Bioenergetic-Related Gene Expression in the Hippocampus Predicts Internalizing vs. Externalizing Behavior in a F₂Cross of Selectively-Bred Rats

AbstractUsing selective breeding, we have produced two rat lines with highly divergent behaviors: bred Low Responders (bLR) are extremely inhibited and anxious in a novel environment, whereas bred High Responders (bHR) are exploratory and sensation-seeking. These traits map onto temperamental extremes predictive of internalizing vs. externalizing psychiatric disorders in humans and can model two divergent paths to drug abuse. To elucidate gene expression underlying these heritable behavioral differences, bHR and bLR rats from generation 37 were bred to produce a F0-F1-F2cross. We then measured exploratory locomotion, anxiety-like behavior, and sensitivity to reward cues (Pavlovian Conditioned Approach) and performed hippocampal RNA sequencing in both F0s (n=24, n=6/phenotype/sex) and F2s (n=250, n=125/sex).Behaviors that diverged during selective breeding remained correlated in F2s, implying a shared genetic basis. Transcriptional profiles associated with F0bHR/bLR lineage showed robust differences, surpassing differences associated with sex, and predicted gene expression patterns associated with F2behavior. Among the bHR/bLR differentially expressed genes (DEGs), we identified 17 genes with expression associated with F2exploratory locomotion, seven of which were located within related quantitative trait loci identified previously in F2s. Convergence between our differential expression study and others targeting similar behavioral traits revealed an additional 26 genes related to behavioral temperament. Gene set enrichment analysis pointed to growth and proliferation upregulated with bHR-like behavior and mitochondrial function, oxidative stress, and microglial activation upregulated with bLR-like behavior. Our findings implicate bioenergetic regulation of hippocampal function in shaping temperamental differences, thereby modulating vulnerability to psychiatric and addictive disorders.