Stress increases descending inhibition in mouse and human colon

Tea-derived exosome-like nanoparticles prevent irritable bowel syndrome induced by water avoidance stress in rat model

BACKGROUND AND AIM

Exosome-like nanoparticles (ELNs) have emerged as crucial mediators of intercellular communication, evaluated as potential bioactive nutraceutical biomolecules. We hypothesized that oral ELNs have some therapeutic effect on irritable bowel syndrome (IBS).

METHODS

In our study, ELNs from tea (Camellia sinensis) leaves were extracted by differential centrifugation. We investigated the role of ELNs by assessing visceral hypersensitivity, body weight, bowel habits, tight junctions, and corticotropin-releasing hormone (CRH) in rats subjected to water avoidance stress (WAS) to mimic IBS with and without ELNs (1 mg/kg per day) for 10 days.

RESULTS

The average diameter of ELNs from LCC, FD and MZ tea tree were 165 ± 107, 168 ± 94, and 168 ± 108 nm, the concentration of ELNs were 1.2 × 1013, 1 × 1013, and 1.5 × 1013 particles/mL, respectively. ELNs can be taken up by intestinal epithelial cells. In WAS rats, ELNs significantly restored weight, recovered tight junctions, decreased CRH, and CRH receptor 1 expression levels and inhibited abdominal hypersensitivity in comparison to positive control.

CONCLUSIONS

Oral tea-derived ELN improves symptoms of IBS by potentially modulating the CRH pathway.

The impact of acute and chronic stress on gastrointestinal physiology and function: a microbiota-gut-brain axis perspective

The physiological consequences of stress often manifest in the gastrointestinal tract. Traumatic or chronic stress is associated with widespread maladaptive changes throughout the gut, although comparatively little is known about the effects of acute stress. Furthermore, these stress-induced changes in the gut may increase susceptibility to gastrointestinal disorders and infection, and impact critical features of the neural and behavioural consequences of the stress response by impairing gut-brain axis communication. Understanding the mechanisms behind changes in enteric nervous system circuitry, visceral sensitivity, gut barrier function, permeability, and the gut microbiota following stress is an important research objective with pathophysiological implications in both neurogastroenterology and psychiatry. Moreover, the gut microbiota has emerged as a key aspect of physiology sensitive to the effects of stress. In this review, we focus on different aspects of the gastrointestinal tract including gut barrier function as well as the immune, humoral and neuronal elements involved in gut-brain communication. Furthermore, we discuss the evidence for a role of stress in gastrointestinal disorders. Existing gaps in the current literature are highlighted, and possible avenues for future research with an integrated physiological perspective have been suggested. A more complete understanding of the spatial and temporal dynamics of the integrated host and microbial response to different kinds of stressors in the gastrointestinal tract will enable full exploitation of the diagnostic and therapeutic potential in the fast-evolving field of host-microbiome interactions.

The enteric nervous system

Of all the organ systems in the body, the gastrointestinal tract is the most complicated in terms of the numbers of structures involved, each with different functions, and the numbers and types of signaling molecules utilized. The digestion of food and absorption of nutrients, electrolytes, and water occurs in a hostile luminal environment that contains a large and diverse microbiota. At the core of regulatory control of the digestive and defensive functions of the gastrointestinal tract is the enteric nervous system (ENS), a complex system of neurons and glia in the gut wall. In this review, we discuss 1) the intrinsic neural control of gut functions involved in digestion and 2) how the ENS interacts with the immune system, gut microbiota, and epithelium to maintain mucosal defense and barrier function. We highlight developments that have revolutionized our understanding of the physiology and pathophysiology of enteric neural control. These include a new understanding of the molecular architecture of the ENS, the organization and function of enteric motor circuits, and the roles of enteric glia. We explore the transduction of luminal stimuli by enteroendocrine cells, the regulation of intestinal barrier function by enteric neurons and glia, local immune control by the ENS, and the role of the gut microbiota in regulating the structure and function of the ENS. Multifunctional enteric neurons work together with enteric glial cells, macrophages, interstitial cells, and enteroendocrine cells integrating an array of signals to initiate outputs that are precisely regulated in space and time to control digestion and intestinal homeostasis.

