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The stomach is extensively innervated by the vagus nerve and the enteric nervous system. The mechanisms through which this innervation affects gastric motility are being unraveled, motivating the first concerted steps towards the incorporation autonomic regulation into computational models of gastric motility. Computational modeling has been valuable in advancing clinical treatment of other organs, such as the heart. However, to date, computational models of gastric motility have made simplifying assumptions about the link between gastric electrophysiology and motility. Advances in experimental neuroscience mean that these assumptions can be reviewed, and detailed models of autonomic regulation can be incorporated into computational models. This review covers these advances, as well as a vision for the utility of computational models of gastric motility. Diseases of the nervous system, such as Parkinson's disease, can originate from the brain-gut axis and result in pathological gastric motility. Computational models are a valuable tool for understanding the mechanisms of disease and how treatment may affect gastric motility. This review also covers recent advances in experimental neuroscience that are fundamental to the development of physiology-driven computational models. A vision for the future of computational modeling of gastric motility is proposed and modeling approaches employed for existing mathematical models of autonomic regulation of other gastrointestinal organs and other organ systems are discussed. [ABSTRACT FROM AUTHOR]

The stomach is extensively innervated by the vagus nerve and the enteric nervous system. The mechanisms through which this innervation affects gastric motility are being unraveled, motivating the first concerted steps towards the incorporation autonomic regulation into computational models of gastric motility. Computational modeling has been valuable in advancing clinical treatment of other organs, such as the heart. However, to date, computational models of gastric motility have made simplifying assumptions about the link between gastric electrophysiology and motility. Advances in experimental neuroscience mean that these assumptions can be reviewed, and detailed models of autonomic regulation can be incorporated into computational models. This review covers these advances, as well as a vision for the utility of computational models of gastric motility. Diseases of the nervous system, such as Parkinson’s disease, can originate from the brain-gut axis and result in pathological gastric motility. Computational models are a valuable tool for understanding the mechanisms of disease and how treatment may affect gastric motility. This review also covers recent advances in experimental neuroscience that are fundamental to the development of physiology-driven computational models. A vision for the future of computational modeling of gastric motility is proposed and modeling approaches employed for existing mathematical models of autonomic regulation of other gastrointestinal organs and other organ systems are discussed.

Motilin, produced in endocrine cells in the mucosa of the upper intestine, is an important regulator of gastrointestinal (GI) motility and mediates the phase III of interdigestive migrating motor complex (MMC) in the stomach of humans, dogs and house musk shrews through the specific motilin receptor (MLN-R). Motilin-induced MMC contributes to the maintenance of normal GI functions and transmits a hunger signal from the stomach to the brain. Motilin has been identified in various mammals, but the physiological roles of motilin in regulating GI motility in these mammals are well not understood due to inconsistencies between studies conducted on different species using a range of experimental conditions. Motilin orthologs have been identified in non-mammalian vertebrates, and the sequence of avian motilin is relatively close to that of mammals, but reptile, amphibian and fish motilins show distinctive different sequences. The MLN-R has also been identified in mammals and non-mammalian vertebrates, and can be divided into two main groups: mammal/bird/reptile/amphibian clade and fish clade. Almost 50 years have passed since discovery of motilin, here we reviewed the structure, distribution, receptor and the GI motility regulatory function of motilin in vertebrates from fish to mammals.

Motilin, produced in endocrine cells in the mucosa of the upper intestine, is an important regulator of gastrointestinal (GI) motility and mediates the phase III of interdigestive migrating motor complex (MMC) in the stomach of humans, dogs and house musk shrews through the specific motilin receptor (MLN-R). Motilin-induced MMC contributes to the maintenance of normal GI functions and transmits a hunger signal from the stomach to the brain. Motilin has been identified in various mammals, but the physiological roles of motilin in regulating GI motility in these mammals are well not understood due to inconsistencies between studies conducted on different species using a range of experimental conditions. Motilin orthologs have been identified in non-mammalian vertebrates, and the sequence of avian motilin is relatively close to that of mammals, but reptile, amphibian and fish motilins show distinctive different sequences. The MLN-R has also been identified in mammals and non-mammalian vertebrates, and can be divided into two main groups: mammal/bird/reptile/amphibian clade and fish clade. Almost 50 years have passed since discovery of motilin, here we reviewed the structure, distribution, receptor and the GI motility regulatory function of motilin in vertebrates from fish to mammals. [ABSTRACT FROM AUTHOR]

The impact of stress on mental and digestive health has been extensively studied, with chronic stress being associated with various disorders. However, age-related differences in the response to acute stress, both behaviorally and physiologically, remain poorly understood. Therefore, this study aimed to develop a model to detect transient stress in mice of different ages. The stressor employed in our experiments was a restraint stress procedure, where mice were subjected to brief periods of immobilization to induce an acute stress response. Male C3H/HeN mice aged 3, 6, 12, and 30 weeks were subjected to acute restrain stress (ARS) by being placed in a 50 ml conical centrifuge tube for 15 min. Subsequently, their behavior, organ tissues, hematological parameters, cortisol concentration, and immune responses were assessed. Following ARS, the increased in time and entries into the center by the 12-week-old mice following stress. In comparison to mice of other ages, those aged 6 weeks demonstrated notable elevations in erythrocytes, platelets, hemoglobin, and hematocrit, all of which were influenced by the time-dependent changes and the recovery process of ARS. Blood corticosterone levels were substantially elevated in all age groups after ARS. Furthermore, ARS induced a notable increase in leukocytes, basophils, residential macrophages, and CD4+ T cells in all age groups except for 3-week-old mice. However, the number of monocyte-derived macrophages and CD8+ T cells did not change significantly. Additionally, mice aged 3 and 6 weeks demonstrated an increase in GFAP+ cells following ARS, whereas NeuN+ cells decreased across all ages. These results suggest that ARS has varying effects on the behavior, cortisol concentration, and quantity of blood cells as well as hepatic immune cells in mice of different ages. These age-dependent responses shed light on the complex interplay between stress and physiological systems and contribute to the broader understanding of stress-related diseases. [ABSTRACT FROM AUTHOR]

In contrast to gastric dysfunction, diabetes-related functional impairments of the small and large intestine have been studied less intensively. The gastrointestinal tract accomplishes several functions, such as mixing and propulsion of luminal content, absorption and secretion of ions, water, and nutrients, defense against pathogens, and elimination of waste products. Diverse functions of the gut are regulated by complex interactions among its functional elements, including gut microbiota. The network-forming tissues, the enteric nervous system) and the interstitial cells of Cajal, are definitely impaired in diabetic patients, and their loss of function is closely related to the symptoms in diabetes, but changes of other elements could also play a role in the development of diabetes mellitus-related motility disorders. The development of our understanding over the recent years of the diabetes-induced dysfunctions in the small and large intestine are reviewed in this article. [ABSTRACT FROM AUTHOR]

Background Proper function of the gastro-esophageal high pressure zone is essential for the integrity of the antireflux barrier. Mechanisms include tonic contractions and the decreased tone during transient lower esophageal sphincter relaxations. Methods We characterized the pharmacology of nicotinic receptors mediating relaxations of the human upper gastric sphincter (clasp and sling fibers) using currently available subtype selective nicotinic antagonists in tissue from organ transplant donors. Donors with either a history of gastro-esophageal reflux disease or histologic evidence of Barrett's esophagus were excluded. Clasp and sling muscle fiber strips were used for one of three paradigms. For paradigm 1, each strip was exposed to carbachol, washed, exposed to nicotinic antagonists then re-exposed to carbachol. In paradigm 2, strips were exposed to a near maximally effective bethanechol concentration then nicotine was added. Strips then were washed, exposed to nicotinic antagonists then re-exposed to bethanechol followed by nicotine. In paradigm 3, strips were exposed to bethanechol then choline or cytisine. Key Results 100 μM methyllycaconitine has no inhibitory effects on relaxations, eliminating homomeric α7 subtypes. Subtypes composed of α4 β2 subunits are also eliminated because choline acts as an agonist and dihydro-beta-erythroidine is ineffective. Conclusions & Inferences Because mecamylamine blocks the relaxations and both choline and cytisine act as agonists in both clasp and sling fibers, the nicotinic receptor subtypes responsible for these relaxations could be composed of α3 β4 β2, α2 β4, or α4 β4 subunits. [ABSTRACT FROM AUTHOR]

