Anatomical registration and three‐dimensional visualization of low and high‐resolution pan‐colonic manometry recordings

Background Colonic propagating sequences (PS) are important for the movement of colonic content and defecation, and aberrant PS patterning has been associated with slow transit constipation. However, because these motor patterns are typically recorded over long periods (24 h +), the visualization of PS spatiotemporal patterning is difficult. Here, we develop a novel method for displaying pan‐colonic motility patterns. Methods A 3D mesh representing the geometry of the human colon was created as follows: (i) Human colon images from the Visible Human Dataset were digitized to create a 3D data cloud, and (ii) A surface mesh was fitted to the cloud using a least‐squares minimization technique. Colonic manometry catheters were placed in the ascending colon of healthy controls and patients with slow transit constipation (STC), with the aid of a colonoscope. The colonic manometry data were interpolated and mapped to the model according to the following anatomical landmarks: cecum, hepatic flexure, splenic flexure, sigmoid‐descending junction, and anus. Key Results These 3D images clearly and intuitively communicate characteristics of normal and abnormal colonic motility. Specifically we have shown the reduced amplitude of the antegrade propagating pressure waves (PPW) throughout the colon and reduced frequency of PPWs at the mid‐colon in patients with STC. Conclusions and Inferences A novel method for the 3D visualization of PS is presented, providing an intuitive method for representing a large volume of physiological data. These techniques can be used to display frequency, amplitude or velocity data, and will help to convey regions of abnormally in patient populations.     

In search of objective manometric criteria for colonic high-amplitude propagated pressure waves

Abstract The aims of this study were to explore all characteristics of high-amplitude propagated contractions (HAPCs) that would allow them to be distinguished from nonHAPC colonic pressure waves, and to develop computer algorithms for automated HAPC detection. Colonic manometry recordings obtained from 24 healthy volunteers were used. Automated analysis was performed to detect propagated pressure waves and to determine their amplitude, duration and area under the curve (AUC). For each of these variables distribution plots were made. Automated HAPC counts were compared to visual counts by experienced investigators. Distribution plots of 141093 colonic pressure waves lacked a bimodal pattern, as was also the case for propagated contractions (n = 8758). With increasing high-amplitude thresholds for HAPC detection, a gradual decrease in the automatically detected HAPC number was observed. These findings precluded determination of a threshold. Taking visually detected HAPCs as reference, amplitude thresholds of 100 mmHg in two channels, and 80 mmHg in one channel yielded the highest sensitivity (92%). In conclusion, objective criteria to distinguish HAPCs from other propagated pressure waves on the basis of their amplitude, duration or AUC do not exist. Automated detection of HAPCs using empirically derived criteria leads to an acceptable degree of correlation with visually detected HAPCs.     

High amplitude propagated contractions

While most colonic motor activity is segmental and non‐propulsive, colonic high amplitude propagated contractions (HAPC) can transfer colonic contents over long distances and often precede defecation. High amplitude propagated contractions occur spontaneously, in response to pharmacological agents or colonic distention. A subset of patients with slow transit constipation have fewer HAPC. In this issue of Neurogastroenterology and Motility, Rodriguez et al. report that anal relaxation during spontaneous and bisacodyl‐induced HAPC exceeds anal relaxation during rectal distention in constipated children undergoing colonic manometry. Moreover, and consistent with a neural mechanism, anal relaxation often precedes arrival of HAPC in the left colon. High amplitude propagated contractions are also used to evaluate the motor response to a meal and pharmacological stimuli (e.g., bisacodyl, neostigmine) and to identify colonic inertia during colonic motility testing in chronic constipation. This editorial comprehensively reviews the characteristics, physiology and pharmacology of HAPC, their assessment by manometry, and relevance to constipation and diarrhea.     

