Vagal dysfunction in irritable bowel syndrome assessed by rectal distension and baroreceptor sensitivity

Factors associated with irritable bowel syndrome and Helicobacter pylori infection: public knowledge and awareness of signs and symptoms

OBJECTIVE

To investigate factors related to the risk of developing irritable bowel syndrome (IBS) or Helicobacter pylori infection.

METHODS

This cross-sectional, questionnaire-based study analysed the responses from participants that completed an online questionnaire, which asked about their knowledge of the causes and risk factors associated with IBS and H. pylori infection.

RESULTS

The study analysed responses from 230 participants: 181 females (of 227 participants; 79.7%) and 190 aged 18-40 years (of 228; 83.3%). Of the 230 participants, 40 (17.4%) had been diagnosed by a physician with IBS and 57 (24.8%) had been diagnosed with H. pylori infection. Of 226 participants, 93 (41.2%) had self-medicated with antibiotics in the past 6 months for various reasons. The overall mean ± SD knowledge score about IBS and H. pylori infection for the study cohort (n = 230) was 35.8 ± 19.2%. Wald χ2-test analysis demonstrated that chronic diseases, antibiotic use and having an endoscopy were significantly associated with developing IBS. Male sex and chronic diseases were significantly associated with H. pylori infection. Logistic regression analysis showed no relationship between IBS and H. Pylori infection.

CONCLUSION

Chronic diseases was the only risk factor common for IBS and H. pylori infection.

Best Parameters of Heart Rate Variability for Assessing Autonomic Responses to Brief Rectal Distention in Patients with Irritable Bowel Syndrome

Heart rate variability (HRV) has been used to measure autonomic nervous system (ANS) activity noninvasively. The purpose of this study was to identify the most suitable HRV parameters for ANS activity in response to brief rectal distension (RD) in patients with Irritable Bowel Syndrome (IBS). IBS patients participated in a five-session study. During each visit, an ECG was recorded for 15 min for baseline values and during rectal distension. For rectal distension, a balloon was inflated in the rectum and the pressure was increased in steps of 5 mmHg for 30 s; each distension was followed by a 30 s rest period when the balloon was fully deflated (0 mmHg) until either the maximum tolerance of each patient was reached or up to 60 mmHg. The time-domain, frequency-domain and nonlinear HRV parameters were calculated to assess the ANS activity. The values of each HRV parameter were compared between baseline and RD for each of the five visits as well as for all five visits combined. The sensitivity and robustness/reproducibility of each HRV parameter were also assessed. The parameters included the Sympathetic Index (SI); Root Mean Square of Successive Differences (RMSSD); High-Frequency Power (HF); Low-Frequency Power (LF); Normalized HF Power (HFn); Normalized LF Power (LFn); LF/HF; Respiratory Sinus Arrhythmia (RSA); the Poincare Plot's SD1, SD2 and their ratio; and the pNN50, SDSD, SDNN and SDNN Index. Data from 17 patients were analyzed and compared between baseline and FD and among five sessions. The SI was found to be the most sensitive and robust HRV parameter in detecting the ANS response to RD. Out of nine parasympathetic parameters, only the SDNN and SDNN Index were sensitive enough to detect the parasympathetic modulation to RD during the first visit. The frequency-domain parameters did not show any change in response to RD. It was also observed that the repetitive RD in IBS patients resulted in a decreased autonomic response due to habituation because the amount of change in the HRV parameters was the highest during the first visit but diminished during subsequent visits. In conclusion, the SI and SDNN/SDNN Index are most sensitive at assessing the autonomic response to rectal distention. The autonomic response to rectal distention diminishes in repetitive sessions, demonstrating the necessity of randomization for repetitive tests.

Can the change of vasomotor activity in irritable bowel syndrome patients be detected via color Doppler ultrasound?

BACKGROUND

Irritable bowel syndrome (IBS) is one of the most frequently referred conditions to the gastrointestinal outpatient clinic. The pathophysiology of IBS has not been determined with certainty. Visceral hypersensitivity is indicated as one of the pathophysiologies. The sympathetic nervous system is primarily in charge of controlling the arteries, and its effect is vasospasm in the medium and large arteries, resulting in decreased blood flow.

AIM

To demonstrate, using Doppler evaluation of the brachial artery, that sympathetic activity impairs vasomotor performance due to autonomic neuropathy, which we believe is associated with IBS.

METHODS

There were 58 participants in the study. The control group consisted of 29 healthy patients, while the remaining 29 patients had been diagnosed with IBS. Patients who met the Rome IV criteria and had IBS were included in the study. People with known polyneuropathy or non-IBS chronic conditions that can progress were excluded from the trial, as were those with essential hypertension, diabetes mellitus, cardiovascular disease, or peripheral arterial disease, and patients diagnosed with anxiety or depression. Those with moderate to severe carpal tunnel syndrome or a median nerve lesion due to trauma were also excluded from the trial. A Doppler probe was used to measure the baseline diameter and flow rates of the brachial artery from 2 cm superior to the antecubital fossa. The Doppler probe remained stationary throughout the experiment, allowing for continuous measurements. Then, to activate the sympathetic fibers, an electrical stimulus for 5 s with an intensity of 10 mA and a frequency of 1 Hz was applied to the median nerve at the wrist level via the bipolar stimulus electrode. The artery diameter and flow rates were measured again immediately following the fifth stimulus.

RESULTS

In healthy persons with no history of chronic illness, there was a statistically significant decrease in flow rate after stimulation (P < 0.001). In addition, stimulation resulted in a statistically significant reduction in the diameter of the brachial artery (P < 0.001). Patients diagnosed with IBS had statistically significant vasodilation and an increase in flow rate.

CONCLUSION

Sympathetic stimulation causes a reduction in vascular diameter and blood flow, whereas it has the reverse effect on IBS patients. In investigating the involvement of autonomic neuropathy in the development of IBS, significant changes in brachial artery Doppler parameters were observed before and after stimulation of the median nerve with low-current sensory stimulation. This method is thought to be more user-friendly and comfortable than other methods described in the literature.

