Loss of the integrity of the endothelial barrier causes fluid to leak into the interstitial space, leading to vasogenic cerebral edema . This raises intracranial pressure and can collapse brain capillaries, resulting in arrest of cerebral perfusion. Cerebral edema is caused by a variety of pathological processes, including ischemic insults, inflammation, and malignant brain tumors whose capillaries do not have tight junctions. Astrocytes are less vulnerable than neurons to ischemic injury but they are damaged if there is lactic acidosis. Cytotoxic edema involves the cerebral cortex, whereas vasogenic edema is more pronounced in the white matter.
Vasogenic edema is more important clinically than cytotoxic edema.
Astrocytes are important for regulation of metabolic activities of neurons. They take up GABA and glutamate that are released at synaptic clefts and convert them to glutamine. Glutamine is then transferred to neurons and recycled into GABA and glutamate. Astrocytes are also important for maintaining proper ionic balance in the extracellular fluid. This process, which is called gliosis, is for the CNS what scarring is for extraneural tissues.