Abstract
Animals that experience adverse events in early life often have life-long changes to their physiology and behavior. Long-term effects of stress during early life have been studied extensively, but less attention has been given to the consequences of negative experiences solely during the adolescent phase. Adolescence is a particularly sensitive period of life when regulation of the glucocorticoid “stress” hormone response matures and specific regions in the brain undergo considerable change. Aversive experiences during this time might, therefore, be expected to generate long-term consequences for the adult phenotype. Here we investigated the long-term effects of exposure to chronic unpredictable stress during adolescence on adult decision-making, coping response, cognitive bias, and exploratory behavior in rats. Rats exposed to chronic unpredictable stress (e.g., isolation, crowding, cage tilt) were compared to control animals that were maintained in standard, predictable conditions throughout development. Unpredictable stress during adolescence resulted in a suite of long-term behavioral and cognitive changes including a negative cognitive bias [F(1, 12) = 5.000, P < 0.05], altered coping response [T(1, 14) = 2.216, P = 0.04], and accelerated decision-making [T(1, 14) = 3.245, P = 0.01]. Exposure to chronic stress during adolescence also caused a short-term increase in boldness behaviors; in a novel object test 15 days after the last stressor, animals exposed to chronic unpredictable stress had decreased latencies to leave a familiar shelter and approach a novel object [T(1, 14) = 2.240, P = 0.04; T(1, 14) = 2.419, P = 0.03, respectively]. The results showed that stress during adolescence has long-term impacts on behavior and cognition that affect the interpretation of ambiguous stimuli, behavioral response to adverse events, and how animals make decisions.
Highlights
Negative life experiences can have long-term effects on behavior and physiology (Sheriff et al, 2009; Archard et al, 2012)
We addressed the long-term effects of chronic unpredictable stress during adolescence on behavior and cognition by evaluating changes in cognitive bias, decision-making, associative learning rate, coping response, and motivation to consume a reward in adulthood
Our results show that chronic unpredictable stress during adolescence has long-term effects on coping response, cognitive bias, and decision-making
Summary
Negative life experiences can have long-term effects on behavior and physiology (Sheriff et al, 2009; Archard et al, 2012). Rodent pups that experience isolation at different stages of development exhibit contrasting hormonal responses to stress in adulthood; rat pups separated from their mothers for 2 h a day at postnatal days 2–14 develop a hyperresponsive HPA axis, whereas pups isolated at postnatal days 15–16 develop a hypo-functioning HPA axis (Plotsky and Meaney, 1993; Sánchez et al, 1998; reviewed in Sánchez et al, 2001). Glucocorticoid production in response to a stressor exceeds the adult hormone response in duration and intensity (McCormick et al, 2010). In comparison to adult rats, adolescent rats exposed to an acute stressor show a higher increase in both adrencorticotrophin hormone (ACTH) and glucocorticoids (reviewed in Romeo and McEwen, 2007; Foilb et al, 2011). During adolescence various neural structures involved in stress and reward processing are still immature
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