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

Abstract

In humans, differences in temperament are highly predictive of classes of psychopathology classified as externalizing versus internalizing disorders. To better understand the genetic and neural causes of temperamental differences, we have selectively bred two lines of rats based on their exploration of a novel environment. The bred High Responder (bHR) and bred Low Responder (bLR) rats show contrasting heritable behaviors that map onto human temperamental differences and are associated with two paths to drug abuse—sensation seeking and reactivity to psychosocial stress. To elucidate the genes that underlie the divergent behavior of bHR/bLR rats, we created a bHRxbLR F0-F1-F2 cross and performed behavioral testing, transcriptional profiling, and genetic sequencing. We used RNA-Seq to characterize hippocampal tissue in F0s (n=24, n=6 per phenotype /sex) and F2s (n=250, n=125 per sex) to identify differentially expressed genes related to bHR/bLR lineage and phenotypical behaviors: locomotor response to novelty, anxiety, and Pavlovian Conditioned Approach (PavCA).We found that bHR/bLR phenotypical behaviors remained correlated in the F2s, implying a shared genetic basis. We also found robust differences in hippocampal transcriptional profiles associated with bHR/bLR lineage in the F0s which surpassed the differences associated with sex. These distinct expression profiles were predictive of gene expression patterns associated with F2 bHR/bLR behavior. We then prioritized bHR/bLR differentially expressed genes identified in our current and previous studies as candidates for mediating bHR/bLR phenotypical behaviors in F2s. Seventeen genes were differentially expressed in association with locomotor response to novelty, many of which also had nominal relationships with PavCA behavior. Seven of these genes were located near (+/−1MB) quantitative trait loci for bHR/bLR phenotypical behavior identified in our previous exome sequencing or genome wide association studies: AABR07071904, Ucp2, Ttc30a1, Fzd6, Spg7, Vps9d1, and Afg3l1. We also identified convergence between our model and other genetic rat models targeting internalizing behaviors, with 26 hippocampal genes showing shared patterns of differential expression, including Tmem144 and Mfge8. Our findings provide strong candidates for elucidating genetic and neurobiological factors that may shape differences in temperament and modulate vulnerability to psychiatric and addictive disorders.

Genome-wide association study in a rat model of temperament identifies multiple loci for exploratory locomotion and anxiety-like traits

“…Below, we discuss several of the loci identified in this analysis. Parallel analyses are underway to determine whether the observed variants are associated with differences in gene expression in the brain of the bHR, bLR, or the F 2 cross, and how expression levels might relate to behavioral traits ( Hebda-Bauer et al, 2022 ).…”

Resource: A Curated Database of Brain-Related Functional Gene Sets (Brain.GMT)

“…Overview of Included Gene Sets: Our custom gene set file (Brain.GMT: 918 gene sets, Table 1) was designed to provide greater insight into brain-derived differential expression results than traditional functional ontology. Originally, the gene set file was constructed as part of projects using rodent models of neuropsychiatric disorders performed on tissue from the hippocampus [13][14][15][16] and nucleus accumbens [15], and thus emphasizes gene sets derived from related regions and topics.…”

“…To improve the interpretation of brain-derived differential expression results, we compiled a custom gene set database (Brain.GMT) focused on sets of genes associated with brain function, brain cell-types, brain co-expression networks, and regional gene expression signatures. We initially constructed Brain.GMT as part of projects using hippocampal [13][14][15][16] and nucleus accumbens tissue [15] from rodent models of neuropsychiatric disorders. To rapidly compare our results to existing literature, we also constructed gene sets using differential expression results from related publications and differential expression databases.…”

“…To rapidly compare our results to existing literature, we also constructed gene sets using differential expression results from related publications and differential expression databases. This paper serves as detailed methodological documentation to accompany our transcriptional profiling studies using Brain.GMT [13][14][15][16]. Since we have found Brain.GMT to be exceptionally useful, we also provide detailed guidance to accompany its public release for use by other researchers.…”

Adolescent environmental enrichment induces social resilience and alters neural gene expression in a selectively bred rodent model with anxious phenotype

“…The divergent temperament in bHR and bLR rats is reflected in differences in brain gene expression [20–24]. Recent work has uncovered gene9c differences that underlie these dis9nct phenotypes [25, 26].…”