Interleukin-1beta activates specific populations of enteric neurons and enteric glia in the guinea pig ileum and colon

Enteric glial cells aggravate the intestinal epithelial barrier damage by secreting S100β under high-altitude conditions

Damage to the intestinal epithelial barrier (IEB) has been reported under high-altitude (HA) conditions and may be responsible for HA-associated gastrointestinal (GI) disorders. However, this pathogenetic mechanism does not fully explain the GI stress symptoms, such as flatulence and motility diarrhea, which accompany the IEB damage under HA conditions, especially for the people exposed to HA acutely. In the present study, we collected the blood samples from the people who lived at HA and found the concentration of enteric glial cells (EGCs)-associated biomarkers increased significantly. HA mouse model was then established and the results revealed that EGCs were involved in IEB damage. Zona occludens (ZO)-1, occludin, and claudin-1 expression was negatively correlated with that of glial fibrillary acidic protein (GFAP) and S100β under HA conditions. In order to learn more about how EGCs influence IEB, the in vitro EGC and MODE-K hypoxia experiments that used hypoxic stimulation for simulating in vivo exposure to HA was performed. We found that hypoxia increased S100β secretion in EGCs. And MODE-K cells cultured in medium conditioned by hypoxic EGCs showed low ZO-1, occludin, and claudin-1 levels of expression. Furthermore, treatment of MODE-K cells with recombinant mouse S100β resulted in diminished levels of ZO-1, occludin, and claudin-1 expression. Thus, HA exposure induces greater S100β secretion by EGCs, which aggravates the damage to the IEB. This study has revealed a novel mechanism of IEB damage under HA conditions, and suggest that EGCs may constitute a fresh avenue for the avoidance of GI disorders at HA.

Gut Region-Specific Interleukin 1β Induction in Different Myenteric Neuronal Subpopulations of Type 1 Diabetic Rats

Interleukin 1β (IL1β) is a pro-inflammatory cytokine that may play a crucial role in enteric neuroinflammation in type 1 diabetes. Therefore, our goal is to evaluate the effects of chronic hyperglycemia and insulin treatment on IL1β immunoreactivity in myenteric neurons and their different subpopulations along the duodenum-ileum-colon axis. Fluorescent immunohistochemistry was used to count IL1β expressing neurons as well as the neuronal nitric oxide synthase (nNOS)- and calcitonin gene-related peptide (CGRP)-immunoreactive myenteric neurons within this group. Tissue IL1β level was measured by ELISA in muscle/myenteric plexus-containing homogenates. IL1β mRNA was detected by RNAscope in different intestinal layers. The proportion of IL1β-immunoreactive myenteric neurons was significantly higher in the colon than in the small intestine of controls. In diabetics, this proportion significantly increased in all gut segments, which was prevented by insulin treatment. The proportion of IL1β-nNOS-immunoreactive neurons only increased in the diabetic colon, while the proportion of IL1β-CGRP-immunoreactive neurons only increased in the diabetic ileum. Elevated IL1β levels were also confirmed in tissue homogenates. IL1β mRNA induction was detected in the myenteric ganglia, smooth muscle and intestinal mucosa of diabetics. These findings support that diabetes-related IL1β induction is specific for the different myenteric neuronal subpopulations, which may contribute to diabetic motility disturbances.

Enteric Glia Play a Critical Role in Promoting the Development of Colorectal Cancer

Enteric glia are a distinct population of peripheral glial cells in the enteric nervous system that regulate intestinal homeostasis, epithelial barrier integrity, and gut defense. Given these unique attributes, we investigated the impact of enteric glia depletion on tumor development in azoxymethane/dextran sodium sulfate (AOM/DSS)-treated mice, a classical model of colorectal cancer (CRC). Depleting GFAP⁺ enteric glia resulted in a profoundly reduced tumor burden in AOM/DSS mice and additionally reduced adenomas in the Apc^{Min /+} mouse model of familial adenomatous polyposis, suggesting a tumor-promoting role for these cells at an early premalignant stage. This was confirmed in further studies of AOM/DSS mice, as enteric glia depletion did not affect the properties of established malignant tumors but did result in a marked reduction in the development of precancerous dysplastic lesions. Surprisingly, the protective effect of enteric glia depletion was not dependent on modulation of anti-tumor immunity or intestinal inflammation. These findings reveal that GFAP⁺ enteric glia play a critical pro-tumorigenic role during early CRC development and identify these cells as a potential target for CRC prevention.

Enteric Glia: A New Player in Abdominal Pain

Chronic abdominal pain is the most common gastrointestinal issue and contributes to the pathophysiology of functional bowel disorders and inflammatory bowel disease. Current theories suggest that neuronal plasticity and broad alterations along the brain-gut axis contribute to the development of chronic abdominal pain, but the specific mechanisms involved in chronic abdominal pain remain incompletely understood. Accumulating evidence implicates glial cells in the development and maintenance of chronic pain. Astrocytes and microglia in the central nervous system and satellite glia in dorsal root ganglia contribute to chronic pain states through reactive gliosis, the modification of glial networks, and the synthesis and release of neuromodulators. In addition, new data suggest that enteric glia, a unique type of peripheral glia found within the enteric nervous system, have the potential to modify visceral perception through interactions with neurons and immune cells. Understanding these emerging roles of enteric glia is important to fully understand the mechanisms that drive chronic pain and to identify novel therapeutic targets. In this review, we discuss enteric glial cell signaling mechanisms that have the potential to influence chronic abdominal pain.

The multiple faces of inflammatory enteric glial cells: is Crohn's disease a gliopathy?

Gone are the days when enteric glial cells (EGC) were considered merely satellites of enteric neurons. Like their brain counterpart astrocytes, EGC express an impressive number of receptors for neurotransmitters and intercellular messengers, thereby contributing to neuroprotection and to the regulation of neuronal activity. EGC also produce different soluble factors that regulate neighboring cells, among which are intestinal epithelial cells. A better understanding of EGC response to an inflammatory environment, often referred to as enteric glial reactivity, could help define the physiological role of EGC and the importance of this reactivity in maintaining gut functions. In chronic inflammatory disorders of the gut such as Crohn's disease (CD) and ulcerative colitis, EGC exhibit abnormal phenotypes, and their neighboring cells are dysfunctional; however, it remains unclear whether EGC are only passive bystanders or active players in the pathophysiology of both disorders. The aim of the present study is to review the physiological roles and properties of EGC, their response to inflammation, and their role in the regulation of the intestinal epithelial barrier and to discuss the emerging concept of CD as an enteric gliopathy.

Colonic migrating motor complexes are inhibited in acute tri-nitro benzene sulphonic acid colitis

Background

Inflammatory Bowel Disease (IBD) is characterized by overt inflammation of the intestine and is typically accompanied by symptoms of bloody diarrhea, abdominal pain and cramping. The Colonic Migrating Motor Complex (CMMC) directs the movement of colonic luminal contents over long distances. The tri-nitrobenzene sulphonic acid (TNBS) model of colitis causes inflammatory damage to enteric nerves, however it remains to be determined whether these changes translate to functional outcomes in CMMC activity. We aimed to visualize innate immune cell infiltration into the colon using two-photon laser scanning intra-vital microscopy, and to determine whether CMMC activity is altered in the tri-nitro benzene sulphonic (TNBS) model of colitis.

Methods

Epithelial barrier permeability was compared between TNBS treated and healthy control mice in-vitro and in-vivo. Innate immune activation was determined by ELISA, flow cytometry and by 2-photon intravital microscopy. The effects of TNBS treatment and IL-1β on CMMC function were determined using a specialized organ bath.

