Raphe nuclei

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Brain: Raphe nuclei
Section of the medulla oblongata at about the middle of the olive. (Raphe nuclei not labeled, but 'raphe' labeled at left.)
Latin	nuclei raphes
MeSH	Raphe+Nuclei

The raphe nuclei ("raffe", Greek: ραφή = seam) are a moderate-size cluster of nuclei found in the brain stem. Their main function is to release serotonin to the rest of the brain.^[1] Selective serotonin reuptake inhibitor (SSRI) antidepressants are believed to act in these nuclei, as well as at their targets.^[2]

Anatomy

The raphe nuclei are traditionally considered to be the medial portion of the reticular formation, and they 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 raphe magnus, the raphe pontis, the raphe pallidus, the nucleus centralis superior, nucleus raphe dorsalis, nuclei linearis intermedius and linearis rostralis.^[3] Some scientists chose to group the linearis nuclei into one nucleus, shrinking the number of raphe to seven, e.g., NeuroNames makes the following ordering:^[4]

• Raphe nuclei of medulla
  • Nucleus raphe obscurus (nucleus raphe obscurus)
  • Nucleus raphe magnus (raphe magnus)
  • Nucleus pallidus (raphe pallidus)

• Raphe nuclei of the pontine reticular formation
  • Pontine raphe nucleus (raphe pontis)
  • Inferior central nucleus

• Raphe nuclei of the midbrain reticular formation
  • Superior central nucleus (nucleus centralis superior)
  • Dorsal raphe nucleus (nucleus raphe dorsalis)

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 raphe magnus, pallidus and raphe obscurus, all project towards the spinal cord and brain stem. The more-rostral nuclei, including the raphe pontis, centralis (also called median), dorsal, tend to project towards the brain areas of higher function.^[5]

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 serotonin, a type of monoamine neurotransmitter. It is important to note that pharmacology traditionally affects global serotonin levels, while the actions of the raphe nuclei are dependent on the complex interplay between nuclei.^{[citation needed]}

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.

Further reading

• Currie, David (2005). "A Lecture, Higher Brain Function: Activation of the Brain and Levels of Consciousness". East Tennessee State University. http://faculty.etsu.edu/currie/ras.htm. Retrieved on 18 April 2006. 
• Sari, Youssef (October 2004). "Serotonin_1B receptors: from protein to physiological function and behavior". Neuroscience & Biobehavioral Reviews 28 (6): 565–582. doi:10.1016/j.neubiorev.2004.08.008. http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6T0J-4DPCHW4-2&_coverDate=10%2F01%2F2004&_alid=299916628&_rdoc=1&_fmt=&_orig=search&_qd=1&_cdi=4864&_sort=d&view=c&_acct=C000002898&_version=1&_urlVersion=0&_userid=27541&md5=ed404d8b8b83823517993851bd03c937. Retrieved on 2006-04-18. 

Additional images

Dopamine and serotonin

References

See also

• Locus ceruleus
• Substantia nigra
• Pedunculopontine nucleus
• List of regions in the human brain