Effects of initial tolerance on acquired tolerance to alcohol in two selectively bred rat strains.

The extent to which initial sensitivity to alcohol influences acquired tolerance was investigated in two selectively bred rat lines. These two lines have been selectively bred for differences in initial sensitivity to alcohol. The most affected (MA) line shows about a 90% reduction in motor activity following a 1.5 g/kg dose of alcohol compared with only a 40% reduction in least affected (LA) animals. In an initial investigation using stabilimeter activity, MA animals demonstrated increased tolerance following regular alcohol exposure, while LA animals showed little change from their initial levels of tolerance. In a second study following a similar intubation procedure, tolerance was assessed by sleeping time. Both MA and LA rats evidenced increased tolerance to alcohol, although MA animals did not approach the levels of tolerance shown by LA animals. In both studies the amount of initial tolerance was correlated with the degree of acquired tolerance. The potential for using these animals in the study of the underlying mechanisms of tolerance is discussed.