Prolonged stationary colonic motility recording in seven patients with severe constipation secondary to antidepressants

The aim of this study was to determine whether the colonic motor profile of seven patients with constipation secondary to antidepressants differed from the motility of seven patients with idiopathic constipation and seven healthy volunteers. All constipated patients had very severe constipation. Colonic manometric recordings were performed for 24 h. The number of high amplitude propagating contractions (HAPC) was lower in the two groups of constipated patients than in controls. No HAPC were observed in 5/7 patients with constipation secondary to antidepressants and in 1/7 patients with idiopathic constipation. The overall area under the curve (AUC) in the left colon was lower in the two constipated patient groups than in controls. AUC increased after a 1000-kcal standard meal given at noon in controls but not in the two groups of constipated patients. In conclusion, in patients with constipation secondary to antidepressants, the overall AUC was as poor as in patients with idiopathic constipation, and no colonic response to eating was observed. Moreover, the number of HAPC was more markedly decreased in patients with constipation secondary to antidepressants than in patients with idiopathic constipation.     

Internal anal sphincter relaxation associated with bisacodyl‐induced colonic high amplitude propagating contractions in children with constipation: a colo‐anal reflex?

Background Describe the association of internal anal sphincter (IAS) relaxation with colonic high‐ amplitude peristaltic contractions (HAPCs). Methods Retrospective review of colon manometry tracings of children with constipation to determine the IAS relaxation characteristics associated with HAPC’s (HAPC‐IASR) events and compare them to the those seen during the performance of the anorectal manometry (ARMRAIR) events. Key Results A total of 70 HAPC‐ IASRs were observed in 15 patients, 65 after bisacodyl, two during fasting and three after a meal. In 64% of events, the IAS relaxation started when the HAPC reached left colon and in 36% as proximal as the hepatic flexure. High‐ amplitude peristaltic contraction propagation seems to be important in HAPC‐IASR characteristics; those propagating distal to sigmoid colon demonstrated larger and longer IAS relaxation as well as lower residual pressure, but equivalent resting pressure compared with HAPC’s ending proximal to sigmoid colon. Although IAS resting pressure was comparable for ARM‐RAIRs and HAPC‐IASRs, the duration and magnitude of anal relaxation was higher, and the anal residual pressure was lower in HAPC‐IASRs. Conclusions & Inferences We demonstrated that IAS relaxation in constipated children is associated with HAPCs migrating in the proximal and distal colon; in most cases, starting when peristalsis is migrating through left colon and in an important proportion while migrating proximally. We also demonstrated that HAPC‐IASRs are different from ARM‐RAIRs suggesting a neurally mediated reflex. Finally, the IAS relaxation characteristics are highly dependent on the degree of propagation of HAPCs, which could have important implications in the understanding of defecation disorders.     

Bowel preparation affects the amplitude and spatiotemporal organization of colonic propagating sequences

Background Colonic manometry is performed using either colonoscopically assisted catheter placement, after bowel preparation, or nasocolonic intubation of the unprepared bowel. There has been little systematic evaluation of the effects of bowel cleansing upon colonic propagating pressure wave sequences. Methods Eight healthy volunteers underwent nasocolonic placement of a water‐perfused silicone catheter which recorded pressures at 16 recording sites each spaced 7.5 cm apart in the unprepared colon for 24 h. These measures were compared with those obtained in another eight healthy volunteers in whom the catheter was placed to the caecum at colonoscopy in the prepared colon. Key Results The colonic motor responses to meals and morning waking, and the normal nocturnal suppression did not differ between the two groups, nor were the overall frequency, regional dependence nor extent of propagating sequences (PS) influenced by bowel preparation. Bowel preparation did result in a significant increase in the frequency of high amplitude PS (22 ± 7 vs 8 ± 4 HAPS/24 h; P = 0.003). Additionally, a number of the measures of spatiotemporal organization among consecutive PS (linkage among sequences and predefecatory stereotypical patterning) were significantly altered by bowel preparation. Conclusions & Inferences The overall frequency of PSs, the colonic responses to physiological stimuli such a meal and morning waking and nocturnal suppression, are not influenced by prior bowel preparation. However, investigators wishing to study HAPS frequency, or the more complex spatiotemporal relationships among consecutive PSs, should control for bowel preparation when making comparisons among study groups.     

