Endocrinology of Dominance

Cross references:  Steroids    Steroid Actions     Glucocorticoids 
Dominance Hierarchies in General     Human Cortisol, etc.    

A role for glucocorticoids in the long-term establishment of a social hierarchy.
 
Only abstract available online.  I got the PDF through the library. 
The first set of quotes and comments are based on the abstract. 
The second set are based on the PDF. 

from the abstract 
    "
In the present study, we investigated the role of increasing corticosterone levels before or just after a first social encounter between two rats of a dyad in the establishment and the long-term maintenance of a social hierarchy.
    We show that pre-social encounter corticosterone treatment does not affect the outcome of the hierarchy during a first encounter, but induces a long-term memory for the hierarchy when the corticosterone-injected rat becomes dominant during the encounter, but not when it becomes subordinate.
    Post-social encounter corticosterone leads to a long-term maintenance of the hierarchy only when the subordinate rat of the dyad is injected with corticosterone.
    This corticosterone effect mimics previously reported actions of stress on the same model and, hence, implicates glucocorticoids in the consolidation of the memory for a recently established hierarchy.
"  
My comments
1.  If their
"pre-social encounter corticosterone treatment" was of only one rat in the dyad and preceded the encounter by enough time for the corticosterone to have an effect, then the results of this encounter would seem to run contrary to my expectations. 
    My hypothsis includes the assumption that glucocorticoids lower testosterone by inhibiting the luteinizing hormone receptor on the testis.  Since it is well established that testostone increases aggression, thereby leading to dominance, the injected rat should have become subordinate if there had been enough time for the
corticosterone to have an effect. 
2.  This experiment focused on initial encounters and their consequences.  Perhaps my hypothesis only holds for repeated encounters. 

3.  The article makes no mention of testosterone.  It's my impression that testosterone is the single most important hormone in the dominance hierarchy.  S
ee:  Human Cortisol, etc. .  
 
from the PDF 

    "We have recently developed a model for the assessment of a long-term hierarchy between a pair of rats that, on their first encounter, have equal opportunities to become either dominant of subordinate. Under control conditions, the social rank established through a social interaction and food competition test on the first day, is not maintained when the same animals
are confronted 1 week later. However, if one of the rats is stressed just before their first encounter, the dominance hierarchy developed on day 1 is still clearly observed 1 week later, with the stressed animal becoming subordinate in both social interactions."  
My comment
The fact that the consequences of stressing one of the rats before the initial encounter and injecting them with corticosterone are different has at least two possible explanations. 
1.  The effects of the preliminary stress were due to something other than corticosterone. 
2.  The elapsed time between the injection and the initial encounter was too short for the corticosterone to have the effect it would have had had the elapsed time been longer.   

more from the PDF 
    "Rats were injected with corticosterone or vehicle ... 5 min before the start of the first encounter ..."  
My comment
So maybe 5 min wasn't long enough for the corticosterone to fully inhibit the testosterone receptors on the testis.     



The effect glucocorticoids on aggressiveness in established colonies of rats.
  (PubMed) 

Only abstract available online. 



Relocated Segment #2

This is the more recent of the two 'Relocated Segments'

There's a complex four-way interaction between cortisol, testosterone,
serotonin and arginine vasopressin. 

There's overwhelming experimental evidence that cortisol directly inhibits the testicular receptor for luteinizing hormone, and this, in turn, reduces the level of circulating testosterone [9]. 


 9.  See: 
Rodent Glucocorticoid-Testosterone Interaction   


On the other hand, it's still not clear why elevated cortisol, and the resulting lowered testosterone, are accompanied by an
increase in serotonin activity, as indicated by an elevated 5-HIAA/5-HT ratio.  There are at least twelve 5-HT receptors.  Two, 5-HT1AR and 5-HT3R, are known to be inhibited by testosterone.  Therefore, at these receptors, a lower testosterone level results in an elevated 5-HIAA/5-HT ratio.  However, 5-HT2AR is activated by testosterone, and, therefore, at this receptor, a lower testosterone level results in a lowered 5-HIAA/5-HT ratio.  To obscure the situation even more, the action of testosterone at many of the remaining 5-HT receptors has not yet been determined [10] ,  


10.  See:  Rodent Glucocorticoid-Testosterone Interaction 
                
Testosterone Serotonin Interaction   
                
Rodent Hormone-Nerve Interaction 



The hypothalamus contains receptors for both serotonin [?] -
[19] and arginine vasopressin [?] - [16]

19.  See:   Vasopressin, Serotonin & Aggression     

16.  See:   Lamprey Hormones       

, and an increase in arginine vasopressin at these receptors increases aggression [11] -
[17].  However, the number of receptors present depends on the testosterone level, so that increased testosterone levels increase the number of arginine vasopressin receptors and, therefore, the response to arginine vasopressin and aggression [11] - [18]


17.  See: 
Human Cortisol, etc.      

18. 
See:  Human Cortisol, etc.   


 

The  hypothalamus also contains serotonin receptors
[19], and at least some of these receptors appear to be 5-HT(1B/2C) [?].  

19.  See:  Vasopressin, Serotonin & Aggression     


Serotonin at these receptors reduces the sensitivity of whatever arginine vasopressin receptors are present [12] -
[19].  The response of these receptors to testosterone is not yet known. However, testosterone may reduce the sensitivity of these receptors, i.e., the 5-HIAA/5-HT ratio, and thereby help maintain the ability of arginine vasopressin to initiate aggression.   

19.  See:  Vasopressin, Serotonin & Aggression     

Therefore, testosterone may increase aggression by two mechanisms: increasing the number of arginine vasopressin receptors and interfering with what seems to be the generalized inhibitory effect of serotonin.  This reduction in the generalized inhibitory effect of serotonin also results in what is known in humans as "impulsivity".   

 

Relocated Segment #1

This is the older of the two 'Relocated Segments'


This was originally a portion of the long version of  
Boys without Fathers  . 

There is a complex three way interaction between testosterone, arginine vasotocin/vasopressin and serotonin. 

The hypothalamus contains receptors for arginine vasotocin/vasopressin, and an increase in arginine vasotocin/vasopressin at these receptors increases aggression [20].  However, the number of receptors present depends on the testosterone level, so that increased testosterone levels increase the number of arginine vasotocin/vasopressin receptors and, therefore, the response to arginine vasotocin/vasopressin [21]. 

In addition, the  hypothalamus also contains serotonin receptors, and serotonin at these receptors reduces the sensitivity of whatever arginine vasotocin/vasopressin receptors are present [22].  At the same time, however, as discussed in relation to the amphioxus, testosterone reduces the sensitivity of serotonin receptors and thereby helps maintain the ability of arginine vasotocin/vasopressin to initiate aggression. 

Therefore, testosterone increases aggression by two mechanisms: increasing the number of arginine vasotocin/vasopressin receptors and interfering with the generalized inhibitory effect of serotonin.  This reduction in the generalized inhibitory effect of serotonin also results in what is known in humans as "impulsivity". 

In addition to their potential modulation of the aggression promoting effects of arginine vasotocin/vasopressin outlined above, testosterone, estrogen and serotonin continue to play their roles in reproduction as they had in amphioxus, and serotonin has extended its presence and effects throughout the newly enlarged lamprey brain in a pattern consistent with that found in mammals [23].  Only cortisol does not appear to have achieved the level of importance that it has in mammals.  In fact, it is almost undetectable in lampreys.  This is because the adrenal gland, which is the source of cortisol, has only just begun to evolve [24]. 

??? refs???


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