Editing Neuropil

{{Short description|Type of area in the nervous system}}
{{more citations needed|date=April 2012}}
{{Infobox microanatomy
| Name     = Neuropil
| Latin    = neuropilus
| Image    =
| Caption   =
| Image2    =
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| Precursor  =
| System    = [[Nervous system]]
}}
'''Neuropil''' (or "'''neuropile'''") is any area in the [[nervous system]] composed of mostly [[Myelin|unmyelinated]] [[axons]], [[dendrite]]s and [[glial cell]] processes that forms a synaptically dense region containing a relatively low number of cell bodies. The most prevalent anatomical region of neuropil is the [[brain]] which, although not completely composed of neuropil, does have the largest and highest synaptically concentrated areas of neuropil in the body. For example, the [[neocortex]] and [[olfactory bulb]] both contain neuropil.<ref name="Purves">{{cite book|title=Neuroscience|year=2012|publisher=Sinauer Associates, Inc.|location=Sunderland, Massachusetts|isbn=978-0-87893-695-3|edition=Fifth|editor1=Dale Purves |editor2=George J. Augustine |editor3=David Fitzpatrick |editor4=William C. Hall |editor5=Anthony-Samuel LaMantia |editor6=Leonard E. White<!-- |access-date=20 April 2012|format=Textbook-->|chapter=1}}{{pn|date=February 2022}}</ref>

[[White matter]], which is mostly composed of myelinated axons (hence its white color) and glial cells, is generally not considered to be a part of the neuropil.{{Citation needed|date=January 2009}}

[[File:Gray881.png|thumb]]

Neuropil (pl. neuropils) comes from the Greek: ''neuro'', meaning "tendon, sinew; nerve" and ''pilos'', meaning "felt".<ref>Freeman, Walter J. ''How Brains Make up their Minds '', 2000, p. 47</ref> The term's origin can be traced back to the late 19th century.<ref>{{cite web|last=Pearsall|first=Judy|title=Neuropil|url=http://oxforddictionaries.com/definition/neuropil|archive-url=https://web.archive.org/web/20110611005804/http://oxforddictionaries.com/definition/neuropil|url-status=dead|archive-date=June 11, 2011|work=Oxford Dictionaries Online|publisher=Oxford University Press|access-date=20 April 2012}}</ref>

==Location==
Neuropil has been found in the following regions: outer neocortex layer, [[barrel cortex]], [[inner plexiform layer]] and [[outer plexiform layer]], [[posterior pituitary]], and glomeruli of the [[cerebellum]]. These are all found in humans, with the exception of the barrel cortex, but many species have counterparts similar to our own regions of neuropil. However, the degree of similarity depends upon the composition of neuropil being compared. The concentrations of neuropil within certain regions are important to determine because simply using the proportions of the different postsynaptic elements does not verify the necessary, conclusive evidence. Comparing the concentrations can determine whether or not proportions of different postsynaptic elements contacted a particular axonal pathway. Relative concentrations could signify a reflection of different postsynaptic elements in the neuropil or show that axons sought out and formed synapses only with specific postsynaptic elements.<ref name="White">{{cite book|last1=White|first1=Edward L.|title=Cortical Circuits Synaptic Organization of the Cerebral Cortex Structure, Function, and Theory|year=1989|publisher=Birkhäuser Boston|location=Boston|isbn=978-0-8176-3402-5|first2=Asaf|last2=Keller|author3=Introduction by Thomas A. Woolsey}}</ref>

==Function==
Since neuropils have a diverse role in the nervous system, it is difficult to define a certain overarching function for all neuropils. For instance, the olfactory glomeruli function as sorts of way-stations for the information flowing from the [[olfactory receptor neuron]]s to the olfactory cortex. The inner plexiform layer of the retina is a little more complex. The [[bipolar cell]]s post-synaptic to either rods or cones are either depolarized or hyperpolarized depending on whether the bipolar cells have sign-inverting synapses or a sign-conserving synapses.<ref name="Purves" />

===Efficiency in the brain===
Neurons are necessary for all connections made in the brain, and thus can be thought of as the "wires" of the brain. As in computing, an entity is most efficient when its wires are optimized; therefore, a brain which has undergone millions of years of natural selection would be expected to have optimized neural circuitry. To have an optimized neural system it must balance four variables—it must "minimize conduction delays in axons, passive cable attenuation in dendrites, and the length of 'wire' used to construct circuits" as well as "maximize the density of synapses",<ref name="Dmitri">{{cite journal|first1=Dmitri B.|last1=Chklovskii|first2=Thomas|last2=Schikorski|first3=Charles F.|last3=Stevens|title=Wiring Optimization in Cortical Circuits|journal=Neuron|date=25 April 2002|volume=34|issue=3|pages=341–347<!--|access-date=20 April 2012-->|doi=10.1016/s0896-6273(02)00679-7|pmid=11988166|s2cid=1501543|doi-access=free}}</ref> essentially optimizing the neuropil. Researchers at Cold Spring Harbor Laboratory formulated the optimal balance of the four variables and calculated the optimal ratio of axon plus dendrite volume (i.e. the "wire" volume or neuropil volume) to total volume of grey matter. The formula predicted an optimal brain with 3/5 (60%) of its volume occupied by neuropil. Experimental evidence taken from three mouse brains agrees with this result. The "fraction of wire is 0.59 ± 0.036 for layer IV of visual cortex, 0.62 ± 0.055 for layer Ib of piriform cortex, and 0.54 ± 0.035 for the stratum radiatum of hippocampal field CA1. The overall average is 0.585 ± 0.043; these values are not statistically different from the optimal 3/5."<ref name="Dmitri" />

