Meta-analysis reveals glucocorticoid levels reflect variation in metabolic rate, not 'stress'

Getting used to it? Stress of repeated management procedures in semi-domesticated reindeer

BACKGROUND

Extensive animal production systems, such as reindeer husbandry may represent a system to further study the context dependence of stress responses and the potential implications for animal welfare as research on food animal stress and welfare has so far primarily focused on animals in intensive animal production systems while animals from extensive production systems, such as reindeer, are yet underrepresented. We investigated short- and longer-term stress responses to repeated herding, handling and restraint and its potential effect on animal welfare in semi-domesticated adult female reindeer (Rangifer tarandus tarandus). We also assessed seasonal differences and the potential effect of the additional stressor of calf removal using serum concentrations of glucocorticoids (cortisol, cortisone and corticosterone), their precursors (11-desoxcortisol, 17-α-hydroxyprogesterone and deoxycorticosterone) and catecholamine metabolites (metanephrine and normetanephrine) in combination with the immunological stress proxy leukocyte coping capacity (LCC) and rectal temperature. Additionally, we assessed the interconnections among different stress indices and their suitability as stress indicators to evaluate handling-induced stress in reindeer, where rectal temperature, other than serum cortisol levels, emerged as a robust and integrative stress parameter.

RESULTS

Herding, handling, and restraint elicited a marked and seasonally different short-term stress response with higher stress mediator levels in winter. Further, females who had their calf removed shortly after parturition showed increased stress levels based on LCC. The repeated exposure to the same stressors led to a habituation, with decreasing levels of stress indices to the procedure in both seasons. This outcome implies that reindeer females in the present study were able to cope well with repeated manipulations and that this intensification may not compromise animal welfare. Notably, the traditional stress index body temperature correlated with various stress indices encompassing the HPA axis response (cortisol and corticosterone in summer and additionally cortisone and 11-deoxycortisol in winter), the sympathetic-adrenal-medullary system (metanephrine) as well as the immunological response to stress (LCC), in both seasons.

CONCLUSION

Our results emphasise body (rectal) temperature as a robust and integrative stress parameter in the context of our study. Our findings add to a foundation for evaluating available stress indices in different individual and environmental contexts and may contribute to improved animal management practices aimed at reducing stress levels and enhancing animal welfare.

Corticotropin-releasing hormone receptor 1 mediates the enhanced locomotor activity and metabolic demands to an acute thermal stress in adult zebrafish

We recently showed that Crh-Crhr1 signalling is essential for acute stress-related locomotor activity in zebrafish larvae. However, the possibility that Crhr1 activation may also initiate the acute metabolic demands for stress coping was unexplored. Here, we tested the hypothesis that Crhr1 signalling is essential for the thermal stressor-induced increases in the acute metabolic rate, a key response for coping with the enhanced energy demands during stress. We tested this by using a wildtype (WT) and a ubiquitous Crhr1 knockout (crhr1-/-) zebrafish and subjecting them to an acute thermal stressor (TS: +5°C above ambient for 60 min). The TS induced the heat shock proteins response in both genotypes, but the elevated cortisol response observed in the WT was absent in the crhr1-/- mutant. The TS also increased the locomotor activity and the metabolic rate in the WT fish, but this response was inhibited in the crhr1-/- mutants. To test if this was due to a lack of TS-induced cortisol elevation in the crhr1-/- mutant, we mimicked the response in the WT fish by treating them with metyrapone, an 11β-hydroxylase inhibitor. While metyrapone inhibited the TS-induced cortisol elevation in the WT, it did not affect the metabolic rate. The lack of Crhr1 also reduced the swimming performance, and the lower Ucrit in the mutants corresponded with alterations in muscle energy metabolism. Together, our results indicate that Crh-Crhr1 signalling, independent of downstream cortisol action, is essential for the TS-induced acute hyperlocomotor activity and the associated increases in the metabolic demand for stress coping.

Does seasonal variation in the corticosterone response affect the nutritional ecology of a free-ranging lizard?

