Stress & sleep: A relationship lasting a lifetime.

Stress is an adaptative response aimed at restoring body homeostasis. The classical neuroendocrine stress response involving the activation of the hypothalamic-pituitary-adrenal (HPA) axis modulates many physiological aspects, such as the wake-sleep cycle. In the present review, we will first report a series of human and rodent studies showing that each actor of the HPA axis has the potential to interfere with sleep homeostasis and, then, we will highlight how acute or chronic stress differently modulates the wake-sleep cycle. Moreover, we will present new and interesting studies dealing with the relationship between sleep and stress on a different (longer) time scale. Particularly, we will discuss how the exposure to perinatal stress, probably through epigenetic modulations, is sufficient to cause persistent sleep derangements during adult life. In light of this evidence, the main message of the present review is that the complex relationship between sleep and stress changes dramatically on the basis of the time scale considered and, consequently, "time" should be considered as a critical factor when facing this topic.