What can We Know from Pituitary–Adrenal Hormones About the Nature and Consequences of Exposure to Emotional Stressors?

Abstract

Exposure to stress induces profound physiological and behavioral changes in the organisms and some of these changes may be important regarding stress-induced pathologies and animal models of psychiatric diseases. Consequences of stress are dependent on the duration of exposure to stressors (acute, chronic), but also of certain characteristics such as intensity, controllability, and predictability. If some biological variables were able to reflect these characteristics, they could be used to predict negative consequences of stress. Among the myriad of physiological changes caused by stress, only a restricted number of variables appears to reflect the intensity of the situation, mainly plasma levels of ACTH and adrenaline. Peripheral hypothalamic-pituitary-adrenal (HPA) hormones (ACTH and corticosterone) are also able to reflect fear conditioning. In contrast, the activation of the HPA axis is not consistently related to anxiety as evaluated by classical tests such as the elevated plus-maze. Similarly, there is no consistent evidence about the sensitivity of the HPA axis to psychological variables such as controllability and predictability, despite the fact that: (a) lack of control over aversive stimuli can induce behavioral alterations not seen in animals which exert control, and (b) animals showed clear preference for predictable versus unpredictable stressful situations. New studies are needed to re-evaluate the relationship between the HPA axis and psychological stress characteristics using ACTH instead of corticosterone and taking advantages of our current knowledge about the regulation of this important stress system.

Sex differences in the behavioural and hypothalamic–pituitary–adrenal response to contextual fear conditioning in rats

“…However, the magnitude of the effect is dependent on the severity and length of exposure to the stressors (see Armario et al, 2008 for a review). Results from our lab show that after an acute exposure to IMO a long-term endocrine and/or behavioural sensitization to novel environments can develop, but both phenomena appear to be dissociated (Belda et al, 2008(Belda et al, , 2012Gagliano et al, 2008;Muñoz-Abellán et al, 2008).…”

What is environmental stress? Insights from fish living in a variable environment

“…They include biotic factors such as food availability, the presence of predators, infection with pathogenic organisms or interactions with conspecifics, as well as abiotic factors such as temperature, water availability and toxicants. In addition, psychological and emotional stressors, which involve perceived threats, are extremely important in humans and other mammals (Armario et al, 2012;Campbell and Ehlert, 2012), and they are likely important in other animals as well (Galhardo and Oliveira, 2009). Organisms respond to stressors by mounting a stress response that involves a complex set of behavioural and physiological changes at multiple levels of biological organization.…”

“…The focus of the field of stress biology on these hormonal mechanisms has been such that glucocorticoid release is often treated as the key indicator of the occurrence of stress in vertebrates (Armario et al, 2012;Campbell and Ehlert, 2012), and the term 'stress response' is often treated as synonymous with the glucocorticoid-mediated stress response. While this greatly simplifies the detection of stress, because these hormones are easily quantified, it is not clear that this definition of stress is sufficiently broad as to encompass all situations.…”

Dynamic Status Signal Reflects Outcome of Social Interactions, but Not Energetic Stress

“…For example, many studies have shown that social defeat, in which an individual loses a competitive contest with a rival, induces a wide variety of both transient and persistent detrimental and compensatory physiological changes consistent with stress-responses in a variety of vertebrates (see Buwalda et al, 2005;Hostetler and Ryabinin, 2013 for general reviews), including birds (e.g., Zuk and Johnsen, 2000;Carere et al, 2001Carere et al, , 2003Gleeson, 2006;Hawley, 2006;Hawley et al, 2006). Different sources and kinds of stressors can yield dramatically different physiological responses, involving a variety of pathways, neurotransmitters, and target tissues (Buchanan, 2000;Armario et al, 2012;Hostetler and Ryabinin, 2013). Therefore, it is possible that stress-responses resulting from social interactions may manifest differently than stress-responses derived from other sources, in which case certain dynamic signals could be influenced more by social experience than by other physiological perturbations.…”