Neurotrophin-3 in the development of the enteric nervous system

A narrative review of the effects of dexamethasone on traumatic brain injury in clinical and animal studies: focusing on inflammation

Traumatic brain injury (TBI) is a type of brain injury resulting from a sudden physical force to the head. TBI can range from mild, such as a concussion, to severe, which might result in long-term complications or even death. The initial impact or primary injury to the brain is followed by neuroinflammation, excitotoxicity, and oxidative stress, which are the hallmarks of the secondary injury phase, that can further damage the brain tissue. Dexamethasone (DXM) has neuroprotective effects. It reduces neuroinflammation, a critical factor in secondary injury-associated neuronal damage. DXM can also suppress the microglia activation and infiltrated macrophages, which are responsible for producing pro-inflammatory cytokines that contribute to neuroinflammation. Considering the outcomes of this research, some of the effects of DXM on TBI include: (1) DXM-loaded hydrogels reduce apoptosis, neuroinflammation, and lesion volume and improves neuronal cell survival and motor performance, (2) DXM treatment elevates the levels of Ndufs2, Gria3, MAOB, and Ndufv2 in the hippocampus following TBI, (3) DXM decreases the quantity of circulating endothelial progenitor cells, (4) DXM reduces the expression of IL1, (5) DXM suppresses the infiltration of RhoA + cells into primary lesions of TBI and (6) DXM treatment led to an increase in fractional anisotropy values and a decrease in apparent diffusion coefficient values, indicating improved white matter integrity. According to the study, the findings show that DXM treatment has neuroprotective effects in TBI. This indicates that DXM is a promising therapeutic approach to treating TBI.

Parallels between the Developing Vascular and Neural Systems: Signaling Pathways and Future Perspectives for Regenerative Medicine

Neurovascular disorders, which involve the vascular and nervous systems, are common. Research on such disorders usually focuses on either vascular or nervous components, without looking at how they interact. Adopting a neurovascular perspective is essential to improve current treatments. Therefore, comparing molecular processes known to be involved in both systems separately can provide insight into promising areas of future research. Since development and regeneration share many mechanisms, comparing signaling molecules involved in both the developing vascular and nervous systems and shedding light to those that they have in common can reveal processes, which have not yet been studied from a regenerative perspective, yet hold great potential. Hence, this review discusses and compares processes involved in the development of the vascular and nervous systems, in order to provide an overview of the molecular mechanisms, which are most promising with regards to treatment for neurovascular disorders. Vascular endothelial growth factor, semaphorins, and ephrins are found to hold the most potential, while fibroblast growth factor, bone morphogenic protein, slits, and sonic hedgehog are shown to participate in both the developing vascular and nervous systems, yet have not been studied at the neurovascular level, therefore being of special interest for future research.

SCFA Treatment Alleviates Pathological Signs of Migraine and Related Intestinal Alterations in a Mouse Model of NTG-Induced Migraine

Background: There is a growing realization that the gut–brain axis signaling is critical for maintaining the health and homeostasis of the Central Nervous System (CNS) and the intestinal environment. The role of Short-Chain Fatty Acids (SCFAs), such as Sodium Propionate (SP) and Sodium Butyrate (SB), has been reported to counteract inflammation activation in the central and Enteric Nervous System (ENS). Methods: In this study, we evaluated the role of the SCFAs in regulating the pathophysiology of migraine and correlated dysregulations in the gut environment in a mouse model of Nitroglycerine (NTG)-induced migraine. Results: We showed that, following behavioral tests evaluating pain and photophobia, the SP and SB treatments attenuated pain attacks provoked by NTG. Moreover, treatments with both SCFAs reduced histological damage in the trigeminal nerve nucleus and decreased the expression of proinflammatory mediators. Ileum evaluation following NTG injection reported that SCFA treatments importantly restored intestinal mucosa alterations, as well as the release of neurotransmitters in the ENS. Conclusions: Taken together, these results provide evidence that SCFAs exert powerful effects, preventing inflammation through the gut–brain axis, suggesting a new insight into the potential application of SCFAs as novel supportive therapies for migraine and correlated intestinal alterations.

Neurotrophin-3 Promotes the Neuronal Differentiation of BMSCs and Improves Cognitive Function in a Rat Model of Alzheimer's Disease

Transplantation of bone marrow-derived mesenchymal stem cells (BMSCs) has the potential to be developed into an effective treatment for neurodegenerative diseases such as Alzheimer's disease (AD). However, the therapeutic effects of BMSCs are limited by their low neural differentiation rate. We transfected BMSCs with neurotrophin-3 (NT-3), a neurotrophic factor that promotes neuronal differentiation, and investigated the effects of NT-3 gene overexpression on the differentiation of BMSCs into neurons in vitro and in vivo. We further studied the possible molecular mechanisms. We found that overexpression of NT-3 promoted the differentiation of BMSCs into neurons in vitro and in vivo and improved cognitive function in rats with experimental AD. By contrast, silencing NT-3 inhibited the differentiation of BMSCs and decreased cognitive function in rats with AD. The Wnt/β-catenin signaling pathway was involved in the mechanism by which NT-3 gene modification influenced the neuronal differentiation of BMSCs in vitro and in vivo. Our findings support the prospect of using NT-3-transduced BMSCs for the development of novel therapies for AD.

