Lessons from the porcine enteric nervous system

Influence of polyethylene terephthalate (PET) microplastic on selected active substances in the intramural neurons of the porcine duodenum

BACKGROUND

Currently, society and industry generate huge amounts of plastics worldwide. The ubiquity of microplastics is obvious, but its impact on the animal and human organism remains not fully understood. The digestive tract is one of the first barriers between pathogens and xenobiotics and a living organism. Its proper functioning is extremely important in order to maintain homeostasis. The aim of this study was to determine the effect of microplastic on enteric nervous system and histological structure of swine duodenum. The experiment was carried out on 15 sexually immature gilts, approximately 8 weeks old. The animals were randomly divided into 3 study groups (n = 5/group). The control group received empty gelatin capsules once a day for 28 days, the first research group received daily gelatin capsules with polyethylene terephthalate (PET) particles as a mixture of particles of various sizes (maximum particle size 300 µm) at a dose of 0.1 g/animal/day. The second study group received a dose ten times higher-1 g/animal/day.

RESULTS

A dose of 1 g/day/animal causes more changes in the enteric nervous system and in the histological structure of duodenum. Statistically significant differences in the expression of cocaine and amphetamine regulated transcript, galanin, neuronal nitric oxide synthase, substance P, vesicular acetylcholine transporter and vasoactive intestinal peptide between control and high dose group was noted. The histopathological changes were more frequently observed in the pigs receiving higher dose of PET.

CONCLUSION

Based on this study it may be assumed, that oral intake of microplastic might have potential negative influence on digestive tract, but it is dose-dependent.

Distribution, quantification, and characterization of substance P enteric neurons in the submucosal and myenteric plexuses of the porcine colon

The pig is an important translational model for studying intestinal physiology and disorders for its many homologies with humans, including the organization of the enteric nervous system (ENS), the major regulator of gastrointestinal functions. This study focused on the quantification and neurochemical characterization of substance P (SP) neurons in the pig ascending (AC) and descending colon (DC) in wholemount preparations of the inner submucosal plexus (ISP), outer submucosal plexus (OSP), and myenteric plexus (MP). We used antibodies for the pan-neuronal marker HuCD, and choline acetyltransferase (ChAT) and neuronal nitric oxide synthase (nNOS), markers for excitatory and inhibitory transmitters, for multiple labeling immunofluorescence and high-resolution confocal microscopy. The highest density of SP immunoreactive (IR) neurons was in the ISP (222/mm2 in the AC, 166/mm2 in the DC), where they make up about a third of HuCD-IR neurons, compared to the OSP and MP (19-22% and 13-17%, respectively, P < 0.001-0.0001). HuCD/SP/ChAT-IR neurons (up to 23%) were overall more abundant than HuCD/SP/nNOS-IR neurons (< 10%). Most SP-IR neurons contained ChAT-IR (62-85%), whereas 18-38% contained nNOS-IR with the highest peak in the OSP. A subpopulation of SP-IR neurons contains both ChAT- and nNOS-IR with the highest peak in the OSP and ISP of DC (33-36%) and the lowest in the ISP of AC (< 10%, P < 0.001). SP-IR varicose fibers were abundant in the ganglia. This study shows that SP-IR neurons are functionally distinct with variable proportions in different plexuses in the AC and DC reflecting diverse functions of specific colonic regions.

A study on the congruence and proximity of the sling and clasp fibres at the cardio-esophageal junction of the stomach

BACKGROUND AND AIM

The cardio-oesophageal sphincter that is located in close longitudinal proximity to the origin of the lesser curvature of the stomach has a unique pattern of external muscle fibres whose inner oblique layer would normally form an elongated sling and the middle partially circular layer would form a projecting clasp into the already existing muscular sling of the former congruently, which would result in the formation of an anatomical sphincter in that area that would normally be devoid of the external longitudinal muscle layer coat. Certain authors have disagreed with the notion of this standard literature and have proposed that the clasp and sling fibres need not necessarily be congruent and may even remain independent of each other with partial contributions from the longitudinal muscle layers as well that may arise tangentially in different populations, which may in turn contribute to reflux oesophagitis in that population. Hence, the clasp and sling fibre muscular patterns were observed in six formalin-embalmed cadavers at the department of anatomy in a tertiary care institute as part of routine dissections in series, and the findings were then reported.

FINDINGS

At the junction of the lesser curvature of the stomach with the oesophagus, all six cadavers showed a longitudinal sling pattern as opposed to the conventional oblique sling. The circular muscle layer was found to be merged with the outer longitudinal muscle layer to form the sling that pulled away from the clasp, resulting in a loss of congruency for the same. The clasp fibres, however, were found to be contributed by the inner oblique muscle layer. The conventional perpendicular or tangential merging of the clasp with the sling was not observed; instead, an obtuse, blunt angular merging of the clasp with the sling was observed.

DISCUSSION

The deviation of the sling from the clasp could indicate a lack of a proper fit between them at the cardio-oesophageal sphincter. The lack of robustness in the attachment of the clasp to the sling may possibly contribute to the diminished taut pull of the clasp in this subset of the population. These would be significant determinants for a predisposition to reflux oesophagitis and Barrett's oesophagus.

New insight on the enteric cholinergic innervation of the pig colon by central and peripheral nervous systems: reduction by repeated loperamide administration

Introduction

The central and peripheral nervous systems provide cholinergic innervation in the colon. The ability to assess their neuroanatomical distinctions is still a challenge. The pig is regarded as a relevant translational model due to the close similarity of its enteric nervous system (ENS) with that of human. Opioid-induced constipation is one of the most common side effects of opioid therapy.

Methods

We developed an approach to differentiate the central and peripheral cholinergic innervation of the pig colon using double immunolabeling with a novel mouse anti-human peripheral type of choline acetyltransferase (hpChAT) antibody combined with a rabbit anti-common type of ChAT (cChAT) antibody, a reliable marker of cholinergic neurons in the central nervous system. We examined their spatial configurations in 3D images of the ENS generated from CLARITY-cleared colonic segments. The density was quantitated computationally using Imaris 9.7. We assessed changes in the distal colon induced by daily oral treatment for 4  weeks with the μ opioid receptor agonist, loperamide (0.4 or 3  mg/kg).

Results

The double labeling showed strong cChAT immunoreactive (ir) fibers in the cervical vagus nerve and neuronal somata and fibers in the ventral horn of the sacral (S2) cord while hpChAT immunoreactivity was visualized only in the ENS but not in the vagus or sacral neural structures indicating the selectivity of these two antibodies. In the colonic myenteric plexus, dense hpChAT-ir neurons and fibers and varicose cChAT-ir fibers surrounding hpChAT-ir neurons were simultaneously visualized in 3D. The density of cChAT-ir varicose fibers in the outer submucosal plexus of both males and females were higher in the transverse and distal colon than in the proximal colon and in the myenteric plexus compared to the outer submucosal plexus and there was no cChAT innervation in the inner submucosal plexus. The density of hpChAT in the ENS showed no segmental or plexus differences in both sexes. Loperamide at the highest dose significantly decreased the density hpChAT-ir fibers + somata in the myenteric plexus of the distal colon.

Discussion

These data showed the distinct density of central cholinergic innervation between myenteric and submucosal plexuses among colonic segments and the localization of cChAT-ir fibers around peripheral hpChAT neurons in 3D. The reduction of cholinergic myenteric innervation by chronic opiate treatment points to target altered prokinetic cholinergic pathway to counteract opiate constipation.

E. coli infection disrupts the epithelial barrier and activates intrinsic neurosecretory reflexes in the pig colon

This study aims to assess the barrier integrity and possible activation of enteric neural pathways associated with secretion and motility in the pig colon induced by an enterotoxigenic Escherichia coli (ETEC) challenge. 50 Danbred male piglets were used for this study. 16 were challenged with an oral dose of the ETEC strain F4+ 1.5 × 10⁹ colony-forming unit. Colonic samples were studied 4- and 9-days post-challenge using both a muscle bath and Ussing chamber. Colonic mast cells were stained with methylene blue. In control animals, electrical field stimulation induced neurosecretory responses that were abolished by tetrodotoxin (10^-6M) and reduced by the combination of atropine (10^-4M) and α-chymotrypsin (10U/mL). Exogenous addition of carbachol, vasoactive intestinal peptide, forskolin, 5-HT, nicotine, and histamine produced epithelial Cl^- secretion. At day 4 post-challenge, ETEC increased the colonic permeability. The basal electrogenic ion transport remained increased until day 9 post-challenge and was decreased by tetrodotoxin (10^-6M), atropine (10^-4M), hexamethonium (10^-5M), and ondansetron (10^-5M). In the muscle, electrical field stimulation produced frequency-dependent contractile responses that were abolished with tetrodotoxin (10^-6M) and atropine (10^-6M). Electrical field stimulation and carbachol responses were not altered in ETEC animals in comparison with control animals at day 9 post-challenge. An increase in mast cells, stained with methylene blue, was observed in the mucosa and submucosa but not in the muscle layer of ETEC-infected animals on day 9 post-challenge. ETEC increased the response of intrinsic secretory reflexes and produced an impairment of the colonic barrier that was restored on day 9 post-challenge but did not modify neuromuscular function.

