astrocyte

Astrocytes are star-shaped glial cells of the central nervous system that perform a wide range of support and regulatory roles for neurons. They are the most abundant glial cell type in the brain and spinal cord, and they modestly differ in gray matter (protoplasmic) versus white matter (fibrous) regions. During development, astrocytes arise from radial glia and populate neural tissue; mature astrocytes express markers such as GFAP and S100β.

Key functions of astrocytes include maintaining extracellular ion balance, particularly potassium, and clearing neurotransmitters from synapses, notably glutamate and GABA, to limit excitotoxicity. They supply metabolic support to neurons through glycolysis and the astrocyte–neuron lactate shuttle, and they contribute to the formation and maintenance of the blood–brain barrier by enwrapping capillaries with endfeet. Astrocytes also regulate cerebral blood flow in response to neuronal activity, participate in synapse formation and remodeling, and facilitate waste clearance via the glymphatic system, aided by aquaporin-4 water channels at their endfeet.

Astrocytes communicate through complex networks linked by gap junctions and exhibit intracellular calcium signaling that can propagate across networks. They play a role in immune and inflammatory responses within the CNS and help shape neural circuitry during development and learning.

In disease, astrocytes participate in reactive astrogliosis and glial scar formation following injury. Their responses can be protective or detrimental, influencing outcomes in conditions such as stroke, traumatic brain injury, epilepsy, and neurodegenerative diseases.