Astrocytes grown in oculo: Expression of cell morphologies on the iris as revealed by GFA immunohistochemistry

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Abstract
Using two experimental approaches, the morphology of central astrocytes growing in vivo with the iris as a substratum were studied. When irides with mature intraocular grafts of cortex cerebri or locus coeruleus were stretch‐prepared as whole mounts and processed for immunohistochemistry with antiserum against glial fibrillary acidic protein (GFA), a restricted halo of fluorescent cells and fibers was seen surrounding the grafts. Similarly, injection into the anterior eye chamber of adult rats, of a cell suspension prepared from cortex cerebri of 10‐day‐old rat pups gave rise to both multiple GFA‐positive astrocytic islets of different sizes and cell densities as well as scattered individual cells on the anterior surface of the host iris. In contrast, astrocytes from similar cell suspensions prepared from young adult animals survived very poorly. In both types of experiments, a large variation in cell morphology ranging from immature epitheloid, via large flat cells with few thick processes, to typical mature star‐shaped astrocytes was observed. This morphological variation is in agreement with that reported for similar cells in tissue culture. Immature‐looking cells always had a strong perinuclear fluorescence; an inverse correlation was observed between cell body size and development of cell processes. Likewise, the fluorescence intensity was higher in well‐developed cells as compared to more immature ones.The morphology of individual cells did not seem to be dependent upon the time in oculo, since no difference was observed between GFA‐positive cells on irides examined 10 days and 6 weeks after injection of a cell suspension. Similarly, a high number of immature‐looking cells was seen in irides with locus coeruleus transplants grafted more than 6 months earlier. Instead, the cell density seemed to be the crucial factor. Thus, star‐shaped, well‐developed cells were seen growing singly or in less dense groups whereas denser areas contained mainly immature‐looking cells.Astrocytic processes had a tendency to follow the course of already existing intrinsic GFA‐positive bundles and fibers in the iris. However, exceptions to this were occasionally seen. The fluorescence intensity was clearly higher in astrocytes growing on the iris than in intrinsic GFA‐positive structures, suggesting molecular differences between central and peripheral GFA‐immunoreactive material.