Corticotropin-releasing factor 1 receptor-mediated mechanisms inhibit colonic hypersensitivity in rats

Origin and Function of Monocytes in Inflammatory Bowel Disease

Inflammatory bowel disease (IBD), including Crohn's disease (CD) and ulcerative colitis (UC), is a chronic disease resulting from the interaction of various factors such as social elements, autoimmunity, genetics, and gut microbiota. Alarmingly, recent epidemiological data points to a surging incidence of IBD, underscoring an urgent imperative: to delineate the intricate mechanisms driving its onset. Such insights are paramount, not only for enhancing our comprehension of IBD pathogenesis but also for refining diagnostic and therapeutic paradigms. Monocytes, significant immune cells derived from the bone marrow, serve as precursors to macrophages (Mφs) and dendritic cells (DCs) in the inflammatory response of IBD. Within the IBD milieu, their role is twofold. On the one hand, monocytes are instrumental in precipitating the disease's progression. On the other hand, their differentiated offsprings, namely moMφs and moDCs, are conspicuously mobilized at inflammatory foci, manifesting either pro-inflammatory or anti-inflammatory actions. The phenotypic spectrum of these effector cells, intriguingly, is modulated by variables such as host genetics and the subtleties of the prevailing inflammatory microenvironment. Notwithstanding their significance, a palpable dearth exists in the literature concerning the roles and mechanisms of monocytes in IBD pathogenesis. This review endeavors to bridge this knowledge gap. It offers an exhaustive exploration of monocytes' origin, their developmental trajectory, and their differentiation dynamics during IBD. Furthermore, it delves into the functional ramifications of monocytes and their differentiated progenies throughout IBD's course. Through this lens, we aspire to furnish novel perspectives into IBD's etiology and potential therapeutic strategies.

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.

Stress-induced bladder hypersensitivity: Effect of corticotropin releasing factor receptors assessed by spinal neurophysiology and neurochemistry

Corticotropin releasing factor (CRF) receptors have been implicated in stress-induced hyperalgesia. The present study examined the role of CRF receptors Type 1&2 (CRFR1, CRFR2) in stress-induced bladder hyperalgesia in female rats by quantifying changes in receptor and agonist content following chronic (CFS, 7 daily episodes), acute (AFS, single episode) and control (NFS, no episodes) footshock protocols. ELISAs demonstrated that CFS lead to an increase in spinal thoracolumbar and lumbosacral spinal cord CRFR2 content and a decrease in lumbosacral spinal cord CRFR1 content. Content of the endogenous CRFR2 agonist, urocortin 2, was also increased in lumbosacral spinal cord and bladder tissues of CFS-pretreated rats, but urocortin 3 was decreased. Correlative single unit studies of lumbosacral dorsal horn neurons excited by bladder distension, in anesthetized rats that had undergone CFS, AFS or NFS protocols, used a before-after methodology with administration of a CRFR1 antagonist (antalarmin, 24 μg), CRFR2 antagonist (aSVG30, 12 μg) or normal saline topically to the exposed spinal cord following primary characterization. aSVG30 produced a reduction of neuronal responses evoked by bladder distension in CFS-pretreated rats but no statistically significant effects of aSVG30, antalarmin or vehicle were noted in other groups tested with the exception that antalarmin had an inhibitory effect on spontaneous activity in NFS-pretreated rats. The present findings are consistent with previous experiments using reflex responses to bladder distension as endpoints and further support a role for CRFR2-related mechanisms in stress-induced bladder hypersensitivity. This suggests CRFR2 antagonists may have efficacy in the treatment of bladder pain.

Superior control of inflammatory pain by corticotropin-releasing factor receptor 1 via opioid peptides in distinct pain-relevant brain areas

Background

Under inflammatory conditions, the activation of corticotropin-releasing factor (CRF) receptor has been shown to inhibit pain through opioid peptide release from immune cells or neurons. CRF’s effects on human and animal pain modulation depend, however, on the distribution of its receptor subtypes 1 and 2 (CRF-R1 and CRF-R2) along the neuraxis of pain transmission. The objective of this study is to investigate the respective role of each CRF receptor subtype on centrally administered CRF-induced antinociception during inflammatory pain.

Methods

The present study investigated the role of intracerebroventricular (i.c.v.) CRF receptor agonists on nociception and the contribution of cerebral CRF-R1 and/or CRF-R2 subtypes in an animal model of Freund’s complete adjuvant (FCA)-induced hind paw inflammation. Methods used included behavioral experiments, immunofluorescence confocal analysis, and reverse transcriptase-polymerase chain reaction.

Results

Intracerebroventricular, but systemically inactive, doses of CRF elicited potent, dose-dependent antinociceptive effects in inflammatory pain which were significantly antagonized by i.c.v. CRF-R1-selective antagonist NBI 27914 (by approximately 60%) but less by CRF-R2-selective antagonist K41498 (by only 20%). In line with these findings, i.c.v. administration of CRF-R1 agonist stressin I produced superior control of inflammatory pain over CRF-R2 agonist urocortin-2. Intriguingly, i.c.v. opioid antagonist naloxone significantly reversed the CRF as well as CRF-R1 agonist-elicited pain inhibition. Consistent with existing evidence of high CRF concentrations in brain areas such as the thalamus, hypothalamus, locus coeruleus, and periaqueductal gray following its i.c.v. administration, double-immunofluorescence confocal microscopy demonstrated primarily CRF-R1-positive neurons that expressed opioid peptides in these pain-relevant brain areas. Finally, PCR analysis confirmed the predominant expression of the CRF-R1 over CRF-R2 in representative brain areas such as the hypothalamus.

Conclusion

Taken together, these findings suggest that CRF-R1 in opioid-peptide-containing brain areas plays an important role in the modulation of inflammatory pain and may be a useful therapeutic target for inflammatory pain control.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-022-02498-8.

An enriched environment reduces chronic stress-induced visceral pain through modulating microglial activity in the central nucleus of the amygdala

Cognitive behavioral therapy (CBT) improves the quality of life for patients with brain-gut disorders; however, the underlying mechanisms of CBT remain to be explored. Previously, we showed that environmental enrichment (EE), an experimental paradigm that mirrors positive behavioral intervention, ameliorates chronic stress-induced visceral hypersensitivity in a rodent model via mechanisms involving altered activity in the central nucleus of amygdala (CeA). In the present study, we investigated whether microglia-mediated synaptic plasticity in the CeA is a potential mechanism underlying the protective effects of EE against stress-induced visceral hypersensitivity. We stereotaxically implanted corticosterone (CORT) micropellets onto the dorsal margin of the CeA shown previously to induce colonic hypersensitivity. Animals were housed in EE cages or standard cages for 14 days after CORT implantation. Visceral sensitivity was assessed via visceromotor behavioral response to colorectal distension. Microglial morphology, microglia-mediated synaptic engulfment, and the expression of synaptic pruning-related signals complement component 1q (C1q), complement component 3 (C3), and C3 receptor (C3R) were measured using immunofluorescence and RNAscope assay. We found that housing CORT implanted rats in EE cages for 14 days attenuated visceral hypersensitivity in both male and female rats as compared with control rats maintained in standard housing. EE reduced CORT-induced microglial remodeling and microglia-mediated synaptic pruning with reduced C1q and CR3, but not C3, expression. Our data suggest that exposure to EE is sufficient to ameliorate stress-induced visceral pain via reducing amygdala microglia-modulated neuronal plasticity.NEW & NOTEWORTHY Clinical studies show that cognitive behavioral therapy (CBT) is effective in ameliorating visceral pain in patient with irritable bowel syndrome (IBS), yet the underlying mechanisms remain unexplored. By using environmental enrichment (EE), an experimental paradigm that mirrors positive behavioral intervention, we demonstrated that microglia-mediated synaptic plasticity in the CeA explains, plays a role, at least in part, in the positive effects of EE to reduce visceral hypersensitivity.