Glyphosate affects the neurochemical phenotype of the intramural neurons in the duodenum in the pig

BACKGROUND

Glyphosate-based herbicides have been one of the most intensively used pollutants worldwide and food products containing glyphosate are an essential component of human and animal diet. The aim of present study was to determine the effect of glyphosate intoxication on the neurochemical properties of the enteric nervous system (ENS) neurons located in the wall of the porcine duodenum.

METHODS

Fifteen sexually immature gilts divided into 3 groups were used: control-animals receiving empty gelatin capsules; G1-animals receiving a low dose of glyphosate-corresponding to the theoretical maximum daily intake (TMDI) - 0.05 mg/kg bw/day; G2-animals receiving a higher dose of glyphosate-corresponding to the acceptable daily intake (ADI)-0.5 mg/kg/day in gelatin capsules orally for 28 days. After this time, the animals were euthanized and small intestine samples were collected. Frozen sections were then subjected to the procedure of double immunofluorescent staining.

KEY RESULTS

Glyphosate supplementation led to alterations in the neurochemical code of the ENS neurons in the porcine duodenum. Generally, increased population of neurons immunoreactive to PACAP, CGRP, CART, nNOS, and a decreased number of VAChT-like immunoreactive neurons were noted.

CONCLUSIONS AND INFERENCES

It may be a first preclinical symptom of digestive tract dysfunction in the course of glyphosate intoxication and further studies are needed to assess the toxicity and risks of glyphosate to humans.

Acrylamide-Induced Changes in the Pituitary Adenylate Cyclase-Activating Polypeptide (PACAP) Immunoreactivity in Small Intestinal Intramural Neurons in Pigs

BACKGROUND

A particularly pressing problem is determining consumer-safe doses of potentially health- and life-threatening substances, such as acrylamide. The aim of the study was to determine how acrylamide affects the pituitary adenylate cyclase-activating polypeptide (PACAP)-immunoreactive intramural neurons in the small intestine of sexually immature gilts.

METHODS

The study was conducted on 15 sexually immature Danish gilts receiving for 28 days empty gelatin capsules or acrylamide in low (0.5 µg/kg of body weight (b.w.)/day) and high (5 µg/kg b.w./day) doses. After euthanasia, intestinal sections were stained using the double immunofluorescence staining procedure.

RESULTS

Studies have shown that oral administration of acrylamide in both doses induced a response of intramural neurons expressed as an increase in the population of PACAP-immunoreactive neurons in the small intestine. In the duodenum, only in the myenteric plexus (MP) was an increase in the number of PACAP-immunoreactive (IR) neurons observed in both experimental groups, while in the outer submucous plexus (OSP) and inner submucous plexus (ISP), an increase was noted only in the high-dose group. In the jejunum, both doses of acrylamide led to an increase in the population of PACAP-IR neurons in each enteric plexus (MP, OSP, ISP), while in the ileum, only supplementation with the higher dose of acrylamide increased the number of PACAP-IR enteric neurons in the MP, OSP, and ISP.

CONCLUSIONS

The obtained results suggest the participation of PACAP in acrylamide-induced plasticity of enteric neurons, which may be an important line of defence from the harmful action of acrylamide on the small intestines.

Isolation, Expansion, and Endoscopic Delivery of Autologous Enteric Neuronal Stem Cells in Swine

The enteric nervous system (ENS) is an extensive network of neurons and glia within the wall of the gastrointestinal (GI) tract that regulates many essential GI functions. Consequently, disorders of the ENS due to developmental defects, inflammation, infection, or age-associated neurodegeneration lead to serious neurointestinal diseases. Despite the prevalence and severity of these diseases, effective treatments are lacking as they fail to directly address the underlying pathology. Neuronal stem cell therapy represents a promising approach to treating diseases of the ENS by replacing the absent or injured neurons, and an autologous source of stem cells would be optimal by obviating the need for immunosuppression. We utilized the swine model to address key questions concerning cell isolation, delivery, engraftment, and fate in a large animal relevant to human therapy. We successfully isolated neural stem cells from a segment of small intestine resected from 1-month-old swine. Enteric neuronal stem cells (ENSCs) were expanded as neurospheres that grew optimally in low-oxygen (5%) culture conditions. Enteric neuronal stem cells were labeled by lentiviral green fluorescent protein (GFP) transduction, then transplanted into the same swine from which they had been harvested. Endoscopic ultrasound was then utilized to deliver the ENSCs (10,000-30,000 neurospheres per animal) into the rectal wall. At 10 and 28 days following injection, autologously derived ENSCs were found to have engrafted within rectal wall, with neuroglial differentiation and no evidence of ectopic spreading. These findings strongly support the feasibility of autologous cell isolation and delivery using a clinically useful and minimally invasive technique, bringing us closer to first-in-human ENSC therapy for neurointestinal diseases.

Involvement of interstitial cells of Cajal in nicotinic acetylcholine receptor-induced relaxation of the porcine lower esophageal sphincter

The interstitial cells of Cajal (ICCs) play an important role in coordinated gastrointestinal motility. The present study aimed to elucidate whether or how ICCs are involved in the lower esophageal sphincter (LES) relaxation induced by stimulation of the nicotinic acetylcholine receptor. The application of 1,1-dimethyl-4-phenyl-piperazinium (DMPP; a nicotinic acetylcholine receptor agonist) induced a transient relaxation in the circular smooth muscle of the porcine LES. DMPP-induced relaxation was abolished by not only 1 μM tetrodotoxin but also the inhibition of ICC activity by pretreatment with 100 μM carbenoxolone (a gap junction inhibitor), pretreatment with 100 μM CaCCinh-A01 (an anoctamin-1 blocker acting as a calcium-activated chloride channel inhibitor), and pretreatment with Cl^--free solution. However, pretreatment with 100 μM N^ω-nitro-L-arginine methyl ester had little effect on DMPP-induced relaxation. Furthermore, DMPP-induced relaxation was inhibited by pretreatment with 1 mM suramin, a purinergic P2 receptor antagonist, but not by 1 μM VIP (6-28), a vasoactive intestinal peptide (VIP) receptor antagonist. Stimulation of the purinergic P2 receptor with adenosine triphosphate (ATP) induced relaxation, which was abolished by the inhibition of ICC activity by pretreatment with CaCCinh-A01. In conclusion, membrane hyperpolarization of the ICCs via the activation of anoctamin-1 plays a central role in DMPP-induced relaxation. ATP may be a neurotransmitter for inhibitory enteric neurons, which stimulate the ICCs. The ICCs act as the interface of neurotransmission of nicotinic acetylcholine receptor in order to induce LES relaxation.

Effect of NSAIDs Supplementation on the PACAP-, SP- and GAL-Immunoreactive Neurons in the Porcine Jejunum

Side effects associated with nonsteroidal anti-inflammatory drugs (NSAIDs) treatment are a serious limitation of their use in anti-inflammatory therapy. The negative effects of taking NSAIDs include abdominal pain, indigestion nausea as well as serious complications such as bleeding and perforation. The enteric nervous system is involved in regulation of gastrointestinal functions through the release of neurotransmitters. The present study was designed to determine, for the first time, the changes in pituitary adenylate cyclase-activating polypeptide (PACAP), substance P (SP) and galanin (GAL) expression in porcine jejunum after long-term treatment with aspirin, indomethacin and naproxen. The study was performed on 16 immature pigs. The animals were randomly divided into four experimental groups: control, aspirin, indomethacin and naproxen. Control animals were given empty gelatin capsules, while animals in the test groups received selected NSAIDs for 28 days. Next, animals from each group were euthanized. Frozen sections were prepared from collected jejunum and subjected to double immunofluorescence staining. NSAIDs supplementation caused a significant increase in the population of PACAP-, SP- and GAL-containing enteric neurons in the porcine jejunum. Our results suggest the participation of the selected neurotransmitters in regulatory processes of the gastrointestinal function and may indicate the direct toxic effect of NSAIDs on the ENS neurons.

Fast synaptic excitatory neurotransmission in the human submucosal plexus

BACKGROUND

Acetylcholine is the main excitatory neurotransmitter in the enteric nervous system (ENS) in all animal models examined so far. However, data for the human ENS is scarce.

METHODS

We used neuroimaging using voltage and calcium dyes, Ussing chamber, and immunohistochemistry to study fast synaptic neurotransmission in submucosal plexus neurons of the human gut.