Results

TNBS colitis increased epithelial barrier permeability in-vitro and in-vivo. Colonic IL-1β concentrations, colonic and systemic CD11b+ cell infiltration, and the number of migrating CD11b+ cells on colonic blood vessels were all increased in TNBS treated mice relative to controls. CMMC frequency and amplitude were inhibited in the distal and mid colon of TNBS treated mice. CMMC activity was not altered by superfusion with IL-1β.

Conclusions

TNBS colitis damages the epithelial barrier and increases innate immune cell activation in the colon and systemically. Innate cell migration into the colon is readily identifiable by two-photon intra-vital microscopy. CMMC are inhibited by inflammation, but this is not due to direct effects of IL-1β.

HIV-1 Tat-induced diarrhea evokes an enteric glia-dependent neuroinflammatory response in the central nervous system

Despite the effectiveness of combined anti-retroviral therapy, human immunodeficiency virus (HIV) infected-patients frequently report diarrhea and neuropsychological deficits. It is claimed that the viral HIV-1 Trans activating factor (HIV-1 Tat) protein is responsible for both diarrhea and neurotoxic effects, but the underlying mechanisms are not known. We hypothesize that colonic application of HIV-1 Tat activates glial cells of the enteric nervous system (EGCs), leading to a neuroinflammatory response able to propagate to the central nervous system. We demonstrated that HIV-1 Tat-induced diarrhea was associated with a significant activation of glial cells within the colonic wall, the spinal cord and the frontal cortex, and caused a consistent impairment of the cognitive performances. The inhibition of glial cells activity by lidocaine, completely abolished the above-described effects. These observations point out the role of glial cells as putative effectors in HIV-1 Tat-associated gastrointestinal and neurological manifestations and key regulators of gut-brain signaling.

Impairment of Small Intestinal Function in Ulcerative Colitis: Role of Enteric Innervation

Small intestinal dysfunction has been described in patients with ulcerative colitis and in experimental animal models of colitis. This is demonstrated by a decrease in fluid, electrolyte, amino acid, fat and carbohydrate absorption as well as by deranged intestinal motility. Histopathological changes in the small intestines in colitis have not been consistently demonstrated, but there is evidence of structural and biochemical alterations as shown by increased intestinal permeability and a decrease in the expression of multiple brush border membrane enzymes such as disaccharidases and aminopetidases, in both humans and experimental animals. The pathophysiology of this dysfunction has not been elucidated, but it is thought to include alterations in neural circuitry such as increased neuronal excitability, neuronal damage and changes of neuropeptidergic innervation and receptors as well as an increase in local production of pro-inflammatory cytokines and alterations in the production of some neurohumoral mediators. In the following, we provide an update on the advancement of clinical and scientific contributions to elucidate the underlying mechanisms of the alteration of the functions of apparently intact small intestinal segments, induced by ulcerative colitis.

Effects of Oxaliplatin Treatment on the Enteric Glial Cells and Neurons in the Mouse Ileum

Oxaliplatin, currently used for treatment of colorectal and other cancers, causes severe gastrointestinal side effects, including nausea, vomiting, diarrhea, and constipation that are attributed to mucosal damage. However, delayed onset and long-term persistence of these side effects suggest that damage to the enteric nervous system (ENS) regulating physiological function of the gastrointestinal tract may also occur. The ENS comprises myenteric and submucosal neurons and enteric glial cells (EGCs). This study aimed to investigate the effects of oxaliplatin treatment on enteric neurons and EGCs within the mouse ileum. BALB/c mice received repeated intraperitoneal injections of oxaliplatin (3 mg/kg, 3 injections/week). Tissues were collected 3, 7, 14, and 21 days from the commencement of treatment. Decreases in glial fibrillary acidic protein-immunoreactive (IR) EGCs and protein gene product 9.5/β-Tubulin III-IR neurons as well as increase in s100β-IR EGCs after chronic oxaliplatin administration were observed in both the myenteric and submucosal plexi. Changes in EGCs were further observed in cross-sections of the ileum at day 14 and confirmed by Western blotting. Alterations in EGCs correlated with loss of myenteric and submucosal neurons in the ileum from oxaliplatin-treated mice. These changes to the ENS may contribute to the mechanisms underlying gastrointestinal side effects associated with oxaliplatin treatment.

TLR2 and TLR9 modulate enteric nervous system inflammatory responses to lipopolysaccharide

BACKGROUND

Accumulating evidence suggest that the enteric nervous system (ENS) plays important roles in gastrointestinal inflammatory responses, which could be in part mediated by Toll-like receptor (TLR) activation. The aim of this study was to characterise the expression and functionality of TLR2/4/9 in the ENS.

METHODS

TLR2/4/9 expression was assessed in the plexuses of adult rats and embryonic ENS cultures by immunofluorescence and quantitative PCR. Following stimulation with TLR2/4/9 ligands or their combinations, activation of NF-kB, production of TNF-α, IL-6 and MCP-1 and chemoattraction of RAW264.7 macrophages were evaluated by means of Western blot, ELISA, immunofluorescence and migration assays in transwell inserts.

RESULTS

TLR2/4/9 staining colocalised with enteric neuronal markers, whereas their presence in enteroglial processes was low to inexistent. Stimulation of ENS cultures with selective ligands induced NF-kB activation and release of cytokines and chemokines by neurons and resident immunocytes. TLR2 neutralisation before lipopolysaccharide (LPS) challenge reduced production of inflammatory mediators, whereas combination of TLR2/4 ligands promoted macrophage migration. Combined stimulation of cultures with LPS and the CpG oligonucleotide 1826 (TLR4/9 ligands) caused a synergic increase in chemoattraction and cytokine production.

CONCLUSIONS

Our results suggest that the ENS, and particularly enteric neurons, can integrate a variety of microbial signals and respond in a relatively selective fashion, depending on the particular TLRs stimulated. These findings additionally suggest that the ENS is capable of initiating a defensive response against pathogens and expanding inflammation.

Mast cell degranulation inhibits motor patterns of human ileum and sigmoid colon in vitro: relevance for postoperative ileus

BACKGROUND

Local release of mast cell proteases during gastrointestinal surgery is associated with the inhibition of motility and postoperative ileus (POI). We determined whether activation of intramuscular mast cell affects the motor patterns of the human ileum and colon and whether proteases are involved.

METHODS

Motor response of ileal and colonic circular muscle strips was measured in organ bath. Mast cell degranulation was induced by compound 48/80 (c48/80; 25-675 μg/mL). Motor response was quantified as tone, rhythmic phasic contractions (RPCs) and contractions to electric field stimulation (EFS; 40 Hz), and bethanechol-evoked contractions. Ketotifen (10(-6) mol/L) and a protease inhibitor cocktail (P8340) were used to evaluate the role of mast cell mediators.

KEY RESULTS

(a) c48/80 impaired the spontaneous and the electrically evoked motor response in small bowel and colonic strips (sigmoid colon EC50 : 460.0 μg/mL for RPCs and 8.9 μg/mL for electrically evoked contraction amplitudes) and bethanechol-evoked contractions. (b) Preincubation with ketotifen (10(-6) mol/L, 1 h) prevented the impairment of RPCs and EFS-evoked contractions in the sigmoid colon and ileum but not in the right colon. (c) Preincubation with P8340 also prevented the impairment of contractions in the sigmoid colon but not in the ileum or the right colon.

CONCLUSIONS & INFERENCES

Mast cell degranulation by c48/80 inhibits the spontaneous and the nerve-mediated motor response in the human ileum and colon. The effect is partially mediated by mast cell proteases and could be relevant in the pathophysiology of POI.

Mast Cell-dependent Mesenteric Afferent Activation by Mucosal Supernatant From Different Bowel Segments of Guinea Pigs With Post-infectious Irritable Bowel Syndrome

Background/Aims

Mesenteric afferent nerves (MANs) play a pivotal role in the visceral-nociceptive perception. Inappropriate activation of MANs may be involved in the pathogenesis of post-infectious irritable bowel syndrome (PI-IBS). However, the underlying mechanisms remain unclear. We assessed the effects of mucosal mediators from different bowel segments of guinea pigs with PI-IBS on MAN firing and the role of mast cells.

