Regional gastrointestinal contractility parameters using the wireless motility capsule: inter-observer reproducibility and influence of age, gender and study country.

BACKGROUND: The wireless motility capsule concurrently measures temperature, pH and pressure as it traverses the gastrointestinal tract. AIMS: To describe normative values for motility/contractility parameters across age, gender and testing centres. METHODS: Healthy participants underwent a standardised wireless motility capsule assessment following an overnight fast and consumption of a meal of known nutritional content. Traces were divided into regions of interest and analysed using 2 software packages (MotiliGI and GIMS Data Viewer). Inter-observer agreement was independently assessed by 2 investigators. RESULTS: Normative data for motility/contractility parameters (maximum amplitude, mean peak amplitude, contraction frequency and motility index) are presented for 107 individuals (62 male, median age 40 years, range 18-78). MotiliGI-Gastric, small bowel and colonic maximal contraction amplitude correlated with age (r = .24, P = .01; r = .22, P = .02; and r = .2, P = .04 respectively). Small bowel motility index was higher in females than males (150.4 ± 12 vs 122 ± 7.6, P = .04). Inter-observer agreement was excellent for transit times, pH and contractility/motility parameters. GIMS Data viewer-Gastric, small bowel and colonic loge motility index correlated with the respective area under the contraction curve, total contractions, sum of amplitudes and contraction frequency (all r>.35, P < .0003) but not with transit times. CONCLUSIONS: Our analysis provides normative data for motility/contractility parameters. Log motility index summarises a number of measures. In future, the measurement of contractile activity with the wireless motility capsule may potentially aid in the diagnosis of disease states such as visceral myopathic disorders.

Social networking sites: a novel portal for communication.

BACKGROUND: The internet has transformed many spheres of society. Most notably the advent of social networking websites, such as MySpace, Bebo and Facebook, have attracted many millions of users worldwide. There are over 350 such sites in operation across the internet. There is a paucity of data in the adult literature examining the medical usage of this interesting facet of modern life. AIMS: To ascertain whether Facebook has user groups that are connected with common medical conditions, and to classify the user groups that were identified as well as enumerating the number of individual users contained therein. METHODS: We conducted a search of the entire Facebook website between December 2007 and January 2009. We used medical and lay nomenclature for the most prevalent non-communicable diseases as identified from the World Health Organisation Burden of Disease publication to identify whether they were represented among individual Facebook users and user groups. RESULTS: We identified 290,962 individual users who were part of 757 groups. Patient groups accounted for 47.4%, patient/carer support groups 28.1%, fund raising groups 18.6%, and others 5.8%. Notably, there were other groups containing representations from the scientific research community in addition to educational resources. The groups with the most individual members pertained to malignant neoplasms and cardiovascular disease (141,458 users) consistent with their worldwide prevalence. CONCLUSIONS: Facebook is providing a readily accessible portal for patients, carers and healthcare professionals to share their experiences of investigation, diagnosis and management of disease. Furthermore, this technology is being used for research, education and fundraising. Further research is warranted to explore the further potential of this new technology.

Age-related changes underlie switch in netrin-1 responsiveness as growth cones advance along visual pathway.

Retinal axons are led out of the eye by netrin-1, an attractive guidance cue which is secreted at the optic nerve head. In the optic pathway, however, netrin-1 is expressed in areas that exclude retinal axon growth. This suggests that axons may change in their responsiveness to netrin-1 as they advance along the pathway. Indeed, in our 'whole-pathway' preparation in Xenopus, a gradual change from attraction to repulsion occurred as retinal axons emerged from progressively distal points along the pathway. We also found that axons that were aged in culture without pathway experience underwent a similar change, which correlated with a decline in cyclic AMP (cAMP) and netrin-1 receptor expression. Cyclic AMP elevators and adenosine A2b receptor agonists rejuvenated the behavior of old growth cones, causing them to regain attraction to netrin-1, whereas antagonists caused young growth cones to be repelled. These findings show that netrin-1 responsiveness is developmentally regulated and suggest that intrinsic changes that lower cAMP levels underlie this regulation.

