Alterations in neurotrophin and neurotrophin-receptor localization in Hirschsprung's disease

The Role of Breast Milk Neurotrophin Levels in Infantile Colic Pathogenesis: A Cross-Sectional Case-Control Study

Objective: Immaturity of the digestive tract and enteric nervous system is a widely accepted theory for infantile colic (IC) etiopathogenesis. The study aimed to show whether neurotrophins that are necessary for normal functioning and development of the gastrointestinal system have a role in the pathogenesis of IC. Materials and Methods: The IC group (n = 75) comprising the mothers of infants with IC and the control group (n = 75) were included to this cross-sectional case-control study. Brain-derived neurotrophic factor (BDNF), glial cell-derived neurotrophic factor (GDNF), ciliary neurotrophic factor (CNTF), and nerve growth factor (NGF) levels of breast milk samples were evaluated by immunosorbent analysis method. Results: The mean age of infants with IC was 7.3 ± 2.8 weeks, while the mean age of the control group was 8.1 ± 2.9 weeks (p = 0.110). No significant difference was found between the breast milk BDNF, GDNF, CNTF, and NGF levels of two groups (p = 0.941, p = 0.510, p = 0.533, p = 0.839, respectively). Conclusions: This is the first report comparing the neurotrophin levels of the breast milk samples taken from the mothers of infants with and without IC. The study demonstrated that breast milk neurotrophin levels of the mothers did not differ significantly between the infants with and without IC.

L1cam alternative shorter transcripts encoding the extracellular domains were overexpressed in the intestine of L1cam knockdown mice

Hirschsprung disease (HSCR) is a congenital disorder of functional bowel obstruction due to the absence of enteric ganglia in distal bowel. Different L1cam variants were reportedly associated with L1cam syndrome and HSCR, whose phenotypes lacked predictable relevance to their genotypes. Using next-generation sequencing (NGS), we found an L1CAM de novo frameshift mutation in a female with mild hydrocephalus and skip-type HSCR. A nearly identical L1cam variant was introduced into FVB/NJ mice via the CRISPR-EZ method. A silent mutation was created via ssODN to gain an artificial Ncol restriction enzyme site for easier genotyping. Six L1cam protein-coding alternative transcripts were quantitatively measured. Immunofluorescence staining with polyclonal and monoclonal L1cam antibodies was used to characterize L1cam isoform proteins in enteric ganglia. Fifteen mice, seven males and eight females, generated via CRISPR-EZ, were confirmed to carry the L1cam frameshift variant, resulting in a premature stop codon. There was no prominent hydrocephalus nor HSCR-like presentation in these mice, but male infertility was noticed after observation for three generations in a total of 176 mice. Full-length L1cam transcripts were detected at a very low level in the intestinal tissues and almost none in the brain of these mice. Alternative shorter transcripts encoding the extracellular domains were overexpressed in the intestine of L1cam knockdown mice. Immunofluorescence confirmed no fulllength L1cam protein in enteric ganglia. These shorter L1cam isoform proteins might play a role in protecting L1cam knockdown mice from HSCR.

KBG syndrome: Clinical features and molecular findings in seven unrelated Korean families with a review of the literature

BACKGROUND

KBG syndrome is a rare genetic disorder involving macrodontia of the upper central incisors, craniofacial, skeletal, and neurologic symptoms, caused either by a heterozygous variant in ANKRD11 or deletion of 16q24.3, including ANKRD11. Diagnostic criteria were proposed in 2007 based on 50 cases, but KBG syndrome remains underdiagnosed.

METHODS

Whole exome sequencing (WES) and array comparative genomic hybridization (array CGH) were conducted for genetic analysis and patient phenotypes were characterized based on medical records.

RESULTS

Eight patients from seven unrelated families were confirmed with KBG syndrome. All patients (8/8, 100%) had some degree of craniofacial dysmorphism and developmental delay or intellectual disabilities. Triangular face, synophrys, anteverted nostril, prominent ears, long philtrum, and tented upper lip, which are typical facial dysmorphism findings in patients with KBG syndrome, were uniformly identified in the eight patients participating in this study, with co-occurrence rates of 4/8 (50%), 4/8 (50%), 4/8 (50%), 4/8 (50%), 5/8 (62.5%), and 5/8 (62.5%), respectively. Various clinical manifestations not included in the diagnostic criteria were observed. Six patients had point mutations in ANKRD11, one had an exonic deletion of ANKRD11, and one had a 16q24.3 microdeletion. According to the ACMG guidelines, all mutations were classified as pathogenic. The c.2454dup (p.Asn819fs*1) mutation in Pt 4 was reported previously. The remaining variants (c.397 + 1G>A, c.226 + 1G>A, c.2647del (p.Glu883Argfs*94), and c.4093C>T (p.Arg1365Ter)) were novel.

CONCLUSION

The clinical and molecular features of eight patients from seven unrelated Korean families with KBG syndrome described here will assist physicians in understanding this rare genetic condition.