Corticotropin-releasing factor receptor 1 (CRF-R1) antagonists: Promising agents to prevent visceral hypersensitivity in irritable bowel syndrome

Corticotropin-releasing factor (CRF) is a 41-amino acid polypeptide that coordinates the endocrine system, autonomic nervous system, immune system, and physiological behavior. CRF is a signaling regulator in the neuro-endocrine-immune (NEI) network that mediates visceral hypersensitivity. Rodent models to simulate changes in intestinal motility similar to those reported in the irritable bowel syndrome (IBS), demonstrate that the CRF receptor 1 (CRF-R1) mediates intestinal hypersensitivity under many conditions. However, the translation of preclinical studies into clinical trials has not been successful possibly due to the lack of sufficient understanding of the multiple variants of CRF-R1 and CRF-R1 antagonists. Investigating the sites of action of central and peripheral CRF is critical for accelerating the translation from preclinical to clinical studies.

Uncovering the pathophysiology of irritable bowel syndrome by exploring the gut-brain axis: a narrative review

Objective

To improve the pathophysiological understanding of irritable bowel syndrome (IBS) by exploring the gut-brain axis.

Background

Disorders of gut-brain interaction (DGBIs) are gastrointestinal (GI) disorders in which alterations in bowel functions occur. IBS, which is one of the most studied DGBIs, is linked with abdominal distress or pain without obvious structural or biochemical anomalies.

Methods

The etiology of IBS has not been clearly described but is known to be multifactorial, involving GI motility changes, post-infectious reactivity, visceral hypersensitivity, gut-brain interactions, microbiota dysbiosis, small intestinal bacterial overgrowth, food sensitivity, carbohydrate malabsorption, and intestinal inflammation.

Conclusions

One of the main features of IBS is the occurrence of structural and functional disruptions in the gut-brain axis, which alter reflective and perceptual nervous system reactions. Herein, we provide a brief summary of this topic. Furthermore, we discuss animal models, which are important in the study of IBS, especially as it is linked with stressors. These animal models cannot fully represent the human disease but serve as important tools for understanding this complicated disorder. In the future, technologies, such as organ-on-a-chip models and metabolomics, will provide novel information regarding the pathophysiology of IBS, which will play an important role in treatment development. Finally, we take a brief glance at how acupuncture treatments may hold potential for patients with IBS.

Amygdalar Corticotropin-Releasing Factor Signaling Is Required for Later-Life Behavioral Dysfunction Following Neonatal Pain

Neonatal pain such as that experienced by infants in the neonatal intensive care unit is known to produce later-life dysfunction including heightened pain sensitivity and anxiety, although the mechanisms remain unclear. Both chronic pain and stress in adult organisms are known to influence the corticotropin-releasing factor (CRF) system in the Central Nucleus of the Amygdala, making this system a likely candidate for changes following neonatal trauma. To examine this, neonatal rats were subjected to daily pain, non-painful handling or left undisturbed for the first week of life. Beginning on postnatal day, 24 male and female rats were subjected to a 4-day fear conditioning and sensory testing protocol. Some subjects received intra-amygdalar administration of either Vehicle, the CRF receptor 1 (CRF₁) receptor antagonist Antalarmin, or the CRF receptor 2 (CRF₂) receptor antagonist Astressin 2B prior to fear conditioning and somatosensory testing, while others had tissue collected following fear conditioning and CRF expression in the CeA and BLA was assessed using fluorescent in situ hybridization. CRF₁ antagonism attenuated fear-induced hypersensitivity in neonatal pain and handled rats, while CRF₂ antagonism produced a general antinociception. In addition, neonatal pain and handling produced a lateralized sex-dependent decrease in CRF expression, with males showing a diminished number of CRF-expressing cells in the right CeA and females showing a similar reduction in the number of CRF-expressing cells in the left BLA compared to undisturbed controls. These data show that the amygdalar CRF system is a likely target for alleviating dysfunction produced by early life trauma and that this system continues to play a major role in the lasting effects of such trauma into the juvenile stage of development.

Central regulatory mechanisms of visceral sensation in response to colonic distension with special reference to brain orexin

Visceral hypersensitivity is a major pathophysiology in irritable bowel syndrome (IBS). Although brain-gut interaction is considered to be involved in the regulation of visceral sensation, little had been known how brain controls visceral sensation. To improve therapeutic strategy in IBS, we should develop a novel approach to control visceral hypersensitivity. Here, we summarized recent data on central control of visceral sensation by neuropeptides in rats. Orexin, ghrelin or oxytocin in the brain is capable of inducing visceral antinociception. Dopamine, cannabinoid, adenosine, serotonin or opioid in the central nervous system (CNS) plays a role in the visceral hyposensitivity. Central ghrelin, levodopa or morphine could induce visceral antinociception via the orexinergic signaling. Orexin induces visceral antinociception through dopamine, cannabinoid, adenosine or oxytocin. Orexin nerve fibers are identified widely throughout the CNS and orexins are implicated in a number of functions. With regard to gastrointestinal functions, in addition to its visceral antinociception, orexin acts centrally to stimulate gastrointestinal motility and improve intestinal barrier function. Brain orexin is also involved in regulation of sleep/awake cycle and anti-depressive action. From these evidence, we would like to make a hypothesis that decreased orexin signaling in the brain may play a role in the pathophysiology in a part of patients with IBS who are frequently accompanied with sleep disturbance, depressive state and disturbed gut functions such as gut motility disturbance, leaky gut and visceral hypersensitivity.

Overexpression of corticotropin-releasing factor in intestinal mucosal eosinophils is associated with clinical severity in Diarrhea-Predominant Irritable Bowel Syndrome

Corticotropin-releasing factor (CRF) has been identified in intestinal mucosal eosinophils and associated with psychological stress and gut dysfunction. Irritable bowel syndrome (IBS) is commonly characterized by altered intestinal motility, immune activation, and increased gut barrier permeability along with heightened susceptibility to psychosocial stress. Despite intensive research, the role of mucosal eosinophils in stress-associated gut dysfunction remains uncertain. In this study, we evaluated eosinophil activation profile and CRF content in the jejunal mucosa of diarrhea-predominant IBS (IBS-D) and healthy controls (HC) by gene/protein expression and transmission electron microscopy. We also explored the association between intestinal eosinophil CRF and chronic stress, and the potential mechanisms underlying the stress response by assessing eosinophil response to neuropeptides. We found that mucosal eosinophils displayed higher degranulation profile in IBS-D as compared to HC, with increased content of CRF in the cytoplasmic granules, which significantly correlated with IBS clinical severity, life stress background and depression. Eosinophils responded to substance P and carbachol by increasing secretory activity and CRF synthesis and release, without promoting pro-inflammatory activity, a profile similar to that found in mucosal eosinophils from IBS-D. Collectively, our results suggest that intestinal mucosal eosinophils are potential contributors to stress-mediated gut dysfunction through CRF production and release.

Pharmacological evaluation of a novel corticotropin-releasing factor 1 receptor antagonist T-3047928 in stress-induced animal models in a comparison with alosetron

BACKGROUND

The major symptoms of irritable bowel syndrome (IBS) are changes in bowel habits and abdominal pain. Psychological stress is the major pathophysiological components of IBS. Corticotropin-releasing factor (CRF) is a well-known integrator in response to psychological stress. In this study, a novel CRF1 receptor antagonist T-3047928 was evaluated in stress-induced IBS models of rats to explore its potency for IBS.