KEY RESULTS

Electrical stimulation of intraganglionic fiber tracts led to fast excitatory postsynaptic potentials (fEPSPs) in 29 submucosal neurons which were all blocked by the nicotinic antagonist hexamethonium. The nicotinic agonist DMPP mimicked the effects of electrical stimulation and had excitatory effects on 56 of 73 neurons. The unselective NMDA antagonist MK-801 blocked fEPSPs in 14 out of 22 neurons as well as nicotine evoked spike discharge. In contrast, the application of NMDA showed only weak effects on excitability or calcium transients. This agreed with the finding that the specific NMDA antagonist D-APV reduced fEPSPs in only 1 out of 40 neurons. Application of AMPA or kainite had no effect in 41 neurons or evoked spike discharge in only one out of 41 neurons, respectively. Immunohistochemistry showed that 98.7 ± 2.4% of all submucosal neurons (n = 6 preparations, 1003 neurons) stained positive for the nicotinic receptor (α₁ , α₂ or α₃ -subunit). Hexamethonium (200 µM) reduced nerve-evoked chloride secretion by 34.3 ± 18.6% (n = 14 patients), whereas D-APV had no effect.

CONCLUSION & INFERENCE

Acetylcholine is the most important mediator of fast excitatory postsynaptic transmission in human submucous plexus neurons whereas glutamatergic fEPSPs were rarely encountered.

Classification of human enteric neurons

Major advances in our understanding of the functional heterogeneity of enteric neurons are driven by the application of newly developed, innovative methods. In contrast to this progress, both animal and human enteric neurons are usually divided into only two morphological subpopulations, “Dogiel type II” neurons (with several long processes) and “Dogiel type I” neurons (with several short processes). This implies no more than the distinction of intrinsic primary afferent from all other enteric neurons. The well-known chemical and functional diversity of enteric neurons is not reflected by this restrictive dichotomy of morphological data. Recent structural investigations of human enteric neurons were performed by different groups which mainly used two methodical approaches, namely detecting the architecture of their processes and target-specific tracing of their axonal courses. Both methods were combined with multiple immunohistochemistry in order to decipher neurochemical codes. This review integrates these morphological and immunohistological data and presents a classification of human enteric neurons which we believe is not yet complete but provides an essential foundation for the further development of human gastrointestinal neuropathology.

Changes Caused by Low Doses of Bisphenol A (BPA) in the Neuro-Chemistry of Nerves Located in the Porcine Heart

Simple Summary

Bisphenol A (BPA) is a substance commonly used in the plastics industry, which is a part of many everyday items. It may leach from plastics and penetrate food, water, soil and air. It is known that BPA negatively affects living organisms. It impairs the functions of the intestine, neurons, reproductive organs, endocrine glands and immune cells. Previous studies have also reported that BPA negatively influences the cardiovascular system, leading to heart arrhythmia, intensification of atherosclerosis, blood hypertension and increased risk of a heart attack. However, many aspects of the influence of BPA on the heart are still poorly understood. One of these aspects is the BPA impact on heart innervation. Therefore, this article aimed to investigate the influence of low doses of BPA on the number of nerves containing selected active substances taking part in neuronal stimuli conduction located in the porcine heart apex. The results indicate that even relatively low doses of BPA are not neutral to the cardiovascular system, because they affect the neurochemical characterization of nerves in the heart. These changes may underlie the negative effects of BPA on the heart.

Abstract

Bisphenol A (BPA) contained in plastics used in the production of various everyday objects may leach from these items and contaminate food, water and air. As an endocrine disruptor, BPA negatively affects many internal organs and systems. Exposure to BPA also contributes to heart and cardiovascular system dysfunction, but many aspects connected with this activity remain unknown. Therefore, this study aimed to investigate the impact of BPA in a dose of 0.05 mg/kg body weight/day (in many countries such a dose is regarded as a tolerable daily intake–TDI dose of BPA–completely safe for living organisms) on the neurochemical characterization of nerves located in the heart wall using the immunofluorescence technique. The obtained results indicate that BPA (even in such a relatively low dose) increases the number of nerves immunoreactive to neuropeptide Y, substance P and tyrosine hydroxylase (used here as a marker of sympathetic innervation). However, BPA did not change the number of nerves immunoreactive to vesicular acetylcholine transporter (used here as a marker of cholinergic structures). These observations suggest that changes in the heart innervation may be at the root of BPA-induced circulatory disturbances, as well as arrhythmogenic and/or proinflammatory effects of this endocrine disruptor. Moreover, changes in the neurochemical characterization of nerves in the heart wall may be the first sign of exposure to BPA.

The Neonatal and Juvenile Pig in Pediatric Drug Discovery and Development

Pharmacotherapy in pediatric patients is challenging in view of the maturation of organ systems and processes that affect pharmacokinetics and pharmacodynamics. Especially for the youngest age groups and for pediatric-only indications, neonatal and juvenile animal models can be useful to assess drug safety and to better understand the mechanisms of diseases or conditions. In this respect, the use of neonatal and juvenile pigs in the field of pediatric drug discovery and development is promising, although still limited at this point. This review summarizes the comparative postnatal development of pigs and humans and discusses the advantages of the juvenile pig in view of developmental pharmacology, pediatric diseases, drug discovery and drug safety testing. Furthermore, limitations and unexplored aspects of this large animal model are covered. At this point in time, the potential of the neonatal and juvenile pig as nonclinical safety models for pediatric drug development is underexplored.

The Endocrine Disruptor Bisphenol A (BPA) Affects the Enteric Neurons Immunoreactive to Neuregulin 1 (NRG1) in the Enteric Nervous System of the Porcine Large Intestine

The enteric nervous system (ENS), located in the wall of the gastrointestinal (GI) tract, is characterized by complex organization and a high degree of neurochemical diversity of neurons. One of the less known active neuronal substances found in the enteric neurons is neuregulin 1 (NRG1), a factor known to be involved in the assurance of normal development of the nervous system. During the study, made up using the double immunofluorescence technique, the presence of NRG1 in the ENS of the selected segment of porcine large intestine (caecum, ascending and descending colon) was observed in physiological conditions, as well as under the impact of low and high doses of bisphenol A (BPA) which is commonly used in the production of plastics. In control animals in all types of the enteric plexuses, the percentage of NRG1-positive neurons oscillated around 20% of all neurons. The administration of BPA caused an increase in the number of NRG1-positive neurons in all types of the enteric plexuses and in all segments of the large intestine studied. The most visible changes were noted in the inner submucous plexus of the ascending colon, where in animals treated with high doses of BPA, the percentage of NRG1-positive neurons amounted to above 45% of all neuronal cells. The mechanisms of observed changes are not entirely clear, but probably result from neurotoxic, neurodegenerative and/or proinflammatory activity of BPA and are protective and adaptive in nature.

Quantitative analysis of enteric neurons containing choline acetyltransferase and nitric oxide synthase immunoreactivities in the submucosal and myenteric plexuses of the porcine colon

The enteric nervous system (ENS) controls gastrointestinal functions. In large mammals' intestine, it comprises an inner (ISP) and outer (OSP) submucous plexus and a myenteric plexus (MP). This study quantifies enteric neurons in the ISP, OSP, and MP of the pig ascending (AC) and descending colon (DC) using the HuC/D, choline acetyltransferase (ChAT), and neuronal nitric oxide synthase (nNOS) neuronal markers in whole mount preparations with multiple labeling immunofluorescence. We established that the ISP contains the highest number of HuC/D neurons/mm², which were more abundant in AC vs. DC, followed by OSP and MP with similar density in AC and DC. In the ISP, the density of ChAT immunoreactive (IR) neurons was very similar in AC and DC (31% and 35%), nNOS-IR neurons were less abundant in AC than DC (15% vs. 42%, P < 0.001), and ChAT/nNOS-IR neurons were 5% and 10%, respectively. In the OSP, 39-44% of neurons were ChAT-IR in AC and DC, while 45% and 38% were nNOS-IR and 10-12% were ChAT/nNOS-IR (AC vs. DC P < 0.05). In the MP, ChAT-IR neurons were 44% in AC and 54% in DC (P < 0.05), nNOS-IR neurons were 50% in both, and ChAT/nNOS-IR neurons were 12 and 18%, respectively. The ENS architecture with multilayered submucosal plexuses and the distribution of functionally distinct groups of neurons in the pig colon are similar to humans, supporting the suitability of the pig as a model and providing the platform for investigating the mechanisms underlying human colonic diseases.

Compression and stretch sensitive submucosal neurons of the porcine and human colon

The pig is commonly believed to be a relevant model for human gut functions-however, there are only a few comparative studies and none on neural control mechanisms. To address this lack we identified as one central aspect mechanosensitive enteric neurons (MEN) in porcine and human colon. We used neuroimaging techniques to record responses to tensile or compressive forces in submucous neurons. Compression and stretch caused Ca-transients and immediate spike discharge in 5-11% of porcine and 15-24% of human enteric neurons. The majority of these MEN exclusively responded to either stimulus quality but about 9% responded to both. Most of the MEN expressed choline acetyltransferase and substance P; nitric oxide synthase-positive MEN primarily occurred in distal colon. The findings reveal common features of MEN in human and pig colon which we interpret as a result of species-independent evolutionary conservation rather than a specific functional proximity between the two species.

