Enteroendocrine cell counts correlate with visceral hypersensitivity in patients with diarrhoea-predominant irritable bowel syndrome

The objective of this study was to determine whether or not the number of enteroendocrine cells (ECs) in the gut is related to visceral hypersensitivity in patients with diarrhoea-predominant irritable bowel syndrome (D-IBS). Twenty-five subjects with D-IBS (mean, 43.1 years; 16 women, nine men) were recruited into our study, along with 13 healthy controls (mean, 40.7 years; nine women, four men). Maximally tolerable pressures were evaluated via barostat testing, and the levels of ECs were immunohistochemically identified and quantified via image analysis. The numbers of ECs between the D-IBS subjects and the controls were not significantly different in the terminal ileum, ascending colon and rectum. However, the maximally tolerable pressures determined in the D-IBS subjects were significantly lower than those of the control subjects (P < 0.01), and we detected a significant relationship between the maximally tolerable pressures and the numbers of ECs in the rectum (r = -0.37, P < 0.01). Rectal sensitivity was enhanced to a greater degree in D-IBS patients exhibiting an elevated level of rectal ECs. This study provides some evidence to suggest that ECs play an important role in visceral hypersensitivity.     

慢性内脏高敏感性大鼠电针后脊髓和大脑c-Fos的表达

BACKGROUND： Visceral hypersensitivity is the main cause of irritable bowel syndrome, c-Fos is a marker of visceral hypersensitivity in the central nervous system. Electroacupuncture can relieve chronic visceral hypersensitivity in rats, but the mechanism is still unknown. OBJECTIVE： To identify c-Fos expression in the spinal cord and cerebral cortex of rats with chronic visceral hypersensitivity, and to test the effects of electroacupuncture on pain sensitivity in rats with chronic visceral hypersensitivity. DESIGN, TIME AND SETTING： A randomized controlled animal experiment was performed at the Animal E：~perimental Center, Shanghai University of Traditional Chinese Medicine, from January to April, 2007. MATERIALS： A total of 24 neonatal, male, Sprague Dawley rats, aged five days old, were equally and randomly assigned into a normal group, a model group, and an electroacupuncture group. Rabbit anti-rat c-Fos antibody and Evision secondary antibody kits （Sigma, USA）, diaminobenzidine kit （Dako, Denmark）, and an LD202H electroacupuncture apparatus （Huawei, Beijing, China） were used in this study. METHODS： Neonatal rats from the model and electroacupuncture groups were used to establish rat models of chronic visceral hypersensitivity by the saccule stimulation method. After model establishment, 0.25 mm diameter electric needles were inserted into Tianshu （ST 25） and Shangjuxu （ST37） at a depth of approximately 0.5 cm, with an square wave （alternating current frequency at 100/20 Hz, amplitude ranged 0.2-0.6 ms, intensity at 1 mA） once for 20 minutes, once a day, for seven days. Rats in the normal and model groups were not treated. MAIN OUTCOME MEASURES： Following 7 days of treatment, c-Fos expression in the spinal cord and cerebral cortex was detected by immunohistochemistry. After the first electroacupuncture treatment, abdominal withdrawal reflex scores were investigated to evaluate the pain threshold for chronic visceral hypersensitivity in rats. RESULTS： Visceral hypersensitivity increased c-Fos staining （P 〈 0.05）, and electroacupuncture significantly decreased the number of these cells to near normal levels （P 〉 0.05）. Abdominal withdrawal reflex scores were significantly lower in the electroacupuncture and normal groups than in the model group （P 〈 0.05） and were similar between the electroacupuncture and normal groups （P 〉 0.05）. CONCLUSION： Electroacupuncture decreases c-Fos expression in the spinal cord and cerebral cortex and increases pain threshold in a chronic visceral hypersensitivity model in rats.     