Large intestine embryogenesis: Molecular pathways and related disorders (Review)

The large intestine, part of the gastrointestinal tract (GI), is composed of all three germ layers, namely the endoderm, the mesoderm and the ectoderm, forming the epithelium, the smooth muscle layers and the enteric nervous system, respectively. Since gastrulation, these layers develop simultaneously during embryogenesis, signaling to each other continuously until adult age. Two invaginations, the anterior intestinal portal (AIP) and the caudal/posterior intestinal portal (CIP), elongate and fuse, creating the primitive gut tube, which is then patterned along the antero‑posterior (AP) axis and the radial (RAD) axis in the context of left‑right (LR) asymmetry. These events lead to the formation of three distinct regions, the foregut, midgut and hindgut. All the above‑mentioned phenomena are under strict control from various molecular pathways, which are critical for the normal intestinal development and function. Specifically, the intestinal epithelium constitutes a constantly developing tissue, deriving from the progenitor stem cells at the bottom of the intestinal crypt. Epithelial differentiation strongly depends on the crosstalk with the adjacent mesoderm. Major molecular pathways that are implicated in the embryogenesis of the large intestine include the canonical and non‑canonical wingless‑related integration site (Wnt), bone morphogenetic protein (BMP), Notch and hedgehog systems. The aberrant regulation of these pathways inevitably leads to several intestinal malformation syndromes, such as atresia, stenosis, or agangliosis. Novel theories, involving the regulation and homeostasis of intestinal stem cells, suggest an embryological basis for the pathogenesis of colorectal cancer (CRC). Thus, the present review article summarizes the diverse roles of these molecular factors in intestinal embryogenesis and related disorders.

ProNGF Is a Cell-Type-Specific Mitogen for Adult Hippocampal and for Induced Neural Stem Cells

The role of proNGF, the precursor of nerve growth factor (NGF), in the biology of adult neural stem cells (aNSCs) is still unclear. Here, we analyzed adult hippocampal neurogenesis in AD11 transgenic mice, in which the constitutive expression of anti-NGF antibody leads to an imbalance of proNGF over mature NGF. We found increased proliferation of progenitors but a reduced neurogenesis in the AD11 dentate gyrus (DG)-hippocampus (HP). Also in vitro, AD11 hippocampal neural stem cells (NSCs) proliferated more, but were unable to differentiate into morphologically mature neurons. By treating wild-type hippocampal progenitors with the uncleavable form of proNGF (proNGF-KR), we demonstrated that proNGF acts as mitogen on aNSCs at low concentration. The mitogenic effect of proNGF was specifically addressed to the radial glia-like (RGL) stem cells through the induction of cyclin D1 expression. These cells express high levels of p75^NTR , as demonstrated by immunofluorescence analyses performed ex vivo on RGL cells isolated from freshly dissociated HP-DG or selected in vitro from NSCs by leukemia inhibitory factor. Clonogenic assay performed in the absence of mitogens showed that RGLs respond to proNGF-KR by reactivating their proliferation and thus leading to neurospheres formation. The mitogenic effect of proNGF was further exploited in the expansion of mouse-induced neural stem cells (iNSCs). Chronic exposure of iNSCs to proNGF-KR increased their proliferation. Altogether, we demonstrated that proNGF acts as mitogen on hippocampal and iNSCs. Stem Cells 2019;37:1223-1237.

Nanomaterial-Based Approaches for Neural Regeneration

Mechanical, thermal, chemical, or ischemic injury of the central or peripheral nervous system results in neuron loss, neurite damage, and/or neuronal dysfunction, almost always accompanied by sensorimotor impairment which alters the patient's life quality. The regenerative strategies for the injured nervous system are currently limited and mainly allow partial functional recovery, so it is necessary to develop new and effective approaches for nervous tissue regenerative therapy. Nanomaterials based on inorganic or organic and composite or hybrid compounds with tunable physicochemical properties and functionality proved beneficial for the transport and delivery/release of various neuroregenerative-relevant biomolecules or cells. Within the following paragraphs, we will emphasize that nanomaterial-based strategies (including nanosized and nanostructured biomaterials) represent a promising alternative towards repairing and regenerating the injured nervous system.

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.

Neurotrophic factors in enteric physiology and pathophysiology

Neurotrophic factors are traditionally recognized for their roles in differentiation, growth, and survival of specific neurons in the central and peripheral nervous system. Some neurotrophic factors are essential for the development and migration of the enteric nervous system along the fetal and post-natal gut. Over the last two decades, several non-developmental functions of neurotrophic factors have been characterized. In the adult gastrointestinal tract, neurotrophic factors regulate gut sensation, motility, epithelial barrier function, and protect enteric neurons and glial cells from damaging insults in the microenvironment of the gut. In this issue of Neurogastroenterology and Motility, Fu et al demonstrate that brain-derived neurotrophic factor plays a role in the pathogenesis of distention-induced abdominal pain in bowel obstruction. In light of this interesting finding, this mini-review highlights some of the recent advances in understanding of the physiological and pathophysiological roles of neurotrophic factors in the adult gut.

Neural Stem Cells, Neural Progenitors, and Neurotrophic Factors

Neural stem cells (NSCs) have been proposed as a promising cellular source for the treatment of diseases in nervous systems. NSCs can self-renew and generate major cell types of the mammalian central nervous system throughout adulthood. NSCs exist not only in the embryo, but also in the adult brain neurogenic region: the subventricular zone (SVZ) of the lateral ventricle. Embryonic stem (ES) cells acquire NSC identity with a default mechanism. Under the regulations of leukemia inhibitory factor (LIF) and fibroblast growth factors, the NSCs then become neural progenitors. Neurotrophic and differentiation factors that regulate gene expression for controlling neural cell fate and function determine the differentiation of neural progenitors in the developing mammalian brain. For clinical application of NSCs in neurodegenerative disorders and damaged neurons, there are several critical problems that remain to be resolved: 1) how to obtain enough NSCs from reliable sources for autologous transplantation; 2) how to regulate neural plasticity of different adult stem cells; 3) how to control differentiation of NSCs in the adult nervous system. In order to understand the mechanisms that control NSC differentiation and behavior, we review the ontogeny of NSCs and other stem cell plasticity of neuronal differentiation. The role of NSCs and their regulation by neurotrophic factors in CNS development are also reviewed.