METHODS

Plasma adrenocorticotropic hormone (ACTH) levels after intravenous oCRH challenge were measured as a pharmacodynamic marker. Efficacies of oral T-3047928 were compared with oral alosetron, a 5-HT3 antagonist, on conditioning fear stress (CFS)-induced defecation, restraint stress (RS)-induced acute visceral pain, specific alteration of rhythm in temperature (SART) stress-induced chronic visceral pain, and normal defecation.

RESULTS

T-3047928 (1-10 mg/kg, p.o.) demonstrated a dose-dependent inhibition on oCRH-induced ACTH secretion. In disease models, T-3047928 suppressed fecal pellet output induced by CFS and improved both acute and chronic visceral hypersensitivity induced by RS and SART stress, respectively. Alosetron was also efficacious in stress-induced defecation and visceral pain models at 1 and 10 mg/kg, respectively. Alosetron, however, also suppressed normal defecation at lower those. On the other hand, T-3047928 did not change normal defecation even at higher dose than those in disease models.

CONCLUSION

T-3047928 is an orally active CRF1 antagonist that demonstrated potent inhibitory effects in stress-associated IBS models with no effect on normal defecation. Therefore, it is suggested that T-3047928 may have a potency as a novel option for IBS-D therapy with minimal constipation risk.

Potential neuro-immune therapeutic targets in irritable bowel syndrome

Irritable bowel syndrome (IBS) is a functional gastrointestinal (GI) disorder characterized by recurring abdominal pain and disturbed bowel habits. The aetiology of IBS is unknown but there is evidence that genetic, environmental and immunological factors together contribute to the development of the disease. Current treatment of IBS includes lifestyle and dietary interventions, laxatives or antimotility drugs, probiotics, antispasmodics and antidepressant medication. The gut-brain axis comprises the central nervous system, the hypothalamic pituitary axis, the autonomic nervous system and the enteric nervous system. Within the intestinal mucosa there are close connections between immune cells and nerve fibres of the enteric nervous system, and signalling between, for example, mast cells and nerves has shown to be of great importance during GI disorders such as IBS. Communication between the gut and the brain is most importantly routed via the vagus nerve, where signals are transmitted by neuropeptides. It is evident that IBS is a disease of a gut-brain axis dysregulation, involving altered signalling between immune cells and neurotransmitters. In this review, we analyse the most novel and distinct neuro-immune interactions within the IBS mucosa in association with already existing and potential therapeutic targets.

Amygdala, neuropeptides, and chronic pain-related affective behaviors

Neuropeptides play important modulatory roles throughout the nervous system, functioning as direct effectors or as interacting partners with other neuropeptide and neurotransmitter systems. Limbic brain areas involved in learning, memory and emotions are particularly rich in neuropeptides. This review will focus on the amygdala, a limbic region that plays a key role in emotional-affective behaviors and pain modulation. The amygdala is comprised of different nuclei; the basolateral (BLA) and central (CeA) nuclei and in between, the intercalated cells (ITC), have been linked to pain-related functions. A wide range of neuropeptides are found in the amygdala, particularly in the CeA, but this review will discuss those neuropeptides that have been explored for their role in pain modulation. Calcitonin gene-related peptide (CGRP) is a key peptide in the afferent nociceptive pathway from the parabrachial area and mediates excitatory drive of CeA neurons. CeA neurons containing corticotropin releasing factor (CRF) and/or somatostatin (SOM) are a source of long-range projections and serve major output functions, but CRF also acts locally to excite neurons in the CeA and BLA. Neuropeptide S (NPS) is associated with inhibitory ITC neurons that gate amygdala output. Oxytocin and vasopressin exert opposite (inhibitory and excitatory, respectively) effects on amygdala output. The opioid system of mu, delta and kappa receptors (MOR, DOR, KOR) and their peptide ligands (β-endorphin, enkephalin, dynorphin) have complex and partially opposing effects on amygdala function. Neuropeptides therefore serve as valuable targets to regulate amygdala function in pain conditions. This article is part of the special issue on Neuropeptides.

Animal Models for Functional Gastrointestinal Disorders

Functional gastrointestinal disorders (FGID), such as functional dyspepsia (FD) and irritable bowel syndrome (IBS) are characterized by chronic abdominal symptoms in the absence of an organic, metabolic or systemic cause that readily explains these complaints. Their pathophysiology is still not fully elucidated and animal models have been of great value to improve the understanding of the complex biological mechanisms. Over the last decades, many animal models have been developed to further unravel FGID pathophysiology and test drug efficacy. In the first part of this review, we focus on stress-related models, starting with the different perinatal stress models, including the stress of the dam, followed by a discussion on neonatal stress such as the maternal separation model. We also describe the most commonly used stress models in adult animals which brought valuable insights on the brain-gut axis in stress-related disorders. In the second part, we focus more on models studying peripheral, i.e., gastrointestinal, mechanisms, either induced by an infection or another inflammatory trigger. In this section, we also introduce more recent models developed around food-related metabolic disorders or food hypersensitivity and allergy. Finally, we introduce models mimicking FGID as a secondary effect of medical interventions and spontaneous models sharing characteristics of GI and anxiety-related disorders. The latter are powerful models for brain-gut axis dysfunction and bring new insights about FGID and their comorbidities such as anxiety and depression.

Evidence for Somatic Hypersensitivity in Veterans With Gulf War Illness and Gastrointestinal Symptoms

INTRODUCTION

Over 25% of Persian Gulf War (PGW) veterans with Gulf War Illness (GWI) (chronic health symptoms of undetermined etiology) developed gastrointestinal (GI) (diarrhea and abdominal pain) and other somatic symptoms.

OBJECTIVES

Our study objective was to determine if veterans with GWI and GI symptoms exhibit heightened patterns of somatic pain perception (hypersensitivity) across nociceptive stimuli modalities.

METHODS

Participants were previously deployed GW Veterans with GWI and GI symptoms (n=53); veterans with GWI without GI symptom (n=47); and veteran controls (n=38). We determined pain thresholds for contact thermal, cold pressor, and ischemic stimuli.

RESULTS

Veterans with GWI and GI symptoms showed lower pain thresholds (P<0.001) for each stimulus. There was also overlap of somatic hypersensitivities among veterans with GI symptoms with 20% having hypersensitivity to all 3 somatic stimuli. Veterans with GWI and GI symptoms also showed a significant correlation between mechanical visual analog scale abdominal pain ratings and heat pain threshold, cold pressor threshold, and ischemic pain threshold/tolerance.

DISCUSSION

Our findings show that there is widespread somatic hypersensitivity in veterans with GWI/GI symptoms that is positively correlated with abdominal pain ratings. In addition, veterans with somatic hypersensitivity that overlap have the greatest number of extraintestinal symptoms. These findings may have a translational benefit: strategies for developing more effective therapeutic agents that can reduce and/or prevent somatic and GI symptoms in veterans deployed to future military conflicts.

Visceral Pain

Most of us live blissfully unaware of the orchestrated function that our internal organs conduct. When this peace is interrupted, it is often by routine sensations of hunger and urge. However, for >20% of the global population, chronic visceral pain is an unpleasant and often excruciating reminder of the existence of our internal organs. In many cases, there is no obvious underlying pathological cause of the pain. Accordingly, chronic visceral pain is debilitating, reduces the quality of life of sufferers, and has large concomitant socioeconomic costs. In this review, we highlight key mechanisms underlying chronic abdominal and pelvic pain associated with functional and inflammatory disorders of the gastrointestinal and urinary tracts. This includes how the colon and bladder are innervated by specialized subclasses of spinal afferents, how these afferents become sensitized in highly dynamic signaling environments, and the subsequent development of neuroplasticity within visceral pain pathways. We also highlight key contributing factors, including alterations in commensal bacteria, altered mucosal permeability, epithelial interactions with afferent nerves, alterations in immune or stress responses, and cross talk between these two adjacent organs.

