Stress-induced modulation of pain: Role of the endogenous opioid system.

Depending on its nature, duration, and intensity, stress can exert potent and bidirectional modulatory effects on pain, either reducing pain (stress-induced analgesia) or exacerbating it (stress-induced hyperalgesia). The descending pain pathway has been implicated in both stress-induced analgesia and stress-induced hyperalgesia. The endogenous opioid system is widely distributed throughout the descending pain pathway and regulates nociceptive signaling, emotionality, and the response to stress. Here we review the evidence for a key role of the endogenous opioid system in stress-induced modulation of pain in rodents and humans. Understanding the neurobiological mechanisms underlying opioidergic regulation of stress-pain interactions may help in identifying novel therapeutic strategies for the improved treatment of comorbid pain and stress-related disorders.