Do early‐life events permanently alter behavioral and hormonal responses to stressors?

Abstract

Early-life stimulation (e.g., brief handling) attenuates the behavioral and neuroendocrine responses to stressors encountered in adulthood, particularly with respect to activation of hypothalamic-pituitary-adrenal (HPA) activity. In contrast, if neonates were subjected to a more severe stressor, such as protracted separation from the dam or exposure to an endotoxin, then the adult response to a stressor was exaggerated. These early-life experiences program HPA functioning, including negative feedback derived from stimulation of hippocampal glucocorticoid receptors, and corticotropin-releasing hormone (CRH) and arginine vasopressin (AVP) coexpression in PVN neurons, to modify the response to subsequent stressor experiences. The persistent variations of HPA activity observed in handled/stimulated animals may stem from alterations in dam-pup interactions (e.g. increased arched-back feeding, licking, grooming). In addition genetic makeup is critical in determining stress reactivity. For instance, BALB/cByJ mice are more reactive to stressors than C57BL/6ByJ mice, exhibiting greater HPA hormonal alterations and behavioral disturbances. BALB/cByJ also fail to acquire a spatial learning response in a Morris water-maze paradigm, which has been shown to be correlated with hippocampal cell loss associated with aging. Early-life handling of BALB/cByJ mice prevented these performance deficits and attenuated the hypersecretion of ACTH and corticosterone elicited by stressors. The stressor reactivity may have been related to maternal and genetic factors. When BALB/cByJ mice were raised by a C57BL/6ByJ dam, the excessive stress-elicited HPA activity was reduced, as were the behavioral impairments. However, cross-fostering the more resilient C57BL/6ByJ mice to a BALB/cByJ dam failed to elicit the behavioral disturbances. It is suggested that genetic factors may influence dam-pup interactive styles and may thus proactively influence the response to subsequent stressors among vulnerable animals. In contrast, in relatively hardy animals the early-life manipulations may have less obvious effects.

The impact of early postnatal environmental enrichment on maternal care and offspring behaviour following weaning

“…Environmental enrichment during the perinatal period has been shown to have either positive or detrimental developmental or behavioural effects (Mychasiuk et al 2012;Zhu et al 2006;Mann and Gervais 2011;Anisman et al 1998) and various variables could account for discrepancies between enrichment studies. For example, variability in maternal behaviour could depend on rat strain, in particular as rat strains differ in anxiety-related behaviour (Rosenfeld and Weller 2012;Rex et al 1996).…”

“…Therefore it is not surprising that sensory deprivation during this period has detrimental and long-lasting, if not permanent, effects on the nervous system and a variety of behaviours. Stressful experiences during the early postnatal period can programme an anxious phenotype (Anisman et al 1998). It has been suggested that exposure to adverse environmental factors during the maturation of brain anxiety circuits contributes to the pathogenesis of anxiety disorders (Leonardo and Hen 2008).…”

“…There is evidence that early human handling, but also environmental enrichment, reduce anxiety in rats Levine 1957;Levine et al 1967;Meaney et al 1996;Anisman et al 1998;Fernandez-Teruel et al 2002). Recent reviews of this research have discussed the choice of the appropriate control in some of those studies.…”

Developmental and geographic variation in stress hormones in wild Belding's ground squirrels (Spermophilus beldingi)

“…In laboratory rodents, differences among strains have been observed in basal glucocorticoid levels as well as in stress-induced responses (e.g. Sakaguchi et al, 1984;Anisman et al, 1998). Birds commonly show population differences in response to stressors (e.g.…”

Behavioural and Hormonal Stress Responses to Social Separation in Ravens, Corvus corax

“…1991), but can also be influenced by experiences during ontogeny (Anisman et al. 1998) and the presence of social support (de Waal & van Roosmalen 1979; Heinrichs et al. 2003; Kanitz et al.…”