Brain corticotropin-releasing factor signaling: Involvement in acute stress-induced visceral analgesia in male rats

BACKGROUND

Water avoidance stress (WAS) induces a naloxone-independent visceral analgesia in male rats under non-invasive conditions of monitoring. The objective of the study was to examine the role of brain CRF signaling in acute stress-induced visceral analgesia (SIVA).

METHODS

Adult male Sprague-Dawley rats were chronically implanted with an intracerebroventricular (ICV) cannula. The visceromotor response (VMR) to graded phasic colorectal distension (CRD: 10, 20, 40, 60 mm Hg, 20 seconds, 4 minutes intervals) was monitored using manometry. The VMR to a first CRD (baseline) was recorded 5 minutes after an ICV saline injection, followed 1 hour later by ICV injection of either CRF (30, 100, or 300 ng and 1, 3, or 5 μg/rat) or saline and a second CRD, 5 minutes later. Receptor antagonists against CRF₁ /CRF₂ (astressin-B, 30 μg/rat), CRF₂ (astressin₂ -B, 10 μg/rat), oxytocin (tocinoic acid, 20 μg/rat), or vehicle were injected ICV 5 minutes before CRF (300 ng/rat, ICV) or 15 minutes before WAS (1 hour).

KEY RESULTS

ICV CRF (100 and 300 ng) reduced the VMR to CRD at 60 mm Hg by -36.6% ± 6.8% and -48.7% ± 11.7%, respectively, vs baseline (P < 0.001), while other doses had no effect and IP CRF (10 µg/kg) induced visceral hyperalgesia. Astressin-B and tocinoic acid injected ICV induced hyperalgesia and prevented the analgesic effect of ICV CRF (300 ng/rat) and WAS, while astressin₂ -B only blocked WAS-induced SIVA.

CONCLUSIONS & INFERENCES

These data support a role for brain CRF signaling via CRF₂ in SIVA in a model of WAS and CRD likely mediated by the activation of brain oxytocin pathway.

Brain and Gut CRF Signaling: Biological Actions and Role in the Gastrointestinal Tract

BACKGROUND

Corticotropin-releasing factor (CRF) pathways coordinate behavioral, endocrine, autonomic and visceral responses to stress. Convergent anatomical, molecular, pharmacological and functional experimental evidence supports a key role of brain CRF receptor (CRF-R) signaling in stress-related alterations of gastrointestinal functions. These include the inhibition of gastric acid secretion and gastric-small intestinal transit, stimulation of colonic enteric nervous system and secretorymotor function, increase intestinal permeability, and visceral hypersensitivity. Brain sites of CRF actions to alter gut motility encompass the paraventricular nucleus of the hypothalamus, locus coeruleus complex and the dorsal motor nucleus while those modulating visceral pain are localized in the hippocampus and central amygdala. Brain CRF actions are mediated through the autonomic nervous system (decreased gastric vagal and increased sacral parasympathetic and sympathetic activities). The activation of brain CRF-R2 subtype inhibits gastric motor function while CRF-R1 stimulates colonic secretomotor function and induces visceral hypersensitivity. CRF signaling is also located within the gut where CRF-R1 activates colonic myenteric neurons, mucosal cells secreting serotonin, mucus, prostaglandin E2, induces mast cell degranulation, enhances mucosal permeability and propulsive motor functions and induces visceral hyperalgesia in animals and humans. CRF-R1 antagonists prevent CRF- and stressrelated gut alterations in rodents while not influencing basal state.

DISCUSSION

These preclinical studies contrast with the limited clinical positive outcome of CRF-R1 antagonists to alleviate stress-sensitive functional bowel diseases such as irritable bowel syndrome.

CONCLUSION

The translational potential of CRF-R1 antagonists in gut diseases will require additional studies directed to novel anti-CRF therapies and the neurobiology of brain-gut interactions under chronic stress.

Mechanisms of Stress-induced Visceral Pain

Evidence suggests that long-term stress facilitates visceral pain through sensitization of pain pathways and promotes chronic visceral pain disorders such as the irritable bowel syndrome (IBS). This review will describe the importance of stress in exacerbating IBS-induced abdominal pain. Additionally, we will briefly review our understanding of the activation of the hypothalamic-pituitary-adrenal axis by both chronic adult stress and following early life stress in the pathogenesis of IBS. The review will focus on the glucocorticoid receptor and corticotropin-releasing hormone-mediated mechanisms in the amygdala involved in stress-induced visceral hypersensitivity. One potential mechanism underlying persistent effects of stress on visceral sensitivity could be epigenetic modulation of gene expression. While there are relatively few studies examining epigenetically mediated mechanisms involved in stress-induced visceral nociception, alterations in DNA methylation and histone acetylation patterns within the brain, have been linked to alterations in nociceptive signaling via increased expression of pro-nociceptive neurotransmitters. This review will discuss the latest studies investigating the long-term effects of stress on visceral sensitivity. Additionally, we will critically review the importance of experimental models of adult stress and early life stress in enhancing our understanding of the basic molecular mechanisms of nociceptive processing.

Involvement of Corticotropin-Releasing Factor and Receptors in Immune Cells in Irritable Bowel Syndrome

Irritable bowel syndrome (IBS) is a common functional gastrointestinal disorder defined by ROME IV criteria as pain in the lower abdominal region, which is associated with altered bowel habit or defecation. The underlying mechanism of IBS is not completely understood. IBS seems to be a product of interactions between various factors with genetics, dietary/intestinal microbiota, low-grade inflammation, and stress playing a key role in the pathogenesis of this disease. The crosstalk between the immune system and stress in IBS mechanism is increasingly recognized. Corticotropin-releasing factor (CRF), a major mediator in the stress response, is involved in altered function in GI, including inflammatory processes, colonic transit time, contractile activity, defecation pattern, pain threshold, mucosal secretory function, and barrier functions. This mini review focuses on the recently establish local GI-CRF system, its involvement in modulating the immune response in IBS, and summarizes current IBS animal models and mapping of CRF, CRFR1, and CRFR2 expression in colon tissues. CRF and receptors might be a key molecule involving the immune and movement function via brain-gut axis in IBS.

Psychotropic Effects of an Alcoholic Extract from the Leaves of Albizia zygia (Leguminosae-Mimosoideae)

Background

Albizia zygia is used in Ghanaian traditional medicine for the management of mental disorders. The present study tested the hypothesis that an extract of the leaves of Albizia zygia (AZE) may possess antipsychotic and antidepressant properties.

Method

The novelty- and apomorphine-induced locomotor and rearing behaviours of AZE in mice were explored in an open-field observational test system. The effects of AZE in apomorphine-induced cage climbing test, extract-induced catalepsy, and haloperidol-induced catalepsy on mice were also investigated. Lastly, the forced swimming and tail suspension tests in mice were employed to screen the possible antidepressant effects of AZE.

Results

AZE (100-3000 mg/kg) showed signs of central nervous system (CNS) depression under observation, with no lethality, 24 h after treatment in mice. AZE (100-1000 mg/kg) produced a significant decrease in the frequency of novelty- and apomorphine-induced locomotor activities in mice. The extract also significantly decreased the frequency and duration of apomorphine-induced climbing activities in mice. AZE, while failing to produce any cataleptic event in naïve mice, significantly enhanced haloperidol-induced catalepsy at a dose of 1000 mg/kg. However, AZE did not produce any significant antidepressant effects in the test models employed.

Conclusion

The extract of Albizia zygia exhibited an antipsychotic-like activity in mice.

