IMMUNOHISTOCHEMICAL STAINING FOR GLIAL FIBRILLARY ACIDIC PROTEIN (GFAP) AFTER DEAFFERENTATION OR ISCHEMIC INFARCTION IN RAT VISUAL-SYSTEM -FEATURES OF REACTIVE AND DAMAGED ASTROCYTES

Immunohistochemical staining for glial fibrillary acidic protein (GFAP ) is standard for visualization of reactive astrocytes in tissue secti ons, whereas various forms of astrocytic damage remain to be described in detail. In this study we tested differences in GFAP labeling in re active astrocytes and in glial cells damaged by ischemia and edema. St udies were performed in the anatomically well defined visual system of rat. Basic staining patterns for GFAP were established in subcortical visual nuclei and visual cortex. In the first model, deafferentation of visual centers was performed by unilateral optic nerve lesion, and characteristic changes of GFAP labeling in reactive astrocytes were st udied at 0.5, 1, 1.5, 2, 4, 8 and 21 days after lesion. Initial change s were seen in the deafferented superior colliculus at 1 day after dea fferentation with a diffuse increase and stellate types of reactive ce lls formed at 2-8 days. In the second model, small ischemic infarcts w ere produced in the visual cortex of rats using the method of photoche mically-induced thrombosis. GFAP labeling with a polyclonal antiserum was massively enhanced in the infarct at 4 hr. Characteristic morpholo gical changes in damaged astrocytes were seen which were also identifi ed in experiments with simulated global ischemia. In the surround of t he infarct, swelling of astrocytes also caused increased labeling. At 3-4 days infarction typical reactive astrocytes surrounded the lesione d area. In conclusion, these immunohistochemical studies on GFAP in ra t visual system allow for the following classifications. (a) Normal as trocytes vary in labeling at different anatomical localizations. (b) R eactive astrocytes show enhanced labeling and larger cell-size within an interval of 1-2 days after lesion. (c) Astrocytes damaged by ischem ia reveal increased labeling of disintegrating cellular elements withi n hours after a lesion. (d) Swollen astrocytes undergo enhanced labeli ng in areas with vasogenic edema.