Pars compacta

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Pars compacta
Details
Part ofsubstantia nigra
Identifiers
Latinpars compacta substantiae nigrae
Acronym(s)SNpc
MeSHD065842
NeuroLex IDbirnlex_990
TA98A14.1.06.112
TA25882
FMA62907
Anatomical terms of neuroanatomy

The pars compacta (SNpc) is one of two subdivisions of the

dopaminergic neurons.[1] It projects to the striatum and portions of the cerebral cortex.[2]
It is functionally involved in fine motor control.

Parkinson's disease is characterized by the death of dopaminergic neurons in this region.[1]

Anatomy

In humans, the nerve cell bodies of the pars compacta are coloured black by the pigment neuromelanin. The degree of pigmentation increases with age. This pigmentation is visible as a distinctive black stripe in brain sections and is the origin of the name given to this volume of the brain.[3]

Microanatomy

The neurons have particularly long and thick dendrites. The ventral dendrites, particularly, go down deeply in the

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.[3] The ventral tier is considered as A9v. The dorsal tier A9d is linked to an ensemble comprising also A8 and A10,[4] A8, A9d and A10 representing 28% of dopaminergic neurons. The neurons of the pars compacta receive inhibiting signals from the collateral axons from the neurons of the pars reticulata.[5]

Efferents

The dopaminergic neurons of the pars compacta project many of their

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 pallidum,[6] substantia nigra pars reticulata, and the subthalamic nucleus.[7]

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.[8] 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

Degeneration of pigmented neurons in this region is the principal

charge transfer complexes
may concentrate radical-generating toxins in the substantia nigra.

Pathological changes to the dopaminergic neurons of the pars compacta are also thought to be involved in

clinical depression
.

References

  1. ^
    PMID 12917442
    .
  2. ISBN 978-1-259-64248-7
    .
  3. ^
    S2CID 24287378
    .
  4. PMID 1678193
    .
  5. S2CID 45314308
    .
  6. S2CID 36431241.{{cite journal}}: CS1 maint: multiple names: authors list (link
    )
  7. S2CID 14698708
    .
  8. S2CID 11239586
    .
  9. PMID 16837857
    .
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