Immunocytochemical studies on astroglia of the cat retina under normal and pathological conditions.

The cell density and morphology of astrocytes in whole-mounted adult cat retinae have been studied by immunocytochemical localization of glial fibrillary acidic protein (GFAP). There was a peak density at the optic nerve head of about 2,000 astrocytes/mm2 dropping to approximately 200 astrocytes/mm2 in the far periphery. In the central area there was a local minimum of astrocyte density. Whereas the processes of astroglia in the outermost retinal periphery were radially arranged, thus giving the cells a characteristic star-shaped appearance, the majority of astroglial processes in the central region of the retina were aligned in parallel with the ganglion cell axon bundles. To study the correlation between optic nerve fibres and astrocytes, ganglion cell axons were caused to degenerate following photocoagulation lesions close to the optic disc. Postlesion the processes of astrocytes in the central retina lost their directional preference and linearity, thus appearing to develop a star-shaped morphology typical of astroglia in the far periphery of normal retinae. The density of astrocytes decreased by approximately 50% on the optic disc side of the lesions and by up to 80% on the peripheral side of the lesions. The results show that the morphology and number of astrocytes vary as a function of their proximity to optic nerve fibres and to the density of these fibres.