Fulminant jejuno-ileitis following ablation of enteric glia in adult transgenic mice

Reactive astrocytes protect tissue and preserve function after spinal cord injury

Reactive astrocytes are prominent in the cellular response to spinal cord injury (SCI), but their roles are not well understood. We used a transgenic mouse model to study the consequences of selective and conditional ablation of reactive astrocytes after stab or crush SCI. Mice expressing a glial fibrillary acid protein-herpes simplex virus-thymidine kinase transgene were given mild or moderate SCI and treated with the antiviral agent ganciclovir (GCV) to ablate dividing, reactive, transgene-expressing astrocytes in the immediate vicinity of the SCI. Small stab injuries in control mice caused little tissue disruption, little demyelination, no obvious neuronal death, and mild, reversible functional impairments. Equivalent small stab injuries in transgenic mice given GCV to ablate reactive astrocytes caused failure of blood-brain barrier repair, leukocyte infiltration, local tissue disruption, severe demyelination, neuronal and oligodendrocyte death, and pronounced motor deficits. Moderate crush injuries in control mice caused focal tissue disruption and cellular degeneration, with moderate, primarily reversible motor impairments. Equivalent moderate crush injuries combined with ablation of reactive astrocytes caused widespread tissue disruption, pronounced cellular degeneration, and failure of wound contraction, with severe persisting motor deficits. These findings show that reactive astrocytes provide essential activities that protect tissue and preserve function after mild or moderate SCI. In nontransgenic animals, crush or contusion SCIs routinely exhibit regions of degenerated tissue that are devoid of astrocytes. Our findings suggest that identifying ways to preserve reactive astrocytes, to augment their protective functions, or both, may lead to novel approaches to reducing secondary tissue degeneration and improving functional outcome after SCI.

Enteric glia

The enteric nervous system is composed of both enteric neurones and enteric glia. Enteric glial cells were first described by Dogiel and are now known to outnumber neurones approximately 4 : 1. In the past, these cells were assumed to subserve a largely supportive role; however, recent evidence indicates that enteric glial cells may play a more active role in the control of gut function. In transgenic mouse models, where enteric glial cells are selectively ablated, the loss of glia results in intestinal inflammation and disruption of the epithelial barrier. Enteric glia are activated specifically by inflammatory insults and may contribute actively to inflammatory pathology via antigen presentation and cytokine synthesis. Enteric glia also express receptors for neurotransmitters and so may serve as intermediaries in enteric neurotransmission. Thus, enteric glia may serve as a link between the nervous and immune systems of the gut and may also have an important role in maintaining the integrity of the mucosal barrier and in other aspects of intestinal homeostasis.

Notch1-expressing cells are indispensable for prostatic branching morphogenesis during development and re-growth following castration and androgen replacement

Notch expression is frequently associated with progenitor cells, and its function is crucial for development. Our recent work showing that Notch1 is selectively expressed in basal epithelial cells of the prostate and higher Notch1 expression during development suggests that Notch1-expressing cells may define progenitor cells in the prostate. To test this hypothesis, we have generated a transgenic mouse line in which the Notch1-expressing cells can be ablated in a controlled manner. Specific targeting was achieved by expressing the bacterial nitroreductase, an enzyme that catalyzes its substrate into a cytotoxin capable of inducing apoptosis, under the Notch1 promoter. Cell death in transgenic prostate was confirmed by histological analyses including terminal dUTP nick-end labeling and caspase 3 immunocytochemical staining. We evaluated the consequences of ablation of Notch1-expressing cells in two systems, organ culture of early postnatal prostates and re-growth of prostate in castrated mice triggered by hormone replacement. Our data show that elimination of Notch1-expressing cells inhibited the branching morphogenesis, growth, and differentiation of early postnatal prostate in culture and impaired prostate re-growth triggered by hormone replacement in castrated mice. Furthermore, we found that Notch1 expression following castration and hormone replacement was concomitant with known basal cell markers p63 and cytokeratin 14 and was high in the proliferative human prostate epithelial cells. Taken together, these data suggest that Notch1-expressing cells define the progenitor cells in the prostatic epithelial cell lineage, which are indispensable for prostatic development and re-growth.

Sphingosine-1-phosphate mediates calcium signaling in guinea pig enteroglial cells

The enteric nervous system, which regulates multiple aspects of digestive activity, is composed of two major cell types, neurons and glial cells. Enteric glia, but not enteric neurons, respond to bioactive lipids with calcium signaling. The sphingomyelin metabolite sphingosine-1-phosphate (S1P) caused dose-dependent calcium (Ca(2+)) signaling using extracellular and intracellular Ca(2+). The signal transduction cascade was pertussis toxin-insensitive and involved an extracellular receptor since repetitive exposure yielded diminished responsiveness. Inhibition of either phospholipase C or the inositol 1,4,5-trisphosphate receptor abolished S1P effects. RT-PCR analysis demonstrated the presence of S1P-coupled endothelial differentiation gene (EDG) receptor mRNAs (EDG-1, EDG-3, and EDG-5) within the enteric nervous system. Immunocytochemical analysis demonstrated strong expression of both EDG-1 and EDG-3 and weak expression of EDG-5 in enteric glial cells. Other sphingomyelin cycle components, including sphingomyelin, sphingomyelinase, and sphingosine caused Ca(2+) transients in enteric glia. Related lipids lysophosphatidic acid and sphingosylphosphorylcholine also induced Ca(2+) signaling in enteric glia, suggesting that multiple lipid-activated signaling mechanisms exist in these cells.

The expression and role of Fas ligand in intestinal inflammation

Fas ligand (FasL) is involved in the pathogenesis of inflammatory diseases and immune privilege. We examined the expression of FasL in the enteric nervous system (ENS) in murine colitis and guinea-pig ileitis. We studied FasL immunoreactivity, functional integrity of the ENS, severity of colitis, and distribution of neutrophils in wild type and B6/gld mice that lack functional FasL. In ileitis, the distribution of FasL, CD4+ and CD8+ T cells was examined. FasL expression was increased in the ENS of wild type mice with colitis, but decreased labelling of nerve fibres was noted in B6/gld mice. Neutrophils were more abundant and widely distributed in B6/gld mice. Colitis was more severe and persistent in B6/gld mice 7 days after induction. Functional parameters of intestinal secretion and motility in B6/gld mice were the same as controls. In ileitis, FasL expression was increased in the guinea-pig ENS and returned to control levels following the resolution of inflammation. While T cells were not present in the ENS of controls, they were observed during inflammation, but were excluded from ganglia. The number of enteric neurons was unchanged over the course of inflammation. The expression of FasL is altered in intestinal inflammation and contributes to its resolution in experimental colitis.

