Tolerance to ethanol-induced impairment of water escape in rats bred for ethanol sensitivity.

Rats selectively bred for ethanol (EtOH)- induced reductions in locomotor activity ("least affected" = MA) showed a reversed order of senstivity (i.e., LA more sensitive) to EtOH-induced (1.75 g/kg, IP) impairment of swimming. Thirty days of daily EtOH intubation began the next day, starting at 3.5 g/kg for 4 days, and increasing by 0.5 g/kg after 4 days at each dose, until 6.0 and 6.5 g/kg were given for 5 days each. Subjects were retested on the swim task (1.75 g/kg, IP) following 10, 20, and 30 days of chronic EtOH, and at 10, 20, and 30 days after cessation of EtOH treatment. Rats of each line and sex showed progressively decreasing peak impairment during the chronic treatment period; impairment increased toward initial levels during the post-treatment period. LA rats were more impaired than MA rats prior to, throughout, and subsequent to the chronic treatment period; a significant positive correlation between initial impairment and impairment after 30 days of chronic EtOH was found. No line differences in rates of tolerance acquisition or loss, or in final levels of tolerance as indicated by post-treatment impairment relative to initial impairment were observed. The similarity of the dynamics of EtOH tolerance in rats selectively bred for sensitivity to its acute effects suggests independent genetic influences upon initial ethanol sensitivity as opposed to acquired ethanal tolerance.