==Clinical significance==

===Schizophrenia===
It has been shown that a certain protein [[synaptophysin]]<ref>{{cite journal |last1=Osimo |first1=Emanuele Felice |last2=Beck |first2=Katherine |last3=Reis Marques |first3=Tiago |last4=Howes |first4=Oliver D |title=Synaptic loss in schizophrenia: a meta-analysis and systematic review of synaptic protein and mRNA measures |journal=Molecular Psychiatry |date=2019 |volume=24 |issue=4 |pages=549–561 |doi=10.1038/s41380-018-0041-5 |pmid=29511299 |pmc=6004314 }}</ref> is lost in people with [[schizophrenia]] that causes dendrites and spines to deteriorate in the [[dorsolateral prefrontal cortex]], a part of the neocortex, which plays a key role in information processing, attention, memory, orderly thinking and planning which are all functions that deteriorate in people with schizophrenia. The deterioration of the neuropil in this cortex has been proposed as a contributor to schizophrenia pathophysiology.{{cn|date=February 2022}}

===Alzheimer's disease===
[[Alzheimer's]] is a neuropathological disease that is hypothesized to result from the loss of dendritic spines and/or deformation of these spines in the patient's frontal and temporal cortices. Researchers have tied the disease to a decrease in the expression of [[DBN1|drebrin]], a protein thought to play a role in [[long-term potentiation]], meaning the neurons would lose plasticity and have trouble forming new connections. This malfunction presents itself in the form of helical filaments that tangle together in the neuropil. This same phenomenon seems to occur in the elderly as well.<ref>{{cite journal|last=Braak|first=Heiko and Eva|title=Occurrence of neuropil threads in the senile human brain and in Alzheimer's disease: A third location of paired helical filaments outside of neurofibrillary tangles and neuritic plaques|journal=Neuroscience Letters|doi=10.1016/0304-3940(86)90288-0|volume=65|issue=3|pages=351–355|year=1986|pmid=2423928|s2cid=38340590}}</ref><ref>{{cite book|last=Smythies|first=John|title=Disorders of Synaptic Plasticity and Schizophrenia|url=https://archive.org/details/internationalrev00smyt|url-access=limited|year=2004|publisher=Elsevier Academic Press|location=San Diego, California|isbn=978-0-12-366860-8|pages=[https://archive.org/details/internationalrev00smyt/page/n22 6]–7}}</ref>

==Other animals==
===Other mammals===
A significant non-human area of neuropil is the [[barrel cortex]] found in mammals with [[whiskers]] (e.g. cats, dogs and rodents); each "barrel" in the cortex is a region of neuropil where the input from a single whisker terminates.<ref>{{cite web|last=Wollsey |first=Thomas |title=Barrel Cortex |url=http://nslc.wustl.edu/courses/bio3411/woolsey/2010/Lecture11/WoolseyTA03.pdf |access-date=21 April 2012 }}{{dead link|date=June 2017 |bot=InternetArchiveBot |fix-attempted=yes }}</ref>

===Arthropods===
The [[optic lobe (arthropods)|optic lobe]] of [[arthropods]] and the [[ganglia]] of the [[arthropod brain]] as well as the ganglia in the [[ventral nerve cord]] are unmyelinated and therefore belong to the class of neuropils.

==Research==
Research has focused on where neuropil is found in many different species in order to unveil the range of significance it has and possible functions.