Methods

PI-IBS was induced in guinea pigs by Trichinella spiralis infection. Inflammation in terminal ileum, proximal and distal colon was scored with hematoxylin-eosin staining, and mast cell infiltration was assessed with immunofluorescence. We determined the effects of supernatant extracted from the mucosa of different bowel segments of PI-IBS on MANs activity, and assessed the role of mast cells in this process.

Results

Eight weeks after infection, intestinal inflammation resolved, whereas mast cell numbers increased significantly in terminal ileum and proximal colon (P < 0.05) compared with findings in controls. Mucosal supernatant from different bowel segments of PI-IBS models, but not from controls, significantly enhanced the frequency of MAN firing (terminal ileum 41.01 ± 7.60 Hz vs. 26.55 ± 0.67 Hz, P = 0.001; proximal colon 45.90 ± 11.20 Hz vs. 30.88 ± 6.92 Hz, P = 0.002; distal colon 48.25 ± 9.70 Hz vs. 29.47 ± 6.13 Hz, P < 0.001). In addition, the excitatory effects were inhibited by mast cell stabilizer Nasmil (terminal ileum, 32.71 ± 2.52 Hz, P = 0.030; proximal colon, 30.94 ± 4.44 Hz, P = 0.002; distal colon, 27.15 ± 5.83 Hz, P < 0.001).

Conclusions

Supernatant from the intestinal mucosa of different bowel segments of PI-IBS models markedly enhanced the MAN firing in a mast cell-dependent manner, indicating that mast cell-mediated MAN activation plays an important role in the pathogenesis of PI-IBS.

Changes of cytokine levels in a mouse model of post-infectious irritable bowel syndrome

BACKGROUND

Irritable bowel syndrome (IBS) is a highly prevalent functional gastrointestinal disorder. Post-infectious IBS (PI-IBS) is caused by an acute gastrointestinal infection preceding the onset of symptoms. However, the pathophysiology of PI-IBS is not clear, and the purpose of this study was to investigate the probable immune mechanisms of PI-IBS.

METHODS

C57BL/6 mice were randomly assigned to either an infection group or a control group. Mice in the infection group were infected with Trichinella spiralis to establish a model of PI-IBS (500 Trichinella), while control mice received only salt solution. Visceral sensitivity of colorectal distention in mice was evaluated by abdominal withdrawal reflex scores and intestinal inflammation was assessed using hematoxylin-eosin staining; at day 56 post-infection, the mRNA and protein levels of specific cytokines in the gut segments were detected using reverse-transcription polymerase chain reaction and enzyme-linked immunoabsorbent assay.

RESULTS

Levels of interferon γ and interleukin (IL)-17 in the PI-IBS group were significantly increased in the duodenum and ileum, and IL-10 was decreased in the jejunum, ileum, and colon compared with control mice. However, the expression level of IL-1β was not significantly different between the two groups.

CONCLUSIONS

The present study suggests that the local low-grade inflammation and immune activation that are an important component of the pathophysiology of PI-IBS are primarily induced and maintained by specific cytokines.

The enteric glia: identity and functions

Enteric glial cells were first described at the end of the 19th century, but they attracted more interest from researchers only in the last decades of the 20th. Although, they have a different embryological origin, the enteric GLIA share many characteristics with astrocytes, the main glial cell type of the central nervous system (CNS), such as in their expression of the same markers and in their functions. Here we review the construction of the enteric nervous system (ENS), with a focus on enteric glia, and also the main studies that have revealed the action of enteric glia in different aspects of gastrointestinal tract homeostasis, such as in the intestinal barrier, in communications with neurons, and in their action as progenitor cells. We also discuss recent discoveries about the roles of enteric glia in different disorders that affect the ENS, such as degenerative pathologies including Parkinson's and prion diseases, and in cases of intestinal diseases and injury.

Heterogeneity and phenotypic plasticity of glial cells in the mammalian enteric nervous system

Enteric glial cells are vital for the autonomic control of gastrointestinal homeostasis by the enteric nervous system. Several different functions have been assigned to enteric glial cells but whether these are performed by specialized subtypes with a distinctive phenotype and function remains elusive. We used Mosaic Analysis with Double Markers and inducible lineage tracing to characterize the morphology and dynamic molecular marker expression of enteric GLIA in the myenteric plexus. Functional analysis in individually identified enteric glia was performed by Ca(2+) imaging. Our experiments have identified four morphologically distinct subpopulations of enteric glia in the gastrointestinal tract of adult mice. Marker expression analysis showed that the majority of glia in the myenteric plexus co-express glial fibrillary acidic protein (GFAP), S100β, and Sox10. However, a considerable fraction (up to 80%) of glia outside the myenteric ganglia, did not label for these markers. Lineage tracing experiments suggest that these alternative combinations of markers reflect dynamic gene regulation rather than lineage restrictions. At the functional level, the three myenteric glia subtypes can be distinguished by their differential response to adenosine triphosphate. Together, our studies reveal extensive heterogeneity and phenotypic plasticity of enteric glial cells and set a framework for further investigations aimed at deciphering their role in digestive function and disease.

Urocortin 2 blocks the suppression of gastric antral contractions induced by lipopolysaccharide in freely moving conscious rats

Lipopolysaccharide (LPS) inhibits gastric antral contractions in conscious rats. Since LPS regulates corticotropin-releasing factor type 2 receptor (CRF2) expression in the rat stomach, and activation of peripheral CRF2 alters gastric motility, we tried to determine the role of peripheral CRF2 in the LPS-induced suppression of gastric antral contractions. Intraluminal gastric pressure waves were measured in freely moving conscious non-fasted rats using the perfused manometric method. We assessed the area under the manometric trace as the motor index (MI), and compared this result with those obtained 1h before and after intraperitoneal injection of drugs. LPS (0.2 mg/kg) significantly decreased MI. Indomethacin (10 mg/kg) itself did not alter MI but blocked this inhibitory action by LPS. Astressin 2-B (200 μg/kg), a selective CRF2 antagonist, modified neither the basal MI nor the action by LPS. Meanwhile, urocortin 2 (30 μg/kg), a selective CRF2 agonist, reversed the suppression by LPS without affecting the basal MI. This action by urocortin 2 was blocked by pretreatment with astressin 2-B. In conclusion, LPS inhibited gastric antral contractions possibly through a prostaglandin-dependent pathway. Peripheral CRF2 stimulation reversed this response by LPS.

Postoperative ileus involves interleukin-1 receptor signaling in enteric glia

BACKGROUND & AIMS

Postoperative ileus (POI) is a common consequence of abdominal surgery that increases the risk of postoperative complications and morbidity. We investigated the cellular mechanisms and immune responses involved in the pathogenesis of POI.

METHODS

We studied a mouse model of POI in which intestinal manipulation leads to inflammation of the muscularis externa and disrupts motility. We used C57BL/6 (control) mice as well as mice deficient in Toll-like receptors (TLRs) and cytokine signaling components (TLR-2(-/-), TLR-4(-/-), TLR-2/4(-/-), MyD88(-/-), MyD88/TLR adaptor molecule 1(-/-), interleukin-1 receptor [IL-1R1](-/-), and interleukin (IL)-18(-/-) mice). Bone marrow transplantation experiments were performed to determine which cytokine receptors and cell types are involved in the pathogenesis of POI.

