Modulation Of Gastrointestinal Function Research Articles

Expression and function of vasoactive intestinal peptide receptors in human lower esophageal sphincter.

Vasoactive intestinal peptide (VIP) is an important neurotransmitter involved in the modulation of gastrointestinal function through the stimulation of VIP receptors. However, the expression of VPAC1R, VPAC2R and PAC1R in the human Lower esophageal sphincter (LES) has not been fully clarified. Therefore, the purpose of this study is to explore the expression of these receptors in the human Lower esophageal sphincter, the responses of the Lower esophageal sphincter to Vasoactive intestinal peptide, and the role of Vasoactive intestinal peptide receptors in the responses. Sling and clasp fiber samples of LES were acquired from patients undergoing subtotal esophagectomy, while circular muscle bundles from the esophagus and gastric fundus were used as control groups. Western blotting and RT-PCR technology were performed to determine the expression of the three VIP receptor subtypes. The isometric tension responses of the muscle sample strips to Ro25-1553 and PG99-465, and the effect of electrical field stimulation (EFS) on the sling and clasp fibers were studied. We found that VPAC2R messenger RNA (mRNA) and protein were expressed in the sling and clasp fibers of human LES. However, no VPAC1R or PAC1R mRNA and protein expressions were found in the LES samples. The sling and clasp fibers of the LES produced significant concentration-dependent relaxation following exposure to Ro25-1553 and EFS could induce them to produce frequency-dependent relaxation. Furthermore, the relaxation responses of the LES were inhibited by PG99-465 and induced by EFS and Ro25-1553. VPAC2R, but not VPAC1R or PAC1R, is expressed by the human LES. The relaxation responses of the LES generated by the VIP receptor agonist Ro25-1553 and EFS could be inhibited by the selective VPAC2 receptor antagonist PG99-465. VPAC2R may be important for the generation of relaxation and functional regulation of the LES.

Developmental Regulation of Chloride Currents in the Dorsal Motor Nucleus of the Vagus of the Rat

Tonically firing parasympathetic neurons of the dorsal motor nucleus of the vagus (DMV) modulate the functions of the proximal gastrointestinal (GI) tract. The pacemaker activity of DMV neurons is modulated by synaptic inputs from adjacent autonomic areas, including the nuclei of the tractus solitarius. Functional maturation of these vagal sensorimotor neurocircuits results from intense synaptogenesis and neuronal reorganization in the first postnatal weeks and their maturation may be assessed by the analysis of their time constant of synaptic current decay.Prior studies have shown that, in adult rats, perfusion with the GABAA antagonist bicuculline (BIC) increases the firing rate of DMV neurons, and BIC microinjection in the DMV increase gastric motility and pancreatic exocrine secretions, indicating a prominent role of brainstem GABA synapses in the modulation of GI functions. Conversely, glycine synapses do not appear to be present in GI‐related brainstem neurocircuits of adult rats.The aim of the present study was to examine GABA and glycine‐ mediated chloride currents in the development of synaptic inputs onto DMV neurons. Using whole cell recordings, miniature inhibitory currents were recorded in rats from postnatal day 1 (P1) to postnatal day 30 (P30), and analyzed for decay constant and event frequency. Between P1–15, the baseline frequency was 1.9±0.35 events.s−1 and the current decay constant was 10.3±1.4 ms (N=30). These values were not altered by maturation (P>0.05 for both parameters).Perfusion of the slice with the GABAA antagonist bicuculline (1 or 10uM) either abolished completely or decreased the frequency and the decay constant of the inhibitory events to a similar extent in neurons from P1–15 rats or >P15 rats (N=37 and N=65 for 1 and 10uM, respectively). Conversely, while perfusion with the glycine antagonist strychnine (1μM) did not decrease event frequency significantly in any of the groups, it increased the current decay constant (from 8.2±0.65 to 11.9±0.75ms and from 7.6±0.57 to 10.5±0.79ms, in P1–15 and >P15,neurons, respectively). Strychnine altered inhibitory currents in a significantly larger percentage of P1–15 (N=67) neurons, and blocked all events in 3 cells from P1–15 rats, but not in >P15 rats (n=58; p<0.05 vs P1–15).These data suggest that the development of brainstem vagal neurocircuits involves an early phase, during which GABA and glycine neurotransmission appear co‐released by the same neurons. The role of glycine in synaptic transmission appears to start declining at approximately P15. Disruption of this developmental switch from GABA‐glycine to purely GABAergic transmission may occur in response to early life stress, infection or inflammation, which may lead to adverse consequences in vagal efferent control of visceral functions.Support or Funding InformationFunding: NIH DK 99350 and DK 78364 & NSF IOS‐1148978

Vagal tone: effects on sensitivity, motility, and inflammation.