In vitro non-viral murine pro-neurotrophin 3 gene transfer into rat bone marrow stromal cells

Neurotrophin 3 (NT-3) is an important factor for promoting prenatal neural development, as well as regeneration, axogenesis and plasticity in postnatal life. Therapy with NT-3 was reported to improve the condition of patients suffering from degenerative diseases and traumatic injuries, however, the disadvantage of NT-3 protein delivery is its short half-life, thus our alternative approach is the use of NT-3 gene therapy. In this study, the bone marrow stromal cells (BMSCs) were isolated from adult rats, cultured for 4 passages and transfected with either pEGFP-N1 or a constructed vector containing murine proNT-3 (pSecTag2/HygroB-murine proNT-3) using Lipofectamine 2000 followed by Hygromycin B (200mg/kg). The transfection efficiency of the transiently transfected BMSCs was evaluated using the green fluorescence protein containing vector (pEGFP-N1). A quantitative evaluation of the NT-3 expression of mRNA using real time qRT-PCR shows that there was double fold increase in NT-3 gene expression compared with non-transfected BMSCs, also, the culture supernatant yielded double fold increase in NT-3 using ELISA technique, the data were supported by immunoblotting technique. This suggests that the use of this transfection technique can be useful for gene therapy in different neurological disorders with neurodegenerative or traumatic origins.

Neurotrophin Signaling and Stem Cells-Implications for Neurodegenerative Diseases and Stem Cell Therapy

Neurotrophins (NTs) are members of a neuronal growth factor protein family whose action is mediated by the tropomyosin receptor kinase (TRK) receptor family receptors and the p75 NT receptor (p75NTR), a member of the tumor necrosis factor (TNF) receptor family. Although NTs were first discovered in neurons, recent studies have suggested that NTs and their receptors are expressed in various types of stem cells mediating pivotal signaling events in stem cell biology. The concept of stem cell therapy has already attracted much attention as a potential strategy for the treatment of neurodegenerative diseases (NDs). Strikingly, NTs, proNTs, and their receptors are gaining interest as key regulators of stem cells differentiation, survival, self-renewal, plasticity, and migration. In this review, we elaborate the recent progress in understanding of NTs and their action on various stem cells. First, we provide current knowledge of NTs, proNTs, and their receptor isoforms and signaling pathways. Subsequently, we describe recent advances in the understanding of NT activities in various stem cells and their role in NDs, particularly Alzheimer's disease (AD) and Parkinson's disease (PD). Finally, we compile the implications of NTs and stem cells from a clinical perspective and discuss the challenges with regard to transplantation therapy for treatment of AD and PD.

ENS Development Research Since 1983: Great Strides but Many Remaining Challenges

The first enteric nervous system (ENS) conference, organized by Marcello Costa and John Furness, was held in Adelaide, Australia in 1983. In this article, we review what was known about the development of the ENS in 1983 and then summarize some of the major advances in the field since 1983.

Neurotrophic Factors and Their Potential Applications in Tissue Regeneration

Neurotrophic factors are growth factors that can nourish neurons and promote neuron survival and regeneration. They have been studied as potential drug candidates for treating neurodegenerative diseases. Since their identification, there are more and more evidences to indicate that neurotrophic factors are also expressed in non-neuronal tissues and regulate the survival, anti-inflammation, proliferation and differentiation in these tissues. This mini review summarizes the characteristics of the neurotrophic factors and their potential clinical applications in the regeneration of neuronal and non-neuronal tissues.

Role of p75 neurotrophin receptor in stem cell biology: more than just a marker

p75(NTR), the common receptor for both neurotrophins and proneurotrophins, has been widely studied because of its role in many tissues, including the nervous system. More recently, a close relationship between p75(NTR) expression and pluripotency has been described. p75(NTR) was shown to be expressed in various types of stem cells and has been used to prospectively isolate stem cells with different degrees of potency. Here, we give an overview of the current knowledge on p75(NTR) in stem cells, ranging from embryonic to adult stem cells, and cancer stem cells. In an attempt to address its potential role in the control of stem cell biology, the molecular mechanisms underlying p75(NTR) signaling in different models are also highlighted. p75(NTR)-mediated functions include survival, apoptosis, migration, and differentiation, and depend on cell type, (pro)neurotrophin binding, interacting transmembrane co-receptors expression, intracellular adaptor molecule availability, and post-translational modifications, such as regulated proteolytic processing. It is therefore conceivable that p75(NTR) can modulate cell-fate decisions through its highly ramified signaling pathways. Thus, elucidating the potential implications of p75(NTR) activity as well as the underlying molecular mechanisms of p75(NTR) will shed new light on the biology of both normal and cancer stem cells.

Neurotrophic factor NT-3 displays a non-canonical cell guidance signaling function for cephalic neural crest cells

Chemotactic cell migration is triggered by extracellular concentration gradients of molecules segregated by target fields. Neural crest cells (NCCs), paradigmatic as an accurately moving cell population, undergo wide dispersion along multiple pathways, invading with precision defined sites of the embryo to differentiate into many derivatives. This report addresses the involvement of NT-3 in early colonization by cephalic NCCs invading the optic vesicle region. The results of in vitro and in vivo approaches showed that NCCs migrate directionally up an NT-3 concentration gradient. We also demonstrated the expression of NT-3 in the ocular region as well as their functional TrkB, TrkC and p75 receptors on cephalic NCCs. On whole-mount embryo, a perturbed distribution of NCCs colonizing the optic vesicle target field was shown after morpholino cancelation of cephalic NT-3 or TrkC receptor on NCCs, as well as in situ blocking of TrkC receptor of mesencephalic NCCs by specific antibody released from inserted microbeads. The present results strongly suggest that, among other complementary cell guidance factor(s), the chemotactic response of NCCs toward the ocular region NT-3 gradient is essential for spatiotemporal cell orientation, amplifying the functional scope of this neurotrophic factor as a molecular guide for the embryo cells, besides its well-known canonical functions.

Genetic fate-mapping of tyrosine hydroxylase-expressing cells in the enteric nervous system

BACKGROUND

During development of the enteric nervous system, a subpopulation of enteric neuron precursors transiently expresses catecholaminergic properties. The progeny of these transiently catecholaminergic (TC) cells have not been fully characterized.

