Role of corticotropin-releasing factor pathways in stress-related alterations of colonic motor function and viscerosensibility in female rodents

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.

Neuropeptide and cytokine regulation of pain in the context of substance use disorders

Substance use disorders (SUDs) are frequently accompanied by affective symptoms that promote negative reinforcement mechanisms contributing to SUD maintenance or progression. Despite their widespread use as analgesics, chronic or excessive exposure to alcohol, opioids, and nicotine produces heightened nociceptive sensitivity, termed hyperalgesia. This review focuses on the contributions of neuropeptide (CRF, melanocortin, opioid peptide) and cytokine (IL-1β, TNF-α, chemokine) systems in the development and maintenance of substance-induced hyperalgesia. Few effective therapies exist for either chronic pain or SUD, and the common interaction of these disease states likely complicates their effective treatment. Here we highlight promising new discoveries as well as identify gaps in research that could lead to more effective and even simultaneous treatment of SUDs and co-morbid hyperalgesia symptoms.

Associations Between Colonic Motor Patterns and Autonomic Nervous System Activity Assessed by High-Resolution Manometry and Concurrent Heart Rate Variability

Abnormal colonic motility may be associated with dysfunction of the autonomic nervous system (ANS). Our aim was to evaluate if associations between colonic motor patterns and autonomic neural activity could be demonstrated by assessing changes in heart rate variability (HRV) in healthy volunteers. A total of 145 colonic motor patterns were assessed in 11 healthy volunteers by High-Resolution Colonic Manometry (HRCM) using an 84-channel water-perfused catheter. Motor patterns were evoked by balloon distention, a meal and luminal bisacodyl. The electrocardiogram (ECG) and cardiac impedance were assessed during colonic manometry. Respiratory sinus arrhythmia (RSA) and root mean square of successive differences of beat-to-beat intervals (RMSSD) served as measures of parasympathetic reactivity while the Baevsky's Stress Index (SI) and the pre-ejection period (PEP) were used as measures of sympathetic reactivity. Taking all motor patterns into account, our data show that colonic motor patterns are accompanied by increased parasympathetic activity and decreased sympathetic activity that may occur without eliciting a significant change in heart rate. Motor Complexes (more than one motor pattern occurring in close proximity), High-Amplitude Propagating Pressure Waves followed by Simultaneous Pressure Waves (HAPW-SPWs) and HAPWs without SPWs are all associated with an increase in RSA and a decrease in SI. Hence RSA and SI may best reflect autonomic activity in the colon during these motor patterns as compared to RMSSD and PEP. SI and PEP do not measure identical sympathetic reactivity. The SPW, which is a very low amplitude pressure wave, did not significantly change the autonomic measures employed here. In conclusion, colonic motor patterns are associated with activity in the ANS which is reflected in autonomic measures of heart rate variability. These autonomic measures may serve as proxies for autonomic neural dysfunction in patients with colonic dysmotility.

Antagonizing the corticotropin releasing hormone receptor 1 with antalarmin reduces the progression of endometriosis

Endometriosis is a disorder in which endometrial tissue is found outside the uterus causing pain, infertility and stress. Finding effective, non-hormonal and long-term treatments for endometriosis still remains one of the most significant challenges in the field. Corticotropin releasing hormone (CRH) is one of the main signaling peptides within the hypothalamic pituitary adrenal (HPA) axis released in response to stress. CRH can affect nervous and visceral tissues such as the uterus and gut via activation of two types of CRH receptors: CRHR1 and CRHR2. Our aim was to determine if blocking CRHR1 with antalarmin will reduce endometriosis progression. In experiment 1 we induced endometriosis in female rats by suturing uterine horn tissue next to the intestinal mesentery and allowed to progress for 7 days. We determined that after 7 days, there was a significant increase in CRHR1 within endometriotic vesicles as compared to normal uterus. In Experiment 2, we induced endometriosis and administered either antalarmin (20 mg/kg, i.p.) or vehicle during the first 7 days after surgery. A separate group of sham surgery rats served as non-endometriosis controls. Endometriosis was allowed to progress until 60 days after surgery, at which time rats were tested for anxiety behaviors. At the time of sacrifice, endometriotic vesicles, uterus and blood were collected. Treatment with antalarmin significantly reduced the size (67% decrease) and number (30% decrease) of endometriotic vesicles. Antalarmin also prevented the increase in CRH and CRHR1 mRNA within endometriotic vesicles but not of glucocorticoid receptor. Endometriosis did not change anxiety behaviors in the open field and zero-maze tests and prior antalarmin administration did not modify this. Our data provides the first in-vivo demonstration for use of CRHR1 antagonist for the treatment of endometriosis opening the possibility for further exploring CRH signaling as a treatment target for this debilitating disease.

[Gender Difference in Functional Gastrointestinal Disorders]

Functional gastrointestinal diseases (FGIDs) are known to be influenced more by a lowering of the quality of life, such as mental health and sleep quality, compared to organic diseases. Genetic, microbiological, molecular biological, and social environmental factors are involved in the pathophysiology of FGIDs. In particular, mental factors, such as depression and anxiety, play a major role in the development of FGIDs. The prevalence of most FGIDs is higher in women. Gender needs to be analyzed in patients with FGIDs because it can have a great influence on the onset of FGIDs. Because there are differences in the treatment response according to gender, further research in the development of therapeutic drugs considering this gender difference will be needed, and ultimately it will be possible to lower the prevalence of FGIDs and improve the quality of life of patients.

The Influence of Early Life Experience on Visceral Pain

Pain is the most reported and troublesome symptom of nearly all functional disorders affecting the genitourinary and gastrointestinal organs. Patients with irritable bowel syndrome (IBS), interstitial cystitis/painful bladder syndrome (IC/PBS), vulvodynia, and/or chronic prostatitis/chronic pelvic pain syndrome (CP/CPPS; collectively termed chronic pelvic pain syndromes) report pain severe enough to impact quality of life and often suffer from symptoms of or are diagnosed with more than one of these syndromes. This increased comorbidity between chronic pelvic pain syndromes, and with pain disorders of disparate body regions, as well as with mood disorders, can be influenced by disruptions in the hypothalamic-pituitary-adrenal (HPA) axis, which regulates the response to stress and influences the perception of pain. Experiencing trauma, neglect, or abuse in early life can permanently affect the functioning of the HPA axis. As such, a significant proportion of patients suffering from comorbid chronic pelvic pain syndromes report a history of early life stress or trauma. Here we will report on how these early life experiences influence chronic pelvic pain in patients. We will also discuss various rodent models that have been developed to study this phenomenon to understand the mechanisms underlying HPA axis dysfunction, as well as potential underlying mechanisms connecting these syndromes to one another.