Effects of endocrine disrupting chemicals in pigs

Endocrine-disrupting chemicals (EDCs) are compounds that interfere with the expression, synthesis, and activity of hormones in organisms. They are released into the environment from flame retardants and products containing plasticizers. Persistent pesticides, such as dichlorodiphenyltrichloroethane (DDT) and hexachlorobenzene, also disrupt the endocrine system through interaction with hormone receptors. Endogenous hormones, such as 17β-estradiol (E2), are released in the urine and feces of farm animals and seep into terrestrial and aquatic ecosystems through sewage. Pigs are widely used as animal models to determine the effects of EDCs because they are physiologically, biochemically, and histologically similar to humans. EDCs primarily disrupt the reproductive and nervous systems of pigs. Moreover, embryonic development during the prenatal and early postnatal periods is particularly sensitive to EDCs. Mycotoxins, such as zearalenone, are food contaminants that alter hormonal activities in pigs. Mycotoxins also alter the innate immune system in pigs, making them vulnerable to diseases. It has been reported that farm animals are exposed to various types of EDCs, which accumulate in tissues, such as those of gonads, livers, and intestines. There is a lack of an integrated understanding of the impact of EDCs on porcine reproduction and development. Thus, this article aims to provide a comprehensive review of literature regarding the effects of EDCs in pigs.

The Influence of Bisphenol a on the Nitrergic Nervous Structures in the Domestic Porcine Uterus

Bisphenol A (BPA) is one of the most common environmental pollutants among endocrine disruptors. Due to its similarity to estrogen, BPA may affect estrogen receptors and show adverse effects on many internal organs. The reproductive system is particularly vulnerable to the impact of BPA, but knowledge about BPA-induced changes in the innervation of the uterus is relatively scarce. Therefore, this study aimed to investigate the influence of various doses of BPA on nitrergic nerves supplying the uterus with the double immunofluorescence method. It has been shown that even low doses of BPA caused an increase in the number of nitrergic nerves in the uterine wall and changed their neurochemical characterization. During the present study, changes in the number of nitrergic nerves simultaneously immunoreactive to substance P, vasoactive intestinal polypeptide, pituitary adenylate cyclase-activating peptide, and/or cocaine- and amphetamine-regulated transcript were found under the influence of BPA. The obtained results strongly suggest that nitrergic nerves in the uterine wall participate in adaptive and/or protective processes aimed at homeostasis maintenance in the uterine activity under the impact of BPA.

Changes in the Neurochemical Characterization of Enteric Neurons in the Porcine Duodenum After Administration of Low-Dose Salmonella Enteritidis Lipopolysaccharides

Lipopolysaccharides (LPS), also known as lipoglycans or endotoxins, form part of the outer membrane of Gram-negative bacteria. Previous studies have described the various harmful impacts of LPS on humans and animals. Nevertheless, many aspects of these effects are still not fully explained. One of them is the influence of endotoxins on the neurochemical characterization of neurons within the enteric nervous system (ENS), which is found in the intestinal wall and plays important adaptive roles during pathological processes and exposures. In this study, the impact of a low single dose of Salmonella Enteritidis LPS on the duodenal enteric neurons immunoreactive to substance P (SP), vasoactive intestinal polypeptide (VIP), pituitary adenylate cyclase activating peptide (PACAP-27), and cocaine- and amphetamine-regulated transcript (CART) was studied using a double immunofluorescence technique. During the study, it was shown that even a low dose of LPS affects the number of enteric neurons containing the neuropeptides studied, and these changes were dependent on the type of the enteric plexus. The most visible changes concerned the SP-like immunoreactive (LI) neurons in the outer submucous plexus (LPS caused an increase in the percentage of these neurons from15.74 ± 0.61 to 21.72 ± 0.79%). Furthermore, the VIP-LI neurons in the inner submucous plexus were seen to decrease from 12.64 ± 0.83 to 5.96 ± 0.58%. The mechanisms behind these noted fluctuations are not clear, but it may be connected with the pro-inflammatory and neurotoxic activity of LPS.

Animal Models for Functional Gastrointestinal Disorders

Functional gastrointestinal disorders (FGID), such as functional dyspepsia (FD) and irritable bowel syndrome (IBS) are characterized by chronic abdominal symptoms in the absence of an organic, metabolic or systemic cause that readily explains these complaints. Their pathophysiology is still not fully elucidated and animal models have been of great value to improve the understanding of the complex biological mechanisms. Over the last decades, many animal models have been developed to further unravel FGID pathophysiology and test drug efficacy. In the first part of this review, we focus on stress-related models, starting with the different perinatal stress models, including the stress of the dam, followed by a discussion on neonatal stress such as the maternal separation model. We also describe the most commonly used stress models in adult animals which brought valuable insights on the brain-gut axis in stress-related disorders. In the second part, we focus more on models studying peripheral, i.e., gastrointestinal, mechanisms, either induced by an infection or another inflammatory trigger. In this section, we also introduce more recent models developed around food-related metabolic disorders or food hypersensitivity and allergy. Finally, we introduce models mimicking FGID as a secondary effect of medical interventions and spontaneous models sharing characteristics of GI and anxiety-related disorders. The latter are powerful models for brain-gut axis dysfunction and bring new insights about FGID and their comorbidities such as anxiety and depression.

Influence of Acrylamide Administration on the Neurochemical Characteristics of Enteric Nervous System (ENS) Neurons in the Porcine Duodenum

The digestive tract, especially the small intestine, is one of the main routes of acrylamide absorption and is therefore highly exposed to the toxic effect of acrylamide contained in food. The aim of this experiment was to elucidate the effect of low (tolerable daily intake—TDI) and high (ten times higher than TDI) doses of acrylamide on the neurochemical phenotype of duodenal enteric nervous system (ENS) neurons using the pig as an animal model. The experiment was performed on 15 immature gilts of the Danish Landrace assigned to three experimental groups: control (C) group—pigs administered empty gelatine capsules, low dose (LD) group—pigs administered capsules with acrylamide at the TDI dose (0.5 μg/kg body weight (b.w.)/day), and the high dose (HD) group—pigs administered capsules with acrylamide at a ten times higher dose than the TDI (5 μg/kg b.w./day) with a morning feeding for 4 weeks. Administration of acrylamide, even in a low (TDI) dose, led to an increase in the percentage of enteric neurons immunoreactive to substance P (SP), calcitonin gene-related peptide (CGRP), galanin (GAL), neuronal nitric oxide synthase (nNOS), and vesicular acetylcholine transporter (VACHT) in the porcine duodenum. The severity of the changes clearly depended on the dose of acrylamide and the examined plexus. The obtained results suggest the participation of these neuroactive substances in acrylamide-inducted plasticity and the protection of ENS neurons, which may be an important line of defence from the harmful action of acrylamide.

Somatostatin as an Active Substance in the Mammalian Enteric Nervous System

Somatostatin (SOM) is an active substance which most commonly occurs in endocrine cells, as well as in the central and peripheral nervous system. One of the parts of the nervous system where the presence of SOM has been confirmed is the enteric nervous system (ENS), located in the wall of the gastrointestinal (GI) tract. It regulates most of the functions of the stomach and intestine and it is characterized by complex organization and a high degree of independence from the central nervous system. SOM has been described in the ENS of numerous mammal species and its main functions in the GI tract are connected with the inhibition of the intestinal motility and secretory activity. Moreover, SOM participates in sensory and pain stimuli conduction, modulation of the release of other neuronal factors, and regulation of blood flow in the intestinal vessels. This peptide is also involved in the pathological processes in the GI tract and is known as an anti-inflammatory agent. This paper, which focuses primarily on the distribution of SOM in the ENS and extrinsic intestinal innervation in various mammalian species, is a review of studies concerning this issue published from 1973 to the present.

Involvement of different receptor subtypes in prostaglandin E2-induced contraction and relaxation in the lower esophageal sphincter and esophageal body

Prostaglandin E₂ (PGE₂) plays a role in the pathogenesis of gastro-esophageal reflux disease (GERD). There are 4 subtypes of PGE₂, PGE₂ receptor 1, 2, 3 and 4 (EP 1-4). In GERD patents, PGE₂, EP2 and EP4 are upregulated. However, the effects of PGE2 on esophageal motility remain elusive. We examined how PGE₂ regulates motility in the porcine circular smooth muscle of the lower esophageal sphincter (LES), and the circular and longitudinal smooth muscle of the esophagus body in organ bath. PGE₂ induced tonic relaxation in the LES and circular smooth muscle, but transient contraction in longitudinal smooth muscle. The relaxation of the LES and circular smooth muscle was similar in pattern and mechanism, but was much larger in the LES. The relaxation was completely blocked by a voltage-gated K⁺ channel blocker or 40 mM K⁺ depolarization, indicating the involvement of K⁺ channel. Longitudinal smooth muscle contraction was completely blocked by an L-type Ca²⁺ channel blocker, showing the contribution of Ca²⁺ movement. The involvement of the EP receptor in motility was examined with selective receptor agonists and antagonists. Activation of EP2 and EP4 caused relaxation in the LES and circular smooth muscle. Compatible with PGE₂, EP2 and EP4 agonists caused more significant relaxation in the LES than in circular smooth muscle. EP1 contributed to the longitudinal smooth muscle contraction. The different effects of PGE₂ in the LES, circular and longitudinal smooth muscle contributes to esophageal motility, their impairment might increase the amount and frequency of esophageal reflux.

