Effect of Adolescent Stress on PFC miRNA Gene Expression

Deaths related to opioid use have skyrocketed in the United States, leading to a public health epidemic. Research has shown that both biological (genes) and environmental (stress) precursors are linked to opioid use. In particular, stress during adolescence – a critical period of frontal lobe development – influences the likelihood of abusing drugs. However, little is known about the biological mechanisms through which adolescent stress leads to long-term risk of opioid use, or whether genetic background moderates this response. Male and female C57BL/6J were exposed to chronic variable social stress (CVSS) or control conditions throughout adolescence and then tested for prefrontal cortex miRNA gene expression. C57BL/6J mice exposed to CVSS had a downregulation of twelve miRNA in the prefrontal cortex compared to control mice. Overall design: Male C57BL/6J mice were assigned to chronic variable social stress (CVSS) or control conditions. To minimize litter effects, littermates were evenly distributed between the CVSS and control groups at weaning. CVSS mice underwent the stress protocol during adolescence (PND 25-59) as previously described (Caruso et al., 2017, 2018c, 2018b, 2018a). Following weaning mice sat undisturbed with littermates (PND 21-25). On PND 25, CVSS mice were individually housed for 3 days followed by social rehousing with 1-2 unfamiliar cage mates for 4 days. This procedure was repeated for 5 consecutive weeks. On PND 59, CVSS mice were rehoused with their original cage mates from weaning until behavioral testing or sacrifice. For control mice, cage mates remained the same from weaning to the end of the study. To equate handling between the control and CVSS conditions, each time CVSS mice were transferred to a new cage for individual or social rehousing, control mice were also moved to new cages. Following CVSS, these mice remained undisturbed (i.e. no behavioral testing) until PND 70 when they were euthanized by cervical dislocation and brains removed. A mouse brain matrix was used to obtain 1 mm slices. The PFC was punched from the slice with a blunt needle that captured both hemispheres and immediately place into RNAlater.