Retinal perivascular astroglia: an immunoperoxidase study.

Different morphological types of retinal perivascular astrocytes have been studied in wholemount preparations of rabbit retina. Astrocytes were immunohistochemically demonstrated using glial fibrillary acidic protein monoclonal antibodies (GFAP clone GA-5). Three types of perivascular astrocytes were found. Type I has an ovoid perikaryon which gives rise to numerous hair-like processes, and it shows strong GFAP reactivity; these cells are associated with medium-size vessels and capillaries. Type II is star-shaped and its spherical perikaryon has a basal cone with four to ten small, protruding, radial processes; these astrocytes show high GFAP reactivity and are located on larger and medium-size vessels. Type III astrocytes show the classic, star-shaped morphology in which processes emerge directly from the perikaryon which lacks a basal cone. However, different from Types I and II, Types III astrocytes show low GFAP reactivity and are positioned between capillaries. These cells are the only ones that can contact other astrocytes of the same type to form a network.