Stress, Neurochemistry of

Abstract

Most neurochemical parameters are altered during or following some form of experimental stress. But, because all stressful treatments (stressors) are complex, involving a variety of stimuli, it is difficult to be certain that the responses are associated unequivocally with stress per se. While the concept of stress is generally understood, there is no generally accepted definition. Stress is subjective; what is stressful for one person may not be so for another, and even what is stressful for one person on one occasion may not be so on another. Thus, most definitions of stress cite the person’s response, the most widely accepted being the activation of the pituitary-adrenal axis. This definition derives from the work of Selye, who discovered the adrenocortical activation in stress and promulgated the theory that stress is a nonspecific (adrenocortical) response. Surprisingly, his theory and the definition that arises from it ignore the stress-related activation of the adrenal medulla and the sympathetic nervous system, established by the pioneering work of Cannon. Most modern researchers accept the ubiquity of the adrenocortical response in stress, but would not agree that the stress response is physiologically nonspecific (for example, the physiological response to cold exposure is not the same as that to heat).