An interneuron (also called internuncial neuron, relay neuron, association neuron, connector neuron, intermediate neuron or local circuit neuron) is a broad class of neurons found in the central nervous system. Interneurons are the central nodes of neural circuits, enabling communication between sensory or motor neurons and the central nervous system (CNS). They play vital roles in reflexes, neuronal oscillations,[2] and neurogenesis in the adult mammalian brain.

Cartoon of a locust interneuron that integrates information about wind in order to control wing motor neurons during flight [1]
NeuroLex IDbirnlex_2534
Anatomical terms of neuroanatomy

Interneurons can be further broken down into two groups: local interneurons and relay interneurons.[3] Local interneurons have short axons and form circuits with nearby neurons to analyze small pieces of information.[4] Relay interneurons have long axons and connect circuits of neurons in one region of the brain with those in other regions.[4] The interaction between interneurons allow the brain to perform complex functions such as learning, and decision-making.


In the neocortex (making up about 80% of the human brain), approximately 20-30% of neurons are interneurons.[5] Investigations into the molecular diversity of neurons is impeded by the inability to isolate cell populations born at different times for gene expression analysis. An effective means of identifying coetaneous interneurons is neuronal birthdating.[6] This can be achieved using nucleoside analogs such as EdU.[7][6]

In 2008, a nomenclature for the features of GABAergic cortical interneurons was proposed, called Petilla terminology.[8]

Spinal cord

A spinal interneuron (relay neuron) forms part of a reflex arc
LocationNervous system
NeuroLex IDbirnlex_2534
Anatomical terms of neuroanatomy


  • Parvalbumin-expressing interneurons
  • CCK-expressing interneurons
  • VIP-expressing interneurons
  • SOM-expressing interneurons[9]



  • Parvalbumin-expressing interneurons[10]
  • Cholinergic interneurons[11][12]
  • Tyrosine hydroxylase-expressing interneurons[13]
  • Calretinin-expressing interneurons[14]
  • Nitric oxide synthase-expressing interneurons[14]


Interneurons in the CNS are primarily inhibitory, and use the neurotransmitter GABA or glycine. However, excitatory interneurons using glutamate in the CNS also exist, as do interneurons releasing neuromodulators like acetylcholine. Interneurons main function is to provide a neural circuit, conducting flow of signals or information between a sensory neuron and or motor neuron.


  1. Pearson, K. G. and Wolf, H. Connections of hindwing tegulae with flight neurones in the locust, Locusta migratoria. J. Exp. Biol. 135: 381-409, 1988
  2. Whittington, M.A; Traub, R.D; Kopell, N; Ermentrout, B; Buhl, E.H (2000). "Inhibition-based rhythms: Experimental and mathematical observations on network dynamics". International Journal of Psychophysiology. 38 (3): 315–36. CiteSeerX doi:10.1016/S0167-8760(00)00173-2. PMID 11102670.
  3. Carlson, Neil R. (2013). Physiology of Behavior (11th ed.). Pearson Higher Education. p. 28. ISBN 978-0-205-23939-9.
  4. Kandel, Eric; Schwartz, James; Jessell, Thomas, eds. (2000). Principles of Neural Science (4th ed.). New York City, New York: McGraw Hill Companies. p. 25. ISBN 978-0-8385-7701-1.
  5. Markram, Henry; et al. (2004). "Interneurons of the neocortical inhibitory system". Nature Reviews Neuroscience. 5 (10): 793–807. doi:10.1038/nrn1519. PMID 15378039.
  6. Ng, Hui Xuan; Lee, Ean Phing; Cavanagh, Brenton L.; Britto, Joanne M.; Tan, Seong-Seng (2017). "A method for isolating cortical interneurons sharing the same birthdays for gene expression studies". Experimental Neurology. 295: 36–45. doi:10.1016/j.expneurol.2017.05.006. PMID 28511841.
  7. Endaya, Berwini; Cavanagh, Brenton; Alowaidi, Faisal; Walker, Tom; Pennington, Nicholas de; Ng, Jin-Ming A.; Lam, Paula Y.P.; Mackay-Sim, Alan; Neuzil, Jiri (2016). "Isolating dividing neural and brain tumour cells for gene expression profiling". Journal of Neuroscience Methods. 257: 121–133. doi:10.1016/j.jneumeth.2015.09.020. PMID 26432933.
  8. Ascoli, Giorgio A.; Alonso-Nanclares, Lidia; Anderson, Stewart A.; Barrionuevo, German; Benavides-Piccione, Ruth; Burkhalter, Andreas; Buzsáki, György; Cauli, Bruno; Defelipe, Javier; Fairén, Alfonso; Feldmeyer, Dirk; Fishell, Gord; Fregnac, Yves; Freund, Tamas F.; Gardner, Daniel; Gardner, Esther P.; Goldberg, Jesse H.; Helmstaedter, Moritz; Hestrin, Shaul; Karube, Fuyuki; Kisvárday, Zoltán F.; Lambolez, Bertrand; Lewis, David A.; Marin, Oscar; Markram, Henry; Muñoz, Alberto; Packer, Adam; Petersen, Carl C. H.; Rockland, Kathleen S.; et al. (2008). "Petilla terminology: Nomenclature of features of GABAergic interneurons of the cerebral cortex". Nature Reviews Neuroscience. 9 (7): 557–68. doi:10.1038/nrn2402. PMC 2868386. PMID 18568015.
  9. Muñoz, W; Tremblay, R; Levenstein, D; Rudy, B (3 March 2017). "Layer-specific modulation of neocortical dendritic inhibition during active wakefulness". Science. 355 (6328): 954–959. doi:10.1126/science.aag2599. PMID 28254942.
  10. Tepper, James M.; Koós, Tibor (1999). "Inhibitory control of neostriatal projection neurons by GABAergic interneurons". Nature Neuroscience. 2 (5): 467–72. doi:10.1038/8138. PMID 10321252.
  11. Zhou, Fu-Ming; Wilson, Charles J.; Dani, John A. (2002). "Cholinergic interneuron characteristics and nicotinic properties in the striatum". Journal of Neurobiology. 53 (4): 590–605. doi:10.1002/neu.10150. PMID 12436423.
  12. English, Daniel F; Ibanez-Sandoval, Osvaldo; Stark, Eran; Tecuapetla, Fatuel; Buzsáki, György; Deisseroth, Karl; Tepper, James M; Koos, Tibor (2011). "GABAergic circuits mediate the reinforcement-related signals of striatal cholinergic interneurons". Nature Neuroscience. 15 (1): 123–30. doi:10.1038/nn.2984. PMC 3245803. PMID 22158514.
  13. Ibanez-Sandoval, O.; Tecuapetla, F.; Unal, B.; Shah, F.; Koos, T.; Tepper, J. M. (2010). "Electrophysiological and Morphological Characteristics and Synaptic Connectivity of Tyrosine Hydroxylase-Expressing Neurons in Adult Mouse Striatum". Journal of Neuroscience. 30 (20): 6999–7016. doi:10.1523/JNEUROSCI.5996-09.2010. PMC 4447206. PMID 20484642.
  14. Ibáñez-Sandoval, Osvaldo; Koós, Tibor; Tecuapetla, Fatuel; Tepper, James M. (2010). "Heterogeneity and Diversity of Striatal GABAergic Interneurons". Frontiers in Neuroanatomy. 4: 150. doi:10.3389/fnana.2010.00150. PMC 3016690. PMID 21228905.
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