Immunohistochemical characterization of putative primary afferent (sensory) myenteric neurons in human small intestine

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.

Types of Neurons in the Human Colonic Myenteric Plexus Identified by Multilayer Immunohistochemical Coding

BACKGROUND AND AIMS

Gut functions including motility, secretion, and blood flow are largely controlled by the enteric nervous system. Characterizing the different classes of enteric neurons in the human gut is an important step to understand how its circuitry is organized and how it is affected by disease.

METHODS

Using multiplexed immunohistochemistry, 12 discriminating antisera were applied to distinguish different classes of myenteric neurons in the human colon (2596 neurons, 12 patients) according to their chemical coding. All antisera were applied to every neuron, in multiple layers, separated by elutions.

RESULTS

A total of 164 combinations of immunohistochemical markers were present among the 2596 neurons, which could be divided into 20 classes, with statistical validation. Putative functions were ascribed for 4 classes of putative excitatory motor neurons (EMN1-4), 4 inhibitory motor neurons (IMN1-4), 3 ascending interneurons (AIN1-3), 6 descending interneurons (DIN1-6), 2 classes of multiaxonal sensory neurons (SN1-2), and a small, miscellaneous group (1.8% of total). Soma-dendritic morphology was analyzed, revealing 5 common shapes distributed differentially between the 20 classes. Distinctive baskets of axonal varicosities surrounded 45% of myenteric nerve cell bodies and were associated with close appositions, suggesting possible connectivity. Baskets of cholinergic terminals and several other types of baskets selectively targeted ascending interneurons and excitatory motor neurons but were significantly sparser around inhibitory motor neurons.

CONCLUSIONS

Using a simple immunohistochemical method, human myenteric neurons were shown to comprise multiple classes based on chemical coding and morphology and dense clusters of axonal varicosities were selectively associated with some classes.

Ageing and the Autonomic Nervous System

The vertebrate nervous system is divided into central (CNS) and peripheral (PNS) components. In turn, the PNS is divided into the autonomic (ANS) and enteric (ENS) nervous systems. Ageing implicates time-related changes to anatomy and physiology in reducing organismal fitness. In the case of the CNS, there exists substantial experimental evidence of the effects of age on individual neuronal and glial function. Although many such changes have yet to be experimentally observed in the PNS, there is considerable evidence of the role of ageing in the decline of ANS function over time. As such, this chapter will argue that the ANS constitutes a paradigm for the physiological consequences of ageing, as well as for their clinical implications.

Integrated analysis of fish intestine biomarkers: Complementary tools for pollution assessment

The gastrointestinal tract and its enteric nervous system are the first routes of food and xenobiotics uptake. Considering the importance of this organ, this study evaluated intestinal biomarkers of Sphoeroides testudineus integrating the data to generate tools for pollution assessment. The fish were collected in three sites of São Paulo Coast and their intestines were analyzed for biochemical, histology, and neuronal density and morphometry biomarkers. To evaluate the differences among the data, a PERMANOVA was applied, followed by a FA/PCA. The PERMANOVA indicated differences (P < 0.001) between the regions (RA, A1, and A2). Four factors were extracted from the FA/PCA (62% cumulative), showing that the animals from A2 presented severe alterations, mainly in intestinal morphometry and neuronal density. A1 alterations refer mainly to the increase of neuronal metabolism. Our results also evidence a gradient of environmental quality related to the protection level (AR > A1 > A2).

Constipation Caused by Anti-calcitonin Gene-Related Peptide Migraine Therapeutics Explained by Antagonism of Calcitonin Gene-Related Peptide's Motor-Stimulating and Prosecretory Function in the Intestine

The development of small-molecule calcitonin gene-related peptide (CGRP) receptor antagonists (gepants) and of monoclonal antibodies targeting the CGRP system has been a major advance in the management of migraine. In the randomized controlled trials before regulatory approval, the safety of these anti-CGRP migraine therapeutics was considered favorable and to stay within the expected profile. Post-approval real-world surveys reveal, however, constipation to be a major adverse event which may affect more than 50% of patients treated with erenumab (an antibody targeting the CGRP receptor), fremanezumab or galcanezumab (antibodies targeting CGRP). In this review article we address the question whether constipation caused by inhibition of CGRP signaling can be mechanistically deduced from the known pharmacological actions and pathophysiological implications of CGRP in the digestive tract. CGRP in the gut is expressed by two distinct neuronal populations: extrinsic primary afferent nerve fibers and distinct neurons of the intrinsic enteric nervous system. In particular, CGRP is a major messenger of enteric sensory neurons which in response to mucosal stimulation activate both ascending excitatory and descending inhibitory neuronal pathways that enable propulsive (peristaltic) motor activity to take place. In addition, CGRP is able to stimulate ion and water secretion into the intestinal lumen. The motor-stimulating and prosecretory actions of CGRP combine in accelerating intestinal transit, an activity profile that has been confirmed by the ability of CGRP to induce diarrhea in mice, dogs and humans. We therefore conclude that the constipation elicited by antibodies targeting CGRP or its receptor results from interference with the physiological function of CGRP in the small and large intestine in which it contributes to the maintenance of peristaltic motor activity, ion and water secretion and intestinal transit.

Identifying Types of Neurons in the Human Colonic Enteric Nervous System

Distinguishing and characterising the different classes of neurons that make up a neural circuit has been a long-term goal for many neuroscientists. The enteric nervous system is a large but moderately simple part of the nervous system. Enteric neurons in laboratory animals have been extensively characterised morphologically, electrophysiologically, by projections and immunohistochemically. However, studies of human enteric nervous system are less advanced despite the potential availability of tissue from elective surgery (with appropriate ethics permits). Recent studies using single cell sequencing have confirmed and extended the classification of enteric neurons in mice and human, but it is not clear whether an encompassing classification has been achieved. We present preliminary data on a means to distinguish classes of myenteric neurons in specimens of human colon combining immunohistochemical, morphological, projection and size data on single cells. A method to apply multiple layers of antisera to specimens was developed, allowing up to 12 markers to be characterised in individual neurons. Applied to multi-axonal Dogiel type II neurons, this approach demonstrated that they constitute fewer than 5% of myenteric neurons, are nearly all immunoreactive for choline acetyltransferase and tachykinins. Many express the calcium-binding proteins calbindin and calretinin and they are larger than average myenteric cells. This methodology provides a complementary approach to single-cell mRNA profiling to provide a comprehensive account of the types of myenteric neurons in the human colon.

Congenital Myenteric Hypoganglionosis

Congenital myenteric hypoganglionosis is a rare developmental disorder characterized clinically by severe and persistent neonatal intestinal pseudoobstruction. The diagnosis is established by the prevalence of small myenteric ganglia composed of closely spaced ganglion cells with sparse surrounding neuropil. In practice, the diagnosis entails familiarity with the normal appearance of myenteric ganglia in young infants and the ability to confidently recognize significant deviations in ganglion size and morphology. We review clinical, histologic, and immunohistochemical findings from 12 patients with congenital myenteric hypoganglionosis in comparison with similar data from age-matched controls and clearly delineate the diagnostic features of the condition. Practical guidelines are provided to assist surgical pathologists, who are likely to encounter this condition only infrequently. The diagnosis typically requires full-thickness intestinal biopsy as the abnormality is confined to the myenteric plexus in many patients. Immunohistochemistry for Hu C/D may be used to confirm hypoganglionosis. Reduced staining for calretinin and NeuN implicates a selective deficiency of intrinsic primary afferent neurons in this disease.