The impact of low and high doses of acrylamide on the intramural neurons of the porcine ileum

The present study was designed to assess the influence of acrylamide supplementation, in tolerable daily intake (TDI) dose and a dose ten times higher than TDI, on the neurochemical phenotype of the ENS neurons and synthesis of proinflammatory cytokines in the wall of the porcine ileum. The study was performed on 15 juvenile female Danish Landrace pigs, divided into three groups: C group- animals receiving empty gelatine capsules, LD group- animals receiving capsules with the TDI dose (0.5 μg/kg b.w./day) of acrylamide and HD group- animals receiving acrylamide in a dose ten times higher than the TDI (5 μg/kg b.w./day) in a morning meal for 28 days. It was established that supplementation of acrylamide led to an increase in substance P (SP)-, calcitonin gene-related peptide (CGRP)-, galanin (GAL)- and vesicular acetylcholine transporter (VAChT)-like immunoreactive (LI) neurons as well as a decrease in neuronal nitric oxide synthase (nNOS) -like immunoreactivity in all types of ileum intramural plexuses. Moreover, using ELISA method, an increase in the level of proinflammatory cytokines (IL-1β, IL-6 and TNF- α) was noted in the ileum wall. The results suggest that SP, CGRP, GAL, nNOS and VACHT participate in the regulation of inflammatory conditions induced by acrylamide supplementation.

Alterations in Galanin-Like Immunoreactivity in the Enteric Nervous System of the Porcine Stomach Following Acrylamide Supplementation

In recent years, a significant increase in the consumption of products containing large amounts of acrylamide (e.g., chips, fries, coffee), especially among young people has been noted. The present study was created to establish the impact of acrylamide supplementation, in tolerable daily intake (TDI) dose and a dose ten times higher than TDI, on the population of galanin-like immunoreactive (GAL-LI) stomach neurons in pigs. Additionally, in the present study, the possible functional co-operation of GAL with other neuroactive substances and their role in acrylamide intoxication was investigated. Using double-labelling immunohistochemistry, alterations in the expression of GAL were examined in the porcine stomach enteric neurons after low and high doses of acrylamide supplementation. Generally, upregulation in GAL-LI immunoreactivity in both myenteric and submucous plexuses was noted in all stomach fragments studied. Additionally, the proportion of GAL-expressing cell bodies simultaneously immunoreactive to vasoactive intestinal peptide (VIP), neuronal nitric oxide synthase (nNOS) and cocaine- and amphetamine- regulated transcript peptide (CART) also increased. The results suggest neurotrophic or/and neuroprotective properties of GAL and possible co-operation of GAL with VIP, nNOS, CART in the recovery processes in the stomach enteric nervous system (ENS) neurons following acrylamide intoxication.

Five-fold Gastrointestinal Electrical Stimulation With Electromyography-based Activity Analysis: Towards Multilocular Theranostic Intestinal Implants

Background/Aims

Motility disorders are common and may affect the entire gastrointestinal (GI) tract but current treatment is limited. Multilocular sensing of GI electrical activity and variable electrical stimulation (ES) is a promising option. The aim of our study is to investigate the effects of adjustable ES on poststimulatory spike activities in 5 GI segments.

Methods

Six acute porcine experiments were performed with direct ES by 4 ES parameter sets (30 seconds, 25 mA, 500 microseconds or 1000 microseconds, 30 Hz or 130 Hz) applied through subserosal electrodes in the stomach, duodenum, ileum, jejunum, and colon. Multi-channel electromyography of baseline and post-stimulatory GI electrical activity were recorded for 3 minutes with hook needle and hook-wire electrodes. Spike activities were algorithmically calculated, visualized in a heat map, and tested for significance by Poisson analysis.

Results

Post-stimulatory spike activities were markedly increased in the stomach (7 of 24 test results), duodenum (8 of 24), jejunum (23 of 24), ileum (18 of 24), and colon (5 of 24). ES parameter analysis revealed that 80.0% of the GI parts (all but duodenum) required a pulse width of 1000 microseconds, and 60.0% (all but jejunum and colon) required 130 Hz frequency for maximum spike activity. Five reaction patterns were distinguished, with 30.0% earlier responses (type I), 42.5% later or mixed type responses (type II, III, and X), and 27.5% non-significant responses (type 0).

Conclusions

Multilocular ES with variable ES parameters is feasible and may significantly modulate GI electrical activity. Automated electromyography analysis revealed complex reaction patterns in the 5 examined GI segments.

Hyperglycaemia-Induced Downregulation in Expression of nNOS Intramural Neurons of the Small Intestine in the Pig

Diabetic autonomic peripheral neuropathy (PN) involves a broad spectrum of organs. One of them is the gastrointestinal (GI) tract. The molecular mechanisms underlying the pathogenesis of digestive complications are not yet fully understood. Digestion is controlled by the central nervous system (CNS) and the enteric nervous system (ENS) within the wall of the GI tract. Enteric neurons exert regulatory effects due to the many biologically active substances secreted and released by enteric nervous system (ENS) structures. These include nitric oxide (NO), produced by the neural nitric oxide synthase enzyme (nNOS). It is a very important inhibitory factor, necessary for smooth muscle relaxation. Moreover, it was noted that nitrergic innervation can undergo adaptive changes during pathological processes. Additionally, nitrergic neurons function may be regulated through the synthesis of other active neuropeptides. Therefore, in the present study, using the immunofluorescence technique, we first examined the influence of hyperglycemia on the NOS- containing neurons in the porcine small intestine and secondly the co-localization of nNOS with vasoactive intestinal polypeptide (VIP), galanin (GAL) and substance P (SP) in all plexuses studied. Following chronic hyperglycaemia, we observed a reduction in the number of the NOS-positive neurons in all intestinal segments studied, as well as an increased in investigated substances in nNOS positive neurons. This observation confirmed that diabetic hyperglycaemia can cause changes in the neurochemical characteristics of enteric neurons, which can lead to numerous disturbances in gastrointestinal tract functions. Moreover, can be the basis of an elaboration of these peptides analogues utilized as therapeutic agents in the treatment of GI complications.

Acrylamide-induced alterations in the cocaine- and amphetamine-regulated peptide transcript (CART)-like immunoreactivity within the enteric nervous system of the porcine small intestines

The main goal of the present study was to determine the influence of low and high doses of acrylamide on CART-like immunoreactivity within the ENS of the porcine small intestines. Investigation was performed on 15 sexually immature female pigs, divided into three groups: control group, where empty gelatin capsules were administered, and two experimental groups, where capsules containing low or high doses of acrylamide were given. After 28days of acrylamide exposure all animals were euthanized with a gradual overdose of anaesthetics. Immediately after euthanasia fragments of the duodenum, jejunum and ileum were collected and fixed. Then, 14μm-thick cryostat sections were processed for routine double-labelling immunofluorescence using primary antisera directed towards a pan neuronal marker - protein gene-product 9.5 (PGP 9.5) and cocaine- and amphetamine-regulated peptide transcript (CART). During the present investigation, CART-LI cell bodies were detected in all types of enteric plexuses of duodenum, jejunum and ileum. Acrylamide intoxication resulted in a significant increase in expression of CART in the intramural neurons of the porcine small intestines, especially in myenteric plexuses. It may suggest participation of CART in neuronal protection and recovery processes within the gut. Moreover, results of the present study suggest that even low doses of acrylamide cause a significant response of ENS neurons.

The influence of experimental inflammation and axotomy on leucine enkephalin (leuENK) distribution in intramural nervous structures of the porcine descending colon

Background

The enteric nervous system (ENS), located in the intestinal wall and characterized by considerable independence from the central nervous system, consists of millions of cells. Enteric neurons control the majority of functions of the gastrointestinal tract using a wide range of substances, which are neuromediators and/or neuromodulators. One of them is leucine–enkephalin (leuENK), which belongs to the endogenous opioid family. It is known that opioids in the gastrointestinal tract have various functions, including visceral pain conduction, intestinal motility and secretion and immune processes, but many aspects of distribution and function of leuENK in the ENS, especially during pathological states, remain unknown.

