Ethanol teratogenicity in mice: a light microscopic study

The objective of this study was to see what, if any, cellular changes occurred in the mouse embryo following a single injection of ethanol, a known teratogen in humans and animals, on day 9 of gestation. No changes were seen until 6 hours after injection, when many degenerating cells and necrotic fragments were seen in the neuroepithelium of the neural groove and of the neural tube. In addition, large clear vacuoles were seen in the cytoplasm of many cells and the pseudopodia at the luminal side of the neural groove appeared swollen. The cytoplasm of the latter also contained vacuoles. When tritiated thymidine was injected 5 hours after ethanol and 1 hour before sacrifice, many degenerating cells were labelled. In addition, many cells with labelled nuclei had abnormal vacuoles in the cytoplasm. Hence, it is likely that the toxicity of ethanol is exerted primarily on some component of the cytoplasm and not on DNA synthesis. Twelve hours after ethanol, the cytoplasmic vacuoles and swollen pseudopodia had disappeared, but dying cells were still evident. By 24 hours, the necrotic debris had been completely phagocytosed by healthy neuroepithelial cells. By 50 hours, the neuroepithelium had been cleared of cell debris, although many ethanol-treated embryos had open defects of the cranial neural tube. Treatment of pregnant mice with single doses of acetaldehyde, also an established teratogen in animals, did not produce any cellular changes. However, a single dose of acetaldehyde is rapidly metabolized by the mother, and would not be comparable to the small but continuous blood levels that a dose of ethanol would produce. Hence, we could not conclude with certainty that the cytotoxic effects of ethanol were exerted directly.