A one-hour active coping stressor reduces small bowel transit time in healthy young adults

Increased fasting small-bowel water content in untreated coeliac disease and scleroderma as assessed by magnetic resonance imaging

Background and aims

The regular overnight migrating motor complex (MMC) ensures that the normal fasting small-bowel water content (SBWC) is minimised. We have applied our recently validated non-invasive magnetic resonance technique to assess SBWC in newly diagnosed coeliac disease (CD), scleroderma (SCD) and irritable bowel syndrome (IBS), conditions possibly associated with small intestinal bacterial overgrowth (SIBO).

Methods

A total of 20 CD and 15 SCD patients with gastrointestinal symptoms were compared to 20 healthy volunteers (HV) and 26 IBS with diarrhoea (IBS-D) patients, as previously reported. All underwent a fasting magnetic resonance imaging (MRI) scan on a 1.5 T Philips Achieva MRI scanner to assess fasting SBWC and colonic volumes. Stool and symptom diaries were completed for one week.

Results

Compared to HV, all patients had significantly increased stool frequency and Bristol stool form score. SBWC was significantly increased in CD (median 109 mL; interquartile range (IQR) 53-224 mL) compared to HV (median 53 mL; IQR 31-98 mL; p < 0.01) and IBS-D (median 42 mL; IQR 28-67 mL; p < 0.01). A variable increase in SBWC was also found in SCD (median 77 mL; IQR 39-158 mL), but this was not significant (p = 0.2). Colonic volumes were similar for all groups, being a median of 547 mL (IQR 442-786 mL) for CD, 511 mL (453-789 mL) for SCD, 612 mL (445-746 mL) for HV and 521 mL (428-757 mL) for IBS-D. When CD patients were subdivided according to the Marsh classification, the higher grades had larger colonic volumes.

Conclusion

Fasting SBWC as assessed by MRI is significantly increased in newly diagnosed CD and SCD but decreased in IBS-D. Future studies should test whether increased resting fluid predisposes to SIBO.

Constipation and diarrhea during the menopause transition and early postmenopause: observations from the Seattle Midlife Women's Health Study

OBJECTIVE

To assess the relationship of constipation and diarrhea severity during the menopause transition (MT) with age, MT stage, reproductive biomarkers, stress-related biomarkers, and stress-related perceptions.

METHODS

From 1990 to 1992, women aged 35 to 55 years were recruited from the greater Seattle area; 291 of them consented to ongoing (1990-2013) annual data collection by daily menstrual calendar, health diary, and annual health questionnaire. A subset (n = 131) provided a first morning voided urine specimen (1997-2013). These were assayed for levels of E1G, follicle-stimulating hormone, testosterone, cortisol, norepinephrine, and epinephrine. Mixed-effects modeling was used to identify how changes in constipation and diarrhea severity over time related to age, MT stage, reproductive biomarkers, stress-related biomarkers, and stress-related perceptions.

RESULTS

In a univariate model, age, late reproductive (LR) stage, tension, and anxiety were all significantly and positively related to constipation severity, whereas cortisol was significantly and negatively associated. In a multivariate model, only tension and cortisol remained significant predictors of constipation severity (P < 0.05). In a univariate model, age, LR stage, and estrone glucuronide were significantly and negatively associated with diarrhea severity, whereas tension, anxiety, and perceived stress were significantly and positively related. In a multivariate model, only tension and age remained significant predictors of diarrhea severity.

CONCLUSIONS

Key reproductive hormones do not play a significant role in constipation or diarrhea severity in the MT. In contrast, stress perception, tension, anxiety, and cortisol do. These factors should be evaluated in further research involving constipation and diarrhea.

The role of substance P in the maintenance of colonic hypermotility induced by repeated stress in rats

BACKGROUND

The mechanism underlying chronic stress-induced gastrointestinal (GI) dysmotility has not been fully elucidated and GI hormones have been indicated playing a role in mediating stress-induced changes in GI motor function.

AIMS

Our objective was to study the possible role of substance P (SP) in the colonic hypermotility induced by repeated water avoidance stress (WAS) which mimics irritable bowel syndrome.

METHODS

Male Wistar rats were submitted to WAS or sham WAS (SWAS) (1h/day) for up to 10 consecutive days. Enzyme Immunoassay Kit was used to detect the serum level of SP. The expression of neurokinin-1 receptor (NK1R) was investigated by Immunohistochemistry and Western blotting. The spontaneous contraction of muscle strip was studied in an organ bath system. L-type calcium channel currents (ICa,L) of smooth muscle cells (SMCs) were recorded by whole-cell patch-clamp technique.

