STAGE-SPECIFIC APOPTOSIS IN THE RAT SEMINIFEROUS EPITHELIUM - QUANTIFICATION OF IRRADIATION EFFECTS

The effects of 3 Gy local X-irradiation on the adult rat testis were s tudied together with exact determination of the radiation dose distrib ution in the testis. Seminiferous tubule segments were isolated 8-66 h ours postirradiation (p.i.), squashed between a microscope slide and a coverslip, and the exact stage of the seminiferous epithelial cycle w as identified under a phase-contrast microscope. The squash preparatio ns were subjected to in situ end labeling (ISEL) for visualization and quantification of apoptotic cells. In controls, the highest numbers o f apoptotic cells were scored in stages XII-XIV and I. In situ end-lab el staining of cells was observed in A(3)-A(4) spermatogonia, spermato cytes at zygotene, pachytene, and meiotic division phases, as well as in early spermatids. in irradiated testes, from 8 hours p.i. and onwar d, intermediate- and B-type spermatogonia were sensitive at stages Il- VI. At 42 hours, in stage I, elevated numbers of degenerating spermato cytes were seen. Most of them had not undergone meiotic divisions at s tage XIV and showed an apoptotic type of degeneration at stage I. At t he time of irradiation, the cells were in stage XIII, suggesting that diakinetic spermatocytes are particularly sensitive to irradiation. Al so, preleptotene-zygotene spermatocytes in stages VII-XII were sensiti ve to irradiation. Apoptotic-type of cell degeneration was confirmed b y living cell squash preparations, electron microscopy, and DNA electr ophoresis. In conclusion, irradiation may provide a useful model syste m for studying apoptosis, and its control in spermatogonia and meiotic ally dividing cells.