Developmental biology of the enteric nervous system: pathogenesis of Hirschsprung's disease and other congenital dysmotilities

Association between gut microbiota and Hirschsprung disease: a bidirectional two-sample Mendelian randomization study

Background

Several studies have pointed to the critical role of gut microbiota (GM) and their metabolites in Hirschsprung disease (HSCR) pathogenesis. However, the detailed causal relationship between GM and HSCR remains unknown.

Methods

In this study, we used two-sample Mendelian randomization (MR) analysis to investigate the causal relationship between GM and HSCR, based on the MiBioGen Consortium's genome-wide association study (GWAS) and the GWAS Catalog's HSCR data. Reverse MR analysis was performed subsequently, and the sensitivity analysis, Cochran's Q-test, MR pleiotropy residual sum, outlier (MR-PRESSO), and the MR-Egger intercept were used to analyze heterogeneity or horizontal pleiotropy. 16S rDNA sequencing and targeted mass spectrometry were developed for initial validation.

Results

In the forward MR analysis, inverse-variance weighted (IVW) estimates suggested that Eggerthella (OR: 2.66, 95%CI: 1.23-5.74, p = 0.01) was a risk factor for HSCR, while Peptococcus (OR: 0.37, 95%CI: 0.18-0.73, p = 0.004), Ruminococcus2 (OR: 0.32, 95%CI: 0.11-0.91, p = 0.03), Clostridiaceae1 (OR: 0.22, 95%CI: 0.06-0.78, p = 0.02), Mollicutes RF9 (OR: 0.27, 95%CI: 0.09-0.8, p = 0.02), Ruminococcaceae (OR: 0.16, 95%CI: 0.04-0.66, p = 0.01), and Paraprevotella (OR: 0.45, 95%CI: 0.21-0.98, p = 0.04) were protective factors for HSCR, which had no heterogeneity or horizontal pleiotropy. However, reverse MR analysis showed that HSCR (OR: 1.02, 95%CI: 1-1.03, p = 0.049) is the risk factor for Eggerthella. Furthermore, some of the above microbiota and short-chain fatty acids (SCFAs) were altered in HSCR, showing a correlation.

Conclusion

Our analysis established the relationship between specific GM and HSCR, identifying specific bacteria as protective or risk factors. Significant microbiota and SCFAs were altered in HSCR, underlining the importance of further study and providing new insights into the pathogenesis and treatment.

The Potential of Flavonoids and Flavonoid Metabolites in the Treatment of Neurodegenerative Pathology in Disorders of Cognitive Decline

Flavonoids are a biodiverse family of dietary compounds that have antioxidant, anti-inflammatory, antiviral, and antibacterial cell protective profiles. They have received considerable attention as potential therapeutic agents in biomedicine and have been widely used in traditional complimentary medicine for generations. Such complimentary medical herbal formulations are extremely complex mixtures of many pharmacologically active compounds that provide a therapeutic outcome through a network pharmacological effects of considerable complexity. Methods are emerging to determine the active components used in complimentary medicine and their therapeutic targets and to decipher the complexities of how network pharmacology provides such therapeutic effects. The gut microbiome has important roles to play in the generation of bioactive flavonoid metabolites retaining or exceeding the antioxidative and anti-inflammatory properties of the intact flavonoid and, in some cases, new antitumor and antineurodegenerative bioactivities. Certain food items have been identified with high prebiotic profiles suggesting that neutraceutical supplementation may be beneficially employed to preserve a healthy population of bacterial symbiont species and minimize the establishment of harmful pathogenic organisms. Gut health is an important consideration effecting the overall health and wellbeing of linked organ systems. Bioconversion of dietary flavonoid components in the gut generates therapeutic metabolites that can also be transported by the vagus nerve and systemic circulation to brain cell populations to exert a beneficial effect. This is particularly important in a number of neurological disorders (autism, bipolar disorder, AD, PD) characterized by effects on moods, resulting in depression and anxiety, impaired motor function, and long-term cognitive decline. Native flavonoids have many beneficial properties in the alleviation of inflammation in tissues, however, concerns have been raised that therapeutic levels of flavonoids may not be achieved, thus allowing them to display optimal therapeutic effects. Dietary manipulation and vagal stimulation have both yielded beneficial responses in the treatment of autism spectrum disorders, depression, and anxiety, establishing the vagal nerve as a route of communication in the gut-brain axis with established roles in disease intervention. While a number of native flavonoids are beneficial in the treatment of neurological disorders and are known to penetrate the blood–brain barrier, microbiome-generated flavonoid metabolites (e.g., protocatechuic acid, urolithins, γ-valerolactones), which retain the antioxidant and anti-inflammatory potency of the native flavonoid in addition to bioactive properties that promote mitochondrial health and cerebrovascular microcapillary function, should also be considered as potential biotherapeutic agents. Studies are warranted to experimentally examine the efficacy of flavonoid metabolites directly, as they emerge as novel therapeutic options.

Ednrb−/− mice with hirschsprung disease are missing Gad2-expressing enteric neurons in the ganglionated small intestine

Hirschsprung disease is most often characterized by aganglionosis limited to the distal colon and rectum, and mice lacking the Endothelin receptor type B (Ednrb) faithfully recapitulate this phenotype. However, despite the presence of enteric ganglia in the small intestine, both human patients and Ednrb−/− mice suffer from dysmotility and altered gastrointestinal function, thus raising the possibility of enteric nervous system (ENS) abnormalities proximal to the aganglionic region. We undertook the present study to determine whether abnormalities with the ENS in ganglionated regions may account for abnormal gastrointestinal function. We performed single-cell RNA sequencing on ENS cells from the small intestine of Ednrb−/− mice and compared the results to a published single-cell dataset. Our results identified a missing population of neurons marked by the enzyme Gad2, which catalyzes the production of γ-Aminobutyric acid (GABA), in the small intestine of Ednrb−/− animals. This result was confirmed by immunostaining enteric ganglia from Ednrb−/− mice and their wild-type littermates. These data show for the first time that ganglionated regions of the Hirschsprung gut lack a neuronal subpopulation, which may explain the persistent gastrointestinal dysfunction after surgical correction of Hirschsprung disease.

The Emerging Role of the Gut-Brain-Microbiota Axis in Neurodevelopmental Disorders

Autism spectrum disorder (ASD; autism) is a prevalent neurodevelopmental disorder associated with changes in gut-brain axis communication. Gastrointestinal (GI) symptoms are experienced by a large proportion of individuals diagnosed with autism. Several mutations associated with autism modify cellular communication via neuronal synapses. It has been suggested that modifications to the enteric nervous system, an intrinsic nervous system of the GI tract, could contribute to GI dysfunction. Changes in gut motility, permeability, and the mucosal barrier as well as shifts in the large population of microbes inhabiting the GI tract could contribute to GI symptoms. Preclinical research has demonstrated that mice expressing the well-studied R451C missense mutation in Nlgn3 gene, which encodes cell adhesion protein neuroligin-3 at neuronal synapses, exhibit GI dysfunction. Specifically, NL3^R451C mice show altered colonic motility and faster small intestinal transit. As well as dysmotility, macrophages located within the gut-associated lymphoid tissue of the NL3^R451C mouse caecum show altered morphology, suggesting that neuro-inflammation pathways are modified in this model. Interestingly, NL3^R451C mice maintained in a shared environment demonstrate fecal microbial dysbiosis indicating a role for the nervous system in regulating gut microbial populations. To better understand host-microbe interactions, further clarification and comparison of clinical and animal model profiles of dysbiosis should be obtained, which in turn will provide better insights into the efforts taken to design personalized microbial therapies. In addition to changes in neurophysiological measures, the mucosal component of the GI barrier may contribute to GI dysfunction more broadly in individuals diagnosed with a wide range of neurological disorders. As the study of GI dysfunction advances to encompass multiple components of the gut-brain-microbiota axis, findings will help understand future directions such as microbiome engineering and optimisation of the mucosal barrier for health.

