DEVELOPMENTAL REMODELING OF RELAY CELLS IN THE DORSAL LATERAL GENICULATE NUCLEUS (dLGN) OF THE MOUSE AND THE ROLE OF RETINAL INNERVATION

The dorsal lateral geniculate nucleus (dLGN) has become an important model for studying many aspects of visual system development. To date, studies have focused on the development of retinal projections and the role of activity in shaping the pattern of synaptic connections made with thalamocortical relay cells. By contrast, little is known about relay cells and the factors that regulate the growth and establishment of their dendritic architecture. In many systems, such growth seems consistent with the synaptotrophic hypothesis which states that synapse formation and dendritic growth work in a concerted fashion such that afferent input and the establishment of functional synapses are needed to shape the maturation of dendritic arbors. To address this, we characterized the development of relay cells in the dLGN of wild-type (WT) mouse. By adopting a loss of function approach, we assessed the manner in which growth and maturation of relay cells were affected by retinal innervation. For this, we made use of the math-null (math5-/-) mouse in which progenitors fail to differentiate into retinal ganglion cells (RGCs), and exhibit a \u3e95% cell loss. Anterograde labeling of RGC axons with cholera toxin subunit B (CTB), immunolabeling of RGC-specific presynaptic machinery in dLGN (e.g. vesicular glutamate transporter 2), and ultrastructural analysis at the electron microscopy level demonstrated that the dLGN is devoid of retinal innervation. We examined the functional and morphological characteristics of relay cells in WT and math5-nulls during early postnatal life by conducting in vitro whole cell recordings in slices containing dLGN. Individual relay cells were labeled by intracellular injection of biocytin, and imaged by confocal microscopy to obtain the 3-D reconstructions of their dendritic trees. Morphometric analysis revealed that relay cells in WT undergo two growth spurts: an early one where cell class specification and dendritic complexity are established and a later one marked by an increase in dendritic field and length. Following the third week, relay cells growth was stabilized. In math5-nulls, relay cells maintained their morphological identity whereby cells could be classified in three groups (Y: spherical, X: bi-conical, W: hemi-spherical). However, the dLGN was highly reduced in size, and relay cells showed disrupted growth spurts. Relay cells had smaller somata and exhibited fluctuations in dendritic complexity and field extent compared to age-matched WTs. Exuberance in dendritic branching was noted in week 2, and by week 5, relay cells had significantly smaller surface area resulting from a loss of dendritic segments and a reduction in dendritic field extent. Control experiments using RT-PCR revealed that these changes were not due to the loss of math5 in the dLGN. Whole cell recordings and voltage responses to square wave current pulses showed that math5-nulls possess the full compliment of intrinsic membrane properties, such as relay cells displayed both burst and tonic firing modes. A cross of the math5-null with a transgenic mouse that expresses GFP in layer VI cortical neurons revealed a dense plexus of corticogeniculate terminals throughout the mature dLGN. However, the rate of corticogeniculate innervation was highly accelerated and was complete a week earlier than WT. Electric stimulation of cortical axons revealed that synapses are functional and responses were indistinguishable from WT. Taken altogether, these observations suggest that retinal innervation plays an important trophic role in the maturation of dLGN and is necessary for the continued maintenance of relay cells’ structural integrity. However, the general form and function of relay cells seem largely unaffected by the loss of retinal innervation

Mechanical Characterization of Cryomilled Al Powder Consolidated by High-Frequency Induction Heat Sintering

In the present investigation, an aluminum powder of 99.7% purity with particle size of ~45 µm was cryomilled for 7 hours. The produced powder as characterized by scanning, transmission electron microscopy, and X-ray diffraction gave a particle size of ~1 µm and grain (crystallite) size of 23±6 nm. This powder, after degassing process, was consolidated using high-frequency induction heat sintering (HFIHS) at various temperatures for short periods of time of 1 to 3 minutes. The present sintering conditions resulted in solid compact with nanoscale grain size (<100 nm) and high compact density. The mechanical properties of a sample sintered at 773 K for 3 minutes gave a compressive yield and ultimate strength of 270 and 390 MPa, respectively. The thermal stability of grain size nanostructured compacts is in agreement with the kinetics models based on the thermodynamics effects

Effect of Nd:YAG Laser Parameters on the Penetration Depth of a Representative Ni–Cr Dental Casting Alloy

