Recent Developments in Stress Research

Recent developments in research on animal stress have led to modifications of earlier theory and have increased our knowledge of how psychological stressors can elicit a physiological stress response. When stress was first studied scientifically, it was considered to be a stereotyped, generalized physiological response of the body to many different kinds of noxious stimuli. It is now known that the physiological stress response of the body is more complex than originally conceived, and that it can vary with different stressors or across species. Psychological stressors can be either endogenous or exogenous. A chronic endogenous buildup of a drive to perform specific behaviors, ie., locomotion in young calves, can result in animals displaying signs of chronic stress: suppressed immune system, altered metabolism and learned helplessness. A sense of control over one’s environment is extremely important in determining the potency of potential stressors. The performance of highly repetitive, stereotyped behaviors called stereotypies has been shown to help animals cope with environments containing little or unvaried stimulation. Psychological stimuli are usually much more potent in eliciting the “clasical stress response” than physical stressors. Based on physiological data, research animals have not adapted to human handling until their overt displays of fear of humans have subsided. Since there is no single measure of stress, it is of paramount importance that the behavioral and physiological variables utilized in stress research are relevant to the particular species and question under study.