Background : Apoptosis is a selective process regulated by intrinsic program, whereby
cells physiologically die. Reported have been a variety of apoptosis detection methods,
such as light or electron microscopy, flow cytometry, and gel electrophoresis of DNA
extractions. Authors intended to induce apoptosis in rat thymocytes and detect DNA
fragmentation by using in situ labeling method.
Methods: Thymus, ileum, and testis were dissected from 3 week old Sprague-Dawley
male rats. For induction of apoptosis, 2×10 7 thymocytes were prepared
and cultured with 1μg/mL dexamethasone for 1, 1.5, 3, and 6 hours, respectively. In
situ apoptosis detection kit were used for DNA labeling. Cultured thymocytes were
observed with electron microscope and apoptotic cells were counted according to
incubation time. Intestinal epithelial cells and testicular spermatogonia were also
investigated for biological apoptosis.
Results: Apoptotic thymocytes, cultured with dexamethasone, were counted 13.6%,
41.8%, 44.7%, after 1, 3, 6 hours of incubation, respectively. Electron microscopic
features of apoptotic thymocytes showed shrinkage of cell volume, disruption and
condensation of euchromatin, dilatation of endoplasmic reticulum, and normal
mitochondria. In intestinal epithelium, marked labeling was observed at the tips of villi,
whereas labeling was confined to the nuclear periphery at the lower part of crypts.
Most testicular spermatogonia revealed strong intensity of DNA labeling with granular
pattern.
Conclusion: Apoptotic induction of rat thymocytes by dexamethsone appears to be
effective at 3 hours of incubation. For evaluation of biological apoptosis, intestinal
epithelium and testis can be used for in situ DNA labeling. Electron microscopy is
useful for morphological identification of apoptotic cells.

Keywords: Apoptosis, Thyrnocyte, Dexamethasone, In situ labeling