RESULTS

Fecal pellet expulsion and spontaneous contraction of proximal colon in rats were increased after repeated WAS. The serum level of SP was elevated following WAS. Immunohistochemistry proved the expression of NK1R in mucosa, muscularis and myenteric plexus. Western blotting demonstrated stress-induced up-regulation of NK1R in colon devoid of mucosa and submucosa. Repeated WAS increased the contractile activities of longitudinal muscle and circular muscle strips induced by SP and this effect was reversed by a selective NK1R antagonist. The ICa,L of SMCs in the WAS rats were drastically increased compared to controls after addition of SP.

CONCLUSIONS

Increased serum SP level and up-regulated NK1R in colon may contribute to stress-induced colonic hypermotility. And L-type calcium channels play a potentially important role in the process of WAS-induced dysmotility.

Brain-Derived Neurotrophic Factor Contributes to Colonic Hypermotility in a Chronic Stress Rat Model

BACKGROUND

Brain-derived neurotrophic factor (BDNF) has prokinetic effects on gut motility and is increased in the colonic mucosa of irritable bowel syndrome.

AIMS

We aimed to investigate the possible involvement of BDNF in stress-induced colonic hypermotility.

METHODS

Male Wistar rats were exposed to daily 1-h water avoidance stress (WAS) or sham WAS for 10 consecutive days. The presence of BDNF and substance P (SP) in the colonic mucosa was determined using enzyme immunoassay kits. Immunohistochemistry and western blotting were performed to assess the expression of BDNF and its receptor, TrkB. The contractions of muscle strips were studied in an organ bath system.

RESULTS

Repeated WAS increased the fecal pellet expulsion and spontaneous contractile activities of the colonic muscle strips. Both BDNF and SP in the colonic mucosa were elevated following WAS. Immunohistochemistry revealed the presence of BDNF and TrkB in the mucosa and myenteric plexus. BDNF and TrkB were both up-regulated in colon devoid of mucosa and submucosa from the stressed rats compared with the control. BDNF pretreatment caused an enhancement of the SP-induced contraction of the circular muscle (CM) strips. TrkB antibody significantly inhibited the contraction of the colonic muscle strips and attenuated the excitatory effects of SP on contractions of the CM strips. Repeated WAS increased the contractile activities of the CM strips induced by SP after BDNF pretreatment, and this effect was reversed by TrkB antibody.

CONCLUSIONS

The colonic hypermotility induced by repeated WAS may be associated with the increased expression of endogenous BDNF and TrkB. BDNF may have potential clinical therapeutic use in modulating gut motility.

Effect of experimental stress on the small bowel and colon in healthy humans

BACKGROUND

Symptoms of irritable bowel syndrome (IBS) are frequently reported to be exacerbated by stress. Animal studies suggest that corticotrophin releasing hormone (CRH) mediates the effect of stress on the bowel. We have shown that stressed IBS patients with diarrhea have constricted small bowels. We hypothesized that we could mimic this effect by applying experimental stress in the form of either hand immersion in ice water or CRH injection in healthy volunteers (HV).

METHODS

The postprandial effect of the cold pressor test (repeated hand immersion in ice cold water) and injection of CRH, were assessed vs control in two groups of 18 HVs.

KEY RESULTS

CRH produced a significant rise from baseline salivary cortisol levels (p = 0.004) not seen with the cold pressor test. Small bowel water content (SBWC) fell postprandially on all four treatments. SBWC was significantly reduced by both stressors but CRH caused a greater effect (anova, p < 0.003 vs p = 0.02). Ascending colon (AC) volume was greater after CRH injection compared with saline (p = 0.002) but no differences were seen with the cold pressor test vs warm water. Postprandial increase in colon volume was also reduced by CRH which also increased the sensations of distension and bloating.

CONCLUSIONS & INFERENCES

Two experimental stressors were shown to constrict the small bowel, mimicking the effect previously seen in IBS-D patients. CRH increased the volume of the AC. We speculate that stress accelerates transfer of water from the small bowel to the AC.

A biomarker panel and psychological morbidity differentiates the irritable bowel syndrome from health and provides novel pathophysiological leads

BACKGROUNDS

The development of a reliable biomarker for irritable bowel syndrome (IBS) remains one of the major aims of research in functional gastrointestinal disorders (FGIDs) and is complicated by the absence of a perfect reference standard. Previous efforts based on genetic and immune markers have showed promise, but have not been robust.