===Recent studies===
In chimpanzees and humans the neuropil provides a proxy measure of total connectivity within a local region because it is composed mostly of dendrites, axons, and synapses.<ref name="Spocter">{{cite journal|last1=Spocter|first1=Muhammad A|last2=Hopkins|first2= William D.|last3=Barks|first3= Sarah K.|last4=Bianchi|first4= Serena|last5=Hehmeyer|first5= Abigail E.|last6=Anderson|first6= Sarah M.|last7=Stimpson|first7= Cheryl D.|last8=Fobbs|first8= Archibald J.|last9=Hof|first9= Patrick R.|last10=Sherwood|first10= Chet C.|title=Neuropil distribution in the cerebral cortex differs between humans and chimpanzees|journal=The Journal of Comparative Neurology|year=2012|doi=10.1002/cne.23074|issn=1096-9861|volume=520|issue=13|pages=2917–2929|pmid=22350926|pmc=3556724}}</ref>

In insects the central complex plays an important role in higher-order brain function. The neuropil in ''Drosophila'' Ellipsoid is composed of four substructures. Each section has been observed in several insects as well as the influence it has on [[behavior]], however the exact function of this neuropil has proven elusive. Abnormal walking behavior and flight behavior are controlled primarily by the central complex and genetic [[mutations]] that disrupt the structure support the hypothesis that the central complex neuropil is a site of behavioral control. However, only specific components of the behavior were affected with the genetic mutations. For example, basic leg coordination of walking was normal, whereas speed, activity, and turning were affected. These observations suggest that the central complex not only plays a role in locomotor behavior, but fine tuning as well. There is also additional evidence that the neuropil may function in [[olfaction|olfactory]] associative learning and [[memory]].<ref name="Renn">{{cite journal|last1=Renn|first1=Susan C. P.|first2=J. Douglas|last2=Armstrong|first3=Mingyao|last3=Yang|first4=Zongsheng|last4=Wang|first5=Xin|last5=An|first6=Kim|last6=Kaiser|first7=Paul H.|last7=Taghert|title=Genetic analysis of the Drosophila ellipsoid body neuropil: Organization and development of the central complex|journal=Journal of Neurobiology|date=Nov 5, 1999|volume=41|issue=2|pages=189–207|issn=0022-3034|doi=10.1002/(sici)1097-4695(19991105)41:2<189::aid-neu3>3.3.co;2-h|pmid=10512977|citeseerx=10.1.1.458.8098}}</ref>

Research has shown reduced neuropil in area 9 of schizophrenics,<ref>{{cite journal |vauthors=Buxhoeveden D, Ror E, Switala A | year = 2000 | title = Reduced interneuronal space in schizophrenia | journal = Biological Psychiatry | volume = 47 | issue = 7| pages = 681–682 | doi=10.1016/s0006-3223(99)00275-9| pmid = 10809534 | s2cid = 33719925 }}</ref> as well as consistent findings of reduced spine density in layer III [[pyramidal neuron]]s of the temporal and frontal cortices.{{Cn|date=February 2022}}

==See also==
* [[Axon]]
* [[Dendrite]]
* [[Dendritic spine]]
* [[Glia]]
* [[Gray matter|Grey matter]]
* [[Neuroanatomy]]
* [[Synapse]]

==Citations==
{{Gray's}}
{{Reflist}}

==Sources==
{{Refbegin}}
* ''Neuropil: Roche Encyclopedia of Medicine'', Dictionary Barn.
* {{cite book|last1=Gazzaniga|first1=Richard B. Ivry|title=Cognitive neuroscience: the biology of the mind|year=2009|publisher=W. W. Norton|location=New York|isbn=978-0-393-92795-5|edition=3rd|first2=George R.|last2=Mangun|first3=Megan S.|last3=Steven}}
* {{cite book|title=Principles of neural science|year=2000|publisher=McGraw-Hill, Health Professions Division|location=New York|isbn=978-0-8385-7701-1|edition=4th|editor1=Eric R. Kandel|editor2=James H. Schwartz|editor3=Thomas M. Jessell|url-access=registration|url=https://archive.org/details/isbn_9780838577011}}
* {{cite book|title=Findings and current opinion in cognitive neuroscience. Current Opinion in Neurobiology|year=1998|publisher=The MIT Press|location=Cambridge, Massachusetts|isbn=978-0-262-69204-5|editor1=Larry R. Squire |editor2=Stephen M. Kosslyn }}
{{Refend}}

==External links==
{{Wiktionary|neuropil}}
{{Commons category}}
* {{BUHistology|04104loa}}—"Nervous Tissue and Neuromuscular Junction: spinal cord, cell bodies of anterior horn cells"
* [http://ccdb.ucsd.edu/sand/main?stype=lite&keyword=neuropil&Submit=Go&event=display&start=1 Neuropil—Cell Centered Database]
* {{OklahomaHistology|3_08}}
* [https://www.ncbi.nlm.nih.gov/books/NBK11154/ "Neuropil—Neural Circuits"]—''Neuroscience''. 2nd edition, Editors: Dale Purves, George J Augustine, David Fitzpatrick, Lawrence C Katz, Anthony-Samuel LaMantia, James O McNamara, and S Mark Williams. Sunderland (MA): Sinauer Associates; 2001. {{ISBN|0-87893-742-0}}.
* https://www.ncbi.nlm.nih.gov/books/NBK11158/

{{Nervous tissue}}
{{Authority control}}

[[Category:Neuroanatomy]]