Initial sensitivity versus acquired tolerance to ethanol in rats selectively bred for ethanol sensitivity.

Chronic tolerance to ethanol-induced sleep, motor impairment (moving belt test), and hypothermia were examined in two lines of rats that had been selectively bred for their different initial sensitivities to ethanol. In agreement with previous work (Mayer et al. 1982, 1983), the least-affected (LA) rats were found to be less sensitive than their most-affected (MA) counterparts in all three tests. Chronic treatment with ethanol resulted in a more rapid and more marked tolerance development in MA animals than in LA ones. The two lines did not differ in final level of tolerance achieved for either sleep time or hypothermia. However, significant differences were observed with respect to the moving belt test, in that at the end of chronic ethanol treatment the MA animals were more resistant to ethanol than the LA ones. These studies support the existence of a relationship, but not necessarily a direct genetic linkage, between initial sensitivity and acquired tolerance.