Evidence for the presence and release of BDNF in the neuronal and non-neuronal structures of the internal anal sphincter

BACKGROUND

Data on the neuromodulatory effects of brain-derived neurotrophic factor (BDNF) in the gastrointestinal tract were recently reported, but there are still no data on the presence, distribution, and release of BDNF in the gastrointestinal tract, including the internal anal sphincter (IAS).

METHODS

We examined the presence and distribution of BDNF and its receptor TrkB in the different IAS structures (neuronal and non-neuronal) via immunohistochemical and immunocytochemical analyses. We also monitored the release of BDNF in an IAS muscle bath (consisting of smooth muscle cells [SMCs], myenteric plexus, and submucosal plexus) before and after different agonists, and electrical field stimulation in the absence and presence of neurotoxin tetrodotoxin.

KEY RESULTS

BDNF/TrkB was found to be present in all layers of the IAS, especially the smooth muscle, mucosa, myenteric plexus, and submucosal plexus. Detailed analyses revealed a significant colocalization between BDNF and TrkB in different structures, especially in the smooth muscle, the SMCs, and both plexuses. Data further showed higher levels of BDNF in the cytosol and that of TrkB toward the periphery of the SMCs.

CONCLUSIONS & INFERENCES

These studies showed that BDNF/TrkB was present not only in the enteric nervous system (ENS), but also in the SMCs. For the neuromodulatory effects, BDNF is released locally from the ENS ((myenteric (10.01 ± 0.23 pg/ml) and submucosal plexus (9.05 ± 0.51 pg/ml)) and the SMCs (18.63 ± 1.63 pg/ml). Collectively, these findings have pathophysiological and therapeutic implications regarding the role of BDNF/TrkB in the IAS-associated rectoanal motility disorders.

BDNF augments rat internal anal sphincter smooth muscle tone via RhoA/ROCK signaling and nonadrenergic noncholinergic relaxation via increased NO release

Presently, there are no studies examining the neuromodulatory effects of brain-derived neurotropic factor (BDNF) on the basal internal anal sphincter (IAS) tone and nonadrenergic noncholinergic (NANC) relaxation. To examine this, we determined the neuromuscular effects of BDNF on basal IAS smooth muscle tone and the smooth muscle cells (SMCs) and the effects of NANC nerve stimulation before and after high-affinity receptor tyrosine kinase receptor B (TrkB) antagonist K252a. We also investigated the mechanisms underlying BDNF-augmented increase in the IAS tone and NANC relaxation. We found that BDNF-increased IAS tone and SMC contractility were TTX resistant and attenuated by K252a. TrkB-specific agonist 7,8-dihydroxyflavone, similar to BDNF, also produced a concentration-dependent increase in the basal tone, whereas TrkB inhibitors K252a and ANA-12 produced a decrease in the tone. In addition, BDNF produced leftward shifts in the concentration-response curves with U46619 and ANG II (but not with bethanechol and K⁺ depolarization), and these shifts were reversed by K252a. Effects of Y27632 and Western blot data indicated that the BDNF-induced increase in IAS tone was mediated via RhoA/ROCK. BDNF-augmented NANC relaxation by electrical field stimulation was found to be mediated via the nitric oxide (NO)/soluble guanylate cyclase (sGC) pathway rather than via increased sensitivity to NO. In conclusion, the net effect of BDNF was that it caused an increase in the basal IAS tone via RhoA/ROCK signaling. BDNF also augmented NANC relaxation via NO/sGC. These findings may have relevance to the role of BDNF in the pathophysiology and therapeutic targeting of the IAS-associated rectoanal motility disorders.NEW & NOTEWORTHY These studies for the first time to our knowledge demonstrate that increased levels of brain-derived neurotrophic factor (BDNF; conceivably released from smooth muscle cells and/or the enteric neurons) has two major effects. First, BDNF augments the internal anal sphincter (IAS) tone via tyrosine kinase receptor B/thromboxane A2-receptor, angiotensin II receptor type 1/RhoA/ROCK signaling; and second, it increases nonadrenergic noncholinergic relaxation via nitric oxide/soluble guanylate cyclase. These studies may have relevance in therapeutic targeting in the anorectal motility disorders associated with the IAS.

Distinctive genetic variation of long-segment Hirschsprung's disease in Taiwan

BACKGROUND

Hirschsprung's disease (HSCR) is a congenital disorder with the absence of myenteric and submucosal ganglion cells within distal gut. Due to multigenic inheritance and interactions, we employed next-generation sequencing (NGS) to investigate genetic backgrounds of long-segment HSCR (L-HSCR) in Taiwan.

METHODS

Genomic DNA extracted from peripheral blood of L-HSCR patients was subjected to capture-based NGS, based on a 31-gene panel. The variants with allele frequency <0.05 and predicted by computational methods as deleterious were further validated by Sanger sequencing in patients and their family as well to tell de novo from inherited variants.

