Myenteric Neurons Research Articles

Expression and Protective Functions of the sst4 Somatostatin Receptor in the Indomethacin‐Induced Gastrointestinal Mucosal Injury Model of the Mouse

IntroductionGastrointestinal ulceration is associated with high mortality despite advanced management, therefore, understanding of the mucosal protective mechanisms is important. Somatostatin is present in the endocrine cells and sensory nerves, and its analogues were shown to reduce mucosal blood flow, pepsin and gastric acid secretion. Our group discovered that its anti‐inflammatory and analgesic actions are exerted via the somatostatin receptor subtype 4 (sst4). Therefore, we investigated its expression and role in gastrointestinal injury.MethodsSst4 gene‐deleted (sst4−/−) and wildtype mice were treated s.c. with indomethacine (IDM; 35 mg/kg) or vehicle. RNA scope in situ hybridization was performed to localize, qPCR to quantify sst4 and somatostatin mRNA. Macroscopic and microscopic lesions in the stomach and small intestine were evaluated after 4 and 48 h. Plasma protein extravasation was measured by fluorescent, neutrophil myeloperoxidase (MPO) activity bioluminescent ex vivo imaging, TNFα, IL‐1 and COX2 mRNA by qPCR.ResultsSomatostatin mRNA is present in the neuroendocrine D‐cells and significantly upregulated 48 h after IDM. Sst4 mRNA in located in the myenteric plexus neurons, it’s expression did not change in response to mucosal injury.IDM‐induced gastric and small intestinal macroscopic lesions (4, 24 h), gastric MPO activity (24, 48 h) and plasma extravasation (30 min) were significantly greater in sst4−/− mice. TNFα, IL‐1, COX2 expressions significantly increased after 4 h in the stomach of sst4−/− mice, but in wild‐types the same pattern was observed only later, at the 48 h time‐point. IDM‐evoked histopathological alterations and small intestinal length reduction were not altered by the sst4 deletion.ConclusionThis is the first evidence for sst4 expression in myenteric plexus neurons and its protective roles against chemically‐induced gastrointestinal mucosal damage and inflammation. This suggests the safety of sst4 agonist drug candidates in the gastrointestinal tract, and even their potential use for gastroprotective indication.Support or Funding InformationSupported by: GINOP‐2.3.2‐15‐2016‐00050 – PEPSYS, GINOP‐2.3.2 STAY ALIVE, EFOP‐3.6.2‐16‐2017‐00008, ÚNKP‐19‐3‐III‐PTE‐211

Multiplexed Immunohistochemistry to Identify Systematically Classes of Human Colonic Myenteric Neurons

ObjectiveThe enteric nervous system (ENS) comprises multiple classes of nerve cells which can be distinguished by combinations of immunohistochemical markers (“chemical coding”) that they express. While many immunohistochemical studies have been carried out, the chemical coding of ENS of human colon has not been characterised systematically.MethodsSurgical specimens of human colon were obtained with prior informed consent (Ethics Approval SAC HREC#207.07), incubated in 83uM colchicine overnight to enhance neuropeptide immunoreactivity, then fixed. Multiplexed indirect immunohistochemistry (5 layers of quadruple labelling) included 13 common neuronal markers; HuC/D, nitric oxide synthase (NOS), choline acetyltransferase (ChAT), 5‐hydroxytryptamie (5‐HT), Substance P/tachykinins (SP), leu‐Enkephalin (ENK), calcitonin gene‐related peptide (CGRP), somatostatin (SOM), Calbindin (Calb), Calretinin (Calret), neurofilament 200 (NF200), vasoactive intestinal polypeptide (VIP) and neuropeptide Y (NPY). Antibodies were eluted between layers. The presence/absence of all 13 markers was recorded for 1303 neurons in human ascending colon (n=6) and 1087 in descending colon (n=5). HuC/D labelled all myenteric nerve cell bodies and was revealed using AMCA as a fluorophore; this staining was resistant to elution and allowed comparison between layers.ResultsChemical codes were surprisingly varied; of 4096 possible codes (212), 108 were present in ascending colon and 112 in descending colon. However, 40 codes accounted for more than 90% of neurons. There was a strong correlation between the rank order of chemical codes in ascending and descending colon (ranked by abundance; Rs=0.884[39]); p<0.001) indicating that there are similar ENS populations in ascending and descending colon. In ascending colon (n=6, 1303 cells) 686 cells (52.6%) were immunoreactive for NOS; 55.5% for ChAT; 9.8% were immunoreactive for both ChAT and NOS and 22 cells (1.7%) lacked both markers. The next most abundant markers were NF200 (50.0%), VIP (31.3%) and calbindin (25.1%). Low frequency markers in myenteric nerve cell bodies included CGRP (0.9%) and SOM (1.3%). A few codes accounted for very large proportions of neurons. For example, putative inhibitory motor neurons, immunoreactive for NOS (with none of the other 11 markers), accounted for 192 of 1303 neurons (14.7%). Dogiel type II neurons (identified by NF200 morphology) were large cells (1795 +/‐ 729 μm2, 25 cells) with NF200, ChAT and SP, with either Calb or Calret (or both) or SOM. It is also possible to identify cell bodies surrounded by dense baskets of varicose axons, which represent strong synaptic inputs. For example, ChAT‐immunoreactivity was present in 55.5% of all myenteric neurons, but made up 93.6% of all myenteric neurons enclosed by dense enkephalin‐immunoreactive inputs.Conclusionsmulti‐layer multiplexed immunoreactivity reveals a wealth of information about the human colonic ENS, making possible systematic identification of classes and identification of some synaptic connectivitySupport or Funding InformationSupported by NIH SPARC grant #1OT2OD24899