The vagus nerve (VN) is a key element of the autonomic nervous system. As a mixed nerve, the VN contributes to the bidirectional interactions between the brain and the gut, i.e., the brain-gut axis. In particular, after integration in the central autonomic network of peripheral sensations such as inflammation and pain via vagal and spinal afferents, an efferent response through modulation of preganglionic parasympathetic neurons of the dorsal motor nucleus of the vagus and/or preganglionic sympathetic neurons of the spinal cord is able to modulate gastrointestinal nociception, motility, and inflammation. A low vagal tone, as assessed by heart rate variability, a marker of the sympatho-vagal balance, is observed in functional digestive disorders and inflammatory bowel diseases. To restore a normal vagal tone appears as a goal in such diseases. Among the therapeutic tools, such as drugs targeting the cholinergic system and/or complementary medicine (hypnosis, meditation…), deep breathing, physical exercise, VN stimulation (VNS), either invasive or non-invasive, appears as innovative. There is new evidence in the current issue of this Journal supporting the role of VNS in the modulation of gastrointestinal functions.

Central nervous system control of gastrointestinal motility and secretion and modulation of gastrointestinal functions.

Although the gastrointestinal (GI) tract possesses intrinsic neural plexuses that allow a significant degree of autonomy over GI functions, the central nervous system (CNS) provides extrinsic neural inputs that regulate, modulate, and control these functions. While the intestines are capable of functioning in the absence of extrinsic inputs, the stomach and esophagus are much more dependent upon extrinsic neural inputs, particularly from parasympathetic and sympathetic pathways. The sympathetic nervous system exerts a predominantly inhibitory effect upon GI muscle and provides a tonic inhibitory influence over mucosal secretion while, at the same time, regulates GI blood flow via neurally mediated vasoconstriction. The parasympathetic nervous system, in contrast, exerts both excitatory and inhibitory control over gastric and intestinal tone and motility. Although GI functions are controlled by the autonomic nervous system and occur, by and large, independently of conscious perception, it is clear that the higher CNS centers influence homeostatic control as well as cognitive and behavioral functions. This review will describe the basic neural circuitry of extrinsic inputs to the GI tract as well as the major CNS nuclei that innervate and modulate the activity of these pathways. The role of CNS-centered reflexes in the regulation of GI functions will be discussed as will modulation of these reflexes under both physiological and pathophysiological conditions. Finally, future directions within the field will be discussed in terms of important questions that remain to be resolved and advances in technology that may help provide these answers.

Ghrelin for regulating appetite and energy balance: A systematic review

Gut hormones play a significant role in regulating feeding and energy balance. Almost all the gut hormones are responsible for reducing appetite i.e. they are anorectic, except for ghrelin which is responsible for increasing the appetite i.e. it has an orexigenic effect. Ghrelin is a 28-amino acid bioactive peptide hormone that was isolated from the stomach in 1999 by Kojima et al. A natural endogenous ligand of the growth hormone (GH) secretagogue receptor, it helps in the regulation of glucose and fat metabolism and regulation of energy balance. It also plays an essential role in regulation of appetite and bodyweight as well as modulation of gastrointestinal functions. The electronic databases, like CENTRAL, DARE, CDSR, Cochrane Methodology Reviews, MEDLINE, PUBMED and other resources. hard copies and unpublished works were searched. Pubmed keyword strategy was tailored to the other databases. The previous studies points out that Ghrelin is a hormone and the only known circulating orexigen produced in response to hunger. Although many substances play a role in the control of appetite, ghrelin is the only known peptide which increases appetite by sending signals of starvation from a stomach to the central nervous system. Besides playing a role in short-term regulation of food intake, ghrelin might also play a role in long-term regulation of energy balance. It also shows effects on the reward and motivation centers in the brain regions. Ghrelin has diverse roles. It also plays an essential role in regulation of appetite and bodyweight as well as modulation of gastrointestinal functions. As ghrelin is disturbed in obesity, it is important to reveal the mechanism of action for the purpose of developing novel therapeutic interventions.