RESULTS

Between 2015/04 and 2018/05, this study enrolled 23 L-HSCR patients, including 15 (65.2%) sporadic cases and 8 (34.8%) familial patients in 4 different families. Six sporadic and seven familial cases showed possible harmful variants across eight different genes, accounting for an overall detection rate of 56.5%. These variants mainly resided in SEMA3C, followed by RET, NRG1, and NTRK1. Three sporadic and 2 familial cases exhibited strong pathogenic variants as a deletional frameshift or stop codon in RET, L1CAM or NRG1. In a HSCR family, the father passed on a pathogenic RET frameshift to two daughters; however, only one developed HSCR.

CONCLUSION

Using NGS, we disclosed deleterious mutations such as a frameshift or stop codon in either familial or sporadic patients. Our cases with isolated L-HSCR or even total colonic aganglionosis appeared to exhibit complex patterns of inheritance and incomplete penetrance even in families with the same genetic variants, reflecting the possible effects of environmental factors and genetic modifiers.

Congenital intestinal stenosis and Hirschsprung's disease: two extremely rare pathologies in a newborn puppy

Background

Hirschsprung’s disease (HSCR) is a common congenital malformation of the enteric nervous system (ENS). During fetal development, ganglion cells of the ENS are derived from neural crest cells that migrate to the bowel. These cells reside principally in two ganglionated plexus: 1) The myenteric plexus, extending from the esophagus to the anus, and 2) submucous plexus, extending from the duodenum to the anus. In large animal species, there is a third plexus called Henle’s or Schabadasch’s plexus.

ENS ganglion cells play a key role in normal gastrointestinal motility, respond to sensory stimuli and regulate blood flow. Both plexus show a high degree of independence from the central nervous system. Alterations in the embryonic development of the ENS can induce multiple pathologies in animal models and humans.

Case presentation

The present case was a female the fifth born in a litter of 5 puppies. At about 2–3 weeks of age, she suffered from abdominal distension, pain, and constipation. At approximately 8–10 weeks of age, the puppy started to vomit abundantly, and the regurgitated food appeared undigested. Progressive abdominal distention was observed, with quite visible peristaltic movements and more frequent vomiting episodes. The abdominal radiographs, based on AP and side projections, revealed an enlargement of the abdominal diameter and an increased width in the epigastric region. At 12 weeks of age, exploratory surgery revealed a stenotic segment in the jejunum, followed by a small transition zone and then a significantly reduced diameter. Immunohistochemical examinations were performed using antibodies against calretinin, S-100 protein, CD56, neuron specific enolase (NSE) and synaptophysin, which are the biological markers for diagnosing HSCR.

Conclusion

A reduced number of ganglion cells (1–3 cells per ganglion) were found. There was no specific staining pattern for many of these; while for others, the pattern was compatible with HSCR. Surgical intervention to remove the stenotic section prolonged the life of the puppy for 13 years. Extremely rare pathologies such as that discussed herein should be studied to understand the pathophysiology and be able to diagnose small species in veterinary medicine in a timely fashion. To our knowledge, this is the first report of congenital intestinal stenosis and Hirschprung’s disease in a newborn puppy.

Electronic supplementary material

The online version of this article (10.1186/s12917-019-1806-z) contains supplementary material, which is available to authorized users.

Ablation of intact hypothalamic and/or hindbrain TrkB signaling leads to perturbations in energy balance

OBJECTIVE

Brain-derived neurotrophic factor (BDNF) and its receptor, tropomyosin receptor kinase B (TrkB), play a paramount role in the central regulation of energy balance. Despite the substantial body of genetic evidence implicating BDNF- or TrkB-deficiency in human obesity, the critical brain region(s) contributing to the endogenous role of BDNF/TrkB signaling in metabolic control remain unknown.

METHODS

We assessed the importance of intact hypothalamic or hindbrain TrkB signaling in central regulation of energy balance by generating Nkx2.1-Ntrk2-/- and Phox2b-Ntrk2+/- mice, respectively, and comparing metabolic parameters (body weight, adiposity, food intake, energy expenditure and glucose homeostasis) under high-fat diet or chow fed conditions.

RESULTS

Our data show that when fed a high-fat diet, male and female Nkx2.1-Ntrk2-/- mice have significantly increased body weight and adiposity that is likely driven by reduced locomotor activity and core body temperature. When maintained on a chow diet, female Nkx2.1-Ntrk2-/- mice exhibit an increased body weight and adiposity phenotype more robust than in males, which is accompanied by hyperphagia that precedes the onset of a body weight difference. In addition, under both diet conditions, Nkx2.1-Ntrk2-/- mice show increased blood glucose, serum insulin and leptin levels. Mice with complete hindbrain TrkB-deficiency (Phox2b-Ntrk2-/-) are perinatal lethal, potentially indicating a vital role for TrkB in visceral motor neurons that control cardiovascular, respiratory, and digestive functions during development. Phox2b-Ntrk2+/- heterozygous mice are similar in body weight, adiposity and glucose homeostasis parameters compared to wild type littermate controls when maintained on a high-fat or chow diet. Interestingly, despite the absence of a body weight difference, Phox2b-Ntrk2+/- heterozygous mice exhibit pronounced hyperphagia.

