Interneuron
{{short description|Neurons that are not motor or sensory}}
{{Infobox neuron
| name = Interneuron
| image = File:Interneuron566-01.svg
|caption = Cartoon of a locust interneuron that integrates information about wind in order to control wing motor neurons during flightPearson, K. G. and Wolf, H. Connections of hindwing tegulae with
flight neurones in the locust, Locusta migratoria. J. Exp. Biol. 135:
381-409, 1988
|location=Nervous system}}
Interneurons (also called internuncial neurons, association neurons, connector neurons, or intermediate neurons) are neurons that are not specifically motor neurons or sensory neurons. Interneurons are the central nodes of neural circuits, enabling communication between sensory or motor neurons and the central nervous system (CNS).{{cite web |url=https://qbi.uq.edu.au/brain/brain-anatomy/types-neurons |title=Types of neurons - Queensland Brain Institute - University of Queensland |format= |date=9 November 2017 |accessdate=}} They play vital roles in reflexes, neuronal oscillations,{{cite journal |doi=10.1016/S0167-8760(00)00173-2 |pmid=11102670 |title=Inhibition-based rhythms: Experimental and mathematical observations on network dynamics |journal=International Journal of Psychophysiology |volume=38 |issue=3 |pages=315–36 |year=2000 |last1=Whittington |first1=M.A |last2=Traub |first2=R.D |last3=Kopell |first3=N |last4=Ermentrout |first4=B |last5=Buhl |first5=E.H |citeseerx=10.1.1.16.6410 }} and neurogenesis in the adult mammalian brain.{{Citation needed|date=April 2021}}
Interneurons can be further broken down into two groups: local interneurons and relay interneurons.{{cite book |last=Carlson |first=Neil R. |title=Physiology of Behavior |url=https://archive.org/details/physiologybehavi00carl_811 |url-access=limited |publisher=Pearson Higher Education |year=2013 |page=[https://archive.org/details/physiologybehavi00carl_811/page/n48 28] |isbn=978-0-205-23939-9 |edition=11th}} Local interneurons have short axons and form circuits with nearby neurons to analyze small pieces of information.{{cite book |editor1-first=Eric |editor1-last=Kandel |editor2-first=James |editor2-last=Schwartz |editor3-first=Thomas |editor3-last=Jessell |year=2000 |title=Principles of Neural Science |edition=4th |location=New York City, New York |publisher=McGraw Hill Companies |page=[https://archive.org/details/isbn_9780838577011/page/25 25] |isbn=978-0-8385-7701-1 |url-access=registration |url=https://archive.org/details/isbn_9780838577011/page/25 }} Relay interneurons have long axons and connect circuits of neurons in one region of the brain with those in other regions. However, interneurons are generally considered to operate mainly within local brain areas.{{cite journal |last1=Kepecs |first1=Adam |last2=Fishell |first2=Gordon |title=Interneuron Cell Types: Fit to form and formed to fit |journal=Nature |year=2014 |volume=505 |issue=7483 |pages=318–326 |publisher=Nature, 2014 HHS Public Access pp 10, 28|doi=10.1038/nature12983 |pmid=24429630 |pmc=4349583 }} The interaction between interneurons allows the brain to perform complex functions such as learning and decision-making.
Structure
In the human brain, approximately 20–30% of the neurons in the neocortex are interneurons, and the remaining majority of neurons are pyramidal.{{cite journal | last1 = Markram | first1 = Henry |display-authors=etal | year = 2004 | title = Interneurons of the neocortical inhibitory system | journal = Nature Reviews Neuroscience | volume = 5 | issue = 10| pages = 793–807 | doi=10.1038/nrn1519 | pmid=15378039| s2cid = 382334 }} 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 [https://en.wiktionary.org/wiki/coetaneous coetaneous] interneurons is neuronal birthdating.{{Cite journal|last1=Ng|first1=Hui Xuan|last2=Lee|first2=Ean Phing|last3=Cavanagh|first3=Brenton L.|last4=Britto|first4=Joanne M.|last5=Tan|first5=Seong-Seng|title=A method for isolating cortical interneurons sharing the same birthdays for gene expression studies|journal=Experimental Neurology|volume=295|pages=36–45|doi=10.1016/j.expneurol.2017.05.006|pmid=28511841|year=2017|s2cid=3377296}} This can be achieved using nucleoside analogs such as EdU.{{Cite journal|last1=Endaya|first1=Berwini|last2=Cavanagh|first2=Brenton|last3=Alowaidi|first3=Faisal|last4=Walker|first4=Tom|last5=Pennington|first5=Nicholas de|last6=Ng|first6=Jin-Ming A.|last7=Lam|first7=Paula Y.P.|last8=Mackay-Sim|first8=Alan|last9=Neuzil|first9=Jiri|title=Isolating dividing neural and brain tumour cells for gene expression profiling|journal=Journal of Neuroscience Methods|volume=257|pages=121–133|doi=10.1016/j.jneumeth.2015.09.020|pmid=26432933|year=2016|s2cid=44969376}}
= Spinal cord =
- Ia inhibitory interneuron: Found in lamina VII. Responsible for inhibiting antagonist motor neuron. 1a spindle afferents activate 1a inhibitory neuron.