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 in the expression of substance P in nerve fibres of the colonic mucosa in dogs suffering from inflammatory bowel disease

Due to its difficult diagnosis and complicated treatment, inflammatory bowel disease (IBD) in dogs is a challenge for the veterinarian. Several aspects connected with pathological changes during IBD still remain unknown. Since one of these aspects is the participation of intestinal innervation in the evolution of the disease, the aim of this study was to demonstrate changes in the number and distribution of intramucosal colonic nerve fibres immunoreactive to substance P (SP) arising as the disease progresses. SP is one of the most important neuronal factors in intestinal innervation which, among other tasks, takes part in the conduction of pain stimuli. Using routine immunofluorescence technique, the density of nerve fibres containing SP was evaluated within mucosal biopsy specimens collected from the descending colon of healthy dogs and animals suffering from IBD of varying severity. The results of the study indicate that during severe IBD the number of nerve fibres containing SP located in the colonic mucosal layer increases in comparison to control animals. The number of SP-positive intramucosal nerves amounted to 10.99 ± 2.11 nerves per observation field in healthy dogs, 14.62 ± 2.86 in dogs with mild IBD, 14.80 ± 0.91 in dogs with moderate IBD and 19.03 ± 6.11 in animals with severe IBD. The observed changes were directly proportional to the intensity of the disease process. These observations may suggest a role of this neuronal substance in pathological processes occurring during IBD. Although the exact mechanism of the observed changes has not been completely explained, the results obtained in this investigation may contribute to improving the diagnosis and treatment of this disease, as well as the staging of canine IBD in veterinary practice.

Mycotoxins and the Enteric Nervous System

Mycotoxins are secondary metabolites produced by various fungal species. They are commonly found in a wide range of agricultural products. Mycotoxins contained in food enter living organisms and may have harmful effects on many internal organs and systems. The gastrointestinal tract, which first comes into contact with mycotoxins present in food, is particularly vulnerable to the harmful effects of these toxins. One of the lesser-known aspects of the impact of mycotoxins on the gastrointestinal tract is the influence of these substances on gastrointestinal innervation. Therefore, the present study is the first review of current knowledge concerning the influence of mycotoxins on the enteric nervous system, which plays an important role, not only in almost all regulatory processes within the gastrointestinal tract, but also in adaptive and protective reactions in response to pathological and toxic factors in food.

Mast cell-nerve interactions correlate with bloating and abdominal pain severity in patients with non-celiac gluten / wheat sensitivity

BACKGROUND

Gastrointestinal (GI) and extra-GI symptoms/manifestations represent key clinical features of patients with non-celiac gluten/wheat sensitivity (NCG/WS). This study aimed to investigate neuro-immune (focusing on mast cells, MCs) interactions in the duodenal submucosa of patients with NCG/WS.

METHODS

Submucosal whole mounts from duodenal biopsies of 34 patients with self-reported NCG/WS, 28 with celiac disease (CD), 13 with functional dyspepsia (FD), and 24 healthy controls (HC) were analyzed by immunohistochemistry. Quantitative data on neuronal and MCs density and the percentage of MCs in close vicinity to nerves were obtained, and correlations among neurons, MC density and MC-nerve distance (D), and symptoms were assessed in the three groups.

KEY RESULTS

The number of submucosal neurons was not different among groups. In NCG/WS, MC density was not different from HC, while it was slightly increased vs. CD (P = .07) and significantly decreased vs. FD (P < .05). The percentage of MCs close to nerves (D < 15 µm) was similarly increased in all three pathological groups vs. HC (P < .001). In NCG/WS, MC infiltration correlated with bloating (P = .001) and abdominal pain severity (P = .03) and the percentage of MCs in proximity to neurons correlated with the number of GI symptoms (D < 5 µm; P = .05), bloating and abdominal pain severity (D < 15um; P = .01).

CONCLUSIONS AND INFERENCES

Submucosal MC infiltration and the close (within 15 µm) MC-to-nerve proximity in the duodenum of NCG/WS patients are features providing a histopathological basis to better understand GI symptoms in this condition.

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.

Infra-anastomotic Innervation of Residual Aganglionic Distal Rectum After Pull-through Surgery for Hirschsprung Disease

BACKGROUND

Descending neurons are important for intestinal reflex activities, including the recto-anal inhibitory reflex involved in normal defecation. Pull-through surgery for Hirschsprung disease results in the anastomosis of ganglionic bowel to native aganglionic rectum just superior to the internal anal sphincter, which potentially could allow for physiologically significant infra-anastomotic innervation.

METHODS

The density and distribution of intramuscular neuronal nitric oxide synthase (nNOS)- and mucosal calretinin-immunoreactive nerves were evaluated proximal and distal to the anastomosis in redo resection specimens after pull-through surgery for Hirschsprung disease. The findings were compared with data collected from cadaveric controls with no history of dysmotility and the distal aganglionic segments of primary rectal resections from patients with Hirschsprung disease.

RESULTS

Native aganglionic rectum of Hirschsprung patients lacks the normal lush intramuscular nNOS- and mucosal calretinin-immunoreactive nerves present in normal bowel. In post-pull-through resection specimens obtained more than 7 months after pull-through surgery, nNOS- and calretinin-positive innervation is at least partially restored for variable distances up to 10 to 12 mm inferior to the anastomosis, respectively.

CONCLUSIONS

Innervation of infra-anastomotic muscularis propria and mucosa in the aganglionic distal rectum occurs to a variable degree after pull-through surgery for Hirschsprung disease and may contribute to individual differences in postoperative obstructive symptoms. Strategies to enhance infra-anastomotic innervation may improve clinical outcome.

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.

Morphological and Immunohistochemical Characterization of Human Intrinsic Gastric Neurons

Our knowledge about human gastric enteric neuron types is even more limited than that of human intestinal types. Here, we immunohistochemically stained wholemounts and sections of gastric specimens obtained from 18 tumor-resected patients. Myenteric wholemounts were labeled for choline acetyl transferase (ChAT), neuronal nitric oxide synthase (NOS), and the human neuronal protein HuC/D (as pan-neuronal marker for quantitative analysis) or alternatively for neurofilament (for morphological evaluation). ChAT-positive neurons outnumbered NOS-positive neurons (56 vs. 27%), and neurons negative for both markers accounted for 17%. Two larger groups of neurons (each between 12 and 14%) costained for ChAT and vasoactive intestinal peptide (VIP) or for NOS and VIP, respectively. Clear morphochemical correlation was found for uniaxonal stubby type I neurons (ChAT+; putative excitatory inter- or motor neurons), for uniaxonal spiny type I neurons (NOS+/VIP+; putative inhibitory motor or interneurons), and for multiaxonal type II neurons (ChAT+; putative afferent neurons; immunostaining of additional wholemounts revealed their coreactivity for somatostatin). Whereas these latter neuron types were already known from the human intestine, the morphology of gastric myenteric neurons coreactive for ChAT and VIP was newly described: they had numerous short, extremely thin dendrites and resembled, together with their cell bodies, a "hairy" head. In our sections, nerve fibers coreactive for ChAT and VIP were commonly found only in the mucosa. We suggest these myenteric ChAT+/VIP+/hairy neurons to be mucosal effector neurons. In contrast to myenteric neurons, the much less common submucosal neurons were not embedded in a continuous plexus and did not display any clear morphochemical phenotypes.

