Studies on Thymus of the Mammal. X. Regeneration of Irradiated Mouse Thymus.

Abstract

The appearance of dividing cells in thymuses regenerating after total-body dose of gamma rays (400 r) was studied in CAF1 male mice, 4-5 weeks old, receiving an injection of colchicine 6 hours previous to their sacrifice. The numbers of resting and dividing cells were significantly reduced 24 hours postirradiation. Increased numbers of mitoses preceded significant increases in the number of cells between the 3d, 5th and 7th days. The highest percentage of mitoses (20.4%) occurred on the 5th day. By the 7th day, the number of cortical cells approached the normal and the percentage of mitotic figures had decreased. The fluctuations in the number of resting and dividing cells after irradiation in the medulla followed no regular pattern. The evidence presented supports the view that the cells repopulating the thymic cortex after irradiation arise in situ.