Tolerance and cross-tolerance to morphine and ethanol in mice selectively bred for differential sensitivity to ethanol.

Ethanol-sensitive long-sleep mice showed greater sensitivity to ethanol-induced hypothermia whereas the less sensitive short-sleep mice showed greater sensitivity to morphine-induced hypothermia. The short-sleep mice, but not the long-sleep mice, displayed a degree of cross-tolerance to the hypothermic effects of ethanol following repeated exposure to morphine.