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High and Low Activity strains of mice were bidirectionally selected for differences in open-field activity (DeFries et al., 1978, Behavior Genetics, 8: 3-13) and subsequently inbred to use as a genetic model for studying anxiety-like behaviors (Booher et al., 2021, Genes, Brain and Behavior, 20: e12730). Hippocampal RNA-sequencing of the High and Low Activity mice identified 3901 differentially expressed protein-coding genes, with both sex-dependent and sex-independent effects. Functional enrichment analysis (PANTHER) highlighted 15 gene ontology terms, which allowed us to create a narrow list of 264 top candidate genes. Of the top candidate genes, 46 encoded four Complexes (I, II, IV and V) and two electron carriers (cytochrome c and ubiquinone) of the mitochondrial oxidative phosphorylation process. The most striking results were in the female high anxiety, Low Activity mice, where 39/46 genes relating to oxidative phosphorylation were upregulated. In addition, comparison of our top candidate genes with two previously curated High and Low Activity gene lists highlight 24 overlapping genes, where Ndufa13, which encodes the supernumerary subunit A13 of complex I, was the only gene to be included in all three lists. Mitochondrial dysfunction has recently been implicated as both a cause and effect of anxiety-related disorders and thus should be further explored as a possible novel pharmaceutical treatment for anxiety disorders.

We conducted whole-genome sequencing of four inbred mouse strains initially selected for high (H1, H2) or low (L1, L2) open-field activity (OFA), and then examined strain distribution patterns for all DNA variants that differed between their BALB/cJ and C57BL/6J parental strains. Next, we assessed genome-wide sharing (3,678,826 variants) both between and within the High and Low Activity strains. Results suggested that about 10% of these DNA variants may be associated with OFA, and clearly demonstrated its polygenic nature. Finally, we conducted bioinformatic analyses of functional genomics data from mouse, rat, and human to refine previously identified quantitative trait loci (QTL) for anxiety-related measures. This combination of sequence analysis and genomic-data integration facilitated refinement of previously intractable QTL findings, and identified possible genes for functional follow-up studies.

High and Low Activity strains of mice (displaying low and high anxiety-like behavior, respectively) with 7.8-20 fold differences in open-field activity were selected and subsequently inbred to use as a genetic model for studying anxiety-like behavior in mice (DeFries et al., 1978, Behavior Genetics, 8:3-13). These strains exhibited differences in other anxiety-related behaviors as assessed using the light-dark box, elevated plus-maze, mirror chamber, and elevated square-maze tests (Henderson et al., 2004, Behavior Genetics, 34: 267-293). The purpose of these experiments was three-fold. First, we repeated a 6-day behavioral battery using updated equipment and software to confirm the extreme differences in anxiety-like behaviors. Second, we tested novel object exploration, a measure of anxiety-like behavior that does not rely heavily on locomotion. Third, we conducted a home cage wheel running experiment to determine whether these strains differ in locomotor activity in a familiar, home cage environment. Our behavioral test battery confirmed extreme differences in multiple measures of anxiety-like behaviors. Furthermore, the novel object test demonstrated that the High Activity mice exhibited decreased anxiety-like behaviors (increased nose pokes) compared to Low Activity mice. Finally, male Low Activity mice ran nearly twice as far each day on running wheels compared to High Activity mice, while female High and Low Activity mice did not differ in wheel running. These results support the idea that the behavioral differences between High and Low Activity mice are likely to be due to anxiety-related factors and not simply generalized differences in locomotor activity.

Alcohol use disorders (AUDs) lead to early death and many devastating consequences for individuals, families and society. Currently, few effective treatments are available, but emerging research suggests exercise might be beneficial in some individuals. To develop the most effective exercise treatment program, more research on intensity, type, timing, stage of addiction, drug involved, sex of subject and subject population is needed. This review highlights the complexity of the interaction between alcohol behaviors and exercise, with a focus on the role of sex and genetics. Moreover, we describe a variety of rodent models used to investigate the neuronal physiology changes that underlie alcohol consumption and exercise. Specifically, current data indicate that moderate exercise may ameliorate neuronal damage caused by alcohol consumption. Additionally, we describe studies of rodent models in the context of hedonic substitution to draw broad conclusions about shared underlying neurobiological mechanisms. Until recently, most studies in rodents were performed only in males, and few studies have utilized different genetic strains of mice or rats. Comparing similar behavioral paradigms across sex and strain, it has become clear that major sex and genetic differences exist for each behavioral context alone (alcohol consumption and exercise) and combined. Therefore, future research in this area should be developed with careful study design and attention to address both of these factors.

The mesolimbic dopaminergic reward pathway is activated by both alcohol and exercise, suggesting exercise as a possible treatment or preventative method for alcohol-use disorders (AUDs). Prior studies conducted in our lab have demonstrated the hedonic substitution of voluntary alcohol consumption for voluntary wheel running in female C57Bl/6Ibg mice, and a trend in male C57Bl/6Ibg mice. Given the important contribution of genetic background on AUDs, this study aims to assess the effects of voluntary wheel running on voluntary alcohol consumption in two moderate alcohol-consuming strains of mice, C3H/Ibg and 129/SvEvTac. Contrary to our previous studies conducted in C57Bl/6Ibg mice, 129/SvEvTac and male C3H/Ibg mice housed without a wheel consumed significantly more alcohol than mice housed with a free or locked wheel. This suggests that 129/SvEvTac and male C3H/Ibg mice are reducing their alcohol consumption due to an enriched environment and not exercise. Interestingly, the three groups of female C3H/Ibg mice (free wheel, locked wheel, no wheel) did not significantly differ in alcohol consumption, suggesting sex-specific differences in C3H/Ibg mice. In addition, genetic and sex effects were observed for running phenotypes in the presence of alcohol. Female 129/SvEvTac and C57Bl/6Ibg mice ran longer distances than male mice, whereas male and female C3H/Ibg mice did not differ in distance run. C3H/Ibg and female 129/SvEvTav mice with access only to water ran longer distances than mice with access to both alcohol and water. However, this effect was not observed in C57Bl/6Ibg or male 129/SvEvTac mice. The results of this mouse model highlight the importance of genetic background and sex on an animal's response to exercise as an enrichment to reduce voluntary alcohol consumption.