Evaluation of the role of cholinergic and nitrergic myenteric neurons in colonic motility using genetically‐encoded optical tools

Activity of neuronal subtypes within the myenteric plexus underlies coordinated patterns of gastro‐intestinal motility. Cholinergic neurons include intrinsic primary afferent neurons (IPAN), ascending interneurons, and excitatory motor neurons (eMNs) projecting to smooth muscle, whereas nitrergic neurons include descending interneurons and inhibitory motor neurons (iMNs) projecting to smooth muscle. The activity of cholinergic eMNs and nitrergic iMNs is believed to produce the two major patterns of motility underlying peristalsis in the colon, namely the periodic colonic migrating motor complex (CMMC) and the intervening periods of tonic inhibition, respectively. The objective of this study was to determine whether a.) such correlated activities of cholinergic eMNs and nitrergic iMNs could be discerned in the myenteric plexus of transgenic mice expressing the genetically‐encoded calcium indicator GCaMP6f in each of these two cell types (i.e., choline acetyltransferase (ChAT)‐GCaMP6f mice or neuronal nitric oxide synthase (nNOS)‐GCaMP6f mice), and b.) optogenetic activation of in these subtypes with genetically‐encoded optical actuator channelrhodopsin‐2 (ChR2) would produce CMMCs (in ChAT‐ChR2 mice) or tonic inhibition (in nNOS‐ChR2 mice). In order to correlate activity patterns, which require imaging of sliced colon, with defined states of motility, which require intact colon with force transducers, we took advantage of CAGGS‐GCaMP3 mice, which show widespread GCaMP3 expression. In loosely pinned preparations imaged at low power, we could easily discern CMMCs, which displayed pronounced movement together with robust smooth muscle Ca2+ responses. Then, we imaged the activity of nitrergic and cholinergic neurons against the backdrop of these movements. In nNOS‐GCaMP6f mice, as expected, we observed large numbers of cells that exhibited tonic Ca2+ responses in between CMMCs. We also observed a subpopulation of nitrergic neurons that exhibited a large phasic response just prior to the CMMC. Consistent with this finding, we found that optogenetic stimulation of the colon of nNOS‐ChR2 mice in between spontaneous CMMCs (i.e., during tonic inhibition) resulted in the generation of CMMCs. These ectopic CMMC were reduced by treatment with the ganglionic nicotinic AChR blocker hexamethonium, suggesting that they were primarily mediated by activation of nitrergic INs. In ChAT‐GCaMP6f mice, we observed fewer cells that exhibited tonic activity in between CMMCs. During CMMCs, we observed many cholinergic neurons that exhibited large phasic responses just after the CMMC was initiated. Similar to the effects in nNOS‐ChR2 mice, optogenetic stimulation of the colon of ChAT‐ChR2 mice in between spontaneous CMMCs produced ectopic CMMCs. Whether these effects are mediated by IPANs, ascending INs or eMNs is under investigation. These studies reveal unexpected complexity in the regulation of colonic motility by cholinergic and nitrergic myenteric neurons.Support or Funding InformationSPARC : OT2OD024899 (Director, Y Tache, UCLA)

Intestinal Bacteria Maintain Adult Enteric Nervous System and Nitrergic Neurons via Toll-like Receptor 2-induced Neurogenesis in Mice

