Small intestinal transections decrease the occurrence of tapeworm-induced myoelectric patterns in the rat

Abstract Luminal infection by the noninvasive tapeworm, H. diminuta, alters rat small intestinal myoelectric activity. The significance of continuity between small intestinal enteric nervous system (ENS) and that of both the stomach/pylorus and colon/caecum regarding the induction of tapeworm-altered myoelectric patterns was evaluated. A total of 32 rats were implanted with four serosal electrodes placed at sites in the duodenum through the mid-jejunum. Sixteen of the 32 rats underwent intestinal transections and anastomoses at both the duodenum and ileum. After recording myoelectrical activity of both normal and transected intestines, eight rats from each group (normal and transected) were infected with H.diminuta. Phase III frequency, duration of the migrating myoelectric complex (MMC), slow wave frequency, percentage of slow waves associated with spike potentials and the occurrence of the the two tapeworm-initiated myoelectric patterns, repetitive bursts of action potentials (RBAP) and sustained spike potentials (SSP), were measured. In infected rats, the frequency of the RBAP and SSP electric patterns were significantly reduced by the double transection. Intestinal transection did not affect the other changes caused by infection, such as decreased MMC phase III frequency and percentage of slow waves associated with spike potentials. In conclusion, a small intestinal ENS in continuity with other segments of the GI tract is required to generate maximal numbers of tapeworm-induced SSP and RBAP myoelectric activity in the small intestine of the rat.     

Slowing of intestinal transit by fat depends on an ondansetron – sensitive, efferent serotonergic pathway

The ileal brake is a neural reflex that slows proximal small bowel transit when fat enters the distal small bowel. In rats, ondansetron, a 5-hydroxytryptamine-3 (5-HT3)-receptor antagonist, abolishes the ileal brake. However, the location of this serotonergic pathway is unknown. Of the known enteric sites responsive to 5-hydroxytryptamine (5-HT), only the myenteric neurone is equipped with 5-HT3 receptors and is located on the efferent limb of reflex response. The aim of this study was to test the hypothesis that slowing of intestinal transit by fat may depend on an ondansetron-sensitive serotonergic pathway located on the efferent limb of this reflex response. In a fistulated dog model that compartmentalized the afferent from the efferent limb of the ileal brake response, ondansetron was delivered luminally into the distal (afferent) or proximal (efferent) half of the small bowel to localize the serotonergic pathway. It was found that activating the ileal brake slowed down the proximal intestinal transit to 30% of control values. The ileal brake was abolished when ondansetron was delivered into the proximal but not the distal small bowel. Our data supports the hypothesis that the 5-HT receptors participating in the ileal brake are on the efferent limb of this neural reflex, possibly on myenteric neurones.     

Analysis of gastrointestinal physiology using a novel intestinal transit assay in zebrafish

Abstract  Gastrointestinal function depends upon coordinated contractions to mix and propel food through the gut. Deregulation of these contractions leads to alterations in the speed of material transit through the gut, with potentially significant consequences. We have developed a method for visualizing intestinal transit, the physiological result of peristaltic contractions, in larval zebrafish. This method allows direct, non-invasive observation of luminal content as it traverses the gut. Using this method, we characterized gastrointestinal transit in zebrafish larvae at 7 days postfertilization. In addition, we used this transit assay to assess the physiological consequences of reduced or absent enteric neurones on intestinal transit in larval zebrafish. This may facilitate the use of the zebrafish for investigating the effect of compounds and candidate genes on gastrointestinal motility.     

Localisation of NK1 receptor immunoreactivity to neurons and interstitial cells of the guinea-pig gastrointestinal tract

