Persistent enhancement of ethanol drinking following a monosodium glutamate-substitution procedure in C57BL6/J and DBA/2J mice

Inbred mouse strains such as C57BL/6J (B6) and DBA/2J (D2) and related strains have been used extensively to help identify genetic controls for a number of ethanol-related behaviors, including acute intoxication and sensitivity to repeated exposures. The disparate ethanol drinking behaviors of B6 mice expressing high-drinking/preference and D2 mice expressing low-drinking/preference have yielded considerable insight into the heritable control of alcohol drinking. However, the B6-high and D2-low drinking phenotypes are contrasted with ethanol-conditioned reward-like behaviors, which are robustly expressed by D2 mice and considerably less expressed by B6 mice. This suggests that peripheral factors, chiefly ethanol taste, may help drive ethanol drinking by these and related strains, which complicates mouse genetic studies designed to understand the relationships between reward-related behaviors and ethanol drinking. Traditional approaches such as the sucrose/saccharin-substitution procedure that normally accentuate ethanol drinking in rodents have had limited success in low drinking/preferring mice such as the D2 line. This may be due to allelic variations of the sweet taste receptor subunit, expressed by many ethanol low-drinking/preferring strains, which would limit the utility of these types of substitution approaches. We have recently shown (McCool & Chappell, 2012) that monosodium glutamate (MSG), the primary component of umami taste, can be used in a substitution procedure to initiate ethanol drinking in both B6 and D2 mice that greatly surpasses that initiated by a more traditional sucrose-substitution procedure. In this study, we show that ethanol drinking initiated by MSG substitution in D2 mice, but not sucrose substitution, can persist for several weeks following removal of the flavor. These findings further illustrate the utility of MSG substitution to initiate ethanol drinking in distinct mouse strains.