The effect of cognitive reappraisal and early-life maternal care on neuroendocrine stress responses.

Early-life adversity (ELA) is related to profound dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis, reflected in both, blunted or exaggerated cortisol stress responses in adulthood. Emotion regulation strategies such as cognitive reappraisal might contribute to this inconsistent finding. Here, we investigate an interaction of early-life maternal care (MC), where low MC represents a form of ELA, and instructed emotion regulation on cortisol responses to acute stress. Ninety-three healthy young women were assigned to a low (n = 33) or high (n = 60) MC group, based on self-reported early-life MC. In the laboratory, participants received regulation instructions, asking to cognitively reappraise (reappraisal group, n = 45) or to focus on senses (control group, n = 48) during subsequent stress exposure, induced by the Trier Social Stress Test. Salivary cortisol and subjective stress levels were measured repeatedly throughout the experiment. Multilevel model analyses confirmed a MC by emotion regulation interaction effect on cortisol trajectories, while controlling for hormonal status. Individuals with low MC in the control compared with the reappraisal group showed increased cortisol responses; individuals with high MC did not differ. These results highlight the significance of emotion regulation for HPA axis stress regulation following ELA exposure. They provide methodological and health implications, indicating emotion regulation as a promising target of treatment interventions for individuals with a history of ELA.

Gonads under stress: A systematic review and meta-analysis on the effects of acute psychosocial stress on gonadal steroids secretion in humans.

Animal research has shown that the hypothalamus-pituitary-gonadal (HPG) axis is inhibited by (chronic and/or severe) stress, which can lead to impaired fertility and reproductive functioning, presumably caused by the inhibition of gonadal steroid secretion and in interactions with glucocorticoids. However, what has not been clarified is how acute psychosocial stress modulates gonadal steroid secretion in humans. Here we summarize the experimental research on the acute effects of stress on the secretion of gonadal steroids in humans. A systematic literature search revealed 21 studies (with N=881 individuals) measuring testosterone, progesterone or estradiol in response to a standardized acute laboratory stressor in healthy humans. Both our literature review and quantitative meta-analysis suggest that in humans, acute stress stimulates rather than inhibits HPG axis activity, although there is a considerable heterogeneity in the reported methods and results. Increased gonadal steroids in response to acute stress contrasts with many animal studies reporting the opposite pattern, at least regarding severe and/or chronic stressors. We discuss methodological issues and challenges for future research and hope to stimulate experimental studies within this area. A better understanding of these mechanisms is needed, and may have important implications for health and disease, as well as the modulation of various behaviors by acute stressors.

Long-COVID-19 autonomic dysfunction: An integrated view in the framework of inflammaging.

The recently identified syndrome known as Long COVID (LC) is characterized by a constellation of debilitating conditions that impair both physical and cognitive functions, thus reducing the quality of life and increasing the risk of developing the most common age-related diseases. These conditions are linked to the presence of symptoms of autonomic dysfunction, in association with low cortisol levels, suggestive of reduced hypothalamic-pituitary-adrenal (HPA) axis activity, and with increased pro-inflammatory condition. Alterations of dopamine and serotonin neurotransmitter levels were also recently observed in LC. Interestingly, at least some of the proposed mechanisms of LC development overlap with mechanisms of Autonomic Nervous System (ANS) imbalance, previously detailed in the framework of the aging process. ANS imbalance is characterized by a proinflammatory sympathetic overdrive, and a concomitant decreased anti-inflammatory vagal parasympathetic activity, associated with reduced anti-inflammatory effects of the HPA axis and cholinergic anti-inflammatory pathway (CAP). These neuro-immune-endocrine system imbalanced activities fuel the vicious circle of chronic inflammation, i.e. inflammaging. Here, we refine our original hypothesis that ANS dysfunction fuels inflammaging and propose that biomarkers of ANS imbalance could also be considered biomarkers of inflammaging, recognized as the main risk factor for developing age-related diseases and the sequelae of viral infections, i.e. LC.

