Developmental events during the early stages of cerebral cortical neurogenesis in man. A correlative light, electron microscopic, immunohistochemical and Golgi study.

The telencephalic vesicles of early human embryos and fetuses ranging from 6-18 weeks of ovulation age were subjected to correlative light and electron microscopic, immunocytochemical and Golgi analysis. The cellular events that take place during the early stages of cortical neurogenesis are characterized by the early maturation of layer I. The deployment of radial glia, the formation of the glia limitans, the establishment of the pial-glial barrier, and the migration and maturation of Cajal-Retzius cells within the marginal zone (MZ) all take place by 6-7 weeks. Neurons destined to populate the cortical plate (CP) arrive within the MZ by 7-8 weeks of age and appear to divide the MZ into two layers. Progressive compaction of CP neurons and widening of the intermediate zone characterize the next stage. It is suggested that the early establishment of the pial-glial barrier and the early maturation of the layer I are critical to the subsequent growth and development of the CP.