Antinociceptive and hypothermic crosstolerance between continuous and intermittent cold-water swims in rats.

Antinociceptive responses induced by continuous (CCWS: 2 degrees C, 3 min) and intermittent (ICWS: 2 degrees C, 18 10-s swims, 18 10-s recoveries) cold-water swims differ in their sensitivity to opioid antagonists and crosstolerance with morphine. The present study examined whether CCWS and ICWS antinociception and hypothermia displayed crosstolerance in rats. Jump thresholds were significantly increased following acute exposure to CCWS (30 min) and ICWS (30-60 min). CCWS antinociception displayed tolerance (90% reduction) to CCWS after 14 days and crosstolerance (100% reduction) to ICWS on the fifteenth day. ICWS antinociception displayed tolerance (74% reduction) to ICWS and crosstolerance (81% reduction) to CCWS. Core body temperatures were significantly decreased following acute exposure to CCWS (30 min) and ICWS (30-90 min). Although CCWS and ICWS hypothermia displayed tolerance to the same stressor and crosstolerance to the other stressor, the changes in the antinociceptive and hypothermic effects failed to correlated significantly with each other.