Literature review: enteric nervous system development, genetic and epigenetic regulation in the etiology of Hirschsprung's disease

Hirschsprung's disease (HSCR) is a developmental disorder of the enteric nervous system (ENS) derived from neural crest cells (NCCs), which affects their migration, proliferation, differentiation, or preservation in the digestive tract, resulting in aganglionosis in the distal intestine. The regulation of both NCCs and the surrounding environment involves various genes, signaling pathways, transcription factors, and morphogens. Therefore, changes in gene expression during the development of the ENS may contribute to the pathogenesis of HSCR.

This review discusses several mechanisms involved in the development of ENS, confirming that deviant genetic and epigenetic patterns, such as DNA methylation, histone modification, and microRNA (miRNA) regulation, can contribute to the development of neurocristopathy. Specifically, the epigenetic regulation of miRNA expression and its relationship to cellular interactions and gene activation through various major pathways in Hirschsprung's disease will be discussed.

Global Proteomic Profile Integrated to Quantitative and Morphometric Assessment of Enteric Neurons: Investigation of the Mechanisms Involved in the Toxicity Induced by Acute Fluoride Exposure in the Duodenum

The enteric nervous system is responsible for controlling the gastrointestinal tract (GIT) functions. Enteric neuropathies are highly correlated to the development of several intestinal disturbances. Fluoride (F) is extensively applied for dental health improvement and its ingestion can promote systemic toxicity with mild to severe GIT symptomatology and neurotoxicity. Although F harmful effects have been published, there is no information regarding noxiousness of a high acute F exposure (25 mg F/kg) on enteric neurons and levels of expression of intestinal proteins in the duodenum. Quantitative proteomics of the duodenum wall associated to morphometric and quantitative analysis of enteric neurons displayed F effects of a high acute exposure. F-induced myenteric neuroplasticity was characterized by a decrease in the density of nitrergic neurons and morphometric alterations in the general populations of neurons, nitrergic neurons, and substance P varicosities. Proteomics demonstrated F-induced alterations in levels of expression of 356 proteins correlated to striated muscle cell differentiation; generation of precursor metabolites and energy; NADH and glutathione metabolic process and purine ribonucleoside triphosphate biosynthesis. The neurochemical role of several intestinal proteins was discussed specially related to the modulation of enteric neuroplasticity. The results provide a new perspective on cell signaling pathways of gastrointestinal symptomatology promoted by acute F toxicity.

Altered Caecal Neuroimmune Interactions in the Neuroligin-3R451C Mouse Model of Autism

The intrinsic nervous system of the gut interacts with the gut-associated lymphoid tissue (GALT) via bidirectional neuroimmune interactions. The caecum is an understudied region of the gastrointestinal (GI) tract that houses a large supply of microbes and is involved in generating immune responses. The caecal patch is a lymphoid aggregate located within the caecum that regulates microbial content and immune responses. People with Autism Spectrum Disorder (ASD; autism) experience serious GI dysfunction, including inflammatory disorders, more frequently than the general population. Autism is a highly prevalent neurodevelopmental disorder defined by the presence of repetitive behavior or restricted interests, language impairment, and social deficits. Mutations in genes encoding synaptic adhesion proteins such as the R451C missense mutation in neuroligin-3 (NL3) are associated with autism and impair synaptic transmission. We previously reported that NL3^R451C mice, a well-established model of autism, have altered enteric neurons and GI dysfunction; however, whether the autism-associated R451C mutation alters the caecal enteric nervous system and immune function is unknown. We assessed for gross anatomical changes in the caecum and quantified the proportions of caecal submucosal and myenteric neurons in wild-type and NL3^R451C mice using immunofluorescence. In the caecal patch, we assessed total cellular density as well as the density and morphology of Iba-1 labeled macrophages to identify whether the R451C mutation affects neuro-immune interactions. NL3^R451C mice have significantly reduced caecal weight compared to wild-type mice, irrespective of background strain. Caecal weight is also reduced in mice lacking Neuroligin-3. NL3^R451C caecal ganglia contain more neurons overall and increased numbers of Nitric Oxide (NO) producing neurons (labeled by Nitric Oxide Synthase; NOS) per ganglion in both the submucosal and myenteric plexus. Overall caecal patch cell density was unchanged however NL3^R451C mice have an increased density of Iba-1 labeled enteric macrophages. Macrophages in NL3^R451C were smaller and more spherical in morphology. Here, we identify changes in both the nervous system and immune system caused by an autism-associated mutation in Nlgn3 encoding the postsynaptic cell adhesion protein, Neuroligin-3. These findings provide further insights into the potential modulation of neural and immune pathways.

Enteric neuronal cell therapy reverses architectural changes in a novel diphtheria toxin-mediated model of colonic aganglionosis

Hirschsprung disease (HSCR) is characterized by absence of the enteric nervous system (ENS) in the distal bowel. Despite removal of the aganglionic segment, gastrointestinal (GI) problems persist. Cell therapy offers potential treatment but use of genetic models is limited by their poor survival. We have developed a novel model of aganglionosis in which enteric neural crest-derived cells (ENCDCs) express diphtheria toxin (DT) receptor. Local DT injection into the colon wall results in focal, specific, and sustained ENS ablation without altering GI transit or colonic contractility, allowing improved survival over other aganglionosis models. Focal ENS ablation leads to increased smooth muscle and mucosal thickness, and localized inflammation. Transplantation of ENCDCs into this region leads to engraftment, migration, and differentiation of enteric neurons and glial cells, with restoration of normal architecture of the colonic epithelium and muscle, reduction in inflammation, and improved survival.

Derivation of enteric neuron lineages from human pluripotent stem cells

The enteric nervous system (ENS) represents a vast network of neuronal and glial cell types that develops entirely from migratory neural crest (NC) progenitor cells. Considerable improvements in the understanding of the molecular mechanisms underlying NC induction and regional specification have recently led to the development of a robust method to re-create the process in vitro using human pluripotent stem cells (hPSCs). Directing the fate of hPSCs toward the enteric NC (ENC) results in an accessible and scalable in vitro model of ENS development. The application of hPSC-derived enteric neural lineages provides a powerful platform for ENS-related disease modeling and drug discovery. Here we present a detailed protocol for the induction of a regionally specific NC intermediate that occurs over the course of a 15-d interval and is an effective source for the in vitro derivation of functional enteric neurons (ENs) from hPSCs. Additionally, we introduce a new and improved protocol that we have developed to optimize the protocol for future applications in regenerative medicine, in which components of undefined activity have been replaced with fully defined culture conditions. This protocol provides access to a broad range of human ENS lineages within a 30-d period.