CONCLUSION

Taken together, our findings suggest that the hypothalamus is a key brain region involved in endogenous BDNF/TrkB signaling and central metabolic control and that endogenous hindbrain TrkB likely plays a role in modulating food intake and survival of mice. Our findings also show that female mice lacking TrkB in the hypothalamus have a more robust metabolic phenotype.

Stimulation of synthesis and release of brain-derived neurotropic factor from intestinal smooth muscle cells by substance P and pituitary adenylate cyclase-activating peptide

BACKGROUND

Brain-derived neurotrophic factor (BDNF) is a neurotrophin present in the intestine where it participates in survival and growth of enteric neurons, augmentation of enteric circuits, and stimulation of intestinal peristalsis and propulsion. Previous studies largely focused on the role of neural and mucosal BDNF. The expression and release of BDNF from intestinal smooth muscle and the interaction with enteric neuropeptides has not been studied in gut.

METHODS

The expression and secretion of BDNF from smooth muscle cultured from the rabbit intestinal longitudinal muscle layer in response to substance P (SP) and pituitary adenylate cyclase-activating peptide (PACAP) was measured by western blot and enzyme-linked immunosorbent assay. BDNF mRNA was measured by reverse-transcription polymerase chain reaction.

KEY RESULTS

The expression of BNDF protein and mRNA was greater in smooth muscle cells (SMCs) from the longitudinal muscle than from circular muscle layer. PACAP and SP increased the expression of BDNF protein and mRNA in cultured longitudinal SMCs. PACAP and SP also stimulated the secretion of BDNF from cultured longitudinal SMCs. Chelation of intracellular calcium with BAPTA (1,2-bis-(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid) prevented SP-induced increase in BDNF mRNA and protein expression and SP-induced secretion of BDNF.

CONCLUSIONS & INFERENCES

Neuropeptides known to be present in enteric neurons innervating the longitudinal layer increase the expression of BDNF mRNA and protein in SMCs and stimulate the release of BDNF. Considering the ability of BDNF to enhance smooth muscle contraction, this autocrine loop may partially explain the characteristic hypercontractility of longitudinal muscle in inflammatory bowel disease.

Brain-derived neurotrophic factor enhances cholinergic contraction of longitudinal muscle of rabbit intestine via activation of phospholipase C

Brain-derived neurotrophic factor (BDNF) belongs to the neurotrophin family of proteins best known for its role in neuronal survival, differentiation, migration, and synaptic plasticity in central and peripheral neurons. BDNF is also widely expressed in nonneuronal tissues including the gastrointestinal tract. The role of BDNF in intestinal smooth muscle contractility is not well defined. The aim of this study was to identify the role of BDNF in carbachol (CCh)- and substance P (SP)-induced contraction of intestinal longitudinal smooth muscle. BDNF, selective tropomyosin-related kinase B (TrkB) receptor agonists, and pharmacological inhibitors of signaling pathways were examined for their effects on contraction of rabbit intestinal longitudinal muscle strips induced by CCh and SP. BDNF activation of intracellular signaling pathways was examined by Western blot in homogenates of muscle strips and isolated muscle cells. One-hour preincubation with BDNF enhanced intestinal muscle contraction induced by CCh but not by SP. The selective synthetic TrkB agonists LM 22A4 and 7,8-dihydroxyflavone produced similar effects to BDNF. The Trk antagonist K-252a, a TrkB antibody but not p75NTR antibody, blocked the effect of BDNF. The enhancement of CCh-induced contraction by BDNF was blocked by the phospholipase C (PLC) antagonist U73122, but not by ERK1/2 or Akt antagonists. Direct measurement in muscle strips and isolated muscle cells showed that BDNF caused phosphorylation of TrkB receptors and PLC-γ, but not ERK1/2 or Akt. We conclude that exogenous BDNF augments the CCh-induced contraction of longitudinal muscle from rabbit intestine by activating TrkB receptors and subsequent PLC activation.

The developmental etiology and pathogenesis of Hirschsprung disease

The enteric nervous system is the part of the autonomic nervous system that directly controls the gastrointestinal tract. Derived from a multipotent, migratory cell population called the neural crest, a complete enteric nervous system is necessary for proper gut function. Disorders that arise as a consequence of defective neural crest cell development are termed neurocristopathies. One such disorder is Hirschsprung disease (HSCR), also known as congenital megacolon or intestinal aganglionosis. HSCR occurs in 1/5000 live births and typically presents with the inability to pass meconium, along with abdominal distension and discomfort that usually requires surgical resection of the aganglionic bowel. This disorder is characterized by a congenital absence of neurons in a portion of the intestinal tract, usually the distal colon, because of a disruption of normal neural crest cell migration, proliferation, differentiation, survival, and/or apoptosis. The inheritance of HSCR disease is complex, often non-Mendelian, and characterized by variable penetrance. Extensive research has identified a number of key genes that regulate neural crest cell development in the pathogenesis of HSCR including RET, GDNF, GFRα1, NRTN, EDNRB, ET3, ZFHX1B, PHOX2b, SOX10, and SHH. However, mutations in these genes account for only ∼50% of the known cases of HSCR. Thus, other genetic mutations and combinations of genetic mutations and modifiers likely contribute to the etiology and pathogenesis of HSCR. The aims of this review are to summarize the HSCR phenotype, diagnosis, and treatment options; to discuss the major genetic causes and the mechanisms by which they disrupt normal enteric neural crest cell development; and to explore new pathways that may contribute to HSCR pathogenesis.