Expression of the fructose transporter GLUT5 in patients with fructose malabsorption

BACKGROUND

 Patients with abdominal symptoms are frequently diagnosed with fructose malabsorption (FM). Fructose is absorbed by monosaccharide transporters located in the brush border of the human small intestine. The aim of this study was to investigate the histoanatomical distribution of the main fructose transporter GLUT5.

MATERIALS AND METHODS

 We studied 223 patients diagnosed with FM by a hydrogen breath test and grouped according to their response to a fructose-free diet. The control group were 42 healthy individuals and 29 patients with celiac disease (CD). The fructose breath test was done with 50 g fructose. The expression of Glut5 in duodenal biopsy specimens was studied by immunohistochemistry. The Kruskal-Wallis-test and Mann-Whitney U-test were used to carry out the statistical analysis.

RESULTS

 The histoanatomical expression pattern of GLUT5 did not differ significantly between those patients with FM who responded completely to a fructose-free diet (n = 183) and healthy individuals (n = 42); nor did it correlate to H2 production measured in fructose breath testing. In patients with FM, the GLUT5 expression pattern did not differ between those individuals responding to a fructose-free diet and those who did not. However, GLUT5 expression pattern was significantly different in patients with CD (n = 29) compared to patients with FM and to healthy individuals (p = 0.009).

CONCLUSION

 GLUT5 expression patterns are not be related to adult patients with FM. However, in secondary malabsorption, a decreased GLUT5 expression was found. Further investigation is needed to understand the essential factors in FM and the influence on functional gastrointestinal disorders.

Acute visceral pain relief mediated by A3AR agonists in rats: involvement of N-type voltage-gated calcium channels

ABSTRACT

Pharmacological tools for chronic visceral pain management are still limited and inadequate. A3 adenosine receptor (A3AR) agonists are effective in different models of persistent pain. Recently, their activity has been related to the block of N-type voltage-gated Ca2+ channels (Cav2.2) in dorsal root ganglia (DRG) neurons. The present work aimed to evaluate the efficacy of A3AR agonists in reducing postinflammatory visceral hypersensitivity in both male and female rats. Colitis was induced by the intracolonic instillation of 2,4-dinitrobenzenesulfonic acid (DNBS; 30 mg in 0.25 mL 50% EtOH). Visceral hypersensitivity was assessed by measuring the visceromotor response and the abdominal withdrawal reflex to colorectal distension. The effects of A3AR agonists (MRS5980 and Cl-IB-MECA) were evaluated over time after DNBS injection and compared to that of the selective Cav2.2 blocker PD173212, and the clinically used drug linaclotide. A3AR agonists significantly reduced DNBS-evoked visceral pain both in the postinflammatory (14 and 21 days after DNBS injection) and persistence (28 and 35 days after DNBS) phases. Efficacy was comparable to effects induced by linaclotide. PD173212 fully reduced abdominal hypersensitivity to control values, highlighting the role of Cav2.2. The effects of MRS5980 and Cl-IB-MECA were completely abolished by the selective A3AR antagonist MRS1523. Furthermore, patch-clamp recordings showed that A3AR agonists inhibited Cav2.2 in dorsal root ganglia neurons isolated from either control or DNBS-treated rats. The effect on Ca2+ current was PD173212-sensitive and prevented by MRS1523. A3AR agonists are effective in relieving visceral hypersensitivity induced by DNBS, suggesting a potential therapeutic role against abdominal pain.

Baroreceptor Modulation of the Cardiovascular System, Pain, Consciousness, and Cognition

Baroreceptors are mechanosensitive elements of the peripheral nervous system that maintain cardiovascular homeostasis by coordinating the responses to external and internal environmental stressors. While it is well known that carotid and cardiopulmonary baroreceptors modulate sympathetic vasomotor and parasympathetic cardiac neural autonomic drive, to avoid excessive fluctuations in vascular tone and maintain intravascular volume, there is increasing recognition that baroreceptors also modulate a wide range of non-cardiovascular physiological responses via projections from the nucleus of the solitary tract to regions of the central nervous system, including the spinal cord. These projections regulate pain perception, sleep, consciousness, and cognition. In this article, we summarize the physiology of baroreceptor pathways and responses to baroreceptor activation with an emphasis on the mechanisms influencing cardiovascular function, pain perception, consciousness, and cognition. Understanding baroreceptor-mediated effects on cardiac and extra-cardiac autonomic activities will further our understanding of the pathophysiology of multiple common clinical conditions, such as chronic pain, disorders of consciousness (e.g., abnormalities in sleep-wake), and cognitive impairment, which may result in the identification and implementation of novel treatment modalities. © 2021 American Physiological Society. Compr Physiol 11:1373-1423, 2021.

Vagus nerve assessment via ultrasonography in irritable bowel syndrome. Are there any changes of dimension in the vagus nerve?

BACKGROUND/AIM

Irritable bowel syndrome (IBS) is the functional gastrointestinal disorder which has closely relationship with Central Nervous System (CNS). VN is the major connector between CNS and Enteric Nervous System (ENS). The aim of this study was to investigate the possible changes of dimension of Vagus Nerve (VN) with Vagus ultrasonography (VU) in IBS.

MATERIAL AND METHODS

A total 119 patients which is consisted of 66 IBS patients appropriated with Rome IV criterias and 53 patients of control group were enrolled to the study. All patients were underwent to colonoscopy for role-out the organic pathologies, such as polyposis, inflammatory bowel syndromes, diverticulosis and colon cancer. Right Vagus (RV) and left Vagus (LV) nerve areas and diameters were calculated with VU.

RESULTS

There were no statistical difference of RV (p=0.445) and LV (p=0.944) diameter between two groups. There were also no statistical difference of RV (p=0.549) and LV (p=0.874) areas between IBS and control groups.

CONCLUSION

VU clearly depicted that there is no changes of dimension in VN areas and diameters in the IBS. This might show that VN is only a transporter of abnormal neuronal stimulations according to IBS pathophisiology.