Associations of diurnal cortisol parameters with cortisol stress reactivity and recovery: A systematic review and meta-analysis.

Researchers commonly assess the functioning of the hypothalamic-pituitary-adrenal (HPA) axis by measuring natural fluctuations of its end product cortisol throughout the day or in response to a standardized stressor. Although it is conceivable that an individual releasing relatively more cortisol when confronted with a laboratory stressor does the same in everyday life, inconsistencies remain in the literature regarding associations between diurnal cortisol parameters and cortisol stress responses. Hence, the current meta-analysis aggregated findings of 12 studies to examine overall associations of diurnal cortisol parameters (including total output, diurnal slope, and cortisol awakening response [CAR]) with cortisol stress reactivity and recovery in the Trier Social Stress Test (TSST). There were no significant overall associations of total output, slope, or CAR with stress reactivity. Lower total diurnal cortisol output was significantly related to better stress recovery, whereas diurnal slope and CAR were unrelated to stress recovery. Moderation analyses revealed that associations between diurnal cortisol and cortisol stress responses were dependent on the computation method of cortisol parameters, questioning the convergence and validity of commonly employed measures of stress reactivity and recovery. Overall, it seems that we cannot predict characteristics of the diurnal cortisol rhythm from a one-time measure of stress reactivity in a standardized psychosocial laboratory paradigm.

Hypothalamic-pituitary-adrenal axis recovery after intermediate-acting glucocorticoid treatment in client-owned dogs.

BACKGROUND: In dogs, duration of hypothalamic-pituitary-adrenal (HPA) axis suppression after systemic glucocorticoid treatment is reported to vary from a few days to up to 7 weeks after glucocorticoid discontinuation. These data are derived mainly from experimental studies in healthy dogs and not from animals with spontaneous disease. HYPOTHESIS AND OBJECTIVE: To determine the timeline for recovery of the HPA axis in a group of ill dogs treated with intermediate-acting glucocorticoids (IAGCs). ANIMALS: Twenty client-owned dogs that received IAGC for at least 1 week. METHODS: Single-center prospective observational study. An ACTH stimulation test, endogenous ACTH concentration, serum biochemistry profile, and urinalysis were performed at T0 (2-6 days after IAGC discontinuation) and then every 2 weeks (eg, T1, T2, T3) until HPA axis recovery was documented (post-ACTH cortisol concentration > 6 µg/dL). RESULTS: The median time of HPA axis recovery was 3 days (range, 2-133 days). Eleven of 20 dogs showed recovery of the HPA axis at T0, 6/20 at T1, and 1 dog each at T2, T5, and T9. Dose and duration of treatment were not correlated with timing of HPA axis recovery. Activities of ALT and ALP were significantly correlated with the post-ACTH cortisol concentration (rs = -0.34, P = .03; rs = -0.31, P = .05). Endogenous ACTH concentration was significantly correlated with pre (r = 0.72; P < .0001) and post-ACTH cortisol concentrations (r = 0.35; P = .02). The timing of HPA axis recovery of the dogs undergoing an alternate-day tapering dose was not different compared to dogs that did not (3.5 vs 3 days, P = .89). CONCLUSION AND CLINICAL IMPORTANCE: Most dogs experienced HPA axis recovery within a few days after IAGC discontinuation. However, 2/20 dogs required >8 weeks.

HPA flexibility and FKBP5: promising physiological targets for conservation.

