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J Korean Soc Ther Radiol Oncol. 2001 Jun;19(2):146-152. Korean. Original Article.
Oh WY , Song MH , Chung EJ , Seong JS , Suh CO .
Department of Therapeutic Radiology, National Medical Center.
Department of Radiation Oncology, Yonsei University, College of Medicine, Yonsei Cancer Center, Seoul, Korea.

PURPOSE: To investigate the regulation of apoptosis and cell cycle in mouse brain irradiation. MATERIALS AND METHODS: 8-week old male mice, C57B1/6J were given whole body gamma-radiation with a single dose of 25 Gy using Cobalt 60 irradiator. At different times 1, 2, 4, 8 and 24hr after irradiation, mice were killed and brain tissues were collected. Apoptotic cells were scored by TUNEL assay. Expression of p53, Bcl-2, and Bax and cell cycle regulating molecules; cyclins B1, D1, E and cdk2, cdk4, p34cdc2 were analysed by Western blotting. Cell cycle was analysed by Flow cytometry. RESULTS: The peak of radiation induced apoptosis is shown at 8 hour after radiation. With a single 25 Gy irradiation, the peak of apoptotic index in C57B1/6J is 24.0+/-0.25 (p<0.05) at 8 hour after radiation. Radiation upregulated the expression of p53/tubulin, Bax/tubulin, and Bcl-2/tubulin with 1.3, 1.1 and 1.45 fold increase, respectively were shown at the peak level at 8 hour after radiation. The levels of cell cycle regulating molecules after radiation are not changed significantly except cyclin D1 with 1.3 fold increase. Fractions of Go-G1, G2-M and S phase in the cell cycle does not specific changes by time. CONCLUSIONS: In mouse brain tissue, radiation induced apoptosis is particularly shown in a specific area, subependyma. These results and lack of radiation induced changes in cell cycle offer better understanding of radiation response of normal brain tissue.

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