Tachykinins, including substance P, neurokinin A, and neuropeptides K and γ, are expressed widely in the peripheral nervous system where they affect smooth muscle contraction, exocrine gland secretion, vascular permeability, and neurotransmission. Substance P, the preferred ligand for the NK1 receptor, is found in high concentrations in the enteric nervous system. In the present study, the localisation and distribution of the NK1 receptor was studied throughout the gastrointestinal tract of the guinea-pig by using a polyclonal antiserum raised against the C-terminal 15 amino acids of the NK1 receptor. Co-localisation with other neuronal markers was examined in the ileum. Nerve cell bodies reactive for the NK1 receptor were found in the myenteric plexus of all regions and the submucous plexus of the small and large intestines. In the small intestine, the interstitial cells of Cajal were also immunoreactive. Immunoreactivity was largely confined to cell surfaces. Almost all immunoreactive myenteric nerve cells had Dogiel type I morphology, and most of these were immunoreactive for nitric oxide synthase, a transmitter of inhibitory neurons to the muscle and of descending interneurons. Neuropeptide Y-containing secretomotor neurons in the submucous and myenteric plexuses also exhibited NK1 receptor immunoreactivity. NK1 receptors were present on a minority of tachykinin immunoreactive neurons of submucous ganglia. The results suggest that receptors on the longitudinal muscle might not be conventional NK1 receptors, that excitation of the circular muscle of the ileum is indirect, perhaps via the interstitial cells of Cajal, and that enteric inhibitory neurons may be excited via NK1 receptors. © 1996 Wiley-Liss, Inc.     

Slow transit constipation: a model of human gut dysmotility. Review of possible aetiologies

Slow transit constipation is a severe condition of gut dysmotility that predominantly affects young women and may result in surgical intervention. Current medical treatments for STC are often ineffective, and the outcome of surgery is unpredictable. STC was first described almost a century ago. Since this time, progress in improving therapy for this condition has been complicated by a lack of understanding of the aetiology, and great variation in the methods and criteria used for the study of patients with this debilitating disorder. It is difficult to find unequivocal data, and harder still to give a definitive picture of the cause or causes of STC. Here we consider the evidence for various aetiologies of STC, in the light of the physiological and pathological findings.     

Cannabinoid type 1 receptor modulates intestinal propulsion by an attenuation of intestinal motor responses within the myenteric part of the peristaltic reflex

Cannabinoid-1 (CB1) receptor activation affects gastrointestinal propulsion in vivo. It was our aim to further characterize the involved myenteric mechanisms in vivo and in vitro. In CB1(-/-) mice and wild-type littermates we performed in vivo transit experiments by charcoal feeding and in vitro electrophysiological recordings in mouse small intestinal smooth muscle. Ascending neuronal contraction (ANC) following electrical field stimulation was studied in rat ileum in a partitioned organ bath separating the aboral stimulation site from the oral recording site. The knockout animals displayed an accelerated upper gastrointestinal transit compared to control animals. The CB1 receptor antagonist AM251 stimulated the force of the ANC in a concentration dependent manner when added in the oral chamber. Anandamide significantly inhibited the ANC when added in the oral chamber. Neither AM251 nor anandamide had an influence on the contraction latency. No effects were observed when drugs were added in the aboral chamber, proving a CB1 mediated action on the neuromuscular junction. Resting membrane potentials and neuronal induced inhibitory junction potentials in CB1(-/-) mice were unchanged as compared to wild type. However, the electrophysiological slow waves were more sensitive to blockade of Ca(2+) channels in CB1(-/-) mice. Our data strongly suggest a physiological involvement of the CB-1 receptor in the regulation of small intestinal motility. Therefore, CB1 receptors are a promising target for the treatment of motility disorders.     

Effects of modulators of Ca2+-activated, intermediate-conductance potassium channels on motility of the rat small intestine, in vivo

The movements of the intestine shift between different motor patterns, including between propulsion and mixing, but there is little information concerning mechanisms that may lead to changes in the patterns of motility. We have investigated the influence on intestinal motility of drugs that affect the after-hyperpolarization potential (AHP) of intrinsic primary afferent neurons (IPANs). The current of the AHP is carried by the intermediate conductance, calcium-activated, potassium (IK) channel. In anaesthetized rats, the IK channel blocker, 1-[(2-chlorophenyl)diphenylmethyl]-1H-pyrazole (0.05-1 mg kg(-1), i.v.) disrupted the regular propulsive pressure waves that occur in the small intestine and reduced propulsion of the contents (after 1 mg kg(-1), the fluid propelled was <25% of control). If the propulsion in the intestine was regular, the IK channel opener, 5,6-dichloro-1-ethyl-2-benzimidazolinone (DC-EBIO, 0.1 mg kg(-1) h(-1)) had no effect. DC-EBIO (0.1 mg kg(-1) h(-1)) restored propulsive activity after the nitric oxide synthase inhibitor, Nomega-nitro-l-arginine had changed motility to a mixing pattern. We suggest that the AHP determines the synchrony of action potential firing in synaptically coupled IPANs, and that this synchrony influences the patterns of firing of muscle motor neurons, and hence the pattern of contraction of the muscle and whether the pattern is predominantly propulsive or predominantly mixing.     

