Editing Chemical synapse (section)

==Volume transmission==
When a neurotransmitter is released at a synapse, it reaches its highest concentration inside the narrow space of the synaptic cleft, but some of it is certain to diffuse away before being reabsorbed or broken down.  If it diffuses away, it has the potential to activate receptors that are located either at other synapses or on the membrane away from any synapse.  The extrasynaptic activity of a neurotransmitter is known as ''volume transmission''.<ref>{{cite journal |vauthors=Zoli M, Torri C, Ferrari R |title=The emergence of the volume transmission concept |journal=Brain Res. Brain Res. Rev. |volume=26 |pages=136–47 |year=1998 |pmid=9651506 |doi=10.1016/S0165-0173(97)00048-9 |issue=2–3|s2cid=20495134 |display-authors=etal}}</ref>  It is well established that such effects occur to some degree, but their functional importance has long been a matter of controversy.<ref>{{cite journal |vauthors=Fuxe K, Dahlström A, Höistad M |title=From the Golgi-Cajal mapping to the transmitter-based characterization of the neuronal networks leading to two modes of brain communication: wiring and volume transmission |journal=Brain Res Rev |volume=55 |pages=17–54 |year=2007 |pmid=17433836 |doi=10.1016/j.brainresrev.2007.02.009 |issue=1|display-authors=etal|url=https://iris.unipa.it/bitstream/10447/9980/1/2007%20Brain%20Res%20rev.pdf |hdl=10447/9980 |s2cid=1323780 |hdl-access=free }}</ref>

Recent work indicates that volume transmission may be the predominant mode of interaction for some special types of neurons.  In the mammalian cerebral cortex, a class of neurons called [[neurogliaform cells]] can inhibit other nearby cortical neurons by releasing the neurotransmitter GABA into the extracellular space.<ref name="Olah2009">{{cite journal |vauthors=Oláh S, Füle M, Komlósi G |title=Regulation of cortical microcircuits by unitary GABA-mediated volume transmission |journal=Nature |volume=461 |pages=1278–81 |year=2009 |pmid=19865171 |doi=10.1038/nature08503 |issue=7268 |pmc=2771344|bibcode = 2009Natur.461.1278O |display-authors=etal}}</ref> Along the same vein, GABA released from neurogliaform cells into the extracellular space also acts on surrounding [[astrocyte]]s, assigning a role for volume transmission in the control of ionic and neurotransmitter homeostasis.<ref>{{cite journal |vauthors=Rózsa M, Baka J, Bordé S, Rózsa B, Katona G, Tamás G |title=Unitary GABAergic volume transmission from individual interneurons to astrocytes in the cerebral cortex |journal=Brain Structure and Function |volume=222 |issue=1 |pages=651–659 |year=2015|pmid=26683686 |doi=10.1007/s00429-015-1166-9  |s2cid=30728927 |display-authors=etal|url=http://publicatio.bibl.u-szeged.hu/7829/1/2015%20-%20R%C3%B3zsa%20et%20al.%20-%20Unitary%20GABAergic%20volume%20transmission%20from%20individual%20interneurons%20to%20astrocytes%20in%20the%20cerebral%20cortex%20-%20Brain%20St.pdf }}</ref> Approximately 78% of neurogliaform cell boutons do not form classical synapses. This may be the first definitive example of neurons communicating chemically where classical synapses are not present.<ref name="Olah2009" />