Associations among neurophysiology measures in irritable bowel syndrome (IBS) and their relevance for IBS symptoms

Abnormal gut-brain interactions are common in irritable bowel syndrome (IBS), but the associations between neurophysiological measures and their relation to gastrointestinal (GI) symptoms are poorly understood. Our aim was to explore these relationships and define the most relevant neurophysiology measures for GI symptom severity in IBS. IBS patients underwent small intestinal motility (manometry; fasted and fed contraction frequency, phase III time) and secretion (transmural potential difference), rectal sensorimotor (barostat; sensory thresholds, tone response, compliance), autonomic nervous system (baroreceptor sensitivity and effectiveness), and colonic motor function (transit time) examinations. GI symptom severity (GSRS-IBS), and anxiety and depression (HAD) as a proxy measure of central nervous system (CNS) dysfunction, were assessed. In total 281 IBS patients (Rome II criteria) were included (74% females, median age 36 [interquartile range 28-50] years). Significant correlations between neurophysiology measures were stronger within, rather than between, different neurophysiological examinations. The strongest neurophysiology-symptom correlations occurred between a combination of CNS and visceral sensitivity parameters, and GSRS-IBS total score and pain domain (ρ = 0.40, p < 0.001, and ρ = 0.38, p < 0.001). Associations between GI symptoms in IBS and individual and combinations of neurophysiological factors occurred, primarily in CNS and visceral sensitivity measures, providing new insights into the clinical presentation of IBS.

Interoceptive Abilities in Inflammatory Bowel Diseases and Irritable Bowel Syndrome

Alexithymia is usually described by three main dimensions difficulty identifying feelings (DIF), difficulty describing feelings (DDF), and externally oriented thinking (EOT). The most commonly used questionnaire investigating alexithymia, the Toronto Alexithymia Scale (TAS-20), supports this three-factor structure. One important assumption is that alexithymia severity is associated to vulnerability to somatic diseases, among them gastrointestinal disorders. However, the association between alexithymia and gastrointestinal disorders is not systematic, thus questioning the role of alexithymia as a vulnerability factor for those illnesses. A recent factor analysis suggested another four-factor structure for the TAS-20: difficulties in awareness of feelings (DAF), difficulties in interoceptive abilities (DIA), externally oriented thinking (EOT), and poor affective sharing (PAS). We assume that DIA and DAF might be more relevant to investigate the association between alexithymia and gastrointestinal disorders. The rationale is that DIA and DAF reflect impairments in emotion regulation that could contribute to an inappropriate autonomic and HPA axis homeostasis in irritable bowel syndrome (IBS), ulcerative colitis (UC), or Crohn's disease (CD). The aim of this study was to investigate whether DIA and DAF are associated with the presence of IBS, UC or CD, while checking for anxiety, depression, parasympathetic (vagus nerve) activity and cortisol levels. We recruited control participants (n=26), and patients in remission who were diagnosed with IBS (n=24), UC (n=18), or CD (n=21). Participants completed questionnaires to assess anxiety, depression, and alexithymia. A blood sample and an electrocardiogram were used to measure the level of cortisol and parasympathetic activity, respectively. Logistic regressions with the four-factor structure of the TAS-20 revealed that DIA was a significant predictor of IBS (W(1)=6.27, p=.01). Conversely, DIA and DAF were not significant predictors in CD and UC patients. However, low cortisol level was a significant predictor of UC (W(1)=4.67, p=.035). Additional logistic regressions based on the original 3-factor structure of TAS-20 (DIF, DDF, and EOT) showed that only DDF was a significant predictor of CD [W(1)=6.16, p < .001]. The present study suggests that DIA is an important dimension for assessing potential risk for gastrointestinal diseases, in particular for IBS.

Chronic pain-related changes in cardiovascular regulation and impact on comorbid hypertension in a general population: the Tromsø study

Heart rate variability (HRV) and baroreflex sensitivity (BRS) are indexes reflecting the ability to maintain cardiovascular homeostasis amidst changing conditions. Evidence primarily from small studies suggests that both HRV and BRS may be reduced in individuals with chronic pain (CP), with potential implications for cardiovascular risk. We compared HRV and BRS between individuals with CP (broadly defined) and pain-free controls in a large unselected population sample. Participants were 1143 individuals reporting clinically meaningful CP and 5640 pain-free controls who completed a 106-second cold pressor test (CPT). Participants self-reported hypertension status. Resting HRV and BRS were derived from continuous beat-to-beat blood pressure recordings obtained before and after the CPT. Hierarchical regressions for the pre-CPT period indicated that beyond effects of age, sex, and body mass index, the CP group displayed significantly lower HRV in both the time domain (SDNN and rMSSD) and frequency domain (high-frequency HRV power), as well as lower BRS. Results were somewhat weaker for the post-CPT period. Mediation analyses indicated that for 6 of 7 HRV and BRS measures tested, there were significant indirect (mediated) effects of CP status on the presence of comorbid hypertension via reduced HRV or BRS. Results confirm in the largest and broadest sample tested to date that the presence of CP is linked to impaired cardiovascular regulation and for the first time provide support for the hypothesis that links between CP and comorbid hypertension reported in previous population studies may be due in part to CP-related decrements in cardiovascular regulation.

Preliminary report: parasympathetic tone links to functional brain networks during the anticipation and experience of visceral pain

The mechanisms that underpin the anti-nociceptive effect of the parasympathetic nervous system (PNS) on visceral pain remain incompletely understood. We sought to describe the effect of resting parasympathetic tone on functional brain networks during the anticipation and experience of oesophageal pain. 21 healthy participants had their resting cardiac vagal tone (CVT), a validated measure of the PNS, quantified, and underwent functional magnetic resonance imaging during the anticipation and experience of painful oesophageal distention. The relationship between resting CVT and functional brain networks was examined using 11 hypothesis-driven nodes and network-based statistics. A network comprising all nodes was apparent in individuals with high resting CVT, compared to those with low CVT, during oesophageal pain (family wise error rate (FWER)-corrected p < 0.048). Functional connections included the thalamus-amygdala, thalamus-hypothalamus, hypothalamus-nucleus accumbens, amygdala-pallidum, pallidum-nucleus accumbens and insula-pallidum. A smaller network was seen during pain anticipation, comprising the amygdala, pallidum and anterior insula (FWER-corrected p < 0.049). These findings suggest that PNS tone is associated with functional brain networks during the anticipation and experience of visceral pain. Given the role of these subcortical regions in the descending inhibitory modulation of pain, these networks may represent a potential neurobiological explanation for the anti-nociceptive effect of the PNS.

