Chronic social stress: Changes in behavioral and physiological indices of emotion

Abstract

Subordination constitutes a natural and often chronic stress condition for males of virtually all species of social mammals. Subordinate male rats of mixed-sex groups maintained in visible burrow systems show high-magnitude changes in adrenal and gonadal steroid hormones and, in a subpopulation, disruptions in hypothalamic pituitary adrenal axis function. Changes in brain serotonin systems have been extensively documented in both colony subordinates and colony dominants, with other regional neurotransmitter system changes also indicated. The group experience seems to change a variety of behaviors both inside the colony situation and in tests run outside the colonies and may disrupt the relationship found in controls between hypothalamic pituitary adrenal response to an acute stressor and defensive behavior. Comparisons of these patterns of stress response with those of other chronic stress models such as learned helplessness and chronic mild stress suggest that, in terms of adrenal and gonadal steroid hormone response, subordination constitutes a more severe stressor. Some involvement of the serotonin system has been demonstrated for both subordination and more traditional models, and other systems may prove to be involved in both. However, a central feature of both learned helplessness and chronic mild stress paradigms is a specific criterion behavior or behaviors, emphasized as models for particular psychopathologies. Thus, learned helplessness and chronic mild stress studies have tended to emphasize the effects of pharmacological agents on these models, whereas work with subordination has been focused on analysis of the biobehavioral stress process itself.