Distribution and Neurochemistry of the Porcine Ileocaecal Valve Projecting Sensory Neurons in the Dorsal Root Ganglia and the Influence of Lipopolysaccharide from Different Serotypes of Salmonella spp. on the Chemical Coding of DRG Neurons in the Cell Cultures

The ileocecal valve (ICV)—a sphincter muscle between small and large intestine—plays important roles in the physiology of the gastrointestinal (GI) tract, but many aspects connected with the innervation of the ICV remain unknown. Thus, the aim of this study was to investigate the localization and neurochemical characterization of neurons located in the dorsal root ganglia and supplying the ICV of the domestic pig. The results have shown that such neurons mainly located in the dorsal root ganglia (DRG) of thoracic and lumbar neuromers show the presence of substance P (SP), calcitonin gene-related peptide (CGRP), and galanin (GAL). The second part of the experiment consisted of a study on the influence of a low dose of lipopolysaccharide (LPS) from Salmonella serotypes Enteritidis Minnesota and Typhimurium on DRG neurons. It has been shown that the LPS of these serotypes in studied doses does not change the number of DRG neurons in the cell cultures, but influences the immunoreactivity to SP and GAL. The observed changes in neurochemical characterization depend on the bacterial serotype. The results show that DRG neurons take part in the innervation of the ICV and may change their neurochemical characterization under the impact of LPS, which is probably connected with direct actions of this substance on the nervous tissue and/or its pro-inflammatory activity.

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.

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.

The Influence of Low Doses of Zearalenone and T-2 Toxin on Calcitonin Gene Related Peptide-Like Immunoreactive (CGRP-LI) Neurons in the ENS of the Porcine Descending Colon

The enteric nervous system (ENS) can undergo adaptive and reparative changes in response to physiological and pathological stimuli. These manifest primarily as alterations in the levels of active substances expressed by the enteric neuron. While it is known that mycotoxins can affect the function of the central and peripheral nervous systems, knowledge about their influence on the ENS is limited. Therefore, the aim of the present study was to investigate the influence of low doses of zearalenone (ZEN) and T-2 toxin on calcitonin gene related peptide-like immunoreactive (CGRP-LI) neurons in the ENS of the porcine descending colon using a double immunofluorescence technique. Both mycotoxins led to an increase in the percentage of CGRP-LI neurons in all types of enteric plexuses and changed the degree of co-localization of CGRP with other neuronal active substances, such as substance P, galanin, nitric oxide synthase, and cocaine- and amphetamine-regulated transcript peptide. The obtained results demonstrate that even low doses of ZEN and T-2 can affect living organisms and cause changes in the neurochemical profile of enteric neurons.

Immunohistochemical panel for the diagnosis of Hirschsprung's disease using antibodies to MAP2, calretinin, GLUT1 and S100

AIMS

The diagnosis of Hirschsprung's disease is currently based on the identification of aganglionosis and the presence of an increase in acetylcholinesterase-positive hypertrophic nerve fibres in the large bowel submucosa. However, acetylcholinesterase staining is laborious and requires a skilled technician. The aim of this study was to identify a method for diagnosing Hirschsprung's disease reliably using an immunohistochemical panel of recently proposed markers.

METHODS AND RESULTS

Sixty-nine specimens from 37 patients were evaluated. MAP2 and calretinin antibodies were shown to stain ganglia reliably in the submucosal and myenteric plexuses of normal tissue. By contrast, reduced staining of ganglia was observed in patients with Hirschsprung's disease. Staining for GLUT1 and S100 was used to evaluate the number and thickness of nerve fibres. Gain of GLUT1 and S100 expression was in contrast to the loss of calretinin and MAP2. Hypertrophic submucosal nerve fibres in Hirschsprung's disease develop a perineurium with a ring-like GLUT1 staining pattern similar in size and intensity to that observed in deeper subserosal tissue.

CONCLUSIONS

The diagnosis of Hirschsprung's disease using immunohistochemical panels could be as accurate as with conventional frozen section techniques. In particular, the use of a combination of markers for ganglia and hypertrophic nerve fibres highlighting a prominent perineurium in Hirschsprung's disease could be an alternative method.

Chagasic megacolon: enteric neurons and related structures

Megacolon, the irreversible dilation of a colonic segment, is a structural sign associated with various gastrointestinal disorders. In its hereditary, secondary form (e.g. in Hirschsprung's disease), dilation occurs in an originally healthy colonic segment due to an anally located, aganglionic zone. In contrast, in chronic Chagas' disease, the dilated segment itself displays pathohistological changes, and the earliest and most prominent being found was massive loss of myenteric neurons. This neuron loss was partial and selective, i.e. some neurons containing neuronal nitric oxide synthase and/or vasoactive intestinal peptide (VIP) were spared from neuron death. This disproportionate survival of inhibitory neurons, however, did not completely correlate with the calibre change along the surgically removed, megacolonic segments. A better correlation was observed as to potentially contractile muscle tissue elements and the interstitial cells of Cajal. Therefore, the decreased densities of α-smooth muscle actin- and c-kit-immunoreactive profiles were estimated along resected megacolonic segments. Their lowest values were observed in the megacolonic zones itself, whereas less pronounced decreases were found in the non-dilated, transitional zones (oral and anal to dilation). In contrast to the myenteric plexus, the submucosal plexus displayed only a moderate neuron loss. Neurons co-immunoreactive for VIP and calretinin survived disproportionately. As a consequence, these neurons may have contributed to maintain the epithelial barrier and allowed the chagasic patients to survive for decades, despite their severe disturbance of colonic motility. Due to its neuroprotective and neuroeffectory functions, VIP may play a key role in the development and duration of chagasic megacolon.

Mucosal layers and related nerve fibres in non-chagasic and chagasic human colon--a quantitative immunohistochemical study

Chagasic megacolon is accompanied by extensive myenteric and, simultaneously, moderate submucosal neuron loss. Here, we examined changes of the innervation pattern of the lamina propria (LP) and muscularis mucosae (MM). Two alternating sets of cryosections were taken from seven non-chagasic colonic and seven chagasic megacolonic specimens (the latter included both the dilated megacolonic and the non-dilated transitional oral and anal zones) and were immunohistochemically triple-stained for smooth-muscle actin (SMA), synaptophysin (SYN) and glial acid protein S100 and, alternatively, for SMA, vasoactive intestinal peptide (VIP) and somatostatin (SOM). Subsequent image analysis and statistical evaluation of nervous tissue profile areas revealed that, in LP, the most extreme differences (i.e. increase in thickness or decrease in nerve, glia and muscle tissue profile area, respectively) compared with control values occurred in the dilated megacolonic zone itself. In contrast, the most extreme differences in the MM were in the anal-to-megacolonic zone (except the profile area of muscle tissue, which was lowest in the megacolonic zone). This parallels our previous results in the external muscle coat. A partial and selective survival of VIP-immunoreactive in contrast to SOM-immunoreactive nerve fibres was observed in both mucosal layers investigated. Thus, VIPergic nerve elements might be crucial for the maintenance of the mucosal barrier. The differential changes of neural tissue parameters in LP and MM might reflect a multifactorial rather than a pure neurogenic development of megacolon in chronic Chagas' disease.