RESULTS

Development of POI did not require TLRs 2, 4, or 9 or MyD88/TLR adaptor molecule 2 but did require MyD88, indicating a role for IL-1R1. IL-1R1(-/-) mice did not develop POI; however, mice deficient in IL-18, which also signals via MyD88, developed POI. Mice given injections of an IL-1 receptor antagonist (anakinra) or antibodies to deplete IL-1α and IL-1β before intestinal manipulation were protected from POI. Induction of POI activated the inflammasome in muscularis externa tissues of C57BL6 mice, and IL-1α and IL-1β were released in ex vivo organ bath cultures. In bone marrow transplantation experiments, the development of POI required activation of IL-1 receptor in nonhematopoietic cells. IL-1R1 was expressed by enteric glial cells in the myenteric plexus layer, and cultured primary enteric glia cells expressed IL-6 and the chemokine monocyte chemotactic protein 1 in response to IL-1β stimulation. Immunohistochemical analysis of human small bowel tissue samples confirmed expression of IL-1R1 in the ganglia of the myenteric plexus.

CONCLUSIONS

IL-1 signaling, via IL-1R1 and MyD88, is required for development of POI after intestinal manipulation in mice. Agents that interfere with the IL-1 signaling pathway are likely to be effective in the treatment of POI.

Expression and function of NIK- and IKK2-binding protein (NIBP) in mouse enteric nervous system

BACKGROUND

NIK- and IKK2-binding protein (NIBP)/TRAPPC9 is expressed in brain neurons, and human NIBP mutations are associated with neurodevelopmental disorders. The cellular distribution and function of NIBP in the enteric nervous system (ENS) remain unknown.

METHODS

Western blot and reverse transcription-polymerase chain reaction analysis were used respectively to identify the protein and mRNA expression of NIBP and other neuronal markers. Multi-labeled immunofluorescent microscopy and confocal image analysis were used to examine the cellular distribution of NIBP-like immunoreactivity (IR) in whole mount intestine. Enteric neuronal cell line (ENC) was infected with lentivirus carrying NIBP or its shRNA expression vectors and treated with vehicle or tumor necrosis factor (TNF)α.

KEY RESULTS

NIBP is expressed at both mRNA and protein levels in different regions and layers of the mouse intestine. NIBP-like-IR was co-localized with various neuronal markers, but not with glial, smooth muscular, or interstitial cells of Cajal markers. A small population of NIBP-expressing cells and fibers in extra-ganglionic and intra-ganglionic area were negative for pan-neuronal markers HuD or Peripherin. Relatively high NIBP-like-IR was found in 35-44% of myenteric neurons and 9-10% of submucosal neurons. Approximately 98%, 87%, and 43% of these relatively high NIBP-expressing neurons were positive for choline acetyltransferase, neuronal nitric oxide synthase and Calretinin, respectively. NIBP shRNA knockdown in ENC inhibited TNFα-induced NFκB activation and neuronal differentiation, whereas NIBP overexpression promoted it.

CONCLUSIONS & INFERENCES

NIBP is extensively expressed in the ENS with relatively high level in a subpopulation of enteric neurons. Various NIBP expression levels in different neurons may represent dynamic trafficking or posttranslational modification of NIBP in some functionally active neurons and ultimately regulate ENS plasticity.

Enhanced excitability of guinea pig ileum myenteric AH neurons during and following recovery from chemical colitis

Inflammation of the colon changes motor function of more proximal regions of the gastrointestinal tract. Colitis alters the neurophysiology of enteric neurons within the region of inflammation, which may contribute to altered colonic motor and secretory function. This study seeks to test the hypothesis that colitis alters the neurophysiology of myenteric neurons in the non-inflamed ileum, and that altered neurophysiology coincides with altered small bowel motor function. Trinitrobenzene sulfonic acid (TNBS)-induced colitis was associated with hyperexcitability of AH neurons in the ileum myenteric plexus, demonstrated by depolarized neurons and increased numbers of action potentials, but without changes in the action potential duration or afterhyperpolarization typical of plasticity in these cells. There were no changes in synaptic transmission of either AH neurons or S neurons observed in the current study. The onset of AH neuron hyperexcitability occurred 24 h following administration of TNBS, and persisted to eight weeks, a time point following the resolution of colitis. Small bowel transit was reduced as early as 12 h after TNBS and resolved by 48 h after TNBS. While AH neurons play a central role in coordinating motor function of the ileum, changes in excitability of these neurons did not coincide with changes in small bowel transit.

Submucous rather than myenteric neurons are activated by mucosal biopsy supernatants from irritable bowel syndrome patients

BACKGROUND

We previously showed that colonic mucosal biopsy supernatants from patients with irritable bowel syndrome (IBS) activate neurons of the human submucous plexus, an area with densely packed immune cells. Based on the concept that mucosa-nerve signaling is altered in IBS, we tested in this study whether the nerve sensitizing effect of IBS mucosal biopsy supernatants is more prominent in the submucous than myenteric plexus.

METHODS

Fast neuroimaging with the voltage-sensitive dye Di-8-ANEPPS was used to record activity of guinea-pig submucous and myenteric neurons after application of constipation (C)- and diarrhea (D)-IBS supernatants (three each) and four supernatants from healthy control subjects. Results are based on recordings from 4731 neurons.

KEY RESULTS

Control supernatants did not evoke significant responses in submucous or myenteric neurons. In contrast, all IBS supernatants evoked a significant spike discharge (median 3.6 Hz) in 46% of submucous neurons. This activation was significantly stronger than in the myenteric plexus where even twice the amount of supernatants evoked a lower spike frequency (median 2.1Hz) in only 8.5% of neurons. Pharmacological studies revealed serotonin, histamine, and proteases as components mediating neuronal activation. Individual application of these components revealed that only serotonin evoked a significantly stronger activation of submucous compared with myenteric neurons.

CONCLUSIONS & INFERENCES

Direct neuronal activation by IBS mucosal biopsy supernatants is primarily a feature of submucous rather than myenteric neurons. This is associated with a stronger excitation of submucous neurons by serotonin. The plexus-specific effects support the concept that altered mucosa-nerve signaling underlies disturbances in IBS.

Cytokines and irritable bowel syndrome: where do we stand?

Irritable bowel syndrome (IBS) is a functional gastrointestinal disorder, which presents with one or more gastrointestinal symptoms without any structural or organic abnormality. The etiology and pathophysiological mechanisms of IBS remain uncertain. Residual or reactivated inflammation at the molecular level is considered the underlying mechanism of post-infectious IBS. On the other hand, genetic variations in the immunological components of the body, including cytokine gene polymorphisms, are proposed as a potential mechanism of IBS even in patients without previous gastrointestinal infection. Several studies have suggested imbalanced cytokine signaling as an etiology for IBS. In this review, recent findings on cytokine profiles and cytokine gene polymorphisms in patients with IBS are described and the role of cytokines in animal models of IBS is discussed.

Colonic soluble mediators from the maternal separation model of irritable bowel syndrome activate submucosal neurons via an interleukin-6-dependent mechanism

Irritable bowel syndrome (IBS) is characterized by episodic bouts of abdominal pain, bloating, and altered bowel habit. Accumulating evidence has linked immune activation with IBS, including reports of increases in circulating levels of the proinflammatory cytokine interleukin (IL)-6. However, it is unknown whether IL-6 contributes directly to disease manifestation. As enteric nervous activity mediates motility and secretory function, the aims of this study were to determine the effects of IL-6 on submucosal neurons and related gastrointestinal (GI) function. In these studies, we examined the colons of maternally separated (MS) rats, which exhibit elevated circulating levels of IL-6 in addition to GI dysfunction. To our knowledge, these studies are the first to provide evidence of the sensitivity of submucosal neurons to colonic secretions from MS rats (n = 50, P < 0.05), thus recapitulating clinical biopsy data. Moreover, we demonstrated that the excitatory action is IL-6 dependent. Thereafter, the impact of IL-6 on neuronal and glial activation and absorpto/secretory function was pharmacologically characterized. Other proinflammatory cytokines including IL-8 (n = 30, P > 0.05), IL-1β (n = 56, P > 0.05), and TNF-α (n = 56, P > 0.05) excited fewer neurons. Both muscarinic and nicotinic cholinergic receptors participate in the effect and cause downstream activation of ERK, JAK-STAT, and NF-κB signaling cascades. Functionally, IL-6 increases transepithelial resistance and enhances neurally and cholinergically mediated ion transport. These data provide a role for IL-6 in colonic secretory functions and relate these effects to GI dysfunction in an animal model of IBS, thereby elucidating a potential relationship between circulating levels of IL-6 and aberrant GI function.