Challenging events in the environment that are both predictable (e.g. seasonal patterns in breeding activities) and unpredictable (e.g. predator encounter) are known to induce a glucocorticoid response that facilitates metabolic requirements during the challenge. Given its role in mobilizing energy, glucocorticoid levels can influence the nutritional ecology of an individual by shifting dietary intake or retention patterns, but this relationship has not been tested in free-ranging vertebrates. Using a tropical lizard species (Psammophilus dorsalis) as a model system, we tested whether the elemental composition of dietary intake and excretion (faecal samples) varies with stress-induced corticosterone levels in males and females across different seasons. From free-ranging lizards in the wild, we measured levels of stress-induced corticosterone and glucose in blood and determined diet composition from gut-flushing. Elemental composition of the diet was determined by analysing the carbon and nitrogen content of identified prey Orders caught from the wild. We also collected faecal samples and estimated their elemental composition. We found that stress-induced corticosterone levels varied across seasons, with the lowest levels during the breeding season for both males and females. Despite high variation in corticosterone responsiveness, lizards did not shift the elemental composition of their diets and maintained an intake carbon:nitrogen ratio of 4.56. We did, however, find a negative correlation between stress-induced corticosterone levels and faecal elemental composition, suggesting selective retention of both carbon and nitrogen in individuals that have higher corticosterone responsiveness. This study highlights the interplay between corticosterone responsiveness and nutritional ecology, challenging the existing links in literature and illustrating how free-ranging animals, such as lizards, adjust the elemental composition of excretion and not dietary intakes as a potential strategy to modulate natural physiological and ecological challenges.

Unconscious will as a neurobehavioral mechanism against adversity

Incentive salience theory both explains the directional component of motivation (in terms of cue attraction or "wanting") and its energetic component, as a function of the strength of cue attraction. This theory characterizes cue- and reward-triggered approach behavior. But it does not tell us how behavior can show enhanced vigor under reward uncertainty, when cues are inconsistent or resources hidden. Reinforcement theory is also ineffective in explaining enhanced vigor in case reward expectation is low or nil. This paper provides a neurobehavioral interpretation of effort in situations of adversity (which always include some uncertainty about outcomes) that is complementary to the attribution of incentive salience to environmental cues. It is argued that manageable environmental challenges activate an unconscious process of self-determination to achieve "wanted" actions. This unconscious process is referred to as incentive effort, which involves the hypothalamo-pituitary-adrenal (HPA) axis, noradrenaline, as well as striatal dopamine. Concretely, HPA-induced dopamine release would have the function to make effort-or effortful actions-"wanted" in a challenging context, in which the environmental cues are poorly predictive of reward-i.e., unattractive. Stress would only emerge in the presence of unmanageable challenges. It is hypothesized that incentive effort is the core psychological basis of will-and is, for this reason, termed "willing."

Ionizing radiation has negligible effects on the age, telomere length and corticosterone levels of Chornobyl tree frogs

The accident that occurred at the Chornobyl nuclear power plant (Ukraine, 1986) contaminated a large extension of territory after the deposition of radioactive material. It is still under debate whether the chronic exposure to the radiation levels currently present in the area has long-term effects on organisms, such as decreases in longevity. Here, we investigate whether current levels of radiation in Chornobyl negatively impact the age of the Eastern tree frog Hyla orientalis. We also explore whether radiation induces changes in an ageing marker, telomere length or the stress hormone corticosterone. We found no effect of total individual absorbed radiation (including both external and internal exposure) on frog age (n = 197 individuals sampled in 3 consecutive years). We also did not find any relationship between individual absorbed radiation and telomere length, nor between individual absorbed radiation and corticosterone levels. Our results suggest that radiation levels currently experienced by Chornobyl tree frogs may not be high enough to cause severe chronic damage to semi-aquatic vertebrates such as this species. This is the first study addressing age and stress hormones in Chornobyl wildlife, and thus future research will confirm if these results can be extended to other taxa.

Longitudinal analysis of cortisol changes during pubertal development in indigenous Qom girls

Pubertal research has primarily focused on hypothalamic-pituitary-gonadal axis (HPG) regulation of puberty, though the hypothalamic-pituitary-adrenal axis (HPA) is increasingly considered critical. Heightened HPA function proxied by increasing cortisol levels may play a role in accelerated pubertal timing. However, the extent to which cortisol varies across ages and its relation to pubertal changes in linear growth are less well substantiated. We explored relationships between age, linear growth, adiposity, C-peptide (proxy for insulin), and cortisol across puberty, and we tested whether higher cortisol levels are associated with earlier ages at menarche and peak height velocity. We utilize longitudinal data (n = 777 urine samples) from Qom females ages 7-14 (n = 46) and test our pre-registered analysis using Bayesian longitudinal mixed effects models and joint modeling techniques. We find limited evidence supporting the overarching hypothesis that HPA upregulation is associated with pubertal maturation or timing. We find some evidence that HPA upregulation, as proxied by cortisol, may be more clearly related to differences in relative linear growth at early-mid puberty, as measured by height-for-age z-scores. Transdisciplinary perspectives on puberty, including the assumption that stressors acting via cortisol accelerate pubertal development, are discussed.

