Development and reversal of tolerance and its relationship to physical dependence on ethanol in the rat.

Tolerance to ethanol, as assessed by loss of the righting reflex or by improved performance in the aerial righting reflex test, was only observed in animals which did not show signs of a withdrawal reaction. With long exposure periods to ethanol vapor, tolerance was no longer present in animals exhibiting withdrawal reactions. These data are consistent with the hypothesis that a reversal of tolerance precedes prior to the development of physical dependence on ethanol.