The development of astrocytes and blood vessels in the postnatal rabbit retina.

Antibodies to glial fibrillary acidic protein (GFAP) have been used to study the shape and location of astrocytes in whole mount preparations of developing postnatal rabbit retina. At all developmental stages GFAP-positive astrocytes were detectable. At birth, they were few in number and only weakly labelled. With further development, their number as well as their labelling intensity increased. Following Nissl counterstaining it was observed that GFAP-positive astrocytes, always situated in the nerve fibre layer, are capable of cell division during about the first 4 postnatal weeks. GFAP-positive astrocytes were always confined to a wing-shaped area extending horizontally from both sides of the optic nerve head. It is suggested that astrocytes are not generated in the entire rabbit retina, which is in clear contrast to the second glial cell type of the rabbit retina, the Müller cell; and it has been concluded that the confinement of astrocytes to the medullary rays region in the adult rabbit is established during ontogenesis, and is not due to a secondary restriction of astrocytes to this region. Horizontal sections cut through entire rabbit retinae at various postnatal stages revealed that the first intraretinal blood vessels are not found before postnatal day 9. This is more than 1 week later than the first astrocytes are detectable. It is suggested that, at least in the rabbit, retinal astrocytes do not co-migrate with blood vessel endothelial cells from the optic disc into the retina, a hypothesis considered recently for the cat retina. It was, however, not possible to decide unequivocally if, in this material, astroglial progenitors are derived from retinal neuroepithelial cells or invade the retina from the optic nerve head.