The Experts below are selected from a list of 216 Experts worldwide ranked by ideXlab platform

Francisco J Alvarez - One of the best experts on this subject based on the ideXlab platform.

  • Role of primary afferents in the developmental regulation of motor axon synapse numbers on Renshaw cells
    The Journal of Comparative Neurology, 2016
    Co-Authors: Valerie C. Siembab, Travis M Rotterman, Laura Gomez-perez, Neil A Shneider, Francisco J Alvarez
    Abstract:

    : Motor function in mammalian species depends on the maturation of spinal circuits formed by a large variety of interneurons that regulate motoneuron firing and motor output. Interneuron activity is in turn modulated by the organization of their synaptic inputs, but the principles governing the development of specific synaptic architectures unique to each premotor interneuron are unknown. For example, Renshaw cells receive, at least in the neonate, convergent inputs from sensory afferents (likely Ia) and motor axons, raising the question of whether they interact during Renshaw cell development. In other well-studied neurons, such as Purkinje cells, heterosynaptic competition between inputs from different sources shapes synaptic organization. To examine the possibility that sensory afferents modulate synaptic maturation on developing Renshaw cells, we used three animal models in which afferent inputs in the ventral horn are dramatically reduced (ER81(-/-) knockout), weakened (Egr3(-/-) knockout), or strengthened (mlcNT3(+/-) transgenic). We demonstrate that increasing the strength of sensory inputs on Renshaw cells prevents their deselection and reduces motor axon synaptic density, and, in contrast, absent or diminished sensory afferent inputs correlate with increased densities of motor axons synapses. No effects were observed on other glutamatergic inputs. We conclude that the early strength of Ia synapses influences their maintenance or weakening during later development and that heterosynaptic influences from sensory synapses during early development regulates the density and organization of motor inputs on mature Renshaw cells.

  • alterations in the motor neuron renshaw cell circuit in the sod1g93a mouse model
    The Journal of Comparative Neurology, 2013
    Co-Authors: Hanna Wootz, Anders Enjin, Martin Larhammar, Eileen Fitzsimonskantamneni, Travis M Rotterman, Elodie Andre, Kalicharan Patra, Klas Kullander, Brigitte Van Zundert, Francisco J Alvarez
    Abstract:

    : Motor neurons become hyperexcitable during progression of amyotrophic lateral sclerosis (ALS). This abnormal firing behavior has been explained by changes in their membrane properties, but more recently it has been suggested that changes in premotor circuits may also contribute to this abnormal activity. The specific circuits that may be altered during development of ALS have not been investigated. Here we examined the Renshaw cell recurrent circuit that exerts inhibitory feedback control on motor neuron firing. Using two markers for Renshaw cells (calbindin and cholinergic nicotinic receptor subunit alpha2 [Chrna2]), two general markers for motor neurons (NeuN and vesicular acethylcholine transporter [VAChT]), and two markers for fast motor neurons (Chondrolectin and calcitonin-related polypeptide alpha [Calca]), we analyzed the survival and connectivity of these cells during disease progression in the Sod1(G93A) mouse model. Most calbindin-immunoreactive (IR) Renshaw cells survive to end stage but downregulate postsynaptic Chrna2 in presymptomatic animals. In motor neurons, some markers are downregulated early (NeuN, VAChT, Chondrolectin) and others at end stage (Calca). Early downregulation of presynaptic VAChT and Chrna2 was correlated with disconnection from Renshaw cells as well as major structural abnormalities of motor axon synapses inside the spinal cord. Renshaw cell synapses on motor neurons underwent more complex changes, including transitional sprouting preferentially over remaining NeuN-IR motor neurons. We conclude that the loss of presynaptic motor axon input on Renshaw cells occurs at early stages of ALS and disconnects the recurrent inhibitory circuit, presumably resulting in diminished control of motor neuron firing. J. Comp. Neurol. 521:1449-1469, 2013. © 2012 Wiley Periodicals, Inc.