Role of mast cell activation and degranulation in irritable bowel syndrome

Irritable bowel syndrome (IBS) is a common functional gastrointestinal disorder whose treatment is unsatisfactory as its pathophysiology is multifactorial. The factors involved in IBS pathophysiology include visceral hypersensitivity, intestinal dysmotility, psychological factors, dysregulated gut-brain axis, intestinal microbiota alterations, impaired intestinal permeability, and mucosal immune alterations. Recently, mucosal immune alterations have received much attention in IBS. Mast cells are abundant in the intestine, and they communicate with adjacent cells such as epithelial, neuronal, smooth muscle cells or other immune cells through the mediators released when they are activated. Many studies have suggested that mast cells play a role in the pathophysiology of IBS. This review will focus on the role of mast cells in IBS.

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.

Age, Gender and Women's Health and the Patient

Patients with functional gastrointestinal disorders (FGIDs) often experience distress, reduced quality of life, a perceived lack of validation, and an unsatisfactory experience with health care providers. A health care provider can provide the patient with a framework in which to understand and legitimize their symptoms, remove self-doubt or blame, and identify factors that contribute to symptoms that the patient can influence or control. This framework is implemented with the consideration of important factors that impact FGIDs, such as gender, age, society, and the patient's perspective. Although the majority of FGIDs, including globus, rumination syndrome, IBS, bloating, constipation, functional abdominal pain, sphincter of Oddi dyskinesia, pelvic floor dysfunction, and extra-intestinal manifestations, are more prevalent in women than men, functional chest pain, dyspepsia, vomiting, and anorectal pain do not appear to vary by gender. Studies suggest sex differences in somatic but not visceral pain perception, motility, and central processing of visceral pain; although further research is required in autonomic nervous system dysfunction, genetics and immunologic/microbiome. Gender differences in response to psychological treatments, antidepressants, fiber, probiotics, and anticholinergics have not been adequately studied. However, a greater clinical response to 5-HT3 antagonists but not 5-HT4 agonists has been reported in women compared with men.

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.

Influence of Jianpi Huashi granule on CRF and CRFR1 expression in the brain-gut axis of rats with diarrhea-predominant irritable bowel syndrome

AIM: To evaluate the effect of Jianpi Huashi granule on corticotropin releasing factor (CRF) and corticotropin releasing factor receptor 1 (CRFR1) expression in the colon, hippocampus and hypothalamus of rats with diarrhea-predominant irritable bowel syndrome (D-IBS).

METHODS: A rat model of D-IBS was established by intragastric administration of Sennae decoction combined with restraint stress. Rats were divided into several groups. Jianpi Huashi granule was given to rats in Jianpi Huashi groups, pinaverium bromide tablets to rats in the positive group and water to the other groups. ELISA was used to detect the content of CRF in the colon. Immunohistochemistry assay was used to detect the expression of CRFR1 in the colon, hippocampus, and hypothalamus, and CRF in the hippocampus and hypothalamus. RT-PCR was used to detect the expression of CRF and CRFR1 mRNAs in the colon and hippocampus.

RESULTS: In the D-IBS model group, the content of CRF in the colon (67.1 ± 3.8 vs 36.0 ± 3.0) and the expression of CRF in the hippocampus and hypothalamus (0.23 ± 0.02 vs 0.09 ± 0.01, 0.17 ± 0.02 vs 0.09 ± 0.01) were increased significantly compared to the normal group (P < 0.01 for all). The expression of CRFR1 in the colon, hippocampus and hypothalamus was also increased significantly (0.17 ± 0.01 vs 0.03 ± 0.01, 0.20 ± 0.02 vs 0.09 ± 0.01, 0.19 ± 0.02 vs 0.07 ± 0.01, P < 0.01 for all). The expression of CRF and CRFR1 mRNAs in the colon and hippocampus was significantly increased in the model group compared to the normal group (0.89 ± 0.04 vs 0.09 ± 0.01, 1.09 ± 0.09 vs 0.21 ± 0.04, 0.56 ± 0.01 vs 0.15 ± 0.05, 1.26 ± 0.14 vs 0.23 ± 0.06, P < 0.01 for all). After treatment, the expression of CRF in the colon and hippocampus in all treatment groups was significantly decreased (51.0 ± 3.4, 54.6 ± 4.1, 45.1 ± 4.7, 43.3 ± 3.9 vs 67.1 ± 3.8; 0.18 ± 0.02, 0.19 ± 0.02, 0.15 ± 0.02, 0.11 ± 0.01 vs 0.23 ± 0.02, P < 0.01 for all), and the expression of CRF in the positive control group, medium- and high-dose Jianpi Huashi granule groups in the hypothalamus was significantly decreased (0.15 ± 0.02, 0.13 ± 0.01, 0.12 ± 0.01 vs 0.17 ± 0.02, P < 0.05 or P < 0.01). The expression of CRFR1 in the colon, hippocampus and hypothalamus in the positive control group, medium- and high-dose Jianpi Huashi granule groups was significantly reduced (0.10 ± 0.01, 0.08 ± 0.01, 0.05 ± 0.01 vs 0.17 ± 0.01, 0.16 ± 0.01, 0.14 ± 0.02, 0.13 ± 0.01 vs 0.20 ± 0.02, 0.15 ± 0.02, 0.13 ± 0.01, 0.11 ± 0.01 vs 0.19 ± 0.02, P < 0.05 or P < 0.01). The expression of CRF mRNA in the colon in all treatment groups was significantly reduced (0.63 ± 0.04, 0.76 ± 0.06, 0.32 ± 0.06, 0.13 ± 0.03 vs 0.89 ± 0.04, P < 0.01 for all), while the expression of CRF mRNA in the hippocampus in the medium- and high-dose Jianpi Huashi granule groups was significantly decreased (0.76 ± 0.11, 0.67 ± 0.10 vs 1.09 ± 0.09, P < 0.01 for all). The expression of CRFR1 mRNA in the colon in the positive control group, medium- and high-dose Jianpi Huashi granule groups was significantly reduced (0.47 ± 0.03, 0.40 ± 0.06, 0.24 ± 0.06 vs 0.56 ± 0.01, P < 0.05 or P < 0.01), while the expression of CRFR1 mRNA in the hippocampus in the medium- and high-dose Jianpi Huashi granule groups was significantly decreased (0.62 ± 0.06, 0.60 ± 0.07 vs 1.26 ± 0.14, P < 0.01 for all).