Calretinin-immunoreactive mucosal innervation in very short-segment Hirschsprung disease: a potentially misleading observation

Absent calretinin-immunoreactive (CRir) mucosal innervation in aganglionic rectal biopsies is considered a useful diagnostic finding for Hirschsprung disease. Analysis of a series of rectosigmoid resections from patients with short-segment (>2-cm aganglionic, n  =  9) and very short-segment (≤2-cm aganglionic, n  =  9) Hirschsprung disease demonstrates that CRir mucosal nerves extend into the proximal 1-2 cm of aganglionic bowel, where their presence in distal rectal biopsies could complicate diagnosis of very short-segment disease. Indeed, retrospective analysis of preoperative, aganglionic, distal rectal biopsies from 4 of 9 patients with very short-segment Hirschsprung disease revealed CRir mucosal innervation. Accurate diagnosis was possible based on generous histopathological submucosal sampling to exclude ganglion cells and the presence of abundant large-caliber submucosal nerves (more than 4 nerves >30 µm thick/×200 field or more than 2 nerves >40 µm thick/×200 field). Absent CRir mucosal innervation supports the diagnosis of Hirschsprung disease, but the presence of CRir mucosal nerves does not exclude aganglionosis, especially in distal rectal biopsies from patients with very short-segment Hirschsprung disease.

What neurons hide behind calretinin immunoreactivity in the human gut?

Calretinin (CALR) is often used as an immunohistochemical marker for the histopathological diagnosis of human intestinal neuropathies. However, little is known about its distribution pattern with respect to specific human enteric neuron types. Prior studies revealed CALR in both myenteric and submucosal neurons, most of which colabel with choline acetyl transferase (ChAT). Here, we specified the chemical code of CALR-positive neurons in small and large intestinal wholemounts in a series of 28 patients. Besides other markers, we evaluated the labeling pattern of CALR in combination with vasoactive intestinal peptide (VIP). In colonic submucosa, CALR and VIP were almost completely colocalized in about three-quarters of all submucosal neurons. In the small intestinal submucosa, both the colocalization rate of CALR and VIP as well as the proportion of these neurons were lower (about one-third). In the myenteric plexus of both small intestine and colon, CALR amounted to 11 and 10 %, respectively, whereas VIP to 5 and 4 % of the whole neuron population, respectively. Colocalization of both markers was found in only 2 and 3 % of myenteric neurons, respectively. In section specimens, nerve fibers coreactive for CALR and VIP were found in the mucosa but not in the muscle coat. Summarizing the present and earlier results, CALR was found in at least one submucosal and two myenteric neuron populations. Submucosal CALR+/VIP+/ChAT± neurons innervate mucosal structures. Furthermore, CALR immunoreactivity in the myenteric plexus was observed in morphological type II (supposed primary afferent) and spiny type I (supposed inter- or motor-) neurons.

Effects of inflammation and axotomy on expression of acetylcholine transferase and nitric oxide synthetase within the cocaine- and amphetamine-regulated transcript-immunoreactive neurons of the porcine descending colon

This study reports changes in expression of acetylcholine transferase (AChT) and nitric oxide synthetase (NOS) in neurons immunoreactive for cocaine- and amphetamine-regulated transcript (CART) peptides during chemically-driven inflammation and axotomy in the porcine descending colon. The co-localization of the neurotransmitters with CART was studied by double immunofluorescence in the myenteric plexus (MP) and outer submucosal plexus (OSP) of the porcine descending colon under physiological and selected pathological conditions. In control animals, neurons expressing CART also expressed AChT in 25.37 ± 0.98% and 26.73 ± 0.96% in the MP and OSP, respectively. Neuronal co-expression of CART with NOS occurred in 90.66 ± 2.13% and 88.09 ± 2.96% in the MP and OSP, respectively. Following axotomy the number of neurons co-expressing CART and AChT decreased to 16.50 ± 3.20% in the MP and increased to 35.49 ± 2.04% in the OSP, while the number of neurons co-expressing CART and NOS increased to 96.66 ± 2.38% in the MP and 97.46 ± 2.22% in the OSP. Experimentally-induced colitis resulted in an increase in the number of neurons co-expressing CART and AChT to 42.40 ± 2.28% in the MP and 63.62 ± 1.83% in the OSP. Similarly, in these animals the number of neurons co-expressing CART and NOS increased to 93.9 ± 2.58% in the MP and 90.43 ± 2.09% in the OSP. Sham-operated controls showed expression levels of 26.22 ± 0.66% (MP) and 27.02 ± 1.73% (OSP) for simultaneous CART and AChT expression and 94.18 ± 0.93% (MP) and 88.21 ± 0.81% (OSP) for CART and NOS co-localization. These data confirm that the examined neurotransmitters have a role in traumatic and inflammatory responses of enteric neurons.

Substance P as a neuronal factor in the enteric nervous system of the porcine descending colon in physiological conditions and during selected pathogenic processes

The present investigation pertains to changes in substance P-like immunoreactive (SP-LI) nerve structures of the enteric nervous system (ENS) in the porcine descending colon, caused by chemically-induced inflammation and nerve injury (axotomy). The distribution pattern of SP-LI structures was studied using the double immunofluorescence technique in the myenteric (MP), outer submucous (OSP) and inner submucous (ISP) plexuses, as well as in the circular muscle and mucosal layers. Under physiological conditions, SP-LI neurons have been shown to constitute 4.13 ± 0.24%, 3.36 ± 0.26%, and 7.92 ± 0.16% in the MP, OSP, and ISP, respectively. Changes in SP-immunoreactivity depended on the pathological factor studied. The numbers of the SP-LI perikarya amounted to 7.89 ± 0.34, 5.56 ± 0.30, and 19.96 ± 0.57 in chemically-induced colitis, and 4.28 ± 0.13%, 7.18 ± 20%, and 11.62 ± 0.48% after axotomy in MP, OSP, and ISP, respectively. The both studied processes generally resulted in an increase in the number of SP-LI nerve fibers in the circular muscle and mucosal layers. The obtained results suggest that SP-LI nerve structures of the ENS may participate in various pathological processes in the porcine descending colon and exact functions of SP probably depend on the type of the pathological factor.

