Dervla O’Malley

Do interactions between stress and immune responses lead to symptom exacerbations in irritable bowel syndrome

Irritable bowel syndrome (IBS) is a common, debilitating gastrointestinal (GI) disorder, with a worldwide prevalence of between 10% and 20%. This functional gut disorder is characterized by episodic exacerbations of a cluster of symptoms including abdominal pain, bloating and altered bowel habit, including diarrhea and/or constipation. Risk factors for the development of IBS include a family history of the disorder, childhood trauma and prior gastrointestinal infection. It is generally accepted that brain-gut axis dysfunction is fundamental to the development of IBS; however the underlying pathophysiological mechanisms remain elusive. Additional considerations in comprehending the chronic relapsing pattern that typifies IBS symptoms are the effects of both psychosocial and infection-related stresses. Indeed, co-morbidity with mood disorders such as depression and anxiety is common in IBS. Accumulating evidence points to a role for a maladaptive stress response in the initiation, persistence and severity of IBS-associated symptom flare-ups. Moreover, mechanistically, the stress-induced secretion of corticotropin-releasing factor (CRF) is known to mediate changes in GI function. Activation of the immune system also appears to be important in the generation of IBS symptoms and increasing evidence now implicates low-grade inflammation or immune activation in IBS pathophysiology. There is a growing body of research focused on understanding at a molecular, cellular and in vivo level, the relationship between the dysregulated stress response and immune system alterations (either individually or in combination) in the etiology of IBS and to the occurrence of symptoms.

Neonatal maternal separation in the rat impacts on the stress responsivity of central corticotropin-releasing factor receptors in adulthood

RationaleAdverse events during early developmental stages can induce persistent changes in central stress circuits, leading to increased stress sensitivity in adulthood, as is apparent in the maternally separated (MS) rat model. It is widely accepted that the stress peptide corticotropin-releasing factor (CRF) by binding to CRF1 and 2 receptors (CRFR1 and CRFR2) is key to these phenotypic changes.ObjectivesThese studies aim to investigate the effects of maternal separation on central expression of CRFR1 and CRFR2 under basal conditions and following an acute psychological stressor in adulthood.MethodsWestern blotting techniques were employed to examine changes in receptor expression in the hypothalamus, pre-frontal and frontal cortices, amygdala and hippocampus of MS rats as compared to controls. Additionally, the effects of an acute psychological stressor (open field exposure) on these changes were assessed.ResultsUnder basal conditions, CRFR1 was elevated in the hypothalamus of MS rats. Exposure to an acute stress had limited effects in non-separated animals but induced significant changes in CRFR1 in the hypothalamus, pre-frontal cortex and hippocampus of MS rats. Additionally, stress-induced increases in CRFR2 were observed in the amygdala of MS rats.ConclusionsThese data demonstrate the discrete and significant alterations in how the brain CRF system responds to acute stress following maternal separation. These studies illustrate that early life perturbations induce persistent changes in central CRF receptor expression and increased sensitivity to stress, which may contribute to the stress-related behavioural changes observed in these animals.

Alterations in colonic corticotropin-releasing factor receptors in the maternally separated rat model of irritable bowel syndrome: differential effects of acute psychological and physical stressors.

Early-life stress is a key predisposing factor to the development of functional gastrointestinal (GI) disorders. Thus, changes in stress-related molecular substrates which influence colonic function may be important in understanding the pathophysiology of such disorders. Activation of peripheral corticotropin-releasing factor (CRF) receptors is thought to be important in the maintenance of GI function homeostasis. Therefore, immunofluorescent and Western blotting techniques were utilized to investigate colonic expression of CRF receptors in the maternal separation (MS) model as compared to non-separated (NS) rats. Receptor expression was also assessed following exposure to two different acute stressors, the open field (OF) and colorectal distension (CRD). Immunofluorescent dual-labeling demonstrated increased activation of both CRFR1 (MS: 79.6+/-4.4% vs. NS: 43.8+/-6.8%, p<0.001) and CRFR2 (MS: 65.9+/-3.2% vs. NS: 51.6+/-5.8%, p<0.05) positive cells in MS rats. Protein expression of CRFR1 and CRFR2 in the proximal colon was similar under baseline conditions and not affected by exposure to an OF stressor in either cohort. In contrast, distal CRFR1 and CRFR2 levels were higher in MS rats but were significantly reduced post OF stress. Moreover, decreases in expression of CRFR1 in the proximal and distal colon of NS rats following exposure to CRD were blunted in MS rats. CRD also caused an increase in the functional isoform of CRFR2 in the distal colon of MS rats with no effect in NS colons. This study demonstrates that acute stressors alter colonic CRF receptor expression in a manner that is determined by the underlying stress sensitivity of the subject.