The enteric nervous system (ENS) exists in close proximity to luminal bacteria. Intestinal microbes regulate ENS development, but little is known about their effects on adult enteric neurons. We investigated whether intestinal bacteria or their products affect the adult ENS via toll-like receptors (TLRs) in mice. We performed studies with conventional C57/BL6, germ-free C57/BL6, Nestin-creERT2:tdTomato, Nestin-GFP, and ChAT-cre:tdTomato. Mice were given drinking water with ampicillin or without (controls). Germ-free mice were given drinking water with TLR2 agonist or without (controls). Some mice were given a blocking antibody against TLR2 or a TLR4 inhibitor. We performed whole gut transit, bead latency, and geometric center studies. Feces were collected and analyzed by 16S ribosomal RNA gene sequencing. Longitudinal muscle myenteric plexus (LMMP) tissues were collected, analyzed by immunohistochemistry, and levels of nitric oxide were measured. Cells were isolated from colonic LMMP of Nestin-creERT2:tdTomato mice and incubated with agonists of TLR2 (receptor for gram-positive bacteria), TLR4 (receptor for gram-negative bacteria), or distilled water (control) and analyzed by flow cytometry. Stool from mice given ampicillin had altered composition of gut microbiota with reduced abundance of gram-positive bacteria and increased abundance of gram-negative bacteria, compared with mice given only water. Mice given ampicillin had reduced colon motility compared with mice given only water, and their colonic LMMP had reduced numbers of nitrergic neurons, reduced neuronal nitric oxide synthase production, and reduced colonic neurogenesis. Numbers of colonic myenteric neurons increased after mice were switched from ampicillin to plain water, with increased markers of neurogenesis. Nestin-positive enteric neural precursor cells expressed TLR2 and TLR4. In cells isolated from the colonic LMMP, incubation with the TLR2 agonist increased the percentage of neurons originating from enteric neural precursor cells to approximately 10%, compared with approximately 0.01% in cells incubated with the TLR4 agonist or distilled water. Mice given an antibody against TLR2 had prolonged whole gut transit times; their colonic LMMP had reduced total neurons and a smaller proportion of nitrergic neurons per ganglion, and reduced markers of neurogenesis compared with mice given saline. Colonic LMMP of mice given the TLR4 inhibitor did not have reduced markers of neurogenesis. Colonic LMMP of germ-free mice given TLR2 agonist had increased neuronal numbers compared with control germ-free mice. In the adult mouse colon, TLR2 promotes colonic neurogenesis, regulated by intestinal bacteria. Our findings indicate that colonic microbiota help maintain the adult ENS via a specific signaling pathway. Pharmacologic and probiotic approaches directed towards specific TLR2 signaling processes might be developed for treatment of colonic motility disorders related to use of antibiotics or other factors.

High-fat diet-induced alterations to gut microbiota and gut-derived lipoteichoic acid contributes to the development of enteric neuropathy.

High-fat diet, microbial alterations and lipopolysaccharide (LPS) are thought to cause enteric diabetic neuropathy and intestinal dysmotility. However, the role of the gut microbiota, lipoteichoic acid (LTA) from Gram-positive bacteria and short-chain fatty acids (SCFAs) in the development of diabetic enteric neuropathy and intestinal dysmotility is not well understood. Our aim was to examine the role of the gut microbiota, LTA and SCFAs in the development of diabetic enteric neuropathy and intestinal dysmotility. We fed germ-free (GF) and conventionally raised (CR) mice either a high-fat (HFD) or standard chow diet (SCD) for 8weeks. We analyzed the microbial community composition in CR mice using 16S rRNA sequencing and damage to myenteric neurons using immunohistochemistry. We also studied the effects of LPS, LTA, and SCFAs on duodenal muscularis externa contractions and myenteric neurons using cultured preparations. High-fat diet ingestion reduced the total number and the number of nitrergic myenteric neurons per ganglion in the duodenum of CR but not in GF-HFD mice. GF mice had fewer neurons per ganglion compared with CR mice. CR mice fed a HFD had increased abundance of Gram-positive bacteria. LTA and LPS did not affect the frequency of duodenal muscularis contractions after 24hours of cultured but reduced the density of nitrergic myenteric neurons and increased oxidative stress and TNFα production in myenteric ganglia. SCFAs did not affect muscularis contractions or injure myenteric neurons. Gut microbial alterations induced increase in Gram-positive bacterial LTA may contribute to enteric neuropathy.

Robust, 3-Dimensional Visualization of Human Colon Enteric Nervous System Without Tissue Sectioning

Small, 2-dimensional sections routinely used for human pathology analysis provide limited information about bowel innervation. We developed a technique to image human enteric nervous system (ENS) and other intramural cells in 3 dimensions. Using mouse and human colon tissues, we developed a method that combines tissue clearing, immunohistochemistry, confocal microscopy, and quantitative analysis of full-thickness bowel without sectioning to quantify ENS and other intramural cells in 3 dimensions. We provided 280 adult human colon confocal Z-stacks from persons without known bowel motility disorders. Most of our images were of myenteric ganglia, captured using a 20× objective lens. Full-thickness colon images, viewed with a 10× objective lens, were as large as 4× 5 mm2. Colon from 2 pediatric patients with Hirschsprung disease was used to show distal colon without enteric ganglia, as well as a transition zone and proximal pull-through resection margin where ENS was present. After testing a panel of antibodies with our method, we identified 16 antibodies that bind to molecules in neurons, glia, interstitial cells of Cajal, and muscularis macrophages. Quantitative analyses demonstrated myenteric plexus in 24.5% ± 2.4% of flattened colon Z-stack area. Myenteric ganglia occupied 34% ± 4% of myenteric plexus. Single myenteric ganglion volume averaged 3,527,678 ± 573,832 mm3 with 38,706 ± 5763 neuron/mm3 and 129,321 ± 25,356 glia/mm3. Images of large areas provided insight into why published values of ENS density vary up to 150-fold-ENS density varies greatly, across millimeters, so analyses of small numbers of thin sections from the same bowel region can produce varying results. Neuron subtype analysis revealed that approximately 56% of myenteric neurons stained with neuronal nitric oxide synthase antibody and approximately 33% of neurons produce and store acetylcholine. Transition zone regions from colon tissues of patients with Hirschsprung disease had ganglia in multiple layers and thick nerve fiber bundles without neurons. Submucosal neuron distribution varied among imaged colon regions. We developed a 3-dimensional imaging method for colon that provides more information about ENS structure than tissue sectioning. This approach could improve diagnosis for human bowel motility disorders and may be useful for other bowel diseases as well.

