Glutamate receptor activity is required for normal development of tectal cell dendrites in vivo

Glutamatergic retinotectal inputs mediated principally by NMDA receptors can be recorded from optic tectal neurons early during their morphological development in Xenopus tadpoles. As tectal cell dendrites elaborate, retinotectal synaptic responses acquire an AMPA receptor-mediated synaptic component, in addition to the NMDA component. Here, we tested whether glutamatergic activity was required for the elaboration of dendritic arbors in Xenopus optic tectal neurons. In vivo time-lapse imaging of single DiI-labeled neurons shows that the NMDA receptor antagonist APV (100 microM) blocked the early development of the tectal cell dendritic arbor, whereas the AMPA receptor antagonist CNQX (20 microM) or the sodium channel blocker TTX (1 microM) did not. The decreased dendritic development is attributable to failure to add new branches and extend preexisting branches. These observations indicate that NMDA-type glutamatergic activity promotes the initial development of the dendritic arbor. At later stages of tectal neuron development when AMPA receptor-mediated synaptic transmission is strong, both APV and CNQX decrease dendritic arbor branch length, consistent with a role for glutamatergic synaptic transmission in maintaining dendritic arbor structure. These results indicate that AMPA and NMDA receptors can differentially influence dendritic growth at different stages of neuronal development, in correlation with changes in the relative contribution of the receptor subtype to synaptic transmission.     

Internal structure of a turbulent premixed flame using Rayleigh scattering

The flame-turbulence interaction in a premixed 0.75-equivalence-ratio rod-stabilized propane-air flame was investigated using an instantaneous Rayleigh scattering method. The experimental technique permitted the structure of the flame to be evaluated independently of the flame-front oscillations, thereby providing a means of estimating the effect of flame movement on the measured statistical turbulence characteristics of the flame.The measurements show that the thickness of the instantaneous flame is essentially constant with downstream distance and is of the same order of magnitude as the laminar flame thickness. Flame-front movements are found to be largely responsible for the high values of density fluctuation intensities in the time-averaged flame. The nature of the instantaneous reaction profile and the spatial structure of the flame change with increased distance from the flameholder. Comparison of the experimental density fluctuations with those predicted by the Bray-Moss-Libby model indicates that flame breakup influences the nature of the assumed probability distribution functions in theoretical models.     

A critical role for IL-4 in regulating disease severity in experimental allergic encephalomyelitis as demonstrated in IL-4-deficient C57BL/6 mice and BALB/c mice

Experimental allergic encephalomyelitis (EAE) is a T cell-mediated autoimmune disease of the central nervous system (CNS) that has served as the principal experimental model for multiple sclerosis (MS). Susceptibility to disease is thought to correlate with the ability to generate a Th1-type cytokine profile in myelin-responsive T cells, whereas T cells producing a Th2 cytokine pattern, in particular IL-4, are thought to be nonencephalitogenic and also to confer protection against a Th1-type response. However, recent studies using a variety of genetically engineered animals in which the genes for Th1-type cytokines and/or their receptors have been inactivated have called into question the Th1-Th2 paradigm in experimental allergic encephalomyelitis. In this report we have addressed the contribution of IL-4 to disease expression by studying two strains of mice, C57BL/6 and BALB/c, in which the gene for IL-4 has been inactivated. The IL-4-deficient C57BL/6 mice, and to a lesser extent the IL-4-deficient BALB/c mice, developed a more severe form of clinical disease, a more extensive pathologic involvement of the spinal cord, and an increased expression of proinflammatory cytokines in the CNS than their wild-type littermates. BALB/c and C57BL/6 mice showed a slightly different cytokine profile in the CNS. Both groups of animals recovered from the acute clinical episode in a time frame that was essentially identical to that found in the wild-type controls. We conclude that IL-4 plays an important role in modulating the severity of the encephalitogenic process, but does not by itself contribute to spontaneous remission from the disease.     

Intermediate Voltage Microscopy

Examining the advantages and limitations of electron microscopy at inter-mediate voltages (greater than ≈100 kV but less than 500 kV), this article emphasizes aspects of microscopy that cannot be performed using ≈100 kV instruments as well as applications that previously required instruments operating at greater than 500 kV. Based on early results, intermediate voltage microscopy appears to be achieving theoretical predictions. In the area of analytical microscopy, however, further research is necessary to explore its full potential. Nevertheless, these new classes of microscopes have enabled high resolution imaging and microanalysis with the same instrument.     

Corrosion and Grounding Systems

Corrosion that occurs in the presence of dissimilar metals in the same electrolyte, or same metal in different electrolytes, or in different concentrations of the same electrolyte, has caused numerous problems in operating electric systems. This corrosion is the result of a potential difference existing between two surfaces which forces an electric current to flow. This effect is often ignored or overlooked in electrical grounding design, with the premise that electrical system protection will be hampered by the incorporation of corrosion protection. By careful design, however, both sets of requirements can be met. Some of the principles that determine corrosion and how these conditions exist in underground systems of cement plants are reviewed. The principles of grounding design are analyzed and suggestions to improve the design to minimize corrosion are discussed.     

Microstructural study of a high-strength stress-corrosion resistant 7075 aluminium alloy

A heat-treatment procedure providing for enhanced stress-corrosion cracking resistance without any sacrifice of yield strength in 7075 aluminium alloy is investigated using transmission electron microscopy. It is suggested that the heat treatment (known as retrogression and re-ageing) provides for large grain-boundary precipitates and coherent matrix precipitates. The latter provides for the high strength levels while the grainboundary precipitates provide for enhanced stress-corrosion cracking resistance. A hydrogen embrittlement mechanism of stress-corrosion cracking is assigned to this alloy system.