Opioid-like analgesia in defeated mice

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Science  19 Mar 1982:
Vol. 215, Issue 4539, pp. 1520-1522
DOI: 10.1126/science.7199758


Mice exposed to repeated attacks by other mice showed decreased nociception in response to radiant heat focused on their tails. This form of analgesia was blocked by centrally acting opiate antagonists and was not observed in morphine-tolerant mice; furthermore, mice repeatedly subjected to defeat. Mice of the CXBK strain, which respond weakly to morphine, displayed only moderate analgesia following defeat. These findings suggest that endogenous opioid-mediated analgesic mechanisms are readily activated by situations involving biologically significant forms of stress, such as defeat.