The brain-body energy conservation model of aging

Aging involves seemingly paradoxical changes in energy metabolism. Molecular damage accumulation increases cellular energy expenditure, yet whole-body energy expenditure remains stable or decreases with age. We resolve this apparent contradiction by positioning the brain as the mediator and broker in the organismal energy economy. As somatic tissues accumulate damage over time, costly intracellular stress responses are activated, causing aging or senescent cells to secrete cytokines that convey increased cellular energy demand (hypermetabolism) to the brain. To conserve energy in the face of a shrinking energy budget, the brain deploys energy conservation responses, which suppress low-priority processes, producing fatigue, physical inactivity, blunted sensory capacities, immune alterations and endocrine 'deficits'. We term this cascade the brain-body energy conservation (BEC) model of aging. The BEC outlines (1) the energetic cost of cellular aging, (2) how brain perception of senescence-associated hypermetabolism may drive the phenotypic manifestations of aging and (3) energetic principles underlying the modifiability of aging trajectories by stressors and geroscience interventions.

Corticosterone after early adolescent stress prevents social avoidance, aversive behavior, and morphine-conditioned place preference in adulthood

RATIONALE

Stress during childhood or adolescence increases vulnerability to psychiatric disorders in adults. In adult rodents, the delayed effects of stress can increase anxiety-like behavior. These effects, however, can be prevented with post-stress administration of corticosterone (CORT). The effectiveness of CORT in preventing adolescent stress-induced emotional behavior alterations in adulthood has yet to be investigated.

OBJECTIVES

Here, we investigated the interactions between early adolescent stress and exogenous corticosterone on adult social, aversive, and drug-seeking behavior in mice, which are translationally related to symptoms associated with psychiatric and substance abuse disorders.

METHODS AND RESULTS

A single administration of CORT in drinking water (400ug/mL) for 24 h after social defeat or context fear conditioning prevents defeat-induced social avoidance, alters fear processing, prevents adolescent stress-induced anhedonia, and prevents stress-potentiated morphine place preference in adulthood. Exogenous CORT did not immediately prevent stress-induced potentiation of morphine conditioned-place preference in adolescents but did so in adult mice. However, when administered to adolescent mice, CORT also prevented the incubation of morphine-conditioned place preference into adulthood. Lastly, exogenous CORT administration blunted endogenous corticosterone but was unrelated to freezing behavior during a fear test.

CONCLUSIONS

This is the first demonstration of adolescent post-stress CORT promoting socio-emotional resilience and preventing drug-seeking behavior. Our data suggest elevated corticosterone after a stress experience promotes resilience for at least 40 days across the developmental transition from adolescence to adulthood and is effective for socio-emotional and drug-seeking behavior. These results are critical for understanding how adolescent stress impacts emotional and drug-seeking behavior into adulthood.

Corticosterone release in very young siblicidal seabird chicks (Rissa tridactyla) is sensitive to environmental variability and responds rapidly and robustly to external challenges

In birds, patterns of development of the adrenocortical response to stressors vary among individuals, types of stressors, and species. Since there are benefits and costs of exposure to elevated glucocorticoids, this variation is presumably a product of selection such that animals modulate glucocorticoid secretion in contexts where doing so increases their fitness. In this study, we evaluated hypothalamo-pituitary-adrenal (HPA) activity in first-hatched free-living seabird nestlings that engage in intense sibling competition and facultative siblicide (black-legged kittiwakes, Rissa tridactyla). We sampled 5 day old chicks (of the ∼45 day nestling period), a critical early age when food availability drives establishment of important parent-offspring and intra-brood dynamics. We experimentally supplemented parents with food ("supplemented") and measured chick baseline corticosterone secretion and capacity to rapidly increase corticosterone in response to an acute challenge (handling and 15 min of restraint in a bag). We also used topical administration of corticosterone to evaluate the ability of chicks to downregulate physiologically relevant corticosterone levels on a short time scale (minutes). We found that 5 day old chicks are not hypo-responsive but release corticosterone in proportion to the magnitude of the challenge, showing differences in baseline between parental feeding treatments (supplemented vs non-supplemented), moderate increases in response to handling, and a larger response to restraint (comparable to adults) that also differed between chicks from supplemented and control nests. Topical application of exogenous corticosterone increased circulating levels nearly to restraint-induced levels and induced downregulation of HPA responsiveness to the acute challenge of handling. Parental supplemental feeding did not affect absorbance/clearance or negative feedback. Thus, while endogenous secretion of corticosterone in young chicks is sensitive to environmental context, other aspects of the HPA function, such as rapid negative feedback and/or the ability to clear acute elevations in corticosterone, are not. We conclude that 5 day old kittiwake chicks are capable of robust adrenocortical responses to novel challenges, and are sensitive to parental food availability, which may be transduced behaviorally, nutritionally, or via maternal effects. Questions remain about the function of such rapid, large acute stress-induced increases in corticosterone in very young chicks.

