Thedorsal raphe nucleusis one of theraphe nuclei.It is situated in thebrainstemat the midline. It has rostral and caudal subdivisions:
- The rostral aspect of thedorsalraphe is further divided into interfascicular, ventral, ventrolateral and dorsal subnuclei.
- The projections of thedorsalraphe have been found to vary topographically, and thus the subnuclei differ in their projections.[1]
| Dorsal raphe nucleus | |
|---|---|
 Outline of the dorsal raphe nucleus:DRifinterfascicular subnucleus,DRvventral subnucleus,DRvlventrolateral subnucleus,DRddorsal subnucleus,mlfmedial longitudinal fasciculus,Aqcerebral aqueduct,IVntrochlear nucleus. | |
| Details | |
| Identifiers | |
| Latin | nucleus raphes posterior, nucleus raphes dorsalis |
| MeSH | D065847 |
| NeuroNames | 512 |
| NeuroLexID | birnlex_982 |
| TA98 | A14.1.05.604 |
| TA2 | 5957 |
| FMA | 68462 |
| Anatomical terms of neuroanatomy | |
Anatomy
editEfferents
editThe DRN issues serotonergic efferents to the hippocampal formation, limbic lobe, and amygdala (these efferents are involved in regulation of memory processing).[2]
Neurophysiology
editSerotonergic neurotransmission
editThe 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 synthesizingsubstance Pare 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.[3]
The dorsal raphe nucleus is rich inpre-synapticserotonin5-HT1Aautoreceptors,and it's believed that the action of theselective serotonin reuptake inhibitors(SSRIs) in this region is responsible for the latency of their antidepressant effect.[4]
Research
editNaloxone-induced morphine withdrawal
editThe dorsal raphe nucleus has also been implicated in naloxone-induced morphine withdrawal. It is known that endogenousopioid receptorsexist in the dorsal raphe nucleus, 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 dorsal raphe nucleus can partially alleviatemorphinewithdrawal symptoms via electrical stimulation of the raphe nucleus in question.[5]
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 raphes magnus and inducedanalgesiaupon 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.
Narcolepsy
editWu M.F.et al.studied the dorsal raphe nucleus as it pertained tonarcolepsy.This is logical, as the raphe nuclei have been known to play a role in the sleep/wake cycle.Cataplexyis 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 duringREMsleep, when all muscle tone is lost except for the eyes. The dorsal raphe nucleus has been known to project to the lateralhypothalamus,along with thelocus coeruleusand thetuberomammillary nucleus.The neurotransmitters of these three aforementioned nuclei, which project to the lateral hypothalamus, areserotonin,norepinephrineandhistaminerespectively. These neurotransmitters are fully active during waking hours, partially active during non-REM sleep, and have almost ceased during REM sleep. In cats withpontinelesions, their normalatoniais not present, the dorsal raphe nucleus is fully active, as opposed to the cessation of action under normal conditions. A muscle relaxant, known asMephenesin,reduces activity of the dorsal nucleus, as well as microinjections ofcarbachol(which induces atonia while awake).[6]
Depression and suicide
editThe rostral raphe nuclei, both themedian raphe nucleusand particularly the dorsal raphe nucleus have long been implicated in depression. Some studies have suggested that the dorsal raphe may be decreased in size in people with depression and, paradoxically, an increased cell density in those who die by suicide.[7][8][9]
Other animals
editAn increased number of cells in the lateral aspects of the dorsal raphe is characteristic of primates (including humans).[citation needed]
Rat
editResearch
editTen percent of the axons from the dorsal raphe nucleus of the rat have been shown to project to theamygdala,[10]while only medium cells seem to project to the caudate and putamen and olfactory bulb.[11][12]
See also
editReferences
edit- ^O'Hearn E, Molliver ME (December 1984). "Organization of raphe-cortical projections in rat: a quantitative retrograde study".Brain Res. Bull.13(6): 709–26.doi:10.1016/0361-9230(84)90232-6.PMID6099744.S2CID4761755.
- ^Patestas, Maria A.; Gartner, Leslie P. (2016).A Textbook of Neuroanatomy(2nd ed.). Hoboken, New Jersey: Wiley-Blackwell. p. 432.ISBN978-1-118-67746-9.
- ^Baker KG, Halliday GM, Hornung JP, Geffen LB, Cotton RG, Törk I (1991). "Distribution, morphology and number of monoamine-synthesizing and substance P-containing neurons in the human dorsal raphe nucleus".Neuroscience.42(3): 757–75.doi:10.1016/0306-4522(91)90043-N.PMID1720227.S2CID23034680.
- ^Briley M, Moret C (October 1993). "Neurobiological mechanisms involved in antidepressant therapies".Clin Neuropharmacol.16(5): 387–400.doi:10.1097/00002826-199310000-00002.PMID8221701.
- ^Pourshanazari, A.A.; Alaei; Rafati (2000). "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): 63–7.
- ^Wu MF, John J, Boehmer LN, Yau D, Nguyen GB, Siegel JM (January 2004)."Activity of dorsal raphe cells across the sleep–waking cycle and during cataplexy in narcoleptic dogs".J. Physiol.554(Pt 1): 202–15.doi:10.1113/jphysiol.2003.052134.PMC1664742.PMID14678502.
- ^Underwood MD, Khaibulina AA, Ellis SP, Moran A, Rice PM, Mann JJ, Arango V (August 1999)."Morphometry of the dorsal raphe nucleus serotonergic neurons in suicide victims".Biol Psychiatry.46(4): 473–83.doi:10.1016/S0006-3223(99)00043-8.PMID10459396.S2CID19780741.
- ^Arango V, Underwood MD, Boldrini M, Tamir H, Kassir SA, Hsiung S, Chen JJ, Mann JJ (December 2001)."Serotonin 1A receptors, serotonin transporter binding and serotonin transporter mRNA expression in the brainstem of depressed suicide victims".Neuropsychopharmacology.25(6): 892–903.doi:10.1016/S0893-133X(01)00310-4.hdl:2158/200883.PMID11750182.
- ^Matthews PR, Harrison PJ (March 2012)."A morphometric, immunohistochemical, and in situ hybridization study of the dorsal raphe nucleus in major depression, bipolar disorder, schizophrenia, and suicide".J Affect Disord.137(1–3): 125–134.doi:10.1016/j.jad.2011.10.043.PMC3314923.PMID22129767.
- ^Ma QP, Yin GF, Ai MK, Han JS (December 1991). "Serotonergic projections from the nucleus raphe dorsalis to the amygdala in the rat".Neurosci. Lett.134(1): 21–4.doi:10.1016/0304-3940(91)90499-J.PMID1815148.S2CID5713957.
- ^Steinbusch HW, Nieuwenhuys R, Verhofstad AA, Van der Kooy D (1981). "The nucleus raphe dorsalis of the rat and its projection upon the caudatoputamen. A combined cytoarchitectonic, immunohistochemical and retrograde transport study".J. Physiol. (Paris).77(2–3): 157–74.PMID6169825.
- ^Petzold GC, Hagiwara A, Murthy VN (June 2009). "Serotonergic modulation of odor input to the mammalian olfactory bulb".Nat. Neurosci.12(6): 784–91.doi:10.1038/nn.2335.PMID19430472.S2CID33863055.