Neuroepithelial stem cells differentiate into neuronal phenotypes and improve intestinal motility recovery after transplantation in the aganglionic colon of the rat

The purpose of this study was to elucidate the possibility and the biological significance of intracolonic grafting of neuroepithelial stem cells (NESCs) as a therapeutic strategy for neuronal replacement in disorders of the enteric nervous system (ENS) such as aganglionosis. The enteric plexus of rat colon were eliminated by serosal application of the cationic surfactant benzalkonium chloride. NESCs were harvested from the neural tube of embryonic rat, labelled with bromodeoxyuridine (BrdU), and transplanted into the denervated colon. After 2, 4 and 8 weeks, grafted cells were visualized in colon sections by fluorescent double-staining for BrdU and neuronal, astrocytic, neurochemical or stem cell markers. Eight weeks post-transplantation, the intestinal motility was assessed by measuring the changes of intraluminal pressure responding to inflating stimulation and the responses to electrical field stimulation (EFS). Our results indicate that when transplanted into the denervated gut, NESCs survived and could differentiate into neurons and glial cells in vivo. Furthermore, inflation stimulated contraction and EFS-induced response were observed in NESCs grafted group compared with no reaction in denervated group. Therefore, NESCs can survive and function in the denervated rat colon in vivo, which indicates that NESCs provide a promising cellular replacement candidate for ENS.     

Effect of chronic, extrinsic denervation on functional NANC innervation with vasoactive intestinal polypeptide and substance P in longitudinal muscle of rat jejunum.

Abstract Intestinal denervation contributes to enteric motor dysfunction after intestinal transplantation [small bowel transplantation (SBT)]. Our aim was to determine long‐term effects of extrinsic denervation on functional non‐adrenergic, non‐cholinergic innervation with vasoactive intestinal polypeptide (VIP) and substance P. Contractile activity of jejunal longitudinal muscle from six age‐matched, naïve control rats (NC) and eight rats 1 year after syngeneic SBT were studied in tissue chambers. Spontaneous contractile activity did not differ between groups. Exogenous VIP inhibited contractile activity dose‐dependently in both groups, greater in NC than in SBT. The VIP antagonist ([d ‐p‐Cl‐Phe⁶,Leu¹⁷]‐VIP) and the nitric oxide synthase inhibitor l ‐N^G‐nitro arginine prevented inhibition by exogenous VIP and electrical field stimulation (EFS) in both groups. Exogenous substance P increased contractile activity dose‐dependently, greater in NC than in SBT. The substance P antagonist ([d ‐Pro²,d ‐Trp^7,9]‐substance P) inhibited effects of exogenous substance P and increased the EFS‐induced inhibitory response. Immunohistofluorescence showed staining for tyrosine hydroxylase in the jejunoileum 1 year after SBT suggesting sympathetic reinnervation. In rat jejunal longitudinal muscle after chronic denervation, response to exogenous VIP and substance P is decreased, while endogenous release of both neurotransmitters is preserved. These alterations in excitatory and inhibitory pathways occur despite extrinsic reinnervation and might contribute to enteric motor dysfunction after SBT.     

Intestinal motor stimulation by the 5-HT4 receptor agonist ML10302: differential involvement of tachykininergic pathways in the canine small bowel and colon

