Responsivity and development of tolerance to the motor impairing effects of moderate doses of ethanol in alcohol-preferring (P) and -nonpreferring (NP) rat lines

Background: Research comparing the alcohol-preferring (P) and -nonpreferring (NP) rat lines has detected an apparent association between ethanol preference and lower responsivity to ethanol, as well as the capacity to develop and maintain tolerance to ethanol's effects However, past studies of tolerance to ethanol's effects generally involved relatively high doses. The present study examined recovery from functional impairment induced by moderate doses of ethanol after a single dose (responsivity) and after multiple doses (development of tolerance) in the P and NP rat lines. Method: Adult female P and NP rats were trained, for 5 consecutive days, to stay on an oscillating bar for 120 sec. Rats were then assigned to one of three groups to receive 1.0, 1.25, or 1.5 g/kg ethanol for 5 consecutive test days. Rats were tested each day at 15-min intervals, following intraperitoneal injection, until recovery to the 120 sec criterion. Results: On the first test day, NP rats took longer to recover to criterion than the P rats following the 1.0 and 1.25 g/kg doses, whereas at the 1.5 g/kg dose no line difference was evident. Trunk blood alcohol concentrations (BACs), associated with time to recovery, indicated higher values fur the P than NP rat on day 1 following injection of the two lower doses. Compared to day 1, NP rats demonstrated significantly shorter times to recovery beginning on day 2 following injections of the 1.0 and 1.25 g/kg doses. However, NP rats did not show significantly different recovery times on days 2-5 compared to day 1 following injection of the 1.5 g/kg dose. The shorter recovery times at the 1.0 and 1.25 g/kg doses were associated with BACs at recovery on day 3 being equal to or greater than values obtained on day I. In contrast, compared to day 1, P rats did not show shorter recovery times until days 3 and 5 following the 1.0 and 1.25 g/kg doses, respectively. However, P rats did demonstrate shorter recovery times on day 2 and higher BACs on day 3 compared to day 1 following the 1.5 g/kg dose. Conclusion: With regard to motor impairment, lower responsivity to moderate doses of ethanol may be a factor associated with high alcohol-seeking behavior. The present results confirm past research supporting an association between ethanol preference and low ethanol responsivity but at doses that are more reflective of those self-administered by P rats.