Selectively bred lines of mice show response and drug specificity for genetic regulation of acute functional tolerance to ethanol and

Genetic regulation of acute tolerance to ethanol may be asso-ciated with ethanol consumption and other ethanol-related be-haviors in rodents. We have used lines of mice, selectively bred for high and low acute functional tolerance (HAFT and LAFT, respectively) to ethanol-induced loss of balance to test this hypothesis. Replicate HAFT and LAFT lines differ in AFT to ethanol-induced loss of balance by 4.4- and 5-fold, respec-tively. Frequency distributions and mean AFT scores for those lines, F1, and backcrosses show a dominance for the HAFT phenotype. Time courses for acquisition and decay showed that AFT to ethanol-induced loss of balance developed rapidly, could be maintained up to 6 h with repeated doses, and de-cayed 6 h after peak tolerance and discontinuance of ethanol administration. The lines did not differ in initial sensitivity as measured by brain ethanol concentration at loss of balance, indicating that initial sensitivity and AFT to loss of balance were not coselected traits. Surprisingly, HAFT versus LAFT lines did not differ in development of AFT to loss of righting response, or hypothermia, indicating different mechanisms or neuronal sys-tems mediate genetic influences on these measures. Voluntary ethanol consumption was low in both of the replicate lines, but HAFT lines consumed greater amounts of ethanol than LAFT lines. The HAFT and LAFT lines developed AFT to pentobarbi-tal-induced loss of balance, however, there were no line differ-ences in rates or extent of the AFT development. These results show that genetic regulation of AFT development is drug- as well as response-specific. Exposure to ethanol during a single session of intoxication results in decreased responsiveness to effects of ethanol on the central nervous system. This rapid adaptation, referred to as acute tolerance, is observed in animals and humans and is influenced by environmental factors and by genotype i