817 Time course of radiation-induced apoptosis in the adult rat spinal cord

Radiation-induced apoptosis has been reported in thymic, lymphoid and hematopoietic cells but is infrequently documented in other adult mammalian cell types. In this study, we examined the time course of radiation-induced apoptosis in the adult cervical rat spinal cord following a single dose of 8 or 25 Gy. Apoptosis was assessed by morphological criteria under light and electron microscopy, and immunohistochemically in-situ using ApopTag to detect 3’-OH ends of DNA fragments. Little evidence of apoptosis (0.3 ± 0.3 apoptotic nuclei/spinal cord section) was observed in control un-irradiated spinal cord. A significant increase in the number of apoptotic cells was seen at 4 hr, the number peaked at 8 hr (53.7 ± 3.5 per spinal cord section after 8 Gy, and 60.7 ± 8.7 after 22 Gy) and returned to the baseline level by 24 h. A dose of 22 Gy induced apoptosis than 8 Gy at 4, 6, 10 and 12 h ( P