Postinflammatory visceral sensitivity and pain mechanisms

Abstract  The inflammatory reaction is normally tightly regulated, and as soon as the original insult has been cleared, a resolution phase starts that aims at leading the tissues back to a normal physiological state. However, after intestinal inflammation, a number of patients develop postinflammatory hypersensitivity symptoms, which can be defined as an excessive sensitivity to gut nociceptive stimulation. The pain experienced by those patients has been largely studied in the context of postinfectious intestinal diseases. The mechanisms of postinflammatory persistent visceral pain involve peripheral and central neuroplastic changes, low-grade chronic inflammation that sensitizes visceral afferent pathways and sensitization of non-neuronal resident cells of the gut. Several molecular determinants such as neurokinins, serotonin, proteases and voltage-gated ion channels seem to play a significant role in the control of postinflammatory visceral sensation. This review tries to give insights into the mechanisms of persistent visceral pain following the resolution of intestinal inflammation and tries to identify what needs to be done to further advance the field of postinflammatory hypersensitivity clinical management.     

Irritable bowel syndrome in childhood: visceral hypersensitivity and psychosocial aspects

Abstract Visceral hypersensitivity is often considered to play a major etiologic role in the pathophysiology of irritable bowel syndrome in adults, and some authors argue that this increased sensitivity is mainly due to psychological factors. In contrast, there are no data in children with irritable bowel syndrome which confirm this relationship. The aim of the study was to evaluate the relationship between psychosocial aspects and sensorymotor function in children affected by irritable bowel syndrome. Ten children fulfilling the Rome II criteria for irritable bowel syndrome and seven healthy controls were enrolled. We studied the thresholds and the perception of visceral stimuli in the rectum by means of an electronic barostat (isobaric phasic distentions, 3 mmHg/1 min, interval 1 min) and a validated questionnaire. Personality features were evaluated by means of the Big Five Questionnaire for Children. Sleep, mood disturbance, anxiety and individual performance (missed school days, school results and social activities) were also evaluated. Children with irritable bowel syndrome showed significantly lower thresholds for discomfort (14.8 ± 3.5 vs 22.3 ± 6.9 mmHg, P = 0.010) and a higher cumulative perception score (28.2 ± 11.1 vs 12.3 ± 8.0, P = 0.005) compared with healthy controls. A higher emotional instability (57.8 ± 7.0 vs 48.7 ± 10.1, P = 0.047), sleep disturbance (7.2 ± 1.0 vs 9.3 ± 0.5, P = 0.004) and anxiety (6.3 ± 2.0 vs 2.3 ± 1.7, P = 0.009) were observed in irritable bowel syndrome patients. Moreover, in a multivariate analysis, the cumulative perception score was significantly related to emotional instability (P = 0.042). In conclusion children with irritable bowel syndrome exhibit visceral hypersensitivity and psychosocial impairment. Emotional instability, as a personality feature in these children, seems to modulate the perception response to visceral stimulations.     

A selective,high affinity 5‐HT2B receptor antagonist inhibits visceral hypersensitivity in rats

Background RS‐127445 is a selective, high affinity 5‐HT_2Breceptor antagonist. We investigated whether 5‐HT_2Breceptor antagonists can reduce colonic visceral hypersensitivity caused by restraint stress or by proximal colonic inflammation. Methods Visceral hypersensitivity was induced in rats by either restraint stress or injection of 2, 4, 6‐trinitrobenzene sulfonic acid (TNBS) into the proximal colon. Restraint stress produced a significant increase in numbers of abdominal contractions evoked by colorectal distension (CRD), measured as a quantitative index of visceral nociception in rats. Seven days after TNBS injection, the pain threshold to CRD at the non‐inflamed distal colon, that was determined as the minimum pressure required to evoke abdominal cramp, was significantly decreased. The effect of RS‐127445 on visceral hypersensitivity was assessed in either naïve or TNBS‐treated rats. Key Results Oral administration of a selective, high affinity 5‐HT_2Breceptor antagonist, RS‐127445, significantly inhibited visceral hypersensitivity provoked by restraint stress (35 to 74% inhibition at 1 to 10 mg kg^?1). Oral RS‐127445 produced a significant suppression of TNBS‐induced visceral hypersensitivity (15 to 62% inhibition at 3 to 30 mg kg^?1), although it was without significant effect on the visceral nociceptive threshold of naïve rats. RS‐127445 (1 to 30 mg kg^?1, p.o.) also dose‐dependently reduced the restraint stress‐induced defecation in naïve and TNBS‐treated rats. Conclusions & Inferences These results suggest that 5‐HT_2Breceptors are involved in signaling from the colon in rats in which there is visceral hypersensitivity and that a selective 5‐HT_2Breceptor antagonist could have therapeutic potential for the treatment of gut disorders characterized by visceral hypersensitivity.     