Distention of the colon is associated with initiation of propagated contractions in children

Abstract  The presence of high-amplitude propagating contractions (HAPCs) has been identified as a marker of colonic neuromuscular integrity. The physiologic mechanisms of HAPCs initiation have yet to be determined. Distention secondary to colonic filling has been hypothesized as physiologic initiator. The aim of this study was to study the effect of intraluminal balloon distention in the colon of children with defecatory disorders. Colonic manometry was performed with a polyethylene balloon situated at the proximal end of the catheter, which was placed in the most proximal colonic segment reached during colonoscopy. A stepwise pressure controlled distention of the balloon was performed using barostat computer (10–50 mmHg). Propagated contractions were defined as those that migrated over at least three recording sites. They were divided into HAPCs, amplitude >60 mmHg and low-amplitude propagating contractions (LAPCs), amplitude <60 mmHg. Children with spontaneous HAPCs or HAPCs after bisacodyl provocation were considered to have normal motility. Twenty children completed the study. Among the 14 children with normal colonic motility, balloon distention elicited HAPCs in four and LAPCs in 10 children. No HAPC were elicited in six children with abnormal motility and LAPCs were seen in four of them. The balloon-induced propagated contractions had similar characteristics as those occurring spontaneously and after bisacodyl provocation but the pressure needed to elicit them and their amplitude was inconsistent. These findings suggest that intraluminal distention can trigger propagated contractions in children. This mechanism of action for induction of propagated contractions is not as consistent as the motor response found in response to bisacodyl administration.     

High‐resolution colonic manometry accurately predicts colonic neuromuscular pathological phenotype in pediatric slow transit constipation

Background Severe pediatric slow transit constipation (STC) is commonly due to intrinsic colonic neuromuscular disease. We sought to correlate neuromuscular histological phenotypes in pediatric STC with colonic manometric phenotypes using high‐resolution manometry (HRM). We tested the hypothesis that failure of motor quiescence (FQ) between bisacodyl‐induced high amplitude propagating sequences (HAPSs) might predict neuromuscular pathology. Methods Eighteen children (10 males, median age: 7.5 years) with refractory STC underwent stationary colonic HRM before segmental colonic resection. Six age‐matched constipated children with normal colonic transit served as controls. Colonic resection specimens underwent histopathological analysis. Conventional manometric parameters and area under the curve (AUC) during a 1‐min period following bisacodyl‐induced HAPSs [PBAUC₁], as measure of FQ, were calculated. Key Results Numbers of postbisacodyl HAPSs in descending and sigmoid segments were lower in patients than controls (P < 0.01, respectively). Low amplitude propagating sequences (LAPSs) were common prebisacodyl in controls and rare in STC (P < 0.001), whereas postbisacodyl LAPS were more common in STC (P < 0.001). Postbisacodyl, both retrograde propagating contractions and bursts of contractions were present in STC patients only (P < 0.001 and P < 0.01). Postbisacodyl simultaneous pressurization was seen only in STC (P < 0.05 and P < 0.001, in descending and rectosigmoid segments). Histological abnormalities were present in 17/18. Fourteen were neurogenic, one neuro‐myogenic, and two myogenic. In segments with HAPS, PBAUC₁ was predictive of colonic neuropathy using a cutoff of 205 mmHg.s^‐1 (Sensitivity 100%, specificity 86%, PPV92%, NPV100%). Conclusions & Inferences PBAUC₁ is increased in multiple colonic segments in neuropathic pediatric STC and constitutes a sensitive and specific biomarker of neuropathy.     