Development of novel selective cell ablation in the mammary gland and brain to study cell-cell interactions and chemoprevention

We have generated transgenic mice which express the gene encoding Escherichia coli nitroreductase (NTR) specifically in the luminal epithelial cells of the mammary gland and the glial cells of the brain. The enzyme activates an antitumour drug CB 1954, to produce a cross-linking agent that kills all cells expressing the enzyme. We have shown that administration of the antitumour drug CB 1954 rapidly and selectively kills these cells. Original experiments demonstrated the ability to ablate the luminal cells in the mammary gland with no apparent bystander effect. Subsequently, astrocytes expressing nitroreductase under the targeting of the GFAP promoter were selectively ablated following administration of the prodrug CB 1954 produces a degeneration of granular neurones due to changes in glutamate levels. Recent experiments demonstrated inhibition of myc-dependent mammary tumours using the same enzyme (nitroreductase)-prodrug (CB 1954), combination. Owing to the ease of control of NTR-mediated cell ablation, we anticipate that this system will supersede herpes simplex virus type 1 thymidine kinase. There are widespread potential applications for this approach in the dissection of complex cellular interactions during development and in the adult organism. The present transgenic models also have important applications for the study in vivo of novel prodrugs that can be selected for variable degrees of bystander effects. Such studies will have particular significance for those groups advocating the use of NTR as an appropriate enzyme for gene-directed enzyme prodrug therapy by providing models of a wide range of human disease for mechanistic and therapeutic experimentation. The results clearly demonstrate that the model has potential to study chemoprevention and fundamental questions on cell-cell interactions in cell biology.

Human ENS regulates the intestinal epithelial barrier permeability and a tight junction-associated protein ZO-1 via VIPergic pathways

Although the enteric nervous system (ENS) has been shown to regulate various mucosal functions, its role in the physiological control of the human intestinal epithelial barrier is unknown. The aim of this study was to investigate whether the ENS is able to modulate epithelial barrier permeability and a key tight junction-associated protein, zonula occludens-1 (ZO-1). Therefore, we developed a co-culture model, consisting of human submucosa containing the submucosal neuronal network and human polarized colonic epithelial monolayers (HT29-Cl.16E or Caco-2). Submucosal neurons were activated by electrical field stimulation (EFS). Permeability was assessed by measuring the flux of paracellular permeability markers (FITC-dextran or FITC-inulin) across epithelial monolayers. Expression of ZO-1 was determined by immunofluorescence, quantitative immunoblot analysis, and real time RT-PCR. Using the coculture model, we showed that EFS of submucosal neurons resulted in a reduction in FITC-dextran or FITC-inulin fluxes, which was blocked by TTX. In HT29-Cl.16E, the effect of submucosal neuron activation was blocked by a VIP receptor antagonist (VIPra) and reproduced by VIP. Furthermore, ZO-1 expression (mRNA, protein) assessed in HT29-Cl.16E, was significantly increased after submucosal neuron activation by EFS. These effects on ZO-1 expression were blocked by TTX and VIPra and reproduced by VIP. In conclusion, our results strongly suggest a modulatory role of VIPergic submucosal neuronal pathways on intestinal epithelial barrier permeability and ZO-1 expression.

An HSV-TK transgenic mouse model to evaluate elimination of fibroblasts for fibrosis therapy

Pathological fibroproliferation after tissue injury is harmful and may lead to organ dysfunction. Unfortunately, fibroproliferative diseases remain intractable to current therapeutic strategies. Thus, new therapeutic approaches are needed. One possible approach is to promote resolution of physiological fibroproliferation that follows injury before it becomes pathological by activating apoptosis selectively in fibrotic lesions. However, it is not known whether selective elimination of fibroblasts will prevent fibrosis or impede repair or worsen injury by eliminating topographic signals essential to organ reconstitution. To address this question, a tractable in vivo model system is needed in which fibroblasts can be targeted to undergo apoptosis at a chosen time and place. We developed transgenic mice expressing HSV-TK from the type I collagen promoter to determine whether selective elimination of fibroblasts actively forming fibrotic lesions is an effective therapeutic strategy for fibroproliferative disorders. The transgene renders fibroblasts actively forming fibrotic tissue susceptible to ganciclovir. To validate the transgenic model we examined whether administration of ganciclovir prevents the development of fibrosis in sponges implanted subcutaneously in the backs of the transgenic mice. We demonstrate that fibroblasts/myofibroblasts isolated from sponges express HSV-TK protein and are selectively ablated by ganciclovir in vitro. In adult transgenic mice, ganciclovir treatment attenuated the development of fibrotic tissue in the sponges both biochemically and histologically. We conclude that this transgenic model system is an ideal approach to determine whether targeted ablation of fibroblasts is an effective therapeutic strategy for fibrotic diseases.

The ablation of glial fibrillary acidic protein-positive cells from the adult central nervous system results in the loss of forebrain neural stem cells but not retinal stem cells

The adult mammalian forebrain subependyma contains neural stem cells (NSCs) capable of self-renewal and multilineage differentiation. The in vivo identification of NSCs has not been definitively addressed using a loss of function approach. Using a transgenic mouse expressing herpes-simplex virus thymidine kinase from the glial fibrillary acidic protein (GFAP) promotor, we have selectively killed dividing GFAP-positive cells in the presence of ganciclovir (GCV) and shown a > 95% loss in the numbers of NSCs, as assayed by the formation of clonally derived neurospheres in vitro. This loss is seen following 3 days of GCV exposure in vivo or in vitro only and cannot be rescued by coculturing with pure astrocyte populations or control (green fluorescent protein-expressing) subependymal cells. Exposure to GCV in vitro has no effect on adult retinal stem cells hence, we conclude that adult forebrain NSCs comprise a subpopulation of the GFAP-positive cells within the subependyma.

Immune networks in animal models of inflammatory bowel disease

The animal models of inflammatory bowel disease provide a framework to define the immunopathogenesis of intestinal inflammation. Studies in these models support the hypothesis that exaggerated immune responses to normal enteric microflora are involved in the initiation and perpetuation of chronic intestinal inflammation. A major pathway involves development of acquired immune responses by the interactions of CD4+ T-cell receptor alphabeta T cells with antigen-presenting cells (dendritic cells). Immunoregulatory cells, including Tr1 cells, Th3 cells, and CD4+ CD25+ T cells and B cells, directly or indirectly affect the T-cell receptor alphabeta T cell-induced immune responses and bridge innate and acquired immunity. The study of these complicated immune networks provides the rationale for the development of new therapeutic interventions in inflammatory bowel disease.

