Nucleus raphe dorsalis
Encyclopedia
The dorsal raphe nucleus is located on the midline of the brainstem and is part of the raphe nucleus, consisting of the rostral and caudal subdivisions.
An increased number of cells in the lateral aspects of the dorsal raphe is characteristic of humans and other primates.
Serotonergic neurons are found throughout the dorsal raphe nucleus and tend to be larger than other cells. A substantial population of cells synthesizing substance P
are found in the rostral aspects, many of these co-express serotonin and substance P. There is also a population of catecholamine synthesizing neurons in the rostral dorsal raphe, and these cells appear to be relatively large.
The dorsal raphe nucleus is rich in pre-synaptic serotonin 5-HT1A autoreceptors, and it's believed that the action of the selective serotonin reuptake inhibitors (SSRIs) in this region is responsible for the latency of their antidepressant effect.
, while only medium cells seem to project to the caudate and putamen and olfactory bulb.,
withdrawal symptoms via electrical stimulation of the raphe nucleus in question.
These are fascinating results; however no control was provided for the spread of electrical charge to other parts of the brain stem. It is quite possible that the charge spread to the nucleus raphe magnus and induced analgesia upon the rats. Knowing that the spread of charge across such a short area is very plausible, as is an alternate connection to the raphe magnus, these results could be called into question.
, this is logical, as the raphe nuclei have been known to play a role in the sleep/wake cycle. Cataplexy
is the symptom of narcolepsy when full awareness of the environment is maintained, but all muscle tone is lost. This has thought to be a dissociation of what normally happens during REM sleep, when all muscle tone is lost except for the eyes. The raphe dorsalis have been known to project to the lateral hypothalamus
, along with the locus coeruleus and the tuberomammillary nucleus
. The neurotransmitters of these three aforementioned nuclei, which project to the lateral hypothalamus, are serotonin
, norepinephrine
and histamine
respectively. These neurotransmitters are fully active during waking hours, partially active during non-REM sleep, and have almost ceased during REM sleep. In cats with pontine
lesions, their normal atonia is not present, the raphe dorsalis is fully active, as opposed to the cessation of action under normal conditions. A muscle relaxant, known as Mephenesin
, reduces to activity of the dorsal nucleus, as well as microinjections of carbachol
(which induces atonia while awake).
- The rostral aspect of the dorsal raphe is further divided into interfascicular, ventral, ventrolateral and dorsal subnuclei.
- The projections of the dorsal raphe have been found to vary topographically, and thus the subnuclei differ in their projections.
An increased number of cells in the lateral aspects of the dorsal raphe is characteristic of humans and other primates.
Serotonin
The dorsal raphe is the largest serotonergic nucleus and provides a substantial proportion of the serotonin innervation to the forebrain.Serotonergic neurons are found throughout the dorsal raphe nucleus and tend to be larger than other cells. A substantial population of cells synthesizing substance P
Substance P
In the field of neuroscience, substance P is a neuropeptide: an undecapeptide that functions as a neurotransmitter and as a neuromodulator. It belongs to the tachykinin neuropeptide family. Substance P and its closely related neuropeptide neurokinin A are produced from a polyprotein precursor...
are found in the rostral aspects, many of these co-express serotonin and substance P. There is also a population of catecholamine synthesizing neurons in the rostral dorsal raphe, and these cells appear to be relatively large.
The dorsal raphe nucleus is rich in pre-synaptic serotonin 5-HT1A autoreceptors, and it's believed that the action of the selective serotonin reuptake inhibitors (SSRIs) in this region is responsible for the latency of their antidepressant effect.
Projections
Ten percent of the axons from the nucleus raphe dorsalis of the rat have been shown to project to the amygdalaAmygdala
The ' are almond-shaped groups of nuclei located deep within the medial temporal lobes of the brain in complex vertebrates, including humans. Shown in research to perform a primary role in the processing and memory of emotional reactions, the amygdalae are considered part of the limbic system.-...
