RADIATION-INDUCED CELL-DEATH IN THE MOUSE TESTIS - RELATIONSHIP TO APOPTOSIS

The killing of male germ cells by radiation and other toxicants has re cently been attributed to apoptosis, but a critical evaluation of the presence of the different features of apoptosis has not been performed . In this study, mouse testes exposed to radiation were examined by li ght microscopy, electron microscopy and terminal transferase-mediated end labeling (TUNEL) to determine whether the cells were apoptotic acc ording to several criteria. Testes were irradiated with single doses o f gamma rays of up to 5 Gy. Although the maximum response was produced by 5 Gy, even 0.5 Gy induced marked changes. The numbers of abnormal spermatogonia reached a peak 12 h after irradiation and then declined, and the total number of spermatogonia began to decline at 12 h. These changes were most prominent among the B spermatogonia and early prele ptotene spermatocytes. When examined by both light and electron micros copy, the majority of the abnormal spermatogonia showed condensation o f nuclear chromatin and some showed features similar to necrosis, but the typical morphological characteristics of apoptosis, margination of chromatin and nuclear fragmentation, were rare. Many of the abnormal spermatogonia were TUNEL-positive, with the maximum number occurring a t 12 h after irradiation. Although the morphological features of radia tion-induced spermatogonial degeneration were not typical of apoptosis , the TUNEL staining, the rapid onset of degeneration and the sensitiv ity to low doses suggest that the mechanism of radiation-induced sperm atogonial degeneration is closely related to apoptosis. (C) 1997 by Ra diation Research Society.