Glial-derived neurotrophic factor regulates apoptosis in colonic epithelial cells

BACKGROUND & AIMS

Ablation of the enteric glia leads to a fulminant hemorrhagic jejunoileitis. We hypothesized that glial-derived neurotrophic factor (GDNF) may be involved in mucosal protection of the gut. Therefore, we examined the regulation of GDNF and its receptor (GFR-alpha1) in colonic inflammation and its effects on colonic epithelial cell apoptosis.

METHODS

The expression of GDNF and GFR-alpha1 was investigated in experimental colitis of rats and in human inflammatory bowel disease (IBD). GDNF-induced activation of Akt (protein kinase B [PKB]) and mitogen-activated protein kinase (MAPK) in the colonic epithelial cell lines HT-29 and SW480 was studied. Furthermore, the antiapoptotic potency of GDNF in SW480 cells was evaluated.

RESULTS

GDNF was specifically up-regulated in experimental rat colitis and in IBD. In contrast, GFR-alpha1 was constitutively expressed in rat and human colonic epithelium. GDNF potently activated MAPK and Akt (PKB) in colonic epithelial cells. Moreover, GDNF strongly prevented apoptosis in SW480 cells. Our data show that GDNF-mediated protection against apoptosis depends on activation of the MAPK and phosphatidylinositol 3-kinase/Akt (PKB) pathways.

CONCLUSIONS

GDNF is up-regulated in IBD and has strong antiapoptotic properties in colonic epithelial cells. This points to a novel role of the neurotrophic factor GDNF for mucosal protection and regeneration in IBD.

Inflammatory bowel disease: dysfunction of GALT and gut bacterial flora (II)

The precise cause(s) of Crohn's disease and ulcerative colitis are unknown. From animal models and human studies it is well established that gut bacterial flora are essential for inducing the bowel inflammation. Animal models, when kept in a germ-free environment, do not develop colitis until the gut flora is reconstituted. It is not clear whether the bacterial antigens (Ags) from the normal flora or some other pathogenic bacterial Ags induce/propagate the inflammatory process in inflammatory bowel disease (IBD). Despite extensive research it has not been possible to identify any specific bacteria or virus as a credible cause of IBD. Recent understanding of quorum sensing molecules (QSMs) secreted by bacteria helps to explain the community behaviour in bacterial species. When QSMs reach a defined concentration, they activate bacterial proliferation and a number of virulence genes. Also, these molecules have been found to modulate the immune system to the advantage of the gut bacteria. They have not been well studied, however, in the gut. Inappropriate secretion of QSMs may alter the gut-associated lymphoid tissue (GALT) and, thereby, deregulate the immune tolerance normally present. Usefulness of probiotics and their immune modulating effects are being increasingly reported. Probiotics are also being used in the treatment of IBD. The interaction between the epithelial cells and the gut flora is very important as this is the first line of contact; this interaction may determine the induction of tolerance and mucosal integrity or immune activity, tissue inflammation and abnormal permeability. The latter is documented in patients with IBD and their healthy relatives. This may be an important factor in disruption of mucosal integrity and GALT dysfunction.

The predominant neural stem cell isolated from postnatal and adult forebrain but not early embryonic forebrain expresses GFAP

Periventricular germinal zones (GZs) of developing and adult brain contain neural stem cells (NSCs), the cellular identities and origins of which are not defined completely. We used tissue culture techniques and transgenic mice expressing herpes simplex virus thymidine kinase (HSV-TK) from the mouse glial fibrillary acid protein (GFAP) promoter to test the hypothesis that certain NSCs express GFAP. To do so, we determined the relative proportions of multipotent neurospheres that are formed by GFAP-expressing cells derived from GZs at different stages of development. In this transgenic model, dividing GFAP-expressing cells are ablated selectively by treatment with the antiviral agent ganciclovir (GCV). Single-cell analysis showed that transgene-derived HSV-TK was present only in GFAP-expressing cells. GCV applied in vitro eliminated growth of multipotent neurospheres from GZs of postnatal and adult transgenic mice but not early embryonic (embryonic day 12.5) transgenic mice. GCV prevented growth of secondary multipotent neurospheres prepared after passage of primary transgenic neurospheres derived from all three of these developmental stages. In addition, GCV prevented growth of multipotent neurospheres from transgenic astrocyte-enriched cell cultures derived from postnatal GZ, and elaidic acid GCV given for 4 d to adult transgenic mice in vivo abolished the ability to grow multipotent neurospheres from GZ. Extensive control experiments, including clonal analysis, demonstrated that failure of neurosphere growth was not merely secondary to loss of GFAP-expressing support cells or the result of a nonspecific toxic effect. Our findings demonstrate that the predominant multipotent NSCs isolated from postnatal and adult but not early embryonic GZs express GFAP, and that NSCs exhibit heterogeneous expression of intermediate filaments during developmental maturation.

Interleukin-10 and nerve growth factor have reciprocal upregulatory effects on intestinal epithelial cells

The intestinal mucosa is in a constant state of controlled inflammation, but the processes whereby this occurs are poorly understood. The aims of this study were to look at the role of IL-10 and nerve growth factor (NGF) in intestinal epithelial cell regulation. The human colon epithelial cell lines T84, HT-29, and CACO-2 were used. RT-PCR, flow cytometry analysis, and immunohistochemistry were applied to measure the cytokine changes in epithelial cells induced by recombinant cholera toxin and its B subunit, IL-10, and NGF. Cholera toxin B subunit caused selective dose-dependent increased mRNA for IL-10 in T84 cells and the protein in T84, HT-29, and CACO-2 cells. IL-10 dose dependently selectively increased NGF mRNA in T84 cells and intracellular protein synthesis in all three epithelial cell lines. The effect of NGF was reciprocal, selective, and dose dependent because it increased mRNA for IL-10 and IL-10 synthesis. Our results suggest that the epithelium may actively participate in downregulation through innate mechanisms involving IL-10 and NGF. The reciprocal interaction suggests for the first time that NGF may be involved in local downregulation by mucosal epithelium and thus may play a potent protective role in response to injury, by prevention of undue inflammation.

Autoimmune islet destruction in spontaneous type 1 diabetes is not beta-cell exclusive

Pancreatic islets of Langerhans are enveloped by peri-islet Schwann cells (pSC), which express glial fibrillary acidic protein (GFAP) and S100beta. pSC-autoreactive T- and B-cell responses arise in 3- to 4-week-old diabetes-prone non-obese diabetic (NOD) mice, followed by progressive pSC destruction before detectable beta-cell death. Humans with probable prediabetes generate similar autoreactivities, and autoantibodies in islet-cell autoantibody (lCA) -positive sera co-localize to pSC. Moreover, GFAP-specific NOD T-cell lines transferred pathogenic peri-insulitis to NOD/severe combined immunodeficient (NOD/SCID) mice, and immunotherapy with GFAP or S100beta prevented diabetes. pSC survived in rat insulin promoter Iymphocytic choriomeningitis virus (rip-LCMV) glycoprotein/CD8+ T-cell receptor(gp) double-transgenic mice with virus-induced diabetes, suggesting that pSC death is not an obligate consequence of local inflammation and beta-cell destruction. However, pSC were deleted in spontaneously diabetic NOD mice carrying the CD8+/8.3 T-cell receptor transgene, a T cell receptor commonly expressed in earliest islet infiltrates. Autoimmune targeting of pancreatic nervous system tissue elements seems to be an integral, early part of natural type 1 diabetes.

