Differential mediation of cold water swim stress-induced antinociception by delta-opioid receptor subtypes in diabetic mice.

The involvement of delta-opioid receptor subtypes in cold water swim stress (CWSS)-induced antinociception in diabetic mice was compared with that in non-diabetic mice. Three-minute swim stress produced significant antinociception in both diabetic and non-diabetic mice as determined by the tail-pinch test. However, the extent of CWSS-induced antinociception in diabetic mice was significantly greater than that in non-diabetic mice. Pretreatment with naltriben, a selective delta 2-opioid receptor antagonist, significantly attenuated CWSS-induced antinociception in both non-diabetic and diabetic mice. In contrast, although 7-benzylidenenaltrexone, a selective delta 1-opioid receptor antagonist, significantly attenuated CWSS-induced antinociception in diabetic mice, it had no effect in non-diabetic mice. These results suggest that CWSS-induced antinociception in non-diabetic mice is mediated by delta 2-opioid receptors, whereas CWSS-induced antinociception in diabetic mice is mediated by both delta 1- and delta 2-opioid receptors. Furthermore, the enhanced CWSS-induced antinociception in diabetic mice may be due to the activation of delta 1-opioid receptors.