Gliosis is the multiplication of astrocytes in the brain due to enjury or damage, often leading to the formation of glial scar. Astrocytes are glial cells, which perform a supporting rol in the CNS. When neurons die, they are replaced by astrocytes, which react to injury by hypertrophy and up-regulation of the glial-fibrillary acidic protein. During gliosis, the astrocyte's nucleus enlarges and becomes vesicular and nucleolus becomes prominent. Previously scant cytoplasm expands and becomes bright pink and irregular from which arise numerous processes.
Gliosis is an important feature of many diseases of the central nervous system, which include Alzheimer's disease, multiple sclerosis, and Korsakoff's syndrome. Bergmann gliosis is associated with anoxic injury and is characterized by death of Purkinje cells.