Uncovering the genetic lesions underlying the most severe form of Hirschsprung disease by whole-genome sequencing

Hirschsprung disease (HSCR) is a complex birth defect characterized by the lack of ganglion cells along a variable length of the distal intestine. A large proportion of HSCR patients remain genetically unexplained. We applied whole-genome sequencing (WGS) on 9 trios where the probands are sporadically affected with the most severe form of the disorder and harbor no coding sequence variants affecting the function of known HSCR genes. We found de novo protein-altering variants in three intolerant to change genes-CCT2, VASH1, and CYP26A1-for which a plausible link with the enteric nervous system (ENS) exists. De novo single-nucleotide and indel variants were present in introns and non-coding neighboring regions of ENS-related genes, including NRG1 and ERBB4. Joint analysis with those inherited rare variants found under recessive and/or digenic models revealed both patient-unique and shared genetic features where rare variants were found to be enriched in the extracellular matrix-receptor (ECM-receptor) pathway (p = 3.4 × 10-11). Delineation of the genetic profile of each patient might help finding common grounds that could lead to the discovery of shared molecules that could be used as drug targets for the currently ongoing cell therapy effort which aims at providing an alternative to the surgical treatment.

Neurocristopathies: New insights 150 years after the neural crest discovery

The neural crest (NC) is a transient, multipotent and migratory cell population that generates an astonishingly diverse array of cell types during vertebrate development. These cells, which originate from the ectoderm in a region lateral to the neural plate in the neural fold, give rise to neurons, glia, melanocytes, chondrocytes, smooth muscle cells, odontoblasts and neuroendocrine cells, among others. Neurocristopathies (NCP) are a class of pathologies occurring in vertebrates, especially in humans that result from the abnormal specification, migration, differentiation or death of neural crest cells during embryonic development. Various pigment, skin, thyroid and hearing disorders, craniofacial and heart abnormalities, malfunctions of the digestive tract and tumors can also be considered as neurocristopathies. In this review we revisit the current classification and propose a new way to classify NCP based on the embryonic origin of the affected tissues, on recent findings regarding the molecular mechanisms that drive NC formation, and on the increased complexity of current molecular embryology techniques.

Indolethylamine-N-methyltransferase Polymorphisms: Genetic and Biochemical Approaches for Study of Endogenous N,N,-dimethyltryptamine

N,N-dimethyltryptamine (DMT) is a powerful serotonergic psychedelic whose exogenous administration elicits striking psychedelic effects in humans. Studies have identified DMT and analogous compounds (e.g., 5-hydroxy-DMT, 5-methoxy-DMT) alongside of an enzyme capable of synthesizing DMT endogenously from tryptamine, indolethylamine-N-methyltransferase (INMT), in human and several other mammalian tissues. Subsequently, multiple hypotheses for the physiological role of endogenous DMT have emerged, from proposed immunomodulatory functions to an emphasis on the overlap between the mental states generated by exogenous DMT and naturally occurring altered states of consciousness; e.g., schizophrenia. However, no clear relationship between endogenous DMT and naturally occurring altered states of consciousness has yet been established from in vivo assays of DMT in bodily fluids. The advent of genetic screening has afforded the capability to link alterations in the sequence of specific genes to behavioral and molecular phenotypes via expression of identified single nucleotide polymorphisms (SNPs) in cell and animal models. As SNPs in INMT may impact endogenous DMT synthesis and levels via changes in INMT expression and/or INMT structure and function, these combined genetic and biochemical approaches circumvent the limitations of assaying DMT in bodily fluids and may augment data from prior in vitro and in vivo work. Therefore, all reported SNPs in INMT were amassed from genetic and biochemical literature and genomic databases to consolidate a blueprint for future studies aimed at elucidating whether DMT plays a physiological role.

Identification of two novel PCDHA9 mutations associated with Hirschsprung's disease

Hirschsprung's disease (HSCR) is a complex disorder with multiple pathogenic gene mutations. Protocadherin alpha 9 (PCDHA9) was identified as a potential candidate gene for HSCR by whole-exome sequencing in a Chinese family. Sanger sequencing in 298 HSCR cases revealed two sporadic Chinese patients with a novel missence PCDHΑ9 mutation (NM_031857; c.1280C > T[p.Ala427Val]) and one sporadic Chinese patient with another novel missence PCDHΑ9 mutation (c.1425C > G[p.Phe475Leu]).The silico predictions and 3D modeling suggest the deleterious effect of identified mutations on protein function. Immunohistochemistry analysis showed PCDHΑ9 was predominantly expressed in the myenteric plexus of human colon tissues. For mouse embryos, PCDHΑ9 was expressed in the stomach but rarely seen in the intestine during E10.5-12.5, then obviously expressed in the intestinal mucosa at E13.5 and extensively expressed in intestinal muscularis and mucosa at E14.5. Moreover, the down-regulation of PCDHΑ9 in the SH-SY5Y cell line promoted the proliferation and migration rate but inhibited the apoptotic rate. In summary, PCDHΑ9 is potentially related to HSCR and the clustered protocadherins (Pcdhs) may involve in the enteric nervous system (ENS) ontogeny.

Chronic treatment with fluoride affects the jejunum: insights from proteomics and enteric innervation analysis

Gastrointestinal symptoms are the first signs of fluoride (F) toxicity. In the present study, the jejunum of rats chronically exposed to F was evaluated by proteomics, as well as by morphological analysis. Wistar rats received water containing 0, 10 or 50 mgF/L during 30 days. HuC/D, neuronal Nitric Oxide (nNOS), Vasoactive Intestinal Peptide (VIP), Calcitonin Gene Related Peptide (CGRP), and Substance P (SP) were detected in the myenteric plexus of the jejunum by immunofluorescence. The density of nNOS-IR neurons was significantly decreased (compared to both control and 10 mgF/L groups), while the VIP-IR varicosities were significantly increased (compared to control) in the group treated with the highest F concentration. Significant morphological changes were seen observed in the density of HUC/D-IR neurons and in the area of SP-IR varicosities for F-treated groups compared to control. Changes in the abundance of various proteins correlated with relevant biological processes, such as protein synthesis, glucose homeostasis and energy metabolism were revealed by proteomics.

Hirschsprung's disease: clinical dysmorphology, genes, micro-RNAs, and future perspectives

On the occasion of the 100th anniversary of Dr. Harald Hirschsprung's death, there is a worldwide significant research effort toward identifying and understanding the role of genes and biochemical pathways involved in the pathogenesis as well as the use of new therapies for the disease harboring his name (Hirschsprung disease, HSCR). HSCR (aganglionic megacolon) is a frequent diagnostic and clinical challenge in perinatology and pediatric surgery, and a major cause of neonatal intestinal obstruction. HSCR is characterized by the absence of ganglia of the enteric nervous system, mostly in the distal gastrointestinal tract. This review focuses on current understanding of genes and pathways associated with HSCR and summarizes recent knowledge related to micro RNAs (miRNAs) and HSCR pathogenesis. While commonly sporadic, Mendelian patterns of inheritance have been described in syndromic cases with HSCR. Although only half of the patients with HSCR have mutations in specific genes related to early embryonic development, recent pathway-based analysis suggests that gene modules with common functions may be associated with HSCR in different populations. This comprehensive profile of functional gene modules may serve as a useful resource for future developmental, biochemical, and genetic studies providing insights into the complex nature of HSCR.