AIM

To evaluate an extensive panel of gene expression and serology markers combined with psychological measures in differentiating IBS from health and between subtypes of IBS.

METHODS

Of subjects eligible for analysis (N = 244), 168 met criteria for IBS (60 IBS-C, 57 IBS-D and 51 mixed), while 76 were free of any FGID. A total of 34 markers were selected based on pathways implicated in pathophysiology of IBS or whole human genome screening. Psychological measures were recorded that covered anxiety, depression and somatisation. Models differentiating disease and health were based on unconditional logistic regression and performance assessed through area under the receiver-operator characteristic curve (AUC), sensitivity and specificity.

RESULTS

The performance of a combination of 34 markers was good in differentiating IBS from health (AUC = 0.81) and was improved considerably with the addition of four psychological markers (combined AUC = 0.93). Of the 34 markers considered, discrimination was derived largely from a small subset. Good discrimination was also obtained between IBS subtypes with the best being observed for IBS-C vs. IBS-D (AUC = 0.92); however, psychological variables provided almost no incremental discrimination subtypes over biological markers (combined AUC = 0.94).

CONCLUSIONS

A combination of gene expression and serological markers in combination with psychological measures shows exciting progress towards a diagnostic test for IBS compared with healthy subjects, and to discriminate IBS-C from IBS-D.

Inhibitory effects of various types of stress on gastric tone and gastric myoelectrical activity in dogs

OBJECTIVE

Stress impairs gastrointestinal motility, causing, for example, delayed gastric emptying and altered intestinal transit. However, little is known about the effect of various stress factors on gastric tone and gastric myoelectrical activity (GMA). The aim of this study was to assess the effect of various kinds of stress on gastric tone and GMA in a canine model.

MATERIAL AND METHODS

Six dogs, implanted with a gastric cannula and one pair of gastric seromuscular electrodes, were studied. Three kinds of stress (visual, thermal, or audio stimulation) were applied in separate sessions. GMA and gastric tone were recorded for 30 min at baseline and 30 min during stress.

RESULTS

Visual stress (blinding) did not alter gastric tone or GMA; cold stress (ice water) and audio stress (loud noise) significantly inhibited gastric tone: gastric volume was increased from 107.2+/-13.5 ml at baseline to 135.6+/-23.8 ml with cold stress (p=0.041), and from 106.4+/-5.7 ml at baseline to 159.2+/-15.1 ml with audio stress (p=0.007). Although the dominant frequency or power of gastric slow waves was not altered, the percentage of normal gastric slow waves was markedly reduced from 98.3+/-0.8 to 87.5+/-3.7 with cold stress and from 90.2+/-3.3 to 80.6+/-2.9 with audio stress (p<0.05).

CONCLUSIONS

Cold- and audio stress inhibit gastric tone and impair gastric slow waves, whereas visual stress does not seem to have such effects. These findings will help to increase our understanding of gastrointestinal motor disorders related to stress.

The identification of peroxisome proliferator-activated receptor alpha-independent effects of oleoylethanolamide on intestinal transit in mice

Oleoylethanolamide (OEA) is an endogenous lipid produced in the intestine that mediates satiety by activation of peroxisome proliferator-activated receptor alpha (PPARalpha). OEA inhibits gastric emptying and intestinal motility, but the mechanism of action remains to be determined. We investigated whether OEA inhibits intestinal motility by activation of PPARalpha. PPARalpha immunoreactivity was examined in whole mount preparations of mouse gastrointestinal (GI) tract. The effect of OEA on motility was assessed in wildtype, PPARalpha, cannabinoid CB(1) receptor and CB(2) receptor gene-deficient mice and in a model of accelerated GI transit. In addition, the effect of OEA on motility was assessed in mice injected with the PPARalpha antagonist GW6471, transient receptor potential vanilloid 1 antagonist SB366791 or the glucagon-like peptide 1 antagonist exendin-3(9-39) amide. PPARalpha immunoreactivity was present in neurons in the myenteric and submucosal plexuses throughout the GI tract. OEA inhibited upper GI transit in a dose-dependent manner, but was devoid of an effect on whole gut transit or colonic propulsion. OEA-induced inhibition of motility was still present in PPARalpha, CB(1) and CB(2) receptor gene-deficient mice and in the presence of GW6471, SB366791 and exendin-3(9-39) amide, suggesting neither PPARalpha nor the cannabinoids and other likely receptors are involved in mediating the effects of OEA. OEA blocked stress-induced accelerated upper GI transit at a dose that had no effect on physiological transit. We show that PPARalpha is found in the enteric nervous system, but our results suggest that PPARalpha is not involved in the suppression of motility by OEA.