CONCLUSION: Jianpi Huashi granule regulates colonic motility and visceral sensitivity in rats with D-IBS possibly by modulating the expression of CRF and CRFR1 in the colon, hippocampus and hypothalamus.

Sex and estrogen affect the distribution of urocortin-1 immunoreactivity in brainstem autonomic nuclei of the rat

Urocortin-1 (UCN-1), a neuropeptide closely related to the hypothalamic hormone corticotropin-releasing factor, has been associated with stress, feeding behaviors, cardiovascular control, and to exhibit functional gender differences. This study was done to investigate whether estrogen (E; 17β-estradiol) treatment (9 weeks) altered UCN-1 immunoreactivity in brainstem autonomic nuclei in female Wistar rats. Experiments were done in age matched adult males (controls), females (intact), and ovariectomized (OVX) only and OVX+E (30pg/ml plasma) treated females. All animals received intracerebroventricular injections of colchicine and were then perfused transcardially with Zamboni's fixative. Coronal brainstem sections (40μm) were cut and processed immunohistochemically for UCN-1. In males, moderate UCN-1 fiber labeling was found in the nucleus of the solitary tract (NTS) and throughout the rostral ventral lateral medulla (RVLM). Additionally, a few UCN-1 immunoreactive neurons were observed in hypoglossal nucleus (XII), facial nucleus (FN) and nucleus ambiguus (Amb). In intact females and OVX+E females, fewer UCN-1 labeled fibers were found within NTS compared to males. In contrast, the RVLM was more densely innervated in the female cases. Furthermore, in both intact and OVX+E females UCN-1 labeled neurons were found not only within Amb, FN and XII, but also within NTS, RVLM and nucleus raphé pallidus (RP). In OVX only animals, moderate to dense UCN-1 fiber labeling was observed in the NTS complex and throughout RVLM compared to males and the other female groups. However, in contrast to all other groups, UCN-1 labeled neurons were found in greater number within Amb, FN, NTS, dorsal motor nucleus of the vagus, XII, RVLM, magnocellular reticular nucleus and RP. These data not only suggest that sex differences exist in the distribution of UCN-1 within brainstem autonomic areas, but that circulating level of E may play an important role with regards to the function of these UCN-1 neurons during stress responses.

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.

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.

Oxytocin regulates gastrointestinal motility, inflammation, macromolecular permeability, and mucosal maintenance in mice

Enteric neurons express oxytocin (OT); moreover, enteric neurons and enterocytes express developmentally regulated OT receptors (OTRs). Although OT (with secretin) opposes intestinal inflammation, physiological roles played by enteric OT/OTR signaling have not previously been determined. We tested hypotheses that OT/OTR signaling contributes to enteric nervous system (ENS)-related gastrointestinal (GI) physiology. GI functions and OT effects were compared in OTR-knockout (OTRKO) and wild-type (WT) mice. Stool mass and water content were greater in OTRKO mice than in WT. GI transit time in OTRKO animals was faster than in WT; OT inhibited in vitro generation of ENS-dependent colonic migrating motor complexes in WT but not in OTRKO mice. Myenteric neurons were hyperplastic in OTRKO animals, and mucosal exposure to cholera toxin (CTX) in vitro activated Fos in more myenteric neurons in OTRKO than WT than in WT mice; OT inhibited the CTX response in WT but not in OTRKO mice. Villi and crypts were shorter in OTRKO than in WT mice, and transit-amplifying cell proliferation in OTRKO crypts was deficient. Macromolecular intestinal permeability in OTRKO was greater than WT mice, and experimental colitis was more severe in OTRKO mice; moreover, OT protected WT animals from colitis. Observations suggest that OT/OTR signaling acts as a brake on intestinal motility, decreases mucosal activation of enteric neurons, and promotes enteric neuronal development and/or survival. It also regulates proliferation of crypt cells and mucosal permeability; moreover OT/OTR signaling is protective against inflammation. Oxytocinergic signaling thus appears to play an important role in multiple GI functions that are subject to neuronal regulation.

Gender-related differences in irritable bowel syndrome: Potential mechanisms of sex hormones

According to epidemiological studies, twice as many women as men are affected by irritable bowel syndrome (IBS) in western countries, suggesting a role for sex hormones in IBS pathophysiology. Despite growing evidence about the implications of sex hormones in IBS symptom modulation, data on mechanisms by which they influence disease development are sparse. This review aims to determine the state of knowledge about the role of sex hormones in sensorimotor dysfunctions and to address the possible interplay of sex hormones with common risk factors associated with IBS. The scientific bibliography was searched using the following keywords: irritable bowel syndrome, sex, gender, ovarian hormone, estradiol, progesterone, testosterone, symptoms, pain, sensitivity, motility, permeability, stress, immune system, brain activity, spinal, supraspinal, imaging. Ovarian hormones variations along the menstrual cycle affect sensorimotor gastrointestinal function in both healthy and IBS populations. They can modulate pain processing by interacting with neuromodulator systems and the emotional system responsible for visceral pain perception. These hormones can also modulate the susceptibility to stress, which is a pivotal factor in IBS occurrence and symptom severity. For instance, estrogen-dependent hyper-responsiveness to stress can promote immune activation or impairments of gut barrier function. In conclusion, whereas it is important to keep in mind that ovarian hormones cannot be considered as a causal factor of IBS, they arguably modulate IBS onset and symptomatology. However, our understanding of the underlying mechanisms remains limited and studies assessing the link between IBS symptoms and ovarian hormone levels are needed to improve our knowledge of the disease evolution with regard to gender. Further studies assessing the role of male hormones are also needed to understand fully the role of sex hormones in IBS. Finally, investigation of brain-gut interactions is critical to decipher how stress, ovarian hormones, and female brain processing of pain can translate into gut dysfunctions.

