A SUBPOPULATION OF REACTIVE ASTROCYTES AT THE IMMEDIATE SITE OF CEREBRAL CORTICAL INJURY

We have identified an early-appearing intermediate filament-associated protein (IFAP-70/280 kDa) in radial glia and their immediate derivati ves. This IFAP is absent in the adult CNS. In this study, we examined the reexpression of this early glial differentiation trait in rat reac tive astrocytes induced by stab injury of the cerebrum. Double-label i mmunofluorescence microscopy demonstrated that by 36 h postlesion, IFA P-70/280 kDa was present in a few GFAP-positive astrocytes in the area adjacent to the wound. As the gliotic reaction progressed, the number ofIFAP-positive reactive astrocytes increased and by 5-6 days postles ion, IFAP-70/280 kDa was present in most of the hypertrophied astrocyt es in tissue immediately adjacent to the wound. By 8 days postlesion, while the number of IFAP-negative reactive astrocytes away from the wo und diminished, the IFAP-containing reactive astrocytes close to the w ound persisted. Concurrently, they began to change from a stellate for m to an elongated shape, with their longitudinal axes radiating from t he wound. The immunoreactivity of this IFAP started to diminish at 20 days postlesion, and by 30 days postlesion, it was not observed in the remaining gliotic cells. These results demonstrate that reactive astr ocytes induced by stab-wound injury can be divided into two subtypes: persistent IFAP-70/280 kDa-containing cells which are close to the wou nd in the area of the glial scar and transient IFAP-70/280 kDa-negativ e cells which are farther from the wound. The reappearance of IFAP-70/ 280 kDa also suggests that some reactive astrocytes have the capacity to recapitulate early developmental stages. (C) 1997 Academic Press.