Differential concentration-response curves for oral ethanol self-administration in C57BL/6J and BALB/cJ mice

In an earlier study ethanol drinking was induced by reducing mice to 80% of their free-feeding weight and feeding them their daily food allotment prior to the experimental session. The mice were given an ascending series of ethanol concentrations (1 to 8%). The inducing condition was subsequently eliminated to determine if the drinking of 8% ethanol would persist in its absence. Eight percent ethanol served as a reinforcer for the C57BL/6J mice but not for the BALB/cJ mice. The purpose of the present study was to examine strain differences in ethanol maintained behavior over a range of concentrations from 1 to 32% (w/v). Ethanol served as a reinforcer for the C57BL/6J mice at concentrations of 4, 8 and 16%. Lever presses and volume of liquid consumed per unit of body weight were inverted U-shaped functions of ethanol concentration. Post-session blood ethanol levels confirmed intake of pharmacologically significant amounts of ethanol. Results with the BALB/cJ mice were very different from those with the C57BL/6J mice. The level of responding did not increase above baseline levels at any of the concentrations tested, and levels of responding decreased below baseline at 32%. Thus, ethanol did not serve as a reinforcer for the BALB/cJ mice at any of the concentrations tested. These results demonstrate that over a range of ethanol concentrations genotype is an important determinant of ethanol reinforced behavior.