Extracerebral Dysfunction in Animal Models of Autism Spectrum Disorder

Genetic factors might be largely responsible for the development of autism spectrum disorder (ASD) that alone or in combination with specific environmental risk factors trigger the pathology. Multiple mutations identified in ASD patients that impair synaptic function in the central nervous system are well studied in animal models. How these mutations might interact with other risk factors is not fully understood though. Additionally, how systems outside of the brain are altered in the context of ASD is an emerging area of research. Extracerebral influences on the physiology could begin in utero and contribute to changes in the brain and in the development of other body systems and further lead to epigenetic changes. Therefore, multiple recent studies have aimed at elucidating the role of gene-environment interactions in ASD. Here we provide an overview on the extracerebral systems that might play an important associative role in ASD and review evidence regarding the potential roles of inflammation, trace metals, metabolism, genetic susceptibility, enteric nervous system function and the microbiota of the gastrointestinal (GI) tract on the development of endophenotypes in animal models of ASD. By influencing environmental conditions, it might be possible to reduce or limit the severity of ASD pathology.

Genetics of enteric neuropathies

Abnormal development or disturbed functioning of the enteric nervous system (ENS), the intrinsic innervation of the gastrointestinal tract, is associated with the development of neuropathic gastrointestinal motility disorders. Here, we review the underlying molecular basis of these disorders and hypothesize that many of them have a common defective biological mechanism. Genetic burden and environmental components affecting this common mechanism are ultimately responsible for disease severity and symptom heterogeneity. We believe that they act together as the fulcrum in a seesaw balanced with harmful and protective factors, and are responsible for a continuum of symptoms ranging from neuronal hyperplasia to absence of neurons.

Acetylcholinesterase histochemistry (AChE)--A helpful technique in the diagnosis and in aiding the operative procedures of Hirschsprung disease

Background

Hirschsprung’s disease (HD) is an anomaly characterized by the absence of myenteric and submucosal ganglion cells (GC) in the distal alimentary tract. Diagnosis of HD is made by the absence of GC and missing out on even a single ganglion cell can be very devastating. Acetylcholinesterase (AChE) histochemistry, done on frozen sections is said to be a very useful ancillary technique in the diagnosis and in aiding the operative procedures of HD.

Methods

To assess this, 73 samples from 42 suspected/known cases of HD were subjected to frozen section analysis with rapid haematoxylin and eosin, toluidin blue stain along with AChE histochemistry. The remnant sample was paraffin embedded for routine haematoxylin and eosin staining.

Results

On frozen section analysis, 33 samples showed absence of ganglion cells, AChE histochemistry showed a positive staining pattern in 17 samples and paraffin embedded routine, H&E stained sections showed absence of ganglion cells in 19 samples. Sensitivity and specificity of both tests ie frozen section rapid H&E/AChE histochemistry in the diagnosis of HD, were calculated taking paraffin embedded H&E stained sections as the gold standard. Sensitivity of frozen section rapid H&E in the diagnosis of HD is 57.57 % and specificity is 79.10 %. The p-value is <0.0001, which is significant. The sensitivity of AChE histochemistry in the diagnosis of HD is 90.47 % and specificity is 96.36 %. The p-value is <0.0001, which is significant.

Conclusions

Acetylcholineesterase (AChE) histochemistry is a very useful ancillary technique in the diagnosis and in aiding the operative procedures of HD. It acts as a double check in the diagnosis of HD.

Exact Solutions of Coupled Multispecies Linear Reaction-Diffusion Equations on a Uniformly Growing Domain

Embryonic development involves diffusion and proliferation of cells, as well as diffusion and reaction of molecules, within growing tissues. Mathematical models of these processes often involve reaction–diffusion equations on growing domains that have been primarily studied using approximate numerical solutions. Recently, we have shown how to obtain an exact solution to a single, uncoupled, linear reaction–diffusion equation on a growing domain, 0 < x < L(t), where L(t) is the domain length. The present work is an extension of our previous study, and we illustrate how to solve a system of coupled reaction–diffusion equations on a growing domain. This system of equations can be used to study the spatial and temporal distributions of different generations of cells within a population that diffuses and proliferates within a growing tissue. The exact solution is obtained by applying an uncoupling transformation, and the uncoupled equations are solved separately before applying the inverse uncoupling transformation to give the coupled solution. We present several example calculations to illustrate different types of behaviour. The first example calculation corresponds to a situation where the initially–confined population diffuses sufficiently slowly that it is unable to reach the moving boundary at x = L(t). In contrast, the second example calculation corresponds to a situation where the initially–confined population is able to overcome the domain growth and reach the moving boundary at x = L(t). In its basic format, the uncoupling transformation at first appears to be restricted to deal only with the case where each generation of cells has a distinct proliferation rate. However, we also demonstrate how the uncoupling transformation can be used when each generation has the same proliferation rate by evaluating the exact solutions as an appropriate limit.

Survival probability for a diffusive process on a growing domain

We consider the motion of a diffusive population on a growing domain, 0<x<L(t), which is motivated by various applications in developmental biology. Individuals in the diffusing population, which could represent molecules or cells in a developmental scenario, undergo two different kinds of motion: (i) undirected movement, characterized by a diffusion coefficient, D, and (ii) directed movement, associated with the underlying domain growth. For a general class of problems with a reflecting boundary at x=0, and an absorbing boundary at x=L(t), we provide an exact solution to the partial differential equation describing the evolution of the population density function, C(x,t). Using this solution, we derive an exact expression for the survival probability, S(t), and an accurate approximation for the long-time limit, S=lim(t→∞)S(t). Unlike traditional analyses on a nongrowing domain, where S≡0, we show that domain growth leads to a very different situation where S can be positive. The theoretical tools developed and validated in this study allow us to distinguish between situations where the diffusive population reaches the moving boundary at x=L(t) from other situations where the diffusive population never reaches the moving boundary at x=L(t). Making this distinction is relevant to certain applications in developmental biology, such as the development of the enteric nervous system (ENS). All theoretical predictions are verified by implementing a discrete stochastic model.

Exact solutions of linear reaction-diffusion processes on a uniformly growing domain: criteria for successful colonization

Many processes during embryonic development involve transport and reaction of molecules, or transport and proliferation of cells, within growing tissues. Mathematical models of such processes usually take the form of a reaction-diffusion partial differential equation (PDE) on a growing domain. Previous analyses of such models have mainly involved solving the PDEs numerically. Here, we present a framework for calculating the exact solution of a linear reaction-diffusion PDE on a growing domain. We derive an exact solution for a general class of one-dimensional linear reaction—diffusion process on 0<x<L(t), where L(t) is the length of the growing domain. Comparing our exact solutions with numerical approximations confirms the veracity of the method. Furthermore, our examples illustrate a delicate interplay between: (i) the rate at which the domain elongates, (ii) the diffusivity associated with the spreading density profile, (iii) the reaction rate, and (iv) the initial condition. Altering the balance between these four features leads to different outcomes in terms of whether an initial profile, located near x = 0, eventually overcomes the domain growth and colonizes the entire length of the domain by reaching the boundary where x = L(t).