Colonic epithelial expression of ErbB2 is required for postnatal maintenance of the enteric nervous system

We utilized the Cre-LoxP system to establish erbB2 conditional mutant mice in order to investigate the role of erbB2 in postnatal development of the enteric nervous system. The erbB2/nestin-Cre conditional mutants exhibit retarded growth, distended colons, and premature death, resembling human Hirschsprung's disease. Enteric neurons and glia are present at birth in the colon of erbB2/nestin-Cre mutants; however, a marked loss of multiple classes of enteric neurons and glia occurs by 3 weeks of age. Furthermore, we demonstrate that the requirement for erbB2 in maintaining the enteric nervous system is not cell autonomous, but rather erbB2 signaling in the colonic epithelia is required for the postnatal survival of enteric neurons and glia.

Role of enteric glial cells in inflammatory bowel disease

Enteric glial cells (EGCs) represent an extensive but relatively poorly described cell population within the gastrointestinal tract. Accumulating data suggest that EGCs represent the morphological and functional equivalent of CNS astrocytes within the enteric nervous system (ENS). The EGC network has trophic and protective functions toward enteric neurons and is fully implicated in the integration and the modulation of neuronal activities. Moreover, EGCs seem to be active elements of the ENS during intestinal inflammatory and immune responses, sharing with astrocytes the ability to act as antigen-presenting cells and interacting with the mucosal immune system via the expression of cytokines and cytokine receptors. Transgenic mouse systems have demonstrated that specific ablation of EGC by chemical ablation or autoimmune T-cell targeting induces an intestinal pathology that shows similarities to the early intestinal immunopathology of Crohn's disease. EGCs may also share with astrocytes the ability to regulate tissue integrity, thereby postulating that similar interactions to those observed for the blood-brain barrier may also be partly responsible for regulating mucosal and vascular permeability in the gastrointestinal tract. Disruption of the EGC network in Crohn's disease patients may represent one possible cause for the enhanced mucosal permeability state and vascular dysfunction that are thought to favor mucosal inflammation.

Strategies for regeneration and repair in spinal cord traumatic injury

Spinal cord injury is frequently followed by the loss of supraspinal control of sensory, autonomic and motor functions at the sublesional level. In order to enhance recovery in spinal cord-injured patients, we have developed three fundamental strategies in experimental models. These strategies define in turn three chronological levels of postlesional intervention in the spinal cord. Neuroprotection soon after injury using pharmacological tools to reduce the progressive secondary injury processes that follow during the first week after the initial lesion. This strategy was conducted up to clinical trials, showing that a pharmacological therapy can reduce the permanent neurological deficit that usually follows an acute injury of the central nervous system (CNS). A second strategy, which is initiated not long after the lesion, aims at promoting axonal regeneration by acting on the main barrier to regeneration of lesioned axons: the glial scar. Finally a mid-term substitutive strategy is the management of the sublesional spinal cord by sensorimotor stimulation and/or supply of missing key afferents, such as monoaminergic systems. These three strategies are reviewed. Only a combination of these different approaches will be able to provide an optimal basis for potential therapeutic interventions directed to functional recovery after spinal cord injury.

Neurospheres modified to produce glial cell line-derived neurotrophic factor increase the survival of transplanted dopamine neurons

Glial cell line-derived neurotrophic factor (GDNF) has been shown to increase the survival of dopamine neurons in a variety of in vitro and in vivo model systems. Therefore, it constitutes an important therapeutic protein with the potential to ameliorate dopamine neuronal degeneration in Parkinson's disease or to support dopamine neuronal replacement strategies. However, biophysical and practical considerations present obstacles for the direct delivery of the GDNF protein to CNS neurons. Here we show that rodent neural precursor cells isolated and expanded in culture as neurospheres (NS) can be genetically modified to express green fluorescent protein (GFP) or to release GDNF using lentiviral constructs. GDNF-NS increased the fibre outgrowth of primary embryonic dopamine neurons in cocultures, showing that the protein was released in biologically significant quantities. Furthermore, after transplantation into the 6-hydroxydopamine-lesioned rat striatum, GDNF-NS significantly increased the survival of cografted primary dopamine neurons. However, this was not reflected in behavioural recovery in these animals. We found that, by 6 weeks, few cells expressed GDNF or GFP, suggesting either that transgene expression was down-regulated over time or that the cells died. This may explain the initial effects on dopamine neuronal survival within the graft but the lack of long-term effect on subsequent fibre outgrowth and behaviour. Providing sustained levels of neural precursor-mediated transgene expression can be achieved following transplantation in the future; this approach may prove beneficial as an alternative therapeutic strategy in the cell-based management of Parkinson's disease.

Adult rodent neurogenic regions: the ventricular subependyma contains neural stem cells, but the dentate gyrus contains restricted progenitors

Neurogenesis persists in two adult brain regions: the ventricular subependyma and the subgranular cell layer in the hippocampal dentate gyrus (DG). Previous work in many laboratories has shown explicitly that multipotential, self-renewing stem cells in the subependyma are the source of newly generated migrating neurons that traverse the rostral migratory stream and incorporate into the olfactory bulb as interneurons. These stem cells have been specifically isolated from the subependyma, and their properties of self-renewal and multipotentiality have been demonstrated in vitro. In contrast, it is a widely held assumption that the "hippocampal" stem cells that can be isolated in vitro from adult hippocampus reside in the neurogenic subgranular layer and represent the source of new granule cell neurons, but this has never been tested directly. Primary cell isolates derived from the precise microdissection of adult rodent neurogenic regions were compared using two very different commonly used culture methods: a clonal colony-forming (neurosphere) assay and a monolayer culture system. Importantly, both of these culture methods generated the same conclusion: stem cells can be isolated from hippocampus-adjacent regions of subependyma, but the adult DG proper does not contain a population of resident neural stem cells. Indeed, although the lateral ventricle and other ventricular subependymal regions directly adjacent to the hippocampus contain neural stem cells that exhibit long-term self-renewal and multipotentiality, separate neuronal and glial progenitors with limited self-renewal capacity are present in the adult DG, suggesting that neuron-specific progenitors and not multipotential stem cells are the source of newly generated DG neurons throughout adulthood.

