Functional MRI Techniques Suggesting that the Stress System Interacts with Three Large Scale Core Brain Networks to Help Coordinate the Adaptive Response: A Systematic Review

OBJECTIVE

Synthesis of functional MRI (fMRI) and functional connectivity (FC) analysis data on human stress system (SS) function, as it relates to the dynamic function of the Salience (SN), Default Mode (DMN) and Central Executive (CEN) networks.

METHODS

Systematic search of Medline, Scopus, Clinical Trials.gov, and Google Scholar databases of studies published prior to September 2022 resulted in 28 full-text articles included for qualitative synthesis.

RESULTS

Acute stress changes the states of intra-/inter- neural network FCs and activities from those of resting, low arousal state in the SN, DMN and CEN, during which intra- and inter-network FCs and activities of all three networks are low. SS activation is positively linked to the activity of the SN and negatively to that of the DMN, while, in parallel, it is associated with an initial decrease and a subsequent increase of the intra- network FC and activity of the CEN. The FC between the DMN and the CEN increases, while those between the SN and the CEN decrease, allowing time for frontal lobe strategy input and "proper" CEN activity and task decision. SN activation is linked to sensory hypersensitivity, "impaired" memory, and a switch from serial to parallel processing, while trait mindfulness is associated with FC changes promoting CEN activity and producing a "task-ready state".

CONCLUSION

SS activation is tightly connected to that of the SN, with stress hormones likely potentiating the intra-network FC of the latter, attenuating that of the DMN, and causing a biphasic suppression- to-activation response of the CEN, all adaptive changes favoring proper decisions and survival.

The relationship between balance and urinary cortisol and neopterin in autistic children

Autism Spectrum Disorder (ASD) is a neurodevelopmental condition characterized by stereotyped behavior, restricted interests and social/communicative deficits. The physiological etiology of ASD is not currently understood, however recent research has implicated dysregulation of the immune system as a central feature. The interplay between the stress systems, the immune system and the brain has been well-documented and implicated in other psychiatric and neurological disorders. This interplay suggests a role for the hypothalamic-pituitary-adrenal (HPA) axis in the etiology of ASD. We assessed levels of urinary cortisol and neopterin as markers of immune function and HPA activation in a cohort of 50 children from the central Johannesburg region. Additionally, we used the Autism Treatment Evaluation Checklist to assess autistic symptomatology and the Bruininks-Oseretsky Motor Proficiency Test (Second Edition) (BOT-2) to assess motor skills. No relationships were found between cortisol and autistic symptomatology. No relationships were found between neopterin and any of the other measures. However, a relationship was observed between urinary cortisol and performance on balance-related tasks from the BOT-2 (P < 0.05). Our findings support a theory of neurological interconnectedness between postural modulation and activation of the stress system, which has not previously been documented in children with ASD.

Basic Concepts and Hormonal Regulators of the Stress System

BACKGROUND

Human organisms have to cope with a large number of external or internal stressful stimuli that threaten - or are perceived as threatening - their internal dynamic balance or homeostasis. To face these disturbing forces, or stressors, organisms have developed a complex neuroendocrine system, the stress system, which consists of the hypothalamic-pituitary-adrenal axis and the locus caeruleus/norepinephrine-autonomic nervous system.

SUMMARY

Upon exposure to stressors beyond a certain threshold, the activation of the stress system leads to a series of physiological and behavioral adaptations that help achieve homeostasis and increase the chances of survival. When, however, the stress response to stressors is inadequate, excessive, or prolonged, the resultant maladaptation may lead to the development of several stress-related pathologic conditions. Adverse environmental events, especially during critical periods of life, such as prenatal life, childhood, and puberty/adolescence, in combination with the underlying genetic background, may leave deep, long-term epigenetic imprints in the human expressed genome.

KEY MESSAGES

In this review, we describe the components of the stress system and its functional interactions with other homeostatic systems of the organism; we present the hormonal regulators of the stress response, and we discuss the development of stress-related pathologies.

