Extracellular matrix in the CNS

The extracellular matrix (ECM) occupies the space between neurons and glial cells and accounts for 10%–20% of the total volume of the brain. During CNS development, the ECM provides a microenvironment that regulates cell migration, axonal guidance, and synaptogenesis; in the adult CNS, it contributes to maintenance of synaptic stability and regulates repair following injury, in part by restricting aberrant remodeling. The ECM molecules may be arranged diffusely, forming an ECM matrix, or condense to create specific compartments in the extracellular space; these include perineuronal nets (PNNs), perisynaptic nets, and the basement membrane contributing to the blood–brain barrier (BBB).