Stress-induced analgesia in the mouse: strain comparisons.

Inescapable footshock is capable of differentially activating opioid- and non-opioid-mediated mechanisms of stress-induced analgesia in the rat, depending on the temporal and intensive parameters of its administration. In this study we compared the effects of opioid and non-opioid stress analgesia in two strains of mice, one known to be deficient in central opioid binding sites (CXBK) and one normal in this regard (C57BL/6BY). We found that although the C57 strain showed robust opioid and non-opioid stress analgesia, the CXBK strain only showed stress analgesia of the non-opioid type.