Oral infection of C57BL/6 mice with Toxoplasma gondii: a new model of inflammatory bowel disease?

Infection with Toxoplasma gondii is naturally acquired through the oral route by ingestion of undercooked or raw meat containing cysts of the parasite or through ingestion of contaminated water or food contaminated with cysts or oocysts. Following peroral infection with 100 cysts of the ME49 strain of T. gondii, C57BL/6 mice die within 13 days after infection, whereas BALB/c mice survive. At day 7 of infection, massive necrosis of the villi and mucosal cells in the ilea is observed in C57BL/6 but not BALB/c mice. CD4(+) T cells, interferon-gamma, tumor necrosis factor-alpha, and inducible nitric oxide synthase mediate the development of necrosis. These findings indicate a Th1-type immunopathology, with parasite replication appearing to be involved in the first 3 days of infection. Murine and human studies on the immunopathogenesis of inflammatory bowel disease (e.g., Crohn's disease) also indicate a Th1-type immunopathology. The shared and distinct features of oral infection of mice with T. gondii and murine models of inflammatory bowel disease are discussed herein.

Enteric glial cells. An upstream target for induction of necrotizing enterocolitis and Crohn's disease?

As a direct consequence of the sophisticated arrangement of its intrinsic neurons, the gastrointestinal tract is unique among peripheral organs, in its ability to mediate its own reflexes. Neurons of the enteric nervous system are intimately associated with enteric glial cells. These supporting cells do not resemble Schwann cells, the glial cell found in all other parts of the peripheral nervous system, but share many similarities with astrocytes of the central nervous system. Ablation of enteric glial cells in adult transgenic mice has demonstrated that these cells are essential to maintain the integrity of the small intestine. Acute loss of enteric glial cells induces massive pathological changes with similarities to necrotizing enterocolitis (NEC) and early Crohn's disease. These human conditions share some mechanistic similarities. Identification of enteric glial cell dysfunction/loss as sufficient to induce necrotic/inflammatory bowel disease may be important to understand the pathogenesis of both NEC and Crohn's disease.

Enterocolitis induced by autoimmune targeting of enteric glial cells: a possible mechanism in Crohn's disease?

Early pathological manifestations of Crohn's disease (CD) include vascular disruption, T cell infiltration of nerve plexi, neuronal degeneration, and induction of T helper 1 cytokine responses. This study demonstrates that disruption of the enteric glial cell network in CD patients represents another early pathological feature that may be modeled after CD8(+) T cell-mediated autoimmune targeting of enteric glia in double transgenic mice. Mice expressing a viral neoself antigen in astrocytes and enteric glia were crossed with specific T cell receptor transgenic mice, resulting in apoptotic depletion of enteric glia to levels comparable in CD patients. Intestinal and mesenteric T cell infiltration, vasculitis, T helper 1 cytokine production, and fulminant bowel inflammation were characteristic hallmarks of disease progression. Immune-mediated damage to enteric glia therefore may participate in the initiation and/or the progression of human inflammatory bowel disease.

A review and rationale for the use of genetically engineered animals in the study of traumatic brain injury

The mechanisms underlying secondary cell death after traumatic brain injury (TBI) are poorly understood. Animal models of TBI recapitulate many clinical and pathologic aspects of human head injury, and the development of genetically engineered animals has offered the opportunity to investigate the specific molecular and cellular mechanisms associated with cell dysfunction and death after TBI, allowing for the evaluation of specific cause-effect relations and mechanistic hypotheses. This article represents a compendium of the current literature using genetically engineered mice in studies designed to better understand the posttraumatic inflammatory response, the mechanisms underlying DNA damage, repair, and cell death, and the link between TBI and neurodegenerative diseases.

Mucosal acid challenge activates nitrergic neurons in myenteric plexus of rat stomach

We tested the hypothesis that intrinsic neurons of the rat gastric myenteric plexus can be activated by an acid (HCl) challenge of the mucosa. Activated neurons were visualized by immunohistochemical detection of c-Fos, a marker for neuronal excitation. The neurochemical identity of the neurons activated by the HCl challenge was determined by colocalizing c-Fos with a marker for excitatory pathways, choline acetyltransferase (ChAT), and a marker for inhibitory pathways, nitric oxide synthase (NOS). Two hours after intragastric administration of HCl or saline, stomachs were removed and immunofluorescence triple labeling of myenteric neurons was carried out on whole mount preparations. Treatment with 0.35, 0.5, and 0.7 M HCl induced c-Fos in 8%, 56%, and 64%, respectively, of NOS-positive but not ChAT-positive neurons. c-Fos was also seen in glial cells of HCl-treated rats, whereas in saline-treated animals c-Fos was absent from the myenteric plexus. HCl treatment did not change the proportion of ChAT- and NOS-immunoreactive neurons in the myenteric ganglia. It is concluded that gastric acid challenge concentration-dependently stimulates a subpopulation of nitrergic, but not cholinergic, myenteric plexus neurons, which may play a role in muscle relaxation, vasodilatation, and/or secretion.

Glial control of neuronal development

Reciprocal interactions between differentiating glial cells and neurons define the course of nervous system development even before the point at which these two cell types become definitively recognizable. Glial cells control the survival of associated neurons in both Drosophila and mammals, but this control is dependent on the prior neuronal triggering of glial cell fate commitment and trophic factor expression. In mammals, the growth factor neuregulin-1 and its receptors of the ErbB family play crucial roles in both events. Similarly, early differentiating neurons and their associated glia rely on reciprocal signaling to establish the basic axon scaffolds from which neuronal connections evolve. The importance of this interactive signaling is illustrated by the action of glial transcription factors and of glial axon guidance cues such as netrin and slit, which together regulate the commissural crossing of pioneer axons at the neural midline. In these and related events, the defining principle is one of mutually reinforced and mutually dependent signaling that occurs in a network of developing neurons and glia.

Conditional cell ablation by stringent tetracycline-dependent regulation of barnase in mammalian cells

Conditional expression of suicide genes in vivo has a wide range of applications in biological research and requires a minimal basal promoter activity in the uninduced state. To reduce basal activity of tetracycline (tc)-inducible target promoters we combined synthetic tet operators in varying numbers with a core promoter derived from the plant viral 35S promoter. An optimized promoter, P(TF), was found to exert a stringent regulation of luciferase in combination with tTA and rtTA in different mammalian cell lines. We linked P(TF) to the barnase gene, coding for a highly active RNase from Bacillus amyloliquefaciens. Stable cell clones expressing barnase under control of tTA exerted cell death only after tc withdrawal, correlating with a 10-fold induction of barnase mRNA expression. Directing tTA expression through a neuron-specific enolase promoter (P(NSE)) leads to barnase expression and cell death in neuronal cells after tc withdrawal. Taken together, our data demonstrate that a stringent control of barnase expression in the uninduced state improves cell ablation studies, as high frequencies of transgene propagation in both cell lines and in transgenic mice are observed.

