Fine structural aspects of the cranial neuroepithelium in early embryos of the rhesus monkey.

Temporal changes in the ultrastructure of cranial neuroepithelial cells and their developmental interactions with adjacent chordamesodermal cells were analyzed during early neurogenesis in rhesus monkey embryos at stages 8-12 (19-28 days of gestation). In the neural plate and early neural fold stages, microtubules and apical microfilaments are not as prominent in the neuroepithelial cells as they are after the neural tube closes, whereas gap junctional vesicles are more evident prior to closure. Initially, the association between neuroepithelial cells and the presumptive notochordal cells is relatively closer than that between neuroepithelial cells and mesenchymal cells. After neural tube closure, the notochord becomes more distant. Cytoplasmic processes from neuroepithelial cells, notochordal cells, and mesenchymal cells interact via the neural basal lamina. In the rhesus monkey embryo, the ultrastructural features of neuroepithelial cells and their interactions with adjacent chordamesodermal cells are similar to those which have been observed in the mouse at comparable stages of gestation.