Indeed, a large number of primate and rodent models have been created to directly manipulate early-life experience, in order to generate resilience or vulnerability (see Maras and Baram, 2012 and Huang, 2014 for recent reviews). Broadly categorized, these paradigms aim to model early-life adversity such as chronic stress (Schmidt et al., 2011 and Molet et al., 2014), or to create a nurturing early-life

environment, typically based on optimized maternal care or novelty (see Akers et al., 2008, Champagne Doxorubicin supplier et al., 2008, Korosi and Baram, 2009, Baram et al., 2012 and Tang et al., 2014). Indeed, rodents raised in these distinct environments generally develop vulnerability (Huot et al., 2002, Romeo et al., 2004, Brunson et al., 2005, Champagne et al., 2008 and van Hasselt et al., 2012) or resilience (Liu et al., 1997, Fenoglio et al., 2005 and van Hasselt et al., 2012) to future stress and to cognitive and/or emotional deficits. Although the influence of early-life experience on life-time resilience and vulnerability are well established, the underlying mechanisms are not fully XAV-939 manufacturer understood. It is now generally agreed that enduring changes in the expression of important genes might be involved, and that these changes might persist via epigenetic mechanisms including histone and DNA modifications (Meaney and Szyf, 2005, Borrelli

et al., 2008, Roth et al., 2009, McClelland et al., 2011, Sun et al., 2013 and Morrison et al., 2014). However, fundamental and crucial questions remain unanswered. For examples, what is the essence of the experience or environmental-signal that is perceived by the developing brain? How does the signal reach important neurons that change in response to the early-life experience? What

are these neurons that are re-programmed to enable the structural and functional plasticity that underlies resilience? How do these neurons know to modulate their epigenetic machinery? We attempt to address these questions here. As mentioned above, direct manipulation of maternal care patterns has yielded long-lasting resilience or vulnerability to cognitive and emotional deficits. We briefly describe the frameworks for bi-directional not manipulation of maternal signals to young rodents that have been employed by our group, because the robust outcomes enable examination of the underlying mechanisms. The handling paradigm (Levine, 1957, Plotsky and Meaney, 1993 and Avishai-Eliner et al., 2001a), which involves brief (15 min) daily separation of rat pups from the mother during the first weeks of life, was used as a model of enhanced maternal care. These brief separations promoted increased maternal-derived sensory input upon reunion with their mothers (Fig. 1) (Liu et al., 1997 and Fenoglio et al., 2006).