A120 INFLUENCE OF THE MICROBIOTA ON THE POSTNATAL DEVELOPMENT OF THE ENTERIC NERVOUS SYSTEM IS DEPENDENT ON MOUSE STRAIN

Abstract Background Gastrointestinal function depends on the normal formation of the enteric nervous system (ENS) during fetal and postnatal development. Prior research in an outbred strain of mice (NIH Swiss) has shown that the absence of the gut microbiome in germ-free (GF) mice results in morphological and functional abnormalities of the ENS compared to specific pathogen free (SPF) mice, including an alteration in proportion of nitrergic neurons. Increasing research has been suggesting that the genetic background of the host can impact the host response to the GF state. Aims We tested the hypothesis that the absence of the microbiome in an inbred mouse strain (C57BL/6) could influence the development of the ENS during early postnatal life. Methods C57BL/6 GF and SPF mice were sacrificed at postnatal day 3 (P3) and P28 (n=4–5 per group). Ileum and colon were collected at P3 and P28 and processed for whole mount preparations. The neuronal network in the myenteric plexus was visualized by immunohistochemistry using antibodies against the pan-neuronal marker PGP9.5. Neuronal cell bodies and nitrergic neurons were identified by immunolabeling with antibodies to the neuronal marker HuC/D and to neuronal nitric oxide (nNOS). Nerve fibre density was quantified by measuring the percentage of PGP9.5-positive pixels (μm2) compared to the whole field using an image analysis program (Volocity; reported as %). Proportions of nitrergic to myenteric neurons were determined by manually counting (blinded) the number of nNOS-positive neurons and dividing by the total number of HuC/D-positive cells per field (reported as %). Results We found a significant increase in nerve density at P3 in the GF compared to SPF mice in both ileum (43% vs. 37%; p=0.03) and colon (45% vs. 39%; p=0.03). No significant differences, however, were identified between GF and SPF mice at P28 in either ileum (27% vs. 25%; n.s.) or colon (31% vs. 32%; n.s.). At P3, no significant differences in proportion of nitrergic neurons were seen in the GF compared to SPF ileum (27% vs. 27%; n.s.). Conclusions In contrast to earlier observations in the NIH Swiss mice, in which GF mice had decreased nerve density and an increase in nitrergic neurons at P3, our findings reveal an opposite response in nerve density in the C57BL/6 mice and no change in nitrergic neurons. These results suggest that the genetic strain of the mouse model can influence the host response to changes in the microbiome. Further studies are needed to further elucidate potential underlying mechanisms. Funding Agencies NSERC

Intrinsic sensory neurons provide direct input to motor neurons and interneurons in mouse distal colon via varicose baskets.

Connections from intrinsic primary afferent neurons (IPANs), to ascending motor and interneurons have been described in guinea pig colon. These mono- and polysynaptic circuits may underlie polarized motor reflexes evoked by local gut stimulation. There is a need to translate findings in guinea pig to mouse, a species increasingly used in enteric neuroscience. Here, mouse distal colon was immunolabeled for CGRP, a marker of putative IPANs. This revealed a combination of large, intensely immunofluorescent axons in myenteric plexus and circular muscle, and thinner varicose axons with less immunofluorescence. The latter formed dense, basket-like varicosity clusters (CGRP+ baskets) that enveloped myenteric nerve cell bodies. Immunolabeling after 4-5 days in organ culture caused loss of large CGRP+ axons, but not varicose CGRP+ fibers and CGRP+ baskets. Baskets were characterized further by triple labeling with CGRP, nitric oxide synthase (NOS) and calretinin (CALR) antibodies. Approximately half (48%) of nerve cell bodies inside CGRP+ baskets lacked both NOS and CALR, while two overlapping populations containing NOS and/or CALR comprised the remainder. Quantitative analysis revealed CGRP+ varicosities were most abundant in baskets, followed by CALR+ varicosities, with a high degree of colocalization between the two markers. Few NOS+ varicosities occurred in baskets. Significantly higher proportions of CALR+ and CGRP+ varicosities colocalized in baskets than in circular muscle. In conclusion, CGRP+ baskets in mouse colon are formed by intrinsic enteric neurons with a neurochemical profile consistent with IPANs and have direct connections to both excitatory and inhibitory neurons.

Homeoprotein OTX1 and OTX2 involvement in rat myenteric neuron adaptation after DNBS-induced colitis.

