Brain: Dorsal raphe nucleus
Outline of the nucleus raphe dorsalis: DRif interfascicular subnucleus, DRv ventral subnucleus, DRvl ventrolateral subnucleus, DRd dorsal subnucleus, mlf medial longitudinal fasciculus, Aq cerebral aqueduct, IVn trochlear nucleus.
Latin	nucleus raphe posterior, nucleus raphe dorsalis
NeuroNames	hier-503
Dorlands/Elsevier	n_11/12582845

The dorsal raphe nucleus consists of rostral and caudal subdivisions. 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 ^[1]. An increased number of cells in the lateral aspects of the dorsal raphe is characteristic of humans and other primates. 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 synthesising substance P are found in the rostral aspects, many of these co-express serotonin and substance P. There is also a population of catecholamine synthesising neurons in the rostral dorsal raphe, and these cells appear to be relatively large ^[2]. The nucleus raphe dorsalis is rich in serotonin 5-HT1a autoreceptors and it is believed that it is the action of serotonin-specific reuptake inhibitors (SSRIs) in this region that is responsible for the latency of SSRI antidepressant effect ^[3]. The medial longitudinal fasciculus (MLF) is a group of axons on each side of the brainstem, that carry information about the direction that the eyes should move. ... The mesencephalic duct, also known as the aqueduct of Sylvius or the cerebral aqueduct, contains cerebrospinal fluid (CSF), is within the mesencephalon (or midbrain) and connects the third ventricle in the diencephalon to the fourth ventricle, which is between the pons and cerebellum. ... The nucleus of the trochlear nerve is located in the midbrain, at the level of the inferior colliculus. ... Latin is an ancient Indo-European language originally spoken in Latium, the region immediately surrounding Rome. ... NeuroNames is a system of nomenclature for the brain and related structures. ... Elseviers logo. ... SSRI is an acronym that stands for several things: It is a class of antidepressants called selective serotonin reuptake inhibitor SSRI also is used as the stock symbol for Silver Standard Resources Inc. ...

Ten percent of the axons from the nucleus raphe dorsalis have been shown to project to the amygdala ^[4], while only medium cells seem to project to the caudate and putamen ^[5]. The nucleus raphe dorsalis has also been implicated in naloxone-induced morphine withdrawal. It is known that endogenous opiate 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 morphine withdrawal symptoms via electrical stimulation of the raphe nucleus in question (Pourshanazari, A.A. ; Alaei ; Rafati ; Effects of Electrical Stimulation of Nucleus Raphe Dorsalis on initiation of morphine self administration in rats. Medical Journal of Islamic Academy of Sciences 13:2, 63-67, 2000). 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. Wu M.F. et al. studied the raphe dorsalis as it pertained to narcolepsy, 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) (Wu et al. Activity of Dorsal raphe cells across the sleep-waking cycle during cataplexy in narcoleptic dogs. Journal of Physiology. 2004 Jan 1;554 (Pt 1):202-15)[6]. This article or section does not cite its references or sources. ... This article does not adequately cite its references or sources. ... Narcolepsy is a neurological condition most characterized by Excessive Daytime Sleepiness (EDS). ... Cataplexy is a medical condition which often affects people who have narcolepsy, a disorder whose principal signs are EDS (Excessive Daytime Sleepiness), sleep attacks, and disturbed nighttime sleep. ... Rapid eye movement (REM) is the stage of sleep during which the most vivid (though not all) dreams occur. ... The hypothalamus (from Greek ὑποθαλαμος = under the thalamus) is a region of the mammalian brain located below the thalamus, forming the major portion of the ventral region of the diencephalon and functioning to regulate certain metabolic processes and other autonomic activities. ... The Locus ceruleus, also spelled locus coeruleus, (Latin for the blue bit) is a nucleus in the brain stem apparently responsible for the physiological reactions involved in stress and panic. ... Serotonin (5-hydroxytryptamine, or 5-HT) is a monoamine neurotransmitter synthesized in serotonergic neurons in the central nervous system (CNS) and enterochromaffin cells in the gastrointestinal tract of animals including humans. ... Norepinephrine (INN) or noradrenaline (BAN) is a catecholamine and a phenethylamine with chemical formula C8H11NO3. ... This article or section does not cite its references or sources. ... For other uses, see Pons (disambiguation). ... In medicine, atony (or atonia, or atonic) refers to a muscle that has lost its strength. ... Mephenesin is a centrally acting muscle relaxant. ... Clinical Info Chemistry and pharmacokinetics Carbachol is a choline ester and a positively charged quaternary ammonium compound. ...

See also

• Raphe nuclei

The raphe nuclei (Latin for the bit in a fold or seam) is a moderately sized cluster of nuclei found in the brain stem, and releases serotonin to the rest of the brain. ...

References

1. ^  O'Hearn E, Molliver ME. Organization of raphe-cortical projections in rat: a quantitative retrograde study. Brain Res Bull. 1984 Dec;13(6):709-26.
2. ^  Baker KG, Halliday GM, Hornung J-P, Geffen LB, Cotton RGH, Tork I. Distribution, morphology and number of monoamine-synthesizing and substance P-containing neurons in the human dorsal raphe nucleus. Neuroscience. 1991;42(3):757-75.
3. ^  Briley M, Moret C. Neurobiological mechanisms involved in antidepressant therapies. Clin Neuropharmacol. 1993 Oct;16(5):387-400.
4. ^  Ma QP, Yin GF, Ai MK, Han JS. Serotonergic projections from the nucleus raphe dorsalis to the amygdala in the rat. Neurosci Lett. 1991 Dec 16;134(1):21-4.
5. ^  Steinbusch HW, Nieuwenhuys R, Verhofstad AA, Van der Kooy D. The nucleus raphe dorsalis of the rat and its projection upon the caudatoputamen. A combined cytoarchitectonic, immunohistochemical and retrograde transport study. Journal of Physiology (Paris). 1981;77(2-3):157-74.