Results of 24-h manometric recording of colonic motor activity with endoluminal instillation of bisacodyl in patients with severe chronic slow transit constipation

The aims of this study were to assess the prevalence of manometric colonic abnormalities and to evaluate the motor effect of intraluminal bisacodyl in a cohort of refractory constipated patients. Twenty-four hour colonic motility recordings were performed in 40 patients referred for a severe intractable chronic constipation. At the end of each recording session the motor effects of the endoluminal instillation of 10 mg bisacodyl were assessed. These patients were compared with 20 healthy subjects. The number of high-amplitude propagating contractions (HAPC) was significantly decreased in patients with slow transit constipation (12 +/- 11.6 vs 1 +/- 8.6, P < 0.001). Based on manometric patterns four groups of patients were isolated. Ten patients had no spontaneous HAPC, no food-induced colonic motor response and significantly lower colonic activity in transverse colon (374 +/- 1220 vs 3249 +/- 3458, P < 0.05). Five patients had significantly increased sigmoid segmental motility (20298 +/- 6364 vs 88780 +/- 3643, P < 0.001) and eight patients had significantly lower number of HAPC without other manometric abnormalities while 17 patients had normal colonic motility recordings. Endoluminal bisacodyl was able to induce HAPCs in all groups of patients. Patients with severe slow transit refractory constipation represented a heterogeneous group and endoluminal bisacodyl was able to promote a propagated motor activity in a majority of patients even in those suspected of having an inert colon.     

Motility of the left colon in children and adolescents with functional constpation; a retrospective comparison between solid‐state and water‐perfused colonic manometry

Background

Using water‐perfused (WP) high‐resolution manometry, we recently demonstrated that children with functional constipation (FC) lacked the postprandial increase in distal colonic cyclic motor patterns that was observed in healthy adults. Our aim was to determine if similar results could be detected using a solid‐state (SS) manometry catheter.

Methods

We performed a retrospective analysis of 19 children with FC (median age 11.1 years, 58% male) who underwent colonic manometry with a SS catheter (36 sensors, 3 cm apart). Data were compared with previously published data using a WP catheter (36 sensors, 1.5 cm apart) recorded from 18 children with FC (median age 15 years; 28% male).

Key Results

The cyclic motor patterns recorded by the SS catheter did not differ from those previously recorded by the WP catheter. There was no detected increase in this activity in response to the meal in either group. Long‐single motor patterns were recorded in most patients (n = 16, 84%) with the SS catheter. The number of these events did not differ from the WP recordings. In the SS data, HAPCs were observed in 4 children prior to the meal, in 5 after the meal. This did not differ significantly from the WP data.

Conclusions & Inferences

These data recorded by SS manometry did not differ from WP manometry data. Regardless of the catheter used, both studies revealed an abnormal colonic response to a meal, indicating a pathology which is not related to the catheter used to record these data.     

Does magnetic stimulation of sacral nerve roots modify colonic motility? Results of a randomized double‐blind sham‐controlled study

Abstract  Although sacral nerve root stimulation (SNS) can result in a symptomatic improvement of faecal incontinence, the mechanism of action remains unknown. The aim of this study was to assess whether short-term magnetic SNS can inhibit pharmacologically induced propulsive colonic contractions. Twelve healthy volunteers (median age: 43.5 years old) were studied on two separate occasions and randomized into either active (15 Hz, 100% output intensity for 5 s min⁻¹ for 30 min) or sham rapid rate lumbosacral magnetic stimulation (rLSMS). Colorectal motility was recorded with a manometric catheter located at the most proximal transducer in the left colon and the most distal, in the rectum. Colonic contractions were provoked by instilling Bisacodyl. The effects of rLSMS on colonic, sigmoid and rectal contractions were monitored and recorded after Bisacodyl instillation. The appearance of high-amplitude contractions propagated or not (HAC/HAPC) provoked by Bisacodyl instillation was significantly delayed during active compared to sham stimulation ( P  = 0.03). There was no difference in the characteristics of HAC/HAPC (i.e. frequency, amplitude, duration, velocity of propagation) or the motility index with active or sham stimulation. The perception of urgency tended to be decreased with rLSMS following Bisacodyl instillation. The catheter was expulsed within a median of 16.5 min (range 8–39) after Bisacodyl administration during active stimulation compared to 14 min (range 5–40) during sham stimulation ( P  = 0.03). This study suggests that rLSMS could delay the appearance of the first Bisacodyl-induced colonic contractions.     