BackgroundInflammatory bowel diseases are associated with remodeling of neuronal circuitries within the enteric nervous system, occurring also at sites distant from the acute site of inflammation and underlying disturbed intestinal functions. Homeoproteins orthodenticle OTX1 and OTX2 are neuronal transcription factors participating to adaptation during inflammation and underlying tumor growth both in the central nervous system and in the periphery. In this study, we evaluated OTX1 and OTX2 expression in the rat small intestine and distal colon myenteric plexus after intrarectal dinitro-benzene sulfonic (DNBS) acid-induced colitis.MethodsOTX1 and OTX2 distribution was immunohistochemically investigated in longitudinal muscle myenteric plexus (LMMP)-whole mount preparations. mRNAs and protein levels of both OTX1 and OTX2 were evaluated by qRT-PCR and Western blotting in LMMPs.ResultsDNBS-treatment induced major gross morphology and histological alterations in the distal colon, while the number of myenteric neurons was significantly reduced both in the small intestine and colon. mRNA levels of the inflammatory markers, TNFα, pro-IL1β, IL6, HIF1α and VEGFα and myeloperoxidase activity raised in both regions. In both small intestine and colon, an anti-OTX1 antibody labeled a small percentage of myenteric neurons, and prevalently enteric glial cells, as evidenced by co-staining with the glial marker S100β. OTX2 immunoreactivity was present only in myenteric neurons and was highly co-localized with neuronal nitric oxide synthase. Both in the small intestine and distal colon, the number of OTX1- and OTX2-immunoreactive myenteric neurons significantly increased after DNBS treatment. In these conditions, OTX1 immunostaining was highly superimposable with inducible nitric oxide synthase in both regions. OTX1 and OTX2 mRNA and protein levels significantly enhanced in LMMP preparations of both regions after DNBS treatment.ConclusionsThese data suggest that colitis up-regulates OTX1 and OTX2 in myenteric plexus both on site and distantly from the injury, potentially participating to inflammatory-related myenteric ganglia remodeling processes involving nitrergic transmission.

The Influence of a Hyperglycemic Condition on the Population of Somatostatin Enteric Neurons in the Porcine Gastrointestinal Tract.

Simple SummaryDiabetes mellitus is a chronic metabolic disorder, in the course of which prolonged episodes of hyperglycemia are common. Hyperglycemia leads to damage and disruption in the proper function of many organs, including the gastrointestinal tract. Alimentary tract functions are regulated by triple innervation, in which the enteric nervous system plays a dominant role. Appropriate digestive functions are controlled by numerous biologically active substances which are synthesized and released through enteric neurons. One of the most common substances that occurs in the gastrointestinal tract is somatostatin. This peptide is involved in the regulation of a wide range of digestive functions, such as intestinal motility, secretory activity, and others. Furthermore, somatostatin participates in sensory and pain stimuli as well as modulation and release of other active factors. Somatostatin is also involved in the response of neurons to many pathological conditions. In this study, it was found that somatostatin secreted by enteric neurons has an important effect in hyperglycemic conditions induced by streptozotocin injection in the swine diabetes model. These data could provide useful information for further investigations into the functions of neuroactive substances in digestive tract pathophysiology in the course of diabetes.Somatostatin (SOM) is the most common agent in the gastrointestinal (GI) tract that is involved in the regulation of several gastric functions, as well as in gastric disorders. Hyperglycemia, which develops as a consequence of improperly treated diabetes, can cause numerous disturbances in the appropriate functioning of the gastrointestinal tract. High glucose level is toxic to neurons. One of the lines of defense of neurons against this glucotoxicity are changes in their chemical coding. To better understood the role of SOM secreted by enteric neurons in neuronal response on elevated glucose level, pancreatic β cells were destroyed using streptozotocin. Due to the close similarity of the pig to humans, especially the GI tract, the current study used pigs as an animal model. The results revealed that the number of enteric neurons immunoreactive to SOM (SOM-IR) in a physiological state clearly depend on the part of the GI tract studied. In turn, experimentally induced diabetes caused changes in the number of SOM-IR neurons. The least visible changes were observed in the stomach, where an increase in SOM-IR neurons was observed, only in the submucosal plexus in the corpus. However, diabetes led to an increase in the population of myenteric and submucosal neurons immunoreactive to SOM in all segments of the small intestine. The opposite situation occurred in the descending colon, where a decrease in the number of SOM-IR neurons was visible. This study underlines the significant role of SOM expressed in enteric nervous system neurons during diabetes.

Increased expression of CART, nNOS, VIP, PACAP, SP and GAL in enteric neurons of the porcine stomach prepyloric region following hydrochloric acid infusion.

