Anti-ganglioside (anti-GM1) antibodies have been implicated in the pathogenesis of Guillain-Barré syndrome, multifocal motor neuropathy and motor neuron diseases. It has been held that they may interfere with saltatory conduction by blocking sodium channels. We tested this hypothesis by analysing action potentials from 140 single nerve fibres in 22 rat ventral roots using external longitudinal current measurement. High-titre anti-GM1 sera from Guillain-Barré syndrome or multifocal motor neuropathy patients, or anti-GM1 rabbit sera were applied to the rat ventral root, where saltatory conduction in single motor fibres was serially observed for 4-12 h (mean 8.2 h). For control experiments, we also tested anti-galactocerebroside (anti-GalC) sera, which causes acute demyelinative conduction block, and tetrodotoxin (TTX), a sodium channel blocker. Conduction block was found in 82% of the fibres treated with anti-GalC sera and 100% treated with TTX, but only in 2% (one out of 44) treated with the patients' sera and 5% (two out of 38) treated with rabbit anti-GM1 sera. All the nodes blocked by anti-GM1 sera revealed intense passive outward membrane current, in the internode just beyond the last active node. This pattern of current flow was similar to that in fibres blocked by demyelination with anti-GalC sera, and quite different from that seen in fibres blocked by reducing sodium currents with TTX. Our findings suggest that anti-GM1 sera neither mediate conduction block nor block sodium channels on their own. We conclude that physiological action of the antibody alone is insufficient to explain clinically observed conduction block in human diseases.
iNPH often appears as a shunt-responsive type of parkinsonism and reversible white matter lesions among the geriatric population.
To investigate the chemical composition of possible primitive melts of the Martian mantle, we performed melting experiments of a model Martian mantle derived by Dreibus and Wänke (DWM) at pressures from 1.0 to 4.5 GPa. The chemical compositions of partial melts are systematically related to pressure. The partial melts at pressure of 1.0 GPa in spinel stability field show high Al 2 O 3 and low FeO contents. The partial melts at higher pressure in garnet stability field are, however, characterized by a relatively high FeO content, low Al 2 O 3 content and high CaO/Al 2 O 3 ratio. In garnet stability field, clinopyroxene (= Ca -rich phase) contribute significantly to melt formation near the solidus temperature, although garnet (= Al -rich phase) is stable at temperature above solidus. Therefore Al -poor and Ca -rich partial melt are formed at higher pressure. Comparing the shergottite chemistry with the chemical trends of the partial melts obtained by the experiments, we suggest that one of basaltic shergottite with a high Al 2 O 3 and low CaO/Al 2 O 3 ratio, QUE94201, resembles the composition of the DWM partial melts in major -element chemistry in a low degree (<20%) partial melt of DWM at pressure of 1.0 GPa and temperature of 1360 °C. We conclude that the olivine -poor (or olivine -free) basaltic magma with low CaO/Al 2 O 3 ratio and high Al 2 O 3 could be primitive melts derived from the upper mantle of Mars if the actual Martian mantle is similar in composition to DWM.
Two preliminary experiments, heating of rutilated quartz grains with 0.082 wt% TiO2 on average from Bunt Island, Napier Complex, East Antarctica and a synthetic TiO2–SiO2 (rutile–cristobalite) system in air at 1300 °C for 39 days, showed increasing solubility of TiO2 in silica minerals with temperature. Bunt quartz was converted to cristobalite and traversed by many transparent seams with the disappearence of needles and spots of rutile. Unreacted host grains retained many fine needles of rutile. The seams are homogeneous and slightly enriched in TiO2 up to 0.149 wt% on average, which is about one-fifth lower than that of the synthesized TiO2–SiO2 cristobalite (0.767 wt% on average). Area analyses with an electron beam in the raster mode at a magnification of ×5000 gave 0.308 wt% TiO2 for the bulk composition of the Bunt quartz. This indicates that needles of rutile exsolved from the TiO2-saturated quartz at the cooling stage, or during retrograde metamorphism. Natural examples of quartz in geologically and petrologically well-characterized metamorphic rocks were chemically analysed to examine the temperature controls on the Ti saturation level in quartz. The TiO2 content of quartz in equilibrium with rutile increases sensitively with the metamorphic temperature, which can be expressed as where XTiO2Qtz is the mole fraction of TiO2, or the number of Ti atoms per formula unit based on a two-oxygen atom normalization. This empirical equation is very useful to evaluate the metamorphic temperatures for ultrahigh-temperature granulites. The temperatures calculated by the existing Ti-in-quartz thermometer are about 200 °C higher than those estimated by the present thermometer, potentially because of underestimates of Ti solubility in quartz in the previous calibration.
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