The development of astrocytes in the cat retina: evidence of migration from the optic nerve.

To test recent ideas of the origin of retinal astrocytes we have studied the distribution of astrocytes, identified by anti-GFAP antibodies, in the developing retina of the cat. GFAP+ cells first appeared at the optic disc at E53 (embryonic day 53). At subsequent ages, GFAP+ cells covered successively larger regions surrounding the optic disc, and were found at the edge of the retina by P35 (postnatal day 35). During development, the GFAP+ cells near the optic disc were strongly related to blood vessels and axon bundles; in a more peripheral zone they were closely associated with the immature capillary net; while the most peripheral GFAP+ cells appeared to extend exploratory processes towards the margin of the retina. The velocity at which the 'front' of GFAP+ cells spread over the retina was estimated at 170-240 microns/day. At no time during development were GFAP+ cells observed in the area centralis. Except at the area centralis, the spread of GFAP+ cells preceded the formation of capillaries, by a small but distinct margin. GFAP+ cells also extended for a short distance from the optic disc along the proximal part of the hyaloid artery. These results support the view that retinal astrocytes migrate into the retina from the optic disc, in close association with the formation of retinal vasculature.