Changes in salivary physiological stress markers induced by muscle stretching in patients with irritable bowel syndrome

Background

Psychophysiological processing has been reported to play a crucial role in irritable bowel syndrome (IBS) but there has been no report on modulation of the stress marker chromogranin A (CgA) resulting from muscle stretching. We hypothesized that abdominal muscle stretching as a passive operation would have a beneficial effect on a biochemical index of the activity of the sympathetic/adrenomedullary system (salivary CgA) and anxiety.

Methods

Fifteen control and eighteen untreated IBS subjects underwent experimental abdominal muscle stretching for 4 min. Subjects relaxed in a supine position with their knees fully flexed while their pelvic and trunk rotation was passively and slowly moved from 0 degrees of abdominal rotation to about 90 degrees or the point where the subject reported feeling discomfort.

Changes in the Gastrointestinal Symptoms Rating Scale (GSRS), State Trait Anxiety Inventory (STAI), Self-rating Depression Scale (SDS), ordinate scale and salivary CgA levels were compared between controls and IBS subjects before and after stretching. A three-factor analysis of variance (ANOVA) with period (before vs. after) as the within-subject factor and group (IBS vs. Control), and sex (men vs. female) as the between-subject factors was carried out on salivary CgA.

Results

CgA showed significant interactions between period and groups (F[1, 31] = 4.89, p = 0.03), and between groups and sex (F[1, 31] = 4.73, p = 0.03). Interactions between period and sex of CgA secretion were not shown (F[1, 3] = 2.60, p = 0.12). At the baseline, salivary CgA in IBS subjects (36.7 ± 5.9 pmol/mg) was significantly higher than in controls (19.9 ± 5.5 pmol/mg, p < 0.05). After the stretching, salivary CgA significantly decreased in the IBS group (25.5 ± 4.5 pmol/mg), and this value did not differ from that in controls (18.6 ± 3.9 pmol/mg).

Conclusion

Our results suggest the possibility of improving IBS pathophysiology by passive abdominal muscle stretching as indicated by CgA, a biochemical index of the activity of the sympathetic/adrenomedullary system.

Effects of psychological stress on small intestinal motility and bacteria and mucosa in mice

AIM: To investigate the effects of psychological stress on small intestinal motility and bacteria and mucosa in mice, and to explore the relationship between small intestinal dysfunction and small intestinal motility and bacteria and mucosa under psychological stress.

METHODS: Sixty mice were randomly divided into psychological stress group and control group. Each group were subdivided into small intestinal motility group (n = 10), bacteria group (n = 10), and D-xylose administered to stomach group (n = 10). An animal model with psychological stress was established housing the mice with a hungry cat in separate layers of a two-layer cage. A semi-solid colored marker (carbon-ink) was used for monitoring small intestinal transit. The proximal small intestine was harvested under sterile condition and processed for quantitation for aerobes (Escherichia coli) and anaerobes (Lactobacilli). The quantitation of bacteria was expressed as log₁₀(colony forming units/g). D-xylose levels in plasma were measured for estimating the damage of small intestinal mucosa.

RESULTS: Small intestinal transit was inhibited (39.80±9.50% vs 58.79±11.47%, P<0.01) in mice after psychological stress, compared with the controls. Psychological stress resulted in quantitative alterations in the aerobes (E. coli). There was an increase in the number of E. coli in the proximal small intestinal flora (1.78±0.30 log₁₀(CFU/g) vs 1.37±0.21 log₁₀(CFU/g), P<0.01), and there was decrease in relative proportion of Lactobacilli and E. coli of stressed mice (0.53±0.63 vs 1.14±1.07, P<0.05), while there was no significant difference in the anaerobes (Lactobacilli) between the two groups (2.31±0.70 log₁₀(CFU/g) vs 2.44±0.37 log₁₀(CFU/g), P>0.05). D-xylose concentrations in plasma in psychological stress mice were significantly higher than those in the control group (2.90±0.89 mmol/L vs 0.97±0.33 mmol/L, P<0.01).

