Mouse inbred strain differences in ethanol drinking to intoxication

Abstract

Recently, we described a simple procedure, Drinking in the Dark (DID), in which C57BL/6J mice self-administer ethanol to a blood ethanol concentration (BEC) above 1 mg/ml. The test consists of replacing the water with 20% ethanol in the home cage for 4 h early during the dark phase of the light/dark cycle. Three experiments were conducted to explore this high ethanol drinking model further. In experiment 1, a microanalysis of C57BL/6J behavior showed that the pattern of ethanol drinking was different from routine water intake. In experiment 2, drinking impaired performance of C57BL/ 6J on the accelerating rotarod and balance beam. In experiment 3, 12 inbred strains were screened to estimate genetic influences on DID and correlations with other traits. Large, reliable differences in intake and BEC were detected among the strains, with C57BL/6J showing the highest values. Strain means were positively correlated with intake and BEC in the standard (24 h) and a limited (4 h) two-bottle ethanol vs. water test, but BECs reached higher levels for DID. Strain mean correlations with other traits in the Mouse Phenome Project database supported previously reported genetic relationships of high ethanol drinking with low chronic ethanol withdrawal severity and low ethanol-conditioned taste aversion. We extend these findings by showing that the correlation estimates remain relatively unchanged even after correcting for phylogenetic relatedness among the strains, thus relaxing the assumption that the strain means are statistically independent. We discuss applications of the model for finding genes that predispose pharmacologically significant drinking in mice.

Ethanol Withdrawal-Associated Drinking and Drinking in the Dark: Common and Discrete Genetic Contributions

“…Two-three weeks before and during drinking tests, mice were housed individually in standard polycarbonate or polysulfone cages with stainless steel wire bar tops on Bed-o-cob bedding. Details of the apparatus for testing DID are given in Ref [7]. Cages were changed bi-weekly.…”

“…Here we report analyses of data from the 4th day of the DID tests for g/kg intake across all 4 hr, and BEC (mg/ml) at the end of the test. We employed procedures identical to those employed in the earlier study of 12 strains [7]. We combined the two data sets, employing strain averages weighted for number of mice in each experiment for the two strains (C57BL/6J and FVB/NJ) that were tested in both experiments (neither Experiment nor Strain × Experiment were significant in a 2-way ANOVA [Fs(1,30) < 1.39, ps > 0.24]).…”

“…We combined the two data sets, employing strain averages weighted for number of mice in each experiment for the two strains (C57BL/6J and FVB/NJ) that were tested in both experiments (neither Experiment nor Strain × Experiment were significant in a 2-way ANOVA [Fs(1,30) < 1.39, ps > 0.24]). We used only the data from males reported by Rhodes [7]. …”

“…The high-preferring C57BL/6J inbred mouse strain drank more than 4 g/kg in 4 hr and reached BECs > 100 mg% in this “drinking in the dark” (DID) test [6]. A subsequent survey of 12 inbred strains showed substantial genetic variability in DID as assessed by both intake and BEC [7]. Further establishing a genetic basis for DID, we successfully bred a line of High Drinking in the Dark (HDID-1) mice by mating those animals that reached the highest BECs after DID [8].…”

“…Given that nearly all traits related to ethanol thus far surveyed across multiple murine genotypes have revealed the presence of genetic influence, it is to be expected that the post-CIE drinking escalation would differ in magnitude across inbred strains. Comparisons across 7 inbred strains for their mean intake data for DID and g/kg daily consumption in a two-bottle preference test have suggested a substantial degree of positive correlation for these two traits (r = 0.70, see [7]). A comparison of HDID-1 and the HS control mice from which they were bred on limited access two-bottle preference for 15% ethanol showed modestly (but significantly) greater drinking in HDID-1 than HS [14].…”