During the course of a comparative study of morphogenetic processes in mouse and chick adrenal development (Ba-Omar, 1989) an extensive occurence cell death, previously unreported, during embryonic stages was found. Cell death has been reported previously in neonatal rats (Wyllie et al, 1973a,b) where it occurs amongst scattered cells mainly in the inner part of the cortex. Sivaram ( 1965) has reported cell death in the centre of young post-hatching and adult adrenals Adrenal glands of mouse embryos and chick embryos were dissected out, fixed in Karnovsky's fixative (Karnovsky, 1965) and processed for EM. Semithin sections were cut and then stained with toluidine blue, and ultrathm sections were stained with uranyl acetate and lead citrate (Reynolds, 1963). Sections were examined by a light microscopy and transmission electron microscopy. The dying cells were darkly stained. They were observed in mouse 14-18 day old and some chick 17-19 days old embryos. The dying cells were seen around the centre and at the periphery of the gland. TEM observations confirmed that these cells were of both chromaffin and cortical types, and that they showed ultrastructural features associated with dying cells such as the presence of vacuoles, shrinkage of the nuclei and by their irregular shape.The dying cells generally appeared to retain contact with their neighbours in both mouse and chick embryos. Wyllie et al (1973a, b) indicated that "apoptotic bodies" were consistently rounded up and had lost contact with their neighbours. There was no sign of neighbouring cells changing into macrophages nor of specialised macrophages. We never observed the remains of dying cells within the cytoplasm of other cells. It may therefore be that these dying cells were eliminated by means of the circulatory system, as suggested by Wyllie et al ( 1973 a,b).
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