Transitional zone pull through: surgical pathology considerations

Incomplete resection of the transitional zone (TZ) between histologically normal and aganglionic bowel in Hirschsprung disease is a putative cause of postoperative dysmotility. A review of literature indicates that diverse histopathological indexes have been used to define the TZ, and validated and reproducible diagnostic criteria have not been established. As a consequence, the proximal margin of the TZ is difficult to delimit, and the length of the TZ in a given patient depends on the diagnostic criteria used. Seromuscular biopsies are inadequate to exclude TZ, as diagnostic indexes may involve only a portion of the bowel circumference or the submucosa. Most published investigations of postoperative outcome after a TZ pull through (TZPT) conclude that the latter can cause persistent obstructive symptoms, which necessitate reoperation. However, the results of these studies are difficult to translate into clinical practice because most lack appropriate controls, and the overwhelming majority provide inadequate histopathological descriptions for reference at the time of intraoperative frozen section analysis. At present, a conservative approach based on frozen section examination of the entire proximal margin of the resection to exclude obvious subcircumferential aganglionosis (contiguous gap between ganglia of more than one-eighth of the circumference), hypoganglionosis (continuous string of myenteric ganglia comprised of 1 or 2 ganglion cells without surrounding neuropil), or hypertrophic submucosal nerves (>2 nerves with widths ≥40 μm per high-power field) seems prudent. Well-controlled studies to correlate proximal margin histology, especially subtle anatomic or immunohistochemical changes, with postoperative outcome are needed.

Increased incidence of Hirschsprung's disease in patients with hypoplastic left heart syndrome--a common neural crest-derived etiology?

BACKGROUND

The enteric ganglions and the outflow tract of the heart originate from the neural crest. Impaired migration or differentiation of the neural crest cells causes Hirschsprung's disease (HD) and results in the development of cardiac outflow tract malformations. We hypothesize that the incidence of HD and bowel disorders associated with HD are increased in patients with hypoplastic left heart syndrome (HLHS) including left cardiac outflow tract obstruction.

METHODS

All consecutive patients treated for HLHS at our institution during 1969 to 2005 were retrospectively reviewed. The number of patients with histologically confirmed HD or clinical findings characteristic of HD such as constipation and delayed meconium were recorded from the patient records.

RESULTS

A total of 113 patients (65 males) were identified. At the time of survey, 57 patients (51%) were alive. Overall, there were 26 (23%) patients with constipation, and 9/23 (39%) had delayed passage of meconium after 48 hours. Despite frequent bowel disorders only 4 (3.5%) patients had undergone histologic examination of the rectum. Hirschsprung's disease was detected in 3 patients (95% confidence interval, 0.62-8.77). The expected number of HD cases in the study population was 0.026 giving 117-fold significant increase in the incidence of HD among patients with HLHS when compared to general Finnish population.

CONCLUSIONS

The incidence of HD is increased in patients with HLHS. These results point to a common neural crest-derived embryologic origin of HD and HLHS and warrant further studies.

A novel point variant in NTRK3, R645C, suggests a role of this gene in the pathogenesis of Hirschsprung disease

Hirschsprung disease (HSCR) is a developmental disorder characterized by the absence of ganglion cells in the myenteric and submucosal plexuses due to a defect in the migration process of neural crest neuroblasts. Manifestation of the disease has been linked to the dysfunction of two principal signalling pathways involved in the enteric nervous system (ENS) formation: the RET-GDNF and the EDN3-EDNRB receptor systems. However, the NTF3/NTRK3 signalling pathway plays an essential role in the development of the ENS suggesting a potential role for those genes in the pathogenesis of HSCR. We have sought to evaluate the candidature of the NTRK3 gene, which encodes the TrkC receptor, as a susceptibility gene for Hirschsprung disease. Using dHPLC technology we have screened the NTRK3 coding region in 143 Spanish HSCR patients. A total of four previously described polymorphisms and 12 novel sequence variants were detected. Of note, the novel R645C mutation was detected in 2 affected siblings of a HSCR family also carrying a RET splicing mutation. Using bioinformatics tools we observed that the presence of an additional cysteine residue might implicate structural alterations in the mutated protein. We propose haploinsufficiency as the most probable mechanism for the NTRK3 R645C mutation. NTRK3 and RET mutations in this family only appear together in the HSCR patients, suggesting that they per se are necessary but not sufficient to produce the phenotype. In addition, it is quite probable that the contribution of other still unidentified modifier genes, may be responsible for the different phenotypes (length of aganglionosis) in the two affected members.