Stomach hyperacidity leads to damage of the mucus/bicarbonate barrier, ulcerations and the development of stomach cancer. Key regulators of the mucosal barrier/luminal acid balance are neurotransmitters secreted by intramural neurons. The aim of the current study was to determine the expression of gastric neuropeptides and nNOS in the porcine stomach following hydrochloric acid instillation. We report on increased expression of enteric neurotransmitters involved in adaptive reaction to an experimentally-induced hyperacidity state. The investigation was conducted on eight 12-18 kg pigs. The influence of intragastric infusion of hydrochloric acid on the expression of cocaine- and amphetamine-regulated transcript peptide (CART), neuronal nitric oxide synthase (nNOS), vasoactive intestinal polypeptide (VIP), pituitary adenylate cyclase-activating peptide (PACAP), substance P (SP) and galanin (GAL) in the submucous and myenteric gastric neurons of the pig has been studied with double immunofluorescence. A mimicked hyperacidity state significantly increased the proportion of enteric neurons immunoreactive to CART, nNOS, VIP, PACAP, SP and GAL in the submucous gastric neurons. In the myenteric plexus, a significant increase of the number of VIP-, CART- and GAL-immunoreactive (IR) neurons was found. Similarly, the percentage of myenteric nNOS-IR and PACAP-IR neurons tended to increase, while the fraction of SP-IR cells did not change. Stomach hyperacidity modifies the expression of the studied neurotransmitters in a specific way depending on the location of the neurons in particular plexuses of the stomach. Increased numbers of neurons expressing CART, nNOS, VIP, PACAP, SP and GAL clearly indicate their regulatory engagement in the restoration of the physiological gastric balance following hyperacidity.

Thyrotropin releasing hormone (TRH) in the brainstem: Role of Pavlov’s vagally mediated cephalic phase of gastric secretion

Pavlov’s seminal observation that sham feeding in dogs stimulates gastric acid secretion through the vagus nerve pioneered the concept of the cephalic phase of digestion. This has been subsequently extended to a wide range of mammals including humans. In the last decades, experimental evidence in rats established that the three amino acid peptide thyrotropinreleasing hormone (TRH) expressed in the brainstem plays a key role in the vagal stimulation of digestive secretory-motor function. The dorsal motor nucleus of the vagus (DMN) neurons expresses TRH receptor subtype 1 (TRH-R1) and receives input of TRH containing fibers arising from TRH synthesizing neurons in medullary raphe nuclei. The activation of TRHTRH-R1 signaling excites the firing of DMN neurons leading to the activation of vagal efferent discharges and gastric myenteric cholinergic neurons. This results in a vagally mediated and atropine-sensitive stimulation of gastric secretory and propulsive motor function, along with duodenal and pancreatic secretion. Importantly, the blockade of TRH or TRH-R1 in the brainstem inhibits the gastric acid response to sham feeding in rats. Collectively, these convergent data support the physiological relevance of medullary TRHTRH-R1 signaling as the end effector of the vagally mediated stimulation of digestive process in the cephalic phase.

Chronic ingestion of deoxynivalenol-contaminated diet dose-dependently decreases the area of myenteric neurons and gliocytes of rats.

Deoxynivalenol (DON), a mycotoxin produced by Fusarium spp., is commonly found in cereals ingested by humans and animals. Its ingestion is correlated with hepatic, hematologic, renal, splenic, cardiac, gastrointestinal, and neural damages, according to dose, duration of exposure and species. In this work, the effects of the ingestion of DON-contaminated diet at concentrations considered tolerable for human and animal intake were assessed. Male Wistar rats aging 21days were allotted to five groups that were given, for 42days, diets contaminated with different concentrations of DON (0, 0.2, 0.75, 1.75, and 2mgkg-1 of chow). Food ingestion, bodyweight, oxidative status and morphometric analyses of gliocytes, and neurons of jejunal myenteric ganglia were recorded. At these concentrations, there was no food rejection, decrease in bodyweight gain, changes in oxidative status, or loss of either neurons or gliocytes. However, DON decreased gliocyte area, general neuronal population, nitrergic, cholinergic and NADH-diaphorase positive subpopulations and, as a result, ganglion area. It was concluded that, even in the absence of visible effect, DON exposure reduces cell body area of gliocytes and neurons of the myenteric plexus of the rat jejunum.

Mu and Delta Opioid Receptors Are Coexpressed and Functionally Interact in the Enteric Nervous System of the Mouse Colon.

Background & AimsFunctional interactions between the mu opioid receptor (MOR) and delta opioid receptor (DOR) represent a potential target for novel analgesics and may drive the effects of the clinically approved drug eluxadoline for the treatment of diarrhea-predominant irritable bowel syndrome. Although the enteric nervous system (ENS) is a likely site of action, the coexpression and potential interaction between MOR and DOR in the ENS are largely undefined. In the present study, we have characterized the distribution of MOR in the mouse ENS and examined MOR-DOR interactions by using pharmacologic and cell biology techniques.MethodsMOR and DOR expression was defined by using MORmCherry and MORmCherry–DOR-eGFP knockin mice. MOR-DOR interactions were assessed by using DOR-eGFP internalization assays and by pharmacologic analysis of neurogenic contractions of the colon.ResultsAlthough MOR was expressed by approximately half of all myenteric neurons, MOR-positive submucosal neurons were rarely observed. There was extensive overlap between MOR and DOR in both excitatory and inhibitory pathways involved in the coordination of intestinal motility. MOR and DOR can functionally interact, as shown through heterologous desensitization of MOR-dependent responses by DOR agonists. Functional evidence suggests that MOR and DOR may not exist as heteromers in the ENS. Pharmacologic studies show no evidence of cooperativity between MOR and DOR. DOR internalizes independently of MOR in myenteric neurons, and MOR-evoked contractions are unaffected by the sequestration of DOR.ConclusionsCollectively, these findings demonstrate that although MOR and DOR are coexpressed in the ENS and functionally interact, they are unlikely to exist as heteromers under physiological conditions.

