Glucocorticoids and nervous system plasticity

Sodium butyrate facilitates CRHR2 expression to alleviate HPA axis hyperactivity in autism-like rats induced by prenatal lipopolysaccharides through histone deacetylase inhibition

Short-chain fatty acids (SCFAs, especially butyric acid) have been demonstrated to play a promising role in the development of autism spectrum disorders (ASD). Recently, the hypothalamic-pituitary-adrenal (HPA) axis is also suggested to increase the risk of ASD. However, the mechanism underlying SCFAs and HPA axis in ASD development remains unknown. Here, we show that children with ASD exhibited lower SCFA concentrations and higher cortisol levels, which were recaptured in prenatal lipopolysaccharide (LPS)-exposed rat model of ASD. These offspring also showed decreased SCFA-producing bacteria and histone acetylation activity as well as impaired corticotropin-releasing hormone receptor 2 (CRHR2) expression. Sodium butyrate (NaB), which can act as histone deacetylases inhibitors, significantly increased histone acetylation at the CRHR2 promoter in vitro and normalized the corticosterone as well as CRHR2 expression level in vivo. Behavioral assays indicated ameliorative effects of NaB on anxiety and social deficit in LPS-exposed offspring. Our results imply that NaB treatment can improve ASD-like symptoms via epigenetic regulation of the HPA axis in offspring; thus, it may provide new insight into the SCFA treatment of neurodevelopmental disorders like ASD. IMPORTANCE Growing evidence suggests that microbiota can affect brain function and behavior through the "microbiome-gut-brain'' axis, but its mechanism remains poorly understood. Here, we show that both children with autism and LPS-exposed rat model of autism exhibited lower SCFA concentrations and overactivation of HPA axis. SCFA-producing bacteria, Lactobacillus, might be the key differential microbiota between the control and LPS-exposed offspring. Interestingly, NaB treatment contributed to the regulation of HPA axis (such as corticosterone as well as CRHR2) and improvement of anxiety and social deficit behaviors in LPS-exposed offspring. The potential underlying mechanism of the ameliorative effect of NaB may be mediated via increasing histone acetylation to the CRHR2 promoter. These results enhance our understanding of the relationship between the SCFAs and the HPA axis in the development of ASD. And gut microbiota-derived SCFAs may serve as a potential therapeutic agent to neurodevelopmental disorders like ASD.

Confronting the loss of trophic support

Classic experiments with peripheral sympathetic neurons established an absolute dependence upon NGF for survival. A forgotten problem is how these neurons become resistant to deprivation of trophic factors. The question is whether and how neurons can survive in the absence of trophic support. However, the mechanism is not understood how neurons switch their phenotype to lose their dependence on trophic factors, such as NGF and BDNF. Here, we approach the problem by considering the requirements for trophic support of peripheral sympathetic neurons and hippocampal neurons from the central nervous system. We developed cellular assays to assess trophic factor dependency for sympathetic and hippocampal neurons and identified factors that rescue neurons in the absence of trophic support. They include enhanced expression of a subunit of the NGF receptor (Neurotrophin Receptor Homolog, NRH) in sympathetic neurons and an increase of the expression of the glucocorticoid receptor in hippocampal neurons. The results are significant since levels and activity of trophic factors are responsible for many neuropsychiatric conditions. Resistance of neurons to trophic factor deprivation may be relevant to the underlying basis of longevity, as well as an important element in preventing neurodegeneration.

Psychological stress induces an increase in cholinergic enteric neuromuscular pathways mediated by glucocorticoid receptors

Introduction

Repeated acute stress (RASt) is known to be associated with gastrointestinal dysfunctions. However, the mechanisms underlying these effects have not yet been fully understood. While glucocorticoids are clearly identified as stress hormones, their involvement in RASt-induced gut dysfunctions remains unclear, as does the function of glucocorticoid receptors (GR). The aim of our study was to evaluate the involvement of GR on RASt-induced changes in gut motility, particularly through the enteric nervous system (ENS).

Methods

Using a murine water avoidance stress (WAS) model, we characterized the impact of RASt upon the ENS phenotype and colonic motility. We then evaluated the expression of glucocorticoid receptors in the ENS and their functional impact upon RASt-induced changes in ENS phenotype and motor response.

Results

We showed that GR were expressed in myenteric neurons in the distal colon under basal conditions, and that RASt enhanced their nuclear translocation. RASt increased the proportion of ChAT-immunoreactive neurons, the tissue concentration of acetylcholine and enhanced cholinergic neuromuscular transmission as compared to controls. Finally, we showed that a GR-specific antagonist (CORT108297) prevented the increase of acetylcholine colonic tissue level and in vivo colonic motility.