The ultrastructural changes in diabetic and idiopathic gastroparesis are not well studied and it is not known whether there are different defects in the two disorders. As part of the Gastroparesis Clinical Research Consortium, full thickness gastric body biopsies from 20 diabetic and 20 idiopathic gastroparetics were studied by light microscopy. Abnormalities were found in many (83%) but not all patients. Among the common defects were loss of interstitial cells of Cajal (ICC) and neural abnormalities. No distinguishing features were seen between diabetic and idiopathic gastroparesis. Our aim was to provide a detailed description of the ultrastructural abnormalities, compare findings between diabetic and idiopathic gastroparesis and determine if patients with apparently normal immunohistological features have ultrastructural abnormalities. Tissues from 40 gastroparetic patients and 24 age- and sex-matched controls were examined by transmission electron microscopy (TEM). Interstitial cells of Cajal showing changes suggestive of injury, large and empty nerve endings, presence of lipofuscin and lamellar bodies in the smooth muscle cells were found in all patients. However, the ultrastructural changes in ICC and nerves differed between diabetic and idiopathic gastroparesis and were more severe in idiopathic gastroparesis. A thickened basal lamina around smooth muscle cells and nerves was characteristic of diabetic gastroparesis whereas idiopathic gastroparetics had fibrosis, especially around the nerves. In conclusion, in all the patients TEM showed abnormalities in ICC, nerves and smooth muscle consistent with the delay in gastric emptying. The significant differences found between diabetic and idiopathic gastroparesis offers insight into pathophysiology as well as into potential targeted therapies. [ABSTRACT FROM AUTHOR]

Nitrergic neurotransmission at the smooth muscle neuromuscular junctions requires nitric oxide (NO) release that is dependent on the transport and docking of neuronal NO synthase (nNOS) a to the membrane of nerve terminals. However, the mechanism of translocation of nNOSα in actin-rich varicosities is unknown. We report here that the processive motor protein myosin Va is necessary for nitrergic neurotransmission. In wild-type mice, nNOSα-stained enteric varicosities cobcalized with myosin Va and its tail constituent light chain 8 (LC8). In situ proximity ligation assay showed close association among nNOSα, myosin Va, and LC8. nNOSα was associated with varicosity membrane. Varicosities showed nitric oxide production upon stimulation with KCI. Intracellular microelectrode studies showed nitrergic IJP and smooth muscle hyperpolarizing responses to NO donor diethylenetriamine-NO (DNO). In contrast, enteric varicosities from myosin Va-deficient DBA (for dilute, brown, non-agouti) mice showed near absence of myosin Va but normal nNOSα and LC8. Membrane-bound nNOSα was not detectable, and the varicosities showed reduced NO production. Intracellular recordings in DBA mice showed reduced nitrergic IJPs but normal hyperpolarizing response to DNO. The nitrergic slow IJP was 9.1 ± 0.7 mV in the wild-type controls and 3.4 ± 0.3 mV in the DBA mice (P < 0.0001). Deficiency of myosin Va resulted in loss of nitrergic neuromuscular neurotransmission despite normal presence of nNOSα in the varicosities. These studies reveal the critical importance of myosin Va in nitrergic neurotransmission by facilitating transport of nNOSα to the varicosity membrane. [ABSTRACT FROM AUTHOR]

Objective. Patients with ulcerative colitis in remission (UCR) frequently report irritable bowel syndrome (IBS)-like symptoms. Recent studies have pointed to the role of mast cells in mediating visceral hypersensitivity in IBS. We hypothesized that visceral hypersensitivity is frequently present in patients with UCR and is related to the quantity and activity of mast cells in the sigmoid mucosa. Material and methods. A group of 17 controls and 19 patients with UCR were studied. Rectal compliance and perception were measured by electronic barostat. Sigmoid biopsies were taken to quantify the amount of mast cells, degranulating mast cells and mast cells in close proximity to mucosal nerve endings. Results. Visceroperception significantly increased in UCR ( p < 0.05) versus controls. Rectal perception correlated positively with IBS-like symptoms in UCR ( r == 0.969; p < 0.05). The amount of mucosal mast cells (per 100 crypts) was significantly increased in UCR versus controls: 228 ±± 20 versus 163 ±± 18 ( p < 0.05). In the UCR patients a higher percentage of mucosal mast cells was in close proximity to nerve endings (58 ±± 4 vs. 38 ±± 3% in controls; p < 0.05) or was degranulating (40 ±± 7 vs. 16 ±± 4% in controls; p < 0.05). There was a significant but weak correlation between quantity of mucosal mast cells and pain perception ( r == 0.32; p < 0.05). Conclusion. Rectal hypersensitivity is associated with mucosal presence and activation of mast cells and with IBS-like symptoms in patients with UCR. [ABSTRACT FROM AUTHOR]

Purpose: Adult slow-transit constipation (STC) occurs predominantly in females and is associated with low numbers of substance P (SP)-containing nerves in colonic circular muscle.Aim: To determine if reduced SP nerves is female predominant in paediatric STC.Methods: Children with STC were identified from records of more than 600 nuclear transit studies (NTS) and intestinal biopsies done for intractable chronic constipation between November 1998 and March 2009. Colonic seromuscular biopsies collected from hepatic and splenic flexures, and sigmoid colon were processed for immunohistochemistry. Nerve fibre density in circular muscle containing SP was measured qualitatively by a pathologist.Results: Eighty-eight children with chronic constipation had both NTS and intestinal biopsies. Seventy-eight children (52 M; age 2-15.5 years; mean 7.7 years) had STC diagnosed by NTS. SP was reduced in 10/26 girls, but only 11/52 boys.Conclusion: In this sample, STC was more common in boys than girls. However, in girls with STC, SP deficiency occurred in 40%, when compared with 20% of boys. During puberty, the percentage of girls with reduced SP decreased, whilst the percentage of boys increased. These results suggest that STC is heterogeneous and that there are some gender differences, the implication of which requires further investigation. [ABSTRACT FROM AUTHOR]

Constipation is a common problem in the elderly, and abnormalities in the neural innervation of the colon play a significant role in abnormalities in colonic motility leading to delayed colonic transit. The scope of this review encompasses the latest advances to enhance our understanding of the aging colon with emphasis on enteric neurodegeneration, considered a likely cause for the development of constipation in the aging gut in animal models. Neural innervation of the colon and the effects of aging on intrinsic and extrinsic nerves innervating the colonic smooth muscle is discussed. Evidence supporting the concept that neurologic disorders, such as Parkinson's disease, not only affect the brain but also cause neurodegeneration within the enteric nervous system leading to colonic dysmotility is presented. Further research is needed to investigate the influence of aging on the gastrointestinal tract and to develop novel approaches to therapy directed at protecting the enteric nervous system from neurodegeneration. [ABSTRACT FROM AUTHOR]