Symptomatology Correlations Between the Diaphragm and Irritable Bowel Syndrome

Irritable bowel syndrome (IBS) is one of the most debilitating and common gastrointestinal disorders; nevertheless, its pathophysiology is still unclear. It affects 11% of the world's population, and is characterized by alternating periods of pain and/or motility disorders with periods of remission and without any evidence of any structural and functional organic variation. It has been recently proposed that an altered contractile ability of the diaphragm muscle might adversely influence intestinal motility. The text reviews the diaphragm's functions, anatomy, and neurological links in correlation with the presence of chronic symptoms associated to IBS, like chronic low back pain, chronic pelvic pain, chronic headache, and temporomandibular joint dysfunction, vagus nerve inflammation, and depression and anxiety. The interplay between an individual's breath dynamic and intestinal behaviour is still an unaddressed point in the physiopathology of IBS, and the paucity of scientific studies should recommend further research to better understand the importance of breathing in this syndrome.

Asymmetries in reciprocal baroreflex mechanisms and chronic pain severity: Focusing on irritable bowel syndrome

BACKGROUND

Objective measures of pain severity remain ill defined, although its accurate measurement is critical. Reciprocal baroreflex mechanisms of blood pressure (BP) control were found to impact differently on pain regulation, and thus their asymmetry was hypothesized to also connect to chronic pain duration and severity.

METHODS

Seventy-eight female patients with irritable bowel syndrome (IBS) and 27 healthy women were assessed for IBS severity and chronicity, negative affect, and various measures of resting autonomic function including BP, heart rate and its variability (HRV), baroreceptor-sensitivity to activations and inhibitions, gains of brady- and tachy-cardiac baro-responses, gains of BP falls/rises, and BP start points for these spontaneous baroreflexes.

KEY RESULTS

IBS directly and indirectly (through increased negative affect) was associated with asymmetry between baroreceptor activations/inhibitions compared to symmetrical baroreflex reciprocity in the healthy women. In the IBS group, independently of specific IBS symptoms, pain chronicity was associated with (i) decreased BP falls coupled with either (a) decreased tachycardia associated with lower disease severity (earlier "pain resilience" mechanism), or (b) decreased bradycardia associated with higher disease severity (later "pain decompensation" mechanism), or (ii) increased BP start point for baroreceptor activations coupled with either (a) BP increase (delayed "pain adaptation" mechanism) or (b) affect-related HRV decrease (delayed "pain aggravation" mechanism).

CONCLUSION AND INFERENCES

We anticipate the findings to be a starting point for validating these autonomic metrics of pain suffering and pain coping mechanisms in other chronic pain syndromes to suggest them as biomarkers of its severity and duration for profiling and correct management of chronic pain patients.

Morphology of subcortical brain nuclei is associated with autonomic function in healthy humans

The autonomic nervous system (ANS) is a brain body interface which serves to maintain homeostasis by influencing a plethora of physiological processes, including metabolism, cardiorespiratory regulation and nociception. Accumulating evidence suggests that ANS function is disturbed in numerous prevalent clinical disorders, including irritable bowel syndrome and fibromyalgia. While the brain is a central hub for regulating autonomic function, the association between resting autonomic activity and subcortical morphology has not been comprehensively studied and thus was our aim. In 27 healthy subjects [14 male and 13 female; mean age 30 years (range 22-53 years)], we quantified resting ANS function using validated indices of cardiac sympathetic index (CSI) and parasympathetic cardiac vagal tone (CVT). High resolution structural magnetic resonance imaging scans were acquired, and differences in subcortical nuclei shape, that is, 'deformation', contingent on resting ANS activity were investigated. CSI positively correlated with outward deformation of the brainstem, right nucleus accumbens, right amygdala and bilateral pallidum (all thresholded to corrected P < 0.05). In contrast, parasympathetic CVT negatively correlated with inward deformation of the right amygdala and pallidum (all thresholded to corrected P < 0.05). Left and right putamen volume positively correlated with CVT (r = 0.62, P = 0.0047 and r = 0.59, P = 0.008, respectively), as did the brainstem (r = 0.46, P = 0.049). These data provide novel evidence that resting autonomic state is associated with differences in the shape and volume of subcortical nuclei. Thus, subcortical morphological brain differences in various disorders may partly be attributable to perturbation in autonomic function. Further work is warranted to investigate these findings in clinical populations. Hum Brain Mapp 39:381-392, 2018. © 2017 Wiley Periodicals, Inc.

Baroreflex mechanisms in Irritable Bowel Syndrome: Part I. Traditional indices

OBJECTIVE

This study was conducted to present evidence of differences in autonomic regulation of cardiovascular activity and its role in the severity of specific (disease-related) and non-specific (negative affect and chronic pain-related) symptoms in individuals with Irritable Bowel Syndrome (IBS).

METHODS

Seventy-eight female patients with IBS and 27 healthy women age 18-62 years were assessed for IBS symptoms, negative affect, and baroreceptor sensitivity (BRS), blood pressure (BP), heart rate, and heart rate variability (HRV) at rest. Direct and indirect regression effects were examined with application of the bootstrap procedure to validate findings.

RESULTS

IBS was reliably related to lower resting BRS, higher BP, and higher negative affect compared to healthy controls. Longer disease duration (chronicity) was related to BRS decrease coupled with systolic BP increase (95% CIs=-0.14 to -0.01). Three autonomic mechanisms associated with BRS decrease were found to further regulate severity of IBS symptoms. Lower BRS was related to higher IBS severity in general if the effect was transferred through the decrease of low frequency power of HRV (e.g., 95% CIs=-0.039 to -0.001 for abdominal pain severity). However, lower BRS was related to lower IBS severity in general if the effect was transferred through diastolic BP increase (95% CIs=0.01-0.11 for abdominal pain severity). Lower BRS was related to higher abdominal pain severity coupled with high negative affect if the effect was transferred through the decrease of higher frequency power of HRV (95% CIs=-0.026 to -0.003).