Prolonged IL-1beta exposure alters neurotransmitter and electrically induced Ca(2+) responses in the myenteric plexus

BACKGROUND Infection and inflammatory diseases of the gut results in profound changes of intestinal motor function. Acute administration of the pro-inflammatory cytokine interleukin-1beta (IL-1beta) was shown to have excitatory and neuromodulatory roles in the myenteric plexus. Here we aimed to study the effect of prolonged IL-1beta incubation on the response of myenteric neurones to different stimuli. METHODS Longitudinal muscle myenteric plexus preparations (LMMP's) of the guinea pig jejunum were incubated for 24 h in medium with or without IL-1beta. After loading with Fluo-4, calcium imaging was used to visualize activation of neurones. The response to application of serotonin (5-HT), substance P (SP) and ATP or to electrical fibre tract stimulation (eFTS) was tested. Expression of nNOS, HuD, calbindin and calretinin was compared by immunohistochemistry. KEY RESULTS IL-1beta concentration-dependently influenced the neuronal responsiveness and duration of the [Ca(2+)](i) rises to 5-HT and ATP, while it also affected the Ca(2+)-transient amplitudes induced by 5-HT, ATP and SP. Ca(2+)-transients in response to eFTS were observed in significantly more neurones per ganglion after IL-1beta (10(-10) and 10(-11) mol L(-1)). Peak [Ca(2+)](i) rise after eFTS was concentration-dependently decreased by IL-1beta. The duration of the [Ca(2+)](i) rise after eFTS was prolonged after IL-1beta 10(-12) mol L(-1). IL-1beta (10(-9) mol L(-1)) incubation did not affect the number of nNOS, calretinin and calbindin expressing neurones, nor did it induce neuronal loss (HuD). CONCLUSIONS & INFERENCES In this study, IL-1beta differentially modulates the neuronal response to eFTS and neurotransmitter application in the myenteric plexus of guinea pigs. This cytokine could be implicated in the motility disturbances observed during gastrointestinal inflammation.

Plasticity and neural stem cells in the enteric nervous system

The enteric nervous system (ENS) is a highly organized part of the autonomic nervous system, which innervates the whole gastrointestinal tract by several interconnected neuronal networks. The ENS changes during development and keeps throughout its lifespan a significant capacity to adapt to microenvironmental influences, be it in inflammatory bowel diseases or changing dietary habits. The presence of neural stem cells in the pre-, postnatal, and adult gut might be one of the prerequisites to adapt to changing conditions. During the last decade, the ENS has increasingly come into the focus of clinical neural stem cell research, forming a considerable pool of neural crest derived stem cells, which could be used for cell therapy of dysganglionosis, that is, diseases based on the deficient or insufficient colonization of the gut by neural crest derived stem cells; in addition, the ENS could be an easily accessible neural stem cell source for cell replacement therapies for neurodegenerative disorders or traumatic lesions of the central nervous system.

Lipopolysaccharides enhance the action of bradykinin in enteric neurons via secretion of interleukin-1beta from enteric glial cells

Functional changes of the enteric nervous system have been observed under inflammatory states of inflammatory bowel disease increasing the endotoxin level. The aim of the present study was to determine the effect of lipopolysaccharides (LPS) on myenteric neuron-glia interaction in vitro. We examined the increase of the intracellular Ca(2+) concentration ([Ca(2+)](i)) and the release of interleukin-1beta (IL-1beta) or prostaglandin E(2) (PGE(2)) and COX-2 expression in myenteric plexus cells from the rat intestine induced by LPS. LPS potentiated BK-induced [Ca(2+)](i) increases in both myenteric neurons and enteric glial cells, which were suppressed by a B1R antagonist. Only in enteric glial cells, a B1R agonist increased [Ca(2+)](i). The effects of LPS were blocked by pretreatment with an interleukin-1 receptor antagonist or by reducing the density of enteric glial cells in culture. LPS prompted the release of IL-1beta from enteric glial cells. The augmenting effects of IL-1beta on the BK-induced neural [Ca(2+)](i) increase and PGE(2) release from enteric glial cells were abolished by a phospholipase A(2) (PLA(2)) inhibitor and a COX inhibitor, and partly suppressed by a COX-2 inhibitor. IL-1beta up-regulated the COX-2 expression in enteric glial cells. LPS promotes IL-1beta secretion from enteric glial cells, resulting in augmentation of the neural response to BK through PGE(2) release via glial PLA(2) and COX-2. The alteration of the regulatory effect of glial cells may be the cause of the changes in neural function in the enteric nervous system in inflammatory bowel disease.

Voltage-gated delayed rectifier K v 1-subunits may serve as distinctive markers for enteroglial cells with different phenotypes in the murine ileum

Due to entangled results concerning K(v)1 subunit distribution in the gastrointestinal wall, we aimed to unravel the expression of the delayed rectifier potassium subunits K(v)1.1 and K(v)1.2 in the murine ileum. Presence and distribution of both subunits were determined in cryosections and whole-mount preparations of the ileum of three different murine strains by indirect immunofluorescence, and analysed by conventional fluorescence and confocal microscopy. Distribution of both subunits was similar in the ileum of the three strains. K(v)1.1 immunoreactivity (IR) was found in some S100-expressing enteroglial cells (EGC) located at the periphery of myenteric ganglia, in S100-positive EGC along interganglionic, intramuscular and vascular nerve fibres, and in S100-positive EGC of the submucous plexus. K(v)1.1 IR was also observed in some GFAP-expressing EGC at the periphery of myenteric ganglia, and in GFAP-positive EGC of submucous ganglia. K(v)1.2 IR was detected in some intramuscular S100-positive EGC, in almost all submucous S100-expressing EGC, and in a few GFAP-expressing EGC. K(v)1.2 IR was also expressed in a majority of enteric neurons. Coding of these neurons showed that all cholinergic and most nitrergic neurons express K(v)1.2. In conclusion, the results showed that K(v)1.1 and K(v)1.2 were predominantly expressed in distinct EGC phenotypes. K(v)1.2 was also observed in distinct neuron subpopulations. Our results support the active role of EGC with distinct phenotypes in intestinal functions, which is relevant in view of their modulating role on intestinal barrier and inflammatory responses.

Intestinal cytokine response of commercial source broiler chicks to Salmonella typhimurium infection

Development of molecular-based immunotherapeutic strategies for controlling Salmonella Typhimurium (ST) infection in poultry requires a better understanding of intestinal and cecal cytokine responses. Accordingly, an experiment was conducted to measure changes in intestinal cytokine expression when commercial source broiler chickens were challenged with a nalidixic acid-resistant ST. Ross broiler chicks were nonchallenged with ST (control treatment) or challenged by orally giving 7.8 x 10(6) cfu at 4 d of age (STC treatment). Each treatment consisted of 4 replicate pens with 14 chicks per pen. Expression levels of proinflammatory cytokines, interferon-gamma, and antiinflammatory interleukin (IL)-10 were determined at 5 and 10 d postchallenge (PC). Intestinal flushes were also collected from each treatment at 7 d PC to estimate IgA and IgG. Results showed an upregulation in IL-1beta mRNA in STC chicks at 5 d PC. By 10 d PC, the expression of IL-1beta was further increased and accompanied by an upregulation of IL-6 and interferon-gamma mRNA, whereas IL-10 mRNA expression decreased. It was concluded that ST induced an intestinal mucosal inflammatory response in commercial source broiler chicks less than 2 wk of age.

