Differential stress induced c-Fos expression and identification of region-specific miRNA-mRNA networks in the dorsal raphe and amygdala of high-responder/low-responder rats

Chronic stress triggers a variety of physical and mental health problems, and how individuals 2 cope with stress influences risk for emotional disorders. To investigate molecular mechanisms 3 underlying distinct stress coping styles, we utilized rats that were selectively-bred for differences 4 in emotionality and stress reactivity. We show that high novelty responding (HR) rats readily 5 bury a shock probe in the defensive burying test, a measure of proactive stress coping behavior, 6 while low novelty responding (LR) rats exhibit enhanced immobility, a measure of reactive 7 coping. Shock exposure in the defensive burying test elicited greater activation of HR rats’ 8 caudal dorsal raphe serotonergic cells compared to LRs, but lead to more pronounced 9 activation throughout LRs’ amygdala (lateral, basolateral, central, and basomedial nuclei) 10 compared to HRs. RNA-sequencing revealed 271 mRNA transcripts and 33 microRNA species 11 that were differentially expressed in HR/LR raphe and amygdala. We mapped potential 12 microRNA-mRNA networks by correlating and clustering mRNA and microRNA expression and 13 identified networks that differed in either the HR/LR dorsal raphe or amygdala. A dorsal raphe 14 network linked three microRNAs which were down-regulated in LRs (miR-206-3p, miR-3559-5p, 15 and miR-378a-3p) to repression of genes related to microglia and immune response (Cd74, 16 Cyth4, Nckap1l, and Rac2), the genes themselves were up-regulated in LR dorsal raphe. In the 17 amygdala, another network linked miR-124-5p, miR-146a-5p, miR-3068-3p, miR-380-5p, miR-18 539-3p, and miR-7a-1-3p with repression of chromatin remodeling-related genes (Cenpk, 19 Cenpq, Itgb3bp, and Mis18a). Overall this work highlights potential drivers of gene-networks 20 and downstream molecular pathways within the raphe and amygdala that contribute to 21 individual differences in stress coping styles and stress vulnerabilities.