Physiological responses to a changing winter climate in an early spring-breeding amphibian

Climate change is swiftly altering environmental winter conditions, leading to significant ecological impacts such as phenological shifts in many species. As a result, animals might face physiological mismatches due to longer or earlier activity periods and are at risk of being exposed to late spring freezes. Our study points for the first time to the complex physiological challenges that amphibians face as a result of changing thermal conditions due to winter climate change. We investigated the physiological responses to a period of warmer winter days and sudden spring freeze in the common toad (Bufo bufo) by acclimating them to 4°C or 8°C for 48 h or exposing them to 4°C or -2°C for 6 h, respectively. We assessed the daily energy demands, determined body condition and cold tolerance, explored the molecular responses to freezing through hepatic tissue transcriptome analysis, and measured blood glucose levels. Toads acclimated to higher temperatures showed a higher daily energy expenditure and a reduced cold tolerance suggesting faster depletion of energy stores and the loss of winter acclimation during warmer winters. Blood sugar levels were higher in frozen toads indicating the mobilization of cryoprotective glucose with freezing which was further supported by changed patterns in proteins related to glucose metabolism. Overall, our results emphasize that increased thermal variability incurs physiological costs that may reduce energy reserves and thus affect amphibian health and survival. This might pose a serious threat to breeding adults and may have subsequent effects at the population level.

Excess glucocorticoids inhibit murine bone turnover via modulating the immunometabolism of the skeletal microenvironment

Elevated bone resorption and diminished bone formation have been recognized as the primary features of glucocorticoid-associated skeletal disorders. However, the direct effects of excess glucocorticoids on bone turnover remain unclear. Here, we explored the outcomes of exogenous glucocorticoid treatment on bone loss and delayed fracture healing in mice and found that reduced bone turnover was a dominant feature, resulting in a net loss of bone mass. The primary effect of glucocorticoids on osteogenic differentiation was not inhibitory; instead, they cooperated with macrophages to facilitate osteogenesis. Impaired local nutrient status - notably, obstructed fatty acid transportation - was a key factor contributing to glucocorticoid-induced impairment of bone turnover in vivo. Furthermore, fatty acid oxidation in macrophages fueled the ability of glucocorticoid-liganded receptors to enter the nucleus and then promoted the expression of BMP2, a key cytokine that facilitates osteogenesis. Metabolic reprogramming by localized fatty acid delivery partly rescued glucocorticoid-induced pathology by restoring a healthier immune-metabolic milieu. These data provide insights into the multifactorial metabolic mechanisms by which glucocorticoids generate skeletal disorders, thus suggesting possible therapeutic avenues.

Effects of cooling on thyroid hormone secretion and growth of eastern bluebird (Sialia sialis) nestlings

Achieving endothermic homeothermy is a critical aspect of avian development. In pre-homeothermic altricial nestlings, variation in parental brooding behavior results in variable exposure of nestlings to cooling, with consequences for the developing endocrine system. Nestlings facing repeated cooling challenges may benefit from upregulation of thyroid hormone secretion, allowing for earlier onset of thermoregulatory capability to mitigate the potentially negative effects of exposure to non-optimal temperatures during development. We examined the effects of (1) a single cooling challenge on thyroid hormone secretion in pre-homeothermic nestlings, and (2) repeated cooling challenges prior to the onset of homeothermy on nestling growth and thyroid hormone secretion prior to fledging. We found that pre-homeothermic eastern bluebird nestlings exposed to a single cooling challenge increased circulating triiodothyronine (T3), demonstrating that the thyroid system can be activated by cooling early in life. However, we found no consequences of repeated cooling during the first week of life on nestling growth or baseline T3 levels prior to fledging. This work addresses how the nestling hypothalamic-pituitary-thyroid axis responds to acute cooling challenges prior to the development of endothermic homeothermy; future work will confirm whether such responses allow nestlings to hasten the onset of physiological thermoregulation when conditions demand it.