Discussion

Our study suggests that RASt-induced functional changes in motility are, at least partly, due to a GR-dependent enhanced cholinergic component in the ENS.

Dimerization of the Glucocorticoid Receptor and Its Importance in (Patho)physiology: A Primer

The glucocorticoid receptor (GR) is a very versatile protein that comes in several forms, interacts with many proteins and has multiple functions. Numerous therapies are based on GRs’ actions but the occurrence of side effects and reduced responses to glucocorticoids have motivated scientists to study GRs in great detail. The notion that GRs can perform functions as a monomeric protein, but also as a homodimer has raised questions about the underlying mechanisms, structural aspects of dimerization, influencing factors and biological functions. In this review paper, we are providing an overview of the current knowledge and insights about this important aspect of GR biology.

Stress-induced blood brain barrier disruption: Molecular mechanisms and signaling pathways

Stress is a nonspecific response to a threat or noxious stimuli with resultant damaging consequences. Stress is believed to be an underlying process that can trigger central nervous system disorders such as depression, anxiety, and post-traumatic stress disorder. Though the pathophysiological basis is not completely understood, data have consistently shown a pivotal role of inflammatory mediators and hypothalamo-pituitary-adrenal (HPA) axis activation in stress induced disorders. Indeed emerging experimental evidences indicate a concurrent activation of inflammatory signaling pathways and not only the HPA axis, but also, peripheral and central renin-angiotensin system (RAS). Furthermore, recent experimental data indicate that the HPA and RAS are coupled to the signaling of a range of central neuro-transmitter, -mediator and -peptide molecules that are also regulated, at least in part, by inflammatory signaling cascades and vice versa. More recently, experimental evidences suggest a critical role of stress in disruption of the blood brain barrier (BBB), a neurovascular unit that regulates the movement of substances and blood-borne immune cells into the brain parenchyma, and prevents peripheral injury to the brain substance. However, the mechanisms underlying stress-induced BBB disruption are not exactly known. In this review, we summarize studies conducted on the effects of stress on the BBB and integrate recent data that suggest possible molecular mechanisms and signaling pathways underlying stress-induced BBB disruption. Key molecular targets and pharmacological candidates for treatment of stress and related illnesses are also summarized.

Hypothalamic-pituitary-adrenal axis function in traumatic spinal cord injury-related neuropathic pain: a case-control study

PURPOSE

This study aimed to investigate the hypothalamic-pituitary-adrenal (HPA) axis in spinal cord injury (SCI)-related neuropathic pain (NP) using dynamic adrenocorticotropic hormone (ACTH) stimulation tests.

METHODS

This case-control study was conducted with 22 patients diagnosed with traumatic chronic spinal cord injury (15 with and 7 without neuropathic pain) and ten age- and sex-matched healthy control subjects. Collected data included socio-demographic variables, SCI characteristics, and level of NP using a numeric rating scale (NRS) and the Leeds Assessment of Neuropathic Symptoms and Signs pain scale (LANSS). HPA axis function was measured via low-dose (1 μg) and standard-dose (250 μg) ACTH tests (LDT and SDT, respectively).

RESULTS

No significant differences existed regarding peak cortisol responses or area under the curve (AUC) of cortisol responses between the SCI patients with NP and healthy controls using LDT and SDT. In the SCI patients without pain, cortisol responses were significantly lower than those in the healthy controls for LDT and SDT. Peak cortisol and AUC responses of the LDT and SDT were positively correlated with NRS in SCI patients with NP.

CONCLUSIONS

This study demonstrated that, in chronic SCI patients with NP, basal cortisol levels are relatively higher compared to healthy controls, and that HPA axis can be activated with low- and standard-dose ACTH stimulation tests. Although NP following SCI was not significantly associated with hypo- or hypercortisolemia, either after low- or standard-dose ACTH stimulation test, the severity of NP during chronic SCI may be positively associated with HPA axis activity.

The brain development of infants with intrauterine growth restriction: role of glucocorticoids

Brain injury is a serious complication of intrauterine growth restriction (IUGR), but the exact mechanism remains unclear. While glucocorticoids (GCs) play an important role in intrauterine growth and development, GCs also have a damaging effect on microvascular endothelial cells. Moreover, intrauterine adverse environments lead to fetal growth restriction and the hypothalamus-pituitary-adrenal (HPA) axis resetting. In addition, chronic stress can cause a decrease in the number and volume of astrocytes in the hippocampus and glial cells play an important role in neuronal differentiation. Therefore, it is speculated that the effect of GCs on cerebral neurovascular units under chronic intrauterine stimulation is an important mechanism leading to brain injury in infants with growth restrictions.

