Dorsal Raphe Nucleus

Cross references:     Raphe Nuclei   Brainstem    Ventral Tegmental Area 
 Locus Ceruleus (LC)
Bed Nucleus of the Stria Terminalis   
Edinger-Westphal nucleus    Amygdala   Hippocampus    Striatum   Nucleus Accumbens Septi   Hypothalamus  
Paraventricular nucleus (PVN)     CRF Receptors
Corticotropin-releasing factor family (CRF)
Corticotropin-releasing hormone (CRH)   Urocortin   Serotonin  
CRH & Serotonin    Stress     Learned Helplessness 

For a discussion of the family of raphe nuclei, please see  
Raphe Nuclei

Dorsal raphe nucleus (Wiki)   
    "The dorsal raphe nucleus (DRN) is located on the midline of the Brainstem and is part of the raphe nucleus, consisting of the 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]"  
    "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 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"  
The dorsal raphe nucleus is rich in pre-synaptic serotonin 5-HT1A autoreceptors
  (see: Serotonin Receptors)."    
My comment
    This Wikipedia article does not mention the caudal DRN specifically.  Yet, the articles in 
CRH & Serotonin  and  CRH Receptor   stress that it is the serotonergic neurons in the caudal, and not the rostral, DRN that respond to uncontrollable Stress .     

Organization of raphe-cortical projections in rat: a quantitative retrograde study (foot note #1 from above). 
    "Retrograde transport of a fluorescent dye was employed to study the projections from raphe nuclei to neocortex in the rat.  The spatial distributions of labeled raphe cells were analyzed quantitatively to determine whether the nuclei are topographically organized with respect to different cortical targets.
    The dorsal raphe nucleus (DRN), exclusive of the lateral wing regions, has a predominantly (3:1) ipsilateral projection with decreasing numbers of cells projecting to frontal, parietal, and occipital cortex. Overlapping cell groups within the DRN project differentially to these three cortical areas: DRN cells innervating frontal cortex extend more rostrally and laterally than those to either parietal or occipital cortex.
    The medium raphe and B9 projections are bilaterally symmetric, with equal cell numbers projecting to frontal, parietal, and occipital cortex. The rostro-caudal distributions of cells that project to disparate cortical areas differ in B9 but not in MR. The percentage of cortically projecting cells that are serotonergic is 80% for the DRN, 60% in the MR and 33% in the B9 cell group.
    The dorsal raphe nucleus and the B9 cell group are organized heterogeneously, and overlapping sets of neurons project differentially upon particular areas of neocortex. In contrast, the median raphe nucleus projects uniformly upon the neocortex and does not exhibit topographic organization.
    The three rostral raphe nuclei (DR, MR and B9) are each organized according to different rules with regard to their efferent projections to cortex. The differential organization of the raphe nuclei suggests that groups of cells within these three raphe nuclei are likely to innervate different combinations of cortical targets and thus to have different functional effects." 
My comment
    This reference provides an unequivocal answer to my question about projections from the raphe to the cortex.     

From the Ongoing Blog  

I'll come back later and spend more time on this. 


Now that I've satisfied my curiosity about the salamander  Dorsal Raphe Nucleus , I'm going to look at salamander locomotion. 
    See:   Early Behavior


A Wikipedia footnote provides unequivocal affirmation that there are indeed abundant projections from the raphe to the cortex as well as to numerous subcortical structures in addition to the  Nucleus Accumbens Septi  .   See:   Dorsal Raphe Nucleus .     

Of course, the above findings were for rats rather than salamanders, but, since I'm studying salamanders to understand humans, I'm going to accept that, although we humans have both direct and indirect connections between the Dorsal Raphe Nucleus  and the Nucleus Accumbens Septi , the direct connection may not be present at the evolutionary level of the salamanders.  

I have an ulterior motive for all of this.  I'm working toward an interpretation of human behavior which includes the possibility that there are times when our subcortical brain shapes our behavior with only minimal input from the cortex.          


Since Herrick is so thorough, I had expected that his diagrams would be totally comprehensive.  However, as noted in Comment 2 on Fundamental Principles... - 1948 in Lamprey Nervous System , there does seem to be an indirect path from the Raphe Nuclei  to the Nucleus Accumbens Septi via the Thalamus in the lamprey , and there's no reason to believe that it would be lost in the evolutionary step up to the salamander.       


I think I succeeded in finding the  Raphe Nuclei  in BTS Fig 087 
BTS Fig 088  BTS Fig 089  BTS Fig 090  and  BTS Fig 091  , and I've included the labels for these figures in  Figure Labels  .   However, this does not solve the problem discussed below.  In fact, consideration of Figure Abbreviations suggests that the problem is worse than I thought. 

Figure Abbreviations lists four tracts originating in the Tegmentum .  They are:   

tr.teg.b., tractus tegmento-bulbaris          
        See:  BTS Fig 013    BTS Fig 019 
    2.  tr.teg.inp., tractus tegmento-interpeduncularis   
        See:  BTS Fig 019   
    3., tractus tegmento-isthmialis   
        See:  BTS Fig 021   
    4.  tr.teg.p.; tr.teg.ped., tractus tegmeiito-peduncularis   
        See:  BTS Fig 018  .  

As you can see, none of these tracts goes anywhere near the Thalamus , much less either the Nucleus Accumbens Septi  or the Striatum  .  


ooking for the correlate of the Dorsal Raphe Nucleus in the Brain of the Tiger Salamander  has led me to what may be a major insight. 

I'll have to go back and review my notes to confirm this, but my memory is that the best explanation I could find for the 
Impulsivity exhibited by Boys without Fathers  was that diminished delivery of Serotonin from the Dorsal Raphe Nucleus  to the Nucleus Accumbens Septi  increased the level of Dopamine at the inhibitory D2 receptors, thus reducing the inhibitory GABA  output and thereby increasing  Impulsivity .       

However, this hypothesis includes the unstated assumption that there is a direct connection between the
Dorsal Raphe Nucleus and the Nucleus Accumbens Septi .  Although I've just begun to look, at first glance, I don't see one.  At first glance, it looks to me that any input from the Dorsal Raphe Nucleus to the Nucleus Accumbens Septi is relayed by the Thalamus .  If this turns out to be the case, my hypothesis is going to need considerable modification.  


Although Nucleus , Tract and  Fascicle   all discuss particular structures, none of them mention the  Raphe Nuclei .  Since the Dorsal Raphe Nucleus plays such an important role in the behavior of Boys without Fathers  , I'm going to spend some time looking for its correlate in the Brain of the Tiger Salamander .

My focus at the moment is neural architecture .  I'll come back later and work on endocrinology.