CONCLUSIONS

These findings indicate that different cardiovascular mechanisms are associated with IBS development and the increase and decrease of severity of IBS symptoms. Their assessment suggests ways to personalize treatment of IBS.

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.

Chronic pain, body mass index and cardiovascular disease risk factors: tests of moderation, unique and shared relationships in the Study of Women's Health Across the Nation (SWAN)

Chronic pain may be related to cardiovascular disease (CVD) risk. The current study examined whether persistent bodily pain was related to cardiovascular disease risk factors, whether these effects were moderated by body mass index (BMI), and, if not, whether chronic pain accounted for unique variance in CVD risk factors. Participants were women (N = 2,135) in the Study of Women's Health Across the Nation. A high pain frequency variable (high pain in 0 through 4 assessments) was coded to reflect the frequency of high levels of bodily pain across the first 3 years of the study. Six CVD risk factors and BMI were measured at follow-up year 3. High pain frequency and BMI were correlated significantly with risk factors, although effects for the former were small. Hierarchical multiple regressions revealed high pain frequency × BMI interactions for 5 of 6 CVD risk factors. Dissecting the interactions revealed a similar pattern across 4 risk factors: for women with normal BMI, there was a "dose-response" in which increasing frequency of high pain revealed increasingly worse CVD risk factor levels, whereas for women with obese BMI, high pain frequency was unrelated to risk factors. For obese women, increasing frequency of high pain was associated with higher blood glucose. Although BMI is a well-established CVD risk factor, evaluation of CVD risk level may be improved by considering the incidence of persistent pain, particularly in normal weight women (BMI < 25 kg/m(2)) lower BMI.

Functional gastrointestinal disorders are associated with the joint hypermobility syndrome in secondary care: a case-control study

BACKGROUND

The overlap of unexplained gastrointestinal (GI) and somatic symptoms is well established in patients with functional gastrointestinal disorders (FGID). Joint hypermobility syndrome (JHS) is a non-inflammatory connective tissue disorder associated with GI and somatic symptoms. We aimed to determine whether there is an association between diagnosis of JHS and FGID and the impact of this association on comorbidities and quality of life (QOL).

METHODS

Prospective case-control study in secondary care GI clinics over 2 years. JHS was assessed by the first author prior to consultation in 641 consecutive new patients. Diagnosis of FGID (cases, n = 336) or organic disorders (controls, n = 305) was established blind to JHS status. JHS prevalence was compared in cases (FGID patients) and controls (organic disorders patients). Extra-intestinal comorbidity and QOL were compared in FGID patients with and without JHS.

KEY RESULTS

JHS prevalence was higher in FGID compared to organic GI disorders (39.0% vs 27.5%, ORadj: 1.51, CI: 1.07-2.12, p = 0.02), and particularly associated with functional gastroduodenal disorders (44.1%, ORadj: 2.08, CI: 1.25-3.46, p = 0.005), specifically postprandial distress syndrome (51%, ORadj: 1.99, CI: 1.06-3.76, p = 0.03). FGID patients with JHS had increased chronic pain (23.2% vs 11.9%, p = 0.01), fibromyalgia (10.5% vs 3.1%, p = 0.01), somatization scores (13 vs 10, p < 0.001), urinary autonomic scores (30.5 vs 20.7, p = 0.03), and worse pain-related QOL scores (45.0 vs 63.5, p = 0.004).

CONCLUSIONS & INFERENCES

JHS is significantly associated with FGID, and this subgroup of patients have increased comorbidity and decreased QOL. Further research is required to understand the pathophysiological basis of this association.

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.

Chronic pain and cardiovascular stress responses in a general population: the Tromsø Study

We tested whether cardiovascular stress responsiveness is elevated in individuals experiencing chronic pain in a large general population sample. Blood pressure (BP) and heart rate (HR) were assessed at rest, during the cold pressor test, and during subsequent recovery in 554 individuals reporting daily chronic pain and 3,082 individuals free of chronic pain. After correcting for potential confounds, differences as a function of chronic pain status were noted for only 5 of 23 cardiovascular outcomes despite very high statistical power. Compared to the pain-free group, the chronic pain group displayed higher baseline HR/mean arterial pressure (MAP) ratio (p = .03), greater systolic BP (SBP) reactivity during the cold pressor test (p = .04), and higher HR/MAP ratio (p = .047) and significantly less SBP (p = .017) and MAP (p = .041) return to baseline during recovery. Findings suggest that changes in cardiovascular stress responsiveness associated with chronic pain are of limited clinical significance and unlikely to contribute to increased cardiovascular risk in the chronic pain population.

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.

Autonomic functioning in irritable bowel syndrome measured by heart rate variability: a meta-analysis

OBJECTIVE

To analyze autonomic functioning which presented as the high frequency (HF) component of heart rate variability, a measurement of vagal tone, and the ratio of low frequency (LF) to HF (LF : HF), an indicator of sympathovagal balance in irritable bowel syndrome (IBS) patients.

METHODS

We identified relevant studies by performing a literature search of MEDLINE, EMBASE and the ISI Web of Knowledge to 31 March 2013. Pooled effect sizes with 95% confidence interval (CI) were calculated using a random effects model. Between-study heterogeneity was assessed using the Q test and I(2) statistic.

RESULTS

In all, 11 articles including 392 IBS patients and 263 controls met the inclusion criteria of the analysis. IBS patients had lower HF band power (Hedges's g = -0.38, 95% CI -0.68 to -0.09) than the controls (I(2)  = 63.6%, P = 0.003). Moreover, IBS patients showed a higher LF : HF (Hedges's g = 0.43, 95% CI 0.13-0.74), with no significant heterogeneity. A subgroup analysis of the HF index according to the recording time yielded different results for the IBS patients and controls. Additionally, constipation-predominant IBS (IBS-C) patients had decreased HF band power, whereas no significant difference was found in LF : HF.

CONCLUSIONS

Impaired parasympathetic functioning and abnormal sympathovagal balance may be involved in the pathogenesis of IBS. Vagal dysfunction is more obvious in the IBS-C subgroup.