Convergence of neuro-endocrine-immune pathways in the pathophysiology of irritable bowel syndrome

Disordered signalling between the brain and the gut are generally accepted to underlie the functional bowel disorder, irritable bowel syndrome (IBS). However, partly due to the lack of disease-defining biomarkers, understanding the aetiology of this complex and multifactorial disease remains elusive. This common gastrointestinal disorder is characterised by alterations in bowel habit such as diarrhoea and/or constipation, bloating and abdominal pain, and symptom exacerbation has been linked with periods of stress, both psychosocial and infection-related. Indeed, a high level of comorbidity exists between IBS and stress-related mood disorders such as anxiety and depression. Moreover, studies have observed alterations in autonomic output and neuro-endocrine signalling in IBS patients. Accumulating evidence indicates that a maladaptive stress response, probably mediated by the stress hormone, corticotropin-releasing factor contributes to the initiation, persistence and severity of symptom flares. Other risk factors for developing IBS include a positive family history, childhood trauma, dietary factors and prior gastrointestinal infection. An emerging role has been attributed to the importance of immune factors in the pathophysiology of IBS with evidence of altered cytokine profiles and increased levels of mucosal immune cells. These factors have also been shown to have direct effects on neural signalling. This review discusses how pathological changes in neural, immune and endocrine pathways, and communication between these systems, contribute to symptom flares in IBS.

Crosstalk between interleukin-6 and corticotropin-releasing factor modulate submucosal plexus activity and colonic secretion.

BACKGROUND Irritable bowel syndrome (IBS) is a common disorder of the gut with symptoms such as diarrhoea, constipation, abdominal pain and bloating, that are frequently exacerbated by stress. Circulating levels of the pro-inflammatory cytokine, interleukin-6 (IL-6), which can activate colonic enteric neurons, are elevated in IBS patients. These studies aim to explore the relationship between IL-6 and the stress peptide, corticotropin-releasing factor (CRF) in colonic submucosal neurons. METHODS Calcium imaging, Ussing chamber electrophysiology and immunohistochemistry were conducted on rat distal colons to investigate potential crosstalk between IL-6 and CRF. KEY RESULTS Colonic secretions from the maternal separation rat model of IBS stimulated increases in intracellular calcium in naïve submucosal neurons via CRF1 receptors (n=15, p<0.05). Moreover, IL-6 (n=50, p<0.01) but not IL-1β (n=46, p>0.05) or TNFα (n=46, p>0.05) potentiated the CRF-evoked calcium response. CRF (1μM, 1h, n=5) stimulation also induced colonic secretion of IL-6 and inhibited the pro-secretory effects of IL-6 on colonic ion transfer (n=12). CONCLUSIONS AND INFERENCES These studies demonstrate the modulatory effects of CRF on colonic IL-6 secretion, neuronal activation and secretory function. These findings may provide an insight into the molecular mechanisms underlying symptom flares in IBS during periods of high stress.

Respiratory Control in the mdx Mouse Model of Duchenne Muscular Dystrophy

Duchenne muscular dystrophy (DMD) is a genetic disease caused by defects in the dystrophin gene resulting in loss of the structural protein dystrophin. Patients have reduced diaphragm functional capacity due to progressive muscle weakness. Respiratory morbidity in DMD is further characterised by hypoxaemic periods due to hypoventilation. DMD patients die prematurely due to respiratory and cardiac failure. In this study, we examined respiratory function in young adult male mdx (dystrophin deficient) mice (C57BL/10ScSn-Dmd(mdx)/J; n = 10) and in wild-type controls (WT; C57BL/10ScSnJ; n = 11). Breathing was assessed in unrestrained, unanaesthetised animals by whole-body plethysmography. Ventilatory parameters were recorded during air breathing and during exposure to acute hypoxia (F(i)O(2) = 0.1, 20 min). Data for the two groups of animals were compared using Students t tests. During normoxic breathing, mdx mice had reduced breathing frequency (p = 0.011), tidal volume (p = 0.093) and minute ventilation (p = 0.033) compared to WT. Hypoxia increased minute ventilation in WT and mdx animals. Mdx mice had a significantly increased ventilatory response to hypoxia which manifest as an elevated % change from baseline for minute ventilation (p = 0.0015) compared to WT. We conclude that mdx mice have impaired normoxic ventilation suggestive of hypoventilation. Furthermore, mdx mice have an enhanced hypoxic ventilatory response compared to WT animals which we speculate may be secondary to chronic hypoxaemia. Our results indicate that a significant respiratory phenotype is evident as early as 8 weeks in the mdx mouse model of DMD.

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.

