Gliotransmitter

Gliotransmitters are chemicals released from glial cells that facilitate neuronal communication between neurons and other glial cells. They are usually induced from Ca²⁺ signaling,^[1] although recent research has questioned the role of Ca²⁺ in gliotransmitters and may require a revision of the relevance of gliotransmitters in neuronal signalling in general.^[2]

While gliotransmitters can be released from any glial cell, including oligodendrocytes, astrocytes, and microglia, they are primarily released from astrocytes.^{[citation needed]} Astrocytes rely on gap junctions for coupling, and are star-like in shape, which allows them to come into contact with many other synapses in various regions of the brain. Their structure also makes them capable of bidirectional signaling. It is estimated that astrocytes can make contact with over 100,000 synapses, allowing them to play an essential role in synaptic transmission.^[1] While gliotransmission primarily occurs between astrocytes and neurons, gliotransmission is not limited to these two cell types.^[3] Besides the central nervous system, gliotransmission also occurs among motor nerve terminals and Schwann cells in the peripheral nervous system. Another occurrence of gliotransmission takes place between glial cells in the retina, called Müller cells, and retinal neurons.^[3]