5-Hydroxytryptamine (5-HT)4 receptor agonists stimulate gut motility through cholinergic pathways, although there are data suggesting that noncholinergic (tachykininergic) excitatory pathways may also be involved. Differences may exist between the small bowel and colon. Our aims were: (i) to compare the prokinetic effect exerted by the 5-HT4 receptor agonist ML10302 in the canine small bowel and colon in vivo; and (ii) to investigate the role of tachykininergic pathways in mediating this response. In fasting, conscious dogs, chronically fitted with electrodes and strain-gauge force transducers along the small bowel and colon, intravenous injection of ML10302 (35 microg kg-1) immediately stimulated spike activity and significantly increased propagated myoelectrical events at both intestinal levels. In the small bowel, the effects of ML10302 were unchanged by previous administration of the selective NK1 tachykinin receptor antagonist SR140333, the NK2 tachykinin receptor antagonist SR48968, or the NK3 tachykinin receptor antagonist SR142801. In the colon, all tachykinin receptor antagonists significantly inhibited stimulation of spike and mechanical activity by ML10302, without affecting ML10302-induced propagated myoelectrical events. Atropine (100 microg kg-1 i.v.) suppressed the stimulatory effect of ML10302 at both intestinal levels. In conclusion, the 5-HT4 receptor agonist ML10302 induced significant prokinesia both in the small bowel and colon through activation of cholinergic pathways. Tachykininergic pathways are not involved in the ML10302-induced prokinesia in the small bowel, but they play an important role in mediating the colonic motor response to ML10302.     

The involvement of nitric oxide synthase neurons in enteric neuropathies

Nitric oxide (NO), produced by the neural nitric oxide synthase enzyme (nNOS) is a transmitter of inhibitory neurons supplying the muscle of the gastrointestinal tract. Transmission from these neurons is necessary for sphincter relaxation that allows the passage of gut contents, and also for relaxation of muscle during propulsive activity in the colon. There are deficiencies of transmission from NOS neurons to the lower esophageal sphincter in esophageal achalasia, to the pyloric sphincter in hypertrophic pyloric stenosis and to the internal anal sphincter in colonic achalasia. Deficits in NOS neurons are observed in two disorders in which colonic propulsion fails, Hirschsprung's disease and Chagas' disease. In addition, damage to NOS neurons occurs when there is stress to cells, in diabetes, resulting in gastroparesis, and following ischemia and reperfusion. A number of factors may contribute to the propensity of NOS neurons to be involved in enteric neuropathies. One of these is the failure of the neurons to maintain Ca(2+) homeostasis. In neurons in general, stress can increase cytoplasmic Ca(2+), causing a Ca(2+) toxicity. NOS neurons face the additional problem that NOS is activated by Ca(2+). This is hypothesized to produce an excess of NO, whose free radical properties can cause cell damage, which is exacerbated by peroxynitrite formed when NO reacts with oxygen free radicals.     

Counteracting effect of papaverine on morphine inhibition of gastrointestinal transit in mice

Abstract  Oral papaverine has been shown to be capable of antagonizing the constipation induced by a single dose of oral morphine. The primary aim of the present study was to ascertain whether papaverine is also capable of counteracting morphine-induced decrease of upper gastrointestinal transit (UGT) after repeated parenteral administration of the opioid. We next investigated the mechanisms(s) responsible for the counteracting effect of papaverine, by analysing whether this effect was changed by pretreatment with N ^G-nitro- l -arginine methyl ester ( l -NAME), dexamethasone, indomethacin or capsaicin. Papaverine, co-administered with morphine, counteracted the morphine-induced decrease in UGT in mice pretreated with morphine for 3 days but did not do so in naive animals. The counteracting effect of papaverine was antagonized by l -NAME, but not by indomethacin. In mice pretreated with both morphine and dexamethasone, papaverine failed to antagonize the effect of morphine. Capsaicin pretreatment completely abolished the effect of a single dose of morphine, the effect being partially restored by the 3 days pretreatment with morphine. In mice pretreated with both capsaicin and morphine, the UGT decrease elicited by morphine was lower than in the other experimental groups and was not modified by papaverine. Our results show that papaverine can counteract the morphine inhibition of UGT in mice repeatedly exposed to the opioid. Papaverine exerts its action through a nitric oxide synthase-mediated mechanism; this mechanism is only effective after repeated morphine administration and does not operate when capsaicin-sensitive afferent neurones are ablated.     