Detection and Cellular Tropism of Porcine Astrovirus Type 3 on Breeding Farms.

Astroviruses cause disease in a variety of species. Yet, little is known about the epidemiology of a majority of astroviruses including porcine astrovirus type 3 (PoAstV3), which is a putative cause of polioencephalomyelitis in swine. Accordingly, a cross-sectional study was conducted on sow farms with or without reported PoAstV3-associated neurologic disease in growing pigs weaned from those farms. Additionally, a conveniently selected subset of piglets from one farm was selected for gross and histologic evaluation. The distribution of PoAstV3 in the enteric system was evaluated through in situ hybridization. PoAstV3, as detected by RT-qPCR on fecal samples, was frequently detected across sows and piglets (66–90%) on all farms (65–85%). PoAstV3 was detected subsequently at a similar detection frequency (77% vs 85%) on one farm after three months. Viral shedding, as determined by the cycle quantification value, suggests that piglets shed higher quantities of virus than adult swine. No link between gastrointestinal disease and PoAstV3 was found. However, PoAstV3 was detected by in situ in myenteric plexus neurons of piglets elucidating a possible route of spread of the virus from the gastrointestinal tract to the central nervous system. These data suggest PoAstV3 has endemic potential, is shed in the feces at greater quantities by suckling piglets when compared to sows, and infection is widespread on farms in which it is detected.

Colonic neuronal loss and delayed motility induced by high-fat diet occur independently of changes in the major groups of microbiota in Swiss mice.

Obesity has been linked to gastrointestinal disorders, and the loss of myenteric neurons in the intestine caused by high-fat diets (HFD) has been attributed to changes in microbiota and lipotoxicity. We investigated whether the prebiotic inulin modulates bacterial populations and alleviates neuronal loss in mice fed HFD. Swiss mice were fed purified rodent diet or HFD (59% kcal fat), or both diets supplemented with inulin for 17weeks. Intestinal motility was assessed and a metagenome analysis of the colonic microbiota was performed. The gene expression of inflammatory markers was evaluated, and immunofluorescence was performed for different types of myenteric neurons and glial cells in the distal colon. The HFD caused obesity and delayed colonic motility. The loss of myenteric neurons and glial cells in obese mice affected all of the studied neuronal populations, including neurons positive for myosin-V, neuronal nitric oxide synthase, vasoactive intestinal peptide, and calretinin. Although obese mice supplemented with inulin exhibited improvements in colonic motility, neuronal, and glial cell loss persisted. The HFD did not altered the expression levels of inflammatory cytokines in the intestine or the prevalence of the major groups in microbiota, but inulin increased the proportion of the genus Akkermansia in the obese mice. In Swiss mice, the HFD-induced neuronal loss but did not change the major groups in microbiota. This suggests that, despite the increase in the beneficial bacteria, other factors that are directly linked to excess dietary lipid intake affect the enteric nervous system.

Age related changes of neuropeptide Y-ergic system in the rat duodenum

Neuropeptide Y (NPY) is widely distributed in the autonomic nervous system and acts as a neurotransmitter and a trophic factor. However, there is no report concerning the expression of NPY and its receptors in the intestine during postnatal ontogenesis. In the current study, immunohistochemistry and western blot analysis was used to label NPY, Y1R, Y2R and Y5R receptors in the duodenum from rats of different ages (1-, 10-, 20-, 30-, 60-day-old and 2-year-old).The obtained data suggest age-dependent changes of NPY-mediated gut innervation. NPY-immunoreactive (IR) neurons were observed in the myenteric (MP) and submucous (SP) plexus from the moment of birth. In the MP, the percentage of NPY-IR neurons was low and varied from 4.1 ± 0.32 in 1-day-old to 2.9 ± 0.62 in 2-year-old rats. The proportion of NPY-IR myenteric neurons did not change significantly through the senescence (p > .05). In the SP, the proportion of NPY-IR neurons significantly increased in the first month of life from 56.3 ± 2.4% in 1-day-old to 78.1 ± 5.18% in 20-day-old and significantly decreased from 75.6 ± 4.62% in 30-day-old rats to 59.8 ± 4.24% in 2-year-old rats.The expression of NPY in the duodenum did not change significantly during the development by western blot analysis. The expression of Y1R and Y2R was low in newborns and upregulated in the first ten days of life. The expression of Y5R was maximal in newborn pups and significantly decreased in in the first 20 days.Thus, there are some fluctuation of the percentage of NPY-IR neurons accompanies changes in relation of different subtypes of NPY receptors in the small intestine during postnatal ontogenesis.

