have furthermore demonstrated that environmental enrichment can reverse the effects of postnatal maternal separation on both endocrine and behavioural responses to stress. Environmental enrichment has been used as a procedure that might prevent some of the deleterious effects of stress. In recent years, several experimental animal models have well represented this evidence. On the other hand, experiences, during human infancy, involving dynamic, tender, and stimulating environments, may have positive long lasting effects on the quality of life, can serve as a source of resilience in the face of chronic stress, , and tend to promote resistance to stress and diminish vulnerability to stress-induced illness. These findings are in line with evidence that shows that adverse experiences early in life can have implications in the development and the clinical course of human intestinal disorders, including inflammatory bowel disease (IBD) and intestinal bowel syndrome (IBS) –, where inflammatory and stress stimuli play primary roles. In fact, adult rats separated early postnatally from their mothers have been found to be predisposed to colonic barrier dysfunction, and to have an enhanced mucosal response to stress. Interestingly, the pathophysiological modifications observed in adult rats affect not only the behaviour and the neuroendocrine system, but also the homeostasis of the gastrointestinal tract. In particular, the stress evoked by altering mother–infant interactions during lactation causes the offspring, once adult, to develop a phenotype more susceptible to stress events and characterized by hyperactivation of the Hypothalamus – Pituitary – Adrenal (HPA) axis. “Neonatal maternal deprivation” is one of the best known experimental animal models that well reproduces in rodents the consequence of traumatic experiences occurring in humans in early life. In particular, concerning the latter point, during postnatal life, a critical period for neuroendocrinological and behavioural development processes, different emotional events (negative/trauma or positive/maternal care) may influence, in opposite ways, vulnerability to the effects of stress later in life, possibly by inducing a persistent sensitization in stress-responsive neural circuits –. A number of factors contribute to the qualitative nature of these responses such as: the intensity (high or low) and duration (acute or chronic) of stressors, the individual's ability to initiate an adaptive response, and the phase of the life when the stressor event occurs. Early life experiences profoundly influence the later development, the structure and function of an organism.This phenomenon, called “developmental programming,” is a process whereby an environmental factor acting during a sensitive or vulnerable developmental period exerts effects that, in some cases, will persist throughout life.Īdaptive or maladaptive responses to environmental stressors reflect an animal's capacity to re-establish temporarily disrupted physiological homeostasis.
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