Extracellular Vesicles and the Stress System

Extracellular vesicles (EVs) are membrane-enclosed nanoparticles that contain various biomolecules, including nucleic acids, proteins and lipids, and are manufactured and released by virtually all cell types. There is evidence that EVs are involved in intercellular communication, acting in an autocrine, paracrine or/and endocrine manner. EVs are released by the cells of the central nervous system (CNS), including neurons, astrocytes, oligodendrocytes and microglia, and have the ability to cross the blood-brain barrier (BBB) and enter the systemic circulation. Neuroendocrine cells are specialized neurons that secrete hormones directly into blood vessels, such as the hypophyseal portal system or the systemic circulation, a process that allows neuroendocrine integration to take place. In mammals, neuroendocrine cells are widely distributed throughout various anatomic compartments, with the hypothalamus being a central neuroendocrine integrator. The hypothalamus is a key part of the stress system (SS), a highly conserved neuronal/neuroendocrine system aiming at maintaining systemic homeostasis when the latter is threatened by various stressors. The central parts of the SS are the interconnected hypothalamic corticotropin-releasing hormone (CRH) and the brainstem locus caeruleus-norepinephrine (LC-NE) systems, while their peripheral parts are, respectively, the pituitary-adrenal axis and the sympathetic nervous/sympatho-adrenomedullary systems (SNS-SAM) as well as components of the parasympathetic nervous system (PSNS). During stress, multiple CNS loci show plasticity and undergo remodeling, partly mediated by increased glutamatergic and noradrenergic activity, and the actions of cytokines and glucocorticoids, all regulated by the interaction of the hypothalamic-pituitary-adrenal (HPA) axis and the LC-NE/SNS-SAM systems. In addition, there are peripheral changes due to the increased secretion of stress hormones and pro-inflammatory cytokines in the context of stress-related systemic (para)inflammation. We speculate that during stress, central and peripheral, cellular and molecular alterations take place, with some of them generated, communicated, and spread via the release of stress-induced neural/neuroendocrine cell-derived EVs.

Circadian regulation of memory under stress: Endocannabinoids matter

Organisms ranging from plants to higher mammals have developed 24-hour oscillation rhythms to optimize physiology to environmental changes and regulate a plethora of neuroendocrine and behavioral processes, including neurotransmitter and hormone regulation, stress response and learning and memory function. Compelling evidence indicates that a wide array of memory processes is strongly influenced by stress- and emotional arousal-activated neurobiological systems, including the endocannabinoid system which has been extensively shown to play an integral role in mediating stress effects on memory. Here, we review findings showing how circadian rhythms and time-of-day influence stress systems and memory performance. We report evidence of circadian regulation of memory under stress, focusing on the role of the endocannabinoid system and highlighting its circadian rhythmicity. Our discussion illustrates how the endocannabinoid system mediates stress effects on memory in a circadian-dependent fashion. We suggest that endocannabinoids might regulate molecular mechanisms that control memory function under circadian and stress influence, with potential important clinical implications for both neurodevelopmental disorders and psychiatric conditions involving memory impairments.

Aroclor 1254 inhibits vasotocinergic pathways related to osmoregulatory and stress functions in the gilthead sea bream (Sparus aurata, Linnaeus 1758)

The present study assesses the response of vasotocinergic system in the gilthead sea bream (Sparus aurata) after administering two doses of the polychlorinated biphenyl Aroclor 1254 (15 or 50 μg g^-1 fresh body mass). Seven days post-administration, eight fish of each experimental group were sampled, and the remaining animals were challenged with a hyperosmotic stress by being transferred from seawater (36 ppt) to high salinity water (55 ppt) and being sampled 3 days post-transfer. Aroclor 1254 affected gene expression of avt, together with Avt concentrations in pituitary and plasma, inhibiting the stimulation observed in vasotocinergic system after hyperosmotic challenge. This was noted by the accumulation of Avt at hypophyseal level as well as by its undetectable values in plasma. Hyperosmotic transfer significantly changed branchial avtrv1a, avtrv2, atp1a and cftr mRNA expression levels in control fish, while in Aroclor 1254-treated fish they remained mostly unchanged. This desensitization also occurred for avtrs in hypothalamus, caudal kidney and liver. In addition, an enhancement in plasma cortisol concentration, together with the orchestration of several players of the Hypothalamic-Pituitary-Interrenal axis (crh, crhbp, trh, star), was also observed mostly at the highest dose used (50 μg g^-1 body mass), affecting plasma and hepatic metabolites. Our results demonstrated that Aroclor 1254 compromises the hypoosmoregulatory function of vasotocinergic system in S. aurata, also inducing a concomitant stress response. In summary, this study demonstrates that Aroclor 1254 can be considered an important endocrine disruptor in relation with the correct arrangement of vasotocinergic, metabolic and stress pathways after their stimulation by transfer to hyperosmotic environments.

Salivary cortisol and alpha-amylase diurnal profiles and stress reactivity in children with Attention Deficit Hyperactivity Disorder