Receptor protein tyrosine phosphatases regulate retinal ganglion cell axon outgrowth in the developing Xenopus visual system.

Receptor protein tyrosine phosphatases (RPTPs) are regulators of axon outgrowth and guidance in a variety of different vertebrate and invertebrate systems. Three RPTPs, CRYP-alpha, PTP-delta, and LAR, are expressed in overlapping but distinct patterns in the developing Xenopus retina, including expression in retinal ganglion cells (RGCs) as they send axons to the tectum (Johnson KG, Holt CE. 2000. Expression of CRYP-alpha, LAR, PTP-delta, and PTP-rho in the developing Xenopus visual system. Mech Dev 92:291-294). In order to examine the role of these RPTPs in visual system development, putative dominant negative RPTP mutants (CS-CRYP-alpha, CS-PTP-delta, and CS-LAR) were expressed either singly or in combination in retinal cells. No effect was found on either retinal cell fate determination or on gross RGC axon guidance to the tectum. However, expression of these CS-RPTP constructs differentially affected the rate of RGC axon outgrowth. In vivo, expression of all three CS-RPTPs or CS-PTP-delta alone inhibited RGC axon outgrowth, while CS-LAR and CS-CRYP-alpha had no significant effect. In vitro, expression of CS-CRYP-alpha enhanced neurite outgrowth, while CS-PTP-delta inhibited neurite outgrowth in a substrate-dependent manner. This study provides the first in vivo evidence that RPTPs regulate retinal axon outgrowth.

Semaphorin 3A elicits stage-dependent collapse, turning, and branching in Xenopus retinal growth cones.

The semaphorin receptor, neuropilin-1 (NP-1), was first identified in Xenopus as the A5 antigen and is expressed abundantly in developing retinal ganglion cells (RGCs). Here we show that growth cones acquire responsiveness to semaphorin 3A (Sema 3A) with age and that the onset of responsiveness correlates with the appearance of NP-1 immunoreactivity. Growth cones from "old" (stage 35/36) retinal explants collapse rapidly (5-10 min) in response to Sema 3A and turn away from a gradient of Sema 3A, whereas "young" growth cones (stage 24) are insensitive to Sema 3A. Moreover, transfection of full-length NP-1 into young neurons confers premature Sema 3A sensitivity. When young neurons are aged in culture they develop Sema 3A sensitivity in parallel with those in vivo, suggesting that an intrinsic mechanism of NP-1 regulation mediates this age-dependent change. Sema 3A-induced collapse is transient, and after recovery approximately 30% of growth cones extend new branches within 1 hr, implicating Sema 3A as a branching factor. Pharmacological inhibitors were used to investigate whether these three Sema 3A-induced behaviors (collapse, turning, and branching) use distinct second messenger signaling pathways. All three behaviors were found to be mediated via cGMP. In situ hybridization shows that Sema 3A is expressed in the tectum and at the anterior boundary of the optic tract where axons bend caudally, suggesting that Sema 3A/NP-1 interactions play a role in guiding axons in the optic tract and in stimulating terminal branching in the tectum.

Xenopus Sprouty2 inhibits FGF-mediated gastrulation movements but does not affect mesoderm induction and patterning.