  • Principles of interneuron development learned from Renshaw cells and the motoneuron recurrent inhibitory circuit
    Annals of the New York Academy of Sciences, 2013
    Co-Authors: Francisco J Alvarez, Ana Benito-gonzalez, Valerie C. Siembab
    Abstract:

    Renshaw cells provide a convenient model to study spinal circuit development during the emergence of motor behaviors with the goal of capturing principles of interneuron specification and circuit construction. This work is facilitated by a long history of research that generated essential knowledge about the characteristics that define Renshaw cells and the recurrent inhibitory circuit they form with motoneurons. In this review, we summarize recent data on the specification of Renshaw cells and their connections. A major insight from these studies is that the basic Renshaw cell phenotype is specified before circuit assembly, a result of their early neurogenesis and migration. Connectivity is later added, constrained by their placement in the spinal cord. Finally, different rates of synapse proliferation alter the relative weights of different inputs on postnatal Renshaw cells. Based on this work some general principles on the integration of spinal interneurons in developing motor circuits are derived.

  • the continuing case for the renshaw cell
    The Journal of Physiology, 2007
    Co-Authors: Francisco J Alvarez, Robert E.w. Fyffe
    Abstract:

    Renshaw cell properties have been studied extensively for over 50 years, making them a uniquely well-defined class of spinal interneuron. Recent work has revealed novel ways to identify Renshaw cells in situ and this in turn has promoted a range of studies that have determined their ontogeny and organization of synaptic inputs in unprecedented detail. In this review we illustrate how mature Renshaw cell properties and connectivity arise through a combination of activity-dependent and genetically specified mechanisms. These new insights should aid the development of experimental strategies to manipulate Renshaw cells in spinal circuits and clarify their role in modulating motor output.

  • Primary afferent synapses on developing and adult Renshaw cells.
    The Journal of Neuroscience, 2006
    Co-Authors: George Z Mentis, Valerie C. Siembab, Ricardo Zerda, Michael J. O'donovan, Francisco J Alvarez
    Abstract:

    The mechanisms that diversify adult interneurons from a few pools of embryonic neurons are unknown. Renshaw cells, Ia inhibitory interneurons (IaINs), and possibly other types of mammalian spinal interneurons have common embryonic origins within the V1 group. However, in contrast to IaINs and other V1-derived interneurons, adult Renshaw cells receive motor axon synapses and lack proprioceptive inputs. Here, we investigated how this specific pattern of connectivity emerges during the development of Renshaw cells. Tract tracing and immunocytochemical markers [parvalbumin and vesicular glutamate transporter 1 (VGLUT1)] showed that most embryonic (embryonic day 18) Renshaw cells lack dorsal root inputs, but more than half received dorsal root synapses by postnatal day 0 (P0) and this input spread to all Renshaw cells by P10–P15. Electrophysiological recordings in neonates indicated that this input is functional and evokes Renshaw cell firing. VGLUT1-IR bouton density on Renshaw cells increased until P15 but thereafter decreased because of limited synapse proliferation coupled with the enlargement of Renshaw cell dendrites. In parallel, Renshaw cell postsynaptic densities apposed to VGLUT1-IR synapses became smaller in adult compared with P15. In contrast, vesicular acetylcholine transporter-IR motor axon synapses contact embryonic Renshaw cells and proliferate postnatally matching Renshaw cell growth. Like other V1 neurons, Renshaw cells are thus competent to receive sensory synapses. However, after P15, these sensory inputs appear deselected through arrested proliferation and synapse weakening. Thus, Renshaw cells shift from integrating sensory and motor inputs in neonates to predominantly motor inputs in adult. Similar synaptic weight shifts on interneurons may be involved in the maturation of motor reflexes and locomotor circuitry.

Hong Rong-jing - One of the best experts on this subject based on the ideXlab platform.

Uwe Windhorst - One of the best experts on this subject based on the ideXlab platform.