Hypothalamic-pituitary-adrenal axis (HPA) flexibility is an emerging concept recognizing that individuals that will cope best with stressors will probably be those using their hormones in the most adaptive way. The HPA flexibility concept considers glucocorticoids as molecules that convey information about the environment from the brain to the body so that the organismal phenotype comes to complement prevailing conditions. In this context, FKBP5 protein appears to set the extent to which circulating glucocorticoid concentrations can vary within and across stressors. Thus, FKBP5 expression, and the HPA flexibility it causes, seem to represent an individual's ability to regulate its hormones to orchestrate organismal responses to stressors. As FKBP5 expression can also be easily measured in blood, it could be a worthy target of conservation-oriented research attention. We first review the known and likely roles of HPA flexibility and FKBP5 in wildlife. We then describe putative genetic, environmental and epigenetic causes of variation in HPA flexibility and FKBP5 expression among and within individuals. Finally, we hypothesize how HPA flexibility and FKBP5 expression should affect organismal fitness and hence population viability in response to human-induced rapid environmental changes, particularly urbanization. This article is part of the theme issue 'Endocrine responses to environmental variation: conceptual approaches and recent developments'.

Validity of mental and physical stress models.

Different stress models are employed to enhance our understanding of the underlying mechanisms and explore potential interventions. However, the utility of these models remains a critical concern, as their validities may be limited by the complexity of stress processes. Literature review revealed that both mental and physical stress models possess reasonable construct and criterion validities, respectively reflected in psychometrically assessed stress ratings and in activation of the sympathoadrenal system and the hypothalamic-pituitary-adrenal axis. The findings are less robust, though, in the pharmacological perturbations' domain, including such agents as adenosine or dobutamine. Likewise, stress models' convergent- and discriminant validity vary depending on the stressors' nature. Stress models share similarities, but also have important differences regarding their validities. Specific traits defined by the nature of the stressor stimulus should be taken into consideration when selecting stress models. Doing so can personalize prevention and treatment of stress-related antecedents, its acute processing, and chronic sequelae. Further work is warranted to refine stress models' validity and customize them so they commensurate diverse populations and circumstances.

Modelling the role of glucocorticoid receptor as mediator of endocrine responses to environmental challenge.

Glucocorticoid hormones (GCs) modulate acute 'stress' responses in vertebrates, exerting their actions across many physiological systems to help the organism face and overcome challenges. These actions take place via binding to the glucocorticoid receptor (GR), which determines not only the magnitude of the GC-mediated physiological response but also the negative feedback that downregulates GCs to restore homeostasis. Although GR function is assumed to determine GC regulation capacity, the associations between GR abundance and individuals' coping abilities remain cryptic. We developed a dynamic model fitted to empirical data to predict the effects of GR abundance on both plasma GC response patterns and the magnitude of GC-mediated physiological response. Individuals with higher GRs showed lower GC exposure, stronger physiological responses and greater capacity to adjust this response according to stressor intensity, which may be translated into more resilient and flexible GC phenotypes. Our results also show that among-individual variability in GR abundance challenges the detectability of the association between plasma GC measurements and physiological responses. Our approach provides mechanistic insights into the role of GRs in plasma GC measurements and function, which point at GR abundance fundamentally driving complex features of the GC regulation system in the face of environmental change. This article is part of the theme issue 'Endocrine responses to environmental variation: conceptual approaches and recent developments'.

The effects of selected sedatives on basal and stimulated serum cortisol concentrations in healthy dogs.