The effects of voltage and laser beam (spot) diameter on the penetration depth during laser beam welding in a representative nickel–chromium (Ni–Cr) dental alloy were the subject of this study. The cast alloy specimens were butted against each other and laser welded at their interface using various voltages (160–390 V) and spot diameters (0.2–1.8 mm) and a constant pulse duration of 10 ms. After welding, the laser beam penetration depths in the alloy were measured. The results were plotted and were statistically analyzed with a two-way ANOVA, employing voltage and spot diameter as the discriminating variables and using Holm–Sidak post hoc method (a = 0.05). The maximum penetration depth was 4.7 mm. The penetration depth increased as the spot diameter decreased at a fixed voltage and increased as the voltage increased at a fixed spot diameter. Varying the parameters of voltage and laser spot diameter significantly affected the depth of penetration of the dental cast Ni–Cr alloy. The penetration depth of laser-welded Ni–Cr dental alloys can be accurately adjusted based on the aforementioned results, leading to successfully joined/repaired dental restorations, saving manufacturing time, reducing final cost, and enhancing the longevity of dental prostheses

Developmental remodeling of relay cells in the dorsal lateral geniculate nucleus in the absence of retinal input

Background The dorsal lateral geniculate nucleus (dLGN) of the mouse has been an important experimental model for understanding thalamic circuit development. The developmental remodeling of retinal projections has been the primary focus, however much less is known about the maturation of their synaptic targets, the relay cells of the dLGN. Here we examined the growth and maturation of relay cells during the first few weeks of life and addressed whether early retinal innervation affects their development. To accomplish this we utilized themath5 null (math5−/−) mouse, a mutant lacking retinal ganglion cells and central projections. Results The absence of retinogeniculate axon innervation led to an overall shrinkage of dLGN and disrupted the pattern of dendritic growth among developing relay cells. 3-D reconstructions of biocytin filled neurons frommath5−/− mice showed that in the absence of retinal input relay cells undergo a period of exuberant dendritic growth and branching, followed by branch elimination and an overall attenuation in dendritic field size. However, math5−/− relay cells retained a sufficient degree of complexity and class specificity, as well as their basic membrane properties and spike firing characteristics. Conclusions Retinal innervation plays an important trophic role in dLGN development. Additional support perhaps arising from non-retinal innervation and signaling is likely to contribute to the stabilization of their dendritic form and function

Experimental and Numerical Study of Texture Evolution and Anisotropic Plastic Deformation of Pure Magnesium under Various Strain Paths

The deformation behavior and texture evolution of pure magnesium were investigated during plane strain compression, simple compression, and uniaxial tension at room temperature. The distinctive stages in the measured anisotropic stress-strain responses and numerically computed strain-hardening rates were correlated with texture and deformation mechanisms. More specifically, in plane strain compression and simple compression, the onset of tensile twins and the accompanying texture-hardening effect were associated with the initial high strain-hardening rates observed in specimens loaded in directions perpendicular to the crystallographic c-axis in most of the grains. The subsequent drop in strain-hardening rates in these samples was correlated with the exhaustion of tensile twins and the activation of pyramidal <c+a> slip systems. The falling strain-hardening rates were observed in simple compression and plane strain compression with loading directions parallel to the c-axis where the second pyramidal <c+a> slip systems were the only slip families that can accommodate deformation. For uniaxial tension with the basal plane parallel to the tensile axis, the prismatic <a> and second pyramidal <c+a> slips are the main deformation mechanisms. The predicted relative slip and twin activities from the crystal plasticity simulations clearly showed the effect of texture on the type of activated deformation mechanisms

ON THE EXPONENTIAL CHEBYSHEV APPROXIMATION IN UNBOUNDED DOMAINS: A COMPARISON STUDY FOR SOLVING HIGH-ORDER ORDINARY DIFFERENTIAL EQUATIONS

In this paper we investigate an improved scheme for exponential Chebyshev (EC) collocation method. The improved scheme of the EC functions is derived and introduced for solving high-order linear ordinary differential equations with variable coefficients in unbounded domain. This technique transforms the given differential equation and mixed conditions to matrix equation with unknown EC coefficients. These matrices together with the collocation method are utilized to reduce the solution of higher-order ordinary differential equations to the solution of a system of algebraic equations. The solution is obtained in terms of EC functions. Numerical examples are given to demonstrate the validity and applicability of the method. The obtained numerical results are compared with others existing methods and the exact solution where it shown to be very attractive with good accuracy

Knowledge discovery for friction stir welding via data driven approaches: Part 2 – multiobjective modelling using fuzzy rule based systems

In this final part of this extensive study, a new systematic data-driven fuzzy modelling approach has been developed, taking into account both the modelling accuracy and its interpretability (transparency) as attributes. For the first time, a data-driven modelling framework has been proposed designed and implemented in order to model the intricate FSW behaviours relating to AA5083 aluminium alloy, consisting of the grain size, mechanical properties, as well as internal process properties. As a result, ‘Pareto-optimal’ predictive models have been successfully elicited which, through validations on real data for the aluminium alloy AA5083, have been shown to be accurate, transparent and generic despite the conservative number of data points used for model training and testing. Compared with analytically based methods, the proposed data-driven modelling approach provides a more effective way to construct prediction models for FSW when there is an apparent lack of fundamental process knowledge