Raphe nuclei

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Raphe nuclei
olive. (Raphe nuclei not labeled, but 'raphe' labeled at left.)
Horizontal cross section of the brainstem at the lower pons. The raphe nucleus is labeled #18 in the middle.
Details
Identifiers
Latinnuclei raphe
MeSHD011903
NeuroLex IDnlx_anat_20090205
TA98A14.1.04.257
A14.1.04.318
A14.1.05.402
A14.1.05.601
A14.1.06.401
TA26035, 5955
FMA84017
Anatomical terms of neuroanatomy]

The raphe nuclei (

adenyl cyclase. They function as autoreceptors in the brain and decrease the release of serotonin. The anxiolytic drug Buspirone acts as partial agonist against these receptors.[2] Selective serotonin reuptake inhibitor (SSRI) antidepressants are believed to act in these nuclei, as well as at their targets.[3]

Anatomy

The raphe nuclei are traditionally considered to be the medial portion of the reticular formation, and appear as a ridge of cells in the center and most medial portion of the

brain stem
.

In order from

caudal to rostral, the raphe nuclei are known as the nucleus raphe obscurus, the nucleus raphe pallidus, the nucleus raphe magnus, the nucleus raphe pontis, the median raphe nucleus, dorsal raphe nucleus, caudal linear nucleus.[4] In the first systematic examination of the raphe nuclei, Taber et al.. (1960)[5] originally proposed the existence of two linear nuclei (nucleus linearis intermedius and nucleus linearis rostralis). This study was published before techniques enabling the visualization of serotonin or the enzymes participating in its synthesis had been developed, as first demonstrated by Dahlström and Fuxe in 1964.[6] Later, it was revealed that of these two nuclei, only the former (nucleus linearis intermedius, now known as the caudal linear nucleus), proved to contain serotonin-producing neurons,[7] though both of them contain dopaminergic neurons.[8]

In some works (e.g.[9]), researchers have grouped the nuclei lineares into one nucleus, the nucleus linearis, shrinking the number of raphe to seven, e.g., NeuroNames makes the following ordering:[10]

Nomenclature

The Latin names commonly used for most of these nuclei are grammatically and orthographically incorrect. Latin grammar would require to use the genitive case raphes ('of the seam') instead of the nominative case raphe ('seam') in these Latin expressions. The main authority in anatomical names, Terminologia Anatomica uses for example nucleus raphes magnus[11] instead of the grammatically incorrect nucleus raphe magnus. The spelling raphe/raphes however can also be contested as numerous sources[12][13][14] indicate that raphe is an incorrect Latin rendering of the Ancient Greek word ῥαφή as the initial letter rho with rough breathing (spiritus asper) is normally rendered as rh in Latin.[12] The edition of the Nomina Anatomica that was ratified in Jena in 1935 used rhaphe instead of raphe.[15][16]

Projections

These nuclei interact with almost every pertinent portion of the brain, but only a few of them have specifically independent interaction. These select nuclei are discussed as follows.

Overall, the caudal raphe nuclei, including the nucleus raphe magnus, nucleus raphe pallidus and nucleus raphe obscurus, all project towards the spinal cord and brain stem. The more-rostral nuclei, including the nucleus raphe pontis, nucleus centralis superior (also called median raphe nucleus, mRN) and nucleus raphe dorsalis (dRN) project towards the brain areas of higher function [17]

The numerous projections from the mRN and dRN to key brain structures make serotonergic system fundamental in regulating brain homeostasis. However, studies also show feedback loops from numerous areas of the brain controlling the serotonergic neurons located in the

obsessive compulsive disorder prognosis.[18]

Dopamine and serotonin pathways in the brain

Function

The raphe nuclei have a vast impact upon the central nervous system. Many of the neurons in the nuclei (but not the majority) are serotonergic; i.e., contain

monoamine neurotransmitter and are modulated through fibrous pathways in the midbrain.[19]

Projections from the raphe nuclei also terminate in the dorsal horn of spinal gray matter where they regulate the release of

enkephalins
, which inhibit pain sensation.