Gut microbiota, the immune system, and diet influence the neonatal gut-brain axis

The conceptual framework for a gut-brain axis has existed for decades. The Human Microbiome Project is responsible for establishing intestinal dysbiosis as a mediator of inflammatory bowel disease, obesity, and neurodevelopmental disorders in adults. Recent advances in metagenomics implicate gut microbiota and diet as key modulators of the bidirectional signaling pathways between the gut and brain that underlie neurodevelopmental and psychiatric disorders in adults. Evidence linking intestinal dysbiosis to neurodevelopmental disease outcomes in preterm infants is emerging. Recent clinical studies show that intestinal dysbiosis precedes late-onset neonatal sepsis and necrotizing enterocolitis in intensive care nurseries. Moreover, strong epidemiologic evidence links late-onset neonatal sepsis and necrotizing enterocolitis in long-term psychomotor disabilities of very-low-birth-weight infants. The notion of the gut-brain axis thereby supports that intestinal microbiota can indirectly harm the brain of preterm infants. In this review, we highlight the anatomy and physiology of the gut-brain axis and describe transmission of stress signals caused by immune-microbial dysfunction in the gut. These messengers initiate neurologic disease in preterm infants. Understanding neural and humoral signaling through the gut-brain axis will offer insight into therapeutic and dietary approaches that may improve the outcomes of very-low-birth-weight infants.

Molecular handoffs in nitrergic neurotransmission

Postsynaptic density (PSD) proteins in excitatory synapses are relatively immobile components, while there is a structured organization of mobile scaffolding proteins lying beneath the PSDs. For example, shank proteins are located further away from the membrane in the cytosolic faces of the PSDs, facing the actin cytoskeleton. The rationale of this organization may be related to important roles of these proteins as “exchange hubs” for the signaling proteins for their migration from the subcortical cytosol to the membrane. Notably, PSD95 have also been demonstrated in prejunctional nerve terminals of nitrergic neuronal varicosities traversing the gastrointestinal smooth muscles. It has been recently reported that motor proteins like myosin Va play important role in transcytosis of nNOS. In this review, the hypothesis is forwarded that nNOS delivered to subcortical cytoskeleton requires interactions with scaffolding proteins prior to docking at the membrane. This may involve significant role of “shank,” named for SRC-homology (SH3) and multiple ankyrin repeat domains, in nitric oxide synthesis. Dynein light chain LC8–nNOS from acto-myosin Va is possibly exchanged with shank, which thereafter facilitates transposition of nNOS for binding with palmitoyl-PSD95 at the nerve terminal membrane. Shank knockout mice, which present with features of autism spectrum disorders, may help delineate the role of shank in enteric nitrergic neuromuscular transmission. Deletion of shank3 in humans is a monogenic cause of autism called Phelan–McDermid syndrome. One fourth of these patients present with cyclical vomiting, which may be explained by junctionopathy resulting from shank deficit in enteric nitrergic nerve terminals.

Developmental imaging: the avian embryo hatches to the challenge

The avian embryo provides a multifaceted model to study developmental mechanisms because of its accessibility to microsurgery, fluorescence cell labeling, in vivo imaging, and molecular manipulation. Early two-dimensional planar growth of the avian embryo mimics human development and provides unique access to complex cell migration patterns using light microscopy. Later developmental events continue to permit access to both light and other imaging modalities, making the avian embryo an excellent model for developmental imaging. For example, significant insights into cell and tissue behaviors within the primitive streak, craniofacial region, and cardiovascular and peripheral nervous systems have come from avian embryo studies. In this review, we provide an update to recent advances in embryo and tissue slice culture and imaging, fluorescence cell labeling, and gene profiling. We focus on how technical advances in the chick and quail provide a clearer understanding of how embryonic cell dynamics are beautifully choreographed in space and time to sculpt cells into functioning structures. We summarize how these technical advances help us to better understand basic developmental mechanisms that may lead to clinical research into human birth defects and tissue repair.

Studying autism in rodent models: reconciling endophenotypes with comorbidities

Autism spectrum disorder (ASD) patients commonly exhibit a variety of comorbid traits including seizures, anxiety, aggressive behavior, gastrointestinal problems, motor deficits, abnormal sensory processing, and sleep disturbances for which the cause is unknown. These features impact negatively on daily life and can exaggerate the effects of the core diagnostic traits (social communication deficits and repetitive behaviors). Studying endophenotypes relevant to both core and comorbid features of ASD in rodent models can provide insight into biological mechanisms underlying these disorders. Here we review the characterization of endophenotypes in a selection of environmental, genetic, and behavioral rodent models of ASD. In addition to exhibiting core ASD-like behaviors, each of these animal models display one or more endophenotypes relevant to comorbid features including altered sensory processing, seizure susceptibility, anxiety-like behavior, and disturbed motor functions, suggesting that these traits are indicators of altered biological pathways in ASD. However, the study of behaviors paralleling comorbid traits in animal models of ASD is an emerging field and further research is needed to assess altered gastrointestinal function, aggression, and disorders of sleep onset across models. Future studies should include investigation of these endophenotypes in order to advance our understanding of the etiology of this complex disorder.

Structure activity relationship of synaptic and junctional neurotransmission

Chemical neurotransmission may include transmission to local or remote sites. Locally, contact between 'bare' portions of the bulbous nerve terminal termed a varicosity and the effector cell may be in the form of either synapse or non-synaptic contact. Traditionally, all local transmissions between nerves and effector cells are considered synaptic in nature. This is particularly true for communication between neurons. However, communication between nerves and other effectors such as smooth muscles has been described as nonsynaptic or junctional in nature. Nonsynaptic neurotransmission is now also increasingly recognized in the CNS. This review focuses on the relationship between structure and function that orchestrate synaptic and junctional neurotransmissions. A synapse is a specialized focal contact between the presynaptic active zone capable of ultrafast release of soluble transmitters and the postsynaptic density that cluster ionotropic receptors. The presynaptic and the postsynaptic areas are separated by the 'closed' synaptic cavity. The physiological hallmark of the synapse is ultrafast postsynaptic potentials lasting milliseconds. In contrast, junctions are juxtapositions of nerve terminals and the effector cells without clear synaptic specializations and the junctional space is 'open' to the extracellular space. Based on the nature of the transmitters, postjunctional receptors and their separation from the release sites, the junctions can be divided into 'close' and 'wide' junctions. Functionally, the 'close' and the 'wide' junctions can be distinguished by postjunctional potentials lasting ~1s and tens of seconds, respectively. Both synaptic and junctional communications are common between neurons; however, junctional transmission is the rule at many neuro-non-neural effectors.

Chromosome 21 scan in Down syndrome reveals DSCAM as a predisposing locus in Hirschsprung disease

Hirschsprung disease (HSCR) genetics is a paradigm for the study and understanding of multigenic disorders. Association between Down syndrome and HSCR suggests that genetic factors that predispose to HSCR map to chromosome 21. To identify these additional factors, we performed a dose-dependent association study on chromosome 21 in Down syndrome patients with HSCR. Assessing 10,895 SNPs in 26 Caucasian cases and their parents led to identify two associated SNPs (rs2837770 and rs8134673) at chromosome-wide level. Those SNPs, which were located in intron 3 of the DSCAM gene within a 19 kb-linkage disequilibrium block region were in complete association and are consistent with DSCAM expression during enteric nervous system development. We replicated the association of HSCR with this region in an independent sample of 220 non-syndromic HSCR Caucasian patients and their parents. At last, we provide the functional rationale to the involvement of DSCAM by network analysis and assessment of SOX10 regulation. Our results reveal the involvement of DSCAM as a HSCR susceptibility locus, both in Down syndrome and HSCR isolated cases. This study further ascertains the chromosome-scan dose-dependent methodology used herein as a mean to map the genetic bases of other sub-phenotypes both in Down syndrome and other aneuploidies.

