Cytoarchitecture in cultured rat neocortex explants.

Neocortex explants obtained from 6-day-old rat pups and cultured in a serum-free medium from 5 hr to 13 days in vitro (DIV) show preservation of cytoarchitectural characteristics. Major changes in the size of the explants and their layers occur during the first 2 DIV. A radial arrangement of neurons within layer 2-3-4, which becomes apparent between 2 and 10 DIV, suggests an advance in maturation in culture. In contrast to the situation in vivo, a distinct layer 4 cannot be consistently identified. During the first 2 DIV, a transposition of cells into the pial direction can be seen. Individual degenerated cells are spotted especially in layer 5. The presence of these cells amidst healthy neurons suggests that their death has a functional cause. Neurons at the ventricular border of layer 6 become relatively large in comparison with other neurons. Within the cultured tissue there is a marked increase in GFA reactivity compared to the situation in vivo. The described results clearly indicate that in these cultured explants, both similarities and differences are of interest for studies on the formation of neuronal circuitry within the cerebral cortex.