Vaginal hypersensitivity and hypothalamic-pituitary-adrenal axis dysfunction as a result of neonatal maternal separation in female mice

Early life stress can permanently alter functioning of the hypothalamic-pituitary-adrenal (HPA) axis, which regulates the stress response and influences the perception of pain. Chronic pelvic pain patients commonly report having experienced childhood neglect or abuse, which increases the likelihood of presenting with comorbid chronic pain and/or mood disorders. Animal models of neonatal stress commonly display enhanced anxiety-like behaviors, colorectal hypersensitivity, and disruption of proper neuro-immune interactions in adulthood. Here, we tested the hypothesis that early life stress impacts vaginal sensitivity by exposing mice to neonatal maternal separation (NMS) for 3h/day during the first two (NMS14) or three (NMS21) postnatal weeks. As adults, female mice underwent vaginal balloon distension (VBD), which was also considered an acute stress. Before or after VBD, mice were assessed for anxiety-like behavior, hindpaw sensitivity, and changes in gene and protein expression related to HPA axis function and regulation. NMS21 mice displayed significantly increased vaginal sensitivity compared to naïve mice, as well as significantly reduced anxiety-like behavior at baseline, which was heightened following VBD. NMS21 mice exhibited significant thermal and mechanical hindpaw hypersensitivity at baseline and following VBD. NMS14 mice displayed no change in anxiety-like behavior and only exhibited significantly increased hindpaw mechanical and thermal sensitivity following VBD. Centrally, a significant decrease in negative regulation of the HPA axis was observed in the hypothalamus and hippocampus of NMS21 mice. Peripherally, NMS and VBD affected the expression of inflammatory mediators in the vagina and bladder. Corticotropin-releasing factor (CRF) receptor and transient receptor potential (TRP) channel protein expression was also significantly, and differentially, affected in vagina, bladder, and colon by both NMS and VBD. Together these data indicate that NMS affects both central and peripheral aspects of the HPA axis, which may drive changes in vaginal sensitivity and the development of comorbid chronic pain and mood disorders.

The effect of stress on core and peripheral body temperature in humans

Even though there are indications that stress influences body temperature in humans, no study has systematically investigated the effects of stress on core and peripheral body temperature. The present study therefore aimed to investigate the effects of acute psychosocial stress on body temperature using different readout measurements. In two independent studies, male and female participants were exposed to a standardized laboratory stress task (the Trier Social Stress Test, TSST) or a non-stressful control task. Core temperature (intestinal and temporal artery) and peripheral temperature (facial and body skin temperature) were measured. Compared to the control condition, stress exposure decreased intestinal temperature but did not affect temporal artery temperature. Stress exposure resulted in changes in skin temperature that followed a gradient-like pattern, with decreases at distal skin locations such as the fingertip and finger base and unchanged skin temperature at proximal regions such as the infra-clavicular area. Stress-induced effects on facial temperature displayed a sex-specific pattern, with decreased nasal skin temperature in females and increased cheek temperature in males. In conclusion, the amplitude and direction of stress-induced temperature changes depend on the site of temperature measurement in humans. This precludes a direct translation of the preclinical stress-induced hyperthermia paradigm, in which core temperature uniformly rises in response to stress to the human situation. Nevertheless, the effects of stress result in consistent temperature changes. Therefore, the present study supports the inclusion of body temperature as a physiological readout parameter of stress in future studies.

Frequency of irritable bowel syndrome, entrance examination-related stress, mental health, and quality of life in high school students

The purpose of this study was to examine entrance examination-related stress, mental health, and the quality of life of high school students with and without irritable bowel syndrome. We administered a descriptive survey by collecting data from 1,877 students from eight schools in Gyeonggi province, Korea. This study employed the Rome III criteria for the assessment of irritable bowel syndrome, an entrance examination stress scale for measuring entrance examination-related stress, the revised Symptom Checklist-90-Revised for measuring mental health, and the World Health Organization Quality of Life Scale Abbreviated Version for measuring the quality of life. The frequency of irritable bowel syndrome in students was 19.0%. A majority had a mixed constipation and diarrhea subtype of irritable bowel syndrome. Compared with the high school students without irritable bowel syndrome, those with irritable bowel syndrome reported a significantly higher score on the entrance examination stress scale, Symptom Checklist-90-Revised, and World Health Organization Quality of Life Scale Abbreviated Version. Results suggest support for creating a high school education program that provides knowledge and information about irritable bowel syndrome to students. Furthermore, it is important to explore suitable therapeutic approaches and nursing interventions for this population.

Altered psychobiological responsiveness in women with irritable bowel syndrome

OBJECTIVE

Although stress has been considered an important pathophysiological factor in irritable bowel syndrome (IBS), there is incomplete understanding of its physiological mechanisms. The current study was designed to compare diurnal hypothalamic-pituitary-adrenal (HPA) axis activity in IBS patients and controls and their psychobiological response to a psychosocial stressor.

METHODS

Basal and stimulated HPA axis activity was assessed in 57 women with IBS and 20 matched controls. Psychiatric comorbidity was assessed using a standardized clinical interview. Salivary morning cortisol and diurnal profile were obtained, and the Trier Social Stress Test (TSST) was administered. Levels of cortisol and adrenocorticotropic hormone (ACTH) were measured before and within 1 hour after the stressor. Overall stress experience and stress related to the TSST were assessed using standardized questionnaires.

RESULTS

All subjects showed intact circadian variation of cortisol. However, IBS patients with predominant diarrhea exhibited substantially heightened cortisol levels at awakening (p < .03) and a blunted cortisol awakening response. In response to the TSST, patients exhibited significantly blunted cortisol (p < .05) and slightly attenuated ACTH secretion compared with controls. During the recovery period, ACTH levels were significantly lower (p < .04) in patients than those in healthy subjects. Women with IBS perceived higher stress susceptibility than control subjects did (p < .01).

