VISIBLE BURROW SYSTEM AS A MODEL OF CHRONIC SOCIAL STRESS - BEHAVIORAL AND NEUROENDOCRINE CORRELATES

In mixed-sex rat groups maintained in visible burrow systems (VBS), co nsistent asymmetries in offensive and defensive behaviors of male dyad s are associated with the development of dominance hierarchies. Subord inate males are characterized by particular wound patterns, severe wei ght loss, and a variety of behavioral changes, many of them isomorphic to target symptoms of clinical depression. In two VBS studies, subord inate males showed increased basal levels of plasma corticosterone (CO RT), and increased adjusted adrenal and spleen weights compared to con trols, and often, to dominants as well. Thymus weights and testosteron e levels of subordinates were not reliably different in one study usin g highly aggressive males, but were reduced, along with testes weights , in a second study using unselected males. Glucocorticoid receptor bi nding levels in hippocampus, hypothalamus, and pituitary were not diff erent, nor were aldosterone levels. When tested in a restraint stress procedure, subordinates had higher basal CORT levels, but about 40% of these animals showed a reduced, or absent, CORT response to restraint . These findings indicate that subordination may be reflected in high magnitude changes consistent with physiological indices of prolonged s tress. Dominant rats of such groups may also show physiological change s suggesting stress, particularly when the groups are comprised of hig hly aggressive males only. The VBS colony model thus appears to enable rat groups to produce natural, stress-engendering, social interaction s that constitute a particularly relevant model for investigating the behavioral, neural, and endocrine correlates of chronic stress.