| Dorsal raphe nucleus | |
|---|---|
 Outline of the dorsal raphe nucleus:DRif interfascicular subnucleus,DRv ventral subnucleus,DRvl ventrolateral subnucleus,DRd dorsal subnucleus,mlfmedial longitudinal fasciculus,Aqcerebral aqueduct,IVntrochlear nucleus. | |
| Details | |
| Identifiers | |
| Latin | nucleus raphes posterior, nucleus raphes dorsalis |
| MeSH | D065847 |
| NeuroNames | 512 |
| NeuroLex ID | birnlex_982 |
| TA98 | A14.1.05.604 |
| TA2 | 5957 |
| FMA | 68462 |
| Anatomical terms of neuroanatomy | |
Thedorsal raphe nucleus is one of theraphe nuclei. It is situated in thebrainstem at the midline. It has rostral and caudal subdivisions:
The DRN issues serotonergic efferents to the hippocampal formation, limbic lobe, and amygdala (these efferents are involved in regulation of memory processing).[2]
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 synthesizingsubstance 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.[3]
The dorsal raphe nucleus is rich inpre-synaptic serotonin5-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]
The dorsal raphe nucleus has also been implicated in naloxone-induced morphine withdrawal. It is known that endogenousopioid receptors exist 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 alleviatemorphine withdrawal 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 inducedanalgesia 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 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.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 duringREM sleep, 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 coeruleus and thetuberomammillary nucleus. The neurotransmitters of these three aforementioned nuclei, which project to the lateral hypothalamus, areserotonin,norepinephrine andhistamine respectively. These neurotransmitters are fully active during waking hours, partially active during non-REM sleep, and have almost ceased during REM sleep. In cats withpontine lesions, their normalatonia is 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]
The rostral raphe nuclei, both themedian raphe nucleus and 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]
An increased number of cells in the lateral aspects of the dorsal raphe is characteristic of primates (including humans).[citation needed]
Ten 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]