Gastrointestinal manifestations of pediatric autonomic disorders

Functional gastrointestinal disorders (FGIDs) are currently classified under the Rome criteria based on symptoms and absence of organic disease. Preliminary studies have shown that FGIDs are probably not restricted to the GI tract, but may represent a systemic disorder with comorbidities affecting other parts of the body, including migraine, fatigue, aches and pains, etc. The autonomic nervous system (ANS) provides the extrinsic control of GI motility, secretions, and even immune response. The role of the ANS in the development of FGIDs and comorbidities is still unclear. Limited data demonstrate orthostatic intolerance such as reflex syncope and postural tachycardia syndrome in a large subset of subjects with FGIDs. Some studies have found improvement in the GI symptoms with treatment of the orthostatic intolerance it produces. Prospective studies are needed to determine the chronology of the development of the comorbidities, the triggers that induce these syndromes, and effective treatments. This chapter aims to review current understanding of the role of the ANS in FGIDs.

Hypertension prevalence and diminished blood pressure-related hypoalgesia in individuals reporting chronic pain in a general population: the Tromsø study

Resting blood pressure (BP) is inversely related to pain sensitivity in individuals free of chronic pain, reflecting homeostatic interactions between cardiovascular and pain modulatory systems. Several laboratory studies indicate that BP-related hypoalgesia is diminished in chronic pain patients, suggesting dysfunction in these interacting systems. Separate epidemiological findings reveal elevated hypertension prevalence in the chronic pain population. This study for the first time simultaneously evaluated both hypertension prevalence and BP-related hypoalgesia as they relate to chronic pain in the same sample. Resting BP and pain sensitivity were evaluated in a large general population sample (n=10,135, aged 30-87years). Subjects participated in a standardized 106s cold pressor test, providing pain ratings at 9s intervals. Self-reported presence of chronic pain and history of hypertension and use of antihypertensive medication were assessed. Significant interactions between chronic pain status and resting systolic (P<.001) and diastolic BP (P<.001) on mean pain ratings were observed. These interactions were due to significant (P<.001) BP-related hypoalgesia in individuals free of chronic pain that was twice the magnitude of the hypoalgesia observed in the group reporting chronic pain. Presence of chronic pain was associated with significantly increased odds of comorbid hypertension (P<.001). Within the chronic pain group, higher chronic pain intensity was a significant predictor of positive hypertension status beyond the effects of traditional demographic risk factors (P<.05). Results are consistent with the hypothesis that increased hypertension risk in the chronic pain population might be linked in part to chronic pain-related dysfunction in interacting cardiovascular-pain modulatory systems.

Colorectal distension-evoked potentials in awake rats: a novel method for studies of visceral sensitivity

BACKGROUND

Quantification of the visceromotor response induced by colorectal distension (CRD) in rodents is commonly used for preclinical studies of visceral pain. The model is well established but does not fully assess the central response to stimulation. The aim of this study was to establish a novel model assessing cerebral evoked potentials (CEPs) in response to CRD in awake rats.

METHODS

Epidural recording electrodes were chronically implanted in the skull of female Sprague-Dawley rats. Colorectal distension-induced CEPs were recorded using either rapid balloon distensions (100 ms, 20-80 mmHg) or electric stimulation (1 ms, 1-4 mA) using stimulation probes placed in the distal colon.

KEY RESULTS

Colorectal distension-induced CEPs were separated in three partly temporally overlapping components consisting of five prominent peaks. Peak latencies at 80 mmHg were (P1, N1) 23 ± 1 and 55 ± 4 ms, (N2, P2a, P2b) 91 ± 3, 143 ± 5 and 174 ± 3 ms, and (P3) 297 ± 3 ms. Amplitudes and latencies were, except for the early component, intensity dependent. Intrarectal administration of lidocaine significantly reduced the amplitude of N2 (by 42 ± 6%, P < 0.001) and P2 (by 34 ± 6%, P < 0.001). Electrically induced CEPs were intensity dependent and had similar topography and latencies as the mechanical evoked potentials (P1: 26 ± 2 ms; N1: 61 ± 1 ms; P2: 84 ± 6 ms; N2: 154 ± 6 ms; P3: 326 ± 10 ms), but there were large variations in amplitudes in between repeated electrical stimulations.

CONCLUSIONS & INFERENCES

Colorectal distension-induced CEPs can be recorded reliably in awake rats and may serve as a surrogate marker of colonic sensation and be a useful parameter in studies of visceral sensitivity.

Irritable bowel syndrome: methods, mechanisms, and pathophysiology. Methods to assess visceral hypersensitivity in irritable bowel syndrome

Irritable bowel syndrome (IBS) is a common functional gastrointestinal disorder, characterized by recurrent abdominal pain or discomfort in combination with disturbed bowel habits in the absence of identifiable organic cause. Visceral hypersensitivity has emerged as a key hypothesis in explaining the painful symptoms in IBS and has been proposed as a "biological hallmark" for the condition. Current techniques of assessing visceral perception include the computerized barostat using rectal distensions, registering responses induced by sensory stimuli including the flexor reflex and cerebral evoked potentials, as well as brain imaging modalities such as functional magnetic resonance imaging and positron emission tomography. These methods have provided further insight into alterations in pain processing in IBS, although the most optimal method and condition remain to be established. In an attempt to give an overview of these methods, a literature search in the electronic databases PubMed and MEDLINE was executed using the search terms "assessment of visceral pain/visceral nociception/visceral hypersensitivity" and "irritable bowel syndrome." Both original articles and review articles were considered for data extraction. This review aims to discuss currently used modalities in assessing visceral perception, along with advantages and limitations, and aims also to define future directions for methodological aspects in visceral pain research. Although novel paradigms such as brain imaging and neurophysiological recordings have been introduced in the study of visceral pain, confirmative studies are warranted to establish their robustness and clinical relevance. Therefore, subjective verbal reporting following rectal distension currently remains the best-validated technique in assessing visceral perception in IBS.

Brain-Gut Interactions in IBS

Irritable bowel syndrome (IBS) is a common gastrointestinal disorder with an estimated prevalence of 10–20%. Current understanding of the pathophysiology of IBS is incomplete due to the lack of a clearly identified pathological abnormality and due to the lack of reliable biomarkers. Possible mechanisms believed to contribute to IBS development and IBS like symptoms include physical stressors, such as infection or inflammation, psychological, and environmental factors, like anxiety, depression, and significant negative life events. Some of these mechanisms may involve the brain-gut axis (BGA). In this article we review the current knowledge on the possible involvement of the BGA in IBS and discuss new directions for potential future therapies of IBS.

