Limbic circuitry activation in ethanol withdrawal is regulated by a chromosome 1 locus

Fos activation patterns related to acute ethanol and conditioned taste aversion in adolescent and adult rats

Studies in rats have revealed marked age differences in sensitivity to the aversive properties of ethanol, with a developmental insensitivity to ethanol aversion that is most pronounced during pre- and early adolescence, declining thereafter to reach the enhanced aversive sensitivity of adults. The adolescent brain undergoes significant transitions throughout adolescence, including in regions linked with drug reward and aversion; however, it is unknown how ontogenetic changes within this reward/aversion circuitry contribute to developmental differences in aversive sensitivity. The current study examined early adolescent (postnatal day [P]28-30) and adult (P72-74) Sprague-Dawley male rats for conditioned taste aversion (CTA) after doses of 0, 1.0, or 2.5 g/kg ethanol, and patterns of neuronal activation in response to ethanol using Fos-like immunohistochemistry (Fos+) to uncover regions where age differences in activation are associated with ethanol aversion. An adolescent-specific ethanol-induced increase in Fos+ staining was seen within the nucleus accumbens shell and core. An age difference was also noted within the Edinger-Westphal nucleus (EW) following administration of the lower dose of ethanol, with 1 g/kg ethanol producing CTA in adults but not in adolescents and inducing a greater EW Fos response in adults than adolescents. Regression analysis revealed that greater numbers of Fos+ neurons within the EW and insula (Ins) were related to lower consumption of the conditioned stimulus (CS) on test day (reflecting greater CTA). Some regionally specific age differences in Fos+ were noted under baseline conditions, with adolescents displaying fewer Fos+ neurons than adults within the prelimbic (PrL) cortex, but more than adults in the bed nucleus of the stria terminalis (BNST). In the BNST (but not PrL), ethanol-induced increases in Fos-immunoreactivity (IR) were evident at both ages. Increased ethanol-induced activity within critical appetitive brain regions (NAc core and shell) supports a role for greater reward-related activation during adolescence, possibly along with attenuated responsiveness to ethanol in EW and Ins in the age-typical resistance of adolescents to the aversive properties of ethanol.

Distinct Roles for Two Chromosome 1 Loci in Ethanol Withdrawal, Consumption, and Conditioned Place Preference

We previously identified a region on chromosome 1 that harbor quantitative trait loci (QTLs) with large effects on alcohol withdrawal risk using both chronic and acute models in mice. Here, using newly created and existing QTL interval-specific congenic (ISC) models, we report the first evidence that this region harbors two distinct alcohol withdrawal QTLs (Alcw1₁and Alcw1₂), which underlie 13% and 3–6%, respectively, of the genetic variance in alcohol withdrawal severity measured using the handling-induced convulsion. Our results also precisely localize Alcw1₁ and Alcw1₂ to discreet chromosome regions (syntenic with human 1q23.1–23.3) that encompass a limited number of genes with validated genotype-dependent transcript expression and/or non-synonymous sequence variation that may underlie QTL phenotypic effects. ISC analyses also implicate Alcw1₁and Alcw1₂ in withdrawal-induced anxiety-like behavior, representing the first evidence for their broader roles in alcohol withdrawal beyond convulsions; but detect no evidence for Alcw1₂ involvement in ethanol conditioned place preference (CPP) or consumption. Our data point to high-quality candidates for Alcw1₂, including genes involved in mitochondrial respiration, spatial buffering, and neural plasticity, and to Kcnj9 as a high-quality candidate for Alcw1₁. Our studies are the first to show, using two null mutant models on different genetic backgrounds, that Kcnj9^−/− mice demonstrate significantly less severe alcohol withdrawal than wildtype littermates using acute and repeated exposure paradigms. We also demonstrate that Kcnj9^−/− voluntarily consume significantly more alcohol (20%, two-bottle choice) than wildtype littermates. Taken together with evidence implicating Kcnj9 in ethanol CPP, our results support a broad role for this locus in ethanol reward and withdrawal phenotypes. In summary, our results demonstrate two distinct chromosome 1 QTLs that significantly affect risk for ethanol withdrawal, and point to their distinct unique roles in alcohol reward phenotypes.