Background: Hormone assessment is typically recommended for awake, unsedated dogs. However, one of the most commonly asked questions from veterinary practitioners to the endocrinology laboratory is how sedation impacts cortisol concentrations and the adrenocorticotropic hormone (ACTH) stimulation test. Butorphanol, dexmedetomidine, and trazodone are common sedatives for dogs, but their impact on the hypothalamic-pituitary-adrenal axis (HPA) is unknown. The objective of this study was to evaluate the effects of butorphanol, dexmedetomidine, and trazodone on serum cortisol concentrations. Methods: Twelve healthy beagles were included in a prospective, randomized, four-period crossover design study with a 7-day washout. ACTH stimulation test results were determined after saline (0.5 mL IV), butorphanol (0.3 mg/kg IV), dexmedetomidine (4 µg/kg IV), and trazodone (3-5 mg/kg PO) administration. Results: Compared to saline, butorphanol increased basal (median 11.75 µg/dL (range 2.50-23.00) (324.13 nmol/L; range 68.97-634.48) vs 1.27 µg/dL (0.74-2.10) (35.03 nmol/L; 20.41-57.93); P < 0.0001) and post-ACTH cortisol concentrations (17.05 µg/dL (12.40-26.00) (470.34 nmol/L; 342.07-717.24) vs 13.75 µg/dL (10.00-18.90) (379.31 nmol/L; 275.96-521.38); P ≤ 0.0001). Dexmedetomidine and trazodone did not significantly affect basal (1.55 µg/dL (range 0.75-1.55) (42.76 nmol/L; 20.69-42.76); P = 0.33 and 0.79 µg/dL (range 0.69-1.89) (21.79 nmol/L; 19.03-52.14); P = 0.13, respectively, vs saline 1.27 (0.74-2.10) (35.03 nmol/L; 20.41-57.93)) or post-ACTH cortisol concentrations (14.35 µg/dL (range 10.70-18.00) (395.86 nmol/L; 295.17-496.55); (P = 0.98 and 12.90 µg/dL (range 8.94-17.40) (355.86 nmol/L; 246.62-480); P = 0.65), respectively, vs saline 13.75 µg/dL (10.00-18.60) (379.31 nmol/L; 275.86-513.10). Conclusion: Butorphanol administration should be avoided prior to ACTH stimulation testing in dogs. Further evaluation of dexmedetomidine and trazodone's effects on adrenocortical hormone testing in dogs suspected of HPA derangements is warranted to confirm they do not impact clinical diagnosis.

Longevity, demographic characteristics, and socio-economic status are linked to triiodothyronine levels in the general population.

The hypothalamic-pituitary-thyroid (HPT) axis is fundamental to human biology, exerting central control over energy expenditure and body temperature. However, the consequences of normal physiologic HPT-axis variation in populations without diagnosed thyroid disease are poorly understood. Using nationally representative data from the 2007 to 2012 National Health and Nutrition Examination Survey, we explore relationships with demographic characteristics, longevity, and socio-economic factors. We find much larger variation across age in free T3 than other HPT-axis hormones. T3 and T4 have opposite relationships to mortality: free T3 is inversely related and free T4 is positively related to the likelihood of death. Free T3 and household income are negatively related, particularly at lower incomes. Finally, free T3 among older adults is associated with labor both in terms of unemployment and hours worked. Physiologic TSH/T4 explain only 1.7% of T3 variation, and neither are appreciably correlated to socio-economic outcomes. Taken together, our data suggest an unappreciated complexity of the HPT-axis signaling cascade broadly such that TSH and T4 may not be accurate surrogates of free T3. Furthermore, we find that subclinical variation in the HPT-axis effector hormone T3 is an important and overlooked factor linking socio-economic forces, human biology, and aging.

Cortisol levels across the lifespan in common marmosets (Callithrix jacchus).

Human aging is associated with senescence of the hypothalamic-pituitary-adrenal (HPA) axis, leading to progressive dysregulation characterized by increased cortisol exposure. This key hormone is implicated in the pathogenesis of many age-related diseases. Common marmosets (Callithrix jacchus) display a wide spectrum of naturally occurring age-related pathologies that compare similarly to humans and are increasingly used as translational models of aging and age-related disease. Whether the marmoset HPA axis also shows senescence with increasing age is unknown. We analyzed hair cortisol concentration (HCC) across the lifespan of 50 captive common marmosets, ranging in age from approximately 2 months-14.5 years, via a cross-sectional design. Samples were processed and analyzed for cortisol using enzyme immunoassay. HCC ranged from 1416 to 15,343 pg/mg and was negatively correlated with age. We found significant main effects of age group (infant, adolescent, adult, aged, very aged) and sex on HCC, and no interaction effects. Infants had significantly higher levels of HCC compared with all other age groups. Females had higher HCC than males. There was no interaction between age and sex. These results suggest marmosets do not show dysregulation of the HPA axis with increasing age, as measured via HCC.