  • renshaw cell responses to intra arterial injection of muscle metabolites into cat calf muscles
    Neuroscience Research, 1997
    Co-Authors: Uwe Windhorst, J Meyerlohmann, Dov Kirmayer, Douglas W. Zochodne
    Abstract:

    Abstract Metabolites released during fatiguing muscle contractions excite group III–IV muscle afferents which might inhibit skeleto-motoneuron firing, hypothetically via Renshaw cells. This was tested, in decerebrated, spinalized cats, by recording changes in Renshaw cell spontaneous discharges and responses to antidromic electrical stimulation of motor axons when small-diameter calf muscle afferents were excited by intra-arterially injected bradykinin, serotonin, lactic acid and KCl. Whenever such injections had an effect, it transiently raised or lowered the spontaneous firing rate and almost always decreased the antidromic response to motor axon stimulation. Injection of bradykinin and serotonin commonly decreased the blood pressure and concomitantly the spinal blood flow (as measured using laser Doppler flowmetry), which could have indirectly influenced Renshaw cell firing. But in general, blood pressure and flow changed after the Renshaw cell discharge did, which thus, appears to be modulated independently by group III–IV afferents. These results suggest that the Renshaw cell-mediated effects of neurochemically excited afferents would predominantly disinhibit rather than inhibit motoneurons.

Panagiotis Michaleris - One of the best experts on this subject based on the ideXlab platform.

  • Comparisons of laser powder bed fusion additive manufacturing builds through experimental in situ distortion and temperature measurements
    Additive Manufacturing, 2017
    Co-Authors: Alexander Jay Dunbar, Erik R Denlinger, Michael F. Gouge, Timothy W. Simpson, Panagiotis Michaleris
    Abstract:

    In situ experimental measurements of the laser powder bed fusion build process are completed with the goal gaining insight into the evolution of distortion in the powder bed fusion build process. Utilizing a novel enclosed instrumented system, five experimental builds are performed. Experimental builds compare materials: Ti–6Al–4V and Inconel®718, differing build geometries, and manufacturing machines: EOS M280 and Renishaw AM250. A combination of in situ measurements of distortion and temperature and post-build measurements of final part geometry are used to compare and contrast the different experiments. Experimental results show that builds completed using Inconel®718 distort between 50% and 80% more relative to Ti–6Al–4V depending on substrate size and build geometry. The experimental build completed on the Renishaw AM250 distorted 10.6% more in the Z direction when compared with the identical build completed on the EOS M280 machine. Comparisons of post-build XY cross-sectional area show a 0.3% contraction from the predefined build geometry for the Renishaw AM250 as compared with the 4.5% contraction for the part built using the EOS M280. Recommendations and future work are also discussed.

H.g.m. Edwards - One of the best experts on this subject based on the ideXlab platform.

  • Comparative study of mobile Raman instrumentation for art analysis
    Analytica chimica acta, 2007
    Co-Authors: Peter Vandenabeele, Kepa Castro, Michael D. Hargreaves, Luc Moens, Juan Manuel Madariaga, H.g.m. Edwards
    Abstract:

    In archaeometry, one of the main concerns is to extract information from an art object, without damaging it. Raman spectroscopy is being applied in this research field with recent developments in mobile instrumentation facilitating more routine analysis. This research paper evaluates the performances of five mobile Raman instruments (Renishaw RA100, Renishaw Portable Raman Analyser RX210, Ocean Optics RSL-1, Delta Nu Inspector Raman, Mobile Art Analyser - MArtA) in three different laboratories. A set of samples were collected, in order to obtain information on the spectral performances of the instruments including: spectral resolution, calibration, laser cut-off, the ability to record spectra of organic and inorganic pigments through varnish layers and on the possibilities to identify biomaterials. Spectra were recorded from predefined regions on a canvas painting to simulate the investigation of artworks and the capabilities to record spectra from hardly accessible areas was evaluated.