CONFOCAL MICROSCOPY AND COMPUTER-ASSISTED IMAGE-RECONSTRUCTION OF ASTROCYTES IN THE MAMMALIAN RETINA

The distribution of astrocytes in the vascularized retina of pigs, rat s and cats was investigated by confocal microscopy and computer-assist ed image processing. In whole mounts, immunocytochemical identificatio n was done by staining astrocytes for glial fibrillary acidic protein (GFAP), and blood vessels for alpha-smooth muscle actin or collagen IV . Double-staining was followed through consecutive optical sections an d made it possible to precisely align the two markers in the inner ret ina. The resulting computer-assisted image reconstructions revealed as ymmetric ensheathment of blood vessels by GFAP-positive fibres. The ul trastructural basis for this asymmetry, as studied by electron microsc opy, was found to be different in pigs and cats. In the pig, astrocyte s firmly ensheathed the vessel circumference, but glial filaments were much more abundant on the vitreal and lateral than on the scleral sid e. By contrast, in the cat astrocytes were generally confined to regio ns occupied by axonal bundles and constituted only part of the vascula r glia limitans, else formed by Muller cells. Moreover, our observatio ns unambiguously showed that individual astrocytes maintained simultan eous contact with axons and blood vessels and lined the vitreous body. The physical links provided by astrocytes suggest that they are able to function as central communicating elements between ganglion cells, the vasculature and the vitreous body.