Effects of hydrocortisone on the ultrastructure of the thymic cysts of the chick embryo

Thymi from 80 19-day chick embryos that were injected with 2.5 mg of hydrocortisone on the 15th day of incubation were examined by light and electron microscopy. Six thymic tissue blocks from each embryo were evaluated. Hydrocortisone caused a marked depression of thymic volume due mainly to the depletion of lymphocytes. Cystic structures, consisting of intercellular and intracellular cysts and individual cystic cells, were more numerous per unit area of medullary tissue in treated embryos than in the controls. In the treated group, the shape of cystic cells varied from squamous to columnar, and hypertrophied columnar cells were also evident. The luminal surface possessed well-developed microvilli with membrane invaginations at their bases. The terminal web was prominent and the lateral plasma membranes were highly interdigitated. The rough and smooth-surface endoplasmic reticula and the Golgi complex of thymi from treated embryos were more developed than those in the controls. Mitochondria and vesicles were increased in number following hydrocortisone treatment. Cysts lined partially by cystic and endothelial-like and smooth muscle cells were encountered in the treated group. These structural modifications probably reflect responses to increased absorptive or transport function. The data suggest that hydrocortisone may alter the structure of cystic cells in chick embryos.

Experimental limb dysmorphogenesis as a model of chemical injury response in undifferentiated embryonic tissues: a light and electron microscopical study

A histopathological and ultrastructural analysis of the early stage of limb dysmorphogenesis from 1 hr to 48 hr, following citral administration is presented as a model for studying the reaction to injury of undifferentiated embryonic tissues. Early lesions such as cloudy swelling, hydropic degeneration, enlargement of the extracellular space and retraction of protoplasmic extensions were observed 1 hr after treatment, affecting both epiderm and mesenchyme of the limb. Few pyknotic cells were encountered during the early stages. Cell necrosis and autophagocytosis became more conspicuous at 12 hr post-injection. About the same time the first signs of healing were observed, charcterised by heterophagocytosis and return of mitotic activity. The epiderm being more differentiated, regenerates ad integrum and more rapidly than the mesenchyme. The evolution of these pathological events, which proceed in a spatio-temporal cascade, seem to reflect the pharmacokinetic gradient of the cell-teratogen interactions. The type of limb malformation will depend mainly on the extent of injury and/or healing of the mesenchymal mass, rather than on the injury and/or healing of the surface ectoderm. It is concluded that the reaction to chemical injury of undifferentiated tissues partially mimics the destructive and repair process in adult tissues, but differs in lacking some basic constituents such as oedema, monocyte exudation and granulation tissue formation.