The raphe nuclei 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 antidepressants are believed to act in
these nuclei, as well as at their targets.
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 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, the nucleus linearis, shrinking
the number of raphe to seven, e.g., NeuroNames makes the following ordering:
Raphe nuclei of medulla oblongata Nucleus raphe obscurus
Nucleus raphe magnus Nucleus pallidus
Raphe nuclei of the pontine reticular formation
Nucleus raphe pontis Nucleus centralis inferior
Raphe nuclei of the midbrain reticular formation
Nucleus centralis superior Nucleus raphe dorsalis
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 instead of the
nominative case raphe in these Latin expressions. The main authority in
anatomical names, Terminologia Anatomica uses for example nucleus raphes magnus
instead of the grammatically incorrect nucleus raphe magnus. The spelling
raphe/raphes however can also be contested as numerous sources indicate
that raphe is an incorrect Latin rendering of the Ancient Greek word ῥαφή
as the initial letter rho with rough breathing is normally rendered as rh in
Latin. The edition of the Nomina Anatomica that was ratified in Jena in
1935 used rhaphe instead of raphe. 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 and
nucleus raphe dorsalis project towards the brain areas of higher function
However, studies also show that numerous areas of the brain control the
serotonergic neurons located in the nucleus raphe dorsalis, including the
orbital cortex, cingulate cortex, medial preoptic area, lateral preoptic area,
and several areas of the hypothalamus. The connection between these areas,
particularly between the nucleus raphe dorsalis and the orbital cortices, is
thought to have influences on depression and obsessive compulsive disorder
prognosis. Function
The raphe nuclei have a vast impact upon the central nervous system. Many of the
neurons in the nuclei are serotonergic; i.e., contain serotonin, a type of
monoamine neurotransmitter and are modulated through fibrous pathways in
the midbrain. 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, 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. = 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 on
the raphe nucleus as soon as an hour after injection, suggesting rapid
changes in the nucleus' structure. Changes also occur after 24 hours
suggesting delayed modifications as well.
Further reading Currie, David. "A Lecture, Higher Brain
Function: Activation of the Brain and Levels of Consciousness". East Tennessee
State University. Retrieved 18 April 2006.
Sari, Youssef. "Serotonin1B receptors: from protein to physiological function
and behavior". Neuroscience & Biobehavioral Reviews 28: 565–582.
doi:10.1016/j.neubiorev.2004.08.008. PMID 15527863. Retrieved 2006-04-18.
McKittrick,, Christina; Carolineblanchard, D; Blanchard, R;
McEwen, B; Sakai, R. "Serotonin Receptor Binding in a Colony Model of Chronic
Social Stress". Biological Psychiatry 37: 383–393.
doi:10.1016/0006-3223(94)00152-S. PMID 7772647. Retrieved 2010-08-30.
References See also
Locus ceruleus Substantia nigra
Pedunculopontine nucleus List of regions in the human brain