Peripheral anti-nociceptive effect of nociceptin/orphanin FQ in inflammation and stress-induced colonic hyperalgesia in rats

Nociceptin/orphanin FQ (N/OFQ) and its NOP receptors are present in the central nervous system and in the periphery playing important roles in the modulation of gastrointestinal functions and pain. The aim of this study was to investigate the role of central and peripheral N/OFQ–NOP receptor system in the nociceptive response to colorectal distension (CRD) in basal condition and in two models of gut hypersensitivity triggered by both inflammation and stress. Male Wistar rats were tested in basal and in post-inflammatory conditions, i.e., 5 days after IC TNBS instillation (80 mg/Kg) and received N/OFQ (2 nmol/Kg IP), UFP-101 (a selective NOP receptor antagonist, 10 nmol/Kg IP), N/OFQ+UFP-101, N/OFQ (0.5 nmol/rat ICV) or vehicle. Female rats were tested in basal and after partial restraint stress receiving the same pharmacological treatment. CRD was performed using barostat and abdominal contractions were recorded by electromyography. In basal condition, N/OFQ, ICV and IP injected, did not modify basal visceral sensitivity. Both in TNBS and stress-induced hyperalgesia, IP but not ICV injection of N/OFQ significantly decreased the number of abdominal contractions. Peripheral injection of UFP-101 antagonized N/OFQ effect. Moreover, in post-inflammatory colitis, UFP-101, injected alone, exacerbated visceral hyperalgesia to CRD compared with vehicle. These findings indicate that in rats, N/OFQ, only peripherally injected, reduces visceral hypersensitivity triggered by inflammation or stress without affecting basal sensitivity. N/OFQ visceral anti-hyperalgesic effect involves peripheral NOP receptors. In a post-inflammatory, but not in an acute stress colitis model, N/OFQergic system is endogenously activated.

Urocortin 3/stresscopin in human colon: possible modulators of gastrointestinal function during stressful conditions

Urocortin 3 (Ucn 3) or stresscopin (SCP) is a new member of the corticotropin-releasing factor (CRF) neuropeptide family and is a specific ligand for CRF type 2 receptor (CRF 2). CRF receptors are known to be expressed in the gastrointestinal tract and are considered to play pathophysiological roles, for example, in gastrointestinal motility under stress. We, therefore, examined Ucn 3 expression in the normal human large intestine obtained from surgery and autopsy in order to clarify this local response to stress in human intestine. Both immunohistochemistry and mRNA in situ hybridization demonstrated Ucn 3 expression in myenteric and submucosal nervous plexus, in vascular endothelial cells (VECs) and vascular smooth muscle cells (VSMCs) of blood vessels in subserosa, in smooth muscle layers of the large intestine, and in enterochromaffin cells. In contrast to Urocortin 1 (Ucn 1), Ucn 3 was hardly detected in lamina propria (LP) inflammatory cells in colonic mucosa. In addition, immunohistochemistry demonstrated CRF 2 expression in myenteric and submucosal nervous plexus, in smooth muscle layers, in VECs, in VSMCs and in lamina propria inflammatory cells. Immunoreactive Ucn 3 was also detected in the large intestine by RIA, with high concentrations detected in the rectum (15.4 ± 9.5 pmol/g wet weight, mean ± SEM, n = 3) and sigmoid colon (6.5 ± 3.5 pmol/g wet weight, n = 5). Reverse-phase HPLC of the human large intestine disclosed peaks eluting in the position of synthetic Ucn 3 or SCP. These findings all suggest that Ucn 3 plays some physiological or pathological roles in the modulation of gastrointestinal functions during stressful conditions in different manners from Ucn 1.

Protease-Activated Receptors (PARs) as Therapeutic Targets: Development of Agonists / Antagonists and Modulation of Gastrointestinal Functions

Protease-activated receptors (PARs), a family of G-protein-coupled seven-transmembrane-domain receptors, are activated by proteolytic unmasking of the N-terminal cryptic tethered ligand by certain serine proteases. Among four PAR family members cloned to date, PAR-1, PAR-2 and PAR-4 can also be activated through a non-enzymatic mechanism, which is achieved by direct binding of exogenously applied synthetic peptides based on the tethered ligand sequence, namely PARs-activating peptides, to the body of the receptor. Various peptide mimetics have been synthesized as agonists and / or antagonists for PARs with improved potency, selectivity and stability. The amidation of the C-terminal of PARs-activating peptides increases the potency and metabolic resistance, particularly in vivo . Substitution of the Nterminal serine residue of PAR-2-activating peptides with a furoyl group dramatically enhances both potency and metabolic resistance, providing the most potent PAR-2 agonist. Some peptide mimetics and / or non-peptide compounds have also been developed as antagonists for PAR-1 and PAR-4. PARs are widely distributed in the mammalian body, especially throughout the alimentary systems, and play various roles in physiological / pathophysiological conditions; i.e. modulation of salivary, gastric or pancreatic glandular exocrine secretion and gastrointestinal smooth muscle motility, gastric mucosal cytoprotection, suppression / facilitation of visceral pain and inflammation, etc. Thus, PARs are now considered novel therapeutic targets, and development of selective agonists and / or antagonists for PARs might provide novel strategy for clinical treatment of various diseases that are resistant to current therapeutics. Keywords: protease (proteinase)-activated receptor (par), protease, structure-activity relationship, gastrointestinal tract