Myenteric neuron numbers are maintained in aging mouse distal colon

BACKGROUND Age-associated myenteric neuronal loss has been described in several species. In some studies,cholinergic neurons have been reported to be selectively vulnerable, whereas nitrergic neurons are spared. Aging of the mouse enteric nervous system(ENS) and the subtypes of mouse myenteric neurons that may be lost have been little studied. We therefore investigated changes in the numbers of total neurons and two neuronal subpopulations in the mouse distal colon during aging. METHODS Wholemount preparations from 3–4-, 12–13-, 18–19-, and 24–25-month-old C57BL/6 mice were double immunolabeled with HuC/D antibody to identify the total neuronal population and antisera to either calbindin or neuronal nitric oxide synthase (nNOS) to identify myenteric neuronal subpopulations. Samples were analyzed by confocal microscopy. New procedures were employed to ensure unbiased counting and to correct for changes in gut dimensions with age and stretch during sample preparation. The density of nerve fibers in the tertiary plexus was also studied. KEY RESULTS No significant change in numbers of total neurons or of either subpopulation with age was measured, but because of gut growth, the density of myenteric neurons decreased between 3–4 and 12–13 months. The density of nNOS-immunoreactive nerve fibers in the tertiary plexus increased significantly with age, up to 18–19 months. Numerous swollen processes of CB and nNOS-immunoreactive neurons were observed in 18–19- and 24–25-month-old animals. Conclusions &Inferences These results indicate that aging does not result in a loss of myenteric neurons in mouse distal colon at the ages studied, although neurodegenerative changes, which may impact on neuronal function, do occur.

The Nav1.9 channel regulates colonic motility in mice

The colonic migrating motor complex (CMMC) is a major pattern of motility that is entirely generated and organized by the enteric nervous system. We have previously demonstrated that the Na_v1.9 channel underlies a tetrodotoxin-resistant sodium current which modulates the excitability of enteric neurons. The aim of this study was to observe the effect of loss of the Na_v1.9 channel in enteric neurons on mouse colonic motility in vitro. The mechanical activity of the circular muscle was simultaneously recorded from three sites, namely, proximal, mid- and distal, along the whole colon of male, age-matched wild-type and Na_v1.9 null mice. Spontaneous CMMCs were observed in all preparations. The mean frequency of CMMCs was significantly higher in the Na_v1.9 null mice (one every 2.87 ± 0.1 min compared to one every 3.96 ± 0.23 min in the wild type). The mean duration of CMMCs was shorter and the mean area-under-contraction was larger in the Na_v1.9 null mice compared to the wild type. In addition, CMMCs propagated preferentially in an aboral direction in the Na_v1.9 null mice. Our study demonstrates that CMMCs do occur in mice lacking the Na_v1.9 channel, but their characteristics are significantly different from controls. Up to now, the Na_v1.9 channel was mainly associated with nociceptive neurons and involved in their hyperexcitability after inflammation. Our result shows for the first time a role for the Na_v1.9 channel in a complex colonic motor pattern.

Substance P- and choline acetyltransferase immunoreactivities in somatostatin-containing, human submucosal neurons

The submucous layers of human small and large intestines contain at least two separate neuron populations. Besides morphological features, they differ in their immunoreactivities for calretinin (CALR) and somatostatin (SOM), respectively. In this study, submucosal wholemounts of 23 patients or body donors (including all segments of small intestine and colon) were immunohistochemically quadruple stained for CALR and SOM as well as for substance P (SP) and choline acetyltransferase (ChAT). We found that all SOM-positive neurons co-stained for ChAT and the majority for SP [between 50% in the small intestinal external submucosal plexus (ESP) and 75% in the colonic ESP]. In contrast, a majority of CALR-neurons contained ChAT (between 77% in the small intestinal ESP and 92% in the large intestinal ESP) whereas less than 4% of CALR-neurons were co-immunoreactive for SP. Another set of wholemounts was co-stained for peripherin, a marker enabling morphological analysis. Where identifiable, both SOM alone- and SOM/SP-neurons displayed a uniaxonal (supposed pseudouniaxonal) morphology. We suggest that the chemical code of SOM-immunoreactive, human submucosal neurons may be "ChAT+/SOM+/SP±". In additional sections double stained for SOM and SP, we regularly found double-labelled nerve fibres only in the mucosa. In contrast, around submucosal arteries mostly SOM alone- fibres were found and the muscularis propria contained numerous SP-alone fibres. We conclude that the main target of submucosal SOM(/SP)-neurons may be the mucosa. Due to their morpho-chemical similarity to human myenteric type II neurons, we further suggest that one function of human submucosal SOM-neurons may be a primary afferent one.

FGF2 deficit during development leads to specific neuronal cell loss in the enteric nervous system

The largest part of the peripheral nervous system is the enteric nervous system (ENS). It consists of an intricate network of several enteric neuronal subclasses with distinct phenotypes and functions within the gut wall. The generation of these enteric phenotypes is dependent upon appropriate neurotrophic support during development. Glial cell line-derived neurotrophic factor (GDNF) and fibroblast growth factor-2 (FGF2) play an important role in the differentiation and function of the ENS. A lack of GDNF or its receptor (Ret) causes intestinal aganglionosis in mice, while fibroblast growth factor receptor signaling antagonist is identified as regulating proteins in the GDNF/Ret signaling in the developing ENS. Primary myenteric plexus cultures and wholemount preparations of wild type (WT) and FGF2-knockout mice were used to analyze distinct enteric subpopulations. Fractal dimension (D) as a measure of self-similarity is an excellent tool to analyze complex geometric shape and was applied to classify the subclasses of enteric neurons concerning their individual morphology. As a consequence of a detailed analysis of subpopulation variations, wholemount preparations were stained for the calcium binding proteins calbindin and calretinin. The fractal analysis showed a reliable consistence of subgroups with different fractal dimensions (D) in each culture investigated. Seven different neuronal subtypes could be differentiated according to a rising D. Within the same D, the neurite length revealed significant differences between wild type and FGF2-knockout cultures, while the subclass distribution was also altered. Depending on the morphological characteristics, the reduced subgroup was supposed to be a secretomotor neuronal type, which could be confirmed by calbindin and calretinin staining of the wholemount preparations. These revealed a reduction up to 40 % of calbindin-positive neurons in the FGF2-knockout mouse. We therefore consider FGF2 playing a more important role in the fine-tuning of the ENS during development as previously assumed.

Selective survival of calretinin- and vasoactive-intestinal-peptide-containing nerve elements in human chagasic submucosa and mucosa

Chronic Chagas' disease is frequently characterized by massive myenteric neuron loss resulting in megacolon with severely and irreversibly disturbed motility. Here, we focused on two submucosal neuron populations, immunoreactive for calretinin (CALR) or somatostatin (SOM), and their respective mucosal nerve fibres in chagasic megacolon. Surgically removed megacolonic segments of seven chagasic patients were compared with seven age- and region-matched non-chagasic control segments. Evaluation included immunohistochemical triple-staining of cryosections for CALR, SOM and peripherin or for CALR and vasoactive intestinal peptide (VIP) and of submucosal whole-mounts for CALR, SOM and the pan-neuronal marker anti-HuC/D. Submucosal neuron counts in chagasic tissue revealed neuron numbers reduced to 51.2 % of control values. In cryosections, nerve fibre area measurements revealed 8.6 % nerve fibre per mucosal area in control segments, but this value decreased to 1.5 % in megacolonic segments. In both evaluations, a disproportionate decrease of SOM-reactive nerve elements was observed. The proportions of SOM-positive neurons related to the total neuron number declined to 2 % (control 10 %) and the proportion of SOM-reactive mucosal nerve fibres related to the whole mucosal area to 0.014 % (control 1.8 %)in chagasic tissue. The second set of cryosections revealed extensive colocalization of CALR with VIP in both surviving submucosal perikarya and mucosal nerve fibres. We suggest that VIP, a neuroprotective and neuroeffectory peptide typically contained in submucosal neurons, allows both the VIP-containing neurons to endure and the patients to survive by maintaining their mucosal barrier, despite the almost complete loss of colonic motility for decades.