Neuropathology of paediatric chronic intestinal pseudo-obstruction and related animal models

Chronic intestinal pseudo-obstruction (CIP) in paediatric patients is due to heterogeneous aetiologies that include primary disorders of the enteric nervous system. These conditions are poorly delineated by contemporary diagnostic approaches, in part because the complex nature of the enteric nervous system may shelter significant physiological defects behind subtle or quantitative anatomical changes. Until recently, relatively few experimental animal models existed for paediatric CIP. However, the availability of rodent models, particularly novel mutants created in the last few years by genetic manipulations, has brought unprecedented opportunities to investigate molecular, cellular, physiological, and histological details of enteric neuropathology. Information gleaned from studies of these animals is likely to change diagnostic and therapeutic approaches to paediatric CIP and related conditions.

A transgenic mouse model for inducible and reversible dysmyelination

Oligodendrocytes are glial cells devoted to the production of myelin sheaths. Myelination of the CNS occurs essentially after birth. To delineate both the times of oligodendrocyte proliferation and myelination, as well as to study the consequence of dysmyelination in vivo, a model of inducible dysmyelination was developed. To achieve oligodendrocyte ablation, transgenic animals were generated that express the herpes virus 1 thymidine kinase (HSV1-TK) gene under the control of the myelin basic protein (MBP) gene promoter. The expression of the MBP-TK transgene in oligodendrocytes is not toxic on its own; however, toxicity can be selectively induced by the systemic injection of animals with nucleoside analogs, such as FIAU [1-(2-deoxy-2-fluoro-beta-delta-arabinofuranosyl)-5-iodouracil]. This system allows us to control the precise duration of the toxic insult and the degree of ablation of oligodendrocytes in vivo. We show that chronic treatment of MBP-TK mice with FIAU during the first 3 postnatal weeks triggers almost a total depletion of oligodendrocytes in the CNS. These effects are accompanied by a behavioral phenotype characterized by tremors, seizures, retarded growth, and premature animal death. We identify the period of highest oligodendrocytes division in the first 9 postnatal days. Delaying the beginning of FIAU treatments results in different degrees of dysmyelination. Dysmyelination in MBP-TK mice is always accompanied by astrocytosis. Thus, this transgenic line provides a model to study the events occurring during dysmyelination of various intensities. It also represents an invaluable tool to investigate remyelination in vivo.

Conditional ablation of neurones in transgenic mice

Conditional targeted ablation of specific cell populations in living transgenic animals is a very powerful strategy to determine cell functions in vivo. This approach would be of particular value to study the functions of distinct neuronal populations; however, the transgene of choice for conditional cell ablation studies in mice, the herpes simplex virus thymidine kinase gene, cannot be used to ablate neurones as its principal mode of action relies on cell proliferation. Here we report that expression of the E.coli nitroreductase gene (Ntr) and metabolism of the prodrug CB1954 (5-aziridin-1-yl-2-4-dinitrobenzamide) to its cytotoxic derivative can be used to conditionally and acutely ablate specific neuronal populations in vivo. As proof of principal, we have ablated olfactory and vomeronasal receptor neurones by expressing Ntr under the control of the olfactory marker protein (OMP) gene promoter. We demonstrate that following CB1954 administration, olfactory and vomeronasal receptor neurones expressing the transgene were selectively eliminated from the olfactory epithelium (OE), and projections to the olfactory bulb (OB) were lost. The functional efficacy of cell ablation was demonstrated using a highly sensitive behavioural test to show that ablated mice had lost the olfactory ability to discriminate distinct odors and were consequently rendered anosmic. Targeted expression of Ntr to specific neuronal populations using conventional transgenes, as described here, or by "knock-in" gene targeting using embryonic stem cells may be of significant value to address the functions of distinct neuronal populations in vivo.

Interleukin-6 expression and regulation in rat enteric glial cells

As yet, little is known about the function of the glia of the enteric nervous system (ENS), particularly in an immune-stimulated environment. This prompted us to study the potential of cultured enteroglial cells for cytokine synthesis and secretion. Jejunal myenteric plexus preparations from adult rats were enzymatically dissociated, and enteroglial cells were purified by complement-mediated cytolysis and grown in tissue culture. Cultured cells were stimulated with recombinant rat interleukin (IL)-1beta, IL-6, and tumor necrosis factor (TNF)-alpha, and IL-6 mRNA expression and secretion were assessed using RT-PCR and a bioassay, respectively. Stimulation with TNF-alpha did not affect IL-6 mRNA expression, whereas IL-1beta stimulated IL-6 mRNA and protein synthesis in a time- and concentration-dependent fashion. In contrast, IL-6 significantly and dose-dependently suppressed IL-6 mRNA expression. In summary, we have presented evidence that enteric glial cells are a potential source of IL-6 in the myenteric plexus and that cytokine production by enteric glial cells can be regulated by cytokines. These findings strongly support the contention that enteric glial cells act as immunomodulatory cells in the enteric nervous system.

Fibroblasts can express glial fibrillary acidic protein (GFAP) in vivo

Neuropathologists use anti-glial fibrillary acidic protein (GFAP) antibodies as specific markers for glial cells, and neurobiologists use GFAP for targeting transgenes to glial cells. Since GFAP has also been detected in non-glial cells, we systematically analyzed GFAP expression in human and murine non-CNS tissues using a panel of anti-GFAP antibodies. In human tissues we confirm previously observed GFAP expression in Schwann cells, myoepithelial cells, and chondrocytes, and show for the first time GFAP expression in fibroblasts of epiglottic and auricular perichondrium, ligamentum flavum, and cardiac valves. In mice we show GFAP expression in Schwann cells, bone marrow stromal cells, chondrocytes, and in fibroblasts of dura mater, skull and spinal perichondrium, and periosteum, connective stroma of oral cavity, dental pulp, and cardiac valves. Anti-GFAP immunoblotting of human non-CNS tissues reveals protein bands with a molecular mass ranging between approximately 35 and approximately 42 kDa. In GFAP-v-src transgenic mice, whose oncogenic v-src transgene transforms GFAP expressing cells, non-CNS tumors originate from fibroblasts. We conclude that human and murine fibroblasts can express GFAP in vivo. The somatic distribution of GFAP expressing fibroblasts indicates origin from the neural crest. Development of non-CNS tumors from fibroblasts in GFAP-v-src mice functionally confirms GFAP expression in these cells.

Reproduction in the Noughties: will the scientists have all the fun?

