The secretion of glucocorticoids (GCs) is a classic endocrine response to stress. Despite that, it remains controversial as to what purpose GCs serve at such times. One view, stretching back to the time of Hans Selye, posits that GCs help mediate the ongoing or pending stress response, either via basal levels of GCs permitting other facets of the stress response to emerge efficaciously, and/or by stress levels of GCs actively stimulating the stress response. In contrast, a revisionist viewpoint posits that GCs suppress the stress response, preventing it from being pathologically overactivated. In this review, we consider recent findings regarding GC action and, based on them, generate criteria for determining whether a particular GC action permits, stimulates, or suppresses an ongoing stressresponse or, as an additional category, is preparative for a subsequent stressor. We apply these GC actions to the realms of cardiovascular function, fluid volume and hemorrhage, immunity and inflammation, metabolism, neurobiology, and reproductive physiology. We find that GC actions fall into markedly different categories, depending on the physiological endpoint in question, with evidence for mediating effects in some cases, and suppressive or preparative in others. We then attempt to assimilate these heterogeneous GC actions into a physiological whole. (Endocrine Reviews 21: 55‐ 89, 2000)

/pdf/how-do-glucocorticoids-influence-stress-responses-4egr3fa2k0.pdf

How do glucocorticoids influence stress responses? Integrating permissive, suppressive, stimulatory, and preparative actions.

Prospective Cohort Study

This meta-analysis reviews 208 laboratory studies of acute psychological stressors and tests a theoretical model delineating conditions capable of eliciting cortisol responses. Psychological stressors increased cortisol levels; however, effects varied widely across tasks. Consistent with the theoretical model, motivated performance tasks elicited cortisol responses if they were uncontrollable or characterized by social-evaluative threat (task performance could be negatively judged by others), when methodological factors and other stressor characteristics were controlled for. Tasks containing both uncontrollable and social-evaluative elements were associated with the largest cortisol and adrenocorticotropin hormone changes and the longest times to recovery. These findings are consistent with the animal literature on the physiological effects of uncontrollable social threat and contradict the belief that cortisol is responsive to all types of stressors.

http://anthro.vancouver.wsu.edu/media/Course_files/anth-260-edward-h-hagen/acute-stressors-and-cortisol-responses-a-theoretical-integration-and-synthesis-of-laboratory-research-1.pdf

Acute stressors and cortisol responses: a theoretical integration and synthesis of laboratory research.

In response to stress, the brain activates several neuropeptide-secreting systems. This eventually leads to the release of adrenal corticosteroid hormones, which subsequently feed back on the brain and bind to two types of nuclear receptor that act as transcriptional regulators. By targeting many genes, corticosteroids function in a binary fashion, and serve as a master switch in the control of neuronal and network responses that underlie behavioural adaptation. In genetically predisposed individuals, an imbalance in this binary control mechanism can introduce a bias towards stress-related brain disease after adverse experiences. New candidate susceptibility genes that serve as markers for the prediction of vulnerable phenotypes are now being identified.

Stress and the brain: from adaptation to disease

In its simplest definition, a trait is a surrogate of organismal performance, and this meaning of the term has been used by evolutionists for a long time. Over the last three decades, developments in community and ecosystem ecology have forced the concept of trait beyond these original boundaries, and trait-based approaches are now widely used in studies ranging from the level of organisms to that of ecosystems. Despite some attempts to fix the terminology, especially in plant ecology, there is currently a high degree of confusion in the use, not only of the term "trait" itself, but also in the underlying concepts it refers to. We therefore give an unambiguous definition of plant trait, with a particular emphasis on functional trait. A hierarchical perspective is proposed, extending the "performance paradigm" to plant ecology. "Functional traits" are defined as morpho-physiophenological traits which impact fitness indirectly via their effects on growth, reproduction and survival, the three components of individual performance. We finally present an integrative framework explaining how changes in trait values due to environmental variations are translated into organismal performance, and how these changes may influence processes at higher organizational levels. We argue that this can be achieved by developing "integration functions" which can be grouped into functional response (community level) and effect (ecosystem level) algorithms.

/pdf/let-the-concept-of-trait-be-functional-2ppbgwsn3s.pdf

Let the concept of trait be functional

Increasingly, levels of the ‘stress hormones’ cortisol and corticosterone are being used by ecologists as indicators of physiological stress in wild vertebrates. The amplitude of hormonal response is assumed to correlate with the overall health of an animal and, by extension, the health of the population. However, much of what is known about the physiology of stress has been elucidated by the biomedical research community. I summarize five physiological mechanisms that regulate hormone release during stress that should be useful to ecologists and conservationists. Incorporating these physiological mechanisms into the design and interpretation of ecological studies will make these increasingly popular studies of stress in ecological settings more rigorous. Vertebrates cope with unpredictable and noxious stimuli (STRESSORS; see Glossary) by mounting a STRESS RESPONSE

https://www.cell.com/trends/ecology-evolution/pdf/S0169-5347(04)00063-1.pdf

Physiological stress in ecology: lessons from biomedical research

Seasonal changes in plasma glucocorticoid concentrations in free-living vertebrates.

Evaluating corticosterone (CORT) responses to stress in free-living vertebrates requires knowing the unstressed titers prior to capture. Based upon laboratory data, the assumption has been that samples collected in less than 3 min of capture will reflect these unstressed concentrations. This assumption was tested for six species using samples collected from 945 individuals at 0-6 min after capture. Samples were from five avian species trapped at multiple times of year and one reptilian species, comprising a total of 14 different data sets for comparisons. For seven of 14 data sets, including five species, there was no significant increase in corticosterone titers within 3 min of capture. In six of the 14 data sets, corticosterone titers increased significantly after 2 min, and in one data set, the increase started at 1.5 min. In all seven of the cases showing an increase before 3 min, however, corticosterone titers from the time of increase to 3 min were significantly lower than titers after 30 min of restraint stress. These results indicate a high degree of confidence for these species that samples collected in less than 2 min reflect unstressed (baseline) concentrations, and that samples collected from 2-3 min also will likely reflect baseline concentrations but at worst are near baseline.

/pdf/collecting-baseline-corticosterone-samples-in-the-field-is-1o04zyoo7h.pdf

Collecting baseline corticosterone samples in the field: is under 3 min good enough?

https://www.webpages.uidaho.edu/fish511/Readings/Readings%202010/Romero_2009%20%20Allostasis.pdf

L. Michael Romero

Papers

How do glucocorticoids influence stress responses? Integrating permissive, suppressive, stimulatory, and preparative actions.

Physiological stress in ecology: lessons from biomedical research

Seasonal changes in plasma glucocorticoid concentrations in free-living vertebrates.

Collecting baseline corticosterone samples in the field: is under 3 min good enough?

The Reactive Scope Model - a new model integrating homeostasis, allostasis, and stress.