Results

During this experiment, the distribution of leuENK – like immunoreactive (leuENK-LI) nervous structures using the immunofluorescence technique were studied in the porcine colon in physiological conditions, during chemically-induced inflammation and after axotomy. The study included the circular muscle layer, myenteric (MP), outer submucous (OSP) and inner submucous plexus (ISP) and the mucosal layer. In control animals, the number of leuENK-LI neurons amounted to 4.86 ± 0.17%, 2.86 ± 0.28% and 1.07 ± 0.08% in the MP, OSP and ISP, respectively. Generally, both pathological stimuli caused an increase in the number of detected leuENK-LI cells, but the intensity of the observed changes depended on the factor studied and part of the ENS. The percentage of leuENK-LI perikarya amounted to 11.48 ± 0.96%, 8.71 ± 0.13% and 9.40 ± 0.76% during colitis, and 6.90 ± 0.52% 8.46 ± 12% and 4.48 ± 0.44% after axotomy in MP, OSP and ISP, respectively. Both processes also resulted in an increase in the number of leuENK-LI nerves in the circular muscle layer, whereas changes were less visible in the mucosa during inflammation and axotomy did not change the number of leuENK-LI mucosal fibers.

Conclusions

LeuENK in the ENS takes part in intestinal regulatory processes not only in physiological conditions, but also under pathological factors. The observed changes are probably connected with the participation of leuENK in sensory and motor innervation and the neuroprotective effects of this substance. Differences in the number of leuENK-LI neurons during inflammation and after axotomy may suggest that the exact functions of leuENK probably depend on the type of pathological factor acting on the intestine.

The Influence of High and Low Doses of Bisphenol A (BPA) on the Enteric Nervous System of the Porcine Ileum

Bisphenol A, used in the production of plastic, is able to leach from containers into food and cause multidirectional adverse effects in living organisms, including neurodegeneration and metabolic disorders. Knowledge of the impact of BPA on enteric neurons is practically non-existent. The destination of this study was to investigate the influence of BPA at a specific dose (0.05 mg/kg body weight/day) and at a dose ten times higher (0.5 mg/kg body weight/day), given for 28 days, on the porcine ileum. The influence of BPA on enteric neuron immunoreactive to selected neuronal active substances, including substance P (SP), vasoactive intestinal polypeptide (VIP), galanin (GAL), vesicular acetylcholine transporter (VAChT—used here as a marker of cholinergic neurons), and cocaine- and amphetamine-regulated transcript peptide (CART), was studied by the double immunofluorescence method. Both doses of BPA affected the neurochemical characterization of the enteric neurons. The observed changes depended on the type of enteric plexus but were generally characterized by an increase in the number of cells immunoreactive to the particular substances. More visible fluctuations were observed after treatment with higher doses of BPA. The results confirm that even low doses of BPA may influence the neurochemical characterization of the enteric neurons and are not neutral for living organisms.

Calbindin D28k-Immunoreactivity in Human Enteric Neurons

Calbindin (CALB) is well established as immunohistochemical marker for intrinsic primary afferent neurons in the guinea pig gut. Its expression by numerous human enteric neurons has been demonstrated but little is known about particular types of neurons immunoreactive for CALB. Here we investigated small and large intestinal wholemount sets of 26 tumor patients in order to evaluate (1) the proportion of CALB⁺ neurons in the total neuron population, (2) the colocalization of CALB with calretinin (CALR), somatostatin (SOM) and vasoactive intestinal peptide (VIP) and (3) the morphology of CALB⁺ neurons. CALB⁺ neurons represented a minority of myenteric neurons (small intestine: 31%; large intestine: 25%) and the majority of submucosal neurons (between 72 and 95%). In the submucosa, most CALB⁺ neurons co-stained for CALR and VIP (between 69 and 80%) or for SOM (between 20 and 3%). In the myenteric plexus, 85% of CALB⁺ neurons did not co-stain with the other markers investigated. An unequivocal correlation between CALB reactivity and neuronal morphology was found for myenteric type III neurons in the small intestine: uniaxonal neurons with long, slender and branched dendrites were generally positive for CALB. Since also other neurons displayed occasional CALB reactivity, this protein is not suited as an exclusive marker for type III neurons.

Neurochemical characterization of nerve fibers in the porcine gallbladder wall under physiological conditions and after the administration of Salmonella enteritidis lipopolysaccharides (LPS)

Lipopolysaccharides (LPS, bacterial endotoxin) are a component of the cellular membrane of Gram-negative bacteria, which is known as an important pathological factor. In spite of many previous studies describing multidirectional negative effects of LPS on living organisms, the knowledge concerning the influence of bacterial endotoxins on the gallbladder innervation is extremely scarce. The present study, based on the immunofluorescence technique, describes the changes in the neurochemical characterization of nerves within various parts of the porcine gallbladder (neck, body and fundus) after the administration of low doses of LPS. The obtained results show that even low doses of bacterial endotoxins affect the nerve structures within the gallbladder wall and the intensity of fluctuations in immunoreactivity to particular substances clearly depends on the part of the investigated organ. The most evident changes were observed in the case of fibers exhibiting the presence of neuropeptide Y (an increase from 7.84 ± 0.17 to 14.66 ± 0.37) in the neck, substance P (an increase from 0.88 ± 0.1 to 8.4 ± 0.3) in the body and the vesicular acetylocholine transporter in the gallbladder's fundus (an increase from 4.29 ± 0.18 to 11.01 ± 0.26). The mechanisms of the observed changes still remain unclear, but probably they are connected with the pro-inflammatory and/or neurodegenerative activity of LPS.

Bisphenol A Causes Liver Damage and Selectively Alters the Neurochemical Coding of Intrahepatic Parasympathetic Nerves in Juvenile Porcine Models under Physiological Conditions

Bisphenol A (BPA) is an extremely common polymer that is used in typical everyday products throughout the world, especially in food and beverage containers. Within the last ten years, it has been found that the BPA monomer tends to leach into foodstuffs, and nanogram concentrations of it may cause a variety of deleterious health effects. These health problems are very evident in developing children and in young adults. The aim of this study was to expose developing pigs to dietary BPA at both legally acceptable and ten-fold higher levels. Livers that had been exposed to BPA showed vacuolar degeneration, sinusoidal dilatation, vascular congestion and glycogen depletion that increased with exposure levels. Furthermore, the livers of these models were then examined for irregularities and double-labeled immunofluorescence was used to check the innervated hepatic samples for varying neuronal expression of selected neuronal markers in the parasympathetic nervous system (PSNS). It was found that both the PSNS and all of the neuronal markers showed increased expression, with some of them being significant even at recommended safe exposure levels. The implications are quite serious since these effects have been observed at recommended safe levels with expression increasing in-line with exposure levels. The increased neuronal markers studied here have been previously correlated with behavioral/psychological disorders of children and young adults, as well as with childhood obesity and diabetes. However, further research must be performed in order to develop a mechanism for the above-mentioned correlations.

Modulation of the main porcine enteric neuropeptides by a single low-dose of lipopolysaccharide (LPS) Salmonella Enteritidis

Background

The present research was conducted to investigate the influence of a low, single dose of LPS, which does not result in any clinical symptoms of intoxication on the expression of selected neuropeptides within the intestines of the domestic pig.

Methods

This experiment was conducted on immature female pigs of the Pitrain × Duroc breed (n = five per group). Seven days after the intravenous injection of 10 mL saline solution for control animals and 5 μg/kg b.w. (in 10 mL saline solution) LPS Salmonella Enteritidis for the experimental group, the excised segments of duodenum, jejunum, ileum, ileocecal valve, caecum, descending colon, transverse colon, ascending colon and rectum were prepared to extract the main enteric neuropeptides, including GAL, NPY, SOM, SP, VIP.

Results

The results of this research indicate that single low-dose LPS S. Enteritidis produced changes in the content of the selected neuropeptides of the porcine intestine. The most visible changes were observed in the transverse colon, where LPS induced the increase of GAL expression from 19.41 ± 7.121 to 92.92 ± 11.447 ng/g tissue.

Conclusion

The exact functions of the substances studied and mechanisms of responses to LPS action depend on the sections of the intestines. The mechanisms of observed changes are not fully understood, but fluctuations in neuronal active substance levels may be connected with neurodegenerative and/or pro-inflammatory activity of LPS.

Impaired intestinal barrier function and relapsing digestive disease: Lessons from a porcine model of early life stress

Within this issue of Neurogastroenterology and Motility, an article by Pohl et al highlights new insights from a powerful porcine model of the link between early life adversity and relapsing functional gastrointestinal disorders. Early weaning stress closely mimics the early life psychosocial stressors that have been linked to adult onset gastrointestinal dysfunction. This early weaning model provides reproducible and highly translatable outcomes in young stress-challenged pigs. Due to the convincingly comparable neurological and gastroenterological anatomy and physiology between pigs and human beings, gastrointestinal stress and injury studies utilizing swine models will provide invaluable insights to improve our understanding and treatment of gastrointestinal disease in human beings. Future studies to examine mechanisms underlying this link between early life adversity and functional gastrointestinal disorders will explore the roles of gender and hypomaturity in gastrointestinal responses to stress.