Single-day and multi-day exposure to orogastric gavages does not affect intestinal barrier function in mice

Animals involved in common laboratory procedures experience minor levels of stress. The direct effect of limited amounts of stress on gastrointestinal function has not been reported yet. Therefore, this study aimed to assess the effect of single-day and multi-day orogastric gavages on gut physiology in mice. To this end, 12-wk-old female C57Bl6/J mice were randomized to receive treatment with sterile water (200 µL) delivered by orogastric gavages twice daily for a total of 1 or 10 day(s). Control animals did not receive any treatment. Subsequently, gastrointestinal function was assessed by measuring fecal pellet production. Furthermore, ex vivo intestinal barrier and secretory function of the distal colon, proximal colon, and terminal ileum were quantified in Ussing chambers. In mice, single-day gavages did neither influence corticosterone levels nor gastrointestinal function. In mice exposed to multi-day gavages, corticosterone levels were slightly but significantly increased compared with controls after 10 days of treatment. Gastrointestinal motor function was altered, as evidenced by increased fecal pellet counts and a small increase in fecal water content. However, exposure to repeated gavages did not lead to detectable alterations in gastrointestinal barrier function as quantified by the paracellular flux of the probe 4 kDa FITC-dextran as well as transepithelial resistance measurements. Thus, the administration of drugs via single-day or multi-day orogastric gavages leads to no or minor stress in mice, respectively. In both cases, it does not hamper the study of the intestinal barrier function and therefore remains a valuable administration route in preclinical pharmacological research.NEW & NOTEWORTHY Exposure of mice to serial orogastric gavages over the course of 10 days leads to a small but significant increase in plasma corticosterone levels, indicating the presence of a limited amount of stress that is absent after a single-day treatment. This minor stress after multi-day gavages results in increased fecal pellet production and fecal water content in exposed compared with nontreated mice but does not affect the intestinal barrier function in the distal colon, proximal colon, or terminal ileum.

Corticotropin-releasing factor receptor agonists decrease interstitial cells of Cajal in murine colon

BACKGROUND

Peripheral corticotropin-releasing factor (CRF) has been reported to affect gastrointestinal motility through corticotropin-releasing factor receptor located in enteric nervous system (ENS), but less is known about of the relationship between peripheral CRF and interstitial cells of Cajal (ICC).

METHODS

Mice were intraperitoneally injected with CRF receptor agonists to determine their effects on colonic ICC. Chronic heterotypic stress (CHeS) was applied to mice to determine endogenous CRF-CRF receptor signaling on colonic ICC.

RESULTS

We found that stressin1, a selective CRF receptor 1 (CRF₁ ) agonist, significantly increased the expression of CRF₁ but had no effect on the expression of CRF₂ in the smooth muscles of murine colon. The protein expression of c-Kit, Anoctamin-1 (ANO1), and stem cell factor (SCF) in the colonic smooth muscles was significantly decreased in stressin1-treated mice. Accordingly, 2-(4-Chloro-2-methylphenoxy)-N'-(2-methoxybenzylidene) acetohydrazide (Ani 9), a selective ANO1 blocker, had a less significant inhibitory effect on CMMC in stressin1-treated mice compared to the saline-treated ones. Similarly, we also found that ICC and ANO1 were reduced in the colonic smooth muscles of mice by treatment with sauvagine (ip), a CRF₂ agonist. However, different with stressin1, sauvagine decreased the expression of CRF₂ besides increasing CRF₁ expression in the colonic smooth muscles. Similar results of CRF₁ and c-Kit expressions were also obtained from the colon of CHeS-treated mice.

CONCLUSION

All these results suggest that CRF may be involved in the abnormality of colonic motility through peripheral CRF₁ to decrease the number and function of ICC, which provides a potential target for treating stress-induced gastrointestinal motility disorder.

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.

Effects of two different acute and subchronic stressors on gastrointestinal transit in the rat: A radiographic analysis

BACKGROUND

The reaction to stress is an adaptive response necessary for survival. When stressors are repeated, the organism adapts, although these adaptive responses can become dysregulated and result in disease, causing gastrointestinal (GI) disorders. Radiographic methods allow the non-invasive study of how a given factor affects GI transit in the same animal at different time points. These methods have never been applied to study the consequences of stress on GI motor function and their dependency on time and stimulus. Therefore, our aim was to characterize, using radiographic techniques, the effect on GI transit of cold-restraint (CR) and forced swim (FS) stress applied acutely and subchronically in the rat.

METHODS

Male Wistar rats (260-330 g) were submitted to FS or CR stress, during 1 (acute) or 4 (subchronic) consecutive days. To study GI transit, radiographic methods were used. Radiographs were taken 0-24 h after barium intragastric administration on the 1st or 4th day of stress, which was applied 1 h after contrast.

RESULTS

Acute FS or CR slowed down gastric and small intestinal emptying but had opposite effects in the caecum: CR tended to accelerate barium transit and feces formation while FS tended to slow these parameters down. When the stimuli were applied subchronically, GI transit was not completely normalized in most of the studied parameters.

CONCLUSION AND INFERENCES

Mild stress alters GI transit differently depending on the nature of the stressor and its duration. Exposure to mild stressors should be considered as contributing factors to different functional GI disorders.

