Rodent Dominance Hierarchies

Cross references:  Dominance Hierarchies in General 

Role of glucocorticoids in the stress-induced suppression of testicular steroidogenesis in adult male rats. (Goog)     
Only abstract available online.  I got the PDF through the library.   
from the abstract 
    "Immobilization (3 hr) reduced plasma testosterone (T) levels to 24% of control values but did not affect plasma LH levels. This reduction was partially reversed by in vivo injections of the antiglucocorticoid, RU486, prior to the stress session"    
    "Stressed rats had eightfold higher plasma corticosterone levels than controls, and RU486 had no effect on control or stress levels of corticosterone."    
    "Our results suggest that during stress increases in plasma levels of glucocorticoids in male rats act via glucocorticoid receptors on testicular interstitial cells to suppress the testicular response to gonadotropins, and that the decline of testosterone production during immobilization stress is in part mediated by a direct action of glucocorticoids on the testis." 
from the PDF 
    "Exposure to various stressors lowers plasma testosterone (T) levels in primates and rodents and reduces LH-stimulated T secretion. Restraint stress (3 hr) appears to inhibit T secretion by a mechanism that does not involve a reduction of circulating levels of LH since stress did not depress circulating LH levels or affect the conversion of cholesterol to pregnenolone (the primary site of action of LH) by rat testicular cells in vitro.
    The stress-induced disruption of T production appears to occur at a postreceptor site since stress did not affect the binding or affinity of testicular LH receptors but reduced the amount of T produced in response to CAMP stimulation. Evidence suggests that the site of the lesion in T production occurs at the 17a-hydroxylase and 17,20-desmolase steps in the testicular steroidogenic pathway."  


Effects of environmental enrichment on aggressive behavior, dominance hierarchies, and endocrine states in male DBA/2J mice (Goog) 
http://www.ncbi.nlm.nih.gov/pubmed/7824569   
Only abstract available online.  I got the PDF from the library. 
from the abstract   

    "The main findings were:
    (a) Mice in enriched cages (EC) attacked intruders significantly more frequently compared to mice in standard cages (SC);
    (b) In EC groups the position of the dominant male was less stable than in SC groups;
    (c) Plasma corticosterone titers (PCT) were significantly elevated in EC. Activities of tyrosinehydroxylase (TH) and phenylethanolamine-N-methyltranferase (PNMT) did not differ significantly between the housing conditions;
    (d) TH and PNMT activity were significantly enhanced in the dominant males of SC groups compared to subdominant passive males. Intermediate activities for both enzymes were determined for subdominant active males; and
    (e) PCT were significantly elevated in dominant males of the EC groups compared to subdominant active and subdominant passive males and also compared to the dominant males in the SC groups.
    Findings suggest that keeping adult male mice in structured cages can result in increased aggression towards intruders, a change in the social organization, and altered endocrine states, depending on the individual dominance position.
" My comments
This is a complex set of findings. 
1.  
"a) Mice in enriched cages (EC) attacked intruders significantly more frequently compared to mice in standard cages (SC)"  
    Does this mean that more intelligent mice are more aggressive?  
 
2.  Combined finding 1, above, with
    "
e) PCT were significantly elevated in dominant males of the EC groups compared to subdominant active and subdominant passive males and also compared to the dominant males in the SC groups
    Seems to imply that increased corticosterone (PCT) is accompanied by, or results in, increased aggression.  This runs counter to my basic hypothesis.
3.  Perhaps (e) helps explain: 
     "
(b) In EC groups the position of the dominant male was less stable than in SC groups
    Since elevated PCT is an indication of anxiety.   
4.  Tyrosine hydroxylase (TH)  
http://en.wikipedia.org/wiki/Tyrosine_hydroxylase  "is the enzyme responsible for catalyzing the conversion of the amino acid L-tyrosine to dihydroxyphenylalanine (DOPA)", and  "DOPA is a precursor for dopamine, which, in turn, is a precursor for norepinephrine (noradrenaline) and epinephrine (adrenaline)."    
5. 
N-methyltranferase (PNMT)      "Phenylethanolamine N-methyltransferase (PNMT) is an enzyme found in the adrenal medulla that converts Norepinephrine (Noradrenaline) to Epinephrine (Adrenaline).  PNMT is positively influenced by cortisol, which is produced in the adrenal cortex.


Effect of estrogen level on food-seeking dominance among male rats. (Goog) 
Only abstract available online.   I got the PDF from the library.  
    "Following stabilization, the top 3 Ss were injected with estradiol benzoate prior to each day's pairings. This resulted in a temporary disruption of the hierarchy as the treated Ss gradually worked their way to the bottom of the hierarchy which then restabilized in that order. Subsequent withdrawal of treatment led to the gradual reestablishment of the original pretreatment hierarchy. Estrogen is thus seen to have an effect opposite in direction to that of testosterone on dominance among male rats. Unlike testosterone, however, the effect did not long outlast the treatment.
 

Effects of different forms of environmental enrichment on behavioral,
endocrinological, and immunological parameters in male mice (Biosis) 
Only abstract available online.    I got the PDF from the library.       


Effects of a running wheel-igloo enrichment on aggression, hierarchy linearity, and stereotypy in group-housed male CD-1 (ICR) mice (Biosis)
Only abstract available online.    I got the PDF from the library.     


Effects of environmental enrichment on males of a docile inbred strain of mice (Biosis) 
Only abstract available online.    I got the PDF from the library.  


The effect glucocorticoids on aggressiveness in established colonies of rats.
  (PubMed) 
Only abstract available online.  I got the PDF through the library.   


Genomic and non-genomic effects of glucocorticoids on aggressive behavior in male rats (BioSis) 
Only abstract available online.  I got the PDF through the library.  

 
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