Adaptative responses of myenteric neurons of Sphoeroides testudineus to environmental pollution

Contamination in estuarine regions affects the local biota damaging the ecosystems and reaching humans. The gastrointestinal tract is a dynamic environment capable of obtaining nutrients and energy from food while it protects the host against harmful toxins and pathogens from the external environment. These functions are modulated by the enteric nervous system and changes in its structure can result in gastrointestinal disorders. The objective of this study was to evaluate if the environmental contaminants have effects on the myenteric neuronal plasticity of pufferfish Sphoeroides testudineus. Animals were collected in Barra do Una River, located at Jureia-Itatins Mosaic of Protected Areas (reference area – RA) and in the Santos Estuarine System (impacted area – IA). Morpho-quantitative analyses of the general and metabolically active myenteric neuronal populations of the proximal and distal intestine were made. Disarrangement was observed in the general organization of the myenteric plexus, with an expressive reduction of the neuronal groups (nodes) in the animals of IA. The vulnerability of the myenteric plexus was evidenced by a decrease in density and cellular profile of the general neuronal population, followed by an increase of the metabolism of the remaining neurons, which in turn was verified by a growth of the area of the cellular and nuclear profiles of the metabolically active neuronal population. Through these analyses, we concluded that animals inhabiting polluted regions present alterations in the myenteric neuronal plasticity, as a way of maintaining the functions of the gastrointestinal tract.

The enteric nervous system undergoes significant chemical and synaptic maturation during adolescence in mice

Adolescence is a critical period of development. It is very likely that there is significant maturation of the enteric nervous system (ENS) of the gut during this stage of life, especially since there are substantial changes in factors known to influence the ENS including diet and microbiota during this time, but this remains unknown. To examine maturation of the ENS during adolescence, we performed immunohistochemistry using advanced microscopy and analytical methods to compare enteric neurons and glia of the duodenum and colon of mice taken prior to weaning with those of young adult mice. We found significant changes in the architecture of both myenteric and submucosal plexuses and surprisingly found subsets of enteric cells that co-expressed the pan-neuronal marker, Hu, and either glial markers Sox10 or S100β, not both. About 70% and 35% of all Hu ​+ ​neurons in the submucous plexus of the young adult duodenum and colon respectively also expressed S100β. The proportion of Hu+/Sox10 ​+ ​cells in the duodenal myenteric plexus decreased, while the proportion of Hu+/S100β+ cells in the colonic submucosal plexus increased during adolescence. In the submucous plexus, there were significant increases in the proportions of vasoactive intestinal peptide+ and choline acetyltransferase ​+ ​secretomotor neurons, of neurofilament M (NFM)+ neurons in the colon and of calretinin ​+ ​neurons in the duodenum during adolescence. There were no age-dependent changes in the neurochemistry of various myenteric neuronal subtypes, including those immunoreactive for neuronal nitric oxide synthase (nNOS), Calbindin, Calretinin or NFM. There were significant increases in the somata sizes of Calretinin ​+ ​submucosal and myenteric neurons, and nNOS ​+ ​myenteric neurons, and these enteric neurons received significantly more synaptophysin ​+ ​contacts onto their cell bodies during adolescence. This is the first study showing that enteric neurons and glia in the gut undergo significant changes in their anatomy and chemistry during adolescence. Notably changes in synaptic contacts within the enteric circuitry strongly suggest maturation in gastrointestinal function occurs during this time.

The Glucagon-like peptide-1 receptor agonist, exendin-4, ameliorated gastrointestinal dysfunction in the Wistar Kyoto rat model of Irritable Bowel Syndrome.

Glucagon-like peptide-1 (GLP-1) is beneficial in relieving pain-related symptoms of Irritable bowel syndrome (IBS), a prevalent, multi-factorial functional bowel disorder characterized by diarrhea and/or constipation, abdominal bloating, and pain. Activation of myenteric neurons has been implicated in the inhibitory effects of GLP-1 on gastrointestinal motility; however, the mechanisms of action underlying this are not clear. A rat model of IBS was used to examine physiological changes evoked by intraperitoneal administration of a GLP-1 receptor agonist, exendin-4. Behavioral and physiological analysis of stress-sensitive Wister Kyoto (WKY) rats was used to determine if administration of exendin-4, in the presence or absence of neutralizing interleukin-6 receptor monoclonal antibodies, modified IBS-like symptoms. Immunofluorescence, calcium imaging, and Western blotting techniques were used to investigate the potential role of enteric neural plexi and tight junction protein expression in this effect. Consistent with the expression of GLP-1 and interleukin-6 receptors in both submucosal and myenteric ganglia, exendin-4 and interleukin-6 stimulated calcium responses in these neurons. In vivo administration of exendin-4 normalized stress-induced defecation and visceral pain sensitivity in WKY rats. No additional changes were noted in rats co-treated with exendin-4 and anti-interleukin-6 receptor antibodies. Mucosal expression of occludin, a tight junction protein, was decreased by exendin-4. Centrally regulated anxiety-like behaviors were not modified. These data suggest that intraperitoneal injection of exendin-4 improves bowel dysfunction in WKY rats without impacting on centrally regulated anxiety-like behaviors. Modulation of enteric neuronal function and tight junction expression appear to underlie the functional benefits of this intervention.