Native astrocytes do not migrate de novo or after local trauma

While transplanted astrocytes migrate in specific patterns in the recipient brains, it is not known whether native astrocytes behave similarly. The ability of normal astrocytes to migrate under non-transplant conditions was therefore explored. Native astrocytes were labelled in situ with fluorescent latex beads. These latex spheres were actively endocytosed by astrocytes in vitro, and it was therefore anticipated that these spheres would also be endocytosed by native astrocytes exposed to them. Labelling was accomplished by dissecting the pia mater away from a small region of the cerebral cortex and overlaying the area with Gelfoam containing fluorescent beads. After 2-4 h, the Gelfoam was removed and the wound was closed. At the end of 2-4 weeks, manipulated brains were harvested for fluorescence microscopy. In this analysis, fluorescent polyspheres had been taken up by both pial fibroblasts and astrocytes at the pial-glial margin. Labelled astrocytes [identified by glial fibrillary acidic protein (GFAP) staining] were neither hyperplastic nor hypertrophic. They were confined to the area of the original labelling site, and did not migrate either laterally across the pial margin or ventrally into the cortical layers. Knife wounding at the time of label application, either in the region of the label or distant from it, produced reactive astrocytes that were hypertrophic. These cells also did not migrate from the label site. These results suggest that astrocytes labelled by this method do not migrate in the absence of some transplant-derived stimulus even when stimulated by local wounding.