Figure 2.

Adaptive and maladaptive glial changes following injury. The degree of astrogliosis depends on the severity of injury. (A) Glia and extracellular matrix at baseline. Astrocytes are tiled, i.e., their processes do not overlap with neighboring astrocytes. Microglia are interspersed throughout the region. (B) Mild injury triggers activation of microglia and astrocytes. Astrocytes and microglia increase in size and acquire more complex process morphology, but astrocytes maintain their tiled formation. This response is considered adaptive because it limits the spread of degeneration away from the site of injury, dampens excitotoxicity, and promotes tissue regeneration. Such glial activation typically resolves within a few weeks after a mild, transient injury. (C) In contrast severe injury causes reactive astrocytes to invade neighboring domains, recruit reactive microglia, and increases secretion of extracellular molecules. This results in formation of a persistent glial scar that can be impenetrable to sprouting axons.