Signal transduction through the FGF receptor is essential for the specification of the vertebrate body plan. Blocking the FGF pathway in early Xenopus embryos inhibits mesoderm induction and results in truncation of the anterior-posterior axis. The Drosophila gene sprouty encodes an antagonist of FGF signaling, which is transcriptionally induced by the pathway, but whose molecular functions are poorly characterized. We have cloned Xenopus sprouty2 and show that it is expressed in a similar pattern to known FGFs and is dependent on the FGF/Ras/MAPK pathway for its expression. Overexpression of Xsprouty2 in both embryos and explant assays results in the inhibition of the cell movements of convergent extension. Although blocking FGF/Ras/MAPK signaling leads to an inhibition of mesodermal gene expression, these markers are unaffected by Xsprouty2, indicating that mesoderm induction and patterning occurs normally in these embryos. Finally, using Xenopus oocytes we show that Xsprouty2 is an intracellular antagonist of FGF-dependent calcium signaling. These results provide evidence for at least two distinct FGF-dependent signal transduction pathways: a Sprouty-insensitive Ras/MAPK pathway required for the transcription of most mesodermal genes, and a Sprouty-sensitive pathway required for coordination of cellular morphogenesis.

Control of retinal growth and axon divergence at the chiasm: lessons from Xenopus.

Metamorphosis in frogs is a critical developmental process through which a tadpole changes into an adult froglet. Metamorphic changes include external morphological transformations as well as important changes in the wiring of sensory organs and central nervous system. This review aims to provide an overview on the events that occur in the visual system of metamorphosing amphibians and to discuss recent studies that provide new insight into the molecular mechanisms that control changes in the retinal growth pattern as well as the formation of new axonal pathways in the central nervous system. BioEssays 23:319-326, 2001.

Chemotropic responses of retinal growth cones mediated by rapid local protein synthesis and degradation.

Growth cones contain mRNAs, translation machinery, and, as we report here, protein degradation machinery. We show that isolated retinal growth cones immediately lose their ability to turn in a chemotropic gradient of netrin-1 or Sema3A when translation is inhibited. Translation inhibition also prevents Sema3A-induced collapse, while LPA-induced collapse is not affected. Inhibition of proteasome function blocks responses to netrin-1 and LPA but does not affect Sema3A responses. We further demonstrate in isolated growth cones that netrin-1 and Sema3A activate translation initiation factors and stimulate a marked rise in protein synthesis within minutes, while netrin-1 and LPA elicit similar rises in ubiquitin-protein conjugates. These results suggest that guidance molecules steer axon growth by triggering rapid local changes in protein levels in growth cones.

The multiple decisions made by growth cones of RGCs as they navigate from the retina to the tectum in Xenopus embryos.

Retinal ganglion cells (RGCs) of Xenopus laevis send axons along a stereospecific pathway from the retina to their target the optic tectum. Viewed from the point of the growth cone, this journey is reflected by discrete processes of axon initiation, axon outgrowth, navigation, target recognition, and innervation. These processes are characterised by distinct signalling mechanisms that trigger dynamic changes in growth cone morphology and behavior. Here we review work primarily from our laboratory, examining these events from a cellular and molecular perspective, focusing on the roles of FGFs, netrins, receptors, and intracellular effectors.

Ephrin-B regulates the Ipsilateral routing of retinal axons at the optic chiasm.

In Xenopus tadpoles, all retinal ganglion cells (RGCs) send axons contralaterally across the optic chiasm. At metamorphosis, a subpopulation of EphB-expressing RGCs in the ventrotemporal retina begin to project ipsilaterally. However, when these metamorphic RGCs are grafted into embryos, they project contralaterally, suggesting that the embryonic chiasm lacks signals that guide axons ipsilaterally. Ephrin-B is expressed discretely at the chiasm of metamorphic but not premetamorphic Xenopus. When expressed prematurely in the embryonic chiasm, ephrin-B causes precocious ipsilateral projections from the EphB-expressing RGCs. Ephrin-B is also found in the chiasm of mammals, which have ipsilateral projections, but not in the chiasm of fish and birds, which do not. These results suggest that ephrin-B/EphB interactions play a key role in the sorting of axons at the vertebrate chiasm.

Expression of CRYP-alpha, LAR, PTP-delta, and PTP-rho in the developing Xenopus visual system.

