Proliferation of glial precursors during the early development of the chick optic nerve.

The mitotic patterns and cytoarchitecture of the optic stalk were studied in the chick embryo during the period of formation of the optic cup until the elimination of the stalk lumen. Cell proliferation in the superficial regions of the stalk ventral wall is described. Superficial cell proliferation, whose beginning coincides with penetration of the earliest optic fibers, gives rise to an early glioblast plate located internally with respect to the marginal lamina of ganglion cell axon fascicles. The early glioblasts are transformed into marginal glioblasts, which undergo radial mitosis. Radially oriented division seems to favour glioblast penetration towards more internal zones of the stalk. Thus the marginal glioblasts are transformed into inner glioblasts, which continue to proliferate. Cell death in the ventral wall of the optic stalk is in close topographical relation with extracellular spaces which loosen up the consistency of the stalk tissue, favouring invasion of the ventral stalk by optic fibers and the addition of new glioblasts by proliferation of preexisting cells.