Sex-specific interactions between stress axis and redox balance are associated with internalizing symptoms and brain white matter microstructure in adolescents.

Adolescence is marked by the maturation of systems involved in emotional regulation and by an increased risk for internalizing disorders (anxiety/depression), especially in females. Hypothalamic-pituitary-adrenal (HPA)-axis function and redox homeostasis (balance between reactive oxygen species and antioxidants) have both been associated with internalizing disorders and may represent critical factors for the development of brain networks of emotional regulation. However, sex-specific interactions between these factors and internalizing symptoms and their link with brain maturation remain unexplored. We investigated in a cohort of adolescents aged 13-15 from the general population (n = 69) whether sex-differences in internalizing symptoms were associated with the glutathione (GSH)-redox cycle homeostasis and HPA-axis function and if these parameters were associated with brain white matter microstructure development. Female adolescents displayed higher levels of internalizing symptoms, GSH-peroxidase (GPx) activity and cortisol/11-deoxycortisol ratio than males. There was a strong correlation between GPx and GSH-reductase (Gred) activities in females only. The cortisol/11-deoxycortisol ratio, related to the HPA-axis activity, was associated with internalizing symptoms in both sexes, whereas GPx activity was associated with internalizing symptoms in females specifically. The cortisol/11-deoxycortisol ratio mediated sex-differences in internalizing symptoms and the association between anxiety and GPx activity in females specifically. In females, GPx activity was positively associated with generalized fractional anisotropy in widespread white matter brain regions. We found that higher levels of internalizing symptoms in female adolescents than in males relate to sex-differences in HPA-axis function. In females, our results suggest an important interplay between HPA-axis function and GSH-homeostasis, a parameter strongly associated with brain white matter microstructure.

Early childhood multiple or persistent regulatory problems and diurnal salivary cortisol in young adulthood.

BACKGROUND: Early childhood multiple or persistent regulatory problems (RPs; crying, sleeping, or feeding problems) have been associated with a risk of behavioural problems in young adulthood. It has been suggested that this may be due to the possible influence of early RPs on the functioning of the hypothalamic-pituitary-adrenal (HPA) axis. However, associations between early RPs and HPA-axis activity in young adulthood remain unexplored. Thus, the aim of the current study was to investigate whether early childhood multiple or persistent RPs are associated with diurnal salivary cortisol in young adulthood. METHODS: At the ages of 5, 20 and 56 months, RPs of 308 children from the Arvo Ylppö Longitudinal Study were assessed via standardized parental interviews and neurological assessments. Multiple RPs were defined as two or three RPs at the age of 5 months and persistent RPs as at least one RP at 5, 20 and 56 months. At the mean age of 25.4 years (SD= 0.6), the participants donated saliva samples for cortisol at awakening, 15 and 30 min thereafter, 10:30 am, at noon, 5:30 pm, and at bedtime during one day. We used mixed model regressions, and generalized linear models for testing the associations, controlling for important covariates. RESULTS: Of the 308 children, 61 (19.8%) had multiple or persistent RPs in early childhood: 38 had multiple, and 27 had persistent RPs. Persistent RPs were associated with significantly higher cortisol peak and output in the waking period, and cortisol awakening response. On the other hand, multiple RPs were not associated with salivary cortisol. CONCLUSION: Children displaying persistent RPs throughout early childhood show, over two decades later, increased HPA axis activity in response to awakening stress. This may be one physiological mechanism linking early childhood RPs to adulthood behavioural outcomes.

Depression in Women: Potential Biological and Sociocultural Factors Driving the Sex Effect.