The raphe nuclei provide feedback to the

suprachiasmatic nuclei (SCN), thus contributing in circadian rhythms in animals. The SCN transmits to the raphe nuclei via the dorsomedial hypothalamic nucleus altering serotonin levels for sleep/wake states. The raphe nuclei will then transmit feedback to the SCN about the animal's vigilance and levels of alertness. This reciprocal feedback between the two structures provides an adaptable yet stable basis of circadian rhythms.[20]

Thermoregulation

A large increase in sympathetic nerve activity was observed when an excitatory amino acid was injected into the Raphe Pallidus , resulting in both BAT temperature and HR increasing. This suggests that activation of the raphe nucleus results in an increase in sympathetic activity to the BAT.[21]

The raphe pallidus wasn't switched off using 8-OH-DPAT, which in turn reduced body temperature due to a reduced response to cold. This suggests the importance of the raphe nucleus in responding appropriately to the cold.[22]

The raphe nuclei and the effects of ghrelin

More recent studies of the Raphe Nuclei done with rats involve the effects of ghrelin on the dorsal raphe nucleus. When administered, larger doses of ghrelin act centrally on the raphe nucleus, hippocampus, and amygdala which causes dramatic increases in food intake, memory retention, and increases in anxiety. The effects of ghrelin are seen on the raphe nucleus as soon as an hour after injection, suggesting rapid changes in the structure of the nucleus. Changes also occur after 24 hours suggesting delayed modifications as well.[23]

See also

References

  1. ^ Liddell HG, Scott R (1940). A Greek-English Lexicon. Oxford: Clarendon Press. revised and augmented throughout by Sir Henry Stuart Jones with the assistance of Roderick McKenzie
  2. ISBN 978-0-397-51820-3
    . In 1964, Dahlstrom and Fuxe (discussed in [2]), using the Falck-Hillarp technique of histofluorescence, observed that the majority of serotonergic soma are found in cell body groups, which previously had been designated as the raphe nuclei.
  3. PMID 8221701
    .
  4. PMID 2252340
    .
  5. PMID 13836517
    .
  6. PMID 14229500
    .
  7. PMID 2736398
    .
  8. PMID 17574681
    .
  9. ^ Nieuwenhuys R, Voogd J, van Huijzen C (2008). The human central nervous system (4 ed.). Berlin: Springer. pp. 890, 893.
  10. ^ ancil-190 at NeuroNames
  11. ^ Federative Committee on Anatomical Terminology (FCAT) (1998). Terminologia Anatomica. Stuttgart: Thieme.
  12. ^ a b Hyrtl, J. (1880). Onomatologia Anatomica. Geschichte und Kritik der anatomischen Sprache der Gegenwart. Wien: Wilhelm Braumüller. K.K. Hof- und Universitätsbuchhändler.
  13. ^ Foster FD (1891–1893). An illustrated medical dictionary. Being a dictionary of the technical terms used by writers on medicine and the collateral sciences, in the Latin, English, French, and German languages. New York: D. Appleton and Company.
  14. ^ Triepel H (1910). Die anatomischen Namen. Ihre Ableitung und Aussprache. Mit einem Anhang: Biographische Notizen. (Dritte Auflage). Wiesbaden: Verlag J.F. Bergmann.
  15. ^ Kopsch F (1941). Die Nomina anatomica des Jahres 1895 (B.N.A.) nach der Buchstabenreihe geordnet und gegenübergestellt den Nomina anatomica des Jahres 1935 (I.N.A.) (3. Auflage). Leipzig: Georg Thieme Verlag.
  16. ^ Stieve H (1949). Nomina Anatomica. Zusammengestellt von der im Jahre 1923 gewählten Nomenklatur-Kommission, unter Berücksichtigung der Vorschläge der Mitglieder der Anatomischen Gesellschaft, der Anatomical Society of Great Britain and Ireland, sowie der American Association of Anatomists, überprüft und durch Beschluß der Anatomischen Gesellschaft auf der Tagung in Jena 1935 endgültig angenommen. (Vierte Auflage). Jena: Verlag Gustav Fischer.
  17. ^ BilZ0r; Erowid (2005). "Figure 4. Diagram of the human brain showing the divergent serotonergic projections of the raphe nuclei to both cortical and subcortical locations throughout the brain" (PNG). The Neuropharmacology of Hallucinogens: a technical overview. Erowid Pharmacology Vaults. Retrieved 18 April 2006.{{cite web}}: CS1 maint: numeric names: authors list (link)
  18. PMID 9466453
    .
  19. PMID 565370
    .
  20. ISBN 978-3-7643-8560-6
    .
  21. PMID 14596844
    .
  22. PMID 16931649
    .
  23. PMID 14697239
    .

Further reading

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