SUBORDINATION STRESS - BEHAVIORAL, BRAIN, AND NEUROENDOCRINE CORRELATES

In mixed-sex rat groups consistent asymmetries in offensive and defens ive behaviors of male dyads are associated with the development of dom inance hierarchies. Subordinate males can be differentiated from domin ants on the basis of both agonistic and non-agonistic behaviors, wound patterns, weight changes. Their behavior changes suggest chronic defe nsiveness and are also broadly isomorphic to many of the symptoms of d epression; their voluntary alcohol consumption increases, and their li fe-spans are shortened. Both subordinate and dominant males tend to sh ow organ change compared to non-grouped controls, with adrenal and spl een enlargement and thymus reduction. However, these changes appear to be more marked in subordinates, and only subordinates show reduced te stes weights. Basal corticosterone (CORT) levels were sharply higher, and plasma testosterone (T) sharply lower, in subordinates compared to both dominants and controls, and reduced corticosterone binding globu lin further enhanced free CORT for subordinates particularly. Many sub ordinates failed to show a normal CORT response to restraint stress. S ubordinates also appear to show widespread changes in serotonin system s, with increased 5-HIAA/5-HT ratios in a number of brain areas, and a lterations of 5-HT1A receptor binding at some sites. These changes sug gest that subordination, a common and consistent feature of life for m any animals living in social groups, may be a particularly relevant mo del for investigating the behavioral, neural and endocrine correlates of chronic stress.