METHODS

We combined in vivo Cre-lox-based genetic fate-mapping with phenotypic analysis to fate-map enteric neuron subtypes arising from tyrosine hydroxylase (TH)-expressing cells.

KEY RESULTS

Less than 3% of the total (Hu(+) ) neurons in the myenteric plexus of the small intestine of adult mice are generated from transiently TH-expressing cells. Around 50% of the neurons generated from transiently TH-expressing cells are calbindin neurons, but their progeny also include calretinin, neurofilament-M, and serotonin neurons. However, only 30% of the serotonin neurons and small subpopulations (<10%) of the calbindin, calretinin, and neurofilament-M neurons are generated from TH-expressing cells; only 0.2% of nitric oxide synthase neurons arise from TH-expressing cells.

CONCLUSIONS & INFERENCES

Transiently, catecholaminergic cells give rise to subpopulations of multiple enteric neuron subtypes, but the majority of each of the neuron subtypes arises from non-TC cells.

Development and developmental disorders of the enteric nervous system

The enteric nervous system (ENS) arises from neural crest-derived cells that migrate into and along the gut, leading to the formation of a complex network of neurons and glial cells that regulates motility, secretion and blood flow. This Review summarizes the progress made in the past 5 years in our understanding of ENS development, including the migratory pathways of neural crest-derived cells as they colonize the gut. The importance of interactions between neural crest-derived cells, between signalling pathways and between developmental processes (such as proliferation and migration) in ensuring the correct development of the ENS is also presented. The signalling pathways involved in ENS development that were determined using animal models are also described, as is the evidence for the involvement of the genes encoding these molecules in Hirschsprung disease-the best characterized paediatric enteric neuropathy. Finally, the aetiology and treatment of Hirschsprung disease in the clinic and the potential involvement of defects in ENS development in other paediatric motility disorders are outlined.

Genetics of neural crest and neurocutaneous syndromes

Neural crest progenitor cells are identified at the lateral margins of the neural placode at the time of gastrulation. With folding of the placode, these precursors are brought to the dorsal midline of the neural tube at the site of closure, become committed to neural crest lineage and almost immediately migrate peripherally to various predetermined sites in the body and then differentiate as a variety of cellular types in all three of the traditional "germ layers." All of these processes of migration and differentiation of neural crest are precisely genetically programed, temporally and spatially, by a variety of genes. Primary neurocutaneous syndromes are all very different diseases with different genetic mutations, but the unifying factor amongst them is that all are neurocristopathies and can be explained as such, including the tumor-suppressor function of several of these genes, especially those of neurofibromatosis 1 and 2 and tuberous sclerosis. This chapter reviews the principal genes that program neural crest development and also are documented, implicated, or suspected in the pathogenesis of neurocutaneous syndromes. Recent genetic discoveries are noted in epidermal nevus syndrome, including Proteus syndrome and their association with hemimegalencephaly and congenital infiltrating lipomatosis of the face.

Pleiotropic effects of the bone morphogenetic proteins on development of the enteric nervous system

Formation of the enteric nervous system (ENS) from migratory neural crest-derived cells that colonize the primordial gut involves a complex interplay among different signaling molecules. The bone morphogenetic proteins (BMPs), specifically BMP2 and BMP4, play a particularly important role in virtually every stage of gut and ENS development. BMP signaling helps to pattern both the anterior-posterior axis and the radial axis of the gut prior to colonization by migratory crest progenitor cells. BMP signaling then helps regulate the migration of enteric neural crest-derived precursors as they colonize the fetal gut and form ganglia. BMP2 and -4 promote differentiation of enteric neurons in early fetal ENS development and glia at later stages. A major role for BMP signaling in the ENS is regulation of responses to other growth factors. Thus BMP signaling first regulates neurogenesis by modulating responses to GDNF and later gliogenesis through its effects on GGF-2 responses. Furthermore, BMPs promote growth factor dependency for survival of ENS neurons (on NT-3) and glia (on GGF-2) by inducing TrkC (neurons) and ErbB3 (glia). BMP signaling limits total neuron numbers, favoring the differentiation of later born neuronal phenotypes at the expense of earlier born ones thus influencing the neuronal composition of the ENS and the glia/neuron ratio. BMP2 and -4 also promote gangliogenesis via modification of neural cell adhesion molecules and promote differentiation of the circular and then longitudinal smooth muscles. Disruption of BMP signaling leads to defects in the gut and in ENS function commensurate with these complex developmental roles.

Neurotrophin receptor TrkC is an entry receptor for Trypanosoma cruzi in neural, glial, and epithelial cells

Trypanosoma cruzi, the agent of Chagas' disease, infects a variety of mammalian cells in a process that includes multiple cycles of intracellular division and differentiation starting with host receptor recognition by a parasite ligand(s). Earlier work in our laboratory showed that the neurotrophin-3 (NT-3) receptor TrkC is activated by T. cruzi surface trans-sialidase, also known as parasite-derived neurotrophic factor (PDNF). However, it has remained unclear whether TrkC is used by T. cruzi to enter host cells. Here, we show that a neuronal cell line (PC12-NNR5) relatively resistant to T. cruzi became highly susceptible to infection when overexpressing human TrkC but not human TrkB. Furthermore, trkC transfection conferred an ∼3.0-fold intracellular growth advantage. Sialylation-deficient Chinese hamster ovarian (CHO) epithelial cell lines Lec1 and Lec2 also became much more permissive to T. cruzi after transfection with the trkC gene. Additionally, NT-3 specifically blocked T. cruzi infection of the TrkC-NNR5 transfectants and of naturally permissive TrkC-bearing Schwann cells and astrocytes, as did recombinant PDNF. Two specific inhibitors of Trk autophosphorylation (K252a and AG879) and inhibitors of Trk-induced MAPK/Erk (U0126) and Akt kinase (LY294002) signaling, but not an inhibitor of insulin-like growth factor 1 receptor, abrogated TrkC-mediated cell invasion. Antibody to TrkC blocked T. cruzi infection of the TrkC-NNR5 transfectants and of cells that naturally express TrkC. The TrkC antibody also significantly and specifically reduced cutaneous infection in a mouse model of acute Chagas' disease. TrkC is ubiquitously expressed in the peripheral and central nervous systems, and in nonneural cells infected by T. cruzi, including cardiac and gastrointestinal muscle cells. Thus, TrkC is implicated as a functional PDNF receptor in cell entry, independently of sialic acid recognition, mediating broad T. cruzi infection both in vitro and in vivo.