CONCLUSIONS

The enhanced morning cortisol levels in one subgroup of IBS patients may indicate an association between basal HPA axis activity and predominant bowel habit. The downregulated HPA axis reactivity in IBS after the TSST suggests a downregulated sensitivity of the endocrine system. On the contrary, all subjective stress ratings were increased in the IBS group, which may indicate increased stress susceptibility.

Stress and visceral pain: from animal models to clinical therapies

Epidemiological studies have implicated stress (psychosocial and physical) as a trigger of first onset or exacerbation of irritable bowel syndrome (IBS) symptoms of which visceral pain is an integrant landmark. A number of experimental acute or chronic exteroceptive or interoceptive stressors induce visceral hyperalgesia in rodents although recent evidence also points to stress-related visceral analgesia as established in the somatic pain field. Underlying mechanisms of stress-related visceral hypersensitivity may involve a combination of sensitization of primary afferents, central sensitization in response to input from the viscera and dysregulation of descending pathways that modulate spinal nociceptive transmission or analgesic response. Biochemical coding of stress involves the recruitment of corticotropin releasing factor (CRF) signaling pathways. Experimental studies established that activation of brain and peripheral CRF receptor subtype 1 plays a primary role in the development of stress-related delayed visceral hyperalgesia while subtype 2 activation induces analgesic response. In line with stress pathways playing a role in IBS, non-pharmacologic and pharmacologic treatment modalities aimed at reducing stress perception using a broad range of evidence-based mind-body interventions and centrally-targeted medications to reduce anxiety impact on brain patterns activated by visceral stimuli and dampen visceral pain.

Development of mechanical hypersensitivity in rats during heroin and ethanol dependence: alleviation by CRF₁ receptor antagonism

Animal models of drug dependence have described both reductions in brain reward processes and potentiation of stress-like (or anti-reward) mechanisms, including a recruitment of corticotropin-releasing factor (CRF) signaling. Accordingly, chronic exposure to opiates often leads to the development of mechanical hypersensitivity. We measured paw withdrawal thresholds (PWTs) in male Wistar rats allowed limited (short access group: ShA) or extended (long access group: LgA) access to heroin or cocaine self-administration, or in rats made dependent on ethanol via ethanol vapor exposure (ethanol-dependent group). In heroin self-administering animals, after transition to LgA conditions, thresholds were reduced to around 50% of levels observed at baseline, and were also significantly lower than thresholds measured in animals remaining on the ShA schedule. In contrast, thresholds in animals self-administering cocaine under either ShA (1 h) or LgA (6 h) conditions were unaltered. Similar to heroin LgA rats, ethanol-dependent rats also developed mechanical hypersensitivity after eight weeks of ethanol vapor exposure compared to non-dependent animals. Systemic administration of the CRF1R antagonist MPZP significantly alleviated the hypersensitivity observed in rats dependent on heroin or ethanol. The emergence of mechanical hypersensitivity with heroin and ethanol dependence may thus represent one critical drug-associated negative emotional state driving dependence on these substances. These results also suggest a recruitment of CRF-regulated nociceptive pathways associated with escalation of intake and dependence. A greater understanding of relationships between chronic drug exposure and pain-related states may provide insight into mechanisms underlying the transition to drug addiction, as well as reveal new treatment opportunities. This article is part of a Special Issue entitled 'Post-Traumatic Stress Disorder'.

Cutting the vagus nerve below the diaphragm prevents maternal potentiation of infant rat vocalization

In maternal potentiation, the rate of vocalization by a young organism during isolation is greatly enhanced if that isolation has been immediately preceded by an interaction with the mother (or other adult female in the case of rats). The enhancement in isolation-induced vocalization rate does not occur if the young animal had an interaction with other social companions like littermates or with familiar inanimate stimuli like home cage shavings. The present study demonstrates that pups whose vagus nerve is cut below the diaphragm do not potentiate vocalization after an interaction with their dam. The vocalization rates of denervated pups in a first isolation, in the presence of the dam, and during cold exposure do not differ from control pups. Their non-vocal behaviors also appear unaffected by the surgery. Similar to what has been shown in studies of fever-induced behavioral changes, an intact vagus nerve from the gut is necessary for young rat pups to show normal social mediation of their isolation-induced vocal responses.

Stress-related alterations of visceral sensation: animal models for irritable bowel syndrome study

Stressors of different psychological, physical or immune origin play a critical role in the pathophysiology of irritable bowel syndrome participating in symptoms onset, clinical presentation as well as treatment outcome. Experimental stress models applying a variety of acute and chronic exteroceptive or interoceptive stressors have been developed to target different periods throughout the lifespan of animals to assess the vulnerability, the trigger and perpetuating factors determining stress influence on visceral sensitivity and interactions within the brain-gut axis. Recent evidence points towards adequate construct and face validity of experimental models developed with respect to animals' age, sex, strain differences and specific methodological aspects such as non-invasive monitoring of visceromotor response to colorectal distension as being essential in successful identification and evaluation of novel therapeutic targets aimed at reducing stress-related alterations in visceral sensitivity. Underlying mechanisms of stress-induced modulation of visceral pain involve a combination of peripheral, spinal and supraspinal sensitization based on the nature of the stressors and dysregulation of descending pathways that modulate nociceptive transmission or stress-related analgesic response.

Stress and visceral pain: from animal models to clinical therapies

Epidemiological studies have implicated stress (psychosocial and physical) as a trigger of first onset or exacerbation of irritable bowel syndrome (IBS) symptoms of which visceral pain is an integrant landmark. A number of experimental acute or chronic exteroceptive or interoceptive stressors induce visceral hyperalgesia in rodents although recent evidence also points to stress-related visceral analgesia as established in the somatic pain field. Underlying mechanisms of stress-related visceral hypersensitivity may involve a combination of sensitization of primary afferents, central sensitization in response to input from the viscera and dysregulation of descending pathways that modulate spinal nociceptive transmission or analgesic response. Biochemical coding of stress involves the recruitment of corticotropin releasing factor (CRF) signaling pathways. Experimental studies established that activation of brain and peripheral CRF receptor subtype 1 plays a primary role in the development of stress-related delayed visceral hyperalgesia while subtype 2 activation induces analgesic response. In line with stress pathways playing a role in IBS, non-pharmacologic and pharmacologic treatment modalities aimed at reducing stress perception using a broad range of evidence-based mind-body interventions and centrally-targeted medications to reduce anxiety impact on brain patterns activated by visceral stimuli and dampen visceral pain.