, while only medium cells seem to project to the caudate and putamen and olfactory bulb.,
Role in naloxone-induced morphine withdrawal
The nucleus raphe dorsalis has also been implicated in naloxone-induced morphine withdrawal. It is known that endogenous opioid receptors exist on the nucleus raphe dorsalis, and that it is a focal point as an ascending and descending regulator. Pourshanazari et al. showed in their 2000 paper that electrical stimulation of the nucleus raphe dorsalis can partially alleviate morphineMorphine
Morphine is a potent opiate analgesic medication and is considered to be the prototypical opioid. It was first isolated in 1804 by Friedrich Sertürner, first distributed by same in 1817, and first commercially sold by Merck in 1827, which at the time was a single small chemists' shop. It was more...
withdrawal symptoms via electrical stimulation of the raphe nucleus in question.
These are fascinating results; however no control was provided for the spread of electrical charge to other parts of the brain stem. It is quite possible that the charge spread to the nucleus raphe magnus and induced analgesia upon the rats. Knowing that the spread of charge across such a short area is very plausible, as is an alternate connection to the raphe magnus, these results could be called into question.
Role in narcolepsy
Wu M.F. et al. studied the raphe dorsalis as it pertained to narcolepsyNarcolepsy
Narcolepsy is a chronic sleep disorder, or dyssomnia, characterized by excessive sleepiness and sleep attacks at inappropriate times, such as while at work. People with narcolepsy often experience disturbed nocturnal sleep and an abnormal daytime sleep pattern, which often is confused with insomnia...
, this is logical, as the raphe nuclei have been known to play a role in the sleep/wake cycle. Cataplexy
Cataplexy
Cataplexy is a sudden and transient episode of loss of muscle tone, often triggered by emotions. It is a rare disease , but affects roughly 70% of people who have narcolepsy...
is the symptom of narcolepsy when full awareness of the environment is maintained, but all muscle tone is lost. This has thought to be a dissociation of what normally happens during REM sleep, when all muscle tone is lost except for the eyes. The raphe dorsalis have been known to project to the lateral hypothalamus
Hypothalamus
The Hypothalamus is a portion of the brain that contains a number of small nuclei with a variety of functions...
, along with the locus coeruleus and the tuberomammillary nucleus
Tuberomammillary nucleus
The tuberomammillary nucleus is a subnucleus of the posterior third of the hypothalamus. It consists of, largely, histaminergic neurons and is involved with the control of arousal, sleep and circadian rhythm....
. The neurotransmitters of these three aforementioned nuclei, which project to the lateral hypothalamus, are serotonin
Serotonin
Serotonin or 5-hydroxytryptamine is a monoamine neurotransmitter. Biochemically derived from tryptophan, serotonin is primarily found in the gastrointestinal tract, platelets, and in the central nervous system of animals including humans...
, norepinephrine
Norepinephrine
Norepinephrine is the US name for noradrenaline , a catecholamine with multiple roles including as a hormone and a neurotransmitter...
and histamine
Histamine
Histamine is an organic nitrogen compound involved in local immune responses as well as regulating physiological function in the gut and acting as a neurotransmitter. Histamine triggers the inflammatory response. As part of an immune response to foreign pathogens, histamine is produced by...
respectively. These neurotransmitters are fully active during waking hours, partially active during non-REM sleep, and have almost ceased during REM sleep. In cats with pontine
Pontine
Pontine may refer to:* Having to do with the pons, a structure located in the brain stem * Pontine Marshes, a region of Italy near Rome* Pontine Islands, islands of Italy near Circeo...
lesions, their normal atonia is not present, the raphe dorsalis is fully active, as opposed to the cessation of action under normal conditions. A muscle relaxant, known as Mephenesin
Mephenesin
Mephenesin is a centrally acting muscle relaxant. It can be used as an antidote for strychnine poisoning....
, reduces to activity of the dorsal nucleus, as well as microinjections of carbachol
Carbachol
Carbachol , also known as carbamylcholine, is a drug that binds and activates the acetylcholine receptor. Thus it is classified as a cholinergic agonist. It is primarily used for various ophthalmic purposes, such as for treating glaucoma, or for use during ophthalmic surgery...
(which induces atonia while awake).
External links
- NIF Search - Dorsal Raphe Nucleus via the Neuroscience Information FrameworkNeuroscience Information FrameworkThe Neuroscience Information Framework is a repository of global neuroscience web resources, including experimental, clinical, and translational neuroscience databases, knowledge bases, atlases, and genetic/genomic resources.-Description:...