Background The ability to control uptake across the mucosa and protect from damage of harmful substances from the lumen is defined as intestinal barrier function. A disturbed barrier dysfunction has been described in many human diseases and animal models, for example, inflammatory bowel disease, irritable bowel syndrome, and intestinal hypersensitivity. In most diseases and models, alterations are seen both of the paracellular pathway, via the tight junctions, and of the transcellular routes, via different types of endocytosis. Recent studies of pathogenic mechanisms have demonstrated the important role of neuroimmune interaction with the epithelial cells in the regulation of barrier function. Neural impulses from extrinsic vagal and/or sympathetic efferent fibers or intrinsic enteric nerves influence mucosal barrier function via direct effects on epithelial cells or via interaction with immune cells. For example, by nerve-mediated activation by corticotropin-releasing hormone or cholinergic pathways, mucosal mast cells release a range of mediators with effects on transcellular, and/or paracellular permeability (for example, tryptase, TNF-α, nerve growth factor, and interleukins). Purpose In this review, we discuss current physiological and pathophysiological aspects of the intestinal barrier and, in particular, its regulation by neuroimmune factors. [ABSTRACT FROM AUTHOR]

Relaxation of gastrointestinal smooth muscle caused by release of non-adrenergic non-cholinergic (NANC) transmitters from enteric nerves occurs in several physiologic digestive reflexes. Likely candidate NANC inhibitory agents include nitric oxide (NO), adenosine triphosphate (ATP), vasoactive intestinal peptide (VIP), pituitary adenylate cyclase-activating peptide (PACAP), carbon monoxide (CO), protease-activated receptors (PARs), hydrogen sulfide (H2S), neurotensin (NT) and beta-nicotinamide adenine dinucleotide (β-NAD). Multiple NANC transmitters work in concert, are pharmacologically coupled and are closely coordinated. Individual contribution varies regionally in the gastrointestinal tract and between species. NANC inhibition of gastrointestinal smooth muscle involves several intracellular mechanisms, including increase of cyclic guanosine monophosphate (cGMP), increase of cyclic adenosine monophosphate (cAMP) and hyperpolarization of the cell membrane via direct or indirect activation of potassium ion (K+) channels. [ABSTRACT FROM AUTHOR]

Over the past decade there has been an increasing awareness of the role played by commensal bacteria in modulating mucosal immune responses and as a consequence there is now great interest in the therapeutic potential of probiotics and other bacteria based strategies for a range of immune disorders. Here we review current understanding of the mechanisms underlying the immunomodulatory actions of commensal and probiotic bacteria and probiotic organisms. We discuss prominent cell types involved in transducing signals from these bacteria, including epithelial cells, dendritic cells and T regulatory cells. We also draw attention to emerging data indicating interplay between the gut microbiota, enteric neurons and the immune system. There is a focus on the specific aspects of bacteria-host interactions that may influence the ability of a specific organism to confer potentially beneficial changes in immune responses. It is clear that there is still much to learn regarding the determinants of the diverse immune responses elicited by different bacterial strains by building on our current knowledge in these areas it may be possible to design clinically effective, bacteria based strategies to maintain and promote health. [ABSTRACT FROM AUTHOR]

Interstitial cells of Cajal (ICC) are associated with afferent innervation and peristalsis of the stomach suggestive of a key role in the pathophysiology of gastroparesis. We studied changes in the density and ultrastructure of ICC and enteric nerves in the streptozotocin-induced diabetes mellitus (STZ-DM) in Wistar rats using immunohistochemistry and electron microscopy. Gastric emptying was studied in vivo by single-photon emission computed tomography. In the STZ-DM antrum, a marked reduction was observed in the density of the intramuscular ICC (ICC-IM) and ICC located at the submucosal border of the circular muscle layer of the antrum (ICC-SM). The surviving ICC showed lamellar bodies and partial vacuolation of the cytoplasm content, loss of connections between ICC-IM and nerves; it appeared that injured ICC-IM developed into fibroblast-like ICC. ICC associated with Auerbach’s plexus (ICC-AP) in the antrum and ICC in the fundus were not affected significantly except for a loss of connections with nerve structures. Marked reduction in nerve tissue (Protein Gene Product-9.5 positivity) was also restricted to the muscle layers including nitrergic nerves (neuronal nitric oxide synthase positivity). In vivo assessed gastric emptying was markedly reduced in STZ-DM rats. Our data demonstrate in the STZ-DM rat stomach a decreased density of ICC limited to the antrum and to ICC-IM and ICC-SM, and structural degeneration in ICC-IM and associated nerves with a special emphasis on loss of synaptic connections, accompanied by a decrease in gastric emptying. Hence, in this model of gastroparetic diabetes, regional injury to subsets of ICC and nerves are associated with gastric motor dysfunction. [ABSTRACT FROM AUTHOR]

Adrenergic activation of electrogenic K+ secretion in isolated mucosa from guinea pig distal colon was desensitized by peptide-YY (PYY). Addition of PYY or neuropeptide-Y (NPY) to the bathing solution of mucosae in Ussing chambers suppressed the short-circuit current (Isc) corresponding to electrogenic Cl- secretion, whether stimulated by epinephrine (epi), prostaglandin-E2 (POE2), or carbachol (CCh). Neither peptide markedly inhibited the large transient component of synergistic secretion (POE2 + CCh). Sustained Cl- secretory Isc was inhibited ∼65% by PYY or NPY, with IC50s of 4.1 ± 0.9 nM and 9.4 ± 3.8 nM, respectively. This inhibition was eliminated by BIIE0246, an antagonist of the Y2-neuropeptide receptor (Y2-NpR), but not by Yl-NpR antagonist BVD10. Adrenergic sensitivity for activation of K+ secretion in the presence of Y2-NpR blockade by BIIE0246 was (EC505) 2.9 ± 1.2 nM for epi and 13.3 ± 1.0 nM for norepinephrine, approximately fourfold greater than in the presence of PYY. Expression of mRNA for both Yl-NpR and Y2-NpR was indicated by RT-PCR of RNA from colonic mucosa, and protein expression was indicated by immunoblot. Immunoreactivity (ir) for Yl-NpR and Y2-NpR was distinct in basolateral membranes of columnar epithelial cells in the crypts of LieberkUhn as well as intercrypt surface epithe- hum. Adrenergic nerves in proximity with crypts were detected by ir for dopamine-β-hydroxylase, and a portion of these nerves also contained NPYir. BIIE0246 addition increased secretagog-activated Isc, consistent with in vitro release of either PYY or NPY. Thus PYY and NPY were able to suppress Cl- secretory capacity and desensitize the adrenergic K+ secretory response, providing a direct inhibitory counterbalance against secretory activation. [ABSTRACT FROM AUTHOR]

The gastrointestinal tract serves the physiological function of digesting and absorbing nutrients from food and physically mixing and propelling these contents in an oral to anal direction. These functions require the coordinated interaction of several cell types, including enteric nerves, immune cells and smooth muscle. Interstitial cells of Cajal (ICC) are now recognized as another cell type that are required for the normal functioning of the gastrointestinal tract. Abnormalities in ICC numbers and networks are associated with several gastrointestinal motility disorders. This review will describe what is known about the function and role of ICC both in health and in a variety of motility disorders with a focus on unresolved issues pertaining to their role in the control of gastrointestinal motility. [ABSTRACT FROM AUTHOR]

