The organismal response to stress (defined here as a real or perceived threat to homeostasis or well-being) promotes survival via adjustments to ongoing physiological processes and behavior. The activation of multiple interacting processes, including the behavioral, autonomic, endocrine, and immune systems, produces an integrated stress response. While initially adaptive, prolonged activation of molecular pathways engaged by these systems can cause pronounced changes in physiology and behavior that have long-term deleterious implications for survival and well-being. In essence, prolonged or chronic stress changes the rules under which the body regulates homeostasis, requiring new strategies for successful adaptation. This concept lies at the heart of Selye's initial description of the “general adaptation syndrome,” where after an initial “alarm” stress reaction, the organism is able to successfully manage prolonged stress for substantial periods. Only when homeostatic pressure becomes too great does the individual enter into a state of frank distress, with attendant morbidity and mortality (Selye, 1950). Importantly, the process of adaptation comes at a cost to the organism, as stress effector systems are chronically mobilized to meet the homeostatic demands of prolonged
