Astrocytes are cells of the central nervous system which act as both physical and physiological support for the neurones that are embedded between them, regulating water movement, facilitating metabolic exchange between neurones and capillaries, as well as responding to mechanical and biochemical insults to the brain (e.g. gliosis) 1.
Astrocytes are divided into two types 2:
- protoplasmic astrocytes
- fibrous astrocytes
Protoplasmic astrocytes
Protoplasmic astrocytes are particularly abundant in the grey matter, where they are the most abundant glial cells 1,2. They are highly branched with processes distributed fairly uniformly around the cell body. The end-feet of these processes wrap around blood vessels and form the outermost layer of the blood-brain barrier, the subpial glia limitans 2. They have abundant Aquaporin 4 water channel expression and have a role in regulating extracellular fluid transport (known as the glymphatic pathway).
Fibrous astrocytes
Fibrous astrocytes are primarily located within the white matter and have fewer and far longer processes, contacting nodes of Ranvier of axons as well as supporting and wrapping around local capillaries 2.
Histology
Immunohistochemistry
Astrocytes are most easily identified by immunohistochemical staining for GFAP and S100 1.
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