The past 20-30 years have seen major advances in our understanding of human reproduction and in our ability to manipulate it, as well as major social changes in human reproductive and sexual attitudes. Many of these advances and changes developed out of the first successful in vitro fertilisation (IVF) of the human oocyte. It is also the case that 30 years ago few foresaw what was to come, and many were at best doubtful and often were very critical of the scientific work which led to human IVF and to many of the subsequent developments. This lack of foresight provides us with a lesson about the dangers that we face in looking forward and attempting to predict the future. This review will try to convey, not comprehensively but through examples, the flavour of current activities in Assisted Reproduction clinics and research laboratories around the world and what is being talked about for the future in respect of emergent patient demands and anticipated clinical needs. This clinically driven approach will form the basis for consideration of some underlying scientific aspects of reproductive research, some of the ethicolegal issues that may arise, and the implications of this anticipated future for our current approaches to medical education. The future will be considered not simply in terms of the New Reproduction itself but also in its interaction with the opportunities and challenges presented by the New Genetics. It is perhaps in the interaction between these two fields of endeavour that some of the most difficult challenges ahead lie.

Isolation of enteric glia and establishment of transformed enteroglial cell lines from the myenteric plexus of adult rat

Although enteroglial cells (EGCs) may play a key role in the inflammatory response of the enteric nervous system, little is known about their immunophysiological properties. To facilitate further characterization of enteric glia, we have developed a novel method to isolate and purify EGCs from the myenteric plexus. Myenteric plexus preparations were enzymatically dissociated and EGCs purified by complement-mediated cytolysis of contaminating cells and transformed by retroviral gene transfer. Primary and transformed cells were characterized immunohistochemically and by dot-blot analysis. Functionally, c-fos mRNA expression was assessed in primary and transformed enteroglial cells. All cells displayed robust glial fibrillary acidic protein, S-100 and vimentin immunoreactivities, but no Thy-1.1, desmin, smooth muscle alpha-actin or C3 complement receptor immunoreactivity. This confirmed their enteroglial lineage and excluded contamination with other cell types. Both primary and transformed EGCs displayed little constitutive c-fos mRNA expression. This, however, could be upregulated by various stimuli, including proinflammatory cytokines. In summary, we present a novel method to purify EGCs from rat myenteric plexus for tissue culture and to establish transformed EGC lines that retain their glial nature and functional properties. Such cell lines are now available for physiological studies of the functional properties of enteric glia in vitro.

Recent advances in inflammatory bowel disease

The last decade has seen tremendous advances in our knowledge, which has led to genuine improvements in our understanding of the pathogenesis and management of inflammatory bowel disease (IBD). The combined power of cellular and molecular biology has begun to unveil the enigmas of IBD, and, consequently, substantial gains have been made in the treatment of IBD. Refinements in drug formulation have provided the ability to target distinct sites of delivery, while enhancing the safety and efficacy of older agents. Simultaneous progress in biotechnology has fostered the development of new agents that strategically target pivotal processes in disease pathogenesis. This article addresses our current understanding of the pathogenesis of IBD, including the latest developments in animal models and covers agents currently used in the treatment of IBD as well as emerging therapies.

IL-1beta and IL-10 have dual effects on enteric glial cell proliferation

Inflammatory bowel disease is typically accompanied by functional and structural changes of the enteric nervous system. In pathological studies, cellular loss and axonal degeneration have been described in the myenteric plexus. However, more recent studies suggest that the proliferation rate of myenteric glial cells is enhanced in animal models of intestinal inflammation. Therefore, we have investigated the effect of different cytokines on the proliferative response of enteric glial cells (EGCs), comparing transformed enteric glial cell lines, primary astrocyte cultures and transformed oligodendrocytes. Cells were incubated in serum-free chemically defined medium in the presence or absence of either interleukin (IL)-1beta or IL-10 at concentrations ranging between 0.1 and 100 ng mL(-1) for 48 h. Subsequently, [3H]thymidine was added to each culture dish for an additional 6 h, and the amount of incorporated [3H] was assessed. IL-1beta significantly and dose-dependently suppressed [3H]-uptake by EGCs. In contrast, IL-10 induced a biphasic response; IL-10 at low concentrations (0.1 ng mL(-1)) caused a significant suppression of [3H]-uptake, whereas high concentrations (5-100 ng mL(-1)) significantly enhanced [3H] uptake. These results indicate that EGC proliferation can be modulated by cytokines. The differential effects of IL-1beta and IL-10 suggest that during intestinal inflammation there may be a regulatory interplay between different classes of cytokines modulating EGC proliferation.

Consequences of intestinal inflammation on the enteric nervous system: neuronal activation induced by inflammatory mediators

The ENS is responsible for the regulation and control of all gastrointestinal functions. Because of this critical role, and probably as a consequence of its remarkable plasticity, the ENS is often relatively well preserved in conditions where the architecture of the intestine is seriously disrupted, such as in IBD. There are structural and functional changes in the enteric innervation in animal models of experimental intestinal inflammation and in IBD. These include both up and down regulation of transmitter expression and the induction of new genes in enteric neurons. Using Fos expression as a surrogate marker of neuronal activation it is now well established that enteric neurons (and also enteric glia) respond to inflammation. Whether this "activation" is limited to a short-term functional response, such as increased neuronal excitability, or reflects a long-term change in some aspect of the neuronal phenotype (or both) has yet to be firmly established, but it appears that enteric neurons are highly plastic in their response to inflammation.

Inducible ablation of astrocytes shows that these cells are required for neuronal survival in the adult brain

To study the function of astrocytes in the adult brain, we have targeted the expression of E. coli nitroreductase (NTR) to the astrocytes of transgenic mice under the control of the GFAP promoter. The astrocytes expressing NTR were selectively ablated after administration of the prodrug CB1954, resulting in motor discoordination. Histological examination showed that the region most affected in the brain was the cerebellum, in which the Bergmann glia were eliminated and the granular neurons had degenerated. Specific effects were also noted on the dendrites of the Purkinje cells, and the junction between these neurons and granular layer was disrupted. Astrocyte ablation was associated with a dramatic decrease in the expression of glutamate transporters, which may account for the degeneration of granular neurons since the excitotoxic effects of glutamate result in a similar phenotype. These results provide the first evidence that astrocytes are important for the survival of neurons in the adult brain in vivo.

