Astrocytes and Brain Signalling

Abstract

Astrocytes are active, receptive and complex cells that are intimately related to neurons and synapses. They are involved in the regulation of nerve cell activity and in processing neuronal information.

Keywords: astrocytes; calcium; ionic balance; tripartite synapse

Figure 1.

pH regulation by glial cells. Diagram of an astrocyte illustrating the main mechanisms involved in pH regulation. The three major regulatory mechanisms are the Na+/H+ exchanger, the Cl/HCO3 exchanger and the enzyme carbonic anhydrase (CA) that converts carbon dioxide into HCO3. Adapted from Deitmer and Rose .

Figure 2.

The tripartite synapse. By sending processes around the two neuronal elements of the synapse (left panel), astrocytes are ideally positioned to participate actively in synaptic transmission. Once neurotransmitters are released in the synaptic cleft (1), the postsynaptic neuron and the astrocyte process detect this synaptic signal through the binding of neurotransmitters on receptors (2). Then, the subsequent increase in calcium, in the astrocytes (3) induces release of gliotransmitters (4) in the synaptic cleft to modulate synaptic transmission (5) and neuronal excitability (6).

Figure 3.

Mechanisms of Ca2+ waves. Diagram illustrating the mechanisms involved in the production of the glial Ca2+ waves. Upon activation by glutamate, an elevation in inositol trisphosphate (IP3) production causing the release of Ca2+ from internal stores will lead to the release of adenosine trisphosphate (ATP) by the astrocyte. The ATP will activate purinergic receptors of neighbour astrocytes, causing an elevation of Ca2+ and an additional release of ATP, which will extend further on to additional astrocytes. There is also evidence that IP3 could pass through gap junctions from astrocytes to astrocytes.

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Further Reading

Araque A, Parpura V, Sanzgiri RP and Haydon PG (1999) Tripartite synapses: glia, the unacknowledged partner. Trends in Neuroscience 822: 208–215.

Auld DS and Robitaille R (2003) Glial cells and neurotransmission: an inclusive view of synaptic function. Neuron 40: 389–400.

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Halassa MM, Fellin T and Haydon PG (2007) The tripartite synapse: roles for gliotransmission in health and disease. Trends in Molecular Medecine 13: 54–63.

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Perea G and Araque A (2005) Glial calcium signaling and neuron‐glia communication. Cell Calcium 38: 375–382.

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Panatier, Aude, and Robitaille, Richard(Dec 2007) Astrocytes and Brain Signalling. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0000016.pub2]