Toll-Like Receptor 4 in Paraventricular Nucleus Mediates Visceral Hypersensitivity Induced by Maternal Separation

Neonatal maternal separation (MS) is a major early life stress that increases the risk of emotional disorders, visceral pain perception and other brain dysfunction. Elevation of toll-like receptor 4 (TLR4) signaling in the paraventricular nucleus (PVN) precipitates early life colorectal distension (CRD)-induced visceral hypersensitivity and pain in adulthood. The present study aimed to investigate the role of TLR4 signaling in the pathogenesis of postnatal MS-induced visceral hypersensitivity and pain during adulthood. The TLR4 gene was selectively knocked out in C57BL/10ScSn mice (Tlr4^-/-). MS was developed by housing the offspring alone for 6 h daily from postnatal day 2 to day 15. Visceral hypersensitivity and pain were assessed in adulthood. Tlr4^+/+, but not Tlr4^-/-, mice that had experienced neonatal MS showed chronic visceral hypersensitivity and pain. TLR4 immunoreactivity was observed predominately in microglia in the PVN, and MS was associated with an increase in the expression of protein and/or mRNA levels of TLR4, corticotropin-releasing factor (CRF), CRF receptor 1 (CRFR1), tumor necrosis factor-α, and interleukin-1β in Tlr4^+/+ mice. These alterations were not observed in Tlr4^-/- mice. Local administration of lipopolysaccharide, a TLR4 agonist, into the lateral cerebral ventricle elicited visceral hypersensitivity and TLR4 mRNA expression in the PVN, which could be prevented by NBI-35965, an antagonist to CRFR1. The present results indicate that neonatal MS induces a sensitization and upregulation of microglial TLR4 signaling activity, which facilitates the neighboring CRF neuronal activity and, eventually, precipitates visceral hypersensitivity in adulthood. Highlights (1)Neonatal MS does not induce chronic visceral hypersensitivity and pain in Tlr4^-/- mice.(2)Neonatal MS increases the expression of TLR4 mRNA, CRF protein and mRNA, CRFR1 protein, TNF-α protein, and IL-1β protein in Tlr4^+/+ mice.(3)TLR4 agonist LPS (i.c.v.) elicits visceral hypersensitivity and TLR4 mRNA expression in the PVN.

Selective corticotropin-releasing factor 1 receptor antagonist E2508 reduces restraint stress-induced defecation and visceral pain in rat models

N-Cyclopropylmethyl-7-(2,6-dimethoxy-4-methoxymethylphenyl)-2-ethyl-N-(tetrahydro-2H-pyran-4-ylmethyl)pyrazolo[1,5-a]pyridin-3-amine tosylate (E2508) is a newly discovered selective corticotropin-releasing factor 1 receptor antagonist. Here, we investigated the effects of E2508 on wrap restraint stress-induced defecation and visceral pain in rats. Oral pretreatment with E2508 dose-dependently decreased stool weights after 20min wrap restraint stress and significant effects were observed at doses of 30 and 100mg/kg. However, E2508 did not affect basal defecation at doses up to 100mg/kg. In contrast, alosetron, a 5-HT₃ receptor antagonist, decreased both wrap restraint stress-induced and basal stool output at a dose of 0.1mg/kg. In a rat visceral pain model, subcutaneous injections of both E2508 (0.01 and 0.1mg/kg) and alosetron (0.001 and 0.01mg/kg) significantly decreased the number of abdominal muscle contractions induced by colonic distention, suggesting these drugs reduced visceral pain. Together, these results demonstrate E2508 has the potential to be an effective therapy for the treatment of irritable bowel syndrome with a lower risk of adverse events such as constipation compared with the current clinically used 5-HT₃ receptor antagonist.

Neuroimmune Cross Talk in the Gut. Neuroendocrine and neuroimmune pathways contribute to the pathophysiology of irritable bowel syndrome

Irritable bowel syndrome (IBS) is a common disorder characterized by recurrent abdominal pain, bloating, and disturbed bowel habit, symptoms that impact the quality of life of sufferers. The pathophysiological changes underlying this multifactorial condition are complex and include increased sensitivity to luminal and mucosal factors, resulting in altered colonic transit and visceral pain. Moreover, dysfunctional communication in the bidirectional signaling axis between the brain and the gut, which involves efferent and afferent branches of the peripheral nervous system, circulating endocrine hormones, and local paracrine and neurocrine factors, including immune and perhaps even microbial signaling molecules, has a role to play in this disorder. This minireview will examine recent advances in our understanding of the pathophysiology of IBS and assess how cross talk between hormones, immune, and microbe-derived factors and their neuromodulatory effects on peripheral nerves may underlie IBS symptomatology.

Neonatal maternal separation increases susceptibility to experimental colitis and acute stress exposure in male mice

Experiencing early life stress can result in maladjusted stress response via dysregulation of the hypothalamic-pituitary-adrenal axis and serves as a risk factor for developing chronic pelvic pain disorders. We investigated whether neonatal maternal separation (NMS) would increase susceptibility to experimental colitis or exposure to acute or chronic stress. Male mice underwent NMS from postnatal day 1-21 and as adults were assessed for open field behavior, hindpaw sensitivity, and visceromotor response (VMR) to colorectal distension (CRD). VMR was also measured before and after treatment with intracolonic trinitrobenzene sulfonic acid (TNBS) or exposure to acute or chronic water avoidance stress (WAS). Myeloperoxidase (MPO) activity, proinflammatory gene and corticotropin-releasing factor (CRF) receptor expression were measured in distal colon. Baseline VMR was not affected by NMS, but undergoing CRD increased anxiety-like behaviors and mechanical hindpaw sensitivity of NMS mice. Treatment with TNBS dose-dependently decreased body weight and survival only in NMS mice. Following TNBS treatment, IL-6 and artemin mRNA levels were decreased in the distal colon of NMS mice, despite increased MPO activity. A single WAS exposure increased VMR during CRD in NMS mice and increased IL-6 mRNA and CRF₂ protein levels in the distal colon of naïve mice, whereas CRF₂ protein levels were heightened in NMS colon both at baseline and post-WAS exposure. Taken together, these results suggest that NMS in mice disrupts inflammatory- and stress-induced gene expression in the colon, potentially contributing towards an exaggerated response to specific stressors later in life.

Stress and the Microbiota-Gut-Brain Axis in Visceral Pain: Relevance to Irritable Bowel Syndrome

Visceral pain is a global term used to describe pain originating from the internal organs of the body, which affects a significant proportion of the population and is a common feature of functional gastrointestinal disorders (FGIDs) such as irritable bowel syndrome (IBS). While IBS is multifactorial, with no single etiology to completely explain the disorder, many patients also experience comorbid behavioral disorders, such as anxiety or depression; thus, IBS is described as a disorder of the gut-brain axis. Stress is implicated in the development and exacerbation of visceral pain disorders. Chronic stress can modify central pain circuitry, as well as change motility and permeability throughout the gastrointestinal (GI) tract. More recently, the role of the gut microbiota in the bidirectional communication along the gut-brain axis, and subsequent changes in behavior, has emerged. Thus, stress and the gut microbiota can interact through complementary or opposing factors to influence visceral nociceptive behaviors. This review will highlight the evidence by which stress and the gut microbiota interact in the regulation of visceral nociception. We will focus on the influence of stress on the microbiota and the mechanisms by which microbiota can affect the stress response and behavioral outcomes with an emphasis on visceral pain.

