INVOLVEMENT OF APOPTOSIS IN THE RAT GERM-CELL DEGENERATION INDUCED BYNITROBENZENE

Nitrobenezene (NB) produces germ cell degeneration, especially of sper matocytes in rats. To examine the possible involvement of apoptosis in this process, the extent and nature of nuclear DNA fragmentation afte r NE dosing were assessed using both terminal deoxynucleotidyl transfe rase-mediated dUTP nick end-labeling (TUNEL) and DNA gel electrophores is, in addition to conventional histological and electron microscopic procedures. Adult Sprague Dawley rats were treated with a single oral dose of NB (250 mg/kg) and euthanized subsequently at 6, 12, and 24 h and 2, 3, 5, and 7 days. The earliest morphological signs of germ cell degeneration in testes were found in pachytene spermatocytes 24 h aft er dosing. Electron micrographs of degenerating spermatocytes showed m arked nuclear chromatin condensation at the nuclear periphery and crow ding of cytoplasmic constituents, which are characteristic of apoptosi s. Coincident with the appearance of such morphological changes, degen erating spermatocytes contained fragmented DNA as revealed by TUNEL. T he presence of DNA laddering, a hallmark of apoptosis on gel electroph oresis, was first apparent and most prominent at 24 h, gradually becom ing less detectable. No such changes were observed up to 12 h after do sing or in control animals. These results demonstrated unequivocal inv olvement of apoptosis in the induction of germ cell degeneration cause d by NB.