Herpesvirus saimiri pathogenicity enhanced by thymidine kinase of herpes simplex virus

Herpesvirus saimiri can be used as an efficient gene expression vector for human T lymphocytes and thus may allow applications in experimental leukemia therapy. We constructed recombinant viruses for the functional expression of the thymidine kinase (TK) of herpes simplex virus type 1 (HSV) as a suicide gene. These viruses reliably allowed the targeted elimination of transduced nonpermissive human T cells in vitro after the administration of ganciclovir. To test the reliability of this function under the most stringent permissive conditions, in this study we analyzed the influence of the prodrugs ganciclovir and acyclovir in common marmosets on the acute leukemogenesis induced by either wild-type herpesvirus saimiri C488 or by a recombinant derivative expressing TK of HSV. Antiviral drug treatment did not influence the rapid development of acute disease. In contrast, the presence of the HSV tk gene resulted in a faster disease progression. In addition, HSV TK-expressing viruses showed faster replication than wild-type virus in culture at low serum concentrations. Thus, HSV TK accelerates the replication of herpesvirus saimiri and enhances its pathogenicity. This should be generally considered when HSV TK is applied as a transgene in replication-competent DNA virus vectors for gene therapy.

Transgenic animal models for neuropharmacology

The establishment of novel animal models using gene targeting and transgenic technology has opened a new area of neuropharmacological research. For the first time, it became possible to alter the expression of a gene in a specific cell type of an intact animal by either overexpression, inhibition or ablation. This review describes the technology and lists the relevant tools, such as reporter genes, suicide genes, immortalizing genes, and promoters, necessary for the targeted expression of these and other genes in specific cells of the central nervous system. In addition, the problem is discussed that the mouse is the species in which this technology is by far the most developed, while the rat has been used as the model species for neuropharmacology during the last century.

Intestinal lymphoepithelial communication

The close anatomic juxtaposition of epithelial cells with lymphocytes lining the intestinal tract facilitates communication between the two cell types. This intercellular dialogue is important for mucosal development and has a conditioning effect on mucosal structure, function, and response to tissue injury. Lymphoepithelial communication is bi-directional, and mediated in large part, by shared ligands and receptors. The chemical messengers involved include cytokines, growth factors, local hormones, and products of arachidonate metabolism. The interdependency between the epithelium and adjacent lymphoid cells is such that the epithelium is considered to have a central role in the mucosal immune system and is an active participant in both the afferent and efferent limbs of the mucosal immune response. The molecular crosstalk between the epithelium and adjacent lymphocytes is just one aspect of a more complex network of intercellular signalling within the intestinal mucosa and upon which the integrity of the mucosa is dependent. Thus, there are extensive interactions between nerve and immune cells and between the enteric flora and the epithelium and amongst intestinal mesenchymal cells including fibroblasts and vascular endothelial cells. Disruption of any aspect of the mucosal microenvironment, as has been achieved with selective genetically engineered murine models, is associated with impaired mucosal defence and inflammation.

Functional long-term thymidine kinase suicide gene expression in human T cells using a herpesvirus saimiri vector

Herpesvirus saimiri transforms human T lymphocytes to stable growth and persists episomally without genomic integration and without virus production. The transformed T cells retain essential features of their parental cells including the MHC-restricted antigen specificity which may be useful for applications in adoptive immunotherapy. In order to improve the biological safety of such vectors, the prodrug activating gene thymidine kinase of herpes simplex virus was inserted into the genome of herpesvirus saimiri by homologous recombination. After infection with wild-type or cloned recombinant viruses, T cells from tamarin monkeys and from humans were transformed to stable growth. Thymidine kinase-expressing transformed T cells were efficiently eliminated in the presence of low concentrations of ganciclovir. This elimination mechanism remained fully functional over an observation period of 12 months. The potentially immunogenic neomycin resistance gene expression cassette was deleted from the genome of established mutant viruses by using the prokaryotic Cre/LoxP recombination system. At any time during the course of a therapeutic application, thymidine kinase-expressing transformed human T cells might be eliminated after administration of ganciclovir. In principle, this function could be useful for the T cell-dependent immunotherapy of resistant blood cancer while avoiding the risk of uncontrolled graft-versus-host disease.

Ninjurin2, a novel homophilic adhesion molecule, is expressed in mature sensory and enteric neurons and promotes neurite outgrowth

A large number of cell adhesion molecules mediate cell-to-cell and cell-to-extracellular matrix interaction during development, differentiation and regeneration of the peripheral nervous system. Here, we report the identification of a novel cell surface adhesion molecule, ninjurin2 (for nerve injury induced protein 2). Ninjurin2 is a homolog of a homophilic cellular adhesion molecule, ninjurin1, that was previously isolated as a gene induced in Schwann cells after nerve injury. Ninjurin1 and 2 share conserved hydrophobic regions for their transmembrane domains; however, they do not contain comparable adhesion motifs nor do they interact with each other. In the peripheral nervous system, ninjurin2 is expressed constitutively in mature sensory and enteric neurons but not in glial cells or in autonomic ganglia. Ninjurin2 is upregulated in Schwann cells surrounding the distal segment of injured nerve with a time course similar to that of ninjurin1, neural CAM, and L1. Ninjurin2 promotes neurite outgrowth from primary cultured dorsal root ganglion neurons, presumably via homophilic cellular interactions. Ninjurin2 is also highly expressed in hematopoietic and lymphatic tissues. Finally, the ninjurin2 gene is located on human chromosome 12p13 in which several disorders of unknown etiology have been mapped, including inflammatory bowel disease and acrocallosal syndrome.

Glia maintain follower neuron survival during Drosophila CNS development

While survival of CNS neurons appears to depend on multiple neuronal and non-neuronal factors, it remains largely unknown how neuronal survival is controlled during development. Here we show that glia regulate neuronal survival during formation of the Drosophila embryonic CNS. When glial function is impaired either by mutation of the glial cells missing gene, which transforms glia toward a neuronal fate, or by targeted genetic glial ablation, neuronal death is induced non-autonomously. Pioneer neurons, which establish the first longitudinal axon fascicles, are insensitive to glial depletion whereas the later extending follower neurons die. This differential requirement of neurons for glia is instructive in patterning and links control of cell number with axon guidance during CNS development.

Animal models of mucosal inflammation and their relation to human inflammatory bowel disease

Animal models of inflammatory bowel disease (IBD) have been useful in the identification of those immune responses uniquely involved in IBD pathogenesis and in defining the important roles of environmental influences, such as normal luminal bacterial flora and the genetic composition of the host, in modifying IBD-associated inflammation. Recent studies have focused particular attention on CD4+ T cells which produce excessive quantities either of Th1 cytokines (IFN-gamma and TNF) directed by IL-12 or of a Th2 cytokine (IL-4), relative to the production of suppressive cytokines such as IL-10 and transforming growth factor beta. Such insights will be extremely beneficial in the development of novel approaches to the control of IBD-type inflammation, such as the use of anticytokine therapies and gene therapy, and finally, in the identification of the genetic abnormalities and the antigens driving the inflammation that underlies the human disease.

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.