NTF-3, a gene involved in the enteric nervous system development, as a candidate gene for Hirschsprung disease

Hirschsprung disease (HSCR) is a congenital disorder caused by a failure of neural crest cells to migrate, proliferate, and/or differentiate during the enteric nervous system (ENS) development. The requirement of the NTF-3/TrkC signaling for the proper development of the ENS, together with the evidences presented by animal models, led us to investigate the involvement of NTF-3 gene in HSCR. We performed both a mutational screening of NTF-3 and a complete evaluation of 3 polymorphisms as genetic susceptibility factors for HSCR. We identified a novel sequence variant, G76R, present in 2 different patients and absent in controls. We postulate that this variation could generate a lack of mature functional NTF-3 proteins in neural crest cell precursors; thus, altering the NTF-3/TrkC signaling pathway and influencing in the adequate ENS development. Although these results do not provide complete assurance of the involvement of this gene in HSCR, given the polygenic nature of the disease and its etiology, investigation of the genes encoding protein members of the signaling pathways governing the ENS development could provide new key findings in the elucidation of this complex disease.

A genetic approach for investigating vagal sensory roles in regulation of gastrointestinal function and food intake

Sensory innervation of the gastrointestinal (GI) tract by the vagus nerve plays important roles in regulation of GI function and feeding behavior. This innervation is composed of a large number of sensory pathways, each arising from a different population of sensory receptors. Progress in understanding the functions of these pathways has been impeded by their close association with vagal efferent, sympathetic, and enteric systems, which makes it difficult to selectively label or manipulate them. We suggest that a genetic approach may overcome these barriers. To illustrate the potential value of this strategy, as well as to gain insights into its application, investigations of CNS pathways and peripheral tissues involved in energy balance that benefited from the use of gene manipulations are reviewed. Next, our studies examining the feasibility of using mutations of developmental genes for manipulating individual vagal afferent pathways are reviewed. These experiments characterized mechanoreceptor morphology, density and distribution, and feeding patterns in four viable mutant mouse strains. In each strain a single population of vagal mechanoreceptors innervating the muscle wall of the GI tract was altered, and was associated with selective effects on feeding patterns, thus supporting the feasibility of this strategy. However, two limitations of this approach must be addressed for it to achieve its full potential. First, mutation effects in tissues outside the GI tract can contribute to changes in GI function or feeding. Additionally, knockouts of developmental genes are often lethal, preventing analysis of mature innervation and ingestive behavior. To address these issues, we propose to develop conditional gene knockouts restricted to specific GI tract tissues. Two genes of interest are brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (NT-3), which are essential for vagal afferent development. Creating conditional knockouts of these genes requires knowledge of their GI tract expression during development, which little is known about. Preliminary investigation revealed that during development BDNF and NT-3 are each expressed in several GI tract regions, and that their expression patterns overlap in some tissues, but are distinct in others. Importantly, GI tissues that express BDNF or NT-3 are innervated by vagal afferents, and expression of these neurotrophins occurs during the periods of axon invasion and receptor formation, consistent with roles for BDNF or NT-3 in these processes and in receptor survival. These results provide a basis for targeting BDNF or NT-3 knockouts to specific GI tract tissues, and potentially altering vagal afferent innervation only in that tissue (e.g., smooth muscle vs. mucosa). Conditional BDNF or NT-3 knockouts that are successful in selectively altering a vagal GI afferent pathway will be valuable for developing an understanding of that pathway's roles in GI function and food intake.

Brain-derived neurotrophic factor augments peristalsis by augmenting 5-HT and calcitonin gene-related peptide release

BACKGROUND & AIMS

Brain-derived neurotrophic factor (BDNF) acts rapidly to modulate synaptic neurotransmission in the brain. Although present in neurons, glial cells, and mucosal cells of the colon, and in higher concentrations than in brain, the action of BDNF in gut have not been characterized. The aim of this study was to identify the role of BDNF in mediating the peristaltic reflex.

METHODS

BDNF and a specific antiserum were examined for their effects on the peristaltic reflex and release of the sensory mediators serotonin and calcitonin gene-related peptide in rat colon. The peristaltic reflex and release of serotonin and calcitonin gene-related peptide were also examined in genetically modified mice (BDNF(+/-)) with reduced levels of BDNF.

RESULTS

Endogenous brain-derived neurotrophic factor was released into the sensory compartment in a stimulus-dependent manner during the peristaltic reflex induced by mucosal stimulation but not muscle stretch. BDNF stimulated and immunoneutralization of endogenous BDNF reduced ascending contraction and descending relaxation of circular muscle and release of serotonin and calcitonin gene-related peptide during the peristaltic reflex induced by mucosal stimulation but not muscle stretch. The peristaltic reflex and release of serotonin and calcitonin gene-related peptide during the peristaltic reflex induced by mucosal stimulation but not muscle stretch were significantly reduced in BDNF(+/-) mice.