Maternal separation as a model of brain-gut axis dysfunction

RATIONALE

Early life stress has been implicated in many psychiatric disorders ranging from depression to anxiety. Maternal separation in rodents is a well-studied model of early life stress. However, stress during this critical period also induces alterations in many systems throughout the body. Thus, a variety of other disorders that are associated with adverse early life events are often comorbid with psychiatric illnesses, suggesting a common underlying aetiology. Irritable bowel syndrome (IBS) is a functional gastrointestinal disorder that is thought to involve a dysfunctional interaction between the brain and the gut. Essential aspects of the brain-gut axis include spinal pathways, the hypothalamic pituitary adrenal axis, the immune system, as well as the enteric microbiota. Accumulating evidence suggest that stress, especially in early life, is a predisposing factor to IBS.

OBJECTIVE

The objective of this review was to assess and compile the most relevant data on early life stress and alterations at all levels of the brain gut axis.

RESULTS

In this review, we describe the components of the brain-gut axis individually and how they are altered by maternal separation. The separated phenotype is characterised by alterations of the intestinal barrier function, altered balance in enteric microflora, exaggerated stress response and visceral hypersensitivity, which are all evident in IBS.

CONCLUSION

Thus, maternally separated animals are an excellent model of brain-gut axis dysfunction for the study of disorders such as IBS and for the development of novel therapeutic interventions.

Central CRH administration changes formalin pain responses in male and female rats

Corticotropin-releasing hormone (CRH) is suggested to be involved in the regulation of pain. To better evaluate the CRH-mediated behavioral alterations in the formalin inflammatory pain test, we administered CRH or the CRH receptor antagonist α-helical CRH(9-41) (ahCRH) intracerebroventricularly to male and female rats and compared the effects with those of saline control. Nociceptive stimulation was carried out through a subcutaneous injection of dilute formalin (50μL, 10%) in the plantar surface of the hind paw. In both sexes, formalin-induced responses, recorded for 60min, were affected by CRH but not by ahCRH treatment. Paw flexing duration was decreased in both sexes during the formalin interphase period in the CRH-treated group compared to saline control groups; however, licking of the injected paw was markedly increased by the same treatment at other time periods. Treatments induced only a few changes in spontaneous non-pain behaviors, which do not account for the effects on pain response. In conclusion, these data demonstrate the ability of CRH to affect the behavioral responses to an inflammatory nociceptive stimulus, and that the effects can be in opposite directions depending on the behavioral response considered.

Role of corticotrophin-releasing factor in the stress-induced dilation of esophageal intercellular spaces

Corticotrophin-releasing factor (CRF) plays a major role in coordinating stress responses. We aimed to test whether blocking endogenous CRF activity can prevent the stress-induced dilation of intercellular spaces in esophageal mucosa. Eighteen adult male rats were divided into 3 groups: 1) a non-stressed group (the non-stressed group), 2) a saline-pretreated stressed group (the stressed group), 3) and an astressin-pretreated stressed group (the astressin group). Immediately after completing the experiments according to the protocol, distal esophageal segments were obtained. Intercellular space diameters of esophageal mucosa were measured by transmission electron microscopy. Blood was sampled for the measurement of plasma cortisol levels. Mucosal intercellular spaces were significantly greater in the stressed group than in the non-stressed group. Mucosal intercellular spaces of the astressin group were significantly smaller than those of the stressed group. Plasma cortisol levels in the stressed group were significantly higher than in the non-stressed group. Pretreatment with astressin tended to decrease plasma cortisol levels. Acute stress in rats enlarges esophageal intercellular spaces, and this stress-induced alteration appears to be mediated by CRF. Our results suggest that CRF may play a role in the pathophysiology of reflux-induced symptoms or mucosal damage.

Therapeutic utility of non-peptidic CRF1 receptor antagonists in anxiety, depression, and stress-related disorders: evidence from animal models

Adaptive responding to threatening stressors is of fundamental importance for survival. Dysfunctional hyperactivation of corticotropin releasing factor type-1 (CRF(1)) receptors in stress response system pathways is linked to stress-related psychopathology and CRF(1) receptor antagonists (CRAs) have been proposed as novel therapeutic agents. CRA effects in diverse animal models of stress that detect anxiolytics and/or antidepressants are reviewed, with the goal of evaluating their potential therapeutic utility in depression, anxiety, and other stress-related disorders. CRAs have a distinct phenotype in animals that has similarities to, and differences from, those of classic antidepressants and anxiolytics. CRAs are generally behaviorally silent, indicating that CRF(1) receptors are normally in a state of low basal activation. CRAs reduce stressor-induced HPA axis activation by blocking pituitary and possibly brain CRF(1) receptors which may ameliorate chronic stress-induced pathology. In animal models sensitive to anxiolytics and/or antidepressants, CRAs are generally more active in those with high stress levels, conditions which may maximize CRF(1) receptor hyperactivation. Clinically, CRAs have demonstrated good tolerability and safety, but have thus far lacked compelling efficacy in major depressive disorder, generalized anxiety disorder, or irritable bowel syndrome. CRAs may be best suited for disorders in which stressors clearly contribute to the underlying pathology (e.g. posttraumatic stress disorder, early life trauma, withdrawal/abstinence from addictive substances), though much work is needed to explore these possibilities. An evolving literature exploring the genetic, developmental and environmental factors linking CRF(1) receptor dysfunction to stress-related psychopathology is discussed in the context of improving the translational value of current animal models.