Strain differences in stress-induced changes in central CRF1 receptor expression

The Wistar Kyoto (WKY) rat is genetically predisposed to increased sensitivity to psychological and physical stressors. Evidence points towards the importance of corticotropin-releasing factor (CRF), a peptide secreted by the paraventricular nucleus of the hypothalamus, in this strains aberrant response to stress. CRF binds to CRF1 and 2 receptors (CRFR1 and CRFR2) which are expressed in both hypothalamic and extra-hypothalamic brain regions. Phosphorylation of the signal transduction molecule, extracellular signal regulated kinase (ERK)1/2 has been linked with stress and the actions of CRF. Western blotting techniques were employed to examine changes in protein expression of CRFR1 and phosphorylated ERK1/2 in hypothalamic and extra-hypothalamic brain regions of open field-stressed Sprague Dawley (SD) and WKY rats. Stress exposure resulted in increased hypothalamic ERK1/2 phosphorylation and subsequent increases in CRFR1 expression in SD but not WKY rats. In extra-hypothalamic brain regions, the stressor caused decreased or unchanged ERK 1/2 phosphorylation in both strains. A potentiated increase in CRFR1 expression was noted in the frontal cortex of WKY rats following the stressor and expression of CRFR1 was reduced in the hippocampus of WKY rats. These data demonstrate region-specific differences in stress-induced changes in expression of CRF receptors and intracellular signaling molecules in stress-sensitive WKY rats and stress-resilient SD rats.

Do prerecorded lecture VODcasts affect lecture attendance of first-yearpre-clinical Graduate Entry to Medicine students?

Abstract Background: There is increasing concern amongst educators that the provision of recorded lectures may reduce student attendance of live lectures. We therefore sought to determine if the provision of prerecorded lecture video podcasts (VODcasts) to first-year Graduate Entry to Medicine (GEM) students, affected attendance at 21 Physiology lectures within three separate pre-clinical modules. Methods: Data on lecture attendance, utilization of VODcasts, and whether VODcasts should replace live lectures were drawn from three surveys conducted in academic years 2014–2015 and 2015–2016 on all first-year GEM students in two first-year pre-clinical modules where prerecorded Physiology VODcasts were available for viewing or downloading prior to scheduled live lectures. Results: A total of 191/214 (89%) students responded to the three surveys, with 84.3% of students attending all 21 lectures in the study. Only 4% of students missed more than one lecture in each of the three lecture series, with 79% indicating that VODcasts should not replace lectures. Conclusion: Therefore, we conclude that the attendance of pre-clinical GEM students at live lectures is not significantly impacted upon by the provision of lecture VODcasts, with most students viewing them as useful revision tools rather than as a replacement for live lectures.

Corticotropin-releasing factor-mediated enhancement of interleukin-6-induced activation of sub-mucosal neurons

405 IL-6 is associated with metabolic syndrome in bipolar disorder A. Prossin , M. McInnis , S. Zalcman , V. Ellingrod a,c a Comprehensive Depression Center, Department of Psychiatry, University of Michigan Medical School, 4250 Plymouth Rd, Ann Arbor, MI 48105, United States b Department of Psychiatry, New Jersey Medical School, University of Medicine and Dentistry of New Jersey, United States c College of Pharmacy, University of Michigan, United States Strong associations exist between pro-inflammatory cytokines (i.e. IL-6) and the metabolic syndrome. In Bipolar Disorder (BD), interleukin-6 (IL-6) is associated with depressed mood, but whether this inflammatory marker accounts for the co-morbidity of metabolic syndrome is unclear.Here we explore the relationship between IL-6 and the presence of metabolic syndrome in BD in an attempt to clarify the role of this potential bio-marker in predicting risk of metabolic syndrome. We studied 78 euthymic BD subjects using a cross-sectional design. Serum IL-6 concentrations were determined with standard ELISAs. The subjects were stratified by presence or absence of metabolic syndrome (NCEP-ATP-III criteria). We compared (Student’s t-test) the differences in IL-6 between these two BD subgroups. We investigated the effects of other variables (i.e. number of criteria of metabolic syndrome) on the relationship between IL-6 and metabolic syndrome in BD using correlations. IL-6 was significantly greater in the BDs with metabolic syndrome as compared to those without. IL-6 was significantly correlated to the number of criteria of metabolic syndrome. These results identify IL-6 as a potential diagnostic marker of metabolic syndrome in BD, a previously understudied relationship.Future longitudinal designs will assess the predictive potential of IL-6 in determining risk of metabolic syndrome in patients with BD. Given the previously identified relationships between IL-6 and mood state in BD, this study furthers the understanding of these common ‘‘mind–body” interactions. doi:10.1016/j.bbi.2010.07.155