Using conventional microelectrode recording techniques, we investigated, in the circular muscle of the mouse caecum, the neurotransmitter(s) involved in the neurally-evoked inhibitory junction potentials (IJPs) and the existence of possible prejunctional mechanisms controlling neurotransmitter release. Electrical field stimulation with single pulses elicited IJPs, consisting only of a “fast” hyperpolarization, while using train stimuli (30–50 Hz) the initial fast hyperpolarization was followed by a slower hyperpolarization. The fast and the slow component were selectively antagonized by apamin, a blocker of calcium-activated potassium channels, and Nω-nitro-l-arginine methyl ester (l-NAME), a nitric oxide synthase inhibitor, respectively. Fast IJPs were antagonized also by P2 purinoceptor antagonists, suramin or 4-[[4-formyl-5-hydroxy-6-methyl-3-[(phosphonooxy)methyl]-2-pyridinyl]azo]-1,3-benzenedisulfonic acid tetrasodium salt (PPADS), P2Y purinoceptor desensitization by adenosine 5′-O-2-thiodiphosphate (ADPβS). 2′-Deoxy-N6-methyl ADP diammonium salt (MRS 2179), P2Y1 purinoceptor antagonist, at the concentration of 1 μM increased the amplitude of the fast IJP, while at the concentration of 10 μM induced a reduction. 8,8′-[Carbonylbis[imino-3,1-phenylenecarbonylimino (4-fluoro-3,1-phenylene) carbonylimino]] bis-1,3,5-naphthalenetrisulfonic acid hexasodium salt (NF 157) and 2,2-dimethyl-propionic acid 3-(2-chloro-6-methylaminopurin-9-yl)-2-(2,2-dimethyl-propionyl-oxymethyl)-propyl ester (MRS 2395), P2Y11 and P2Y12 purinoceptor antagonist, were without any effect. ATP-induced hyperpolarization was affected by apamin and by P2Y purinoceptor desensitization, but not by MRS 2179. 2-(Methylthio)ATP tetrasodium salt hydrate (2-MeSATP), P2Y1 purinoceptor agonist, at a concentration which did not cause changes in the membrane potential, reduced the amplitude of the fast IJPs. This effect was prevented by MRS 2179. Paired nerve stimulation, either using single pulses or train stimuli, did not cause any alteration of the second-evoked IJP. In conclusion, in the circular muscle of the mouse caecum, ATP is responsible for the fast IJP while nitric oxide is responsible for the slow IJP. ATP-mediated response is dependent on ADPβS-sensitive P2Y receptors, which are in part P2Y1, but not P2Y11 or P2Y12 receptor subtypes. In addition, the most substantial finding of this study is the functional demonstration that ATP released by nerve stimulation activates P2Y1 receptors, located prejunctionally, limiting its release by motoneurons. [Copyright &y& Elsevier]

Abstract: Mast cells are well known as versatile cells capable of releasing and producing a variety of inflammatory mediators upon activation and are often found in close proximity of neurons. In addition, inflammation leads to local activation of neurons resulting in the release neuropeptides, which also play an important immune modulatory role by stimulation of immune cells. In intestinal disorders like inflammatory bowel disease (IBD) and irritable bowel syndrome (IBS), the number of mast cells is known to be much higher than in the normal intestine. Moreover, both these disorders are also reported to be associated with alterations in neuropeptide content and in neural innervation. Mutual association between mast cells and enteric nerves has been demonstrated to be increased in pathophysiological conditions and contribute to spreading and amplification of the response in IBD and IBS. In this review the focus lies on studies appointed to the direct interaction between mast cells and nerves in IBD, IBS, and animal models for these disorders so far. [Copyright &y& Elsevier]

Summary: After acute infestation with the Chagas disease parasite, Trypanosoma cruzi, some patients who are serologically positive develop chronic megacolon and megaesophagus, whereas others are symptom-free. Chagas disease with gastrointestinal involvement involves an inflammatory invasion of the enteric plexuses and degeneration of enteric neurons. It is known that glial cells can be involved in enteric inflammatory responses. The aims were to determine the nature of any difference in lymphocytic invasion, enteric neurons, and enteric glial cells in seropositive individuals with and without megacolon. We have compared colonic tissue from serologically positive individuals with and without symptoms and from seronegative controls. Subjects with megacolon had significantly more CD-57 natural killer cells and TIA-1 cytotoxic lymphocytes within enteric ganglia, but numbers of CD-3 and CD-20 immunoreactive cells were not significantly elevated. The innervation of the muscle was substantially reduced to about 20% in megacolon, but asymptomatic seropositive subjects were not different to seronegative controls. Glial cell loss occurred equally in symptomatic and unaffected seropositive subjects, although the proportion with glial fibrillary acidic protein was greater in seropositive, nonsymptomatic subjects. Development of megacolon after acute infection with T cruzi is associated with maintained invasion of enteric ganglia with cytotoxic T cells and loss of muscle innervation, but changes in glial cell numbers are not associated with progression of enteric neuropathy. [Copyright &y& Elsevier]

Abstract: Inflammatory bowel disease is a recurrent intestinal inflammatory disorder that in adults has been associated with changes in enteric nervous system neuropeptide expression. The aim of the present study was to determine whether similar changes were observed in paediatric Crohn''s disease. The distribution of vasoactive intestinal peptide (VIP) and neuronal nitric oxide synthase (nNOS) was determined in colonic tissues from children with ileo-colonic (n =4) and colonic (n =3) Crohn''s disease. The submucosal plexus of inflamed regions showed significant increase in density of VIP immunoreactive neurons (margin, 48% vs. inflamed tissue, 82% of HuC/D positive neurons). The density of submucosal plexus nNOS immunoreactive neurons was too low to be reliably quantified. Using the pan-neuronal marker HuC/D, no significant difference in numbers of HuC/D positive submucosal neurons was evident except where neurons were normalized to length of tissue (margins, 3.6±0.7 vs. inflamed tissue, 4.0±0.6 neurons/ganglia, p =0.33; margins, 2.7±0.4 vs. inflamed tissue, 5.7±1.2, neurons/mm, p =0.03). In the myenteric plexus, there was a significant increase in the percent of NOS neurons (38% vs. 82% of HuC/D positive neurons) while there was no significant difference in percent of VIP neurons (4% vs. 8%). No difference in number of HuC/D positive myenteric neurons among margin and inflamed tissues was observed (margin, 12.2±3.0 vs. inflamed tissue, 12.5±5.1 neurons/ganglia, p =0.50; margins 9.1±2.1 vs. inflamed tissue, 13.7±2.3 neurons/mm, p =0.11). These data demonstrate that inflammation is associated with a differential expression of VIP and nNOS neuronal subpopulations within the two major enteric plexi, likely due to phenotypic switch. Such changes might contribute to the pathogenesis of IBD and ongoing symptoms even in quiescent disease. [Copyright &y& Elsevier]

The feline gastrointestinal (GI) tract is an important model for GI physiology but no immunohistochemical assessment of interstitial cells of Cajal (ICC) has been performed because of the lack of suitable antibodies. The aim of the present study was to investigate the various types of ICC and associated nerve structures in the pyloric sphincter region, by using immunohistochemistry and electron microscopy to complement functional studies. In the sphincter, ICC associated with Auerbach’s plexus (ICC-AP) were markedly decreased within a region of 6–8 mm in length, thereby forming an interruption in this network of ICC-AP, which is otherwise continuous from corpus to distal ileum. In contrast, intramuscular ICC (ICC-IM) were abundant within the pylorus, especially at the inner edge of the circular muscle adjacent to the submucosa. Similar distribution patterns of nerves positive for vesicular acetylcholine transporter (VAChT), nitric oxide synthase (NOS) and substance P (SP) were encountered. Quantification showed a significantly higher number of ICC-IM and the various types of nerves in the pylorus compared with the circular muscle layers in the adjacent antrum and duodenum. Electron-microscopic studies demonstrated that ICC-IM were closely associated with enteric nerves through synapse-like junctions and with smooth muscle cells through gap junctions. Thus, for the first time, immunohistochemical studies have been successful in documenting the unique distribution of ICC in the feline pylorus. A lack of ICC-AP guarantees the distinct properties of antral and duodenal pacemaker activities. ICC-IM are associated with enteric nerves, which are concentrated in the inner portion of the circular muscle layer, being part of a unique innervation pattern of the sphincter. [ABSTRACT FROM AUTHOR]

