, 1967). The relationship between early life stress exposure and subsequent resilience in both primates and rodents follows click here the abovementioned U-shaped curve. Prolonged maternal separation and social isolation in infant rhesus monkeys produce an increased stress response and “despair-like” behavior in subsequent social separation tests (Young et al., 1973). Rats exposed to moderate early life stress show enhanced measures of resilience compared to both severely and minimally stressed rats (Macri and Wurbel, 2007). For example, early postnatal rats exposed to brief daily handling (a moderate stressor) subsequently show attenuated stress response compared to undisturbed pups and pups

exposed to prolonged daily maternal separation (a more severe stressor) (Plotsky and Meaney, 1993 and Macri et al., 2004). Chronic unpredictable stress (CUS) is a useful model for examining stress vulnerability and resilience in rodents (Ricon et al., 2012 and LaPlant et al., 2009). In CUS paradigms, animals are exposed to varying mild stressors sequentially for a period of 1–7 weeks (Krishnan and Nestler, 2011 and Willner, 1997).

Stressors can include mild foot shock, physical restraint, tail suspension, light/dark cycle disruption, food or water restriction, changes to cage mate, etc., and are changed after several hours to minimize habituation (LaPlant et al., 2009 and Willner, 1997). CUS produces a range of depression and anxiety-like behaviors in rodents including Epacadostat order enough anhedonia, measured as decreased sucrose preference, despair-like behavior, measured as increased immobility in the forced swim and tail suspension tests, and novelty suppressed feeding, measured as a decrease in approach to a

novel food item (Krishnan and Nestler, 2011, Mineur et al., 2006 and Feng et al., 2012). Mice exposed to CUS also display decreased grooming, aggression, and sexual behaviors. Certain CUS-induced behavioral changes, such as novelty suppressed feeding, can be reversed only by chronic antidepressant treatment (Willner, 1997), making CUS relevant to human antidepressant responses. Female mice display immobility in the forced swim test after just 6 days of subchronic unpredictable stress (SCUS) whereas males are generally resilient to SCUS and require 20–28 days of CUS exposure to elicit depression- and anxiety-like behavior (Hodes, G.E. et al., Soc. Neurosci. Abstr. 219.01, 2011). Interestingly, age is a factor in response to CUS—male rats exposed to 60 days of CUS in the juvenile period exhibit greater memory retention in a two-way shuttle avoidance task compared to rats exposed to the same stressor in adulthood, indicating enhanced cognitive resilience ( Ricon et al., 2012). Sex differences and age effects in susceptibility to CUS-induced depression and anxiety-like behavior make this a powerful tool for investigating the hormonal and neural basis for stress vulnerability and resilience across the lifespan.