CONCLUSION: Small intestinal dysfunction under psychological stress may be related to the small intestinal motility disorder and dysbacteriosis and the damage of mucosa probably caused by psychological stress.

Effects of psychological stress on small intestinal motility and expression of cholecystokinin and vasoactive intestinal polypeptide in plasma and small intestine in mice

AIM: To investigate the effects of psychological stress on small intestinal motility and expression of cholecystokinin (CCK) and vasoactive intestinal polypeptide (VIP) in plasma and small intestine, and to explore the relationship between small intestinal motor disorders and gastrointestinal hormones under psychological stress.

METHODS: Thirty-six mice were randomly divided into psychological stress group and control group. A mouse model with psychological stress was established by housing the mice with a hungry cat in separate layers of a two-layer cage. A semi-solid colored marker (carbon-ink) was used for monitoring small intestinal transit. CCK and VIP levels in plasma and small intestine in mice were measured by radioimmunoassay (RIA).

RESULTS: Small intestinal transit was inhibited (52.18±19.15% vs 70.19±17.79%, P<0.01) in mice after psychological stress, compared to the controls. Small intestinal CCK levels in psychological stress mice were significantly lower than those in the control group (0.75±0.53 μg/g vs 1.98±1.17 μg/g, P<0.01), whereas plasma CCK concentrations were not different between the groups. VIP levels in small intestine were significantly higher in psychological stress mice than those in the control group (8.45±1.09 μg/g vs 7.03±2.36 μg/g, P<0.01), while there was no significant difference in plasma VIP levels between the two groups.

CONCLUSION: Psychological stress inhibits the small intestinal transit, probably by down-regulating CCK and up-regulating VIP expression in small intestine.

Heart rate variability

BACKGROUND

The authors conducted a study to evaluate the sensitivity of heart rate variability, or HRV, in quantifying the cardiocirculatory reaction to dental stress compared with other clinical parameters more frequently used in clinical practice.

METHODS

Twenty-five healthy subjects (15 men and 10 women aged 19 through 73 years) who underwent dental extractions were enrolled in the study. The authors measured systolic blood pressure, or SBP; diastolic blood pressure, or DBP; heart rate, or HR; and HRV at baseline, immediately after local anesthetic was administered, during the dental extraction and five minutes after the dental extraction. Time domain measures of HRV were based on interbeat intervals and were obtained by using standard deviations of the R-R intervals, which were calculated during a five-minute period in a continuous electrocardiographic record.

RESULTS

Analysis of variance for repeated measures showed no time-related difference between the four study periods with regard to SBP and DBP. However, HR values were significantly different in three of the four periods, and HRV values were significantly different in all four testing periods. Furthermore, HRV values exhibited greater variability in the maximum changes recorded during dental extractions compared with HR values (0 to 80 milliseconds versus 0 to 31 beats/minute, respectively).

CONCLUSIONS

HRV is a highly sensitive parameter for quantifying the sympathetic drive to the heart during a cardiovascular reaction to a dental operation.

CLINICAL IMPLICATIONS

Clinicians may find that HRV evaluation is useful in monitoring patients with heart disease to detect early signs of cardiac impairment related to local, high sympathetic activity and to prevent cardiovascular emergencies.

Inhibitory effects of stress on postprandial gastric myoelectrical activity and vagal tone in healthy subjects

The aim was to investigate gastric myoelectrical activity (GMA) and vagal activity in response to stress. The study was performed in 10 healthy subjects in three sessions (control, relaxation and stress). The control session was composed of 30-min recordings before and 30-min recordings after a test meal. The protocol of two other sessions was similar except that the fasting recording was extended to 60 min and the subjects were continuously watching a horror movie (stress) or guided meditation tape (relaxation) after the 30-min baseline. GMA was recorded using electrogastrography and heart rate variability (HRV) was derived from the electrocardiogram. Meal resulted in a postprandial increase in the dominant frequency (2.91 cpm vs 3.17 cpm, P < 0.007), dominant power (30.0 dB vs 32.5 dB, P < 0.05), and percentage of normal slow waves (79.8%vs 87.4%, P = 0.09). Similar responses were found in the relaxation session. Stress inhibited all these normal postprandial response and reduced the regularity of gastric slow waves (82.0%vs 66.0%, P < 0.01). In addition, spectral analysis of the HRV demonstrated an inhibition of postprandial vagal activity and an increase of postprandial sympathetic activity with stress. Stress has an inhibitory effect on postprandial GMA and this may involve both vagal and sympathetic pathway.