Development of the autonomic nervous system: a comparative view

In this review we summarize current understanding of the development of autonomic neurons in vertebrates. The mechanisms controlling the development of sympathetic and enteric neurons have been studied in considerable detail in laboratory mammals, chick and zebrafish, and there are also limited data about the development of sympathetic and enteric neurons in amphibians. Little is known about the development of parasympathetic neurons apart from the ciliary ganglion in chicks. Although there are considerable gaps in our knowledge, some of the mechanisms controlling sympathetic and enteric neuron development appear to be conserved between mammals, avians and zebrafish. For example, some of the transcriptional regulators involved in the development of sympathetic neurons are conserved between mammals, avians and zebrafish, and the requirement for Ret signalling in the development of enteric neurons is conserved between mammals (including humans), avians and zebrafish. However, there are also differences between species in the migratory pathways followed by sympathetic and enteric neuron precursors and in the requirements for some signalling pathways.

Small-molecule induction of neural crest-like cells derived from human neural progenitors

Neural crest (NC) cells are stem cells that are specified within the embryonic neuroectodermal epithelium and migrate to stereotyped peripheral sites for differentiation into many cell types. Several neurocristopathies involve a deficit of NC-derived cells, raising the possibility of stem cell therapy. In Hirschsprung's disease the distal bowel lacks an enteric nervous system caused by a failure of colonization by NC-derived cells. We have developed a robust method of producing migrating NC-like cells from human embryonic stem cell-derived neural progenitors using a coculture system of mouse embryonic fibroblasts. Significantly, subsequent exposure to Y27632, a small-molecule inhibitor of the Rho effectors ROCKI/II, dramatically increased the efficiency of differentiation into NC-like cells, identified by marker expression in vitro. NC-like cells derived by this method were able to migrate along NC pathways in avian embryos in ovo and within explants of murine bowel, and to differentiate into cells with neuronal and glial markers. This is the first study to report the use of a small molecule to induce cells with NC characteristics from embryonic stem cells that can migrate and generate neurons and support cells in complex tissue. Furthermore, this study demonstrates that small-molecule regulators of ROCKI/II signaling may be valuable tools for stem cell research aimed at treatment of neurocristopathies.

HeyL regulates the number of TrkC neurons in dorsal root ganglia

The basic-helix-loop-helix transcription factor HeyL is expressed at high levels by neural crest progenitor cells (NCPs) that give rise to neurons and glia in dorsal root ganglia (DRG). Since HeyL expression was observed in these NCPs during the period of neurogenesis, we generated HeyL null mutants to help examine the factor's role in ganglion neuronal specification. Homozygous null mutation of HeyL reduced the number of TrkC(+) neurons in DRG at birth including the subpopulation that expresses the ETS transcription factor ER81. Conversely, null mutation of the Hey paralog, Hey1, increased the number of TrkC(+) neurons. Null mutation of HeyL increased expression of the Hey paralogs Hey1 and Hey2, suggesting that HeyL normally inhibits their expression. Double null mutation of both Hey1 and HeyL rescued TrkC(+) neuron numbers to control levels. Thus, the balance between HeyL and Hey1 expression regulates the differentiation of a subpopulation of TrkC(+) neurons in the DRG.

Development of enteric neuron diversity

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

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.

Enteric glial cells express full-length TrkB and depend on TrkB expression for normal development

The embryonic development of the enteric nervous system (ENS) from neural crest precursor cells requires neurotrophic signaling. Neurotrophins (NTs) are a family of growth factors that bind Trk receptors to signal diverse functions, including development and maintenance of different cell populations in the peripheral nervous system. In this study we investigated the expression and cell localization of TrkB, the high affinity receptor for brain-derived neurotrophic factor and NT-4, in the murine ENS using Western blot and immunohistochemistry. The results demonstrate that enteric glial cells within the ENS express full-length TrkB at all stages tested. The ENS of TrkB deficient mice have reduced expression of glial cell markers, and a disarrangement of glial cells and the plexular neuropil. These results strongly suggest TrkB has essential roles in the normal development and maintenance of glial cells in the ENS.

Trypanosoma cruzi promotes neuronal and glial cell survival through the neurotrophic receptor TrkC

Trypanosoma cruzi, the agent of Chagas' disease, promotes neuron survival through receptor tyrosine kinase TrkA and glycosylphosphatidylinositol-anchored glial cell-derived family ligand receptors (GFRalpha). However, these receptors are expressed by only a subset of neurons and at low levels or not at all in glial cells. Thus, T. cruzi might exploit an additional neurotrophic receptor(s) to maximize host-parasite equilibrium in the nervous system. We show here that T. cruzi binds TrkC, a neurotrophic receptor expressed by glial cells and many types of neurons, and that the binding is specifically inhibited by neurotrophin-3, the natural TrkC ligand. Coimmunoprecipitation and competition assays show that the trans-sialidase/parasite-derived neurotrophic factor (PDNF), previously identified as a TrkA ligand, mediates the T. cruzi-TrkC interaction. PDNF promotes TrkC-dependent mitogen-activated protein kinase signaling, neurite outgrowth, and survival of genetically engineered PC12 neuronal cells and glial Schwann cells in a TrkC-dependent manner. Thus, TrkC is a new neurotrophic receptor that T. cruzi engages to promote the survival of neuronal and glial cells. The results raise the possibility that T. cruzi recognition of TrkC underlies regenerative events in nervous tissues of patients with Chagas' disease.

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.

