Raphe Nuclei

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This page will be update by the 27th of Auj. Ninad Mehta

Basic Information

During the mid-nineteen century it was observed that the serum that was left after the clotting of the blood could constrict vascular smooth muscle so as to increase the vascular tone. It was later discovered that blood platelets were a source of this substance. Rapport and his collaborators[1] later isolated this compound and named it serotonin(5-hydrocytryptamine). Since the structure of 5-HT is hydrophilic and this would imply that I would not be able to pass through the blood-brain barrier and thus the presence of 5-HT in the blood suggested that it was produced in the brain. In 1964, Dahlstrom and Fuxe using the method of histoflurescence found that the majority of serotonergic soma was found in the midline of the brainstem. This locus had been designated as the raphe nuclei[2]. One fact that must be kept in mind is that not all the neurons in the raphe nuclei are serotonergic.

Schematic drawing depicting the location of the serotonergic cell body groups in a sagittal section of the rat central nervous system and their major projections. OT, olfactory tuberculum; Sept, septum; C. Put, nucleus caudate-putamen; G. Pal, globus pallidus; T, thalamus; H, habenula; S. Nigra, substantia nigra.[1] http://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=bnchm.figgrp.950


Traditional Dahlstrom and Fuxe described nine group of serotonin-containing cell bodies and they were designated B1 to B9. The figure shows the nine cell bodies and the region of the brain that they invigilate. The B1 to B4 are located in the midpons to caudal medulla. The largest group of serotonergic cells is the B7 . It is continuous with the B6 group of cells and they together from are called as the dorsal raphe nucleus. B8 is termed as median raphe nucleus(the nucleus central superior.) Group B9 is located in the ventrolateral tegmentum of the pons of the midbrain. The dorsal and the median raphe nuclei give rise to distinct projection in the forebrain region. Within this raphe the neurons are organized into groups that send axon to specific areas of the brain. The organized innervations of the fore brain structure by raphe neuron implies to the fact that the function of the neuron is dependent on their origin and terminal projection. Some of the reference use a different method of nomenclature for the Raphe nuclei. NeuroNames has shown a classification of the raphe nuclei into seven parts:-

Raphe nuclei of medulla:-

 Nucleus raphe obscures
 Nucleus raphe magnus
 Nucleus pallidus.

Raphe nuclei of the pontine reticular formation

 Pontine raphe nucleus
 Inferior central nucleus

Raphe nuclei of the Midbrain reticular formation

 Superior central nucleus
 Dorsal Raphe nucleus

Specification of the Neuron

As mentioned earlier the total number of the serotonergic neurons is really small. In Rats the number of neurons is around 20,000 out of some 1010 neurons. The Neurons are generated in the early stages of embryonic development. It has been commonly observed that a day after the generation of the neurons they can start the production of 5-HT[3]. The raphe neurons also start profuse axon tracts and project into many parts of the brain and the spinal cord. Based on the labeled 5-HT uptake experiments and immunohistochemical techniques difference in the raphe nuclei neurons have been observed.

The axons of the neurons from the median raphe nucleus, type M, have coarse large spherical varicosities while the ones from the dorsal raphe, type D, have very fine and small pleomorphic varicosities.

This is a simplified diagram of the D- and the M- type of raphe neurons. http://www.ncbi.nlm.nih.gov/books/bv.fcgi?highlight=raphe%20nuclei&rid=bnchm.section.946#949

Molecular profile

  • Neurotransmitter: ____________
  • Unique molecular markers: ______________


Synaptic Connections

Synaptic Inputs

Synaptic Outputs

Spiking properties



  1. Author1 FM,Author2 FM (year) Title, Journal, vol: pages. PMID.
  2. Author1 FM,Author2 FM (year) Title, Journal, vol: pages. PMID.

Additional information

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