**2.3. Glial scar**

Glial scar is the accompanying pathological phenomenon of various CNS injuries. The site of injury is infiltrated by macrophages from the bloodstream, fibroblasts, astrocytes, microglia, and oligodendrocytes [8]. Later, precursors of oligodendrocytes and meningeal cells are activated. Activated astrocytes proliferate and, together with other glial cells, produce a glial scar that encloses the lesion site and prevents the diffusion of ions, neurotransmitters, and other metabolites from damaged tissue into surrounding healthy tissue [22]. This protects undamaged tissue from inflammation and demyelinization, while at the same time, it also prevents regeneration of nerve fibers, which is a serious problem for the treatment of spinal cord injuries. Activated astrocytes reveal thicker projections that intersect with each other and are connected by tight joints. Astrogliosis is accompanied by increased expression of glial fibrillary acidic protein (GFAP), vimentin, and markers for neural precursor cells (Nestin) [23]. In reactive astrocytes, increased synthesis of extracellular matrix protein CSPGs has been reported, which are inhibitory to axon growth itself [23]. Similarly, oligodendroglia, together with meningeal cells migrating into the lesion, form a significant barrier for axonal growth by producing inhibitory molecules (NOGO) and other proteoglycans [24].
