| Raphe nuclei | |
|---|---|
 Section of themedulla oblongata at about the middle of theolive. (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 | |
| Latin | nuclei raphes |
| MeSH | D011903 |
| NeuroLex ID | nlx_anat_20090205 |
| TA98 | A14.1.04.257 A14.1.04.318 A14.1.05.402 A14.1.05.601 A14.1.06.401 |
| TA2 | 6035,5955 |
| FMA | 84017 |
| Anatomical terms of neuroanatomy | |
Theraphe nuclei (Greek:ῥαφή, "seam")[1] are a moderate-size cluster ofnuclei found in thebrain stem. They have5-HT1 receptors which are coupled withGi/Go-protein-inhibitingadenyl cyclase. They function asautoreceptors in the brain and decrease the release ofserotonin. Theanxiolytic drugBuspirone acts aspartial 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]
The raphe nuclei are traditionally considered to be the medial portion of thereticular formation, andappear as a ridge of cells in the center and most medial portion of thebrain stem.
In order fromcaudal torostral, the raphe nuclei are known as thenucleus raphe obscurus, thenucleus raphe pallidus, thenucleus raphe magnus, thenucleus raphe pontis, themedian raphe nucleus,dorsal raphe nucleus,caudal linear nucleus.[4] In the first systematic examination of the raphe nuclei, Taberet 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, thenucleus linearis, shrinking the number of raphe to seven, e.g.,NeuroNames makes the following ordering:[10]
The Latin names commonly used for most of these nuclei are grammatically and orthographically incorrect. Latin grammar would require to use thegenitive caseraphes ('of the seam') instead of thenominative caseraphe ('seam') in these Latin expressions. The main authority in anatomical names,Terminologia Anatomica uses for examplenucleus raphes magnus[11] instead of the grammatically incorrectnucleus raphe magnus. The spellingraphe/raphes however can also be contested as numerous sources[12][13][14] indicate thatraphe is an incorrect Latin rendering of the Ancient Greek word ῥαφή as the initial letter rho withrough breathing (spiritus asper) is normally rendered asrh in Latin.[12] The edition of theNomina Anatomica that was ratified inJena in 1935 usedrhaphe instead ofraphe.[15][16]
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 thenucleus raphe dorsalis, including the orbital cortex,cingulate cortex, medialpreoptic area, lateralpreoptic area, and several areas of thehypothalamus. The connection between these areas, particularly between thenucleus raphe dorsalis and the orbital cortices, is thought to have influences ondepression andobsessive compulsive disorder prognosis.[18]
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., containserotonin, a type ofmonoamine 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 ofenkephalins, which inhibit pain sensation.
The raphe nuclei provide feedback to thesuprachiasmatic nuclei (SCN), thus contributing in circadian rhythms in animals. The SCN transmits to the raphe nuclei via thedorsomedial 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]
A large increase in sympathetic nerve activity was observed when an excitatory amino acid was injected into theRaphe Pallidus, resulting in both brown adipose tissue (BAT) temperature and heart rate 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]
More recent studies of the Raphe Nuclei done with rats involve the effects ofghrelin on thedorsal raphe nucleus. When administered, larger doses of ghrelin act centrally on the raphe nucleus,hippocampus, andamygdala 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]
revised and augmented throughout by Sir Henry Stuart Jones with the assistance of Roderick McKenzie
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.
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