Cannabinoid CB2 receptors in the enteric nervous system modulate gastrointestinal contractility in lipopolysaccharide-treated rats

Enhanced intestinal transit due to lipopolysaccharide (LPS) is reversed by cannabinoid (CB)2 receptor agonists in vivo, but the site and mechanism of action are unknown. We have tested the hypothesis that CB2 receptors are expressed in the enteric nervous system and are activated in pathophysiological conditions. Tissues from either saline- or LPS-treated (2 h; 65 microg/kg ip) rats were processed for RT-PCR, Western blotting, and immunohistochemistry or were mounted in organ baths where electrical field stimulation was applied in the presence or absence of CB receptor agonists. Whereas the CB2 receptor agonist JWH133 did not affect the electrically evoked twitch response of the ileum under basal conditions, in the LPS-treated tissues JWH133 was able to reduce the enhanced contractile response in a concentration-dependent manner. Rat ileum expressed CB2 receptor mRNA and protein under physiological conditions, and this expression was not affected by LPS treatment. In the myenteric plexus, CB2 receptors were expressed on the majority of neurons, although not on those expressing nitric oxide synthase. LPS did not alter the distribution of CB2 receptor expression in the myenteric plexus. In vivo LPS treatment significantly increased Fos expression in both enteric glia and neurons. This enhanced expression was significantly attenuated by JWH133, whose action was reversed by the CB2 receptor antagonist AM630. Taking these facts together, we conclude that activation of CB2 receptors in the enteric nervous system of the gastrointestinal tract dampens endotoxin-induced enhanced intestinal contractility.

Neuro-immune interactions in inflammatory bowel disease and irritable bowel syndrome: future therapeutic targets

The gastro-intestinal tract is well known for its largest neural network outside the central nervous system and for the most extensive immune system in the body. Research in neurogastroenterology implicates the involvement of both enteric nervous system and immune system in symptoms of inflammatory bowel disease and irritable bowel syndrome. Since both disorders are associated with increased immune cell numbers, nerve growth and activation of both immune cells and nerves, we focus in this review on the involvement of immune cell-nerve interactions in inflammatory bowel disease and irritable bowel syndrome. Firstly, the possible effects of enteric nerves, especially of the nonadrenergic and noncholinergic nerves, on the intestinal immune system and their possible role in the pathogenesis of chronic intestinal inflammatory diseases are described. Secondly, the possible effects of immunological factors, from the innate (chemokines and Toll-like receptors) as well as the adaptive (cytokines and immunoglobulins) immune system, on gastro-intestinal nerves and its potential role in the development of inflammatory bowel disease and irritable bowel syndrome are reviewed. Investigations of receptor-mediated and intracellular signal pathways in neuro-immune interactions might help to develop more effective therapeutic approaches for chronic inflammatory intestinal diseases.

Mycobacterium avium subspecies paratuberculosis infects and multiplies in enteric glial cells

AIM: To establish the role of enteric glial cells during infection with Mycobacterium avium subspecies paratuberculosis (MAP) in Crohn’s disease.

METHODS: In order to establish the role of enteric glial cells during infection with M. avium subspecies paratuberculosis (MAP) in Crohn’s disease, Map adhesion experiments on enteric glial cells were performed as well as expression analysis of Map sigma factors during infection.

RESULTS: In this study, for the first time, we found a high affinity of MAP to enteric glial cells and we analyzed the expression of MAP sigma factors under different conditions of growth.

CONCLUSION: The fact that Map showed a high affinity to the glial cells raises concerns about the complicated etiology of the Crohn’s disease. Elucidation of the mechanisms whereby inflammation alters enteric neural control of gut functions may lead to novel treatments for Crohn’s disease.

Enteric glial cells and their role in gastrointestinal motor abnormalities: Introducing the neuro-gliopathies

The role of enteric glial cells has somewhat changed from that of mere mechanical support elements, gluing together the various components of the enteric nervous system, to that of active participants in the complex interrelationships of the gut motor and inflammatory events. Due to their multiple functions, spanning from supporting elements in the myenteric plexuses to neurotransmitters, to neuronal homeostasis, to antigen presenting cells, this cell population has probably more intriguing abilities than previously thought. Recently, some evidence has been accumulating that shows how these cells may be involved in the pathophysiological aspects of some diseases. This review will deal with the properties of the enteric glial cells more strictly related to gastrointestinal motor function and the human pathological conditions in which these cells may play a role, suggesting the possibility of enteric neuro-gliopathies.

A susceptibility gene set for early onset colorectal cancer that integrates diverse signaling pathways: implication for tumorigenesis

PURPOSE

The causative genes for autosomal dominantly inherited familial adenomatous polyposis (FAP) and hereditary nonpolyposis colorectal cancer have been well characterized. There is, however, another 10% to 15% of early onset colorectal cancers (CRC) in which the genetic components are unclear. In this study, we used microarray technology to systematically search for differentially expressed genes in early onset CRC.

EXPERIMENTAL DESIGN

Young patients with non-FAP or non-hereditary nonpolyposis colorectal cancer, and healthy controls were age- (<or=50 years old), ethnicity- (Chinese), and tissue-matched. RNAs extracted from colonic mucosa specimens were analyzed using GeneChip U133-Plus 2.0 Array.

RESULTS

Seven genes, CYR61, UCHL1, FOS, FOS B, EGR1, VIP, and KRT24, were consistently up-regulated in the mucosa of all six patients compared with the mucosa from four healthy controls. The overexpression of these genes was independently validated with a testing set of six patients and six healthy controls. Principal component analysis clustered the healthy control specimens separately from the patient specimens. Real-time PCR quantification with SYBR-Green on nine other patient specimens not previously used in microarray assays confirmed the up-regulation of these seven genes. These genes function in a multitude of biological processes ranging from transcription, angiogenesis, adhesion, and inflammatory regulation to protein catabolism in various cellular compartments, from extracellular to the nucleus. They integrate known tumorigenesis (Wnt, PI3K, MAP kinase, hypoxia, G protein-coupled receptor), neurologic, insulin-signaling, and NFAT-immune pathways into an intricate biological network.

CONCLUSIONS

The data suggest that the patient's mucosa is primed for tumorigenesis when cellular homeostasis is disrupted, and that the seven overexpressed genes could potentially predict early onset CRC.

Enteric neural pathways mediate the anti-inflammatory actions of glucagon-like peptide 2

Glucagon-like peptide-2 (GLP-2) is an important regulator of nutritional absorptive capacity with anti-inflammatory actions. We hypothesized that GLP-2 reduces intestinal mucosal inflammation by activation of vasoactive intestinal polypeptide (VIP) neurons of the submucosal plexus. Ileitis or colitis was induced in rats by injection of trinitrobenzene sulfonic acid (TNBS), or colitis was induced by administration of dextran sodium sulfate (DSS) in drinking water. Subsets of animals received (1-33)-GLP-2 (50 mug/kg sc bid) either immediately or 2 days after the establishment of inflammation and were followed for 3-5 days. The involvement of VIP neurons was assessed by concomitant administration of GLP-2 and the VIP antagonist [Lys(1)-Pro(2,5)-Arg(3,4)-Tyr(6)]VIP and by immunohistochemical labeling of GLP-2-activated neurons. In all models, GLP-2 treatment, whether given immediately or delayed until inflammation was established, resulted in significant improvements in animal weights, mucosal inflammation indices (myeloperoxidase levels, histological mucosal scores), and reduced levels of inflammatory cytokines (IFN-gamma, TNF-alpha, IL-1beta) and inducible nitric oxide synthase, with increased levels of IL-10 in TNBS ileitis and DSS colitis. Reduced rates of crypt cell proliferation and of apoptosis within crypts in inflamed tissues were also noted with GLP-2 treatment. These effects were abolished with coadministration of GLP-2 and the VIP antagonist. GLP-2 was shown to activate neurons and to increase the number of cells expressing VIP in the submucosal plexus of the ileum. These findings suggest that GLP-2 acts as an anti-inflammatory agent through activation of enteric VIP neurons, independent of proliferative effects. They support further studies to examine the role of neural signaling in the regulation of intestinal inflammation.

Expression of a functional metabotropic glutamate receptor 5 on enteric glia is altered in states of inflammation

The metabotropic glutamate receptor 5 (mGluR5) is expressed by astrocytes and its expression is modulated by inflammation. Enteric glia have many similarities to astrocytes and are the most numerous cell in the enteric nervous system (ENS). We investigated whether enteric glia express a functional mGluR5 and whether expression of this receptor was altered in colitis. In both enteric plexuses of the ileum and colon of guinea pigs and mice, we observed widespread glial mGluR5 expression. Incubation of isolated segments of the guinea pig ileum with the mGluR5 specific agonist RS-2-chloro-5-hydroxyphenylglycine (CHPG) caused a dose-dependent increase in the glial expression of c-Fos and the phosphorylated form of the extracellular signal-regulated kinase 1/2. Preincubation of tissues with the group I metabotropic glutamate receptor antagonist, S-4-carboxyphenylglycine, abolished the effects of CHPG. We examined mGluR5 expression in the guinea pig trinitrobenzene sulfonic acid and the IL-10 gene-deficient (IL-10(-/-)) mouse models of colitis. In guinea pigs, mGluR5 immunoreactivity became diffusely localized over the colonic myenteric ganglia, suggesting a change in receptor distribution. In contrast, glial mGluR5 expression was significantly reduced in the colonic myenteric plexus of IL-10(-/-) mice, as assessed with both real-time quantitative RT-PCR as well as immunohistochemistry and image analysis. These changes occurred without concomitant changes to enteric ganglia or glial fibrillary acidic protein expression in the IL-10(-/-) mouse. Our data suggest that enteric glia are a functional target of the glutamatergic neurotransmitter system in the ENS and that changes in mGluR5 expression may be of physiological significance during colitis.

Water avoidance stress activates colonic myenteric neurons in female rats

Stress stimulates colonic motor function and plays a role in functional bowel disorders, prevalently in women. We examined, in conscious female rats, the influence of water avoidance stress for 60 min on colonic myenteric neuron activity using immunohistochemical detection of Fos as a marker of neuronal activity. In control rats, Fos immunoreactive nuclei were rare in proximal and distal colon and no defecation was observed. Water avoidance stimulated fecal pellet output, which was associated with Fos expression in myenteric ganglia of proximal and distal colon including in a population of peripheral choline acetyltransferase-immunoreactive neurons. Atropine blocked fecal pellet output but not Fos expression in myenteric ganglia. These results indicate that psychological stress stimulates the activity of colonic cholinergic myenteric neurons.

The autonomic nervous system and inflammatory bowel disease

Crohn's disease and ulcerative colitis, collectively known as inflammatory bowel disease (IBD), are chronic, recurring, inflammatory conditions of the intestine. The precise mechanisms underlying the pathogenesis of IBD are not yet clear but they are believed to involve a number of precipitating factors, most notably genetic susceptibility and environmental influences. The autonomic nervous system (ANS) has long been known as a critical regulator of intestinal function and much evidence now exists to suggest that it also plays an important role in the development of IBD. Dramatic changes in the ANS in IBD are apparent from the cellular to the molecular level ultimately leading to altered communication between the ANS and effector cells of the intestine. This review aims to synthesize the current understanding of the pathogenesis of IBD with a particular emphasis on the role that the ANS plays in the progression of these diseases.

5-Hydroxytryptophan activates colonic myenteric neurons and propulsive motor function through 5-HT4 receptors in conscious mice

Serotonin [5-hydroxytryptamine (5-HT)] acts as a modulator of colonic motility and secretion. We characterized the action of the 5-HT precursor 5-hydroxytryptophan (5-HTP) on colonic myenteric neurons and propulsive motor activity in conscious mice. Fos immunoreactivity (IR), used as a marker of neuronal activation, was monitored in longitudinal muscle/myenteric plexus whole mount preparations of the distal colon 90 min after an intraperitoneal injection of 5-HTP. Double staining of Fos IR with peripheral choline acetyltransferase (pChAT) IR or NADPH-diaphorase activity was performed. The injection of 5-HTP (0.5, 1, 5, or 10 mg/kg ip) increased fecal pellet output and fluid content in a dose-related manner, with a peak response observed within the first 15 min postinjection. 5-HTP (0.5-10 mg/kg) dose dependently increased Fos expression in myenteric neurons, with a maximal response of 9.9 +/- 1.0 cells/ganglion [P < 0.05 vs. vehicle-treated mice (2.3 +/- 0.6 cells/ganglion)]. There was a positive correlation between Fos expression and fecal output. Of Fos-positive ganglionic cells, 40 +/- 4% were also pChAT positive and 21 +/- 5% were NADPH-diaphorase positive in response to 5-HTP, respectively. 5-HTP-induced defecation and Fos expression were completely prevented by pretreatment with the selective 5-HT4 antagonist RS-39604. These results show that 5-HTP injected peripherally increases Fos expression in different populations of cholinergic and nitrergic myenteric neurons in the distal colon and stimulates propulsive colonic motor function through 5-HT4 receptors in conscious mice. These findings suggest an important role of activation of colonic myenteric neurons in the 5-HT4 receptor-mediated colonic propulsive motor response.

Role of enteric glia in intestinal physiology: effects of the gliotoxin fluorocitrate on motor and secretory function

The role of enteric glia in gastrointestinal physiology remains largely unexplored. We examined the actions of the gliotoxin fluorocitrate (FC) on intestinal motility, secretion, and inflammation after assessing its efficacy and specificity in vitro. FC (100 microM) caused a significant decrease in the phosphorylation of the glucose analog 2-[N-(7-nitrobenz-2-oxa-1,3-diaz-4-yl)amino]-2-deoxyglucose in enteric glial cultures and a reduction in glial uptake of the fluorescent dipeptide Ala-Lys-7-amino-4-methylcoumarin-3-acetic acid in both the ileum and colon. Dipeptide uptake by resident murine macrophages or guinea pig myenteric neurons was unaffected by FC. Incubation of isolated guinea pig ileal segments with FC caused a specific and significant increase in glial expression of the phosphorylated form of ERK-1/2. Disruption of enteric glial function with FC in mice reduced small intestinal motility in vitro, including a significant decrease in basal tone and the amplitude of contractility in response to electrical field stimulation. Mice treated with 10 or 20 micromol/kg FC twice daily for 7 days demonstrated a concentration-dependent decrease in small intestinal transit. In contrast, no changes in colonic transit or ion transport in vitro were observed. There were no changes in glial or neuronal morphology, any signs of inflammation in the FC-treated mice, or any change in the number of myenteric nitric oxide synthase-expressing neurons. We conclude that FC treatment causes enteric glial dysfunction, without causing intestinal inflammation. Our data suggest that enteric glia are involved in the modulation of enteric neural circuits underlying the regulation of intestinal motility.