Effects of oral administration of rotenone on gastrointestinal functions in mice

Background The systemic rotenone model of Parkinson’s disease (PD) accurately replicates many aspects of the pathology of human PD, especially neurodegeneration of the substantia nigra and lesions in the enteric nervous system (ENS). Nevertheless, the precise effects of oral rotenone on the ENS have not been addressed yet. This study was therefore designed to assess the effects of a chronic oral treatment by rotenone on enteric neurochemical phenotype, gastrointestinal (GI) motility, and intestinal epithelial barrier permeability. Methods Male C57BL6N mice received once daily oral rotenone administration for 28 days. GI functions were analyzed 4 weeks after rotenone treatment. Gastrointestinal motility was assessed by measuring gastric emptying, total transit time, fecal pellet output, and bead latency. Intestinal barrier permeability was evaluated both in vivo and ex vivo. The number of enteric neurons and the enteric neurochemical phenotype were analyzed by immunohistochemistry. Tyrosine hydroxylase (TH) immunostaining of dopaminergic neurons of the substantia nigra was performed in a subset of animals. Key Results Mice treated orally with rotenone had a decrease in fecal pellet output and in jejunal alpha‐synuclein expression as compared with control animals. This was associated with a significant decrease in TH‐immunoreactive neurons in the substantia nigra. No change in gastric emptying, total transit time, intestinal epithelial barrier permeability, and enteric neurochemical phenotype was observed. Conclusions & Inferences Chronic oral treatment with rotenone only induced minor changes in the ENS and did not recapitulate the GI abnormalities seen in PD, while it replicates neurodegeneration of the substantia nigra.     

2型糖尿病中国地鼠模型构建与小檗碱对肝脏过氧化物酶体增殖体激活受体及其靶基因表达的影响

背景：研究表明小檗碱可用于治疗2型糖尿病,但小檗碱治疗糖尿病胰岛素抵抗尤其是肝脏脂诱性胰岛素抵抗的分子机制仍不明确。 目的：观察小檗碱对2型糖尿病中国地鼠模型肝脏过氧化物酶体增殖体激活受体及其靶基因表达的影响。 方法：以高脂饮食及结合小剂量链脲菌素的方法建立胰岛素抵抗和2型糖尿病中国地鼠模型。建模后随机分成4组：对照组给予普通饮食,胰岛素抵抗组给予高脂饮食,2型糖尿病组给予高脂饮食+小剂量链脲菌素,2型糖尿病小檗碱治疗组给予高脂饮食+小剂量链脲菌素+小檗碱,治疗9周。 结果与结论：实时定量PCR结果显示与对照组相比,胰岛素抵抗及2型糖尿病组地鼠肝脏过氧化物酶体增殖体激活受体α,β/d,酰基辅酶A氧化酶,肉碱棕榈酰转移酶1和中链酰基辅酶A脱氢酶的表达降低(P < 0.05),而固醇调节元件结合蛋白1c,2,过氧化物酶体增殖体激活受体γ,脂蛋白脂酶,脂肪酸转运者(FAT/CD36)和脂肪酸结合蛋白(ap2)的表达增加(P < 0.05)。结果证实,小檗碱可改善胰岛素抵抗,并逆转了氧化物酶体增殖体激活的受体及其靶基因表达的改变,小檗碱治疗2型糖尿病地鼠脂诱性胰岛素抵抗的分子机制与氧化物酶体增殖体激活的受体及其靶基因表达的改变相关。     

Tonic inhibition of human small intestinal motility by nitric oxide in children but not in adults

Background Gastrointestinal motility is dependent on neural influences that largely involve the enteric nervous system (ENS). The main motor patterns that occur in the fasted and fed state are noticeably different in children compared with adults. Although the development of the ENS continues after birth, there is no data on the contractile activity of segments of small intestine from young children. This study was designed to provide data on the development of muscle control by the human ENS with particular attention to acetylcholine (ACh) and nitric oxide (NO) as the primary neurotransmitters of enteric motor neurons, respectively. Methods Small intestinal specimens were obtained from 11 children and six adults undergoing surgery for various diseases. The mechanical activity of the circular muscle was recorded in vitro. The effects of N_ω‐nitro‐L‐arginine methyl ester hydrochloride, an inhibitor of NO synthesis, and of atropine, an antagonist of muscarinic receptors, were tested on the spontaneous motility and responses to nerve stimulation. Key Results Spontaneous motility was observed in all preparations. Responses to nerve stimulation were identical in child and adult. No tonic cholinergic excitation of small intestinal motility was observed either in child or in adult. Inhibition of NO synthesis induced a major disinhibition of motility in child but not in adult. Conclusions & Inferences Spontaneous intestinal motility and cholinergic and nitrergic neurotransmission are present from birth. NO provides a tonic inhibition of intestinal motility only in child. Our study indicates that NO may be a major player in shaping the ontogenic development of intestinal motility in human.