Control of neurite growth and guidance by an inhibitory cell-body signal

The development of a functional nervous system requires tight control of neurite growth and guidance by extracellular chemical cues. Neurite growth is astonishingly sensitive to shallow concentration gradients, but a widely observed feature of both growth and guidance regulation, with important consequences for development and regeneration, is that both are only elicited over the same relatively narrow range of concentrations. Here we show that all these phenomena can be explained within one theoretical framework. We first test long-standing explanations for the suppression of the trophic effects of nerve growth factor at high concentrations, and find they are contradicted by experiment. Instead we propose a new hypothesis involving inhibitory signalling among the cell bodies, and then extend this hypothesis to show how both growth and guidance can be understood in terms of a common underlying signalling mechanism. This new model for the first time unifies several key features of neurite growth regulation, quantitatively explains many aspects of experimental data, and makes new predictions about unknown details of developmental signalling

The dynamics of growth cone morphology

Background: Normal brain function depends on the development of appropriate patterns of neural connections. A critical role in guiding axons to their targets during neural development is played by neuronal growth cones. These have a complex and rapidly changing morphology; however, a quantitative understanding of this morphology, its dynamics and how these are related to growth cone movement, is lacking

Retinal pattern and the genetic basis of its formation in zebrafish

The vertebrate nervous system contains an immense diversity of distinct cellular components that are organized into precise spatial patterns. The importance of accurate neuronal architecture is particularly obvious in the retina, where it is necessary for the formation of visual images. The retina is structured in a distinct layered pattern that is remarkably conserved in evolution, including phyla as diverse as primates and teleost fish. Genetic analysis in zebrafish reveals mechanisms that are essential for the formation of this architecture

A dual compartment diffusion chamber for studying axonal chemotaxis in 3D collagen

During nervous system development growing axons are often guided by diffusible chemical gradients. An important contribution to our understanding of the mechanisms involved in this process has been made by in vitro assays. However, an inexpensive and simple assay which allows the establishment of stable and reproducible gradients in a 3D collagen environment has been lacking. Here we present a simple two-compartment diffusion chamber for this purpose. We show that gradient steepnesses of up to 2% are achieved within 1. h post setup, and a gradient persists for at least 2 days. We demonstrate the assay by showing robust chemoattraction of dorsal root ganglion neurites by gradients of nerve growth factor (NGF), and chemorepulsion of olfactory bulb neurites by gradients of Slit2

Calcium signaling in axon guidance

Guidance of axons to their targets in the developing nervous system requires a myriad of downstream signaling molecules to coordinate growth cone movement. One of the most important of these is calcium, and over the past few years many new insights have been gained into the role of calcium in axon guidance. In this review we focus on mechanisms of calcium entry into the growth cone and its downstream effects on both growth cone motility and turning. We particularly highlight the role of calcium concentrations in determining attractive versus repulsive responses to graded guidance cues, and their role in guidance by the morphogen Wnt5a

The response of dorsal root ganglion axons to nerve growth factor gradients depends on spinal level

Directed sensory axon regeneration has the potential to promote functional recovery after peripheral nerve injury. Using a novel guidance assay to generate precisely controllable nerve growth factor gradients, we show for the first time that the guidance and outgrowth response of rat dorsal root ganglion neurons to identical nerve growth factor gradients depends on the rostrocaudal origin of the dorsal root ganglion explant. These findings have implications for the study of peripheral nerve regeneration in response to exogenous neurotrophins such as nerve growth factor, and provide new insight into the clinical potential of nerve growth factor in the treatment of nerve injury. Copyright 2010, Mary Ann Liebert, Inc

Identification of bone morphogenetic proteins 2 and 4 in commercial demineralized freeze-dried bone allograft preparations: pilot study

BACKGROUND: Demineralized freeze-dried bone allografts (DFDBAs) have been proposed as a useful adjunct in periodontal therapy to induce periodontal regeneration through the induction of new bone formation. The presence of bone morphogenetic proteins (BMPs) within the demineralized matrix has been proposed as a possible mechanism through which DFDBA may exert its biologic effect. However, in recent years, the predictability of results using DFDBA has been variable and has led to its use being questioned. One reason for the variability in tissue response may be attributed to differences in the processing of DFDBA, which may lead to loss of activity of any bioactive substances within the DFDBA matrix. Therefore, the purpose of this investigation was to determine whether there are detectable levels of bone morphogenetic proteins in commercial DFDBA preparations. METHODS: A single preparation of DFDBA was obtained from three commercial sources. Each preparation was studied in triplicate. Proteins within the DFDBA samples were first extracted with 4M guanidinium HCI for seven days at 40 degrees celsius and the residue was further extracted with 4M guanidinium HCL/EDTA for seven days at 40 degrees celsius. Two anti-human BMP-2 and -4 antibodies were used for the detection of the presence of BMP's in the extracts. RESULTS: Neither BMP-2 nor BMP-4 was detected in any of the extracts. When recombinant human BMP-2 and -4 were added throughout the extraction process of DFDBA extraction, not only were intact proteins detected but smaller molecular weight fragments were also noted in the extract. CONCLUSIONS: These results indicate that all of the DFDBA samples tested had no detectable amounts of BMP-2 and -4. In addition, an unknown substance present in the DFDBA may be responsible for degradation of whatever BMPs might be present

DISCOVERY OF AN UNLISTED DOME NEAR HORTENSIUS E, located at 25.17º W and 6.07º N

The GLR Group has an ongoing project to discover lunar domes. Our activity has shown both the elusive nature of these volcanic structures and the usefulness of ground-based CCD imaging and digital image analysis in the elucidation of their character [1-2]. In a previous paper [3], some of us described a highland dome located near the crater T. Mayer B. Moreover, we reported some images of the very well known Milichius region, where two lunar cones were detected [3]. A study about these two lunar cones located near the crater Milichius will be published in a forthcoming issue of Selenology, the Journal of the American Lunar Society [4]. In another recent paper, some of us described a study about the well known Milichius dome: the average slope angle of Milichius is 2.72 ° and the summit of the dome was measured to be (211 ± 10) m higher than the surrounding plain [5]. These results strongly suggest that previous estimates of Milichius height were incorrect [6]. Furthermore, some of us recently described another dome located near the crater Vendelinus, investigating its slope and height [7]. The dome field near crater Hortensius has been extensively studied. The ALPO Lunar Dome list reports several low domes in this region, as visible also in our revised lunar dome maps [8]. North of Hortensius there is a group of six well known domes, 6 to 8 km wide, termed “Schlumberge