5-HT2B receptors do not modulate sensitivity to colonic distension in rats with acute colorectal hypersensitivity

The 5-HT4 receptor agonist tegaserod is an effective prokinetic agent that increases gastrointestinal secretion and reduces visceral sensitivity. Tegaserod has both 5-HT4 receptor agonist and 5-HT2B receptor antagonist activity, the latter being a less potent effect of the drug. In a rat model of colonic hypersensitivity, selective 5-HT4 receptor antagonists only partially reversed the antihyperalgesic effect of tegaserod suggesting that non-5-HT4 receptor-mediated mechanisms may also be involved in its overall antihyperalgesic action. The objective of this study was to determine whether 5-HT2B receptors play a role in colonic hypersensitivity. A visceromotor response (VMR) in acutely sensitized animals (intracolonic acetic acid, 0.6%, 1.5 mL) quantified colonic hypersensitivity. Acetic acid produced an increase in the VMR at all distension pressures. However, neither the 5-HT2B receptor agonist BW 723C86, the 5-HT2B antagonist SB204741 or the 5-HT2B/2C antagonist SB 206553 caused any significant inhibition of the VMR. In summary, in the same rodent model in which tegaserod has previously been shown to produce a potent antihyperalgesic effect, 5-HT2B receptors do not appear to mediate colonic hypersensitivity. We conclude that 5-HT2B receptor-mediated mechanisms are unlikely to play a role in the antihyperalgesic action of tegaserod in man.     

Perceptual sensitivity and response bias during rectal distension in patients with irritable bowel syndrome.

Patients with irritable bowel syndrome (IBS) report an increased frequency of sensations during rectal distension in comparison with healthy subjects. This alteration might be due to a psychological response bias leading patients to over report their sensations. The aim of this study was to measure perceptual sensitivity and response bias during rectal distension in healthy subjects and IBS patients using the sensory decision theory (SDT). Thirteen healthy subjects and 22 IBS patients underwent five rectal distensions up to 100 mL, five up to 200 mL and five sham distensions. They were asked to identify the distension by means of an electronic marker. Perceptual sensitivity and response bias were calculated according to the SDT. The patients identified a more 100 mL distensions than the healthy subjects (P = 0.02), whereas there was no difference in the number of identified 200 mL and sham distensions between the two groups. The perceptual sensitivity of IBS patients was significantly greater during 100 mL (P = 0.01), but not during 200 mL distensions. The response bias was not significantly different between the two groups. These data suggest that the increased frequency of sensations reported by IBS patients is not due to a psychological response bias.     

Protease-activated receptor-4 (PAR4): a role as inhibitor of visceral pain and hypersensitivity

