Social stressors, like other stressors, are powerful activators of the 
sympathoadrenomedullary system. Differential housing (single vs. group) and 
social defeat of rats is known to alter the activity of 
catecholamine-synthesizing enzymes in the medulla. The present studies examined 
the effect of 70 days of triad (3 rats per large cage) and individual housing of 
male rats on adrenal mRNA levels of tyrosine hydroxylase (TH), 
dopamine-beta-hydroxylase (DBH) and phenylethanolamine-N-methyltransferase 
(PNMT) and on TH protein levels. Behavioral ratings carried out at the triad 
formation indicated that dominant rats exhibited mostly offensive aggressive 
behaviors. By contrast, subordinate rats expressed primarily defensive 
behaviors, while the subdominant rats displayed intermediate levels of these 
behaviors. Overall, compared with single housing, triad housing resulted in 
lower gene expression for TH, DBH and PNMT and lower TH protein in the adrenals. 
Within triads, gene expression for these enzymes and TH protein concentration 
were higher in subordinate compared with dominant and subdominant rats. The 
dominant rats tended to have the lowest gene expression of these enzymes. These 
data indicate that in rodents, individual housing and a subject's social rank 
have a differential impact on the regulation of catecholamine biosynthesis 
already during the process of gene expression of catecholamine biosynthetic 
enzymes in the adrenals.