[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.
It is estimated that astrocytes can make contact with over 100,000 synapses, allowing them to play an essential role in synaptic transmission.
[5] These cells do not simply carry out functions of structural support, but can also take part in cell-to-cell communication with neurons, microglia, and other astrocytes by receiving inputs, organizing information, and sending out chemical signals.
[1] The definition of a gliotransmitter is not only defined by its presence in glial cells, but is determined by other factors, including its metabolic pathway.
Glutamate is the major excitatory neurotransmitter within the central nervous system that can also be defined as a gliotransmitter due to its ability to increase cytosolic Ca2+ concentrations in astrocytes.
[7] Calcium can enter through NMDAR channels due to the cell's depolarization, which removes the magnesium block, and therefore activating these receptors.
[1] ATP has several functions as a gliotransmitter, including insertion of AMPA receptors into the postsynaptic terminal, paracrine activity through calcium waves in astrocytes, and suppression of synaptic transmission.
[8] ATP plays a role in facilitating neuroinflammation and remyelination by entering into the cell's extracellular space upon injury to activate purinergic receptors, which increase the production of gliotransmitters.
Potassium channels between the astrocyte and the presynaptic terminal make it possible to release K+ ions and avoid accumulation after neuronal activity.
[3] The capability of a human to respond to change in both the external and internal environment is increased due to the hormonal regulation of the tripartite synapse.
[1] Studies have also shown that increased and decreased stimulation of NMDARs, which is controlled by astrocytes, play a role in various neurodegenerative disorders.
The fact that cycloserine, which acts as an agonist for the NMDAR's binding site, is used in the treatment for patients with schizophrenia further supports the glutamate hypothesis.
Although that some studies show that the all excitations caused by gliotransmission lead to epileptic discharges, but it could possibly increase the intensity of length of epileptiform activity.