Figure 2. Appearance of astrocytes and different types of reactive astrocytes in mouse cerebral cortex.

Images show immunohistochemistry for the intermediate filament protein, GFAP, which visualizes the cell cytoskeleton. (A) In healthy cortex, some, but not all astrocytes express detectable levels of GFAP; cell bodies are small and the cytoskeleton is thin and restricted largely to the proximal portions of cell processes. (B) In response to the bacterial antigen, lipopolysaccharide (LPS) injected into the lateral cerebral ventricle, cortical astrocytes become moderately reactive, with up-regulation of GFAP expression such that it is now detectable in all astrocytes. In addition, there is substantial hypertrophy of the astrocyte cell bodies as well as hypertrophy of stem processes and associated cytoskeleton. However, there is no astrocyte proliferation and individual cells continue to respect their individual, non-overlapping domains. (C) In response to a severe traumatic injury that creates a lesion (L) with tissue necrosis and invasion of inflammatory cells, astrocytes not only become reactive but also proliferate in the immediate vicinity of the lesion and form a scar with a dense scar border (SB) that comprises many newly generated astrocytes that do not exhibit individual domains and instead have many overlapping and intermingling processes. All images are at the same magnification. Scale bar = 20 μm (Photos courtesy of the Sofroniew laboratory).