Abstract

Transcriptional profiling of the hippocampus in an F2 cross of a genetic rat model of internalizing vs. externalizing behavior and addiction liability

Hebda-Bauer EK, Hagenauer MH, Blandino P, Meng F, Chitre AS, Ozel AB, Flagel SB, Watson SJ, Palmer AA, Li J, Akil H
51st Annual Meeting of the Society for Neuroscience. 2022.

For 20 years, we have selectively bred two lines of rats (High Responders (bHR) and Low Responders (bLR)) that show contrasting extremes in affective behavior. These extremes map onto human temperamental differences underlying two paths to drug abuse—novelty 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 whole genome sequencing (WGS). 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 (DE) 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 DE associated with bHR/bLR lineage in the F0s (217 genes with FDR<0.10). This surpassed the DE associated with sex and replicated many effects identified in our previous study using only males (Birt et al, 2021). The DE with bHR/bLR lineage was also predictive of DE associated with F2 bHR/bLR phenotypical behavior. Since many generations of selective breeding for a behavioral phenotype should produce an enrichment of alleles influencing that phenotype, we prioritized bHR/bLR DE genes identified in our current and previous studies (Birt et al, 2021) as candidates for mediating bHR/bLR phenotypical behaviors in F2s. Seventeen genes were DE (FDR<0.10) in association with locomotor response to novelty, many of which also had nominal relationships with PavCA (p<0.05, 7/17 genes). Seven of these genes were located nearby (+/-1MB) quantitative trait loci for bHR/bLR phenotypical behavior identified in our previous exome sequencing (Zhou et al, 2019) or WGS study (Chitre et al, in prep), including AABR07071904, Ucp2, Ttc30a1, Fzd6, Spg7, Vps9d1, and Afg3l1. We also identified 26 genes (including Tmem144 and Ucp2) that had been previously identified as DE in the hippocampus of other genetic rat models targeting internalizing behaviors (database: Birt et al, 2021) and which showed similar DE in association with bHR/bLR lineage (FDR<0.10) and F2 bHR/bLR-phenotypical behavior (p<0.05). Together, these genes provide strong candidates for mediating the influence of selective breeding on complex behavior, including exploration, anxiety, and reward learning.