Is Stress More Than a Disease? A Comparative Look at the Adaptativeness of Stress

Abstract

Since the pioneering work of Hans Selye in the 1930s (Selye, 1936, 1937) there has been a tremendous effort to understand how the nervous and endocrine systems coordinate the physiological response to stressors. Most work has focused on understanding the hypothalamic-pituitary-adrenal (HPA) axis and its role in stress. Within the last 20 yr scientists have purified and sequenced corticotropin-releasing hormone (CRH) and its receptors (Vale et al., 1981; DeSouza, 1995). Receptors for corticotropin and the glucocorticoid hormones have been cloned and mechanisms of action elucidated (Mountjoy et al., 1992; Bamberger et al., 1996). Significant progress has been made in defining afferent neuronal circuitry controlling the HPA axis during stress (Herman and Cullinan, 1997) and the link between stress and many major disease states has been clarified. Although a good deal of Selye's original work addressed how organisms adapt to stressors (Selye, 1976), more recent studies have focused on diseaserelated aspects of stress. We are constantly bombarded, both in the scientific press and popular media, with reminders that stress is linked to feeding disorders, cancer, mental health, and reproductive and immune dysfunction as well as a host of other disorders. For a comparative biologist it is difficult to imagine that such a highly coordinated physiological response has evolved over millions of years simply to make animals sick. What are the adaptive features of stress? What are the evolutionary precursors of this response? Why has this response remained virtually unchanged in the vertebrate lineage? These are the questions that prompted the organization of this symposium. It does not take an exhaustive review of the literature to realize that most of what we do know about stress and adaptation comes largely from studies on laboratory mammals that have never seen their natural environment. In recent years, increasing numbers of comparative endocrinologists have become interested in how animals living in their natural environment deal with stress. Four assumptions lie at the heart of this research: