Plasticity of enteric nerve functions in the inflamed and postinflamed gut

Gut microbiota and sirtuins in obesity-related inflammation and bowel dysfunction

Obesity is a chronic disease characterized by persistent low-grade inflammation with alterations in gut motility. Motor abnormalities suggest that obesity has effects on the enteric nervous system (ENS), which controls virtually all gut functions. Recent studies have revealed that the gut microbiota can affect obesity and increase inflammatory tone by modulating mucosal barrier function. Furthermore, the observation that inflammatory conditions influence the excitability of enteric neurons may add to the gut dysfunction in obesity. In this article, we discuss recent advances in understanding the role of gut microbiota and inflammation in the pathogenesis of obesity and obesity-related gastrointestinal dysfunction. The potential contribution of sirtuins in protecting or regulating the circuitry of the ENS under inflamed states is also considered.

Gut feelings: the emerging biology of gut-brain communication

The concept that the gut and the brain are closely connected, and that this interaction plays an important part not only in gastrointestinal function but also in certain feeling states and in intuitive decision making, is deeply rooted in our language. Recent neurobiological insights into this gut-brain crosstalk have revealed a complex, bidirectional communication system that not only ensures the proper maintenance of gastrointestinal homeostasis and digestion but is likely to have multiple effects on affect, motivation and higher cognitive functions, including intuitive decision making. Moreover, disturbances of this system have been implicated in a wide range of disorders, including functional and inflammatory gastrointestinal disorders, obesity and eating disorders.

Altered expression and secretion of colonic interleukin-6 in a stress-sensitive animal model of brain-gut axis dysfunction

Interleukin-6 (IL-6) can activate gastrointestinal submucosal neurons, with associated implications for motility and secretory function. Patients with irritable bowel syndrome (IBS) have elevated levels of circulating IL-6. Colons from the Wistar Kyoto (WKY) rat model of IBS secrete more IL-6 (12.84 pg/ml) than control Sprague Dawley (SD) colons (5.55 pg/ml) and WKY secretions stimulated calcium responses in naïve submucosal neurons of greater amplitude. Recombinant IL-6 activated more submucosal neurons in WKY tissue preparations (p<0.05). These data demonstrate that WKY colonic supernatants activate submucosal neurons using an IL-6-dependent mechanism, thereby providing a link between gastrointestinal dysfunction and alterations in IL-6 levels.

Evidence of overlapping genetic diathesis of panic attacks and gastrointestinal disorders in a sample of male twin pairs

We explored the comorbidity between panic attacks (PA), whose symptoms can include gastrointestinal discomfort, and gastrointestinal disorders (GD). Structural equation modeling was used to analyze data from 1,874 MZ and 1,498 DZ male-male twin pairs from the Vietnam Era Twin Registry. PA and GD were associated (relative risk for GD = 2). The percentage of liability due to genetic factors was estimated to be 37% for PA and 31% for GD. There was significant correlation between the genetic risk factors for PA and GD (estimated r = .55, 95% CI of 34% to 82%) and no evidence of correlation between the environmental causes of PA and GD. Therefore, PA and GD comorbidity can be explained by overlapping genetic factors and not overlapping environmental factors. Although these data cannot identify a biological pathway for such a shared liability, it suggests the presence of GD may be informative for genetic studies of panic.

The Incidence and gastrointestinal infectious risk of functional gastrointestinal disorders in a healthy US adult population

OBJECTIVES

Functional gastrointestinal disorders (FGDs) are recognized sequelae of infectious gastroenteritis (IGE). Within the active duty military population, a group with known high IGE rates, the population-based incidence, risk factors, and attributable burden of care referable to FGD after IGE are poorly defined.

METHODS

Using electronic medical encounter data (1999-2007) on active duty US military, a matched, case-control study describing the epidemiology and risk determinants of FGD (irritable bowel syndrome (IBS), functional constipation (FC), functional diarrhea (FD), dyspepsia (D)) was conducted. Incidence rates and duration of FGD-related medical care were estimated, and conditional logistic regression was utilized to evaluate FGD risk after IGE.

RESULTS

A total of 31,866 cases of FGD identified were distributed as follows: FC 55% (n=17,538), D 21.2% (n=6,750), FD 2.1% (n=674), IBS 28.5% (n=9,091). Previous IGE episodes were distributed as follows: specific bacterial pathogen (n=65, 1.2%), bacterial, with no pathogen specified (n=2155, 38.9%), protozoal (n=38, 0.7%), viral (n=3431, 61.9%). A significant association between IGE and all FGD (odds ratio (OR) 2.64; P<0.001) was seen, with highest risk for FD (OR 6.28, P<0.001) and IBS (OR 3.72, P<0.001), and moderate risk for FC (2.15, P<0.001) and D (OR 2.39, P<0.001). Risk generally increased with temporal proximity to, and bacterial etiology of, exposure. Duration of FGD-related care was prolonged with 22.7% having FGD-associated medical encounters 5 years after diagnosis.

CONCLUSIONS

FGD are common in this population at high risk for IGE. When considering effective countermeasures and mitigation strategies, attention directed toward prevention as well as the acute and chronic sequelae of these infections is needed.

The effects of glucagon-like peptide 2 on enteric neurons in intestinal inflammation

BACKGROUND

Intestinal inflammation alters the structure and function of the enteric nervous system (ENS). Glucagon-like peptide 2 (GLP-2) reduces intestinal inflammation and has trophic effects on isolated neurons. This study examined the effects of GLP-2 treatment on the submucosal plexus of rat colon in the trinitrobenzene sulfonic acid (TNBS) model of colitis.

METHODS

After administration of TNBS or saline/ethanol for controls, animals were allocated to treatment with GLP-2 (50 μg kg⁻¹ day⁻¹, s.c.) or sham injection of vehicle, twice daily. Animals were monitored, following clinical parameters, and killed on day 5. The number of neuronal cell bodies per ganglion was quantified using immunohistochemistry on submucosal whole mount preparations, with further characterization of specific subpopulations using antibodies against vasoactive intestinal polypeptide (VIP), neuronal nitric oxide synthase (nNOS), and enteric glial cells with glial fibrillary acid protein and S100.

KEY RESULTS

Glucagon-like peptide 2 treatment was associated with a significant amelioration of weight loss, and reduced neutrophil infiltration and microscopic colitis scores in the TNBS animals. Inflammation resulted in a loss of enteric neurons in submucosal ganglia; GLP-2 treatment restored the enteric neuronal populations to normal. In control, non-inflamed animals, GLP-2 treatment increased the number of VIP expressing neurons per ganglion; in TNBS-treated animals, GLP-2 prevented an inflammation-induced reduction in the numbers of VIP expressing neurons per ganglion. Glucagon-like peptide 2 did not change the numbers of nNOS neurons or enteric glial cells in either the control, or inflamed state.

CONCLUSIONS & INFERENCES

These findings show that GLP-2 increased the number of VIP expressing neurons in normal animals, and prevents the inflammation-induced loss of neurons in the colonic submucosal ganglia, with an increase in the proportion of VIP expressing neurons. They suggest that GLP-2 may have a role in protecting or regulating the circuitry of the ENS under basal and inflamed states.

Morphological and functional changes in guinea-pig neurons projecting to the ileal mucosa at early stages after inflammatory damage

In the present study the relationship between tissue damage and changed electro-physiological properties of Dogiel type II myenteric neurons within the first 24 hours after induction of inflammation with trinitrobenzene sulfonate (TNBS) in the guinea-pig ileum was investigated. Treatment with TNBS causes damage to the mucosa, inflammatory responses in the mucosa and enteric ganglia and changes in myenteric neuron properties. Thus we hypothesise that the physiological changes in the myenteric neurons could be due to damage to their mucosal processes or inflammation in the vicinity of cell bodies or the processes. We found an association between hyperexcitability of myenteric Dogiel type II neurons and damage to the mucosa and its innervation at 3 and 24 h, times when there was also an inflammatory reaction. The lack of hyperexcitability in neurons from control tissues in which axons projecting to the mucosa were severed suggests that inflammation may be an important contributing factor to the neuronal hyperexcitability at the acute stage of inflammation. Despite mucosal repair and re-innervation of the mucosa before 7 days after induction of inflammation, neuronal hyperexcitability persists. Although the mechanisms underlying neuronal hyperexcitability at the acute stage of inflammation might be different from those underlying long-term changes in the absence of active inflammation in the ganglia, the persistent changes in neuronal excitability may contribute to post-inflammatory gut dysfunctions.

Ion channel remodeling in gastrointestinal inflammation

BACKGROUND

 Gastrointestinal inflammation significantly affects the electrical excitability of smooth muscle cells. Considerable progress over the last few years have been made to establish the mechanisms by which ion channel function is altered in the setting of gastrointestinal inflammation. Details have begun to emerge on the molecular basis by which ion channel function may be regulated in smooth muscle following inflammation. These include changes in protein and gene expression of the smooth muscle isoform of L-type Ca(2+) channels and ATP-sensitive K(+) channels. Recent attention has also focused on post-translational modifications as a primary means of altering ion channel function in the absence of changes in protein/gene expression. Protein phosphorylation of serine/theronine or tyrosine residues, cysteine thiol modifications, and tyrosine nitration are potential mechanisms affected by oxidative/nitrosative stress that alter the gating kinetics of ion channels. Collectively, these findings suggest that inflammation results in electrical remodeling of smooth muscle cells in addition to structural remodeling.

PURPOSE

The purpose of this review is to synthesize our current understanding regarding molecular mechanisms that result in altered ion channel function during gastrointestinal inflammation and to address potential areas that can lead to targeted new therapies.

Identification of subunits of voltage-gated calcium channels and actions of pregabalin on intrinsic primary afferent neurons in the guinea-pig ileum

BACKGROUND

The intrinsic primary afferent neurons (IPANs) in the intestine are the first neurons of intrinsic reflexes. Action potential currents of IPANs flow partly through calcium channels, which could feasibly be targeted by pregabalin. The aim was to determine whether pregabalin-sensitive α2δ1 subunits associate with calcium channels of IPANs and whether α2δ1 subunit ligands influence IPAN neuronal properties.

METHODS

We used intracellular electrophysiological recording and in situ hybridisation to investigate calcium channel subunit expression in guinea-pig enteric neurons.

KEY RESULTS

The α subunits of N (α1B) and R (α1E) type calcium channels, and the auxiliary α2δ1 subunit, were expressed by IPANs. This is the first discovery of the α2δ1 subunit in enteric neurons; we therefore investigated its functional role, by determining effects of the α2δ1 subunit ligand, pregabalin, that inhibits currents carried by channels incorporating this subunit. Pregabalin (10 μmol L(-1)) reduced the action potential duration. The effect was not increased with increase in concentration to 100 μmol L(-1). If N channels were first blocked by ω-conotoxin GVIA (0.5 μmol L(-1)), pregabalin had no effect on the residual inward calcium current. Reduction of the calcium current by pregabalin substantially inhibited the after-hyperpolarising potential (AHP) and increased neuron excitability.

CONCLUSION & INFERENCES

Intrinsic primary afferent neurons express functional N (α1B) channel-forming subunits that are associated with α2δ1 modulatory subunits and are inhibited by pregabalin, plus functional R (α1E) channels that are not sensitive to binding of pregabalin to α2δ subunits. The positive effects of pregabalin in irritable bowel syndrome (IBS) patients might be partly mediated by its effect on enteric neurons.

The chemical code of porcine enteric neurons and the number of enteric glial cells are altered by dietary probiotics

BACKGROUND

The enteric nervous system (ENS) contains chemically coded populations of neurons that serve specific functions for the control of the gastrointestinal tract. The ability of neurons to modify their chemical code in response to luminal changes has recently been discovered. It is possible that enteric neuronal plasticity may sustain the adaptability of the gut to changes in intestinal activity or injury, and that gut neurons may respond to an altered intestinal environment by changing their neuropeptide expression.

METHODS

We used immunohistochemical methods to investigate the presence and localization of several neuronal populations and enteric glia in both the small (ileum) and large (cecum) intestine of piglets. We assessed their abundance in submucosal and myenteric plexus from animals treated with the probiotic Pediococcus acidilactici compared with untreated controls.

KEY RESULTS

The treated piglets had a larger number of galanin- and calcitonin gene-related peptide (CGRP)-immunoreactive neurons than controls, but this was limited to the submucosal plexus ganglia of the ileum. Moreover, immunohistochemistry revealed that glial fibrillary acidic protein-positive enteric glial cells were significantly higher in the inner and outer submucosal plexuses of treated animals.

CONCLUSIONS & INFERENCES

The neuronal and glial changes described here illustrate plasticity of the ENS in response to an altered luminal environment in the gastrointestinal tract.

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

OBJECTIVE

This paper aimed to investigate the relationship between up-regulation of L-type calcium channels and altered motility disorder in a rat model of irritable bowel syndrome (IBS).

METHODS

Male Sprague-Dawley rats were subjected to neonatal maternal separation (NMS) from postnatal day 2-14 or normal handling (NH), and used when weighted 250-300 g. Colonic smooth muscle contractions was studied in an organ bath system. L-type Ca(2+) channel alpha(1c) subunit expression in smooth muscles from rat colon were studied by immunofluorescence and Western blotting analysis. The intracellular calcium concentration ([Ca(2+)](i)) of enzymatically isolated single colonic smooth muscle cell was studied with laser confocal fluorescent microscopy.

RESULTS

The fecal pellets during 1 h water avoidance stress (WAS) were significantly increased; the amplitude of spontaneous contractions and contractions induced by Bay K 8644 (10 nM-1 microM), KCl (10-60 mM) and ACh (100 nM-10 microM) were significantly increased in NMS rats, when comparing with that of NH rats. [Ca(2+)]i induced by Bay K 8644 (1 microM), KCl (40 mM), and ACh (10 microM) significantly increased in muscle cells of NMS rats than NH rats. Further, alpha(1c) protein expression was significantly up-regulated in colonic smooth muscle of NMS rats than NH rats.

CONCLUSION

These results suggest that NMS lead to up-regulation of L-type Ca(2+) channels expression in the colon, which contributes to the colonic motility disorder. Our findings provide direct evidence to help understanding the underlying mechanism of chronic stress-induced colonic motility disorder in IBS.

Short-chain fatty acids regulate the enteric neurons and control gastrointestinal motility in rats

BACKGROUND & AIMS

Little is known about the environmental and nutritional regulation of the enteric nervous system (ENS), which controls gastrointestinal motility. Short-chain fatty acids (SCFAs) such as butyrate regulate colonic mucosa homeostasis and can modulate neuronal excitability. We investigated their effects on the ENS and colonic motility.

METHODS

Effects of butyrate on the ENS were studied in colons of rats given a resistant starch diet (RSD) or intracecal perfusion of SCFAs. Effects of butyrate were also studied in primary cultures of ENS. The neurochemical phenotype of the ENS was analyzed with antibodies against Hu, choline acetyltransferase (ChAT), and neuronal nitric oxide synthase (nNOS) and by quantitative polymerase chain reaction. Signaling pathways involved were analyzed by pharmacologic and molecular biology methods. Colonic motility was assessed in vivo and ex vivo.

RESULTS

In vivo and in vitro, RSD and butyrate significantly increased the proportion of ChAT- but not nNOS-immunoreactive myenteric neurons. Acetate and propionate did not reproduce the effects of butyrate. Enteric neurons expressed monocarboxylate transporter 2 (MCT2). Small interfering RNAs silenced MCT2 and prevented the increase in the proportion of ChAT- immunoreactive neurons induced by butyrate. Butyrate and trichostatin A increased histone H3 acetylation in enteric neurons. Effects of butyrate were prevented by inhibitors of the Src signaling pathway. RSD increased colonic transit, and butyrate increased the cholinergic-mediated colonic circular muscle contractile response ex vivo.

CONCLUSION

Butyrate or histone deacetylase inhibitors might be used, along with nutritional approaches, to treat various gastrointestinal motility disorders associated with inhibition of colonic transit.

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.

Purinergic neuromuscular transmission is selectively attenuated in ulcerated regions of inflamed guinea pig distal colon

This study was undertaken to investigate neuromuscular transmission in regions of the inflamed colon in which motility is disrupted. Propulsive motility was evaluated in segments of control guinea pigs and those treated 6 days previously with trinitrobenzene sulfonic acid. Intracellular recordings were then obtained from circular muscle cells to examine excitatory and inhibitory junction potentials (EJPs and IJPs). In inflamed preparations, propulsion of fecal pellets was temporarily halted or obstructed at sites of mucosal damage, whereas the propulsive motility was linear in control colons. The amplitudes of evoked and spontaneous IJPs were significantly reduced in ulcerated regions of inflamed preparations, but EJPs were comparable to controls. Pharmacological dissection of the IJP revealed that the purinergic component was reduced, while the nitrergic IJP was slightly increased. Furthermore, the reduction in the purinergic IJP in inflamed preparations persisted in the presence of hexamethonium, suggesting that the deficit involved the inhibitory motor neuron and/or smooth muscle. Nerve fibre density was not altered in the circular muscle, and pre-contracted rings of inflamed colon relaxed normally to ATP, suggesting that the deficit involves altered ATP release and/or degradation. The P2Y(1) receptor antagonist MRS2179 slowed propulsive motility indicating that decreased purinergic neuromuscular transmission could contribute to the inflammation-induced motor deficit. We conclude that purinergic inhibitory neuronal input to the circular muscle is selectively reduced in regions of the colon in experimental colitis where the mucosa is damaged, and this is likely to contribute to altered motility in colitis by diminishing downstream relaxation during the peristaltic reflex.

Visceral afferents: what role in post-inflammatory pain?

Several weeks to several months after a bout of inflammation or an infectious event in a visceral organ, while inflammation or infection has resolved, defective nociceptive functions are sometimes still present, characterized by chronic pain symptoms, visceral hyperalgesia and allodynia. Visceral afferents which convey nociceptive messages have been shown to be hyperexcitable in inflammatory states. Only recently, studies have addressed visceral afferent electrical properties and neuroplastic changes in post-inflammatory situations. This review tries to appraise in post-inflammatory hypersensitive states, the most recent advances in the knowledge of visceral afferent inputs, together with in vivo recordings of visceral hyperalgesia and allodynia.