Abstract Protease‐activated receptor‐4 (PAR₄) belongs to the family of receptors activated by the proteolytic cleavage of their extracellular N‐terminal domain and the subsequent binding of the newly released N‐terminus. While largely expressed in the colon, the role of PAR₄ in gut functions has not been defined. We have investigated the effects of PAR₄ agonist on colonic sensations and sensory neuron signalling, and its role in visceral pain. We observed that a single administration of the PAR₄ agonist peptide (AYPGKF‐NH₂), but not the control peptide (YAPGKF‐NH₂) into the colon lumen of mice significantly reduced the visceromotor response to colorectal distension at different pressures of distension. Further, intracolonic administration of the PAR₄ agonist, but not the control peptide, was able to significantly inhibit PAR₂ agonist‐ and transcient receptor potential vanilloid‐4 (TRPV4) agonist‐induced allodynia and hyperalgesia in response to colorectal distension. Protease‐activated receptor‐4 was detected in sensory neurons projecting from the colon, and isolated from the dorsal root ganglia, where it co‐expressed with PAR₂ and TRPV4. In total sensory neurons, PAR₄ agonist exposure inhibited free intracellular calcium mobilization induced by the pro‐nociceptive agonists of PAR₂ and TRPV4. Finally, PAR₄‐deficient mice experienced increased pain behaviour in response to intracolonic administration of mustard oil, compared with wild‐type littermates. These results show that PAR₄ agonists modulate colonic nociceptive response, inhibit colonic hypersensitivity and primary afferent responses to pro‐nociceptive mediators. Endogenous activation of PAR₄ also plays a major role in controlling visceral pain. These results identify PAR₄ as a previously unknown modulator of visceral nociception.     

Distension technique influences the relationship between colonic and rectal hypersensitivity in irritable bowel syndrome

In irritable bowel syndrome (IBS), it remains unclear whether rectal hypersensitivity is a 'marker' of colonic hypersensitivity. Our aim was to examine the relation between colonic and rectal sensitivity in IBS patients, comprising phasic and ramp distension techniques. Twenty IBS patients and 12 healthy subjects (N) underwent stepwise ramp and random phasic barostat distensions in the colon and rectum in random order. The sensory threshold pressure (ramp distension) and the visual analogue scale score (VAS, phasic distension), for pain and non-pain, were recorded. Colonic thresholds were lower, and VAS scores were generally higher, for pain and non-pain sensitivities in IBS compared to N. Rectal thresholds were lower, and VAS scores were higher, for pain but not for non-pain, in IBS compared to N. In IBS, for phasic distension, there was good correlation between the colon and rectum for non-pain (e.g. at 16 mmHg, r=0.59, P=0.006) and pain (r=0.60, P=0.006) sensitivities. In contrast, there was no significant correlation between the colon and rectum for ramp distension. In conclusion, colonic and rectal sensitivity in IBS are correlated in response to phasic but not ramp barostat distensions. The rectum serves as a legitimate 'window' for evaluating colonic hypersensitivity in IBS, provided that phasic distensions are employed.     

Rectal hypersensitivity as hallmark for irritable bowel syndrome: defining the optimal cutoff

Background Visceral hypersensitivity is a frequently observed hallmark of irritable bowel syndrome (IBS). Studies have reported differently about the presence of visceral hypersensitivity in IBS resulting from lack of standardization of the barostat procedure and due to different criteria used to assess hypersensitivity. We aimed to calculate the optimal cutoff to detect visceral hypersensitivity in IBS. Methods A total of 126 IBS patients and 30 healthy controls (HC) were included for assessment of visceroperception by barostat. Pain perception was assessed on a visual analogue scale (VAS). ROC‐curves were used to calculate optimal discriminative cutoff (pressure and VAS‐score) between IBS patients and HC to define hypersensitivity. Furthermore, pain perception to distension sequences below the pressure threshold for hypersensitivity was defined as allodynia. Key Results Irritable bowel syndrome patients showed increased visceroperception compared to HC. Thresholds for first sensation and first pain were lower in IBS patients VS HC (P < 0.01). ROC‐curves showed optimal discrimination between IBS patients and HC at 26 mmHg with a VAS cutoff ≥20 mm. Using this criterion, hypersensitivity percentages were 63.5% and 6.6% in IBS patients and HC, respectively. No significant differences were observed between IBS subtypes. Allodynia was found in a small number of patients (11%). Conclusions & Inferences Optimal cutoff for visceral hypersensitivity was found at pressure 26 mmHg with a VAS ≥20 mm, resulting in 63.5% of IBS patients being hypersensitive and 11% being allodynic. Standardization of barostat procedures and defining optimal cutoff values for hypersensitivity is warranted when employing rectal barostat measurements for research or clinical purposes.