Gastrointestinal defects of the Gas1 mutant involve dysregulated Hedgehog and Ret signaling

The gastrointestinal (GI) tract defines the digestive system and is composed of the stomach, intestine and colon. Among the major cell types lining radially along the GI tract are the epithelium, mucosa, smooth muscles and enteric neurons. The Hedgehog (Hh) pathway has been implicated in directing various aspects of the developing GI tract, notably the mucosa and smooth muscle growth, and enteric neuron patterning, while the Ret signaling pathway is selectively required for enteric neuron migration, proliferation, and differentiation. The growth arrest specific gene 1 (Gas1) encodes a GPI-anchored membrane protein known to bind to Sonic Hh (Shh), Indian Hh (Ihh), and Ret. However, its role in the GI tract has not been examined. Here we show that the Gas1 mutant GI tract, compared to the control, is shorter, has thinner smooth muscles, and contains more enteric progenitors that are abnormally distributed. These phenotypes are similar to those of the Shh mutant, supporting that Gas1 mediates most of the Shh activity in the GI tract. Because Gas1 has been shown to inhibit Ret signaling elicited by Glial cell line-derived neurotrophic factor (Gdnf), we explored whether Gas1 mutant enteric neurons displayed any alteration of Ret signaling levels. Indeed, isolated mutant enteric progenitors not only showed increased levels of phospho-Ret and its downstream effectors, phospho-Akt and phospho-Erk, but also displayed altered responses to Gdnf and Shh. We therefore conclude that phenotypes observed in the Gas1 mutant are due to a combination of reduced Hh signaling and increased Ret signaling.

Transplantation of enteric cells into the aganglionic rodent small intestines

BACKGROUND

Enteric cells, a mixture of cells isolated from the longitudinal and circular muscle of the gut, may contain neural crest stem cells (NCSCs) and therefore may be a potential source to regenerate the enteric nervous system.

MATERIALS AND METHODS

Benzylalkonium chloride (BAC) was employed to ablate the myenteric and submucosal plexi of the rodent jejunum. Enteric cells were then injected into this BAC-treated segment of the jejunum either with or without basic fibroblast growth factor (bFGF) mixed in collagen.

RESULTS

Expression of peripherin, S100, and synaptophysin were found in all of the cell injection sites. Peripherin and S100 expression appeared in close proximity in ganglion-like structures when bFGF was injected simultaneously with enteric cells. Synapses that were formed in the presence of bFGF were elongated compared with those formed in the absence of exogenously delivered bFGF. A small percentage of enteric cells expressed peripherin in the injection site after transplantation.

CONCLUSIONS

Enteric cells transplanted with collagen and bFGF in an aganglionic segment of jejunum regenerated ganglion-like structures and may hold potential as a cellular therapeutic for various motility disorders of the gastrointestinal tract.

Abnormal development of the enteric nervous system in rat embryos and fetuses with congenital diaphragmatic hernia

BACKGROUND/AIM

Esophageal dilatation, gastroesophageal reflux, and intestinal obstruction have been demonstrated in CDH survivors. Abnormal esophageal and intestinal innervations were recently found in rats and babies with this disease. Our aim was to further characterize these malformations in embryos and fetal rats exposed to nitrofen.

METHODS

Pregnant rats received either 100 mg nitrofen or vehicle on E9.5. Fetuses were recovered at E15, E18, and E21. Sections of esophagus and small bowel were histochemically stained with acetylcholinesterase (AChE) and immunostained for PGP9.5. PGP9.5 gen protein were measured on E21 and PGP9.5 mRNA on E15, E18 and E21. Comparisons between groups were made with non-parametrics tests.

RESULTS

Histochemistry and immunohistochemistry showed deficient innervation in all anatomical areas studied at E15, E18, and E21, and WB confirmed this decrease in E21 fetuses. PGP9.5 messenger was decreased in nitrofen-exposed animals on E18 (esophagus) or E15 (small bowel), and increased on E21 in the esophagus and E18 in small bowel.

CONCLUSIONS

Development of the enteric nervous system of the esophagus, stomach, and small bowel is deficient in rat embryos and fetuses exposed to nitrofen. These anomalies could account in part for the long-term gastrointestinal morbidity observed in CDH survivors.

Transplantation of enteric cells expressing p75 in the rodent stomach

BACKGROUND

Neural crest stem cells may hold potential as a cellular therapeutic to repopulate the enteric nervous system. The expression of the low-affinity nerve growth factor receptor, p75, may enrich enteric cells isolated from the neonatal rodent intestinal tract for neural crest stem cells. While these cells have shown tremendous promise in vitro, it remains to be determined whether they will survive and differentiate after in vivo transplantation.

MATERIALS AND METHODS

Cells isolated from the neonatal rodent intestinal muscularis were sorted according to their degree of p75 expression. The parent, p75-high, and p75-low expressing populations were injected into the rodent stomach for 7 d in vivo.

RESULTS

Cells that expressed high levels of p75 also expressed high levels of nestin. Evaluation of the parent, p75-high, and p75-low populations of cells showed 420-, 130-, and 20-fold growth, respectively, after 11 d of culture. Transplantation of these populations of cells into syngeneic rodent stomachs showed cell survival in the injection site after 7 d. Cells expressing either the neuronal marker, peripherin, or the glial marker, S100, were present in and around the injection site when the parent and the p75-high populations were transplanted.

CONCLUSIONS

Enteric cells survive transplantation into the rodent stomach and induce the expression of differentiation markers in and around the injection site. Based on these results, enteric cells may hold potential as a cellular therapeutic in a variety of gastrointestinal disorders.

Molecular development of the extrinsic sensory innervation of the gastrointestinal tract

The extrinsic sensory innervation of the gastrointestinal tract is the conduit through which the gut and the central nervous system communicate. The hindbrain receives information directly from the bowel via the vagus nerve, while information from spinal afferents arrives in the central nervous system through the dorsal root ganglia. This review focuses on the molecular development of these vagal and spinal innervations, with an emphasis on mechanisms that involve axon guidance. During development, axons from both the nodose ganglia and dorsal root ganglia grow into the gut, innervate their appropriate enteric targets and avoid inappropriate cells in the gut wall. These developmental outcomes suggest that both attractive and repellent molecules are important in establishing the normal pattern of the extrinsic sensory innervation. In the fetal mouse gut, the guidance of vagal sensory axons is mediated by axon guidance molecules, such as netrin and the netrin receptor, deleted in colorectal cancer (DCC), as well as extracellular matrix molecules, such as laminin-111. Dorsal root ganglion neurons are known to express, and their axons to respond to, axon guidance molecules. The question of whether or not these molecules are involved in guiding spinal afferents to the bowel, however, has not yet been examined. It is anticipated that a better understanding of how vagal and spinal afferents innervate the fetal gut and reach specific enteric locations will provide deeper insights into the underlying mechanisms of normal and abnormal sensation from the gastrointestinal tract.

