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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.)
Horizontal cross section of the brainstem at the lower pons. The raphe nucleus is labeled #18 in the middle.
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. Selective serotonin reuptake inhibitor (SSRI) antidepressants are believed to act in these nuclei, as well as at their targets.
In order from caudal to rostral, the raphe nuclei are known as the nucleus raphe obscurus, the nucleus raphe magnus, the nucleus raphe pontis, the nucleus raphe pallidus, the median raphe nucleus, dorsal raphe nucleus, nuclei linearis intermedius and linearis rostralis. Some scientists chose to group the nuclei lineares into one nucleus, shrinking the number of raphe to seven, e.g., NeuroNames makes the following ordering:
- Raphe nuclei of the midbrain reticular formation
The Latin names commonly used for most of these nuclei are grammatically incorrect. Latin grammar would require nucleus raphe magnus to be changed to nucleus raphes magnus, for example. Terminologia Anatomica, the main authority on anatomical names, uses the "raphes" form, and so do some scientific papers, but in recent years more than 95% of scientific publications have continued to use the "raphe" form, as this article does.
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) and nucleus raphe dorsalis project towards the brain areas of higher 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.
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 hypothalamus 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.
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- George J. Siegel, ed. (1999). "Understanding the neuroanatomical organization of serotonergic cells in brain provides insight into the functions of this neurotransmitter". Basic Neurochemistry. Bernard W. Agranoff, Stephen K. Fisher, R. Wayne Albers, Michael D. Uhler (Sixth ed.). Lippincott Williams and Wilkins. ISBN 0-397-51820-X. "In 1964, Dahlstrom and Fuxe (discussed in ), 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."
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- "Fig. 5. The midsagittal section of the brain stem indicating the position of the raphe nuclei" (GIF). 1998. Retrieved 18 April 2006.
- NeuroNames ancil-190
- 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.
- J.M. Monti, ed. (2008). "Reciprocal connections between the suprachiasmatic nucleus and the midbrain raphe nuclei: A putative role in the circadian control of behavioral states". Serotonin and Sleep: Molecular, Functional and Clinical Aspects. Samüel Deurveilher and Kazue Semba. Birkhäuser Basel. ISBN 978-3-7643-8560-6.