Calretinin and somatostatin immunoreactivities label different human submucosal neuron populations

In human myenteric plexus, calretinin (CALR) and somatostatin (SOM) coexist in Dogiel Type II neurons, which were considered as intrinsic primary afferent neurons in the guinea pig. The aims of this study were to test if also human submucosal neurons costain immunohistochemically for CALR and SOM and whether these or other neurons display Type II morphology. Two sets of submucosal wholemounts of small and large intestine from 29 patients (median age 65 years) were triple stained for CALR, SOM, and human neuronal protein Hu C/D (HU, a pan-neuronal marker) as well as for CALR, SOM, and peripherin (PER), respectively. Only exceptionally, neurons coreactive for both CALR and SOM were found. The three major groups of neurons were CALR-/HU-coreactive (CALR-neurons), SOM-/HU-coreactive (SOM-neurons), and HU-alone-positive neurons. We observed significantly more CALR-neurons in the external submucosal plexus (ESP) of all regions and more SOM-neurons in the internal submucosal plexus (ISP), although with substantial interindividual variations. Comparisons of small vs. large intestine revealed more SOM-neurons (ESP: 29% vs. 4%, ISP: 40% vs. 13%) but fewer CALR-neurons (ESP: 37% vs. 77%, ISP: 21% vs. 67%) in small intestine. Morphologically, CALR-neurons had multiple processes; in some cases, we identified multidendritic/uniaxonal neurons. In contrast, SOM-neurons had mostly only one process. The functions of both populations as possible primary afferent neurons, interneurons, secretomotor neurons, or vasomotor neurons are discussed. Future morphochemical distinction of these groups may reveal different subgroups.

Neurochemical coding of enteric neurons in adult and embryonic zebrafish (Danio rerio)

Although the morphology and development of the zebrafish enteric nervous system have been extensively studied, the precise neurochemical coding of enteric neurons and their proportional enteric distribution are currently not known. By using immunohistochemistry, we determined the proportional expression and coexpression of neurochemical markers in the embryonic and adult zebrafish intestine. Tyrosine hydroxylase (TH), vasoactive intestinal peptide (VIP), and pituitary adenylate cyclase-activating peptide (PACAP) were observed only in nerve fibers, whereas other markers were also detected in neuronal cell bodies. Calretinin and calbindin had similar distributions. In embryos, all markers, except for choline acetyltransferase (ChAT) and TH, were present from 72 hours postfertilization. Nitrergic neurons, evenly distributed and remaining constant in time, constituted the major neuronal subpopulation. The neuronal proportions of the other markers increased during development and were characterized by regional differences. In the adult, all markers examined were expressed in the enteric nervous system. A large percentage of enteric neurons displayed calbindin and calretinin, and serotonin was the only marker showing significant distribution differences in the three intestinal regions. Colocalization studies showed that serotonin was not coexpressed with any of the other markers. At least five neuronal subpopulations were determined: a serotonergic, a nitrergic noncholinergic, two cholinergic nonnitrergic subpopulations along with one subpopulation expressing both ChAT and neuronal nitric oxide synthase. Analysis of nerve fibers revealed that nitrergic neurons coexpress VIP and PACAP, and that nitrergic neurons innervate the tunica muscularis, whereas serotonergic and cholinergic nonnitrergic neurons innervate the lamina propria and the tunica muscularis.

Localization of muscarinic receptors M1R, M2R and M3R in the human colon

BACKGROUND

Muscarinic acetylcholine receptors (MR) are involved in multiple intestinal reflexes. The cellular localization of subtypes of MRs within enteric circuits mediating muscle and mucosal reflexes remains to be demonstrated. This study aimed to localize the three functionally significant subtypes of MRs in human colon.

METHODS

Reverse transcriptase-PCR was used to determine expression levels of muscarinic receptor subtype (MRs) M1Rs, M2Rs and M3Rs in human colon. Indirect immunofluorescence and confocal microscopy was used to localize MRs in cryostat-cut sections of human colon. Sections were double labeled for multiple cellular and neurochemical markers. Western blotting was used to confirm specificity of the muscarinic antisera used.

KEY RESULTS

All three MR subtypes were expressed in human colon. Immunoreactivity (IR) for M2Rs and M3Rs was most abundant in circular and longitudinal muscle. M1R-IR was most abundant on myenteric and submucosal nerve cells, both cholinergic and nitrergic. M3R-IR was also present on populations on myenteric nerve cell bodies. Immunoreactivity for all three receptors was present on nerve fibers in the circular muscle.

CONCLUSIONS & INFERENCES

In the human colon, subtypes of MRs were present on multiple cell types within the enteric circuits underlying motility, secretory and vasoactive reflexes. The cellular distribution for MRs found in this study agrees with data from functional studies, providing insight into the role MRs have in mediating enteric cholinergic neurotransmission.

Irritable bowel syndrome: epidemiology, diagnosis and treatment: an update for health-care practitioners

Irritable bowel syndrome (IBS), a chronic gastrointestinal disorder, affects from 3-20% of the US population, depending on sociocultural and comorbid factors. IBS is characterized by a symptom complex of abdominal pain and abnormal bowel habits that present as diarrhea or constipation, and general physical weakness in the absence of abnormal morphological, histological or inflammatory markers. The main diagnostic Rome III criteria as established by international professional organizations are based on exclusion criteria and the occurrence and rate of symptoms. Because the pathophysiology and causes of IBS are poorly understood, treatment approaches are mainly focused on symptom management to maintain everyday functioning and improve quality of life for persons with IBS. The mainstay of intervention is pharmacological treatment with antispasmodics and antidiarrheals for diarrhea, prokinetics and high-fiber diets for constipation, and supportive therapy with low-dose antidepressants to normalize gastrointestinal motility. Other interventions include lifestyle and dietary changes, psychotherapy, herbal therapies and acupuncture. The purpose of this review is to critically assess benefits and risks of current treatment approaches as well as promising complementary and alternative therapies.