Stretch‐dependent sensitization of post‐junctional neural effectors in colonic muscles

Background The colon undergoes distension‐induced changes in motor activity as luminal contents or feces increase wall pressure. Input from enteric motor neurons regulates this motility. Here we examined stretch‐dependent responses in circular muscle strips of murine colon. Methods Length ramps (6–31μm s^?1) were applied in the axis of the circular muscle layer in a controlled manner until 5 mN isometric force was reached. Key Results Length ramps produced transient membrane potential hyperpolarizations and attenuation of action potential (AP) complexes. Responses were reproducible when ramps were applied every 30 s. Stretch‐dependent hyperpolarization was blocked by TTX, suggesting AP‐dependent release of inhibitory neurotransmitter(s). Atropine did not potentiate stretch‐induced hyperpolarizations, but increased compliance of the circular layer. N^ω‐nitro‐l ‐arginine (l ‐NNA) inhibited stretch‐dependent hyperpolarization and decreased muscle compliance, suggesting release of NO mediates stretch‐dependent inhibition. Control membrane potential was restored by the NO donor sodium nitorprusside. Stretch‐dependent hyperpolarizations were blocked by l ‐methionine, an inhibitor of stretch‐dependent K⁺ (SDK) channels in colonic muscles. Loss of interstitial cells of Cajal, elicited by Kit neutralizing antibody, also inhibited responses to stretch. In presence of l ‐NNA and apamin, stretch responses became excitatory and were characterized by membrane depolarization and increased AP firing. A neurokinin‐1 receptor antagonist inhibited this stretch‐dependent increase in excitability. Conclusions and Inferences Our data show that stretch‐dependent responses in colonic muscles require tonic firing of enteric inhibitory neurons, but reflex activation of neurons does not appear to be necessary. NO causes activation of SDK channels, and stretch of muscles further activates these channels, explaining the inhibitory response to stretch in colonic muscle strips.     

High‐resolution manometry changes our views of gastrointestinal motility

High‐resolution manometry using catheters with 36 solid‐state sensors spaced 1 cm apart has already become an established technique for esophageal manometry where it has replaced water‐perfused and station pull‐through manometry. Spatiotemporal plots with color coding of pressure have greatly facilitated the analysis of esophageal peristalsis. Although suitable for the length of the esophagus, the solid‐state catheter is insufficient for the study of longer segments of the gastrointestinal tract. A new technique with fiber‐optic sensors has made it possible to construct catheters with 72–144 sensors. Studies of colonic motility have revealed that the most common motor pattern of the colon is a peristaltic contraction that travels 7–10 cm in the retrograde direction. Earlier studies using low‐resolution manometry with 7–45 cm between sensors led us to erroneous conclusions regarding direction and frequency of contractions and they largely missed both antegrade and retrograde contractions traveling short distances. Fiber‐optic high‐resolution manometry holds promise for greatly improving our understanding of gut motor physiology and hopefully also our understanding of patients with symptoms of disordered gut motility.     

