Effects of opioid peptides on peripheral stimulation and "stress"-induced analgesia in animals

This review has established the basis for an opiate pain-inhibitory system as well as pharmacological and physiological evidence suggesting alternative nonopiate systems. The concept of multiple forms of pain inhibition became apparent through the study of stress-induced analgesia and the classification of effects across opioid/nonopioid and neural/neurohormonal dimensions. These effects were compared with traditional pathways identified for opiate pain inhibition, and the use of other environmental forms of analgesia (cervical probing, defeat) were explored similarly. To conceptualize how these multiple analgesic systems might interact, a collateral inhibition model was described for opioid and nonopioid systems, while a synergy model examined two responses from the same class. The existence and further characterization of these multiple systems have obvious clinical and therapeutic importance, and systematic approaches to the mechanisms involved have been identified for further empirical investigation.