Immunohistochemical characteristics of submucosal Dogiel type II neurons in rat colon

Secretory and motility reflexes are evoked by physiological stimuli in the isolated rat distal colon, which is therefore expected to contain intrinsic primary afferent (sensory) neurons. Dogiel type II neurons (putative intrinsic primary afferent neurons) exhibit several long processes emerging from large oval or round cell bodies. This study has examined the immunohistochemical characteristics of type II neurons in the submucosal plexus of rat distal colons by using whole-mount preparations. Neuronal cell bodies positive for both substance P (SP) and calretinin have been observed in colchicine-treated rats. Neurofilament 200 immunostaining has confirmed the type II morphology of SP-positive neurons. Moreover, all submucosal type II neurons identified by neurofilament 200 immunoreactivity are positive for calretinin. Calcitonin gene-related peptide (CGRP)-positive neurons in the submucosal plexus are distinct from type II neurons because they are negative for calretinin and have smaller cell bodies than the SP-positive submucosal type II neurons. Most (73%) of the submucosal neurons including type II neurons exhibit immunoreactivity for the neurokinin-1 receptor (NK1R), a receptor for SP, on the surface of cell bodies. Immunoreactivity for the EP3 receptor (EP3R), a receptor for prostaglandin E2, has been detected in 51% of submucosal neurons including type II neurons. Thus, submucosal type II neurons in the rat distal colon are immunopositive for SP/calretinin but immunonegative for CGRP. SP released from submucosal type II neurons probably acts via NK1Rs on type II and non-type II submucosal neurons to mediate intrinsic reflexes. EP3R-positive submucosal type II neurons may be potential targets of prostaglandin E2.

Changes in the somatostatin (SOM)-like immunoreactivity within nervous structures of the porcine descending colon under various pathological factors

This study reports on changes in the somatostatin-like immunoreactive (SOM-LI) nerve structures of the enteric nervous system (ENS) in the porcine descending colon, caused by chemically driven inflammation, proliferative enteropathy (PE), which is a "natural" inflammation with proliferative changes and nerve injury (axotomy). The distribution pattern of SOM-LI structures was studied using the immunofluorescence technique in the circular muscle layer, the myenteric (MP), outer submucous (OSP) and inner submucous plexuses (ISP) and also in the mucosal layer. Under physiological conditions SOM-LI perikarya have been shown to constitute 1.97+/-0.36%, 2.06+/-0.33% and 4.23+/-0.40% in the MP, OSP and ISP, respectively. Changes in SOM-immunoreactivity depended on the pathological factor and the part of the ENS studied. Numbers of the SOM-LI perikarya amounted 1.81+/-0.30, 1.97+/-0.24 and 11.15+/-0.95 during chemically induced colitis and 3.21+/-0.37%, 4.33+/-0.33% and 4.42+/-0.32% after axotomy in MP, OSP and ISP, respectively. Moreover during PE SOM-positive cell bodies were not observed at all in MP, whereas within OSP and ISP the number of SOM-LI perikarya amounted to 3.34+/-0.36 and 10.92+/-059, respectively. All processes studied resulted in a decrease in the number of SOM-LI nerve fibers in the mucosal layer, whereas within the circular muscle layer chemically induced inflammation and axotomy caused an increase in the number of the SOM-LI nerve fibers contrary to PE, which reduced the number of such fibers. The obtained results suggest that SOM-LI nerve structures of the ENS may participate in various pathological states within the porcine descending colon and their functions probably depend on the type of pathological factor.

Development of enteric neuron diversity

The mature enteric nervous system (ENS) is composed of many different neuron subtypes and enteric glia, which all arise from the neural crest. How this diversity is generated from neural crest-derived cells is a central question in neurogastroenterology, as defects in these processes are likely to underlie some paediatric motility disorders. Here we review the developmental appearance (the earliest age at which expression of specific markers can be localized) and birthdates (the age at which precursors exit the cell cycle) of different enteric neuron subtypes, and their projections to some targets. We then focus on what is known about the mechanisms underlying the generation of enteric neuron diversity and axon pathfinding. Finally, we review the development of the ENS in humans and the etiologies of a number of paediatric motility disorders.

Between celiac disease and irritable bowel syndrome: the "no man's land" of gluten sensitivity

The repertoire of gastrointestinal (GI) symptoms is finite; however, the etiologies and mechanisms underlying symptom generation and perception are diverse and, in many cases, unknown. This review examines the clinical and experimental evidence exploring the putative relationship between gluten sensitivity (GS) and the generation of GI symptoms. It explores the hypothesis that, in a proportion of patients, GS causes functional bowel disorder (FBD)-like symptoms. We propose a model for investigating and understanding the induction of GI symptoms and dysfunction by gluten in FBD and organic disease. We hypothesize that, even in the absence of fully developed celiac disease, gluten can induce symptoms similar to FBD. We discuss the hypothesis that GS and post-infectious irritable bowel syndrome (IBS) provide two triggers that can explain at least part of the spectrum that constitutes IBS, further advancing an understanding of the role of mucosal responses to luminal factors in FBDs. We propose that the animal model of GS in human leukocyte antigen (HLA)- DQ8 mice allows investigation of mucosal pathophysiological changes that occur before the onset of full-blown inflammation in a GS host. A better understanding of how gluten can cause symptoms in sensitive individuals will illuminate the interaction between host genotype, diet, and intestinal microbiota in generating one of the most common GI conditions.

Characterisation of calcitonin gene-related peptide-immunoreactive neurons in the myenteric plexus of rat colon

A mechanical or chemical stimulus applied to the intestinal mucosa induces motility reflexes in the rat colon. Enteric neurons containing calcitonin gene-related peptide (CGRP) have been suggested as intrinsic primary afferent neurons responsible for mediating such reflexes. In the present study, immunohistochemistry was performed on whole-mount stretch preparations to investigate chemical profiles, morphological characteristics and projections of CGRP-containing neurons in the myenteric plexus of the rat colon. CGRP-positive neuronal cell bodies were detected in preparations incubated with colchicine-containing medium, whereas CGRP-positive nerve fibres were found in colchicine-untreated preparations. These neurons had large oval or round cell bodies that were also immunoreactive for the calcium-binding protein calretinin and neurofilament 200. Myenteric neurons positive for both calretinin and neurofilament 200 had several long processes that emerged from the cell body, consistent with Dogiel type II morphology. Application of the neural tracer DiI to the intestinal mucosa revealed that DiI-labelled myenteric neurons each had an oval or round cell body immunoreactive for calretinin. Thus, CGRP-containing myenteric neurons are Dogiel type II neurons and are immunoreactive for calretinin and neurofilament 200 in the rat colon. These neurons probably project to the intestinal mucosa.

Spiny versus stubby: 3D reconstruction of human myenteric (type I) neurons

We have compared the three-dimensional (3D) morphology of stubby and spiny neurons derived from the human small intestine. After immunohistochemical triple staining for leu-enkephalin (ENK), vasoactive intestinal peptide (VIP) and neurofilament (NF), neurons were selected and scanned based on their immunoreactivity, whether ENK (stubby) or VIP (spiny). For the 3D reconstruction, we focused on confocal data pre-processing with intensity drop correction, non-blind deconvolution, an additional compression procedure in z-direction, and optimizing segmentation reliability. 3D Slicer software enabled a semi-automated segmentation based on an objective threshold (interrater and intrarater reliability, both 0.99). We found that most dendrites of stubby neurons emerged only from the somal circumference, whereas in spiny neurons, they also emerged from the luminal somal surface. In most neurons, the nucleus was positioned abluminally in its soma. The volumes of spiny neurons were significantly larger than those of stubby neurons (total mean of stubbies 806 +/- 128 mum(3), of spinies 2,316 +/- 545 mum(3)), and spiny neurons had more dendrites (26.3 vs. 11.3). The ratios of somal versus dendritic volumes were 1:1.2 in spiny and 1:0.3 in stubby neurons. In conclusion, 3D reconstruction revealed new differences between stubby and spiny neurons and allowed estimations of volumetric data of these neuron populations.

