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Objective:Radiation injury includes radiation necrosis and apoptosis. Though some of its mechanism in brain are reported, those in spinal cord are not determined yet. The purpose of this study is to see whether nimodipine, one of calcium channel blockers, is effective for the prevention of high dose irradiation-induced apoptosis in the rat spinal cord. Methods : Forty eight Sprague-Dawley rats were divided into four experimental groups, such as non-treated group(control group) after 5Gy and 10Gy irradiation(n=24), and nimodipine-treated group after 5Gy and 10Gy irradiation(n=24). Each group was divided by irradiation doses. After the drug was administered, the spinal cord was exposed to 5Gy and 10Gy dose of gamma rays using Ir-192. All spinal cord underwent histological examination at 4 hours, 8 hours, 12 hours after irradiation to evaluate the number of apoptotic cells. Apoptotic cells were detected by TUNEL assay, and determined by direct visual counting at×200, magnification Results : In nimodipine-treated group, apoptotic cell counts were reduced significantly, compared to that of control group after irradiation(p<0.05). Conclusion : These results suggest that nimodipine treatment may have effects on the prevention of radiationinduced apoptosis. If it could be established that calcium channel blockers inhibit radiation injury, they might be useful in radiation therapy. Key words:Radiation;Apoptosis;Nimodipine;Spinal cord;Rat.