Otilonium Bromide treatment prevents nitrergic functional and morphological changes caused by chronic stress in the distal colon of a rat IBS model

Irritable bowel syndrome (IBS) is a highly prevalent gastrointestinal disorder characterized by periods of remission and exacerbation. Among the risk factors to develop IBS, psychosocial stress is widely acknowledged. The water avoidance stress repeatedly applied (rWAS) is considered effective to study IBS etio-pathogenesis. Otilonium bromide (OB), a drug with multiple mechanisms of action, is largely used to treat IBS patients. Orally administered, it concentrates in the large bowel and significantly ameliorates the IBS symptomatology. Presently, we tested whether rWAS rats developed neuro-muscular abnormalities in the distal colon and whether OB treatment prevented them. The investigation was focussed on the nitrergic neurotransmission by combining functional and morphological methodologies. The results confirm rWAS as reliable animal model to investigate the cellular mechanisms responsible for IBS: exposure to one-hour psychosocial stress for 10 days depressed muscle contractility and increased iNOS expression in myenteric neurons. OB treatment counteracted these effects. We hypothesize that these effects are due to the corticotropin-releasing factor (CRF) release, the main mediator of the psychosocial stress, followed by a CRF1receptor activation. OB, that was shown to prevent CRF1r activation, reasonably interrupted the cascade events that bring to the mechanical and immunohistochemical changes affecting rWAS rat colon.

Positive Correlation between nNOS and Stress-Activated Bowel Motility Is Confirmed by In Vivo HiBiT System

Neuronal nitric oxide synthase (nNOS) has various roles as a neurotransmitter. However, studies to date have produced insufficient data to fully support the correlation between nNOS and bowel motility. This study aimed to investigate the correlation between nNOS expression and gastrointestinal (GI) tract motility using a stress-induced neonatal maternal separation (NMS) mouse model. In this study, we generated a genetically modified mouse with the HiBiT sequence knock-in into the nNOS gene using CRISPR/Cas9 for analyzing accurate nNOS expression. nNOS expression was measured in the stomach, small intestine, large intestine, adrenal gland, and hypothalamus tissues after establishing the NMS model. The NMS model exhibited a significant increase in nNOS expression in large intestine, adrenal gland, and hypothalamus. Moreover, a significant positive correlation was observed between whole gastrointestinal transit time and the expression level of nNOS. We reasoned that NMS induced chronic stress and consequent nNOS activation in the hypothalamic-pituitary-adrenal (HPA) axis, and led to an excessive increase in intestinal motility in the lower GI tract. These results demonstrated that HiBiT is a sensitive and valuable tool for analyzing in vivo gene activation, and nNOS could be a biomarker of the HPA axis-linked lower intestinal tract dysfunction.

Colonic Hypermotility in a Rat Model of Irritable Bowel Syndrome Is Associated with Upregulation of TMEM16A in Myenteric Plexus

BACKGROUND

Irritable bowel syndrome (IBS) is a common disease with intestinal dysmotility, whose mechanism remains elusive. TMEM16A is a calcium-activated chloride channel (CaCC) involved in intestinal slow-wave generation.

AIMS

To investigate whether TMEM16A is involved in colonic dysmotility in IBS.

METHODS

A rat model of IBS was established by chronic water avoidance stress (WAS). Colonic pathological alterations were evaluated histologically, and intestinal motility was assessed by intestinal transit time (ITT) and fecal water content (FWC). Visceral sensitivity was determined by visceromotor response (VMR) to colorectal distension (CRD). TMEM16A expression was evaluated by RT-PCR, Western blot, and immunofluorescence. Colonic muscle strip contractility was measured by isometric transducers, and the effect of niflumic acid (NFA), a CaCC antagonist, on colonic motility was examined.

RESULTS

After 10 days of WAS exposure, ITT was decreased and FWC was elevated. Furthermore, VMR magnitude of WAS rats in response to CRD was significantly enhanced. Protein and mRNA levels of TMEM16A in colon were considerably increased after WAS. The percentage of TMEM16A-positive neurons in myenteric plexus (MP) of WAS rats was significantly higher than controls. Pharmacological blockade of TMEM16A activity by NFA considerably enhanced ITT, with concentration-dependent declines in FWC and VMR magnitude in NFA-treated rats. Further, spontaneous contraction of colonic strips of NFA-treated rats was significantly ameliorated in a concentration-dependent manner in vitro.

CONCLUSIONS

Upregulation of TMEM16A in MP neurons may play an important role in chronic stress-induced colonic hypermotility, making CaCC-blocking drugs a putatively effective treatment method for colonic hypermotility in IBS.