Borderline personality disorder, trauma, and the hypothalamus-pituitary-adrenal axis

Borderline personality disorder (BPD) is a complex psychiatric illness for which treatment poses a significant challenge due to limited effective pharmacologic treatments, and under-resourced psychological interventions. BPD is one of the most stigmatized conditions in psychiatry today, but can be understood as a modifiable, neurodevelopmental disorder that arises from maladaptive responses to trauma and stress. Stress susceptibility and reactivity in BPD is thought to mediate both the development and maintenance of BPD symptomatology, with trauma exposure considered an early life risk factor of development, and acute stress moderating symptom trajectory. An altered stress response has been characterized in BPD at the structural, neural, and neurobiological level, and is believed to underlie the maladaptive behavioral and cognitive symptomatology presented in BPD. The endocrine hypothalamus-pituitary-adrenal (HPA) axis represents a key stress response system, and growing evidence suggests it is dysfunctional in the BPD patient population. This theoretical review examines BPD in the context of a neurodevelopmental stress-related disorder, providing an overview of measurements of stress with a focus on HPA-axis measurement. Potential confounding factors associated with measurement of the HPA system are discussed, including sex and sex hormones, genetic factors, and the influence of sample collection methods. HPA-axis dysfunction in BPD largely mirrors findings demonstrated in post-traumatic stress disorder and may represent a valuable neuroendocrine target for diagnostic or treatment response biomarkers, or for which novel treatments can be investigated.

Impaired Spinal Glucocorticoid Receptor Signaling Contributes to the Attenuating Effect of Depression on Mechanical Allodynia and Thermal Hyperalgesia in Rats with Neuropathic Pain

Although depression-induced altered pain perception has been described in several laboratory and clinical studies, its neurobiological mechanism in the central nervous system (CNS), particularly in the spinal dorsal horn, remains unclear. Therefore, in this study, we aimed to clarify whether nociceptive sensitivity of neuropathic pain is altered in the olfactory bulbectomy (OB) model of depression and whether glucocorticoid receptor (GR), which is involved in the etio-pathologic mechanisms of both major depression and neuropathic pain, contributes to these processes in the spinal dorsal horn of male Sprague-Dawley rats. The results showed that mechanical allodynia and thermal hyperalgesia induced by spinal nerve ligation (SNL) were attenuated in OB-SNL rats with decreased spinal GR expression and nuclear translocation, whereas non-olfactory bulbectomy (NOB)-SNL rats showed increased spinal GR nuclear translocation. In addition, decreased GR nuclear translocation with normal mechanical nociception and hypoalgesia of thermal nociception were observed in OB-Sham rats. Intrathecal injection (i.t.) of GR agonist dexamethasone (Dex; 4 μg/rat/day for 1 week) eliminated the attenuating effect of depression on nociceptive hypersensitivity in OB-SNL rats and aggravated neuropathic pain in NOB-SNL rats, which was associated with the up-regulation of brain-derived neurotrophic factor (BDNF), TrkB and NR2B expression in the spinal dorsal horn. The present study shows that depression attenuates the mechanical allodynia and thermal hyperalgesia of neuropathic pain and suggests that altered spinal GR-BDNF-TrkB signaling may be one of the reasons for depression-induced hypoalgesia.

Intestinal Barrier and Behavior

The intestinal barrier function contributes to gut homeostasis by modulating absorption of water, electrolytes, and nutrients from the lumen into the circulation while restricting the passage of noxious luminal substances and microorganisms. Chronic conditions such as rheumatoid arthritis, inflammatory bowel disease, and celiac disease are associated to intestinal barrier dysfunction. Here, the hypothesis is that a leaky intestinal wall allowing for indiscriminate passage of intraluminal compounds to the vascular compartment could in turn lead to systemic inflammation. An increasing number of studies are now investigating the association between gut permeability and CNS disorders, under the premise that translocation of intestinal luminal contents could affect CNS function, either directly or indirectly. Still, it is unknown whether disruption of intestinal barrier is a causative agent or a consequence in these situations. Here, we discuss the latest evidence pointing to an association between increased gut permeability and disrupted behavioral responses.