Receptor protein tyrosine phosphatases (RPTPs), are involved in axon outgrowth and guidance not only in the Drosophila visual system (Garrity et al., 1999. Neuron 22, 707-717) but also in the developing vertebrate retina (Ledig et al., 1999a. J. Cell Biol. 147, 375-388). We have cloned a variety of Xenopus RPTPs, including four RPTPs expressed in the developing visual system (LAR, PTP-delta, CRYP-alpha and PTP-rho). These four RPTPs are transcribed in the developing optic vesicle during differentiation and in overlapping but distinct patterns in the developing retina during retinal layer formation. LAR, PTP-delta, and CRYP-alpha are also expressed in retinal ganglion cells during axonogenesis and during axon guidance from the retina to the optic tectum.

p27Xic1, a Cdk inhibitor, promotes the determination of glial cells in Xenopus retina.

p27Xic1, a member of the Cip/Kip family of Cdk inhibitors, besides its known function of inhibiting cell division, induces Müller glia from retinoblasts. This novel gliogenic function of p27Xic1 is mediated by part of the N-terminal domain near but distinct from the region that inhibits cyclin-dependent kinases. Cotransfections with dominant-negative and constitutively active Delta and Notch constructs indicate that the gliogenic effects of p27Xic1 work within the context of an active Notch pathway. The gradual increase of p27Xic1 in the developing retina thus not only limits the number of retinal cells but also increasingly favors the fate of the last cell type to be born in the retina, the Müller glia.

The neuronal architecture of Xenopus retinal ganglion cells is sculpted by rho-family GTPases in vivo.

Dendritogenesis, axonogenesis, pathfinding, and target recognition are all affected in distinct ways when Xenopus retinal ganglion cells (RGCs) are transfected with constitutively active (ca), wild-type (wt), and dominant negative (dn) Rho-family GTPases in vivo. Dendritogenesis required Rac1 and Cdc42 activity. Moreover, ca-Rac1 caused dendrite hyperproliferation. Axonogenesis, in contrast, was inhibited by ca-Rac1. This phenotype was partially rescued by the coexpression of dn cyclin-dependent kinase (Cdk5), a proposed effector of Rac1, suggesting that Rac1 activity must be regulated tightly for normal axonogenesis. Growth cone morphology was particularly sensitive to dn-RhoA and wt-Cdc42 constructs. These also caused targeting errors, such as tectal bypass, suggesting that cytoskeletal rearrangements are involved in target recognition and are transduced by these pathways.

Fibroblast growth factor receptor signaling in Xenopus retinal axon extension.

Fibroblast growth factor receptors (FGFRs) and N-cadherin both regulate axon extension in developing Xenopus retinal ganglion cells (RGCs). Cultured cerebellar neurons have been shown to require FGFR activity for N-cadherin-stimulated neurite outgrowth, raising the possibility that N-cadherin is a FGFR ligand. To investigate this possibility in the developing visual system, retinal neurons were transfected with a dominant-negative FGFR (XFD) and plated on purified N-cadherin substrates. XFD-expressing neurons extended markedly shorter processes than control GFP-expressing neurons, implicating a role for FGFRs in N-cadherin-stimulated neurite outgrowth. To examine whether N-cadherin and FGFRs share the same pathway or use distinct second messenger pathways, specific inhibitors of implicated signaling molecules were added to neurons stimulated by N-cadherin, basic fibroblast growth factor (bFGF), or brain-derived nerve factor (BDNF) (which stimulates RGC outgrowth by a FGFR-independent mechanism). Diacylglycerol (DAG) lipase and Ca2+/calmodulin kinase II inhibitors both significantly reduced outgrowth stimulated by N-cadherin or bFGF but not by BDNF. Furthermore, we show that inhibiting DAG lipase activity in RGC axons extending in vivo toward the optic tectum reversibly slows axon extension without collapsing their growth cones. Thus, a common second-messenger signaling pathway mediating both N-cadherin- and bFGF-stimulated neurite extension is consistent with a model in which N-cadherin directly modulates the FGFR or a model whereby both FGFR and N-cadherin regulate the same second-messenger system.