Localized colonic inflammation increases cytokine levels in distant small intestinal segments in the rat

Local inflammation in the colon has been associated with nutrient malabsorption and altered motility in the small bowel. These remote effects suggest the release of mediators which can act (or alter) the function of intestinal segments located far from the primary area of inflammation. This study describes the changes in the expression of pro-inflammatory cytokines in the colon and in various segments of the small intestine in two rat models of experimental colitis. Colitis was induced by the intracolonic administration of 100 microL of 6% iodoacetamide or 250 microL of 2, 4, 6-trinitrobenzene sulfonic acid. Levels of interleukin one beta, interleukin 6, and tumor necrosis factor alpha were measured by ELISA in tissue homogenate sampled from duodenum, jejunum, ileum and colon at different time intervals. In homogenates of strips isolated from duodenum, jejunum and ileum, tumor necrosis alpha and interleukin-6, increased significantly 3-6 h after iodoacetamide or TNBS administration and remained elevated until the colonic inflammation subsided. Interleukin one beta showed comparable but delayed increase. Similar, but more pronounced increase of the three cytokines was noticed in areas of the colon adjacent to the ulcer. Histologic examinations revealed important inflammatory changes in the colon; however, examination of sections from the small intestines did not reveal significant differences between controls and rats with colitis. In conclusion, expression of pro-inflammatory cytokines is increased in remote segments of the small intestines during colitis. The findings may provide a partial explanation or a molecular substrate for the associated small bowel dysfunction.

Distribution of adrenergic receptors in the enteric nervous system of the guinea pig, mouse, and rat

Adrenergic receptors in the enteric nervous system (ENS) are important in control of the gastrointestinal tract. Here we describe the distribution of adrenergic receptors in the ENS of the ileum and colon of the guinea pig, rat, and mouse by using single- and double-labelling immunohistochemistry. In the myenteric plexus (MP) of the rat and mouse, alpha2a-adrenergic receptors (alpha2a-AR) were widely distributed on neurons and enteric glial cells. alpha2a-AR mainly colocalized with calretinin in the MP, whereas submucosal alpha2a-AR neurons colocalized with vasoactive intestinal polypeptide (VIP), neuropeptide Y, and calretinin in both species. In the guinea pig ileum, we observed widespread alpha2a-AR immunoreactivity on nerve fibers in the MP and on VIP neurons in the submucosal plexus (SMP). We observed extensive beta1-adrenergic receptor (beta1-AR) expression on neurons and nerve fibers in both the MP and the SMP of all species. Similarly, the beta2-adrenergic receptor (beta2-AR) was expressed on neurons and nerve fibers in the SMP of all species, as well as in the MP of the mouse. In the MP, beta1- and beta2-AR immunoreactivity was localized to several neuronal populations, including calretinin and nitrergic neurons. In the SMP of the guinea pig, beta1- and beta2-AR mainly colocalized with VIP, whereas, in the rat and mouse, beta1- and beta2-AR were distributed among the VIP and calretinin populations. Adrenergic receptors were widely localized on specific neuronal populations in all species studied. The role of glial alpha2a-AR is unknown. These results suggest that sympathetic innervation of the ENS is directed toward both enteric neurons and enteric glia.

The distribution of PKC isoforms in enteric neurons, muscle and interstitial cells of the human intestine

In many organs, different protein kinase C (PKC) isoforms are expressed in specific cell types, suggesting that the different PKCs have cell-specific roles, and also that drugs acting on a particular PKC may have effects on the whole organ that are distinguishable from drugs that target other isoforms. Previous studies of the guinea-pig and mouse intestine indicate that there are cell-specific expressions of PKC isoforms in neurons, muscle and the interstitial cells of Cajal. In the present study we have investigated the expression of different PKCs in human intestine. Immunohistochemical studies showed that the forms that are prominent in human enteric neurons are PKCs gamma and epsilon and in muscle the dominant form is PKCdelta. Neurons were weakly stained for PKCbetaI. These observations parallel findings in guinea-pig and mouse, except that in human PKCgamma-IR was not present in the same types of neurons that express it in the guinea-pig. Enteric glial cells were strongly immunoreactive for PKCalpha, which is also the major isoform in enteric glial cells of guinea-pig. In human and guinea-pig, glial cells also express PKCbetaI. Spindle-shaped cells in the mucosa were immunoreactive for PKCalpha and PKCgamma and in the muscle layers similar cells had PKCgamma-IR and PKCtheta-IR. The spindle-shaped cells were similar in morphology to interstitial cells of Cajal. Western analysis and RT-PCR confirmed the presence of the PKC isoform proteins and mRNA in the tissue. We conclude that there is cell-type specific expression of different PKCs in enteric neurons and intestinal muscle in human tissue, and that there are strong similarities in patterns of expression between laboratory animals and human, but some clear differences are also observed.

Human mucosa/submucosa interactions during intestinal inflammation: involvement of the enteric nervous system in interleukin-8 secretion

Interleukin-8 (IL-8) is a key chemokine upregulated in various forms of intestinal inflammation, especially those induced by bacteria such as Clostridium difficile (C. difficile). Although interactions between different mucosal and submucosal cellular components have been reported, whether such interactions are involved in the regulation of IL-8 secretion during C. difficile infection is unknown. Moreover, whether the enteric nervous system, a major component of the submucosa, is involved in IL-8 secretion during an inflammatory challenge remains to be determined. In order to investigate mucosa/submucosa interactions that regulate IL-8 secretion, we co-cultured human intestinal mucosa and submucosa. In control condition, IL-8 secretion in co-culture was lower than the sum of the IL-8 secretion of both tissue layers cultured alone. Contrastingly, IL-8 secretion increased in co-culture after mucosal challenge with toxin B of C. difficile through an IL-1 beta-dependent pathway. Moreover, we observed that toxin B of C. difficile increased IL-8 immunoreactivity in submucosal enteric neurones in co-culture and in intact preparations of mucosa/submucosa, through an IL-1 beta-dependent pathway. IL-1 beta also increased IL-8 secretion and IL-8 mRNA expression in human neuronal cell lines (NT2-N and SH-SY5Y), through p38 and ERK1/2 MAP kinase-dependent pathways. Our results demonstrate that mucosa/submucosa interactions regulate IL-8 secretion during inflammatory processes in human through IL-1 beta-dependent pathways. Finally we observed that human submucosal neurones synthesize IL-8, whose production in neurones is induced by IL-1 beta via MAPK-dependent pathways.

Glial cells in the gut

The enteric nervous system is composed of both neurons and glia. Recent evidence indicates that enteric glia-which vastly outnumber enteric neurons-are actively involved in the control of gastrointestinal functions: they contain neurotransmitter precursors, have the machinery for uptake and degradation of neuroligands, and express neurotransmitter-receptors which makes them well suited as intermediaries in enteric neurotransmission and information processing in the ENS. Novel data further suggest that enteric glia have an important role in maintaining the integrity of the mucosal barrier of the gut. Finally, enteric glia may also serve as a link between the nervous and immune systems of the gut as indicated by their potential to synthesize cytokines, present antigen and respond to inflammatory insults. The role of enteric glia in human disease has not yet been systematically studied, but based on the available evidence it is predictable that enteric glia are involved in the etiopathogenesis of various pathological processes in the gut, particularly such with neuroinflammatory or neurodegenerative components.

Enteric glia

The enteric nervous system is composed of both enteric neurones and enteric glia. Enteric glial cells were first described by Dogiel and are now known to outnumber neurones approximately 4 : 1. In the past, these cells were assumed to subserve a largely supportive role; however, recent evidence indicates that enteric glial cells may play a more active role in the control of gut function. In transgenic mouse models, where enteric glial cells are selectively ablated, the loss of glia results in intestinal inflammation and disruption of the epithelial barrier. Enteric glia are activated specifically by inflammatory insults and may contribute actively to inflammatory pathology via antigen presentation and cytokine synthesis. Enteric glia also express receptors for neurotransmitters and so may serve as intermediaries in enteric neurotransmission. Thus, enteric glia may serve as a link between the nervous and immune systems of the gut and may also have an important role in maintaining the integrity of the mucosal barrier and in other aspects of intestinal homeostasis.