Age-dependent changes in the gut environment restrict the invasion of the hindgut by enteric neural progenitors

The enteric nervous system (ENS) develops from neural crest cells (NCCs) that enter the foregut and hindgut to become enteric neural-crest-derived cells (ENCCs). When these cells of neural crest origin fail to colonize the terminal hindgut, this aganglionic region becomes non-functional and results in a condition in humans known as Hirschsprung's disease (HSCR). One of the genes associated with HSCR is endothelin receptor type B (Ednrb). To study the development of colonic aganglionosis we have utilized a novel knockout mouse (Ednrb(flex3/flex3)), in which the expression of a null Ednrb allele and YFP is confined to NCCs. We have identified two primary cellular defects related to defective EDNRB signaling. First, ENCC advance in Ednrb(flex3/flex3) embryos is delayed shortly after NCCs enter the gut. Apart from this early delay, Ednrb(flex3/flex3) ENCCs advance normally until reaching the proximal colon. Second, as Ednrb(flex3/flex3) ENCCs reach the colon at E14.5, they display migratory defects, including altered trajectories and reduced speed, that are not dependent on proliferation or differentiation. We constructed grafts to test the ability of donor ENCCs to invade a recipient piece of aganglionic colon. Our results indicate that the age of the recipient, and not the age or genotype of donor ENCCs, determines whether the colon is invaded. We identify changes in laminin expression that are associated with the failure of ENCCs to invade recipient tissue. Together, our data suggest that a defect in pre-enteric Ednrb(flex3/flex3) NCCs results in delayed colonic arrival, which, due to environment changes in the colon, is sufficient to cause aganglionosis.

Endoderm-derived Sonic hedgehog and mesoderm Hand2 expression are required for enteric nervous system development in zebrafish

The zebrafish enteric nervous system (ENS), like those of all other vertebrate species, is principally derived from the vagal neural crest cells (NCC). The developmental controls that govern the migration, proliferation and patterning of the ENS precursors are not well understood. We have investigated the roles of endoderm and Sonic hedgehog (SHH) in the development of the ENS. We show that endoderm is required for the migration of ENS NCC from the vagal region to the anterior end of the intestine. We show that the expression of shh and its receptor ptc-1 correlate with the development of the ENS and demonstrate that hedgehog (HH) signaling is required in two phases, a pre-enteric and an enteric phase, for normal ENS development. We show that HH signaling regulates the proliferation of vagal NCC and ENS precursors in vivo. We also show the zebrafish hand2 is required for the normal development of the intestinal smooth muscle and the ENS. Furthermore we show that endoderm and HH signaling, but not hand2, regulate gdnf expression in the intestine, highlighting a central role of endoderm and SHH in patterning the intestine and the ENS.

Topography and morphometry of intestinal mast cells in children with Hirschsprung's disease

Mast cells (MC) are source of many biological active compounds like cytokines, arachidonic acid derivates, proteoglicanes, prostaglandins, proteases, free oxygen radials, NGF, PAF and many more. The role of MC in pathogenesis of Hirschsprung's disease (HD) is not clear. Substances produced by MC may exert an important effect on embryology, growth, differentiation and regeneration of intestinal nervous system. Additionally, MC products modulate inflammation processes thus influencing on the clinical course of HD. Present study was established to evaluate the morphologic MC examination as a support of making diagnosis in HD. The MC topography and morphometry were evaluated in specimens collected from aganglionic colon of patients with diagnosed HD. The results were compared with corresponding data from normally innervated colon of patients suffering from constipation, and normal colon of children not presenting defecation problems. MC were visualized using indirect immunohistochemical method LSAB with mouse antibody against human tryptase. The MC visualized in submucosa and muscular layer in Hirschsprung's disease were significantly larger in comparison with control group (p<0.05). Also the number of MC/mm2 in mucosa and lamina propria in HD was significantly elevated (p<0.05). However, the MC density in submucosa was also higher but it was not high statistically significant. In muscular layer and in serosa density of MC/mm2 was not statistically significant. In the intestinal wall MC in aganglionic segment in Hirschsprung's disease are significantly activated comparing with normally innervated colon segments taken from the patients from other groups. This may confirm the role of MC both in pathogenesis of HD and in the reparation processes of bowel nervous system.

[Hypoganglionosis as a cause of chronic constipation]

Hypoganglionosis comprises 3-5% of gastrointestinal innervation defects which are connected to therapy-resistant chronic constipation in children and adults. Similar to Hirschsprung's disease, hypoganglionosis may be complicated by megacolon formation and must be considered in the differential diagnosis. Three main subtypes may be distinguished: congenital hypoplastic hypoganglionosis occurs predominantly in Hirschsprung's disease proximal to the aganglionic segment and consists of small paucicellular ganglia with increased interganglionic distances. Oligoneuronal dysganglionic hypoganglionosis manifests in childhood. Initially, myenteric ganglia are of normal size and have normal interganglionic spacing and normal neuronal content. However, nerve cells are hypoplastic and ganglia undergo progressive nerve cell loss. This type of hypoganglionosis may progress into atrophic hypoganglionosis, which shows a morphology similar to hypoplastic hypoganglionosis. All subtypes of hypoganglionosis result in decreased acetylcholinesterase activity in the nerve fiber network of the muscularis propria. The pathogenesis of hypoganglionosis is still poorly understood. In Hirschsprung associated hypoganglionosis, mutations in the RET and GDNF-genes have been found. Despite a heterozygote GDNF+/- animal model for hypoganglionosis, no GDNF mutations have so far been demonstrated in human Hirschsprung independent, isolated hypoganglionosis.

New horizons in the pathogenesis of gastrointestinal neuromuscular disease

The term "gastrointestinal neuromuscular disease" can be interpreted variably and encompasses a spectrum of paediatric and adult conditions including achalasia, pseudoobstruction, idiopathic constipation, irritable bowel syndrome, megacolon, and Hirschsprung disease. Although progress has been made in the understanding of the pathophysiology of some conditions, the aetiopathogenesis has been elucidated only in the rare minority. This review critically considers the available evidence for possible pathogenic mechanisms in these disorders.

Enteric nervous system development and Hirschsprung's disease: advances in genetic and stem cell studies

The enteric nervous system (ENS) has been explored by developmental neurobiologists and medical researchers for decades. Whereas developmental biologists have been unravelling the molecular mechanisms underlying the migration, proliferation and differentiation of the neural crest derivatives that give rise to the ENS, human geneticists have been uncovering the genetic basis for diseases of the ENS, notably Hirschsprung's disease. Here we discuss the exciting recent advances, including novel transgenic and genetic tools, a broadening range of model organisms, and the pursuit of ENS stem cells as a therapeutic tool, that are bringing these fields closer together.

Symptomatology, pathophysiology, diagnostic work-up, and treatment of Hirschsprung disease in infancy and childhood

In the majority of infants and children with constipation, no obvious cause can be identified. A rare cause of constipation is Hirschsprung disease (HD). HD is characterized by the absence of ganglion cells from the anorectum for a variable length up to the duodenum. The extent of the aganglionic segment varies, but in most patients the lesion does not extend beyond the rectum and sigmoid colon. This review focuses on the passage of meconium, the recognition of HD, and new insights in its pathophysiology and genetics. The authors also provide a summary of the diagnostic evaluation and treatment of HD in infancy and childhood.