Changes in Somatostatin-Like Immunoreactivity in the Sympathetic Neurons Projecting to the Prepyloric Area of the Porcine Stomach Induced by Selected Pathological Conditions

The aim of the present study was to define changes in the expression of somatostatin (SOM) in the sympathetic perikarya innervating the porcine stomach prepyloric area during acetylsalicylic-acid-induced gastritis (ASA) and experimentally induced hyperacidity (HCL) and following partial stomach resection (RES). On day 1, the stomachs were injected with neuronal retrograde tracer Fast Blue (FB). Animals in the ASA group were given acetylsalicylic acid orally for 21 days. On the 22nd day after FB injection, partial stomach resection was performed in RES animals. On day 23, HCL animals were intragastrically given 5 ml/kg of body weight of a 0.25 M aqueous solution of hydrochloric acid. On day 28, all pigs were euthanized. Then, 14-μm thick cryostat sections of the coeliac-superior mesenteric ganglion (CSMG) complexes were processed for routine double-labelling immunofluorescence. All pathological conditions studied resulted in upregulation of SOM-like (SOM-LI) immunoreactivity (from 14.97 ± 1.57% in control group to 33.72 ± 4.39% in the ASA group, to 39.02 ± 3.65% in the RES group, and to 29.63 ± 0.85% in the HCL group). The present studies showed that altered expression of SOM occurs in sympathetic neurons supplying the prepyloric area of the porcine stomach during adaptation to various pathological insults.

Zinc Transporter 3 (ZnT3) in the Enteric Nervous System of the Porcine Ileum in Physiological Conditions and during Experimental Inflammation

Zinc transporter 3 (ZnT3) is a member of the solute-linked carrier 30 (SLC 30) zinc transporter family. It is closely linked to the nervous system, where it takes part in the transport of zinc ions from the cytoplasm to the synaptic vesicles. ZnT3 has also been observed in the enteric nervous system (ENS), but its reactions in response to pathological factors remain unknown. This study, based on the triple immunofluorescence technique, describes changes in ZnT3-like immunoreactive (ZnT3-LI) enteric neurons in the porcine ileum, caused by chemically-induced inflammation. The inflammatory process led to a clear increase in the percentage of neurons immunoreactive to ZnT3 in all "kinds" of intramural enteric plexuses, i.e., myenteric (MP), outer submucous (OSP) and inner submucous (ISP) plexuses. Moreover, a wide range of other active substances was noted in ZnT3-LI neurons under physiological and pathological conditions, and changes in neurochemical characterisation of ZnT3⁺ cells in response to inflammation depended on the "kind" of enteric plexus. The obtained results show that ZnT3 is present in the ENS in a relatively numerous and diversified neuronal population, not only in physiological conditions, but also during inflammation. The reasons for the observed changes are not clear; they may be connected with the functions of zinc ions and their homeostasis disturbances in pathological processes. On the other hand, they may be due to adaptive and/or neuroprotective processes within the pathologically altered gastrointestinal tract.

Trypsin induces biphasic muscle contraction and relaxation via transient receptor potential vanilloid 1 and neurokinin receptors 1/2 in porcine esophageal body

Duodenal reflux of fluids containing trypsin relates to refractory gastroesophageal reflux disease (GERD). Esophageal peristalsis and clearance are important factors in GERD pathogenesis. However, the function of trypsin in esophageal body contractility is not fully understood. In this study, effects of trypsin on circular smooth muscle (CSM) and longitudinal smooth muscle (LSM) of the porcine esophageal body were examined. Trypsin elicited a concentration dependent biphasic response, a major contraction and a subsequent relaxation only in CSM. In CSM, contraction occurred at trypsin concentrations of 100nM and relaxation at 1μM. A proteinase-activated receptor (PAR)2 activating peptide, SLIGKV-NH₂ (1mM), induced a monophasic contraction. Those responses were unaffected by tetrodotoxin though abolished by the gap junction uncouplers carbenoxolone and octanol. They were also partially inhibited by a transient receptor potential vanilloid type 1 (TRPV1) antagonist and abolished by combination of neurokinin receptor 1 (NK₁) and NK₂ antagonists, but not by an NK₃ antagonist, suggesting a PAR2-TRPV1-substance P pathway in sensory neurons. Substance P (100nM), an agonist for various NK receptors (NK₁, NK₂ and NK₃) with differing affinities, induced significant contraction in CSM, but not in LSM. The contraction was also blocked by the combination of NK₁ and NK₂ antagonists, but not by the NK₃ antagonist. Moreover, substance P-induced contractions were unaffected by the TRPV1 antagonist, but inhibited by a gap junction uncoupler. In conclusion, trypsin induced a biphasic response only in CSM and this was mediated by PAR2, TRPV1 and NK_1/2. Gap junctions were indispensable in this tachykinin-induced response.

Zinc Transporter 3 (Znt3) as an Active Substance in the Enteric Nervous System of the Porcine Esophagus

Zinc transporter 3 (ZnT3), a member of the SLC 30 zinc transporter family, is involved in the transport of zinc ions from the cytoplasm into synaptic vesicles or intracellular organelles. The aim of the present study was to investigate for the first time the percentage of ZnT3-like immunoreactive (ZnT3-LI) neurons in the enteric nervous system (ENS) of the porcine esophagus and denotation of their neurochemical coding. Routine double- and triple-immunofluorescence labeling of cervical, thoracic, and abdominal fragments of esophagus for ZnT3 with protein gene product (PGP 9.5; used as pan-neuronal marker), nitric oxide synthase (NOS), somatostatin, vasoactive intestinal peptide (VIP), vesicular acetylcholine transporter (VAChT), neuropeptide Y (NPY), and galanin (GAL) was performed. The percentage of ZnT3-LI neurons in myenteric ganglia amounted to 50.2 ± 4.7, 63.4 ± 8.3, and 77.1 ± 1.1 % of all PGP 9.5-like immunoreactive neuronal cells in cervical, thoracic, and abdominal esophagus, respectively. In submucous ganglia, these values in particular parts of esophagus amounted to 46.3 ± 6.3, 81.0 ± 8.1, and 74.4 ± 4.4 %. Znt3 co-localized mainly with VAChT, NPY, GAL, NOS, and VIP, but the degree of co-localization depended on the “kind” of enteric ganglia and part of esophagus studied. The obtained results suggest that both ZnT3 and zinc ions may play important and various roles in the neuronal regulation of esophageal functions.

Early life adversity in piglets induces long-term upregulation of the enteric cholinergic nervous system and heightened, sex-specific secretomotor neuron responses

BACKGROUND

Early life adversity (ELA) is a risk factor for the later-life onset of gastrointestinal (GI) diseases such as irritable bowel syndrome (IBS); however, the mechanisms are poorly understood. Here, we utilized a porcine model of ELA, early weaning stress (EWS), to investigate the influence of ELA on the development and function of the enteric nervous system (ENS).

METHODS

Female and castrated male (Male-C) piglets were weaned from their sow either at 15 days of age (EWS) or 28 days of age (late weaning control, LWC). At 60 and 170 days of age, ileal mucosa-submucosa preparations were mounted in Ussing chambers and veratridine- and corticotropin releasing factor (CRF)-releasing factor-evoked short circuit current (Isc ) responses were recorded as indices of secretomotor neuron function. Enteric neuron numbers and the expression of select neurotransmitters and their receptors were also measured.

KEY RESULTS

Compared with LWC pigs, female, but not Male-C EWS, pigs exhibited heightened veratridine-induced Isc responses at 60 and 170 days of age that were inhibited with tetrodotoxin and atropine. Ileum from EWS pigs had higher numbers of enteric neurons that were choline acetyltransferase positive. Markers of increased cholinergic signaling (increased acetylcholinesterase) and downregulated mucosal muscarinic receptor 3 gene expression were also observed in EWS pigs.

CONCLUSIONS & INFERENCES

This study demonstrated that EWS in pigs induces lasting and sex-specific hypersensitivity of secretomotor neuron function and upregulation of the cholinergic ENS. These findings may represent a mechanistic link between ELA and lifelong susceptibility to GI diseases such as IBS.

White paper on guidelines concerning enteric nervous system stem cell therapy for enteric neuropathies

Over the last 20 years, there has been increasing focus on the development of novel stem cell based therapies for the treatment of disorders and diseases affecting the enteric nervous system (ENS) of the gastrointestinal tract (so-called enteric neuropathies). Here, the idea is that ENS progenitor/stem cells could be transplanted into the gut wall to replace the damaged or absent neurons and glia of the ENS. This White Paper sets out experts' views on the commonly used methods and approaches to identify, isolate, purify, expand and optimize ENS stem cells, transplant them into the bowel, and assess transplant success, including restoration of gut function. We also highlight obstacles that must be overcome in order to progress from successful preclinical studies in animal models to ENS stem cell therapies in the clinic.

