Experimental protocols for the study of stress in animals and humans.

1. Stress is the response of an organism to a stressor of physical, chemical, or emotional nature. 2. Exposure to stressors induces behavioral and neuroendocrine consequences in experimental animals as well as in humans, and this complex response can be adaptive or maladaptive. 3. Experimentally, the exposure to different stressors is used in order to study the evoked responses and the mechanisms underlying them, or to modify the behavior of animals in an attempt to reproduce reliable models of psychiatric symptoms with a stress-related component in humans. 4. In animals of the same species, strain, sex and age maintained in controlled environmental conditions we can expect reproducible behavioral and neuroendocrine responses to stressful protocols, that are proportional to the intensity of the stressor and the duration of the exposure. The reproducibility of the response is crucially bound to the controlled experimental conditions used. 5. In human experiments, the main difficulties in controlling experimental conditions are not related to the stressor (intensity and duration of exposure ethically acceptable), but are mainly related to the large interindividual variability in sensitivity to any kind of traumatic stimulus or event that can sometimes be explained on the basis of genetic variables or particular personal histories.