Effects of NGF, NT-3 and GDNF family members on neurite outgrowth and migration from pelvic ganglia from embryonic and newborn mice

Background

Pelvic ganglia are derived from the sacral neural crest and contain both sympathetic and parasympathetic neurons. Various members of the neurotrophin and GDNF families of neurotrophic factors have been shown to play important roles in the development of a variety of peripheral sympathetic and parasympathetic neurons; however, to date, the role of these factors in the development of pelvic ganglia has been limited to postnatal and older ages. We examined the effects of NGF, NT-3, GDNF, neurturin and artemin on cell migration and neurite outgrowth from explants of the pelvic ganglia from embryonic and newborn mice grown on collagen gels, and correlated the responses with the immunohistochemical localization of the relevant receptors in fixed tissue.

Results

Cell migration assays showed that GDNF strongly stimulated migration of tyrosine hydroxylase (TH) cells of pelvic ganglia from E11.5, E14.5 and P0 mice. Other factors also promoted TH cell migration, although to a lesser extent and only at discrete developmental stages. The cells and neurites of the pelvic ganglia were responsive to each of the GDNF family ligands – GDNF, neurturin and artemin – from E11.5 onwards. In contrast, NGF and NT-3 did not elicit a significant neurite outgrowth effect until E14.5 onwards. Artemin and NGF promoted significant outgrowth of sympathetic (TH+) neurites only, whereas neurturin affected primarily parasympathetic (TH-negative) neurite outgrowth, and GDNF and NT-3 enhanced both sympathetic and parasympathetic neurite outgrowth. In comparison, collagen gel assays using gut explants from E11.5 and E14.5 mice showed neurite outgrowth only in response to GDNF at E11.5 and to neurturin only in E14.5 mice.

Conclusion

Our data show that there are both age-dependent and neuron type-dependent differences in the responsiveness of embryonic and neo-natal pelvic ganglion neurons to growth factors.

Signals from the neural crest regulate beta-cell mass in the pancreas

Pancreatic islet cells and neurons share common functions and similar ontogenies, but originate in different germ layers. To determine whether ectoderm-derived cells contribute instructive signals to the developing endoderm-derived pancreas, we defined the chronology of migration and differentiation of neural crest cells in the pancreas, and tested their role in the development of the islets. The homeodomain transcription factor Phox2b marks the neural precursors from the neural crest that colonize the gut to form the enteric nervous system. In the embryonic mouse pancreas, we found Phox2b expressed briefly together with Sox10 along the epithelial-mesenchymal border at E12.5 in cells derived from the neural crest. Downregulation of Phox2b shortly thereafter was dependent upon Nkx2.2 expressed in the adjacent pancreatic epithelium. In Phox2b-/- embryos, neurons and glia did not develop in the pancreas, and Nkx2.2 expression was markedly upregulated in the epithelium. In addition, the number and replication rate of insulin-expressing beta-cells increased in the Phox2b-/-mice. We conclude that, during pancreatic development, Phox2b and Nkx2.2 form a non-cell-autonomous feedback loop that links the neural crest with the pancreatic epithelium, regulates the size of the beta-cell population, and thereby impacts insulin-secretory capacity and energy homeostasis.

Neurotrophic factors in autonomic nervous system plasticity and dysfunction

During development, neurotrophic factors are known to play important roles in regulating the survival of neurons in the autonomic nervous system (ANS) and the formation of their synaptic connectivity with their peripheral targets in the cardiovascular, digestive, and other organ systems. Emerging findings suggest that neurotrophic factors may also affect the functionality of the ANS during adult life and may, in part, mediate the effects of environmental factors such as exercise and dietary energy intake on ANS neurons and target cells. In this article, we describe the evidence that ANS neurons express receptors for multiple neurotrophic factors, and data suggesting that activation of those receptors can modify plasticity in the ANS. Neurotrophic factors that may regulate ANS function include brain-derived neurotrophic factor, nerve growth factor, insulin-like growth factors, and ciliary neurotrophic factor. The possibility that perturbed neurotrophic factor signaling is involved in the pathogenesis of ANS dysfunction in some neurological disorders is considered, together with implications for neurotrophic factor-based therapeutic interventions.

Temporal and regional morphological differences as a consequence of FGF-2 deficiency are mirrored in the myenteric proteome

The enteric nervous system with its intricate network of neurons and glia shows a high plasticity, which not only changes during pre- and postnatal development, but also with disease or changing dietary habits. FGF as a potent neurotrophic factor in the central nervous system might also play a specific role for the ENS development, FGF-2 knockout and corresponding wild-type mice were histologically and functionally analyzed. FGF-2 knockout mice are viable and thrive normally and do apparently not display any obvious neurological deficit. Morphological differences were studied on whole mount preparations of muscle and submucous layer using either cuprolinic blue or immunohistochemical stainings for the neuronal marker PGP 9.5. Ussing-chamber and isometric muscle contraction experiments were performed on isolated gut wall, respectively muscle preparations. Intravital microscopy with GFP-transfected E. coli bacteria was used to investigate influences upon bacterial translocation. In additional experiments the protein pattern of the isolated myenteric plexus of knockout and wild-type mice were compared using 2D-DIGE technology. The morphometric analysis of the myenteric plexus revealed significant differences between FGF-2 knockout and wild-type animals, resulting in larger neurons in the knock out animals, embedded in less densely packed enteric ganglia. While muscle contractility appeared not to be affected, there was a significant difference in bacterial translocation as well as differences in basal chloride secretion to be seen. The observed morphological differences were reflected in the varying protein patterns, which were revealed by 2D-DIGE. A large number of differentially expressed proteins were found in both colonic and duodenal samples. FGF obviously influences the development of well established gastrointestinal functions by various means, thus leading to minor but significant deficiencies. Whether the revealed deficits in the mucous barrier are indebted to the morphological alterations in the ENS cannot yet be proved, but is very likely.