Fully automated analysis of colonic manometry recordings

The purpose of this study was to develop a computer program for fully automated analysis of all presently known motor patterns in human colonic motility recordings. Colonic pressure recordings obtained from 24 healthy volunteers were used. Algorithms were developed for the detection and numerical analysis of five types of pressure waves: antegrade, retrograde, simultaneous, high-amplitude and isolated pressure waves. Furthermore, periodical motor activity was quantified. Validation was performed by comparison with visual analysis by two experienced observers. Patterns recorded during day- and night-time were compared using multiple-factor analysis of variance with Bonferroni correction. Automated analysis correlated well with visual peak detection (r = 0.98, P <0.01) and detection of antegrade pressure waves (r = 0.98, P <0.01). Most motor patterns showed a diurnal variation. During the night, prevalences of antegrade (938 vs 455; P <0.05), retrograde (112 vs 81; P <0.05), high-amplitude (12.9 vs 1.3; P <0.05), isolated pressure waves (1114 vs 765; P <0.05), and periodic motor activity were decreased (7.33 vs 4.47%; P <0.05). However, when expressed as percentage of absolute numbers of pressure waves, prevalences remained constant. In conclusion, fully automated analysis of all hitherto described colonic motility patterns is feasible. During the night, overall wave prevalences markedly decreased, but the distribution over the various motor patterns was preserved.     

Impaired propulsive motility in the distal but not proximal colon of BK channel β1‐subunit knockout mice

Background Large‐conductance Ca²⁺‐activated K⁺ (BK) channels regulate smooth muscle tone. The BK channel β1‐subunit increases Ca²⁺ sensitivity of the α‐subunit in smooth muscle. We studied β1‐subunit knockout (KO) mice to determine if gastrointestinal (GI) motility was altered. Methods Colonic and intestinal longitudinal muscle reactivity to bethanechol and colonic migrating motor complexes (CMMCs) were measured in vitro. Gastric emptying and small intestinal transit were measured in vivo. Colonic motility was assessed in vivo by measuring fecal output and glass bead expulsion time. Myoelectric activity of distal colon smooth muscle was measured in vitro using intracellular microelectrodes. Key Results Bethanechol‐induced contractions were larger in the distal colon of β1‐subunit KO compared to wild type (WT) mice; there were no differences in bethanechol reactivity in the duodenum, ileum, or proximal colon of WT vsβ1‐subunit KO mice. There were more retrogradely propagated CMMCs in the distal colon of β1‐subunit KO compared to WT mice. Gastrointestinal transit was unaffected by β1‐subunit KO. Fecal output was decreased and glass bead expulsion times were increased in β1‐subunit KO mice. Membrane potential of distal colon smooth muscle cells from β1‐subunit KO mice was depolarized with higher action potential frequency compared to WT mice. Paxilline (BK channel blocker) depolarized smooth muscle cells and increased action potential frequency in WT distal colon. Conclusions & Inferences BK channels play a prominent role in smooth muscle function only in the distal colon of mice. Defects in smooth muscle BK channel function disrupt colonic motility causing constipation.     

Solid-state vs water-perfused catheters to measure colonic high-amplitude propagating contractions

Background Solid‐state (SS) manometry catheters with portable data loggers offer many potential advantages over traditional water‐perfused (WP) systems, such as prolonged recordings in a more physiologic ambulatory setting and the lack of risk for water overload. The use of SS catheters has not been evaluated in comparison with perfused catheters in children. This study aims to compare data provided by SS and WP catheters in children undergoing colonic manometry studies. Methods A SS catheter and a WP catheter were taped together such that their corresponding sensors were at the same location. Simultaneous recordings were obtained using the SS and WP catheters (both 8 channels, 10 cm apart) in 15 children with severe defecation disorders referred for colonic manometry. Signals were recorded for a minimum of 1 h during fasting, 1 h after ingestion of a meal, and 1 h after the administration of bisacodyl. Solid‐state signals from the data logger were analyzed against the perfused signals. All high‐amplitude propagated contractions (HAPCs), the most recognizable and interpreted colonic motor event, were evaluated for spatial and temporal features including their durations, amplitudes, and propagation velocities. Key Results A total of 107 HAPCs were detected with SS and 91 with WP catheters. All WP‐HAPC were also observed with SS. Linear regression analysis showed that SS catheters tended to give higher readings in the presence of amplitudes <102 mmHg and lower reading with amplitudes >102 mmHg. An opposite trend was found for the duration of contractions. No significant difference was found for HAPC velocity. Conclusions & Inferences SS catheters are more sensitive in recording HAPCs in children with defecation disorders compared with the more traditional WP assembly. There is a difference in measurements of amplitude between the two systems. Solid‐state catheters offer potential advantages over WP catheters in children, being portable, safer to use, and may provide data over a more prolonged period.     