Intrinsic ruminal innervation in ruminants of different feeding types

According to their feeding habits, ruminants can be classified as grazers, concentrate selectors and those of intermediate type. The different feeding types are reflected in distinct anatomical properties of the forestomachs. The present study was designed to investigate whether the intrinsic innervation patterns of the rumen (the main part of the forestomach) differ between intermediate types and grazers. Myenteric plexus preparations from the rumen of goats (intermediate type), fallow deer (intermediate type), cattle (grazer) and sheep (grazer) were analysed by immunohistochemical detection of the following antigens: Hu-protein (HuC/D), choline acetyltransferase (ChAT), nitric oxide synthase (NOS), vasoactive intestinal peptide (VIP), neuropeptide Y (NPY), substance P (SP), calbindin (CALB) and somatostatin (SOM). Myenteric ganglia of cattle contained 73 +/- 6 neurons per ganglion, whereas the ganglia of sheep were significantly smaller (45 +/- 18 neurons per ganglion). The ganglion density of the myenteric plexus was highest in fallow deer (15 +/- 3 ganglia per cm(2)) and lowest in cattle (6 +/- 1 ganglia per cm(2)). All myenteric neurons were either ChAT or NOS positive. The proportion of NOS-positive neurons was significantly lower in sheep (29.5 +/- 8.2% of all neurons) than in goats (44.2 +/- 9.8%). In all species, additional analysis of the different neuropeptides revealed the following subpopulations in descending order of percentile appearance: ChAT/SP > NOS/VIP/NPY > ChAT/- > NOS/NPY. Expression of CALB was detected in a minority of the ChAT-positive neurons in all species. Somatostatin immunoreactive somata were found only in preparations obtained from fallow deer and sheep. These data suggest that the rumen of grazers is under stronger cholinergic control than the rumen of species belonging to the intermediate type, although most subpopulations of neurons are present in all species. However, whether the strong mixing patterns of low quality roughage during digestion are enabled by the prominent excitatory input of the rumen of grazers requires elucidation in further studies.

Calretinin in the peripheral nervous system of the adult zebrafish

Calretinin is a calcium-binding protein found widely distributed in the central nervous system and chemosensory cells of the teleosts, but its presence in the peripheral nervous system of fishes is unknown. In this study we used Western blot analysis and immunohistochemistry to investigate the occurrence and distribution of calretinin in the cranial nerve ganglia, dorsal root ganglia, sympathetic ganglia, and enteric nervous system of the adult zebrafish. By Western blotting a unique and specific protein band with an estimated molecular weight of around 30 kDa was detected, and it was identified as calretinin. Immunohistochemistry revealed that calretinin is selectively present in the cytoplasm of the neurons and never in the satellite glial cells. In both sensory and sympathetic ganglia the density of neurons that were immunolabelled, their size and morphology, as well as the intensity of immunostaining developed within the cytoplasm, were heterogeneous. In the enteric nervous system calretinin immunoreactivity was detected in a subset of enteric neurons as well as in a nerve fibre plexus localized inside the muscular layers. The present results demonstrate that in addition to the central nervous system, calretinin is also present in the peripheral nervous system of zebrafish, and contribute to completing the map of the distribution of this protein in the nervous system of teleosts.

Quantitative estimation of putative primary afferent neurons in the myenteric plexus of human small intestine

This study aimed at estimating the proportion of human myenteric Dogiel type II neurons, putative intrinsic primary afferent neurons (IPANs), in relation to the entire myenteric neuron population. Since, at present, there is no known single marker, which specifically labels these neurons, we tried to identify the most appropriate marker combination based on the results of an earlier study. For this purpose, 10 wholemounts derived from human small intestinal segments were immunohistochemically triple-stained for calretinin (CALR), somatostatin (SOM) and neurofilaments (NF) and 9 were stained for substance P (SP), SOM and NF. In each wholemount, 15 ganglia selected randomly were evaluated. On the basis of their NF-reactivity, neurons reactive for one or co-reative for both of the other two markers, respectively, were morphologically classified as type II or non-type II neurons. We found that the majorities of neurons co-reactive for CALR/SOM and SP/SOM, respectively, were type II neurons whereas this was not the case for neurons, which were reactive for only one of the two markers. One of the statistical parameters estimated was the positive predictive value, the probability that a neuron displaying CALR/SOM- or SP/SOM-co-reactivity, respectively, is a type II neuron. This value was 97% in case of CALR/SOM- and 95% in case of SP/SOM-co-staining. Although the difference of the statistical parameters between the two stainings was not significant, CALR and SOM were used to estimate indirectly the proportion of type II neurons, in wholemounts co-stained with the pan-neuronal marker neuronal protein HuC/HuD (HU). In these wholemounts, altogether 9.1% of neurons were coreactive for CALR/SOM. We suggest that the proportion of myenteric type II neurons in the human small intestine is related to the proportion of CALR/SOM-co-reactive neurons and may be near to one tenth of the total myenteric neuronal population.

Chemical coding of myenteric neurons with different axonal projection patterns in the porcine ileum

The aim of this study was to perform an immunohistochemical characterization of two different myenteric neuron types of the pig displaying opposite axonal projections. These were type I neurons equipped with lamellar dendrites that projected mainly orally, and type VI neurons that displayed typical axonal dendrites and projected anally. Double immunostainings of longitudinal muscle/myenteric plexus wholemounts from ileal segments of four pigs were performed to visualize neurofilaments (NF) in combination with calcitonin gene-related peptide (CGRP), leu-enkephalin (ENK) and substance P (SP), respectively. Triple immunostainings of wholemounts, using antibodies against neuronal nitric oxide synthase (nNOS) and vasoactive intestinal peptide (VIP) as well as against VIP and galanin (GAL), were performed. We found that 78% of type I neurons immunoreacted to ENK, 21% to CGRP and 24% to SP. The NF-positive type I neurons co-reactive for one of the three above markers displayed mostly frayed outlines of both their somal contours and their broadened dendritic endings. By contrast, most of the non-coreactive type I neurons displayed rather sharply outlined somata and dendrites. No type I neuron immunoreacted to nNOS, VIP or GAL and none of the type VI NF-reactive neurons reacted to CGRP, ENK or SP. All type VI neurons investigated displayed immunoreactivity for nNOS, 92% of which were co-reactive for VIP. Co-reactivity for VIP and GAL was found in 69% of type VI neurons, 21% were positive for VIP but negative for GAL, 9% were negative for both GAL and VIP, and 1% were positive for GAL but negative for VIP. We conclude that there are two subpopulations of morphological type I neurons. One of these displays mainly oral projections and could not be further characterized in this study. The other, which may correspond to neurons innervating the longitudinal and circular muscle layers, were partly immunoreactive for ENK, CGRP and/or SP. Type VI neurons are immunoreactive for nNOS frequently co-localized with VIP and, partly, also GAL. These may be inhibitory motor neurons and are different from VIP/GAL-coreactive minineurons described earlier.