development of the retina and optic stak in rat embryos

ABSTRACT

This work was done to study the prenatal development of the retina and optic chiasma in albino rat embryos in an attempt to provide the mechanism of optic axonal guidance and to elucidate the relation between the cytodifferentation of the retina and its central nervous connection. Thirty rat embryos in age from 12 days to 21 days [full term newborn], were used in this study. The results of the present work indicate that the projection of the outgrowing axons araised from the early developing ganglion cells and extend in the direction of the optic dise has occurred through the extracellular spaces, which formed inside the superficial portion of the retina during the early period of generation. Moreover, the findings of this work suggest that the origin of the retinal macroglial cells [astrocytes] is the neuroepithelial cells of the optic stalk that reach the retina through its blood vessels. Theses cells together with the developing glial cells derived from the floor of dienecphalon are emphasized to act as candidates for guidance of the nerve axons within the retina, optic stalk and optic stalk prior to penetration of the axons are postulated to minimize the resistance of axonal advance through the stalk providing a potential path for the growing axons to reach the diencephalons. This was followed by concomitant maturation of the ganglion cells and differentiation of the inner plexiform layer of retina during the late stages of gestation