NGF is involved in oral ovalbumin‐induced altered colonic contractility in rats: evidence from the blockade of TrkA receptors with K252a

Background Nerve growth factor (NGF)‐mucosal mast cell (MMC) interaction has been implicated in the remodeling of enteric circuitries and associated functional changes. We investigated the involvement of NGF and its receptor TrkA in the altered colonic contractile activity observed in the model of oral ovalbumin (OVA)‐induced MMC hyperactivity in rats. We also studied the role of colonic MMCs as a source of NGF. Methods Rats received oral OVA, alone or with the TrkA antagonist K252a. Colonic co‐expression of NGF/TrkA and rat mast cell protease II (RMCPII) (double immunofluorescence), RMCPII content (ELISA) and expression of NGF, Brain‐derived neurotrophic factor (BDNF) and TrkA/B (QT‐PCR) were assessed. Colonic contractile activity was determined in vivo and in vitro. Key Results TrkA, but not NGF, was localized in colonic MMCs (RMCPII‐positive). Oral ovalbumin exposure increased colonic RMCPII levels but did not change the percentage of TrkA‐positive MMCs. Neither OVA nor K252a, alone or combined, altered NGF, BDNF or TrkA/B expression. Spontaneous colonic activity in vivo and in vitro was altered by OVA, an effect prevented by K252a. Electrical stimulation‐induced contractile responses in vivo and carbachol responses in vitro were increased by OVA in a K252a‐independent manner. In OVA‐treated animals, inhibition of NO synthesis with l ‐NNA significantly enhanced spontaneous colonic activity in vitro, a response completely prevented by K252a. Conclusions & Inferences These results suggest that NGF‐TrkA‐dependent pathways are implicated in colonic contractile alterations observed during OVA exposure in rats. NGF‐TrkA system might represent a potential target for treatment of gastrointestinal disorders characterized by colonic motor alterations.     

Increased colonic motility in a rat model of irritable bowel syndrome is associated with up‐regulation of L‐type calcium channels in colonic smooth muscle cells

Objective This paper aimed to investigate the relationship between up‐regulation of L‐type calcium channels and altered motility disorder in a rat model of irritable bowel syndrome (IBS). Methods Male Sprague–Dawley rats were subjected to neonatal maternal separation (NMS) from postnatal day 2–14 or normal handling (NH), and used when weighted 250–300 g. Colonic smooth muscle contractions was studied in an organ bath system. L‐type Ca²⁺ channel α_1c subunit expression in smooth muscles from rat colon were studied by immunofluorescence and Western blotting analysis. The intracellular calcium concentration ([Ca²⁺]_i) of enzymatically isolated single colonic smooth muscle cell was studied with laser confocal fluorescent microscopy. Results The fecal pellets during 1 h water avoidance stress (WAS) were significantly increased; the amplitude of spontaneous contractions and contractions induced by Bay K 8644 (10 nm –1 μm ), KCl (10–60 mm ) and ACh (100 nm –10 μm ) were significantly increased in NMS rats, when comparing with that of NH rats. [Ca²⁺]i induced by Bay K 8644 (1 μm ), KCl (40 mm ), and ACh (10 μm ) significantly increased in muscle cells of NMS rats than NH rats. Further, α_1c protein expression was significantly up‐regulated in colonic smooth muscle of NMS rats than NH rats. Conclusion These results suggest that NMS lead to up‐regulation of L‐type Ca²⁺ channels expression in the colon, which contributes to the colonic motility disorder. Our findings provide direct evidence to help understanding the underlying mechanism of chronic stress‐induced colonic motility disorder in IBS.     