CONCLUSIONS

Endogenous BDNF enhances the peristaltic reflex by augmenting the release of serotonin and calcitonin gene-related peptide that mediate the sensory limb of the reflex induced by mucosal stimulation.

Neurotrophin-3 in the development of the enteric nervous system

To date, the only neurotrophin that has been shown to influence the development of the enteric nervous system (ENS) is neurotrophin-3 (NT-3). NT-3 plays an essential role in the development of both the neural-crest-derived peripheral nervous system and the central nervous system (i.e., Chalazonitis, 1996, Mol. Neurobiol., 12: 39-53; Sieber-Blum, 1999, Neurotrophins and the Neural Crest, CRC Press, Boca Raton). This review integrates data obtained from our laboratory and from our collaboration with other investigators that demonstrate a late-acting role for NT-3 in the development of enteric neurons in vitro and in vivo. Studies of the biological actions of NT-3 on enteric neuronal precursors in vitro demonstrate that NT-3 acts directly on the precursor cells and that it also acts in combination with other neurotrophic factors such as glial cell line-derived neurotrophic factor and a ciliary neurotrophic factor-like molecule, to promote the survival and differentiation of enteric neurons and glia. Importantly, bone morphogenetic protein-2 (BMP-2) and BMP-4, members of the transforming growth factor-beta (TGF-beta) superfamily, regulate the onset of action of NT-3 during fetal gut development. Analyzes performed on mice deficient in the genes encoding NT-3 or its transducing tyrosine kinase receptor, TrkC, and conversely on transgenic mice that overexpress NT-3 substantiate a physiological role for NT-3 in the development and maintenance of a subset of enteric neurons. There is loss of neurons in both the myenteric and submucosal plexuses of mice lacking NT-3/TrkC signaling and selective hyperplasia in the myenteric plexus of mice overexpressing NT-3. Analyzes performed on transgenic mice that overexpress noggin, a specific BMP-4 antagonist, show significant decreases in the density of TrkC-expressing neurons but significant increase in overall neuronal density of both plexuses. Conversely, overexpression of BMP-4 is sufficient to produce, an increase in the proportion of TrkC-expressing neurons in both plexuses. Overall, our data point to a regulatory role of BMP-4 in the responses of subsets of myenteric and submucosal neurons to NT-3. NT-3 is required for the differentiation, maintenance and proper physiological function of late-developing enteric neurons that are important for the control of gut peristalsis.

Enteric nervous system: development and developmental disturbances--part 1

This review, which is presented in two parts, summarizes and synthesizes current views on the genetic, molecular, and cell biological underpinnings of the early embryonic phases of enteric nervous system (ENS) formation and its defects. In the first part, we describe the critical features of two principal abnormalities of ENS development: Hirschsprung's disease (HSCR) and intestinal neuronal dysplasia type B (INDB) in humans, and the similar abnormalities in animals. These represent the extremes of the diagnostic spectrum: HSCR has agreed and unequivocal diagnostic criteria, whereas the diagnosis and even existence of INDB as a clinical entity is highly controversial. The difficulties in diagnosis and treatment of both these conditions are discussed. We then review the genes now known which, when mutated or deleted, may cause defects of ENS development. Many of these genetic abnormalities in animal models give a phenotype similar or identical to HSCR, and were discovered by studies of humans and of mouse mutants with similar defects. The most important of these genes are those coding for molecules in the GDNF intercellular signaling system, and those coding for molecules in the ET-3 signaling system. However, a range of other genes for different signaling systems and for transcription factors also disturb ENS formation when they are deleted or mutated. In addition, a large proportion of HSCR cases have not been ascribed to the currently known genes, suggesting that additional genes for ENS development await discovery.

SOX10 is abnormally expressed in aganglionic bowel of Hirschsprung's disease infants

BACKGROUND

The primary pathology of Hirschsprung's disease (HD) is a congenital absence of ganglion cells in the caudal most gut. The spastic aganglionic bowel is often innervated by a network of hypertrophied nerve fibres. Recently, mutations of SOX10 have been identified in patients with HD but only in those with Waardenburg-Shah syndrome.

AIMS

To understand the molecular basis for the pathogenesis of HD we intended to determine the specific cell lineages in the enteric nervous system which normally express SOX10 but are affected in disease conditions.

METHODS

We studied colon biopsies from 10 non-syndromic HD patients, aged three months to four years, and 10 age matched patients without HD as normal controls. The absence of mutation in the SOX10 gene of HD patients was confirmed by DNA sequencing. Expression and cellular distribution of SOX10 in bowel segments of normal and HD infants were examined by reverse transcription-polymerase chain reaction and in situ hybridisation.

RESULTS

We found that in normal infants and normoganglionic bowel segments of HD patients, SOX10 was expressed in both neurones and glia of the enteric plexuses and in the nerves among the musculature in normal colon. In the aganglionic bowel segments of patients, SOX10 expression was consistently lower and was found to be associated with the hypertrophic nerve trunks in the muscle and extrinsic nerves in the serosa.

