Ultrastructural changes in the neural tube of 10-day-old mouse embryos exposed to colchicine and hydroxyurea.

The ultrastructural changes in the neural tube of 10-day-old mouse embryos were investigated between 1.5 hr and 4 hr after application of either 1 mg/kg colchicine (Col) or 500 mg/kg hydroxyurea (HU) or simultaneous application of both substances. During the investigated period, the shape of the nuclei of the neuroepithelial cells had changed from elongated to round after Col application. The chromatin in the nuclei was condensed and arranged in clusters. A breakdown of polysomes into ribosomes and an enlargement of the rough ER was observed in the cytoplasm. At the luminal surface, bleb-like cytoplasmic processes of the neuroepithelial cells containing monoribosomes protruded into the lumen. No cell necroses were visible in the neural tube after Col application. A condensation of chromatin in the nuclei of some neuroepithelial cells was visible 1.5 hr after HU application. Shortly thereafter, cell necroses appeared in the neural tube and 4 hr after HU application the entire spinal cord was strongly damaged. After simultaneous application of Col and HU, the ultrastructural changes in the neuroepithelial cells of the neural tube did not differ from the results obtained after Col application alone. In contrast to the results obtained after HU application alone, no necroses occurred after simultaneous application of Col and HU.