The Pharmacology of Visceral Pain

Visceral pain describes pain emanating from the internal thoracic, pelvic, or abdominal organs. Unlike somatic pain, visceral pain is generally vague, poorly localized, and characterized by hypersensitivity to a stimulus such as organ distension. While current therapeutics provides some relief from somatic pain, drugs used for treatment of chronic visceral pain are typically less efficacious and limited by multiple adverse side effects. Thus, the treatment of visceral pain represents a major unmet medical need. Further, more basic research into the physiology and pathophysiology of visceral pain is needed to provide novel targets for future drug development. In concert with chronic visceral pain, there is a high comorbidity with stress-related psychiatric disorders including anxiety and depression. The mechanisms linking visceral pain with these overlapping comorbidities remain to be elucidated. However, persistent stress facilitates pain perception and sensitizes pain pathways, leading to a feed-forward cycle promoting chronic visceral pain disorders. We will focus on stress-induced exacerbation of chronic visceral pain and provide supporting evidence that centrally acting drugs targeting the pain and stress-responsive brain regions may represent a valid target for the development of novel and effective therapeutics.

Gut pain & visceral hypersensitivity

Visceral pain is a highly complex entity whose experience is variable in health and disease. It can occur in patients with organic disease and also in those without any readily identifiable structural or biochemical abnormality such as in the functional gastrointestinal disorders (FGID). Despite considerable progress in our understanding of the culpable underlying mechanisms significant knowledge gaps remain, representing a significant unmet need in gastroenterology. A key, but not universal, pathological feature is that patients with FGID often display heightened sensitivity to experimental gut stimulation, termed visceral hypersensitivity. A plethora of factors have been proposed to account for this epiphenomenon including peripheral sensitization, central sensitization, aberrant central processing, genetic, psychological and abnormalities within the stress responsive systems. Further research is needed, bringing together complementary research themes from a diverse array of academic disciplines ranging from gastroenterology to nociceptive physiology to functional neuro-imaging, to address this unmet need.

Synthesis of new thiazolo[4,5-d]pyrimidines as Corticotropin releasing factor modulators

Corticotropin-releasing factor (CRF) is a neurohormone that plays a crucial role in integrating the body's overall response to stress. It appears necessary and sufficient for the organism to mount functional, physiological and endocrine responses to stressors. CRF is released in response to various triggers such as chronic stress. The role of CRF and its involvement in these neurological disorders suggest that new drugs that can target the CRF function or bind to its receptors may represent a new development of neuropsychiatric medicines to treat various stress-related disorders including depression, anxiety and addictive disorders. Based on pharmacophore of the CRF1 receptor antagonists, a new series of thiazolo[4,5-d] pyrimidines were synthesized as Corticotropin-releasing factor (CRF) receptor modulators and the prepared compounds carry groups shown to produce optimum binding affinity to CRF receptors. Twenty two compounds were evaluated for their CRF1 receptor binding affinity in HEK 293 cell lines and two compounds 5o and 5s showed approximately 25% binding affinity to CRF1 receptors. Selected compounds (5c and 5f) were also evaluated for their effect on expression of genes associated with depression and anxiety disorders such as CRF1, CREB1, MAO-A, SERT, NPY, DatSLC6a3, and DBH and significant upregulation of CRF1 mRNA has been observed with compound 5c.

Corticotropin-releasing factor receptor type 1 and type 2 interaction in irritable bowel syndrome

Irritable bowel syndrome (IBS) displays chronic abdominal pain or discomfort with altered defecation, and stress-induced altered gut motility and visceral sensation play an important role in the pathophysiology. Corticotropin-releasing factor (CRF) is a main mediator of stress responses and mediates these gastrointestinal functional changes. CRF in brain and periphery acts through two subtype receptors such as CRF receptor type 1 (CRF1) and type 2 (CRF2), and activating CRF1 exclusively stimulates colonic motor function and induces visceral hypersensitivity. Meanwhile, several recent studies have demonstrated that CRF2 has a counter regulatory action against CRF1, which may imply that CRF2 inhibits stress response induced by CRF1 in order to prevent it from going into an overdrive state. Colonic contractility and sensation may be explained by the state of the intensity of CRF1 signaling. CRF2 signaling may play a role in CRF1-triggered enhanced colonic functions through modulation of CRF1 activity. Blocking CRF2 further enhances CRF-induced stimulation of colonic contractility and activating CRF2 inhibits stress-induced visceral sensitization. Therefore, we proposed the hypothesis, i.e., balance theory of CRF1 and CRF2 signaling as follows. Both CRF receptors may be activated simultaneously and the signaling balance of CRF1 and CRF2 may determine the functional changes of gastrointestinal tract induced by stress. CRF signaling balance might be abnormally shifted toward CRF1, leading to enhanced colonic motility and visceral sensitization in IBS. This theory may lead to understanding the pathophysiology and provide the novel therapeutic options targeting altered signaling balance of CRF1 and CRF2 in IBS.

Soluble mediators in plasma from irritable bowel syndrome patients excite rat submucosal neurons

BACKGROUND

Episodic bouts of abdominal pain and altered bowel habit are characteristic of irritable bowel syndrome (IBS). Although a comprehensive understanding of IBS pathophysiology remains elusive, support is growing for a primary role for immune activation in disease severity as evidenced by altered cytokine profiles in IBS plasma. Additionally, aberrant stimulation of the stress axis is likely to result in altered plasma constituents.

METHODS

Whole-mount preparations of submucosal plexus from adult male Sprague Dawley rats were exposed to plasma from IBS patients and healthy controls. Ratiometric calcium imaging recordings were used to measure changes in intracellular calcium ([Ca(2+)]i) as a marker of neuronal excitability.

KEY RESULTS

IBS plasma stimulated a robust increase in [Ca(2+)]i (0.09 ± 0.02) whereas plasma from healthy volunteers had little effect (-0.02 ± 0.02, n=24, p<0.001). The neuromodulatory actions of IBS plasma were reduced by pre-neutralisation with anti-interleukin (IL)-6 (p<0.01) but not IL-8, immunoglobulin G or C-reactive protein. Moreover, IBS plasma-evoked responses (0.22 ± 0.06) were inhibited by the corticotrophin releasing factor receptor (CRFR) 1 antagonist, antalarmin (1μM, 0.015 ± 0.02, n=14, p<0.05), but not the CRFR2 antagonist, astressin 2B. Neuronal activation was mediated by ERK/MAPK signalling.

CONCLUSIONS

These data provide evidence that factors present in IBS plasma modulate neuronal activity in the submucosal plexus and that this is likely to involve CRFR1 activation and IL-6 signalling. These neuromodulatory actions of stress and immune factors indicate a potential mechanism by which immune activation during periods of stress may lead to symptom flares in IBS.

Role of Corticotropin-releasing Factor Signaling in Stress-related Alterations of Colonic Motility and Hyperalgesia

The corticotropin-releasing factor (CRF) signaling systems encompass CRF and the structurally related peptide urocortin (Ucn) 1, 2, and 3 along with 2 G-protein coupled receptors, CRF₁ and CRF₂. CRF binds with high and moderate affinity to CRF₁ and CRF₂ receptors, respectively while Ucn1 is a high-affinity agonist at both receptors, and Ucn2 and Ucn3 are selective CRF₂ agonists. The CRF systems are expressed in both the brain and the colon at the gene and protein levels. Experimental studies established that the activation of CRF₁ pathway in the brain or the colon recaptures cardinal features of diarrhea predominant irritable bowel syndrome (IBS) (stimulation of colonic motility, activation of mast cells and serotonin, defecation/watery diarrhea, and visceral hyperalgesia). Conversely, selective CRF₁ antagonists or CRF₁/CRF₂ antagonists, abolished or reduced exogenous CRF and stress-induced stimulation of colonic motility, defecation, diarrhea and colonic mast cell activation and visceral hyperalgesia to colorectal distention. By contrast, the CRF₂ signaling in the colon dampened the CRF₁ mediated stimulation of colonic motor function and visceral hyperalgesia. These data provide a conceptual framework that sustained activation of the CRF₁ system at central and/or peripheral sites may be one of the underlying basis of IBS-diarrhea symptoms. While targeting these mechanisms by CRF₁ antagonists provided a relevant novel therapeutic venue, so far these promising preclinical data have not translated into therapeutic use of CRF₁ antagonists. Whether the existing or newly developed CRF₁ antagonists will progress to therapeutic benefits for stress-sensitive diseases including IBS for a subset of patients is still a work in progress.

