The ultrastructural effects of prednisolone on the mesenchyme of the palatal shelf in the mouse.

The effect of methylprednisolone on the structure of the mesenchymal component of the palatal shelves of fetal mice was studied at the time of shelf reorientation. Pregnant mice received intraperitoneal injections of 8 mg of prednisolone on days 11.5, 12.5, and 13.5 of pregnancy. The mice were killed on day 14.5, and the specimens were either stained with periodic acid-Schiff (PAS) reagent for examination in the light microscope or processed for examination in the electron microscope. It was found that prednisolone treatment resulted in a reduction in the amount of tannic-acid-staining material in the extracellular spaces. It also resulted in a reduction in the collagen within the shelf. The development of skeletal and smooth muscle cells, neurons, and satellite cells was also delayed and the occurrence within the shelves of cells with a high glycogen content was reduced.