- File:Anatomy and physiology of animals A reflex arc.jpg (relay neuron) forms part of a reflex arc]]Ib inhibitory interneuron: Found in lamina V, VI, VII. Afferent or Golgi tendon organ activates it.
= Cortex =
- Parvalbumin-expressing interneurons
- CCK-expressing interneurons
- VIP-expressing interneurons
- SOM-expressing interneurons{{cite journal|last1=Muñoz|first1=W|last2=Tremblay|first2=R|last3=Levenstein|first3=D|last4=Rudy|first4=B|title=Layer-specific modulation of neocortical dendritic inhibition during active wakefulness.|journal=Science|date=3 March 2017|volume=355|issue=6328|pages=954–959|pmid=28254942|doi=10.1126/science.aag2599|bibcode=2017Sci...355..954M|doi-access=free}}
= Cerebellum =
=Striatum=
- Parvalbumin-expressing interneurons{{cite journal |doi=10.1038/8138 |pmid=10321252 |year=1999 |last1=Tepper |first1=James M. |title=Inhibitory control of neostriatal projection neurons by GABAergic interneurons |journal=Nature Neuroscience |volume=2 |issue=5 |pages=467–72 |last2=Koós |first2=Tibor |s2cid=16088859 }}
- Cholinergic interneurons{{cite journal |doi=10.1002/neu.10150 |pmid=12436423 |title=Cholinergic interneuron characteristics and nicotinic properties in the striatum |journal=Journal of Neurobiology |volume=53 |issue=4 |pages=590–605 |year=2002 |last1=Zhou |first1=Fu-Ming |last2=Wilson |first2=Charles J. |last3=Dani |first3=John A. |doi-access=free }}{{cite journal |doi=10.1038/nn.2984 |pmid=22158514 |pmc=3245803 |title=GABAergic circuits mediate the reinforcement-related signals of striatal cholinergic interneurons |journal=Nature Neuroscience |volume=15 |issue=1 |pages=123–30 |year=2011 |last1=English |first1=Daniel F |last2=Ibanez-Sandoval |first2=Osvaldo |last3=Stark |first3=Eran |last4=Tecuapetla |first4=Fatuel |last5=Buzsáki |first5=György |last6=Deisseroth |first6=Karl |last7=Tepper |first7=James M |last8=Koos |first8=Tibor }}
- Tyrosine hydroxylase-expressing interneurons{{cite journal |doi=10.1523/JNEUROSCI.5996-09.2010 |pmid=20484642 |title=Electrophysiological and Morphological Characteristics and Synaptic Connectivity of Tyrosine Hydroxylase-Expressing Neurons in Adult Mouse Striatum |journal=Journal of Neuroscience |volume=30 |issue=20 |pages=6999–7016 |year=2010 |last1=Ibanez-Sandoval |first1=O. |last2=Tecuapetla |first2=F. |last3=Unal |first3=B. |last4=Shah |first4=F. |last5=Koos |first5=T. |last6=Tepper |first6=J. M. |pmc=4447206}}
- Calretinin-expressing interneurons{{cite journal |doi=10.3389/fnana.2010.00150 |title=Heterogeneity and Diversity of Striatal GABAergic Interneurons |journal=Frontiers in Neuroanatomy |volume=4 |year=2010 |last1=Ibáñez-Sandoval |first1=Osvaldo |last2=Koós |first2=Tibor |last3=Tecuapetla |first3=Fatuel |last4=Tepper |first4=James M. |pmid=21228905 |pages=150 |pmc=3016690|doi-access=free }}
- Nitric oxide synthase-expressing interneurons
Function
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.