Abstract: Chloride secretion is important because it is the driving force for fluid movement into the intestinal lumen. The flow of accumulated fluid flushes out invading micro-organisms in defense of the host. Chloride secretion is regulated by neurons in the submucosal plexus of the enteric nervous system. Mechanosensitive enterochromaffin cells that release 5-hydroxytryptamine (5-HT) and activate intrinsic afferent neurons in the submucosal plexus and initiate chloride secretion. Mechanical stimulation by distention may also trigger reflexes by a direct action on intrinsic afferent neurons. Dysregulation of 5-HT release or altered activity of intrinsic afferents is likely to occur in states of inflammation and other disorders. [Copyright &y& Elsevier]

Background and purpose:cGMP mediates nitrergic relaxations of intestinal smooth muscle, but several studies have indicated that cGMP-independent mechanisms may also be involved. We addressed this contention by studying the effect of ODQ and NS2028, specific inhibitors of soluble guanylate cyclase, on nitrergic relaxations of the mouse gut.Experimental approach:Mouse gastric fundus and small intestinal muscle preparations were mounted in organ baths to study relaxations to exogenous NO, NO donors and electrical field stimulation (EFS) of enteric nerves.Key results:In gastric fundus longitudinal muscle strips, ODQ and NS2028 abolished the L-nitroarginine-sensitive relaxations to EFS and the relaxations to NO and NO donors, glyceryl trinitrate (GTN), SIN-1 and sodium nitroprusside (SNP). EFS of intestinal segments and muscle strips showed L-nitroarginine-resistant relaxations, which were abolished by the purinoceptor blocker suramin. In the presence of suramin, ODQ and NS2028 abolished all relaxations to EFS in intestinal segments and strips. ODQ and NS2028 abolished the relaxations to exogenous NO and to the NO donors GTN, SIN-1 and SNP in circular and longitudinal intestinal muscle strips. Intestinal segments showed residual relaxations to NO and GTN.Conclusions and Implications:Our results indicate that relaxations to endogenous NO in the mouse gastric fundus and small intestine are completely dependent on cGMP. ODQ and NS2028 incompletely blocked nitrergic relaxations to exogenous NO in intact intestinal segments. However, it is unlikely that this is due to the involvement of cGMP-independent pathways because ODQ and NS2028 abolished all relaxations to endogenous and exogenous NO in intestinal muscle strips.British Journal of Pharmacology (2007) 150, 88–96. doi:10.1038/sj.bjp.0706964; published online 20 November 2006 [ABSTRACT FROM AUTHOR]

Fundic tone is maintained through a balance of excitatory and inhibitory input to fundic smooth muscle. The aim of this study was to determine the role of serotonin (5-HT) and 5-HT receptors in modulating murine fundic tone. Muscle strips were prepared from the routine fundus. Intracellular recordings were made from circular smooth muscle cells, and the effects of 5-HT on tone and excitatory and inhibitory junction potentials evoked by electrical field stimulation (EFS) were determined. 5-HT induced a concentration-dependent contraction and smooth muscle depolarization that was tetrodotoxin resistant. The 5-HT1B/D receptor antagonists GR-127935 and BRL-155172 significantly inhibited 5-HT-induced contractions. The 5-HT1B/D agonist sumatriptan contracted murine fundic muscle. The 5-HT1B/D receptor agonist buspirone relaxed fundic smooth muscle, and the relaxation was inhibited by WAY-100135 but not by Nw-nitro-ʟ-arginine or tetrodotoxin. 5-HT enhanced both the excitatory and inhibitory responses to EFS. The 5-HT3 receptor antagonist MDL-72222 partly inhibited both the excitatory and inhibitory response elicited by EFS, whereas the 5-HT4 receptor antagonist GR-113808 partly inhibited the EFS-evoked inhibitory response. The 5-HT reuptake inhibitor fluoxetine contracted smooth muscle strips, a contraction that was partially inhibited by GR-127935 and abolished by tetrodotoxin. In conclusion, the data suggest that 5-HT modulates murine fundic contractile activity through several different receptor subtypes. Sustained release of 5-HT maintains fundic tone through postjunctional 5-HT1B/D receptors. 5-HT3 receptors modulate excitatory neural input to murine fundic smooth muscle, and both 5-HT3 and 5-HT4 receptors modulate inhibitory neural input to murine fundic smooth muscle. [ABSTRACT FROM AUTHOR]

Interstitial cells of Cajal (ICC) are proposed to play a role in stretch activation of nerves and are under intense investigation for potential roles in enteric innervation. Most data to support such roles come from in vitro studies with muscle strips whereas data at the whole organ level are scarce. To obtain insight into the role of ICC in distention-induced motor patterns developing at the organ level, we studied distension-induced adaptive relaxation in the isolated whole stomach of wild-type and W/Wv mice. A method was developed to assess gastric adaptive relaxation that gave quantitative information on rates of pressure development and maximal adaptive relaxation. Pressure development was monitored throughout infusion of 1 ml of solution over a 10-min period. The final intraluminal pressure was sensitive to blockade of nitric oxide synthase, in wild-type and W/Wv mice to a similar extent, indicating NO-mediated relaxation in W/Wv mice. Adaptive relaxation occurred between 0.2 and 0.5 ml of solution infusion; this reflex was abolished by TTX, was not sensitive to blockade of nitric oxide synthase, but was abolished by apamin, suggesting that ATP and not nitric oxide is the neurotransmitter responsible for this intrinsic reflex. Despite the absence of intramuscular ICC (ICC-IM), normal gastric adaptive relaxation occurred in the W/Wv stomach. Because pressure development was significantly lower in W/Wv mice compared with wild type in all the conditions studied, including in the presence of TTX, ICC-IM may play a role in development of myogenic tone. In conclusion, a mouse model was developed to assess the intrinsic component of gastric accommodation. This showed that ICC-IM are not essential for activation of intrinsic sensory nerves nor ATP-driven adaptive relaxation nor NO-mediated relaxation in the present model. ICC-IM may be involved in regulation of (distention-induced) myogenic tone. [ABSTRACT FROM AUTHOR]

1 5-Hydroxytryptamine (5-HT) receptor subtypes involved in 5-HT-induced contraction of the chicken gastrointestinal tract were characterized pharmacologically using subtype-selective agonists and antagonists. The proventriculus (area of stomach adjacent to the oesophagus) and ileum are examined. 2 5-HT applied cumulatively caused sustained contraction of the proventriculus that was not decreased by tetrodotoxin, atropine orl-nitro-arginine methylester (l-NAME). α-Methyl-5-HT showed the same potency as that of 5-HT, indicating the involvement of the 5-HT2 receptor. (±)-1-(2,5-dimethoxy-4-iodophenyl)-2-amino-propane (DOI), 5-methoxytryptamine and 1-(3-chlorophenyl)piperazine hydrochloride (mCPP) were potent, and 2-methyl-5-HT, 5-carboxamidotryptamine, BW723C86 and 6-chloro-2-(1-piperazinyl)pyrazine hydrochloride (MK212) were moderate, but (±)-8-hydroxy-2-dipropylaminotetralin hydrobromide (8-OH-DPAT), [endo- N-8-methyl-8-azabicyclo-(3,2,1)oct-3-yl]-2,3-dihydro-(1-methyl)ethyl-2-oxo-1H-benzimidazol-1-carboxamide (BIMU-8) and cisapride were weak agonists. Correlation of pEC50 values of these agonists with documented pEC50 values for 5-HT2C receptor was higher than 5-HT2A and 5-HT2B. 3 Cinanserin, ketanserin, methiothepin, methysergide, mianserin, (8-[5-(2,4-dimethoxy-5-(4-trifluoromethylphenylsulphonamido)phenyl-5-oxopentyl)-1,3,8-triazaspiro[4,5]decane-2,4-dione hydrochloride (RS102221), N-(1-methyl-1H-indolyl-5-yl)- N′-(3-methyl-5-isothiazolyl)urea (SB204741), spiperone and N-desmethylclozapine concentration-dependently inhibited the contractile responses to 5-HT. Correlation of p Kb/p A2 of antagonists with documented p Ki for 5-HT2C receptor was highest among 5-HT2 receptor subtypes. 4 In the methysergide- and ketanserin-treated proventriculus, 5-HT, 2-methyl-5-HT and cisapride did not enhance the electrical field stimulation (5 Hz)-induced cholinergic contractions. 5 5-HT applied non-cumulatively caused transient contraction of ileum, and the responses were partly decreased by atropine or tetrodotoxin. 5-Methoxytryptamine, α-methyl-5-HT, 5-carboxamidotryptamine, L692,247 and DOI were potent agonists. However, 2-methyl-5-HT, cisapride, BW723C86, 8-OH-DPAT and 5-nonyloxytryptamine, mCPP and MK212 were less effective. Ketanserin and methysergide decreased the 5-HT-induced ileal contraction, but neither GR113808 nor SB269970 inhibited the responses. 6 In conclusion, 5-HT causes contraction of the proventriculus via 5-HT2C-like receptors present on smooth muscle. 5-HT also causes contraction of the ileum, but the underlying mechanisms are complex, involving neural and smooth muscle components, and both 5-HT1- and 5-HT2-like receptors. Neural 5-HT receptors similar to 5-HT3/5-HT4 receptors were not found in the chicken proventriculus and ileum. [ABSTRACT FROM AUTHOR]