Injection of corticotropin-releasing hormone into the amygdala aggravates visceral nociception and induces noradrenaline release in rats

BACKGROUND

Corticotropin-releasing hormone (CRH) and its receptor 1 (CRH-R1) play an important role in the colonic response to stress. The central nucleus of the amygdala (CeA) is a major extrahypothalamic site that contains a large number of neurons expressing both CRH and CRH-R1. Here, we verified the hypothesis that CRH in the CeA sensitizes visceral nociception via CRH-R1 with release of noradrenaline, dopamine, and serotonin (5-HT) in the CeA.

METHODS

In male Wistar rats, visceral sensitivity was quantified by recording the visceromotor response to colorectal distension (CRD) with administration of vehicle, CRH, or the CRH-R1 antagonist CP-154526+ CRH or CRH-R1 antagonist CP-154526 alone into the CeA. Simultaneously, extracellular levels of noradrenaline, dopamine, and 5-HT were measured in the CeA using microdialysis. All data were obtained under restraint conditions.

KEY RESULTS

Administration of CRH into the CeA significantly increased the number of abdominal muscle contractions in response to CRD. CP-154526 significantly blocked the number of abdominal muscle contractions in response to CRD with the administration of CRH into the CeA. Noradrenaline in the CeA was increased by CRD, further increased by CRH, and inhibited by CRH-R1 antagonist. Dopamine in the CeA was also exaggerated by CRH but was not inhibited by CRH-R1 antagonist. 5-HT in the CeA was unchanged.

CONCLUSIONS & INFERENCES

These results suggest that CRH in the CeA sensitizes visceral nociception via CRH-R1 with release of noradrenaline.

Early-life stress selectively affects gastrointestinal but not behavioral responses in a genetic model of brain-gut axis dysfunction

BACKGROUND

Early-life stress and a genetic predisposition to display an anxiety- and depressive-like phenotype are associated with behavioral and gastrointestinal (GI) dysfunction. Animals exposed to early-life stress, and those genetically predisposed to display anxiety or depressive behaviors, have proven useful tools in which to study stress-related GI disorders, such as irritable bowel syndrome (IBS). IBS is a heterogeneous disorder, and likely a consequence of both genetic and environmental factors. However, the combined effects of early-life stress and a genetic predisposition to display anxiety- and depression-like behaviors on GI function have not been investigated.

METHODS

We assessed the effect of maternal separation (MS) on behavioral and GI responses in WKY animals relative to a normo-anxious reference strain.

KEY RESULTS

Both non-separated (NS) WKY and WKY-MS animals displayed anxiety-like responses in the open-field test and depressive-like behaviors in the forced swim test relative to Sprague-Dawley rats. However, MS had no further influence on anxiety- and depressive-like behaviors exhibited by this stress-prone rat strain. Similarly, corticosterone levels measured after the OFT were insensitive to MS in WKY animals. However, WKY-MS displayed significantly increased colonic visceral hypersensitivity, fecal output, and altered colonic cholinergic sensitivity.

CONCLUSIONS & INFERENCES

Our data suggest that early-life stress, on the background of a genetic predisposition to display an anxiety- and depressive-like phenotype, selectively influences GI function rather than stress-related behaviors. Thus, our findings highlight the importance of genetic predisposition on the outcome of early-life adversity on GI function.

Corticotrophin-releasing factor 1 activation in the central amygdale and visceral hyperalgesia

Corticotropin-releasing factor (CRF)-CRF1 receptor in the brain plays a key role in stress-related alterations of behavior including anxiety/depression, and autonomic and visceral functions. In particular, CRF1 signaling mediates hypersensitivity to colorectal distension (CRD) in various models (early life adverse events, repeated psychological stress, chronic high anxiety, postcolonic inflammation, or repeated nociceptive CRD). So far, knowledge of brain sites involved is limited. A recent article demonstrates in rats that CRF microinjected into the central amygdala (CeA) induces a hyperalgesic response to CRD and enhances the noradrenaline and dopamine levels at this site. The visceral and noradrenaline, unlike dopamine, responses were blocked by a CRF1 antagonist injected into the CeA. Here, we review the emerging role that CRF-CRF1 signaling plays in the CeA to induce visceral hypersensitivity. In the somatic pain field, CRF in the CeA was shown to induce pain sensitization. This is mediated by the activation of postsynaptic CRF1 receptors and protein kinase A signaling that increases N-methyl-d-aspartate receptor neurotransmission. In addition, the activation of tetraethylamonium-sensitive ion channels such as Kv3 accelerates repolarization and firing rate. Whether facilitation of pain transmission underlies CRF action in the CeA-induced visceral hypersensitivity will need to be delineated. CRF1 signaling in the CeA is also an important component of the neuronal circuitry inducing anxiety-like behavior and positioned at the interphase of the reciprocal relationship between pain and affective state. The hyperactivity of this system may represent the neuroanatomical and biochemical substrate contributing to the coexpression of hypersensitivity to CRD and mood disorders in subsets of irritable bowel syndrome patients.

Stress-induced visceral pain: toward animal models of irritable-bowel syndrome and associated comorbidities

Visceral pain is a global term used to describe pain originating from the internal organs, which is distinct from somatic pain. It is a hallmark of functional gastrointestinal disorders such as irritable-bowel syndrome (IBS). Currently, the treatment strategies targeting visceral pain are unsatisfactory, with development of novel therapeutics hindered by a lack of detailed knowledge of the underlying mechanisms. Stress has long been implicated in the pathophysiology of visceral pain in both preclinical and clinical studies. Here, we discuss the complex etiology of visceral pain reviewing our current understanding in the context of the role of stress, gender, gut microbiota alterations, and immune functioning. Furthermore, we review the role of glutamate, GABA, and epigenetic mechanisms as possible therapeutic strategies for the treatment of visceral pain for which there is an unmet medical need. Moreover, we discuss the most widely described rodent models used to model visceral pain in the preclinical setting. The theory behind, and application of, animal models is key for both the understanding of underlying mechanisms and design of future therapeutic interventions. Taken together, it is apparent that stress-induced visceral pain and its psychiatric comorbidities, as typified by IBS, has a multifaceted etiology. Moreover, treatment strategies still lag far behind when compared to other pain modalities. The development of novel, effective, and specific therapeutics for the treatment of visceral pain has never been more pertinent.

Maternal exposure to low levels of corticosterone during lactation protects against experimental inflammatory colitis-induced damage in adult rat offspring

Opposing emotional events (negative/trauma or positive/maternal care) during the postnatal period may differentially influence vulnerability to the effects of stress later in life. The development and course of intestinal disorders such as inflammatory bowel disease are negatively affected by persistent stress, but to date the role of positive life events on these pathologies has been entirely unknown. In the present study, the effect of early life beneficial experiences in the development of intestinal dysfunctions, where inflammation and stress stimuli play a primary role, was investigated. As a “positive” experimental model we used adult male rat progeny nursed by mothers whose drinking water was supplemented with moderate doses of corticosterone (CORT) (0.2 mg/ml) during the lactation period. Such animals have been generally shown to cope better with different environmental situations during life. The susceptibility to inflammatory experimental colitis induced by intracolonic infusion of TNBS (2,4,6-trinitrobenzenesulphonic acid) was investigated in CORT-nursed rats in comparison with control rats. This mild increase in maternal corticosterone during lactation induced, in CORT-nursed rats, a long lasting protective effect on TNBS-colitis, characterized by improvements in some indices of the disease (increased colonic myeloperoxidase activity, loss of body weight and food intake) and by the involvement of endogenous peripheral pathways known to participate in intestinal disorder development (lower plasma corticosterone levels and colonic mast cell degranulation, alterations in the colonic expression of both corticotrophin releasing factor/CRF and its receptor/CRH-1R). All these findings contribute to suggesting that the reduced vulnerability to TNBS-colitis in CORT-nursed rats is due to recovery from the colonic mucosal barrier dysfunction. Such long lasting changes induced by mild hormonal manipulation during lactation, making the adult also better adapted to colonic inflammatory stress, constitute a useful experimental model to investigate the etiopathogenetic mechanisms and therapeutic treatments of some gastrointestinal diseases.

