETTING: The randomized, controlled, cell molecular biology experiment was performed at Soochow University, China from March 2007 to March 2008.MATERIALS: A total of 120 healthy, adult Sprague Dawley rats were selected for this study. Rat models of moderate acute thoracic (T9) spinal cord injury were established using the modified Allen method.Shuxuening injection was obtained from Zhenbaodao Pharmaceutical Co., Ltd., China. Methylprednisolone was purchased from North China Pharmaceutical Co., Ltd.METHODS: All rats were equally and randomly divided into four groups. Only the spinal cord was exposed in the sham operation group rats. In the trauma group, rats were not treated with drugs following spinal cord injury. Rats in the hormone group were intraperitoneally injected with 30 mg/kg methylprcdnisolone following spinal cord injury. Rats in the ginkgo biloba leaf extract group were intraperitoneally infused with a 1.0 mL/kg Shuxuening injection per day.MAIN OUTCOME MEASURES: At l hour, as well as 1, 3, 5, 7, and 14 days after spinal cord injury,iNOS- and Bcl-2/Bax-positive cells were quantified with immunohistochemistry. Pathological changes were detected using hematoxylin-eosin staining under an optical microscope.RESULTS: Spinal cord injury in the ginkgo biloba leaf extract and hormone groups was milder compared with the trauma group. Demyelination was significantly ameliorated and the necrotic cavity was obviously reduced in the injured spinal cord of rats in the ginkgo biloba leaf extract and hormone groups at each time point, iNOS expression was increased in the injured spinal cord, and reached a peak at 5 days. The number of iNOS-positive cells was lower in the ginkgo biloba leaf extract and hormone groups compared with the trauma group (P < 0.05-0.01). The number of iNOS-positive cells was lower in the ginkgo biloba leaf extract group compared with the hormone group at 7 and 14 days after spinal cord injury (P < 0.05). Bcl-2expression reached a peak at 3 days, and Bax expression reached a peak at 5 days following rat spinal cord injury. Bcl-2 expression was increased, but Bax expression was decreased in the ginkgo biloba leaf extract and hormone groups compared with the trauma group (P < 0.05-0.01). Bcl-2 expression was greater, but Bax expression was reduced in the ginkgo biloba leaf extract group compared with the hormone group at 7 and 14days after spinal cord injury (P < 0.05).CONCLUSION: Ginkgo biloba leaf extract exhibits neuroprotective effects by upregulating Bcl-2expression, downregulating Bax expression, and significantly inhibiting high expressions of iNOS in the injured spinal cord. The neuroprotective effects of ginkgo biloba leaf extract are greater compared with methylprednisolone at 1 week after spinal cord injury.