There is growing evidence for dysregulation of the stress system in individuals with Attention Deficit Hyperactivity Disorder (ADHD). The stress system includes neuroanatomical and functional components that function in concert to maintain homeostasis and its main effectors are the hypothalamic-pituitary-adrenal (HPA) axis and the sympathetic/adrenomedullary nervous system (SNS). As stress system activity demonstrates a distinct circadian variation, we aimed to describe simultaneously, diurnal rhythms of both the HPA axis and the SNS in children with ADHD and a comparison group. Moreover, we attempted to investigate stress responses to a physical stressor, venipuncture, in both groups. Sixty-two prepubertal children with ADHD combined (ADHD-C) or inattentive (ADHD-I) type and 40 typically developing children provided saliva samples at six specific time points during a day, as well as before and 10 min after a scheduled morning venipuncture. Salivary cortisol and α- amylase were selected as reliable noninvasive biomarkers for HPA axis and SNS function and were measured in the samples obtained. Results revealed that children with ADHD-C had lower mean cortisol values both 30 min after awakening and at 18:00 h than controls (p = 0.002 and p = 0.018 respectively), as well as lower mean Cortisol Awakening Response (CAR) and Area Under the Curve for "wake to bed" period (AUC_i) values of cortisol (p = 0.004 and p = 0.001, respectively). Also, mean CAR and cortisol AUC_i were lower in children with ADHD-I than the control group (p = 0.034 and p = 0.038 respectively). Alpha-amylase measurements showed an increase over time (p < 0.001), which was similar in all three groups. Interestingly, α-amylase changes over time were correlated with the corresponding cortisol changes (p < 0.001). Venipuncture, elicited a significant increase only in α-amylase levels and more so in the control group (p = 0.003). These findings suggest a partial hypofunction of the stress system in children with ADHD.

Robotic assisted radical prostatectomy accelerates postoperative stress recovery: Final results of a contemporary prospective study assessing pathophysiology of cortisol peri-operative kinetics in prostate cancer surgery

Objective

To investigate the effects of prostate cancer (PCa) surgery on the stress system and to identify potential independent factors associating with stress recovery.

Methods

The design of the study was prospective and PCa surgery included robot assisted radical prostatectomy (RARP) or retropubic radical prostatectomy (RRP). Between February 2013 to December 2014, 315 consecutive patients were evaluated. The effects of PCa surgery on the stress system were measured by cortisol serum levels before and after surgery on postoperative day (POD) 0, 1, 3, 5 and 45. Cortisol variations in the population and subpopulation (RARP vs. RRP) of patients were investigated by statistical methods. Factors associating with stress recovery were assessed by simple linear regression (SLR) and multiple linear regression (MLR) analysis.

Results

RARP was performed in 75.9% of cases. In the patient population, there were wide serum cortisol perioperative variations. PCa surgery triggered the stress system which immediately (POD 0) responded by cortisol overproduction which induced the negative feedback mechanism that started on POD 1, continued on POD 3, was still ongoing on POD 5 and completely settled on POD 45 (stress recovery). In the subpopulation of patients, significantly lower cortisol serum levels were detected on POD 3–5 in RARP cases in whom cortisol levels were close to preoperative levels (stress recovery) on POD 5. Independent predictive factors of serum cortisol on POD 5 (stress recovery) were preoperative cortisol (p = 0.02), cortisol levels on POD 3 (p < 0.0001) and RARP (p = 0.03) in which the association was negative (stress recovery faster than RRP).

Conclusion

Our study shows that PCa surgery immediately (POD 0) triggers the stress system which respond by overproduction of cortisol which induces the negative feedback mechanism that starts on POD 1, is still ongoing on POD 5, but is completely settled on POD 45. Moreover, after surgical trauma, our study gives evidence that the RARP procedure associates with stress recovery faster than RRP. Further confirmatory studies are required.

Robotic-assisted radical prostatectomy is less stressful than the open approach: results of a contemporary prospective study evaluating pathophysiology of cortisol stress-related kinetics in prostate cancer surgery

The objective of this study was to investigate the effects of prostate cancer (PCA) surgery on the stress system and to identify potential independent factors associating with stress recovery. The design of the study was prospective and PCA surgery included robot-assisted radical prostatectomy (RARP) or retro pubic radical prostatectomy. Between February and December 2013, 151 consecutive patients were evaluated. The effects of PCA surgery on the stress system were measured by cortisol serum levels before and after surgery on post-operative day (POD) 0, 1, 3, 5 and 45. Statistical methods were applied. RARP was performed in 71% of cases. PCA surgery triggered the stress system which immediately (POD 0) responded by cortisol overproduction which induced the negative feedback mechanism that started on POD 1, continued on POD.

Hormesis is applicable as a pro-healthy aging intervention in mammals and human beings

The aging of the population brings new health challenges, and in particular, the need to implement suitable pro-healthy aging interventions. This paper discusses the potential of mild stressors inducing hormesis as a lifespan and healthspan extension strategy and how it can be applied to the human. There is some evidence that the anti-aging benefits of lifestyle factors, such as diet, exercise or engaging in activities may be achieved via hormetic regulation. This supports the validity of the concept in human. There are, however, gaps in knowledge and ethical barriers that need to be addressed to establish the suitability of the approach to the clinical context or the general geriatric population. In particular, we need to find out which stressors are safe for use as anti-aging interventions, when they have to be applied to achieve maximal benefits, how their therapeutic potential is altered by changes in the stress system induced by age and pathological conditions, and the extent to which the occurrence of adverse versus positive effects depends on interacting genetic and experiential factors.