Acute diarrhea is a major cause of morbidity and mortality worldwide. Infants and pre-school children are the most vulnerable in whom there are 2–3 million deaths each year as a result of the associated dehydration and acidosis. Although oral rehydration therapy has reduced mortality during the past 30 years ago, the search for agents that will directly inhibit intestinal secretory mechanisms and thereby reduce faecal losses in patients with high-volume watery diarrhea has continued for more than 20 years. A variety of potential targets for antisecretory agents have been explored which include loci within the enterocyte (the chloride channel, calcium-calmodulin) and other sites such as enteric nerves and endogenous mediators (such as 5-HT, prostaglandins). Although the potential of calcium-calmodulin inhibition has as yet not been realised, preliminary studies suggest that there are chloride channel blockers under development that will find a place in the management of secretory diarrheas. Recent work has highlighted the importance of neurohumoral mechanisms in the pathogenesis of acute diarrhea. Potentiation of the effects of endogenous enkephalin activity by enkephalinase inhibition has already produced a safe, effective anti-secretory drug, racecadotril. Speculative early work indicates that there may be a role for antagonists of 5-HT, substance P, and VIP receptors. There now seems to be a real possibility that antisecretory therapy will become more widely available in the future. Copyright © 2006 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]

Vasoactive intestinal peptide (VIP) has been demonstrated in intestinal mucosal neurones and elicits chloride secretion from enterocytes. These findings have led to the proposal that VIP is a secretomotor neurotransmitter. Confirmation of such a role may now be possible with the development of PG 97-269, a high-affinity, selective antagonist of VIP type 1 (VPAC1) receptor, which is expressed by gut epithelial cells. We have evaluated the VIP antagonism and antisecretory potential of this novel compound using in vitro and in vivo models of intestinal secretion.Monolayers of the human colonic cell line (T84) and muscle-stripped preparations of rat jejunum and human ileum were set up in Ussing chambers for recording of transepithelial resistance and short-circuit current. Ussing chambers were modified to allow electrical stimulation of mucosal neurones. Effects of PG 97-269 on enterotoxin-induced secretion were investigated in perfused rat jejunum in vivo.PG 97-269 competitively antagonised VIP in T84 monolayers. In rat jejunum and human ileum, responses to VIP were inhibited as were responses of rat jejunum to electrical stimulation of mucosal neurons.In perfused rat jejunum, PG 97-269 abolished the effects of VIP on fluid and electrolyte transport and attenuated cholera toxin and Escherichia coli heat labile toxin-induced net fluid and electrolyte secretion.PG 97-269 is a competitive antagonist of enterocyte VIP receptors and effectively inhibits responses of rat and human intestinal mucosa to VIP. Antagonism of secretory responses to electrical stimulation of mucosal neurons and lumenal application of enterotoxins imply a secretory role for VIP in these processes.British Journal of Pharmacology (2005) 144, 994-1001. doi:10.1038/sj.bjp.0706128 [ABSTRACT FROM AUTHOR]

Abstract: Intestinal inflammatory conditions are associated with structural and functional alterations of the enteric nervous system (ENS). While injury to the enteric nervous system is well described, the mechanisms of neuronal injury and neuronal cell loss remain unclear. The aim of the present study was to examine the neural consequences of distal colitis and to assess the role of neutrophil granulocytes in mediating these changes. Colitis was induced in C3H/HEN female mice with dinitrobenzene sulfonic acid. The mice were then sacrificed at 0.5, 1, 1.5, 2, 3, 4, 6, 12, 24, 120 h post instillation of dinitrobenzene sulfonic acid. The inflammatory response was assessed by macroscopic damage score, myeloperoxidase activity and histology. HuC/D and PGP 9.5 immunostaining was used to examine myenteric plexus density and structure, neural cell body numbers and distribution in cross-section and whole mount preparations. Apoptosis was investigated in whole mount preparations double stained with HuC/D and activated caspase-3 or cleaved poly (ADP-ribose) polymerase (PARP). Dinitrobenzene sulfonic acid-induced colitis was associated with a rapid and significant loss of HuC/D immunoreactive myenteric plexus neuronal cell bodies (42% decrease relative to control) that remained unchanged between 6 and 120 h. No change in myenteric plexus density was observed with PGP 9.5 immunostaining. Neuronal apoptosis was evident between 0.5 and 3 h. PARP immunoreactive neurons ranged between 1% and 2.5%. Colitis was associated with significant impairment in colonic propulsive function. Pre-treatment of mice with anti-neutrophil serum attenuated the inflammatory response and partially reduced the extent of myenteric plexus neuronal cell loss. Taken together, these data suggest that acute colitis is associated with loss of myenteric plexus neurons that is partly mediated by neutrophil granulocyte infiltration and is accompanied by impairment of colonic motility. [Copyright &y& Elsevier]

These studies investigated receptors modulating release of mediators of fast excitatory postsynaptic potentials (fEPSPs) in guinea pig ileum myenteric plexus using electrophysiological methods. Fast EPSPs inhibited by >95% by hexamethonium (100 μmol L−1) were cholinergic; mixed fEPSPs were inhibited <95% by hexamethonium. Non-cholinergic fEPSPs were studied in the presence of hexamethonium. The α2-adrenergic receptor agonist UK 14304 inhibited cholinergic (maximum inhibition = 76%, EC50 = 18 nmol L−1), mixed (81%, 21 nmol L−1) and non-cholinergic (76%, 44 nmol L−1) fEPSPs equally. The 5-HT1 receptor agonist 5-carboxamidotryptamine inhibited cholinergic, mixed and non-cholinergic fEPSPs equally. Renzapride, increased non-cholinergic (33%) less than mixed (97%, 13 μmol L−1) fEPSPs. Renzapride inhibited the purely cholinergic fEPSPs (−29%) but potentiated the cholinergic component of mixed fEPSPs (39%). Prucalopride potentiated all fEPSPs equally (30–33%). 5-HT (0.1 μmol L−1) induced potentiation of cholinergic (75%), mixed (97%) and non-cholinergic (84%) fEPSPs was not statistically different. The potentiating effects of renzapride and 5-HT on fEPSPs were inhibited by the 5-HT4 receptor antagonist, SB 204070 (10 nmol L−1). Renzapride (0.3 μmol L−1) blocked 5-HT-induced increases in cholinergic fEPSPs. α2-Adrenergic and 5-HT1 receptors mediate inhibition of transmitter release from cholinergic and mixed terminals. 5-HT and prucalopride, acting at 5-HT4 receptors, facilitate all fEPSPs; renzapride facilitates the cholinergic and non-cholinergic components of mixed fEPSPs but not purely cholinergic fEPSPs. Cholinergic synapses may express few 5-HT4 receptors or a renzapride-insensitive 5-HT4 receptor isoform. [ABSTRACT FROM AUTHOR]