Important sex-related differences have been observed in the onset, prevalence, and clinical phenotype of depression, based on several epidemiological studies. Social, behavioural, and educational factors have a great role in underlying this bias; however, also several biological factors are extensively involved. Indeed, sexually dimorphic biological systems might represent the underlying ground for these disparities, including cerebral structures and neural correlates, reproductive hormones, stress response pathways, the immune system and inflammatory reaction, metabolism, and fat distribution. Furthermore, in this perspective, it is also important to consider and focus the attention on specific ages and life stages of individuals: indeed, women experience during their life specific periods of reproductive transitional phases, which are not found in men, that represent windows of particular psychological vulnerability. In addition to these, other biologically related risk factors, including the occurrence of sleep disturbances and the exposure to childhood trauma, which are found to differentially affect men and women, are also putative underlying mechanisms of the clinical bias of depression. Overall, by taking into account major differences which characterize men and women it might be possible to improve the diagnostic process, as well as treat more efficiently depressed individuals, based on a more personalized medicine and research.

Investigating the effects of acute and chronic stress on DNA damage.

A hallmark of the vertebrate stress response is a rapid increase in glucocorticoids and catecholamines; however, this does not mean that these mediators are the best, or should be the only, metric measured when studying stress. Instead, it is becoming increasingly clear that assaying a suite of downstream metrics is necessary in stress physiology. One component of this suite could be assessing double-stranded DNA damage (dsDNA damage), which has recently been shown to increase in blood with both acute and chronic stress in house sparrows (Passer domesticus). To further understand the relationship between stress and dsDNA damage, we designed two experiments to address the following questions: (1) how does dsDNA damage with chronic stress vary across tissues? (2) does the increase in dsDNA damage during acute stress come from one arm of the stress response or both? We found that (1) dsDNA damage affects tissues differently during chronic stress and (2) the hypothalamic-pituitary-adrenal axis influences dsDNA damage with acute stress, but the sympathetic-adreno-medullary system does not. Surprisingly, our data are not explained by studies on changes in hormone receptor levels with chronic stress, so the underlying mechanism remains unclear.

Early life corticosteroid overexposure: Epigenetic and fetal origins of adult diseases.

The relationship between events occurring during intrauterine development and later-life predisposition to long-term disease, has been described. The fetus responds to excess intrauterine exposure to high levels of corticosteroids, modifying their physiological development and stopping their growth. Fetal exposure to elevated levels of either endogenous (alterations in fetal hypothalamic-pituitary-adrenal axis) or synthetic corticosteroids, is one model of early-life adversity; to developing adult disease. At the molecular level, there are transcriptional changes in metabolic and growth pathways. Epigenetic mechanisms participate in transgenerational inheritance, not genomic. Exposures that change 11ß-hydroxysteroid dehydrogenase type 2 enzyme methylation status in the placenta can result in transcriptional repression of the gene, causing the fetus to be exposed to higher levels of cortisol. More precise diagnosis and management of antenatal corticosteroids for preterm birth, would potentially decrease the risk of long-term adverse outcomes. More studies are needed to understand the potential roles of factors to alter fetal corticosteroid exposure. Long-term infant follow-up is required to determine whether methylation changes in placenta may represent useful biomarkers of later disease risk. This review, summarize recent advances in the programming of fetal effects of corticosteroid exposure, the role of corticosteroids in epigenetic gene regulation of placental 11ß-hydroxysteroid dehydrogenase type 2 enzyme expression and transgenerational effects.

Effects of menstrual cycle phase and ovulation on the salivary cortisol awakening response.

The cortisol awakening response (CAR) is influenced by several state and trait variables, one of which might be the menstrual cycle in women. Previous results suggested that the CAR is enhanced around ovulation, which is why it has been recommended to avoid sampling during the ovulatory phase. In two separate studies, we aimed to replicate previous findings that reported the CAR's modulation across the menstrual cycle, especially during ovulation. In Study 1, a group of 27 healthy naturally cycling women collected saliva at 0, 30, 45, and 60 min post-awakening on two days during their follicular, ovulatory, and luteal phases in a repeated measures design. In Study 2, CAR samples were collected from 30 healthy naturally cycling women on seven consecutive days around the expected ovulation. To increase reliability of CAR measurements, participants' compliance of saliva sampling times was monitored, ovarian steroids (estradiol and progesterone) were collected, and ovulation was confirmed with specific test kits. Contrary to our expectations, we detected no differences in the CAR over the menstrual cycle, and no significant association with variations in estradiol and progesterone. In addition, we excluded confounding effects such as compliance and validated the cycle phase. These results suggest that the CAR is largely robust against hormonal variations across the menstrual cycle, including the mid-cycle phase around ovulation. However, further research is needed to understand the potential ovarian steroid-induced modulation of HPA axis functioning and the menstrual cycle's effects on salivary cortisol levels in psychobiological studies.