Effects of neurotrophin 3 on gastric and colonic motility in awake rats

Neurotrophin 3 (NT3) and its receptors are expressed throughout the gastrointestinal tract, especially in the enteric nervous system. However, little is known about the effects of NT3 on gastrointestinal motility. To investigate the effects of NT3 on gastric or colonic motility under baseline conditions, after subdiaphragmatic vagotomy and in a model of postoperative ileus. Sprague-Dawley rats were equipped with strain gauge transducers on the gastric or colonic wall. Motility was recorded for 30 min, followed by i.v. administration of NT3 and motility-recording for another 60 min. Experiments were performed on three consecutive days and separately in a postoperative ileus model. To evaluate a vagal pathway, experiments were also performed on vagotomized rats. NT3 inhibited gastric motility. This inhibitory effect was reduced by subdiaphragmatic vagotomy. Preoperative treatment with NT3 prolonged the postoperative gastric ileus compared to vehicle treatment. Colonic motility in the intact animal was unchanged by NT3, but was increased postoperatively. NT3 treatment inhibited gastric but not colonic motility. This inhibition of gastric motility seems to be partly mediated by the vagus nerve. NT3 aggravates gastric postoperative ileus but attenuates colonic postoperative ileus, which corresponds to the observed positive effects of NT3 on constipated patients.

Neural crest and the development of the enteric nervous system

The formation of the enteric nervous system (ENS) is a particularly interesting example of the migratory ability of the neural crest and of the complexity of structures to which neural crest cells contribute. The distance that neural crest cells migrate to colonize the entire length of the gastrointestinal tract exceeds that of any other neural crest cell population. Furthermore, this migration takes a long time--over 25% of the gestation period for mice and around 3 weeks in humans. After colonizing the gut, neural crest-derived cells within the gut wall then differentiate into glial cells plus many different types of neurons, and generate the most complex part of the peripheral nervous system.

Biology of the adult enteric neural stem cell

An increasing body of evidence has accumulated in recent years supporting the existence of neural stem cells in the adult gut. There are at least three groups that have obtained them using different methodologies and have described them in vitro. There is a growing amount of knowledge on their biology, but many questions are yet unanswered. Among these questions is whether these cells are part of a permanent undifferentiated pool or are recruited in a regular basis; in addition, the factors and genes involved in their survival, proliferation, migration, and differentiation are largely unknown. Finally, with between 10 and 20% of adults suffering from diseases involving the enteric nervous system, most notably irritable bowel syndrome and gastroesophageal reflux, what is the possible role of enteric nervous stem cells in health and disease?

Isolation and cultivation of neuronal precursor cells from the developing human enteric nervous system as a tool for cell therapy in dysganglionosis

BACKGROUND

The human enteric nervous system (ENS) descends from migrating neural crest cells (NCC) and is structured into different plexuses embedded in the gastrointestinal tract wall. The development of this entity strongly depends on the supply of an appropriate support with trophic factors during organogenesis. The lack of important factors, such as glial cell line-derived neurotrophic factor, leads to severe disturbances in the ENS and, thus, to motility disorders in children. The isolation of neuronal precursor cells as well as their transplantation after expansion in vitro is therefore a hopeful new approach concerning all forms of dysganglionosis in children.

METHODS

We therefore established a way to isolate and expand precursor cells from the developing and postnatal human ENS. Bowel samples were obtained from human fetuses and children (from the 9th week of gestation to 5 years postnatal). Myenteric plexus was isolated by enzymatical digestion and cultivated until spheroid aggregates, the so-called neurospheres, developed. These neurospheres could be differentiated and also be transplanted after dissociation into aganglionic bowel in vitro.

RESULTS

Enteric neurospheres could be grown from different gestational ages, including postmortem material. Undifferentiated proliferating precursor cells were kept in culture for up to 72 days and could be differentiated in neurons and glial cells in vitro.

CONCLUSION

The first results using isolated enteric neurospheres in aganglionic bowel are quite promising and are a basis to develop an appropriate cell therapy for all kinds of dysganglionosis, especially for cases where a surgical approach is not sufficient or not even possible.

Gangliogenesis in the enteric nervous system: Roles of the polysialylation of the neural cell adhesion molecule and its regulation by bone morphogenetic protein-4

The neural crest-derived cells that colonize the fetal bowel become patterned into two ganglionated plexuses. The hypothesis that bone morphogenetic proteins (BMPs) promote ganglionation by regulating neural cell adhesion molecule (NCAM) polysialylation was tested. Transcripts encoding the sialyltransferases, ST8Sia IV (PST) and ST8Sia II (STX), which polysialylate NCAM, were detectable in fetal rat gut by E12 but were downregulated postnatally. PSA-NCAM-immunoreactive neuron numbers, but not those of NCAM, were developmentally regulated similarly. Circular smooth muscle was transiently (E16-20) PSA-NCAM-immunoreactive when it is traversed by migrating precursors of submucosal neurons. Neurons developing in vitro from crest-derived cells immunoselected at E12 with antibodies to p75(NTR) expressed NCAM and PSA-NCAM. BMP-4 promoted neuronal NCAM polysialylation and clustering. N-butanoylmannosamine, which blocks NCAM polysialylation, but not N-propanoylmannosamine, which does not, interfered with BMP-4-induced neuronal clustering. Observations suggest that BMP signaling enhances NCAM polysialylation, which allows precursors to migrate and form ganglionic aggregates during the remodeling of the developing ENS.

Glial cells in the gut

The enteric nervous system is composed of both neurons and glia. Recent evidence indicates that enteric glia-which vastly outnumber enteric neurons-are actively involved in the control of gastrointestinal functions: they contain neurotransmitter precursors, have the machinery for uptake and degradation of neuroligands, and express neurotransmitter-receptors which makes them well suited as intermediaries in enteric neurotransmission and information processing in the ENS. Novel data further suggest that enteric glia have an important role in maintaining the integrity of the mucosal barrier of the gut. Finally, enteric glia may also serve as a link between the nervous and immune systems of the gut as indicated by their potential to synthesize cytokines, present antigen and respond to inflammatory insults. The role of enteric glia in human disease has not yet been systematically studied, but based on the available evidence it is predictable that enteric glia are involved in the etiopathogenesis of various pathological processes in the gut, particularly such with neuroinflammatory or neurodegenerative components.