Abstract 5-hydroxytryptamine (HT)[sub 4] receptor agonists stimulate gastrointestinal motility partly by facilitating acetylcholine release from myenteric neurones. However, the signalling mechanisms that couple 5-HT[sub 4] receptor activation to increased transmitter release in the myenteric plexus are unknown. We used conventional intracellular electrophysiological methods to record fast excitatory postsynaptic potentials (fEPSPs) from neurones in the guinea-pig ileum myenteric plexus preparation. The substituted benzamide, renzapride, acted at 5-HT[sub 4] receptors to facilitate fEPSPs. This response was mimicked by forskolin, an activator of adenylate cyclase. Facilitation of fEPSPs by renzapride and forskolin was not blocked by treating tissues with pertussis toxin (PTX) (2 h, 2 μ g mL[sup -1] ). Facilitation of fEPSPs caused by renzapride was blocked by the non-selective protein kinase inhibitors, staurosporine (1 μ mol L[sup -1] ) and H-8 (30 μ mol L[sup -1] ) and by the selective protein kinase A (PKA) inhibitor, H-89 (10 μ mol L[sup -1] ). These data indicate that 5-HT[sub 4] receptors act via a PTX-resistant mechanism to activate PKA. Protein kinase A activation leads to an increase in transmitter release from myenteric nerve terminals and a facilitation of fast excitatory synaptic transmission. [ABSTRACT FROM AUTHOR]

Abstract With functional evidence emerging that interstitial cells of Cajal (ICC) play a role in smooth muscle innervation, detailed knowledge is needed about the structural aspects of enteric innervation of the human gut. Conventional electronmicroscopy (EM), immunohistochemistry and immuno-EM were performed on the musculature of the distal human ileum focusing on ICC associated with the deep muscular plexus (ICC-DMP) and intramuscular ICC (ICC-IM). ICC-DMP could be identified by EM but not by c-Kit immunohistochemistry. Immuno-EM revealed that ICC-DMP were innervated by both cholinergic and nitrergic nerves, and were the only cells to possess specialized synapse-like junctions with nerve varicosities and gap junction contacts with smooth muscle cells. c-Kit positive ICC near the deep muscular plexus were not ICC-DMP, but ICC-IM located in septa. ICC-IM were innervated by both cholinergic and nitrergic nerves but without specialized contacts. Varicosities of both nerve types were also found scattered throughout the musculature without specialized contact with any ICC. No ICC showed immunoreactivity for neuronal nitric oxide synthase. As ICC-DMP form synapse-like junctions with cholinergic and nitrergic nerves and gap junction contacts with muscle cells, it is hypothfesized that ICC-DMP hold a specialized function related to innervation of smooth muscle of the human intestine. [ABSTRACT FROM AUTHOR]

Background: The involvement of nitric oxide (NO) in vagal control and vasoactive intestinal polypeptide (VIP)-induced effects on antral motility was studied using isolated perfused preparations of porcine gastric antrum with intact vagal innervation. Methods: The presence of NO and VIP-producing neurons was studied using immunohistochemistry and histochemical techniques. Widespread, but not total, co-localization of NO and VIP immunoreactivity was found in the submucosa and in the muscle layers. Results: Electrical stimulation of the vagus nerves for 5 min (8 Hz, 10 mA, 4 msec) increased the motility index from 2.47 ± 0.44 to 11.50 ± 2.02 ( n = 5). This effect was not influenced by the two NO synthase inhibitors N-nitro- L -arginine methyl ester (10 -4 M) and N G -nitro- L -arginine (10 -5 M). However, infusion of inhibitors increased the spontaneous motility index from 2.40 ± 0.08 to 5.36 ± 1.08 ( P < 0.05) and 3.05 ± 1.10 to 4.14 ± 1.04 ( P < 0.05), respectively. The addition of L -arginine reversed this effect. Infusion of VIP 2 × 10 -9 M decreased the motility index from 2.32 ± 0.43 to 1.32 ± 0.27 ( P < 0.05), an effect that was preserved during NO synthase inhibition. Electrical vagus stimulation increased the release of VIP to the venous effluent, an effect that persisted during NO synthase inhibitors. Conclusion: We conclude that NO-producing nerves seem to have a tonic inhibitory action on the porcine antral motility, but are not involved in the motor effects of vagal stimulation or VIP infusion. [ABSTRACT FROM AUTHOR]

Interstitial cells of Cajal (ICC) in the guinea pig intestine, identified by the tyrosine kinase receptor, c-Kit, have been shown with immunohistochemistry to express nucleotide P2X2 and P2X5 receptors. P2X5 receptors have also been demonstrated on interstitial cells in the mouse ileum. It is speculated that release of ATP from enteric nerves, enteric glial cells or from contracting smooth muscle may provide a feedback mechanism for pacemaker activity in the intestine. [Copyright &y& Elsevier]

Interstitial cells of Cajal (ICC) are interposed between enteric neurons and smooth muscle cells in gastrointestinal (GI) muscles. The specific relationships between these cells in the murine proximal colon were studied with conventional and immunoelectron microscopy and immunohistochemistry. Intramuscular interstitial cells (IC-IM) formed discrete networks within the circular muscle layer of the murine proximal colon. Nerve trunks ran in close association with IC-IM and individual nerve trunks came into close contact with multiple IC-IM. Conventional electron microscopy revealed very close (≤20 nm) associations between nerve fibers and IC-IM. Processes of IC-IM also formed close contacts with neighboring smooth muscle cells. At the points of close association between neurons and IC-IM, areas of membrane densification in both pre- and postjunctional cells were present, suggesting specialized contacts or synaptic-like structures. Similar points of contact between neurons and smooth muscle cells were extremely rare. Immunoelectron microscopy demonstrated that IC-IM formed close associations with neurons containing nitric oxide synthase-like immunoreactivity (NOS-LI) or vesicular acetylcholine transporter-like immunoreactivity (vAChT-LI), suggesting innervation by both inhibitory and excitatory motor neurons. IC-IM were also labeled with anti-NOS antibodies. These observations suggest that IC-IM are an integral part of the neuromuscular junction in the colon. These cells may be the primary site of innervation, and neural regulation of the musculature may occur via IC-IM. [ABSTRACT FROM AUTHOR]

Nitric oxide synthase (NOS) requires the substrate L-arginine for NO production to support multiple gastrointestinal functions. We asked, ‘Where do enzymes to regenerate L-arginine from L-citrulline exist?’. We examined loci of immunoreactivities in the canine gastrointestinal tract for arginosuccinate synthetase and arginosuccinate lyase, enzymes that resynthesize L-arginine from L-citrulline, in relation to the distribution of nNOS immunoreactivity or NADPH-diaphorase histochemistry. Arginosuccinate synthetase and lyase were present in many neurones and nerve fibres in the myenteric plexus of the lower oesophageal sphincter (LOS), antrum, pylorus, ileum and colon; in the submucosal plexus of ileum and colon; in longitudinal muscle of ileum and colon; and in nerve bundles in circular muscle everywhere. LOS muscle was also immunoreactive for both enzymes. Circular and longitudinal muscle cells of the ileum and colon and cells resembling interstitial cells of Cajal in the deep muscular plexus of the ileum and the submuscular plexus of the colon also appeared immunoreactive. In neurones, arginosuccinate synthetase and nNOS were usually co-localized. NADPH diaphorase activity was present in LOS and likely in pylorus, but not in muscularis externa of ileum or colon. We conclude that resynthesis of L-arginine probably occurs in enteric nerves, interstitial cells of Cajal (ICC) and LOS muscle; also apparently in some cells without NOS to utilize it. [ABSTRACT FROM AUTHOR]