Gender-affirming hormone therapy effect on cortisol levels in trans males and trans females.

PURPOSE: Previous studies have shown differences in baseline and stimulated cortisol levels between men and women. Whether this difference is secondary to sex hormones or to other factors, such as genetic or epigenetic changes, is unknown. We investigated the effect of gender-affirming hormone treatment (GAHT) on the hypothalamo-pituitary-adrenal axis of transgender subjects in an effort to throw light on this question. METHODS: Ten transgender males (TM) and eight transgender females (TF) underwent a low-dose (1 µg) adrenocorticotropic hormone (ACTH) stimulation test before and 6 months after GAHT initiation. Serum total, free and salivary cortisol (SC) levels were measured at baseline and at 20, 30 and 40 min. RESULTS: For the TM, all three levels were significantly lower at several time points after ACTH injection compared to pretreatment levels following 6 months of treatment (p < .05). Likewise, the overall SC response as calculated by the area under the curve was significantly lower (p = .0053). For the TF, the basal total cortisol (TC) level increased after 6 months of treatment (p < .01) while ACTH-stimulated SC levels decreased significantly. The basal ACTH levels were significantly lower following hormonal therapy (p < .001). CONCLUSION: Stimulated salivary cortisol levels decreased significantly after 6 months of GAHT in both male and female transgender subjects, possibly reflecting a decreased state of anxiety associated with treatment initiation. Additionally, basal and stimulated serum TC levels increased after hormonal treatment in the TF, probably secondary to the effect of oestrogen on cortisol-binding globulin.

Characterizing the alternative feedback mechanisms in the hypothalamic-pituitary-adrenal (HPA) axis and determining a stressed state in the African wild dog (Lycaon pictus).

Glucocorticoids are regulated by the hypothalamic-pituitary-adrenal (HPA) axis and are important in responding to various psychological and physiological stressors. For the African wild dog (Lycaon pictus) only one aspect of the HPA axis has been investigated with no information present on cortisol insufficiency. Here, a pilot study involving both HPA feedback mechanisms is characterized by dynamic function tests (i.e., stimulation and suppression) and a cutoff value for a stressed state is established. Results showed a mean plasma cortisol increase of 40.7% after the administration of Synacthen from initial values, with females recording higher concentrations than males. Using Youden's index, this adaptive response was able to determine a cutoff value of 80.72 ng/ml that infers a stress state. The observed response in the suppression test was similar to that reported in domestic dogs. These results expand the basic knowledge of adrenal function in this endangered species and provide a means in which to determine whether animals are stressed or not. The method used also has application to other species in gauging the degree of stress they are experiencing, which can assist in improving welfare outcomes for captive animals.

Hidden variables in stress neurobiology research.

Among the central goals of stress neurobiology research is to understand the mechanisms by which stressors change neural circuit function to precipitate or exacerbate psychiatric symptoms. Yet despite decades of effort, psychiatric medications that target the biological substrates of the stress response are largely lacking. We propose that the clinical advancement of stress response-based therapeutics for psychiatric disorders may be hindered by 'hidden variables' in stress research, including considerations of behavioral study design (stressors and outcome measures), individual variability, sex differences, and the interaction of the body's stress hormone system with endogenous circadian and ultradian rhythms. We highlight key issues and suggest ways forward in stress neurobiology research that may improve the ability to assess stress mechanisms and translate preclinical findings.