Role of mast cell activation in inducing microglial cells to release neurotrophin

The brain-derived neurotrophic factor (BDNF) plays a critical role in pain hypersensitivity. BDNF is the ligand of P2X4 receptors (P2X4R) in the microglia. The causative factors involving the P2X4R over expression in the microglia remains unclear. Mast cell activation has a close relation with pain hypersensitivity. However, the underlying mechanism between mast cell activation and pain hypersensitivity is unknown. The present study aimed to elucidate the mechanism by which mast cell activation promoted the expression of P2X4R in the microglia. The results of present study showed that mast cell activation markedly promoted the expression of P2X4R and BDNF in microglial cells, which significantly enhanced the release of BDNF from microglial cells upon exposure to adenosine triphosphate. Mast cell-derived tryptase activated PAR2 that resulted in promoting the expression of P2X4R in microglial cells. Pretreatment with antibodies against tryptase or PAR2, or using tryptase-deficient HMC-1 cells or PAR2-deficient microglial cells abolished the increase in P2X4R expression and BDNF release. Increase in mitogen activated protein kinase phosphorylation was observed in the processes of mast cell-induced BDNF release and P2X4R expression. We conclude that mast cell activation has the capacity to promote the expression of P2X4R and BDNF in microglial cells.

Combined administration of secretin and oxytocin inhibits chronic colitis and associated activation of forebrain neurons

BACKGROUND

The pathogenesis of inflammatory bowel disease is unknown; however, the disorder is aggravated by psychological stress and is itself psychologically stressful. Chronic intestinal inflammation, moreover, has been reported to activate forebrain neurons. We tested the hypotheses that the chronically inflamed bowel signals to the brain through the vagi and that administration of a combination of secretin (S) and oxytocin (OT) inhibits this signaling.

METHODS

Three daily enemas containing 2,4,6-trinitrobenzene sulfonic acid (TNBS), which were given to rats produced chronic colitis and ongoing activation of Fos in brain neurons.

KEY RESULTS

Fos was induced in neurons in the paraventricular nucleus of the hypothalamus, basolateral amygdala, central amygdala, and piriform cortex. Subdiaphragmatic vagotomy failed to inhibit this activation of Fos, suggesting that colitis activates forebrain neurons independently of the vagi. When administered intravenously, but not when given intracerebroventricularly, in doses that were individually ineffective, combined S/OT prevented colitis-associated activation of central neurons. Strikingly, S/OT decreased inflammatory infiltrates into the colon and colonic expression of tumor necrosis factor-alpha and interferon-gamma.

CONCLUSIONS & INFERENCES

These observations suggest that chronic colonic inflammation is ameliorated by the systemic administration of S/OT, which probably explains the parallel ability of systemic S/OT to inhibit the colitis-associated activation of forebrain neurons. It is possible that S and OT, which are endogenous to the colon, might normally combine to restrict the severity of colonic inflammatory responses and that advantage might be taken of this system to develop novel means of treating inflammation-associated intestinal disorders.

Duloxetine in the treatment of irritable bowel syndrome: an open-label pilot study

OBJECTIVE

To assess the efficacy of duloxetine for irritable bowel syndrome (IBS).

METHODS

We conducted an open-label 12-week trial of duloxetine 60 mg daily in 15 patients with IBS without concurrent major depressive disorder. The primary outcome measure was average abdominal pain. Secondary measures included IBS symptoms, Clinical Global Impression-Severity, Hamilton Anxiety Rating Scale, IBS Quality-of-Life Scale, and Sheehan Disability Scale. We analyzed changes using random regression and one-sample t-tests.

RESULTS

Fourteen patients completed at least one post-baseline evaluation; eight completed the study. Duloxetine was associated with significant improvement (p < 0.05) in pain, severity of illness, quality of life, loose stool, work and family disability, and anxiety. However, duloxetine did not improve hard stool. Although we found no evidence of serious duloxetine toxicity, seven participants withdrew over the course of the study because of adverse drug events.

CONCLUSIONS

In this small, open-label study, duloxetine appeared to be effective for many features of IBS, but its adverse effects, most notably constipation, limited its use. Since our study excluded individuals with concurrent major depression, it appears that duloxetine may benefit IBS independently of its antidepressant effects. These encouraging but preliminary open-label findings support further investigation of duloxetine treatment in placebo-controlled trials of IBS.

Expression and developmental regulation of oxytocin (OT) and oxytocin receptors (OTR) in the enteric nervous system (ENS) and intestinal epithelium

Although oxytocin (OT) and oxytocin receptor (OTR) are known for roles in parturition and milk let-down, they are not hypothalamus-restricted. OT is important in nurturing and opposition to stress. Transcripts encoding OT and OTR have been reported in adult human gut, and OT affects intestinal motility. We tested the hypotheses that OT is endogenous to the enteric nervous system (ENS) and that OTR signaling may participate in enteric neurophysiology. Reverse transcriptase polymerase chain reaction confirmed OT and OTR transcripts in adult mouse and rat gut and in precursors of enteric neurons immunoselected from fetal rats. Enteric OT and OTR expression continued through adulthood but was developmentally regulated, peaking at postnatal day 7. Coincidence of the immunoreactivities of OTR and the neural marker Hu was 100% in the P3 and 71% in the adult myenteric plexus, when submucosal neurons were also OTR-immunoreactive. Co-localization with NeuN established that intrinsic primary afferent neurons are OTR-expressing. Because OTR transcripts and protein were detected in the nodose ganglia, OT signaling might also affect extrinsic primary afferent neurons. Although OT immunoreactivity was found only in approximately 1% of myenteric neurons, extensive OT-immunoreactive varicosities surrounded many others. Villus enterocytes were OTR-immunoreactive through postnatal day 17; however, by postnatal day 19, immunoreactivity waned to become restricted to crypts and concentrated at crypt-villus junctions. Immunoelectron microscopy revealed plasmalemmal OTR at enterocyte adherens junctions. We suggest that OT and OTR signaling might be important in ENS development and function and might play roles in visceral sensory perception and neural modulation of epithelial biology.

Peripheral corticotropin releasing hormone mediates post-inflammatory visceral hypersensitivity in rats

AIM: To investigate whether peripheral corticotropin releasing hormone (CRH), which is up-regulated in intestinal inflammation, mediates the post-inflammatory visceral hypersensitivity in a rat model of colitis.

