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Zahara5555 (talk | contribs) #WCUG2024 ADDED A PHOTO ON PARS COMPACTA |
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{{Infobox Brain
| Name = Pars compacta
| Latin =
| Acronym = SNpc
| Image =Substantia nigra pars compacta.jpg
| Caption =
| Image2 =
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}}
The '''pars compacta''' ('''SNpc''') is one of two subdivisions of the ''[[substantia nigra]]'' of the [[midbrain]] (the other being the [[pars reticulata]]); it is situated medial to the ''pars reticulata''. It is formed by [[dopaminergic neuron]]s.<ref name=":0" /> It projects to the [[striatum]] and portions of the cerebral cortex.<ref>{{Cite book |last=Martin |first=John D. |title=Neuroanatomy: Text and Atlas
[[Parkinson's disease]] is characterized by the death of dopaminergic neurons in this region.<ref name=":0">{{cite journal |doi=10.1074/jbc.M306017200 |title=Parkin Cleaves Intracellular -Synuclein Inclusions via the Activation of Calpain |year=2003 |last1=Kim |first1=S. J. |journal=Journal of Biological Chemistry |volume=278 |issue=43 |pages=41890–9 |pmid=12917442 |last2=Sung |first2=JY |last3=Um |first3=JW |last4=Hattori |first4=N |last5=Mizuno |first5=Y |last6=Tanaka |first6=K |last7=Paik |first7=SR |last8=Kim |first8=J |last9=Chung |first9=KC |doi-access=free }}</ref>
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=== Microanatomy ===
The neurons have particularly long and thick dendrites. The ventral dendrites, particularly, go down deeply in the [[pars reticulata]]. Other similar neurons are more sparsely distributed in the [[midbrain]] and constitute "groups" with no well-defined borders, although continuous to the pars compacta, in a pre-[[Nucleus ruber|rubral]] position. These have been given, in early works in rats (with not much respect for the anatomical subdivisions), the name of "area A8" and "A10". The pars compacta itself ("A9") is usually subdivided into a ventral and a dorsal tier, the last being [[calbindin]] positive.<ref name=":1">{{cite journal |author1=Francois, C. |author2=Yelnik, J. |author3=Tande, D. |author4=Agid, Y. |author5=Hirsch, E.C. |name-list-style=amp | title=Dopaminergic cell group A8 in the monkey: anatomical organization and projections to the striatum | journal=Journal of Comparative Neurology | pages=334–347 | volume=414 | issue=3 | pmid=10516600 | doi=10.1002/(SICI)1096-9861(19991122)414:3<334::AID-CNE4>3.0.CO;2-X | year=1999|s2cid=24287378 }}</ref><ref>{{Cite journal |last1=Balzano |first1=Tiziano |last2=del Rey |first2=Natalia López-González |last3=Esteban-García |first3=Noelia |last4=Reinares-Sebastián |first4=Alejandro |last5=Pineda-Pardo |first5=José A. |last6=Trigo-Damas |first6=Inés |last7=Obeso |first7=José A. |last8=Blesa |first8=Javier |date=2024-06-17 |title=Neurovascular and immune factors of vulnerability of substantia nigra dopaminergic neurons in non-human primates |journal=npj Parkinson's Disease |language=en |volume=10 |issue=1 |page=118 |doi=10.1038/s41531-024-00735-w |issn=2373-8057 |pmc=11183116 |pmid=38886348}}</ref> The ventral tier is considered as A9v. The dorsal tier A9d is linked to an ensemble comprising also A8 and A10,<ref>{{cite book |author1=Feigenbaum Langer, L. |author2=Jimenez-Castellanos, J. |author3=Graybiel, A.M. |
=== Efferents ===
The dopaminergic neurons of the pars compacta project many of their [[axon]]s along the [[nigrostriatal pathway]] to the [[dorsal striatum]], where they release the [[neurotransmitter]] [[dopamine]]. There is an organization in which dopaminergic neurons of the fringes (the lowest) go to the [[sensorimotor striatum]] and the highest to the [[associative striatum]]. Dopaminergic axons also project to other elements of the [[basal ganglia]], including the lateral and medial [[Globus pallidus|pallidum]],<ref>{{cite journal | author=Lavoie, B., Smith, Y., Parent, A. | title=Dopaminergic innervation of the basal ganglia in the squirrel monkey as revealed by tyrosine hydroxylase immunohistochemistry | year=1989 | pages=36–52 | volume=289 | issue=1 | pmid=2572613 | doi=10.1002/cne.902890104 | journal=The Journal of Comparative Neurology| s2cid=36431241 }}</ref> substantia nigra pars reticulata, and the [[subthalamic nucleus]].<ref>{{cite journal |author1=Cragg S.J. |author2=Baufreton J. |author3=Xue Y. |author4=Bolam J.P. |author5=Bevan M.D. |name-list-style=amp | title=Synaptic release of dopamine in the subthalamic nucleus | journal=European Journal of Neuroscience | year=2004 | pages=1788–1802 | volume=20 | issue=7 | pmid=15380000 | doi=10.1111/j.1460-9568.2004.03629.x|s2cid=14698708 | doi-access=free }}</ref>
==Function==
The function of the dopamine neurons in the ''substantia nigra pars compacta'' (SNc) is complex. Contrary to what was initially believed, SNc neurons do not directly stimulate movement: instead, it plays an indirect role by regulating the more direct role of the striatum, contributing to fine motor control, as has been confirmed in animal models with SNc lesions.<ref>{{cite journal |doi=10.1016/j.neuroscience.2008.01.084 |title=Differential behavioral effects of partial bilateral lesions of ventral tegmental area or substantia nigra pars compacta in rats |year=2008 |last1=Pioli |first1=E.Y. |last2=Meissner |first2=W. |last3=Sohr |first3=R. |last4=Gross |first4=C.E. |last5=Bezard |first5=E. |last6=Bioulac |first6=B.H. |journal=Neuroscience |volume=153 |issue=4 |pages=1213–24 |pmid=18455318|s2cid=11239586 }}</ref> Thus, electrical stimulation of the ''substantia nigra'' does not result in movement, but lack of pars compacta neurons has a large influence on movement, as evidenced by the symptoms of Parkinson's disease.
==Pathology==
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