Production of corticotropin-releasing factor and urocortin from human monocyte-derived dendritic cells is stimulated by commensal bacteria in intestine

AIM: To examine whether commensal bacteria are a contributing cause of stress-related mucosal inflammation.

METHODS: Human peripheral blood monocyte-derived dendritic cells (MoDCs) were stimulated by commensal bacterial strains, including Escherichia coli, Clostridium clostridioforme, Bacteroides vulgatus (B. vulgatus), Fusobacterium varium (F. varium), and Lactobacillus delbrueckii subsp. bulgaricus. After incubation, corticotropin-releasing factor (CRF) and urocortin 1 (UCN1) mRNA in the cells was examined by real-time reverse transcription polymerase chain reaction. Supernatants from the cells were tested for CRF and UCN1 using an enzyme-linked immunosorbent assay.

RESULTS: Both CRF and UCN1 were significantly augmented by B. vulgatus and F. varium at both the mRNA and protein levels. In particular, B. vulgatus stimulated human MoDCs, resulting in extremely high levels of CRF and UCN1.

CONCLUSION: Stimulation of MoDCs by B. vulgatus and F. varium may be associated with CRF/UCN1-related intestinal disorders, such as irritable bowel syndrome and inflammatory bowel disease.

Importance of CRF receptor-mediated mechanisms of the bed nucleus of the stria terminalis in the processing of anxiety and pain

Corticotropin-releasing factor (CRF)-mediated mechanisms in the bed nucleus of the stria terminalis (BNST) have a pivotal role in stress-induced anxiety and hyperalgesia. Although CRF is known to activate two receptor subtypes, CRF1 and CRF2, attempts to delineate the specific role of each subtype in modulating anxiety and nociception have been inconsistent. Here we test the hypothesis that CRF1 and CRF2 receptor activation in the anteriolateral BNST (BNSTAL) facilitates divergent mechanisms modulating comorbid anxiety and hyperalgesia. Microinfusions of the specific antagonists CP376395 and Astressin2B into the BNSTAL were used to investigate CRF1 and CRF2 receptor functions, respectively. We found that CRF1 and CRF2 receptors in the BNSTAL had opposing effects on exploratory behavior in the elevated plus-maze, somatic mechanical threshold, and the autonomic and endocrine response to stress. However, CRF1 or CRF2 receptor antagonism in the BNSTAL revealed complementary roles in facilitating the acoustic startle and visceromotor reflexes. Our results suggest that the net effect of CRF1 and CRF2 receptor activation in the BNSTAL is pathway-dependent and provides important insight into the CRF receptor-associated circuitry that likely underpins stress-induced pathologies.

Physiological underpinnings of irritable bowel syndrome: neurohormonal mechanisms

The gastrointestinal tract is a vast neuroendocrine organ with extensive extrinsic and intrinsic neural circuits that interact to control its function. Circulating and paracrine hormones (amine and peptide) provide further control of secretory, absorptive, barrier, motor and sensory mechanisms that are essential to the digestion and assimilation of nutrients, and the transport and excretion of waste products. Specialized elements of the mucosa (including enteroendocrine cells, enterocytes and immune cells) and the microbiome interact with other intraluminal contents derived from the diet, and with endogenous chemicals that alter the gut's functions. The totality of these control mechanisms is often summarized as the brain-gut axis. In irritable bowel syndrome (IBS), which is the most common gastrointestinal disorder, there may be disturbances at one or more of these diverse control mechanisms. Patients present with abdominal pain in association with altered bowel function. This review documents advances in understanding the pathophysiological mechanisms in the brain-gut axis in patients with IBS. It is anticipated that identification of one or more disordered functions in clinical practice will usher in a renaissance in the management of IBS, leading to effective therapy tailored to the needs of the individual patient.

Disodium cromoglycate reverses colonic visceral hypersensitivity and influences colonic ion transport in a stress-sensitive rat strain

The interface between psychiatry and stress-related gastrointestinal disorders (GI), such as irritable bowel syndrome (IBS), is well established, with anxiety and depression the most frequently occurring comorbid conditions. Moreover, stress-sensitive Wistar Kyoto (WKY) rats, which display anxiety- and depressive-like behaviors, exhibit GI disturbances akin to those observed in stress-related GI disorders. Additionally, there is mounting preclinical and clinical evidence implicating mast cells as significant contributors to the development of abdominal visceral pain in IBS. In this study we examined the effects of the rat connective tissue mast cell (CTMC) stabiliser, disodium cromoglycate (DSCG) on visceral hypersensitivity and colonic ion transport, and examined both colonic and peritoneal mast cells from stress-sensitive WKY rats. DSCG significantly decreased abdominal pain behaviors induced by colorectal distension in WKY animals independent of a reduction in colonic rat mast cell mediator release. We further demonstrated that mast cell-stimulated colonic ion transport was sensitive to inhibition by the mast cell stabiliser DSCG, an effect only observed in stress-sensitive rats. Moreover, CTMC-like mast cells were significantly increased in the colonic submucosa of WKY animals, and we observed a significant increase in the proportion of intermediate, or immature, peritoneal mast cells relative to control animals. Collectively our data further support a role for mast cells in the pathogenesis of stress-related GI disorders.

Effect of early-life stress on chronic functional visceral pain and CRH R1 expression in the paraventricular nucleus in adult rats

AIM: To assess the effect of early-life stress on chronic functional visceral pain and expression of corticotropin releasing hormone receptor 1 (CRH R1) in the hypothalamic paraventricular nucleus (PVN) of rats with chronic functional visceral pain to provide a theoretical basis for the prevention and treatment of abdominal pain-related functional gastrointestinal disorders.

METHODS: Neonatal rats were randomly divided into six groups (n = 10), including a male control group, a female control group, a male separation group, a female separation group, a male distension group and a female distension group. HE staining was used to detect histologic changes in the colon tissue. Western blot and immunofluorescence were used to detect the changes in CRH R1 expression in the PVN. Brain tissue sections were immunostained for c-fos as a marker for activation of the PVN. Furthermore, normal male adult rats were randomly divided into three groups (normal control, saline and lidocaine, n = 6 for each group) to observe the role of PVN in the regulation of chronic functional visceral pain in normal rats by intra-PVN administration of lidocaine (1%, 0.3 µL).

RESULTS: Neonatal maternal separation (NMS) or colorectal distension (CRD) resulted in chronic visceral hypersensitivity without pathological changes in the colon tissue. There was no gender difference in the above change. Electrical discharge of the abdominal external oblique muscle in rats 10, 20, and 30 min after intra-PVN microinjection of 1% lidocaine was decreased significantly under the stimulation of CRD at 60 mmHg compared with normal controls and saline rats. The expression of CRH R1 and c-fos in the PVN of NMS and CRD rats increased compared with control rats.

CONCLUSION: Early-life stress can lead to chronic functional visceral pain in rats in adulthood. Allodynia caused by NMS is more obvious than that by CRD. The PVN and CRH R1 may be involved in the pathogenesis of chronic functional visceral pain caused by early-life stress.