METHODS: We measured mucosal myeloperoxidase (MPO) activity as a marker of inflammation, plasma CRH level, and abdominal withdrawal reflex (AWR) to colorectal distension as a visceral nociceptive response at 2, 7 and 14 d after the induction of colitis with 4% acetic acid.

RESULTS: Colonic inflammation, quantified by MPO activity, significantly increased on d 2 and subsided thereafter, which indicated a resolution of inflammation within 7 d. On the contrary, plasma CRH level and AWR score were increased on d 2, remained high on d 7, and returned to control level on d 14. Intraperitoneal injection of a CRH antagonist, astressin (30 &mgr;g/kg), significantly attenuated the post-inflammatory visceral hypersensitivity on d 7. Furthermore, intraperitoneal administration of CRH (3 and 10 &mgr;g/kg) mimicked the post-inflammatory visceral hypersensitivity in naive rats.

CONCLUSION: These results suggest that increased peripheral CRH mediates the enhanced visceral nociception in rats recovered from experimental colitis.

New horizons in the pathogenesis of gastrointestinal neuromuscular disease

The term "gastrointestinal neuromuscular disease" can be interpreted variably and encompasses a spectrum of paediatric and adult conditions including achalasia, pseudoobstruction, idiopathic constipation, irritable bowel syndrome, megacolon, and Hirschsprung disease. Although progress has been made in the understanding of the pathophysiology of some conditions, the aetiopathogenesis has been elucidated only in the rare minority. This review critically considers the available evidence for possible pathogenic mechanisms in these disorders.

Experimental gastritis in mice enhances anxiety in a gender-related manner

There is a gender-related comorbidity of pain-related and inflammatory bowel diseases with psychiatric diseases. Since the impact of experimental gastrointestinal inflammation on the emotional-affective behavior is little known, we examined whether experimental gastritis modifies anxiety, stress coping and circulating corticosterone in male and female Him:OF1 mice. Gastritis was induced by adding iodoacetamide (0.1%) to the drinking water for at least 7 days. Inflammation was assessed by gastric histology and myeloperoxidase activity, circulating corticosterone determined by enzyme immunoassay, anxiety-related behavior evaluated with the elevated plus maze and stress-induced hyperthermia tests, and depression-like behavior estimated with the tail suspension test. Iodoacetamide-induced gastritis was associated with gastric mucosal surface damage and an increase in gastric myeloperoxidase activity, this increase being significantly larger in female mice than in male mice. The rectal temperature of male mice treated with iodoacetamide was enhanced, whereas that of female mice was diminished. The circulating levels of corticosterone were reduced by 65% in female mice treated with iodoacetamide but did not significantly change in male mice. On the behavioral level, iodoacetamide treatment caused a decrease in nocturnal home-cage activity, drinking and feeding. While depression-related behavior remained unaltered following induction of gastritis, behavioral indices of anxiety were significantly enhanced in female but not male mice. There was no correlation between the estrous cycle and anxiety as well as circulating corticosterone. Radiotracer experiments revealed that iodoacetamide did not readily enter the brain, the blood-brain ratio being 20:1. Collectively, these data show that iodoacetamide treatment causes gastritis in a gender-related manner, its severity being significantly greater in female than in male mice. The induction of gastritis in female mice is associated with a reduction of circulating corticosterone and an enforcement of behavioral indices of anxiety. Gastric inflammation thus has a distinct gender-dependent influence on emotional-affective behavior and its neuroendocrine control.

Physiology, pharmacology, and therapeutic relevance of urocortins in mammals: ancient CRF paralogs

Urocortins, three paralogs of the stress-related peptide corticotropin-releasing factor (CRF) found in bony fish, amphibians, birds, and mammals, have unique phylogenies, pharmacologies, and tissue distributions. As a result and despite a structural family resemblance, the natural functions of urocortins and CRF in mammalian homeostatic responses differ substantially. Endogenous urocortins are neither simply counterpoints nor mimics of endogenous CRF action. In their own right, urocortins may be clinically relevant molecules in the pathogenesis or management of many conditions, including congestive heart failure, hypertension, gastrointestinal and inflammatory disorders (irritable bowel syndrome, active gastritis, gastroparesis, and rheumatoid arthritis), atopic/allergic disorders (dermatitis, urticaria, and asthma), pregnancy and parturition (preeclampsia, spontaneous abortion, onset, and maintenance of effective labor), major depression and obesity. Safety trials for intravenous urocortin treatment have already begun for the treatment of congestive heart failure. Further understanding the unique functions of urocortin 1, urocortin 2, and urocortin 3 action may uncover other therapeutic opportunities.

New insights into the pathogenesis and pathophysiology of irritable bowel syndrome

The pathogenesis and pathophysiology of irritable bowel syndrome is complex and still incompletely known. Potential pathogenetic factors include genes, infectious events, psychological symptoms and other loosely defined environmental factors. Both alterations at the central and peripheral level are thought to contribute to the symptoms of irritable bowel syndrome, including psychosocial factors, abnormal gastrointestinal motility and secretion, and visceral hypersensitivity. Today irritable bowel syndrome is viewed upon as a disorder of dysregulation of the so-called brain-gut axis, involving abnormal function in the enteric, autonomic and/or central nervous systems, with peripheral abnormalities probably dominating in some patients and disturbed central processing of signals from the periphery in others. Lines of evidence also suggest that inflammation within the gastrointestinal tract may be of great importance in at least subgroups of irritable bowel syndrome patients. To conclude, a complex picture of the pathogenesis and pathophysiology of irritable bowel syndrome is emerging, with interactions between several different alterations resulting in the divergent symptom pattern in these patients.

Emerging drugs for irritable bowel syndrome

Irritable bowel syndrome (IBS) is one of the most common chronic gastrointestinal disorders, yet its pathophysiology is incompletely understood and pharmacological treatments remain unsatisfactory. Current therapeutic choices include a range of drugs aimed at normalising bowel habits, reducing pain or treating comorbid psychological symptoms. However, this individual symptom-targeted approach remains unsatisfactory in terms of global symptom relief and patient satisfaction. In the last decade, further characterisation of IBS pathophysiology has provided new and exciting targets at different levels of the brain-gut axis for the development of several candidate drugs. Advances in clinical trial design will help to evaluate these compounds in different IBS patient populations.