Irritable bowel syndrome and food allergy

Irritable bowel syndrome (IBS) is a kind of functional gastrointestinal disease characterized by abdominal pain or discomfort associated with changes in bowel habits. The alternating symptoms of IBS seriously affect the patients' quality of life. Some studies have found that food could cause or aggravate the symptoms of IBS possibly by inducing food allergy and food intolerance. However, the specific mechanisms have not been established yet. Currently there are "bacterial 'toxin' hypothesis", "immune or inflammatory response hypothesis" and "physical or chemical irritation hypothesis" explaining the role of food in the pathogenesis of IBS. It has been known that food factors play a very important role in the pathogenesis of IBS. This article reviews food allergy and the possible mechanisms, diagnosis and treatment of IBS caused by food.

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.

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.

Pathogenic factors involved in the development of irritable bowel syndrome: focus on a microbial role

Irritable bowel syndrome (IBS) is a symptom complex characterized by recurrent abdominal pain or discomfort, and accompanied by abnormal bowel habits, in the absence of any discernible organic abnormality. Its origin remains unclear, partly because multiple pathophysiologic mechanisms are likely to be involved. A significant proportion of patients develop IBS symptoms after an episode of gastrointestinal infection. In addition to gastrointestinal pathogens, recent evidence suggests that patients with IBS have abnormal composition and higher temporal instability of their intestinal microbiota. Because the intestinal microbiota is an important determinant of normal gut function and immunity, this instability may constitute an additional mechanism that leads to symptom generation and IBS. More importantly, a role for altered microbiota composition in IBS raises the possibility of therapeutic interventions through selective antibiotic or probiotic administration. The new concept of functional bowel diseases incorporates the bidirectional communication between the gut and the central nervous system (gut-brain axis), which may explain the multiple facets of IBS by linking emotional and cognitive centers of the brain with peripheral functioning of the gastrointestinal tract and vice versa.

Molecular development of the extrinsic sensory innervation of the gastrointestinal tract

The extrinsic sensory innervation of the gastrointestinal tract is the conduit through which the gut and the central nervous system communicate. The hindbrain receives information directly from the bowel via the vagus nerve, while information from spinal afferents arrives in the central nervous system through the dorsal root ganglia. This review focuses on the molecular development of these vagal and spinal innervations, with an emphasis on mechanisms that involve axon guidance. During development, axons from both the nodose ganglia and dorsal root ganglia grow into the gut, innervate their appropriate enteric targets and avoid inappropriate cells in the gut wall. These developmental outcomes suggest that both attractive and repellent molecules are important in establishing the normal pattern of the extrinsic sensory innervation. In the fetal mouse gut, the guidance of vagal sensory axons is mediated by axon guidance molecules, such as netrin and the netrin receptor, deleted in colorectal cancer (DCC), as well as extracellular matrix molecules, such as laminin-111. Dorsal root ganglion neurons are known to express, and their axons to respond to, axon guidance molecules. The question of whether or not these molecules are involved in guiding spinal afferents to the bowel, however, has not yet been examined. It is anticipated that a better understanding of how vagal and spinal afferents innervate the fetal gut and reach specific enteric locations will provide deeper insights into the underlying mechanisms of normal and abnormal sensation from the gastrointestinal tract.

Relationships between Irritable Bowel Syndrome Pain, Skin Temperature Indices of Autonomic Dysregulation, and Sensitivity to Thermal Cutaneous Stimulation

This study evaluated relationships between irritable bowel syndrome (IBS) pain, sympathetic dysregulation, and thermal pain sensitivity. Eight female patients with diarrhea-predominant IBS and ten healthy female controls were tested for sensitivity to thermal stimulation of the left palm. A new method of response-dependent thermal stimulation was used to maintain pain intensity at a predetermined level (35%) by adjusting thermal stimulus intensity as a function of pain ratings. Clinical pain levels were assessed prior to each testing session. Skin temperatures were recorded before and after pain sensitivity testing. The temperature of palmar skin dropped (1.5°C) when the corresponding location on the opposite hand of control subjects was subjected to prolonged thermal stimulation, but this response was absent for IBS pain patients. The patients also required significantly lower stimulus temperatures than controls to maintain a 35% pain rating. Baseline skin temperatures of patients were significantly correlated with thermode temperatures required to maintain 35% pain ratings. IBS pain intensity was not significantly correlated with skin temperature or pain sensitivity. The method of response-dependent stimulation revealed thermal hyperalgesia and increased sympathetic tone for chronic pain patients, relative to controls. Similarly, a significant correlation between resting skin temperatures and thermal pain sensitivity for IBS but not control subjects indicates that tonic sympathetic activation and a thermal hyperalgesia were generated by the chronic presence of visceral pain. However, lack of a significant relationship between sympathetic tone and ratings of IBS pain casts doubt on propositions that the magnitude of IBS pain is determined by psychological stress.

Psychological adjustment and autonomic disturbances in inflammatory bowel diseases and irritable bowel syndrome

Psychological factors and the autonomic nervous system (ANS) are implicated in the pathogenesis of inflammatory bowel diseases (IBD) and irritable bowel syndrome (IBS). This study aimed to assess, firstly the way IBS and IBD patients cope with their pathology according to their affective adjustment and secondly the possible links between these affective adjustments and ANS reactivity. Patients with Crohn's disease (CD; n=26), ulcerative colitis (UC; n=22), or IBS (n=27) were recruited and compared to 21 healthy subjects based on psychological variables (trait- and state anxiety, depressive symptomatology, negative mood, perceived stress, coping, health locus of control) and sympatho-vagal balance through heart-rate variability monitored at rest. A principal component analysis, performed on all affective variables, isolated a leading factor labelled as "affective adjustment". In each disease, patients were distributed into positive and negative affective adjustment. In all the diseases, a positive affect was associated with problem-focused coping, and a negative affect with emotion-focused coping and external health locus of control. Results show that the sympatho-vagal balance varied according to the disease. In CD presenting positive affectivity, an adapted high sympathetic activity was observed. In UC, a parasympathetic blunt was observed in the presence of negative affectivity and an equilibrated sympatho-vagal balance in the presence of positive affectivity. In contrast, in IBS, an important dysautonomia (with high sympathetic and low parasympathetic tone) was constantly observed whatever the affective adjustment. In conclusion, this study suggests that the equilibrium of the ANS is differentially adapted according to the disease. This equilibrium is conjugated with positive affective and cognitive adjustment in IBD (CD and UC) but not in IBS.

