Experiment
The aim of the current study was to identify QTL associated with variation in sensitivity to acute EtOH (ethanol) challenge in a novel population of 346 (C57BL/6J x 129S1/SvImJ) F2 mice (183 males, 160 females).
Previous studies had shown that the C57BL/6J (B6) and 129S1/SvImJ (S1) inbred mouse strains differ in responses to certain measures of acute EtOH intoxication. QTL analysis of measures of EtOH-induced ataxia (accelerating rotarod), hypothermia, and loss of righting reflex (LORR) duration were performed.
As a measure of EtOH induced hypothermia the basal core body temperature was taken; then mice were injected with 3.5 g/kg EtOH and core temperature was measured 30, 60, 90 and 120 minutes later. The difference between the pre-EtOH temperature and the average temperature over the 4 post-EtOH time points was taken as the dependent measure.
Comparison of the B6, S1, F1 and F2 population means revealed that hypothermia in S1 was greated than the other three genotypes. QTL analysis and multilocus modeling revealed 3 significant loci:
A main effects QTL, Eih3, ethanol induced hypothermia 3, mapped to Chromosome 16 at 30.9 cM peaking at marker rs4182243 with a LOD score of 3.9, p<0.05. Markers flanking the 1.5 LOD confidence interval were rs4165065 (8.13 cM) and rs4200124 (40.0 cM). Eih3 was detected independent of sex.
A second locus, Eih4, ethanol induced hypothermia 4, was detected with an additive sex effect in the model on Chromosome 7 at 18.4 cM peaking at marker rs13479153 with a LOD score of 2.8, p<0.01. Markers flanking the 1.5 LOD confidence interval were rs3700068 (0.0 cM) and rs3716088 (103.1 cM).
A third locus, Eih5, ethanol induced hypothermia 5, was detectable with both additive and interacting effects of sex on Chromosome 3 at 80.2 cM peaking at marker rs3710548 with a LOD score of 3.9, p<0.06. Markers flanking the 1.5 LOD confidence interval were rs3719390 (43.5 cM) and rs30801216 (92.9 cM). Using the GeneWeaver database Hs2st1 appears as a highly connected candidate gene.
Multilocus modeling revealed that taken together the loci and their interactions accounted for 13.1% of the variance in EtOH induced hypothermia [Table 1].
Comparison of the B6, S1, F1 and F2 population trait means revealed that loss of righting response (LORR) in S1 was greater than for the other three genotypes and greater in F2 than in B6.
QTL analysis of LORR revealed:
A signifcant main-effects locus, Elorr3, ethanol induced loss of righting response 3, mapped on Chromosome 4 at 93.4 cM peaking at marker rs3695715 with a combined LOD score of 5.74, p<0.05. Markers flanking the 1.5 LOD confidence interval were rs3663950 (71.8 cM) and rs6279100 (103.79 cM). Elorr3 had a dominant S1 effect; male mice with S1 alleles had a higher loss of righting response time.
Suggestive QTL for ethanol induced loss of righting response were also detected on Chromosome 6 at 52.6 cM, on Chromsome 7, on Chromosome 11 and on Chromosome 9. Multilocus modeling esitmated that together the loci accounted for 16.9% of the total phenotypic variance.
Comparison of the B6, S1, F1, and F2 population means found differences in the average latency to fall across ten trials of rotarod training. Post-hoc tests revealed that scores were higher in B6 than in the other three genotypes, while S1 scores were higher than those for F2. Multiple significant and suggestive main-effect loci were found using a main-effect scan [Table 1]. These loci were all retained in multple-locus modeling, together accounting for 25% of the phenotypic variance.
For the rotarod training index there was a trend toward a significant difference in B6, S1, F1, and F2 populations means. S1 showed a greater improvement in training than F1 or F2. A single suggestive main-effect QTL was detected on Chr 11 at 42.0 cM (peak marker rs13481076) which accounted for 4.4% of the phneotypic varaince.
Comparison of the B6, S1, F1 and F2 population means found a significant difference in the EtOH-induced rotarod ataxia index. Ataxia was greater in the S1 than in the other three genotypes and greater in B6 than in F1. QTL analysis found three suggestive loci on Chrs 8, 9 and 17 from the main-effects scan. Additional scans and multilocus modeling revealed a main effect of sex and several interactions amongst the loci. Taken together, the sex effects, main effects, and interactions among the loci accounted for 22.4% of the phenotypic varaince.
These data confirmed an earlier observation that S1 mice were more sensitive to acute EtOH challenge than B6 mice, and extended them by demonstrating that the strains differed across a broader range of measures at increasing EtOH doses.
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