Distribution of pancreatic polypeptide receptors in the rat brain

Pancreatic polypeptide (PP) is a regulatory peptide that modulates gastrointestinal function. Previously we demonstrated PP receptors in the brainstem and interpeduncular nucleus, and the PP receptors in the brainstem appear to modulate gastric motility and pancreatic exocrine secretion. The purpose of this study is to extend our understanding of the distribution of PP receptors in the rat brain in order to determine the systems that are potentially modulated by PP. Rat brains were studied using 125I-PP receptor autoradiography on cryostat sections of the entire brain cut in three planes (horizontal, sagittal, and coronal). Brain regions exhibiting PP binding sites were confirmed when identified in all three planes of section. Saturable PP binding was identified in the hypothalamus (arcuate and paraventricular n), the rostral forebrain (medial preoptic area, anterior olfactory nucleus, islands of Calleja, the dorsal endopiriform n, piriform cortex, and the bed n of the stria terminalis), medial amygdaloid n; the thalamus (anteromedial thal. n; reuniens thal. n; and paraventricular thal n), the interpeduncular red nucleus, substantia nigra, parabrachial n; locus coeruleus, mesencephalic trigeminal n, dorsal motor n of the vagus, the n solitary tract, and the area postrema. We conclude that PP receptors are distributed widely throughout the rat brain. The distribution of many of these PP binding sites corresponds to brain regions regulating digestion and autonomic function. We speculate, based on the patterns of binding in the olfactory and limbic systems, that PP receptors might be involved in positive reinforcement of ingestion behavioral as well as modulation of gastrointestinal function.

Enteroendocrine peptides in a canine model of orthotopic jejunoileal autotransplantation.

The enteroendocrine cells of the small bowel provide a rich source of regulatory peptides involved in the modulation of gastrointestinal function. Recent work from our laboratory showed that in situ neural isolation (autotransplantation) of the jejunoileum produced marked changes in tissue expression of several neuropeptides. In the present study, we examined the influence of extrinsic innervation on the tissue expression of endocrine peptides localized to various regions of the gastrointestinal tract. Concentrations of immunoreactive gastric inhibitory polypeptide (GIP), neurotensin (NT) and peptide tyrosine tyrosine (PYY) in fasting plasma and regional tissue biopsies were determined before and at varying time points (2, 6, 12 weeks) after a model of canine orthotopic jejunoileal autotransplantation. GIP was not altered in plasma or tissue at any time point. Plasma concentrations of NT and PYY increased after autotransplantation. Following a decrease in tissue concentrations two weeks after autotransplantation, NT increased progressively from 2 to 6 to 12 weeks, reaching a maximal increase of 895% over baseline in proximal ileum. Tissue concentrations of PYY followed much the same pattern as NT, but these trends never achieved statistical significance. Chromatographic characterization of tissue biopsy extracts revealed molecular heterogeneity of NT-like immunoreactivity, while GIP and PYY immunoreactivity coeluted as single species with authentic standards. Taken together with our earlier observations, it appears that disruption of extrinsic and intrinsic neural continuity to the jejunoileum (autotransplantation) does not affect gut endocrine peptides such as GIP and PYY to the same extent as enteric neuropeptides. NT has been localized to neural as well as endocrine cells and is involved in the temporal adaptive response to autotransplantation.

Role of CRF-like peptides in the modulation of gastrointestinal functions

Role of CRF-like peptides in the modulation of gastrointestinal functions

Effect of xenopsin on blood flow, hormone release, and acid secretion

We investigated the effects of the neurotensin analogue xenopsin on regional blood flow, central hemodynamics, and stimulated acid secretion in awake conscious dogs. Organ blood flow, estimated using the radioactive microsphere technique, was significantly increased during the xenopsin infusion to the adrenals, pancreas, and ileum. There was no change in mean arterial pressure or cardiac output (measured by thermodilution). Along with changes in blood flow, there was a significant increase in the hormone output from the pancreas. These included rises in plasma pancreatic polypeptide, insulin, and glucagon. There also was a rise in plasma cortisol levels during the infusion. Substance P levels rose slowly but significantly during the xenospin infusion. There was no change in plasma gastrin levels. Xenopsin produced a significant inhibition of tetragastrin-stimulated gastric acid output. Thus, xenopsin appears to have region-specific influence on blood flow that correlates with region-specific hormonal secretion. In addition, xenopsin, like its mammalian analogue neurotensin, is an inhibitor of stimulated gastric acid secretion. A mammalian xenopsinlike peptide may well be involved in the modulation of gastrointestinal function.