Heightened central affective response to visceral sensations of pain and discomfort in IBS

BACKGROUND Typically, conventional functional imaging methods involve repeated exposures to sensory stimulation. In rectal distension (RD) studies that involve multiple distensions, however, it is difficult to disambiguate the central response to RD from pathological alterations in peripheral neural responses associated with relaxation and accommodation of the rectum. METHODS This study addressed potential confounders found in previous imaging studies by collecting functional magnetic resonance imaging studies (fMRI) data during a single slow ramp-tonic distension paradigm and analysing fMRI signal changes using independent component analysis. KEY RESULTS Compared with controls, IBS participants showed increased activation of the anterior cingulate cortices, insula and ventral medial prefrontal regions suggesting heightened affective responses to painful visceral stimuli. In addition, the failure by IBS patients to down-regulate activity within ventral medial prefrontal and the posterior cingulate/precuneus regions was suggestive of reduced sensitivity to somatic changes and delayed shifts away from rest in ;default network' activity patterns. Controls showed heightened activation of the thalamus, striatal regions and dorsolateral prefrontal cortex suggesting greater arousal and salience-driven sustained attention reactions and greater modulation of affective responses to discomfort and pain. CONCLUSION&INFERENCES This work points to alterations in the central response to visceral pain and discomfort in IBS, highlighting diminished modulation and heightened internalization of affective reactions.

Recent insights on central processing and psychological processes in functional gastrointestinal disorders

There is increasing evidence for a key role of psychological processes and their central nervous system substrates in functional gastrointestinal disorders, although the exact nature of the relationship remains only partially understood. However, progress in this key area of psychosomatic medicine is rapidly being made. In this review article, we will give an overview of recent advances in understanding the complex mechanisms by which psychological processes and functional gastrointestinal disorder symptoms reciprocally influence each other. Various lines of evidence from different branches of biomedical and psychological science will be discussed, particularly epidemiology, patho- and psychophysiology and functional brain imaging, focusing on the most recent and novel findings. We will conclude this paper with a paragraph on new insights into treatment.

5-HT 3 receptors mediate the time-dependent vagal afferent modulation of nociception during chronic food allergen-sensitized visceral hyperalgesia in rats

Converging lines of evidence demonstrate a vagally mediated antinociceptive pathway in animals undergoing acute visceral insults, the contribution of this system to visceral pain following chronic noxious stimuli is unknown. 5-HT(3) receptor (5-HT(3)Rs) on spinal afferents are crucially involved in nociceptive processing, the role of 5-HT(3)Rs on vagal afferents is unclear. The aim of the present study was to determine the contribution of vagal afferents to visceral nociception in rats undergoing chronic luminal allergen stimulation and whether it involves vagal 5-HT(3)Rs. Sensitized rats received chicken egg albumin (EA, 1 mg mL(-1)) in drinking water for 2 weeks (day 1-14). Visceromotor response (VMR) to colorectal distension [colorectal distension (CRD), 60 mmHg] and the levels of mRNA encoding 5-HT(3)R (including 3A and 3B subunits) in the nodose ganglia (NG) were evaluated on day 2, 4, 8 and 15. Chronic EA challenge induced gradually increased visceral nociception, with a peak on day 15. Subdiaphragmatic vagotomy or functional deafferentation with capsaicin abolished this time-dependent manner, inducing hyperalgesia from day 2, lasting to day 15. Intraluminal infusion of a 5-HT(3)R antagonist (granisetron), whether alone or infused after local mucosa anaesthetic with 1% lidocaine, mimicked the effects of vagotomy. The mRNA levels for 5-HT(3B) or 5-HT(3A) subunit in the NG showed an opposite time-course to that of visceral pain, which increased from day 2, then decreased gradually to levels lower than those of controls. Our results demonstrate a time-dependent vagal afferent modulation of chronic allergen-sensitized visceral hyperalgesia, which may involve a 5-HT(3)R pathway.

Visceral pain hypersensitivity in functional gastrointestinal disorders

INTRODUCTION

Functional gastrointestinal disorders (FGIDs) are a highly prevalent group of heterogeneous disorders whose diagnostic criteria are symptom based in the absence of a demonstrable structural or biochemical abnormality. Chronic abdominal pain or discomfort is a defining characteristic of these disorders and a proportion of patients may display heightened pain sensitivity to experimental visceral stimulation, termed visceral pain hypersensitivity (VPH).

SOURCES OF DATA

We examined the most recent literature in order to concisely review the evidence for some of the most important recent advances in the putative mechanisms concerned in the pathophysiology of VPH.

AREAS OF AGREEMENT

VPH may occur due to anomalies at any level of the visceral nociceptive neuraxis. Important peripheral and central mechanisms of sensitization that have been postulated include a wide range of ion channels, neurotransmitter receptors and trophic factors. Data from functional brain imaging studies have also provided evidence for aberrant central pain processing in cortical and subcortical regions. In addition, descending modulation of visceral nociceptive pathways by the autonomic nervous system, hypothalamo-pituitary-adrenal axis and psychological factors have all been implicated in the generation of VPH.

AREAS OF CONTROVERSY

Particular areas of controversy have included the development of efficacious treatment of VPH. Therapies have been slow to emerge, mainly due to concerns regarding safety.

GROWING POINTS

The burgeoning field of genome wide association studies may provide further evidence for the pleiotropic genetic basis of VPH development.

AREAS TIMELY FOR DEVELOPING RESEARCH

Tangible progress will only be made in the treatment of VPH when we begin to individually characterize patients with FGIDs based on their clinical phenotype, genetics and visceral nociceptive physiology.