In addition to these general functions, interneurons in the insect CNS play a number of specific roles in different parts of the nervous system, and also are either excitatory or inhibitory. For example, in the olfactory system, interneurons are responsible for integrating information from odorant receptors and sending signals to the mushroom bodies, which are involved in learning and memory.{{Cite journal |last1=Liou |first1=Nan-Fu |last2=Lin |first2=Shih-Han |last3=Chen |first3=Ying-Jun |last4=Tsai |first4=Kuo-Ting |last5=Yang |first5=Chi-Jen |last6=Lin |first6=Tzi-Yang |last7=Wu |first7=Ting-Han |last8=Lin |first8=Hsin-Ju |last9=Chen |first9=Yuh-Tarng |last10=Gohl |first10=Daryl M. |last11=Silies |first11=Marion |last12=Chou |first12=Ya-Hui |date=2018-06-08 |title=Diverse populations of local interneurons integrate into the Drosophila adult olfactory circuit |journal=Nature Communications |language=en |volume=9 |issue=1 |pages=2232 |doi=10.1038/s41467-018-04675-x |issn=2041-1723 |pmc=5993751 |pmid=29884811|bibcode=2018NatCo...9.2232L }}{{Cite journal |last1=Zheng |first1=Zhihao |last2=Li |first2=Feng |last3=Fisher |first3=Corey |last4=Ali |first4=Iqbal J. |last5=Sharifi |first5=Nadiya |last6=Calle-Schuler |first6=Steven |last7=Hsu |first7=Joseph |last8=Masoodpanah |first8=Najla |last9=Kmecova |first9=Lucia |last10=Kazimiers |first10=Tom |last11=Perlman |first11=Eric |last12=Nichols |first12=Matthew |last13=Li |first13=Peter H. |last14=Jain |first14=Viren |last15=Bock |first15=Davi D. |date=August 2022 |title=Structured sampling of olfactory input by the fly mushroom body |url=|journal=Current Biology |volume=32 |issue=15 |pages=3334–3349.e6 |doi=10.1016/j.cub.2022.06.031 |issn=0960-9822 |pmc=9413950 |pmid=35797998}} In the visual system, interneurons are responsible for processing motion information and sending signals to the optic lobes, which are involved in visual navigation.{{Cite journal |last=Zhu |first=Yan |date=2013-07-29 |title=The Drosophila visual system: From neural circuits to behavior |journal=Cell Adhesion & Migration |language=en |volume=7 |issue=4 |pages=333–344 |doi=10.4161/cam.25521 |issn=1933-6918 |pmc=3739809 |pmid=23880926}}{{Cite journal |last1=Shinomiya |first1=Kazunori |last2=Nern |first2=Aljoscha |last3=Meinertzhagen |first3=Ian A. |last4=Plaza |first4=Stephen M. |last5=Reiser |first5=Michael B. |date=August 2022 |title=Neuronal circuits integrating visual motion information in Drosophila melanogaster |journal=Current Biology |volume=32 |issue=16 |pages=3529–3544.e2 |doi=10.1016/j.cub.2022.06.061 |issn=0960-9822|doi-access=free |pmid=35839763 }}
Interneurons are also important for coordinating complex behaviors, such as flight and locomotion. For example, interneurons in the thoracic ganglia are responsible for coordinating the activity of the leg muscles during walking{{Cite journal |last1=Bidaye |first1=Salil S. |last2=Laturney |first2=Meghan |last3=Chang |first3=Amy K. |last4=Liu |first4=Yuejiang |last5=Bockemühl |first5=Till |last6=Büschges |first6=Ansgar |last7=Scott |first7=Kristin |date=November 2020 |title=Two Brain Pathways Initiate Distinct Forward Walking Programs in Drosophila |journal=Neuron |language=en |volume=108 |issue=3 |pages=469–485.e8 |doi=10.1016/j.neuron.2020.07.032 |pmc=9435592 |pmid=32822613}} and flying.{{Cite journal |last1=King |first1=David G. |last2=Wyman |first2=Robert J. |date=1980-12-01 |title=Anatomy of the giant fibre pathway inDrosophila. I. Three thoracic components of the pathway |url=|journal=Journal of Neurocytology |language=en |volume=9 |issue=6 |pages=753–770 |doi=10.1007/BF01205017 |pmid=6782199 |s2cid=10530883 |issn=1573-7381}}
Interneurons' main function is to provide a neural circuit, conducting flow of signals or information between sensory neurons and motor neurons.{{cite web |url=https://qbi.uq.edu.au/brain/brain-anatomy/types-neurons#:~:text=and%20several%20dendrites.-,Interneurons,forming%20circuits%20of%20various%20complexity. |title=Types of Neurons|website=University of Queensland |date=9 November 2017 |publisher=Queensland Brain Institute |access-date=26 April 2023}}