Recent studies have suggested that enteric inhibitory neurotransmission is mediated via interstitial cells of Cajal in some gastrointestinal tissues. This study describes the physical relationships between enteric neurons and interstitial cells of Cajal in the deep muscular plexus (IC-DMP) of the guinea-pig small intestine. c-Kit and vimentin were colocalized in the cell bodies and fine cellular processes of interstitial cells of the deep muscular plexus. Anti-vimentin antibodies were subsequently used to examine the relationships of interstitial cells with inhibitory motor neurons (as identified by nitric oxide synthase-like immunoreactivity) and excitatory motor neurons (using substance P-like immunoreactivity). Neurons with nitric oxide synthase- and substance P-like immunoreactivities were closely associated with the cell bodies of interstitial cells and ramified along their processes for distances greater than 300 μm. With transmission electron microscopy, we noted close relationships between interstitial cells and the nitric oxide synthase- and substance P-like immunoreactive axonal varicosities. Varicosities of nitric oxide synthase and substance P neurons were found as close as 20 and 25 nm from interstitial cells, respectively. Specialized junctions with increased electron density of pre- and postsynaptic membranes were observed at close contact points between nitric oxide synthase- and substance P-like immunoreactive neurons and interstitial cells. Close structural relationships (approximately 25 nm) were also occasionally observed between either nitric oxide synthase- and substance P-like immunoreactive varicosities and smooth muscle cells of the outer circular muscle layer. The data suggest that interstitial cells in the deep muscle plexus are heavily innervated by excitatory and inhibitory enteric motor neurons. Thus, these interstitial cells may provide an important, but probably not exclusive, pathway for nerve-muscle communication in the small intestine. [ABSTRACT FROM AUTHOR]

We recently showed the involvement of the L-arginine/nitric oxide (NO) pathway in acid-induced duodenal mucosal bicarbonate secretion in rats. The aim of the present study was to confirm this observation in pigs by direct measurements of NO production. Experiments were performed on 16 anaesthetized pigs of both sexes treated with guanethidine (6 mg kg-1, intravenously). A duodenal segment, devoid of pancreaticobiliary influxes, was perfused with saline and the duodenal mucosal bicarbonate secretion was calculated from continuous measurements of pH and Pco2. The perfusate contents of NO and its oxidative product nitrite were determined by chemiluminescence, after reduction of nitrite to NO. Luminal acidification with 30 mM hydrochloric acid increased the output of bicarbonate as well as NO to the perfusate, by 195 ± 45% and 106 ± 10%, respectively. These responses to acid were markedly inhibited by adding the NO synthase inhibitor NG-monomethyl-L-arginine (L-NMMA, 0.3 mM) to the perfusate. The inhibitory effect of L-NMMA could be reversed by administration of L-arginine (3 mM). The study presents simultaneous measurements of bicarbonate and NO outputs to a duodenal luminal perfusate. The results strongly support the view that the L-arginine/NO pathway is involved in the acid-induced duodenal mucosal bicarbonate secretory response. [ABSTRACT FROM AUTHOR]

Pituitary adenylate cyclase-activating polypeptide (PACAP) and helospectin are two vasoactive intestinal polypeptide (VIP)-related neuropeptides that have recently been demonstrated in the mammalian gut; the aim of this study was to reveal their occurrence and localisation in the gastrointestinal tract, swimbladder, urinary bladder and the vagal innervation of the gut of teleosts, using immunohistochemical methods on whole-mounts and sections of these tissues from the Atlantic cod, Gadus morhua and the rainbow trout, Oncorhynchus mykiss. Both PACAP-like and helospectin-like peptides were present in the gut wall of the two species. Immunoreactive nerve fibres were found in all layers but were most frequent in the myenteric plexus and along the circular muscle fibres. Immunoreactivity was also demonstrated in nerves innervating the swimbladder wall, the urinary bladder and blood vessels to the gut. Immunoreactive nerve cell bodies were found in the myenteric plexus of the gut and in the muscularis mucosae of the swimbladder. In the vagus nerve, non-immunoreactive nerve cells were surrounded by PACAP-immunoreactive fibres. Double staining revealed the coexistence of PACAP-like and helospectin-like peptides with VIP in all visualized nerve fibres and in some endocrine cells. It is concluded that PACAP-like and helospectin-like peptides coexist with VIP in nerves innervating the gut of two teleost species. The distribution suggests that both PACAP and helospectin, like VIP, are involved in the control of gut motility and secretion. [ABSTRACT FROM AUTHOR]

Hirschsprung's disease results from the congenital absence of enteric neurons in human distal colon. The reason for aganglionosis is unknown but may reflect an unfavourable microenvironment for neuronal development. We asked if smooth muscle cells from the aganglionic region could affect neuronal development in vitro. Neurons from neonatal mouse superior cervical ganglia were added to cultures of smooth muscle obtained from normal or aganglionic regions of five patients with Hirschsprung's disease. Although neurons initially showed more rapid attachment to aganglionic smooth muscle, this was equal by 60 min and thereafter. Progressive increase in the diameter of the nerve cell body was characteristic of normal maturation in vitro. This was consistently inhibited by 15-22% in neurons grown on aganglionic muscle compared with normal controls over the 6-day test period ( P<0.05). This phenomenon was preserved when the smooth muscle cells were lysed by brief exposure to distilled water before initiation of coculture (16-18% inhibition; P<0.05). These data imply that smooth muscle of the aganglionic colon is less favourable for neuronal development than the normally innervated region and suggest a membrane-linked factor. Clearly, this persists in postnatal life and in vitro and may reflect an abnormality of cellular interaction causing Hirschsprung's disease. [ABSTRACT FROM AUTHOR]

Early weaning (EW) has negative impacts on performance and health that persist from wean-to-finish. The mechanisms linking EW and lifetime performance reductions are poorly understood. The objective of this study was to investigate whether EW influences the long-term development of intestinal epithelial nutrient transporter function and expression and the potential mechanisms. Yorkshire gilts were split-weaned from their sows at 15 d (EW) or 28 d of age (Late Weaning; LW) and transferred to an on-site nursery room. All pigs received the same diets in a standard phase feeding program and were euthanized at 75 d of age. Mid-jejunum and distal ileum were mounted on Ussing chambers to evaluate Na+-dependent glucose and amino acid (AA) transporter function, measured as nutrient-induced changes in short circuit current (Isc). EW gilts exhibited reduced capacity for electrogenic transport of glucose (by ~30%; P < 0.05) and glutamate, glutamine, and alanine by (~ 30–35%; P < 0.05), compared with LW pigs. In contrast, jejunal and ileal lysine transporter function was upregulated (by 110% and 25%, respectively; P < 0.05) in EW pigs. Epithelial expression for glucose transporter (SGLT1) was reduced (P < 0.05) while glucose/fructose transporter (GLUT2), fructose transporter (GLUT5) and lysine transporters (B0AT1, CAT1, and ATB0, +) were enhanced in the EW jejunum. No differences observed in villus morphology between EW and LW pigs. Pretreatment of ileal mucosa on Ussing chambers with the Na+ channel blocker (Tetrodotoxin) or the β-adrenergic receptor blocker (Propranolol) augmented glucose, lysine and alanine transporter function in EW but not LW pigs. Together, these data show that EW in gilts induces lasting and divergent alterations in intestinal nutrient transporter function and expression which is mediated in part by the enteric nervous system and β-adrenergic receptor pathways. These new findings may explain why EW pigs exhibit lasting deleterious impacts on performance. Further mechanism-based investigations could reveal new targets for optimizing performance in EW pigs throughout the production lifespan. [ABSTRACT FROM AUTHOR]