Chondroitin sulfates modulate axon guidance in embryonic Xenopus brain.

Chondroitin sulfate proteoglycans display both inhibitory and stimulatory effects on cell adhesion and neurite outgrowth in vitro. The functional activity of these proteoglycans appears to be context specific and dependent on the presence of different chondroitin sulfate-binding molecules. Little is known about the role of chondroitin sulfate proteoglycans in the growth and guidance of axons in vivo. To address this question, we examined the effects of exogenous soluble chondroitin sulfates on the growth and guidance of axons arising from a subpopulation of neurons in the vertebrate brain which express NOC-2, a novel glycoform of the neural cell adhesion molecule N-CAM. Intact brains of stage 28 Xenopus embryos were unilaterally exposed to medium containing soluble exogenous chondroitin sulfates. When exposed to chondroitin sulfate, NOC-2(+) axons within the tract of the postoptic commissure failed to follow their normal trajectory across the ventral midline via the ventral commissure in the midbrain. Instead, these axons either stalled or grew into the dorsal midbrain or continued growing longitudinally within the ventral longitudinal tract. These findings suggest that chondroitin sulfate proteoglycans indirectly modulate the growth and guidance of a subpopulation of forebrain axons by regulating either matrix-bound or cell surface cues at specific choice points within the developing vertebrate brain.

A critical window for cooperation and competition among developing retinotectal synapses.

In the developing frog visual system, topographic refinement of the retinotectal projection depends on electrical activity. In vivo whole-cell recording from developing Xenopus tectal neurons shows that convergent retinotectal synapses undergo activity-dependent cooperation and competition following correlated pre- and postsynaptic spiking within a narrow time window. Synaptic inputs activated repetitively within 20 ms before spiking of the tectal neuron become potentiated, whereas subthreshold inputs activated within 20 ms after spiking become depressed. Thus both the initial synaptic strength and the temporal order of activation are critical for heterosynaptic interactions among convergent synaptic inputs during activity-dependent refinement of developing neural networks.

A role for the fibroblast growth factor receptor in cell fate decisions in the developing vertebrate retina.

The mature vertebrate retina contains seven major cell types that develop from an apparently homogenous population of precursor cells. Clonal analyses have suggested that environmental influences play a major role in specifying retinal cell identity. Fibroblast growth factor-2 is present in the developing retina and regulates the survival, proliferation and differentiation of developing retinal cells in culture. Here we have tested whether fibroblast growth factor receptor signaling biases retinal cell fate decisions in vivo. Fibroblast growth factor receptors were inhibited in retinal precursors in Xenopus embryos by expressing a dominant negative form of the receptor, XFD. Dorsal animal blastomeres that give rise to the retina were injected with cDNA expression constructs for XFD and a control non-functional mutant receptor, D48, and the cell fates of transgene-expressing cells in the mature retina determined. Fibroblast growth factor receptor blockade results in almost a 50% loss of photoreceptors and amacrine cells, and a concurrent 3.5-fold increase in Müller glia, suggesting a shift towards a Müller cell fate in the absence of a fibroblast growth factor receptor signal. Inhibition of non-fibroblast-growth-factor-mediated receptor signaling with a third mutant receptor, HAVO, alters cell fate in an opposite manner. These results suggest that it is the balance of fibroblast growth factor and non-fibroblast growth factor ligand signals that influences retinal cell genesis.

Target selection: invasion, mapping and cell choice.

Recent research has shown that changes in the concentration of particular molecules lead axons to invade their target, and that concentration changes in other molecules at the borders of the target prevent axons from leaving the target area. After invasion, topographic and lamina-specific cues guide axons to the correct location within the target field. At the level of a single cell or part of a cell, the evidence raises the possibility that axon targeting might be a combinatorial affair whereby specific axons compare the relative concentrations of several molecules on the surface of postsynaptic cells in order to choose a particular target. Both proteins and carbohydrates of various classes play major roles in these processes.