[Stress-induced analgesia].

The emotional responses induced when individuals are confronted with noxious or threatening stimuli, or with a disadvantageous environment, must be a signal of alertness, usually accompanied by an analgesic effect which might be elicited by activation of intrinsic pain-inhibitory systems (stress-induced analgesia, SIA), as one of the basic adaptive mechanisms of animals and humans. In this report, the author will present the involvement of opioid or non-opioid mediated mechanism, role of the emotional responses, endocrinological implication such as hypothalamus-pituitary-adrenal cortex-axis and hypothalamus-sympatho-adrenal medulla-axis, and relation to classical neurotransmitters and their receptors, in the production of analgesia induced by exposure to stresses, especially footshock, forced swimming and psychological stresses. Furthermore, the author also will discuss the possible underlying mechanism in the blockade of the development of tolerance to morphine analgesia by concurrent exposure to footshock or psychological stress, which is one of our recent findings.