Genetic screen for mutations affecting development and function of the enteric nervous system

An intact enteric nervous system is required for normal gastrointestinal tract function. Several human conditions result from decreased innervation by enteric neurons; however, the genetic basis of enteric nervous system development and function is incompletely understood. In an effort to increase our understanding of the mechanisms underlying enteric nervous system development, we screened mutagenized zebrafish for changes in the number or distribution of enteric neurons. We also established a motility assay and rescreened mutants to learn whether enteric neuron number is correlated with gastrointestinal motility in zebrafish. We describe mutations isolated in our screen that affect enteric neurons specifically, as well as mutations that affect other neural crest derivatives or have pleiotropic effects. We show a correlation between the severity of enteric neuron loss and gastrointestinal motility defects. This screen provides biological tools that serve as the basis for future mechanistic studies.

Transplanting the enteric nervous system: a step closer to treatment for aganglionosis

Autologous transplantation can be used to treat Hirschsprung's disease by implantation and proliferation of the crest‐derived stem cells in vitro

Enzymhistochemie des klassischen und des ultrakurzen Morbus Hirschsprung

Hirschsprung's disease is the most important type of gastrointestinal dysmotility in neonatal pathology. Aberrant craniocaudal migration of neural crest stem cells results in an intestinal aganglionic segment of variable length. In 'classical' Hirschsprung's disease (60-75% of cases), the aganglionic segment spans the rectum and sigma. Ultrashort Hirschsprung's disease (5-10%) is restricted to the most distal 3-4 cm or immediate rectoanal transition only. In the normal enteric nervous system, myenteric ganglia modulate the parasympathetic innervation of the sacral roots S2-S4. The absence of myenteric ganglia in Hirschsprung's disease results in massively increased parasympathetic activity with abundant acetylcholine release and pseudo-obstruction in the aganglionic segment. This can be demonstrated in an enzyme histochemical reaction for acetylcholinesterase on frozen sections, which is sufficient to diagnose the classical disease in rectal mucosal biopsies. In ultrashort Hirschsprung's disease, increased acetylcholinesterase activity is demonstrable only in nerve fibres of the muscularis mucosae and submucosa, but not the lamina propria mucosae. Submucosal and myenteric ganglia are physiologically scarce in the most distal rectum; absence of ganglia in a biopsy of the rectoanal transition must not be (wrongly) interpreted as ultrashort Hirschsprung's disease. Therefore, a diagnosis of ultrashort Hirschsprung's disease can be made exclusively using an enzyme histochemical reaction for acetylcholinesterase.

In vivo analysis reveals a critical role for neuropilin-1 in cranial neural crest cell migration in chick

The neural crest provides an excellent model system to study invasive cell migration, however it is still unclear how molecular mechanisms direct cells to precise targets in a programmed manner. We investigate the role of a potential guidance factor, neuropilin-1, and use functional knockdown assays, tissue transplantation and in vivo confocal time-lapse imaging to analyze changes in chick cranial neural crest cell migratory patterns. When neuropilin-1 function is knocked down in ovo, neural crest cells fail to fully invade the branchial arches, especially the 2nd branchial arch. Time-lapse imaging shows that neuropilin-1 siRNA transfected neural crest cells stop and collapse filopodia at the 2nd branchial arch entrances, but do not die. This phenotype is cell autonomous. To test the influence of population pressure and local environmental cues in driving neural crest cells to the branchial arches, we isochronically transplanted small subpopulations of DiI-labeled neural crest cells into host embryos ablated of neighboring, premigratory neural crest cells. Time-lapse confocal analysis reveals that the transplanted cells migrate in narrow, directed streams. Interestingly, with the reduction of neuropilin-1 function, neural crest cells still form segmental migratory streams, suggesting that initial neural crest cell migration and invasion of the branchial arches are separable processes.

The Hlx homeobox transcription factor is required early in enteric nervous system development

Background

Development of the enteric nervous system (ENS) requires interactions between migrating neural crest cells and the nascent gastrointestinal tract that are dependent upon genes expressed by both cell compartments. Hlx, a homeobox transcription factor gene that is expressed in mouse intestinal and hepatic mesenchyme, is required for normal embryonic growth of intestine and liver, and the Hlx^-/- genotype is embryonic lethal. We hypothesized that Hlx is required for ENS development.

Results

Enteric neurons were identified in Hlx^+/+ and Hlx^-/- mouse embryos by immunostaining of embryo sections for the neural markers PGP9.5 and Phox2b, or by staining for β-galactosidase in whole-mount embryos containing the dopamine β-hydroxylase-nLacZ transgene. In Hlx^+/+ embryos, neural crest cells/enteric neurons have moved from the stomach into the intestine by E10.5. By contrast, neural crest cells/enteric neurons remain largely restricted to the lateral stomach mesenchyme of Hlx^-/- embryos, with only a few scattered neural crest cells/enteric neurons in the intestine between E10.5–16.5.

Conclusion

The Hlx homeobox transcription factor is required for early aspects of ENS development.

From the bench to the 'crib'-side: implications of scientific advances to paediatric neurogastroenterology and motility

Paediatric gastrointestinal motility disorders may present in the neonatal period as the result of a congenital insult that occurred during embryonic development or as a manifestation of an abnormal genetic background. Functional gastrointestinal and motility disorders may also be acquired and present during childhood as the first presentation of a condition that can persist or re-occur throughout adolescence and adulthood. These disorders can have a significant psychological and financial impact on the lives of the affected children and their families. Recently, enteric neuroscience research has advanced the understanding of the pathogenesis and treatment of uncommon congenital or developmental gastrointestinal motility disorders such as Hirschsprung disease and chronic intestinal pseudo-obstruction. In addition, research has contributed to improvements in the understanding of more prevalent functional gastrointestinal disorders in children, such as chronic constipation and functional abdominal pain syndromes. The purpose of this review is to highlight these advances with particular regard to the clinical impact they have in the understanding and management of disorders in the field of paediatric neurogastroenterology and motility.

Netrin/DCC-mediated attraction of vagal sensory axons to the fetal mouse gut

Vagal sensory axons and migrating neural crest-derived precursor cells follow similar pathways to reach the gut. The crest-derived cells express the netrin receptor deleted in colorectal cancer (DCC) and migrate toward netrins expressed by the intestinal mucosa and pancreas; this attraction is required for the formation of submucosal and pancreatic ganglia. We tested the hypothesis that enteric netrins also attract vagal sensory fibers. These axons were located as a function of age in fetal mice by applying the lipophilic tracer 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate (DiI) bilaterally to nodose ganglia. DiI-labeled axons were found in the esophagus and proximal stomach by E12 and, more distally, in the small bowel at E14-E16. Transcripts encoding DCC were expressed in the nodose ganglia of mice from E12 to adulthood but were developmentally regulated. Paraesophageal anterior and posterior vagal trunks were DCC immunoreactive from E12 to E16. Transcripts encoding netrin-1 were expressed in the developing foregut and midgut; netrin-1 immunoreactivity was detected in the outer gut mesenchyme and mucosal epithelium. Neurites from explanted E14 nodose ganglia grew selectively toward cocultured E14 distal foregut explants (P < 0.01). Antibodies to DCC specifically abolished this preferential outgrowth (P < 0.05). Nodose axons also grew selectively toward cocultured netrin-secreting 293-EBNA cells (P < 0.005); antibodies to DCC again blocked this preferential outgrowth (P < 0.05). These data suggest that netrins, which are expressed in the bowel, attract DCC-expressing vagal sensory axons.