Axo-axonic synapse

An axo-axonic synapse is a type of synapse, formed by one neuron projecting its axon terminals onto another neuron's axon.[1]

Axo-axonic synapses have been found and described more recently than the other more familiar types of synapses, such as axo-dendritic synapses and axo-somatic synapses. The spatio-temporal properties of neurons get altered by the type of synapse formed between neurons. Unlike the other types, the axo-axonic synapse does not contribute towards triggering an action potential in the postsynaptic neuron. Instead, it affects the probability of neurotransmitter release in the response to any action potential passing through the axon of the postsynaptic neuron.[2] Thus, axo-axonic synapses appear to be very important for the brain in achieving a specialized neural computation.

Axo-axonic synapses are found throughout the central nervous system, including in the hippocampus, cerebral cortex and striatum in mammals;[3][4][5] in the neuro-muscular junctions in crustaceans;[6][7] and in the visual circuitry in dipterans.[8] Axo-axonic synapses can induce either inhibitory or excitatory effects in the postsynaptic neuron.[6][7][9] A classic example of the role of axo-axonic synapses is causing inhibitory effects on motoneurons in the spinal-somatic reflex arc. This phenomenon is known as presynaptic-inhibition.[10][11]

  1. ^ Palay SL (July 1956). "Synapses in the central nervous system". The Journal of Biophysical and Biochemical Cytology. 2 (4 Suppl): 193–202. doi:10.1083/jcb.2.4.193. PMC 2229686. PMID 13357542.
  2. ^ Howard A, Tamas G, Soltesz I (June 2005). "Lighting the chandelier: new vistas for axo-axonic cells". Trends in Neurosciences. 28 (6): 310–6. doi:10.1016/j.tins.2005.04.004. PMID 15927687. S2CID 34853701.
  3. ^ Buhl EH, Han ZS, Lörinczi Z, Stezhka VV, Karnup SV, Somogyi P (April 1994). "Physiological properties of anatomically identified axo-axonic cells in the rat hippocampus". Journal of Neurophysiology. 71 (4): 1289–307. doi:10.1152/jn.1994.71.4.1289. PMID 8035215.
  4. ^ Somogyi P, Freund TF, Cowey A (1982-11-01). "The axo-axonic interneuron in the cerebral cortex of the rat, cat and monkey". Neuroscience. 7 (11): 2577–607. doi:10.1016/0306-4522(82)90086-0. PMID 7155343. S2CID 8693953.
  5. ^ Gobel S (October 1971). "Axo-axonic septate junctions in the basket formations of the cat cerebellar cortex". The Journal of Cell Biology. 51 (1): 328–33. doi:10.1083/jcb.51.1.328. PMC 2108243. PMID 5165176.
  6. ^ a b Atwood HL, Jones A (December 1967). "Presynaptic inhibition in crustacean muscle: axo-axonal synapse". Experientia. 23 (12): 1036–8. doi:10.1007/BF02136434. PMID 4294865. S2CID 27917444.
  7. ^ a b Govind CK, Atwood HL, Pearce J (January 1995). "Inhibitory axoaxonal and neuromuscular synapses in the crayfish opener muscle: membrane definition and ultrastructure". The Journal of Comparative Neurology. 351 (3): 476–88. doi:10.1002/cne.903510313. PMID 7706554. S2CID 24022348.
  8. ^ Cuntz H, Haag J, Forstner F, Segev I, Borst A (June 2007). "Robust coding of flow-field parameters by axo-axonal gap junctions between fly visual interneurons". Proceedings of the National Academy of Sciences of the United States of America. 104 (24): 10229–33. Bibcode:2007PNAS..10410229C. doi:10.1073/pnas.0703697104. PMC 1886000. PMID 17551009.
  9. ^ Szabadics J, Varga C, Molnár G, Oláh S, Barzó P, Tamás G (January 2006). "Excitatory effect of GABAergic axo-axonic cells in cortical microcircuits". Science. 311 (5758): 233–5. Bibcode:2006Sci...311..233S. doi:10.1126/science.1121325. PMID 16410524. S2CID 40744562.
  10. ^ Eccles JC (1961-12-01). "The mechanism of synaptic transmission". Ergebnisse der Physiologie, Biologischen Chemie und Experimentellen Pharmakologie. 51 (1): 299–430. doi:10.1007/BF02269100. PMID 13889060. S2CID 84195141.
  11. ^ Alford S, Schwartz E (2009-01-01), "Presynaptic Inhibition", in Squire LR (ed.), Encyclopedia of Neuroscience, Academic Press, pp. 1001–1006, doi:10.1016/b978-008045046-9.00814-7, ISBN 978-0-08-045046-9