Effects of stress throughout the lifespan on the brain, behaviour and cognition

During stress there is activation of the hypothalamic-pituitary-adrenal (HPA) axis, culminating in the production of glucocorticoids. Glucocorticoids can easily access the brain, where they bind to receptors and influence the brain and behaviour.Different outcomes result from exposure to stress at different periods of an individual's life.Exposure to stress in the prenatal period leads to programming effects, as evidenced by increased reactivity to stress later in life and reduced hippocampal volume in adulthood.Exposure to prenatal stress has been associated with learning impairments, enhanced sensitivity to drugs of abuse, and increases in anxiety and depression-related behaviours in adulthood.Maternal separation is a potent stressor in the postnatal period, and it leads to increased secretion of glucocorticoids that can extend into adulthood. By contrast, exposure to severe abuse during infancy is associated with lower levels of glucocorticoids in both primates and humans.Stress during adolescence has more important effects on the HPA axis than a similar stress exposure during adulthood. Moreover, the effects of stress during adolescence can incubate until adulthood, at which time they will become apparent.The effects of stress exposure on the brain and behaviour in adulthood are similar to those that are observed in childhood and adolescence. However, unlike these latter effects, the former effects are reversible; that is, they usually disappear after cessation of the stressor.In adulthood, chronic exposure to high levels of glucocorticoids has been associated with depressive disorder. By contrast, patients with post-traumatic stress disorder present lower levels of glucocorticoids.The effects of stress during aging are associated with both memory impairments and reduced hippocampal volumes.The life cycle model of stress explains why different disorders emerge in populations exposed to stress at different stages of their lives.