Does depression influence symptom severity in irritable bowel syndrome? Case study of a patient with irritable bowel syndrome and bipolar disorder

OBJECTIVE

Irritable bowel syndrome (IBS) is frequently associated with mood disorder. However, it is typically difficult to distinguish between disturbed mood as a causal agent and disturbed mood as a consequence of the experience of IBS. This report considers the association between mood and symptom severity in a patient with diarrhea-predominant IBS and stable, rapid cycling bipolar disorder with a predominantly depressive course. Such a case provides an important opportunity to determine the direction of the relationship between mood and IBS symptom severity because the fluctuations of mood in bipolar disorder are assumed to be driven largely by biological, rather than psychosocial, processes.

METHODS

The study was carried out prospectively, with ratings of mood and IBS symptom severity made daily by the patient for a period of almost 12 months.

RESULTS

The patient experienced regular and substantial changes in mood as well as fluctuations in the level of IBS symptoms during the study period. Contrary to expectation, the correlation between mood and IBS symptom severity on the same day suggested that the patient experienced less severe IBS symptoms during periods of more severe depression. However, time series analysis revealed no significant association between these two processes when serial dependence within each series was controlled for.

CONCLUSIONS

The unusual co-occurrence of IBS with bipolar disorder provides direct evidence to indicate that depression does not necessarily lead to an increase in the reported severity of IBS, at least in the context of bipolar disorder, and may under certain circumstances actually be associated with a reduction in the severity of IBS symptoms. Factors that might moderate the relationship between depression and symptom severity are discussed.

Circadian pancreatic enzyme pattern and relationship between secretory and motor activity in fasting humans

It is unknown whether nonparallel pancreatic enzyme output occurs under basal conditions in humans. We aimed to determine whether the circadian or wake-sleep cycle influences the relationship among pancreatic enzymes or between pancreatic secretory and jejunal motor activity. Using orojejunal multilumen intubation, we measured enzyme outputs and proximal jejunal motility index during consecutive daytime and nighttime periods in each of seven fasting, healthy volunteers. Enzyme outputs were correlated tightly during daytime phases of wakefulness and nighttime phases of sleep (r > 0.72, P < 0.001). During nocturnal phases of wakefulness, output of proteases (r = 0.84, P < 0.001), but not of amylase and trypsin (r = 0.12), remained associated. Nocturnally, particularly during sleep, pancreatic secretory activity was directly correlated with jejunal motility index (r > 0.50, P < 0.001). In conclusion, parallel secretion of pancreatic enzymes dominates throughout the circadian cycle. Nonparallel secretion during nocturnal phases of wakefulness may be due to merely circadian effects or to the coupling of the wake-sleep and the circadian cycle. The association between fluctuations of secretory and motor activity appears to be particularly tight during the night.

Emerging disease model for functional gastrointestinal disorders

In response to perceived or experienced change that is considered threatening to the individual, the central nervous system mounts a stereotypic response that decreases the sensitivity to pain, modulates the autonomic nervous system outflow, and activates the hypothalamic-pituitary-adrenal (HPA) axis. This response of the "emotional motor system" may or may not be associated with the conscious experience of feelings of fear or anxiety. Alterations in these response systems (either up- or downregulation) may produce symptoms, such as viscero-somatic hypersensitivity, altered bowel habits, or increased anxiety.

Motility of the small intestine

Motility of the small intestine is controlled by myogenic, neural, and hormonal mechanisms and is modulated by external influences such as meals, central nervous system activation, and immune factors. Small-bowel dysmotility is recognized in a number of diseases, but its precise role in symptom generation remains unclear in many instances. We review publications that in the year under review added to the basic understanding of small-intestinal motility as well as its alteration in disease.

Evolving concepts in irritable bowel syndrome

Converging evidence from investigations of the peripheral and central aspects of bidirectional brain-gut interactions is beginning to shape a pathophysiological model of irritable bowel syndrome (IBS) and related functional gastrointestinal (GI) disorders. This neurobiological model includes alterations in autonomic, neuroendocrine, and pain modulatory mechanisms. The frequent association of IBS and other functional GI disorders with co-morbid affective disorders and temporal association of symptom exacerbation with psychosocial or physical stressors are consistent with alterations in the neurobiological mechanisms underlying the central stress response. Renewed interest in drug development for IBS has resulted in development of instruments for the better assessment of the impact of global symptoms on quality of life and in the development of candidate compounds undergoing clinical evaluation.