CONCLUSION

We conclude that SOX10 is normally required postnatally in the functional maintenance of the entire enteric nervous system, including neurones and glia. In non-syndromic HD patients who do not have the SOX10 mutation, the SOX10 gene expressed in the sacral region may be involved in the pathogenesis of the abnormal nerve trunks through interaction with other factors.

Decreased tyrosine kinase C expression may reflect developmental abnormalities in Hirschsprung's disease and idiopathic slow-transit constipation

BACKGROUND

Some patients with Hirschsprung's disease have refractory constipation following excision of aganglionic bowel, as do patients with idiopathic slow-transit constipation (STC). Gut motility depends on enteric neuronal development in response to expression of trophic factors and their receptors. Recent studies indicate the importance of neurotrophin 3 (NT-3) and its high-affinity receptor tyrosine kinase C (trk C) in enteric neuronal development.

METHODS

Blinded quantitative immunohistochemical analysis of colon from patients with Hirschsprung's disease (aganglionic, hypoganglionic and normoganglionic) (n = 5), STC (n = 6) and appropriate age-matched control tissues (n = 5) was performed for NT-3 and trk C. Sural nerve morphometry and immunostaining were undertaken in three patients with STC who had abnormalities on limb autonomic and sensory testing.

RESULTS

A significantly higher proportion of submucous plexus neurones was trk C immunoreactive in control infant than adult colon (mean(s.e.m.) 73(9) versus 16(3) per cent of the total; P < 0.001), in accord with a role in development. The proportion of submucous plexus trk C-immunoreactive neurones was reduced in colon from patients with Hirschsprung's disease (28(7) per cent of total in normoganglionic Hirschsprung's disease; P < 0.007 versus infant controls) and STC (10(1) per cent of total; P = 0.053 versus adult controls). No abnormalities of STC sural nerves were detected by morphometry or immunostaining.

CONCLUSION

Decreased trk C expression may reflect developmental abnormalities in Hirschsprung's disease and idiopathic STC. Trk C activation by NT-3 or drugs may provide novel treatments. Presented in abstract form to the Pacific Association of Pediatric Surgeons, Las Vegas, Nevada, USA, May 2000

Plasticity in the enteric nervous system

Enteric ganglia can maintain integrated functions, such as the peristaltic reflex, in the absence of input from the central nervous system, which has a modulatory role. Several clinical and experimental observations suggest that homeostatic control of gut function in a changing environment may be achieved through adaptive changes occurring in the enteric ganglia. A distinctive feature of enteric ganglia, which may be crucial during the development of adaptive responses, is the vicinity of the final effector cells, which are an important source of mediators regulating cell growth. The aim of this review is to focus on the possible mechanisms underlying neuronal plasticity in the enteric nervous system and to consider approaches to the study of plasticity in this model. These include investigations of neuronal connectivity during development, adaptive mechanisms that maintain function after suppression of a specific neural input, and the possible occurrence of activity-dependent modifications of synaptic efficacy, which are thought to be important in storage of information in the brain. One of the applied aspects of the study of plasticity in the enteric nervous system is that knowledge of the underlying mechanisms may eventually enable us to develop strategies to correct neuronal alterations described in several diseases.

A neuronal subpopulation in the mammalian enteric nervous system expresses TrkA and TrkC neurotrophin receptor-like proteins

Increasing evidence suggests that, in addition to peripheral sensory and sympathetic neurons, the enteric neurons are also under the control of neurotrophins. Recently, neurotrophin receptors have been detected in the developing and adult mammalian enteric nervous system (ENS). Nevertheless, it remains to be established whether neurotrophin receptors are expressed in all enteric neurons and/or in glial cells and whether expression is a common feature in the enteric nervous system of all mammals or if interspecific differences exist. Rabbit polyclonal antibodies against Trk proteins (regarded as essential constituents of the high-affinity signal-transducing neurotrophin receptors) and p75 protein (considered as a low-affinity pan-neurotrophin receptor) were used to investigate the cell localization of these proteins in the ENS of adult man, horse, cow, sheep, pig, rabbit, and rat. Moreover, the percentage of neurons displaying immunoreactivity (IR) for each neurotrophin receptor protein was determined. TrkA-like IR and TrkC-like IR were observed in a neuronal subpopulation in both the myenteric and submucous plexuses, from esophagus to rectum in humans, and in the jejunum-ileum of the other species. Many neurons, and apparently all glial cells, in the human and rat enteric nervous system also displayed p75 IR. TrkB-like IR was found restricted to the glial cells of all species studied, with the exception of humans, in whom IR was mainly in glial cells and a small percentage of enteric neurons (about 5%). These findings indicate that the ENS of adult mammals express neuronal TrkA and TrkC, glial TrkB, and neuronal-glial p75, this pattern of distribution being similar in all examined species. Thus, influence of specific neurotrophins on their cognate receptors may be considered in the physiology and/or pathology of the adult ENS.