Acetylsalicylic acid-induced changes in the chemical coding of extrinsic sensory neurons supplying the prepyloric area of the porcine stomach

Acetylsalicylic acid is a popular drug that is commonly used to treat fever and inflammation, but which can also negativity affect the mucosal layer of the stomach, although knowledge concerning its influence on gastric innervation is very scarce. Thus, the aim of the present study was to study the influence of prolonged acetylsalicylic acid supplementation on the extrinsic primary sensory neurons supplying the porcine stomach prepyloric region. Fast Blue (FB) was injected into the above-mentioned region of the stomach. Acetylsalicylic acid was then given orally to the experimental gilts from the seventh day after FB injection to the 27th day of the experiment. After euthanasia, the nodose ganglia (NG) and dorsal root ganglia (DRG) were collected. Sections of these ganglia were processed for routine double-labelling immunofluorescence technique for substance P (SP), calcitonine gene related peptide (CGRP), galanin (GAL), neuronal isoform of nitric oxide synthase (nNOS) and vasoactive intestinal polypeptide (VIP). Under physiological conditions within the nodose ganglia, the percentage of the FB-labeled neurons immunoreactive to particular substances ranged between 17.9 ± 2.7% (VIP-like immunoreactive (LI) neurons in the right NG) and 60.4 ± 1.7% (SP-LI cells within the left NG). Acetylsalicylic acid supplementation caused a considerable increase in the expression of all active substances studied within both left and right NG and the percentage of neurons positive to particular substances fluctuated from 47.2 ± 3.6% (GAL-LI neurons in the right NG) to 67.2 ± 2.0% (cells immunoreactive to SP in the left NG). All studied substances were also observed in DRG neurons supplying the prepyloric region of the stomach, but the number of immunoreactive neurons was too small to conduct a statistical analysis. The obtained results show that ASA may influence chemical coding of the sensory neurons supplying the porcine stomach, but the exact mechanisms of this action still remain unknown.

(2R,3S,2'' R,3''R)-manniflavanone, a new gastrointestinal smooth muscle L-type calcium channel inhibitor, which underlies the spasmolytic properties of Garcinia buchananii stem bark extract

Garcinia buchananii Baker stem bark extract (GBB) is a traditional medication of diarrhea and dysentery in sub-Saharan Africa. It is believed that GBB causes gastrointestinal smooth muscle relaxation. The aim of this study was to determine whether GBB has spasmolytic actions and identify compounds underlying these actions. Calcium (Ca²⁺) imaging was used to analyze the effect of GBB on Ca²⁺ flashes and Ca²⁺ waves in guinea pig gallbladder and distal colon smooth muscle. Intracellular microelectrode recording was used to determine the effect of GBB, six fractions of GBB, M1–5 and M7, and (2R,3S,2”R,3”R)-manniflavanone, a compound isolated from M3 on action potentials in gallbladder smooth muscle. The technique was also used to analyze the effect of GBB, M3, and (2R,3S,2”R,3”R)-manniflavanone on action potentials in the circular muscle of mouse and guinea pig distal colons, and the effect of GBB and (2R,3S,2”R,3”R)-manniflavanone on slow waves in porcine ileum. GBB inhibited Ca²⁺ flashes and Ca²⁺ waves. GBB, M3 and (2R,3S,2”R,3”R)-manniflavanone inhibited action potentials. L-type Ca²⁺ channel activator Bay K 8644 increased the discharge of action potentials in mouse colon but did not trigger or increase action potentials in the presence of GBB and (2R,3S,2”R,3”R)-manniflavanone. GBB and (2R,3S,2”R,3”R)-manniflavanone inhibited action potentials in the presence of Bay K 8644. GBB and (2R,3S,2”R,3”R)-manniflavanone reduced the amplitude but did not alter the frequency of slow waves in the porcine ileum. In conclusion, GBB and (2R,3S,2”R,3”R)-manniflavanone relax smooth muscle by inhibiting L-type Ca²⁺ channels, thus have potential for use as therapies of gastrointestinal smooth muscle spasms, and arrhythmias.

Early-life stress origins of gastrointestinal disease: animal models, intestinal pathophysiology, and translational implications

Early-life stress and adversity are major risk factors in the onset and severity of gastrointestinal (GI) disease in humans later in life. The mechanisms by which early-life stress leads to increased GI disease susceptibility in adult life remain poorly understood. Animal models of early-life stress have provided a foundation from which to gain a more fundamental understanding of this important GI disease paradigm. This review focuses on animal models of early-life stress-induced GI disease, with a specific emphasis on translational aspects of each model to specific human GI disease states. Early postnatal development of major GI systems and the consequences of stress on their development are discussed in detail. Relevant translational differences between species and models are highlighted.

Architecture and Chemical Coding of the Inner and Outer Submucous Plexus in the Colon of Piglets

In the porcine colon, the submucous plexus is divided into an inner submucous plexus (ISP) on the epithelial side and an outer submucous plexus (OSP) on the circular muscle side. Although both plexuses are probably involved in the regulation of epithelial functions, they might differ in function and neurochemical coding according to their localization. Therefore, we examined expression and co-localization of different neurotransmitters and neuronal markers in both plexuses as well as in neuronal fibres. Immunohistochemical staining was performed on wholemount preparations of ISP and OSP and on cryostat sections. Antibodies against choline acetyltransferase (ChAT), substance P (SP), somatostatin (SOM), neuropeptide Y (NPY), vasoactive intestinal peptide (VIP), neuronal nitric oxide synthase (nNOS) and the pan-neuronal markers Hu C/D and neuron specific enolase (NSE) were used. The ISP contained 1,380 ± 131 ganglia per cm² and 122 ± 12 neurons per ganglion. In contrast, the OSP showed a wider meshwork (215 ± 33 ganglia per cm²) and smaller ganglia (57 ± 3 neurons per ganglion). In the ISP, 42% of all neurons expressed ChAT. About 66% of ChAT-positive neurons co-localized SP. A small number of ISP neurons expressed SOM. Chemical coding in the OSP was more complex. Besides the ChAT/±SP subpopulation (32% of all neurons), a nNOS-immunoreactive population (31%) was detected. Most nitrergic neurons were only immunoreactive for nNOS; 10% co-localized with VIP. A small subpopulation of OSP neurons was immunoreactive for ChAT/nNOS/±VIP. All types of neurotransmitters found in the ISP or OSP were also detected in neuronal fibres within the mucosa. We suppose that the cholinergic population in the ISP is involved in the control of epithelial functions. Regarding neurochemical coding, the OSP shares some similarities with the myenteric plexus. Because of its location and neurochemical characteristics, the OSP may be involved in controlling both the mucosa and circular muscle.

Porcine models of digestive disease: the future of large animal translational research

There is increasing interest in nonrodent translational models for the study of human disease. The pig, in particular, serves as a useful animal model for the study of pathophysiological conditions relevant to the human intestine. This review assesses currently used porcine models of gastrointestinal physiology and disease and provides a rationale for the use of these models for future translational studies. The pig has proven its utility for the study of fundamental disease conditions such as ischemia-reperfusion injury, stress-induced intestinal dysfunction, and short bowel syndrome. Pigs have also shown great promise for the study of intestinal barrier function, surgical tissue manipulation and intervention, as well as biomaterial implantation and tissue transplantation. Advantages of pig models highlighted by these studies include the physiological similarity to human intestine and mechanisms of human disease. Emerging future directions for porcine models of human disease include the fields of transgenics and stem cell biology, with exciting implications for regenerative medicine.

The Influence of Low Doses of Zearalenone on Distribution of Selected Active Substances in Nerve Fibers Within the Circular Muscle Layer of Porcine Ileum

The aim of this study was to investigate, whether low doses (25 % of no observable adverse effect levels values) of zearalenone (ZEN) can affect the expression of active substances in nerve fibers in the muscular layer of porcine ileum. The study was performed on ten immature pigs divided into two groups: experimental group (n = 5), where zearalenone (10 μg/kg body weight) was given for 42 days, and control animals (n = 5), where placebo was administered. Fragments of ileum of all animals were processed for single-labelling immunofluorescence technique using the antibodies against vasoactive intestinal peptide, neuronal form of nitric oxide synthase, cocaine and amphetamine regulatory peptide, galanin, pituitary adenylate cyclase-activating peptide-27 and substance P. The number of nerve fibers immunoreactive to particular substances was evaluated by the counting of nerves per observation field (0.1 mm²). Low doses of zearalenone caused the clear changes in the expression of substances studied. The number of nerve fibers immunoreactive to the majority of substances increased in experimental animals. The exception was only galanin, the expression of which was less after administration of zearalenone. The obtained results for the first time show that even low doses of zearalenone can affect the nerve fibers in the digestive tract.