Drinking Rhythms in Alcohol Preferring Mice

Abstract

Multiple lines of High Alcohol Preferring (HAP) mice were selectively bred for their intake of 10% ethanol (v/v) during 24-h daily access over a four-week period, with the highest drinking lines exhibiting intakes in excess of 20 g/kg/day. Drinking rhythms and corresponding blood ethanol concentrations (BEC) of the highest drinking HAP lines to those of the C57BL/6J (B6) inbred strain. Adult male and female crossed HAP (cHAP), HAP1 and B6 mice had free-choice access to 10% ethanol and water for 3 weeks prior to bi-hourly assessments of intake throughout the dark portion of a reverse 12:12 light dark cycle. In another cohort of cHAP mice, the same procedure was used to assess bi-hourly ethanol intake, and blood samples were taken across the day to look at the pattern of accumulation in these mice. Finally, considering the high level of intake by cHAP mice, we were interested in assessing whether metabolic and functional tolerance develop following chronic free-choice access, which were assessed using 2.0 and 1.75 g/kg challenge doses of 20% ethanol, respectively. cHAP and HAP1 mice maintained an excessive level of intake throughout the dark portion of the cycle, accumulating mean BEC levels of 261.5 + 18.09 and 217.9 + 25.02 mg/dl at 7-8 hours following lights off, respectively. B6 mice drank comparatively modestly, and did not accumulate high BEC levels (53.63 + 8.15 mg/dl). In the cHAP cohort, mean BECs were 112.47 + 19.91 at 2 hours after lights off, 189.00 + 27.40 at 6 hours after lights off, 193.80 + 29.66 at 10 hours after lights off, and 89.68 + 22.19 at 2 hours after lights on. Further, following 3 weeks of ethanol access, cHAP mice had a faster rate of ethanol metabolism and fewer hind slips than water-only exposed mice (ps < .05). In conclusion, the excessive free-choice drinking demonstrated by the HAP1 and cHAP lines, as well as the pattern of sustained high BECs in cHAP mice, challenge the notion that rodents will not reliably and voluntarily sustain ethanol intake at pharmacologically relevant levels. These results suggest that the highest drinking HAP lines may provide a unique opportunity for modeling the excessive intake that has been observed in alcohol-dependent individuals. Further, we observed that cHAP mice develop both metabolic and functional tolerance to the ataxic effects of ethanol following 3 weeks of free-choice access. Together, these findings support HAP mice as translational rodent model of alcoholism, and provide rationale for exploration of the predisposing factors for excessive consumption, as well as the development of physiological, behavioral, and toxicological outcomes following alcohol exposure.