COEXPRESSION OF GFAP AND VIMENTIN IN ASTROCYTES PROLIFERATING IN RESPONSE TO INJURY IN THE MOUSE CEREBRAL HEMISPHERE - A COMBINED AUTORADIOGRAPHIC AND DOUBLE IMMUNOCYTOCHEMICAL STUDY

Changes in the distribution of proliferating astrocytes expressing glial fibrillary acidic protein (GFAP) and/or vimentin were examined in the injured cerebral hemisphere in adult mice. The injury was followed by [H-3]thymidine injections at different time intervals. The brain sections were doubly immunostained for GFAP and vimentin and subjected to autoradiography. In that way three cell types were distinguished immunocytochemically: (1) astrocytes co-expressing glial fibrillary acidic protein (GFAP) and vimentin, (2) astrocytes expressing only GFAP and (3) astrocyte-like cells expressing vimentin. Thereafter, numbers of immunopositive and autoradiographically labelled cells and their locations within the region of injury were recorded at each stage of the experiment. Two hours as well as 1 day after the injury proliferation of GFAP-positive astrocytes and of those co-expressing GFAP and vimentin could only be seen as statistically insignificant phenomena. On day 2 the reactive proliferation of each immunocytochemically defined cell type was already maximal, then gradually decreased and its last signs were recorded on day 8. On day 2, among all the proliferating GFAP-positive astrocytes, 67.2% were also vimentin-positive. Later, the proportion declined to 50.7% and 38.5% on days 4 and 8, respectively. The labelled astrocyte-like vimentin-positive cells were located closest to the lesion margins. In comparison, the astrocytes co-expressing GFAP and vimentin and those expressing exclusively GFAP, occupied regions progressively farther from the lesion site. At the initial stages of the response to injury, vimentin expression in cells starting their reactive proliferation did not precede the expression of GFAP. This was considered as an argument against a hypothesis that reactive astrocyte division induces a two-stage increase in the cytoskeletal protein level in which synthesis of vimentin precedes that of GFAP.