Differential responses of intrinsic and extrinsic innervation of smooth muscle cells in rat colitis

Intestinal smooth muscle cells receive neural input from axons that originate within the intestine, as well as from axons of extrinsic origin. In the inflamed intestine, altered motility may arise from damage to the axon/smooth muscle cell relationship, but the extent of change is unknown. Western blotting, histology and immunocytochemistry were used in the TNBS model of colitis in the rat to evaluate intrinsic and extrinsic axon numbers, which were then correlated with circular smooth muscle cell (CSMC) number during the time course from the acute onset of colitis to apparent recovery, at Day 35 post TNBS. Total axon profiles in the circular smooth muscle layer were reduced by nearly 50% on Day 4 of colitis, to 428 +/- 82 axons/section from 757 +/- 125 in control (n = 8-14 animals). The intrinsic innervation density (axon number per CSMC) dropped sharply by Day 2 to less than 30% of control. Although CSMC number nearly tripled during colitis, innervation density was restored to control levels by Day 6 due to a coordinated three-fold increase in axon number. The subpopulation of extrinsic axons expressing tyrosine hydroxylase showed a unique pattern during colitis, with no initial decrease in axon number, followed by axonal proliferation between Days 6 and 16 post-TNBS. We conclude that loss of intrinsic axons is an early event in colitis, and although reversed by axonal proliferation, transient denervation may promote CSMC hyperplasia as seen in earlier work in vitro. Axonal proliferation of both intrinsic and extrinsic axons is identified as a major homeostatic mechanism, with distinct patterns of damage and repair suggesting a structural basis for the altered motility seen in the inflamed colon.

Embryology of the neural crest: its inductive role in the neurocutaneous syndromes

Neural crest cells are first recognized at the lateral margin of the neural placode shortly after gastrulation, although they are not committed to their diverse fates until later. After dorsal closure of the neural tube, neural crest cells separate and migrate throughout the embryo to form many structures of ectodermal origin (eg, dorsal root and autonomic ganglia, peripheral nerve sheaths) and mesodermal origin (eg, blood vessels, melanocytes, adipose tissue, membranous bone, connective tissue, most of the ocular globe). Terminal differentiation occurs after migration is complete. Three regions of the neural tube generate neural crest: rhombencephalon, mesencephalon, and prosencephalon, each with a different migratory pattern. The most important genes promoting neural crest differentiation and migration are those with a dorsalizing influence in the vertical axis of the neural tube (eg, PAX3, BMP4, ZIC2), some segmentation genes (eg, WNT1), genes that inhibit neural crest (eg, EGR2), and neural crest-specific differentiating genes (eg, SLUG, SOX10). In the neurocutaneous syndromes, diverse features result from abnormal neural crest differentiation, providing a more encompassing embryologic basis for these disorders than the traditional view that these syndromes are somehow related to skin and brain because both are ectodermal derivatives. Abnormal angiogenesis, areas of abnormal pigmentation that sometimes follow the lines of Blashko, nerve sheath proliferations, disorders of chromaffin tissue, lipomes and benign and malignant tumors are frequent features. Many defective genes in neurocutaneous syndromes have an additional function as tumor suppressors. Interactions between genes associated with these disorders and others essential to neural crest formation, migration, and differentiation, are a likely molecular genetic basis for these diseases. The craniofacial abnormalities associated with many cerebral malformations and cutaneous lesions in some neurocutaneous syndromes emphasize an important inductive role of the neural tube in the development of non-neural tissues, mediated through neural crest.

Neurotrophins in murine viscera: a dynamic pattern from birth to adulthood

There is growing evidence that target-derived neurotrophins regulate the function of visceral neurons after birth. However, the postnatal profile of neurotrophin supply from internal organs is poorly described. In this study, we compared neurotrophin concentrations in lysates of murine peripheral target tissues (lung, heart, liver, colon, spleen, thymus, kidney and urinary bladder) at different time points after birth. In most organs, there was a decrease of neurotrophin concentrations in the first weeks after birth. In contrast, there were characteristic increases of specific neurotrophins during adolescence or adulthood. These increases were found for nerve growth factor (NGF) in the heart, thymus, kidney and liver, for brain-derived neurotrophic factor (BDNF) in the lung, and for neurotrophin-3 (NT-3) in the colon. In conclusion, we show that neurotrophins display a very differential and dynamic profile in internal organs after birth.

Enteric nervous system

PURPOSE OF THE REVIEW

The purpose of this review is to provide a synopsis of how the field of enteric neurobiology has advanced during the past 2 years.

RECENT FINDINGS

With more than 500 studies from which to choose, the authors have focused on several themes that illustrate recent progress. There has been an explosion of interest in the development of the enteric nervous system driven by the need to understand development abnormalities, particularly in Hirschsprung disease, and fueled by technical advances for investigating how neural crest-derived cells migrate, proliferate, and differentiate into enteric neurons and glia. The use of neural stem cells as a therapeutic strategy aimed at repopulating regions of bowel, where enteric neurones are reduced or absent, is on the horizon. Enteric reflexes involve interactions between sensory neurons, interneurons, and motor neurons. Recent findings suggest this distinction may be blurred, with neurons having multifunctional properties, perhaps because enteric neurons, unlike their central nervous system counterparts, are directly exposed to mechanical forces that they regulate. Another topic the authors have highlighted is pharmacology, with new tools for investigating ion channels, receptors, and transporters, leading to an expanding list of molecular mechanisms that regulate neuronal excitability. Long-term alterations in the expression of these molecules during disease or injury may underlie many gastrointestinal disorders that currently have unknown etiology. The authors finish with a look to the future and what may be the subject of this review next time.

SUMMARY

Basic science information gathered during the past 2 years provides insight into pathophysiologic processes and will pave the wave for improved understanding of both organic and 'functional' gastrointestinal disorders.