Lesioning of TRPV1 expressing primary afferent neurons prevents PAR-2 induced motility, but not mechanical hypersensitivity in the rat colon

Background Proteinase activated receptor 2 (PAR‐2) is expressed by many neurons in the colon, including primary afferent neurons that co‐express transient receptor potential vanilloid 1 (TRPV1). Activation of PAR‐2 receptors was previously found to enhance colonic motility, increase secretion and produce hypersensitivity to mechanical stimuli. This study examined the functional role of TRPV1/PAR‐2 expressing neurons that innervate the colon by lesioning TRPV1 bearing neurons with the highly selective and potent TRPV1 agonist resiniferatoxin. Methods Colonic motility in response to PAR‐2 activation was evaluated in vitro using isolated segments of descending colon and in vivo using manometry. Colonic mechanical nociceptive thresholds were measured using colorectal distension. Transient receptor potential vanilloid 1 expressing neurons were selectively lesioned with resiniferatoxin. Key Results In vitro, the PAR‐2 agonists, trypsin and SLIGRL did not alter contractions of colon segments when applied alone, however, the agents enhanced acetylcholine stimulated contraction. In vivo, PAR‐2 agonists administered intraluminally induced contractions of the colon and produced hypersensitivity to colorectal distention. The PAR‐2 agonist enhancement of colonic contraction was eliminated when TRPV1 expressing neurons were lesioned with resiniferatoxin, but the PAR‐2 agonist induced hypersensitivity remained in the lesioned animals. Conclusions & Inferences Our findings indicate that TRPV1/PAR‐2 expressing primary afferent neurons mediate an extrinsic motor reflex pathway in the colon. These data, coupled with our previous studies, also indicate that the recently described colospinal afferent neurons are nociceptive, suggesting that these neurons may be useful targets for the pharmacological control of pain in diseases such as irritable bowel syndrome.     

Localization and gestation‐dependent pattern of corticotrophin‐releasing factor receptor subtypes in ovine fetal distal colon

Abstract Meconium passage is frequently observed in association with feto‐maternal stress factors such as hypoxia and infection, but the triggering mechanism is unknown. We hypothesize that differential regulation of corticotrophin‐releasing factor (CRF) receptors during gestation play an important role in determining the susceptibilities of the fetus to stress‐induced in utero meconium passage at term. We examined the innervation patterns of CRF‐receptor type 1 (CRF‐R1), a stimulator of gastrointestinal motility and CRF‐receptor type II (CRF‐R2), an inhibitor of gastrointestinal motility in ovine fetal distal colonic segments from very preterm to term gestation. Both CRF‐R1 and CRF‐R2 receptors were present in muscularis mucosa as well as in longitudinal and circular smooth muscle layers in fetal distal colonic segments at all gestational ages. Quantitative image analysis indicated a 42% increase in CRF‐R1 receptor immunoreactivity in muscularis mucosa and a 30% in longitudinal smooth muscle layers from very preterm to term. In contrast, CRF‐R2 receptor immunoreactivity in muscularis mucosa as well as in longitudinal and circular smooth muscle layers decreased by 38%, 55% and 51%, respectively, at term. The percentage of enteric ganglia and the number of enteric neurons expressing CRF‐R1 receptors were high at term. Western blot analysis identified 235 and 50 kDa molecular species of CRF‐R1 receptors and 37 and 28 kDa molecular species of CRF‐R2 receptors. In summary, we speculate that downregulation of CRF‐R2 receptor abundance with concurrent increases in CRF‐R1 receptor levels in myenteric‐smooth muscle unit with advancing gestation sensitizes the colonic motility responses to stressors.