, 2011). Regulation of HPA axis activity, and specifically reduced expression of CRF (regulated by stress-induced demethylation of regulatory areas of the gene CRF1) was shown in the subset of vulnerable mice that displayed social avoidance (Elliott et al., 2010) and in mice that displayed short latency to defeat in the resident/intruder paradigm (Wood et al., 2010). Supporting this finding, knockdown of CRF levels diminished stress-induced social avoidance (Elliott et al., 2010). In a separate model of chronic subordinate

colony housing, mice selectively bred for low anxiety were behaviorally resilient to subordination stress, and showed distinct HPA axis responses (Füchsl et al., 2013). Several neurotransmission systems Bafilomycin A1 clinical trial are implicated in social-stress resilience vs. vulnerability: in addition to BDNF-control of dopamine mentioned above, differences in the NAc dopaminergic system resulting from differential maternal behavior are correlated

with increased preference for social interactions in a group of highly groomed rat offspring (Peña et al., 2014). Glutamatergic, serotonergic, and GABAergic systems appear to be involved as well. Vulnerable and resilient animals differ significantly in the expression of AMPA receptors in the dorsal hippocampus, and activation of AMPA receptor during the stress exposure prevented the physiological, neuroendocrine, and behavioral effects of chronic social stress exposure (Schmidt et al., 2010). Knockout of serotonin transporter Volasertib ic50 increases the vulnerability to social avoidance following social defeat (Bartolomucci et al., 2010). Finally, supression of the GABAergic system is seen in the pre-frontal cortex of mice showing depressive symptoms following social defeat (Veeraiah et al., 2014), and in amygdala of mice exposed to peripubertal stress (Tzanoulinou et al., 2014). Similar suppression is found in

the cortex of human patients with PTSD (Meyerhoff et al., 2014). Stress exposure below not only alters social interaction, but that social interaction can in turn play a role in buffering or moderating the effects of that stressor, providing adaptive value of social networks for coping with stress exposure. We can think about stress-resilience in multiple layers: life-long programming of stress-resilient individuals originating from the early life environment and in particular through maternal interactions (Parker et al., 2012; Lyons et al., 2010 and Szyf et al., 2007); short-term resilience after an acute moderate stressor promoting better functioning after a secondary stressor (Kirby et al., 2013); or resilience that comes from mitigating (buffering) the effects of stress by positive, supportive social environment, or even by aggressive social interactions. For example, lower ranking baboons that show displacement of aggression on peers have lower CORT levels (Virgin and Sapolsky, 1997).