Abstract

Adolescent environmental enrichment and social stress modulate expression of the same gene families within both nucleus accumbens and hippocampus in a genetic rodent model of stress vulnerability

O'Connor AM, Hagenauer MH, Thew Forrester LC, Richardson ER, Rob FI, Hebda-Bauer EK, Watson SJ, Akil H
50th Annual Meeting of the Society for Neuroscience, Virtual. 2021.

Abstract

Background: Adolescence is a critical period for the development of emotional circuitry and a time of increased vulnerability to environmental influences and stressors. This study examined the impact of adolescent environmental enrichment (EE) and social defeat (SD) stress on gene expression within two emotional brain regions (nucleus accumbens (NACC) and hippocampus (HC)) using RNA-sequencing. These interventions were studied in selectively bred Low Responder (bLR) rats that exhibit elevated anxiety-like behavior and stress vulnerability.

Methods: From postnatal day 35 (P35) to P60, male bLR rats (generations F49-F56) were placed in a complex social and physical environment for 1 hr/day for 5 days/week (EE group) or kept in standard housing (NIL group). From P61-64, the rats experienced either social defeat within the resident-intruder paradigm (SD group) or were placed in a novel cage (NIL group) for 15 min/day. From P65-67, the rats underwent behavioral testing (P65: open field, P66: social interaction, P67: elevated plus maze), and were sacrificed on P68. Brains were flash-frozen and dissected at -20oC (NACC: hole punch, HC: whole dorsal HC). For each sample, a cDNA library was constructed and sequenced (Illumina NovaSeq S2), producing 50bp paired-end reads. Reads were aligned to genome assembly Rnor6 (STAR) and summarized into counts per transcript (featureCounts: Ensembl 96 annotation). Following quality control and normalization, the final datasets contained ~17,000 transcripts/region, with sample sizes of NACC: n=46 (n=10-14/subgroup) and HC: n=25 (n=5-8/subgroup). Differential expression was calculated using the limma/voom method and a model including technical co-variates (RNA concentration, batch). Results were compared to gene sets related to functional ontology (MSigDB:C5), cell type/anatomy (DropViz, BrainInABlender, HippoSeq), and manipulations in brain tissue (GeneWeaver, Gemma, literature) using a custom .GMT file and fast Gene Set Enrichment Analysis.

Results: Within both brain regions there was a convergence of differential expression in association with both manipulations (EE & SD) on a set of genes dominated by the protocadherin family and major histocompatibility complex (RT1), as well as an enrichment of effects within gene sets previously linked to stress, social behavior, and cell type.

Conclusion: Although often treated as opposing interventions, EE and SD share many common features, including social interaction, stress, and a novel environment. Our results indicate that these two interventions can produce both opposing and converging changes in gene expression in emotional circuitry during adolescence.