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Deep-sea hydrothermal venting is now recognized as a major source of iron (Fe), an essential trace element that controls marine productivity. However, the reactions occurring during dispersal from buoyant plumes to neutrally buoyant hydrothermal plumes are still poorly constrained. Here we report for the first time on the dissolved-particulate partition of Fe after in situ filtration at the early stage of mixing at different hydrothermal discharges, i.e., Lucky Strike (37 degrees N), TAG (26 degrees N), and Snakepit (23 degrees N) on the Mid-Atlantic Ridge. We found that hydrothermal iron is almost completely preserved (>90%) in the dissolved fraction, arguing for low iron-bearing sulfide precipitation of iron in basalt-hosted systems with low Fe:H2S ratios. This result can only be explained by a kinetically limited formation of pyrite. The small part of Fe being precipitated as sulfides in the mixing gradient (<10%) is restricted to the inclusion of Fe in minerals of high Cu and Zn content. We also show that secondary venting is a source of Fe-depleted hydrothermal solutions. These results provide new constrains on Fe fluxes from hydrothermal venting.

The objective of this study was to deter-mine the concentrations of different fractions of dissolved copper (after filtration at 0.45 mu m) along the cold part of the hydrothermal fluid-seawater mixing zone on the Tour Eiffel edifice (MAR). Dissolved copper was analyzed by stripping chronopotentiometry (SCP) after chromatographic C-18 extraction. Levels of total dissolved copper (0.03 to 5.15 mu M) are much higher than those reported for deep-sea oceanic waters but in accordance with data previously obtained in this area. Speciation measurements show that the hydrophobic organic fraction (C18Cu) is very low (2 +/- 1%). Dissolved copper is present mainly as inorganic and hydrophilic organic complexes (nonC(18)CU). The distribution of copper along the pH gradient shows the same pattern for each fraction. Copper concentrations increase from pH 5.6 to 6.5 and then remain relatively constant at pH>6.5. Concentrations of oxygen and total sulphides demonstrate that the copper anomaly corresponds to the transition between suboxic and oxic waters. The increase of dissolved copper should correspond to the oxidative redissolution of copper sulphide particles formed in the vicinity of the fluid exit. The presence of such a secondary dissolved copper source, associated with the accumulation of metal sulphide particles, could play a significant role in the distribution of fauna in the different habitats available at vents.

The distribution of Fe, Cu, Zn, Pb, Cd between the dissolved (<2 mu m) and the particulate (>2 mu m) fractions was measured after in-situ filtration in two hydrothermal habitats. The total metal concentration ranges exhibit a clear enrichment compared with the seawater concentration, accounting for the hydrothermal input for all the metals considered. Iron is the predominant metal (5-50 mu M) followed by Zn and Cu. Cd and Pb are present at the nM level. At the scale studied, the behavior of temperature, pH and dissolved iron is semi-conservative whereas the other dissolved and particulate metals are characterized by non-conservative patterns. The metal enrichment of the >2 mu m fraction results from the settlement and accumulation of particulate matter close to the organisms, acting as a secondary metal source. The enrichment observed in the dissolved fraction can be related to the dissolution or oxidation of particles (mainly polymetallic sulfide) or to the presence of small particles and large colloids not retained on the 2 mu m frit. SEM observations indicate that the bulk particulate observed is characteristic of crystalline particles settling rapidly from the high temperature smoker (sphalerite, wurtzite and pyrite), amorphous structures and eroded particles formed in the external zone of the chimney. Precipitation of Zn, Cu, Cd and Ph with Fe as wurtzite, sphalerite and pyrite is the main process taking place within the area studied and is semi-quantitative. The distribution of the dominant observed fauna has been related to the gradient resulting from the dilution process, with the alvinellids worms colonizing the hotter and more variable part of the mixing zone, but also to the metallic load of the mixing zone. Dissolved and particulate metal concentrations are therefore necessary abiotic factors to be studied in a multiparametric approach to understand the faunal distribution in hydrothermal ecosystems. (C) 2007 Elsevier B.V. All rights reserved.

We analyzed thymocyte and thymic regulatory T cell (CD4SPCD25+Foxp3+cells, Treg) development in thymoma with and without myasthenia gravis (MG, MG-thymoma, non-MG-thymoma) and in MG-associated non-neoplastic thymus (MG-NNT). An increased number of immature CD4+CD8(-)CD3(-) thymocytes through the CD4+CD8+ to CD4+CD8(-) transition and an abnormal T cell receptor Vbeta (TCRVbeta) development through the CD4+CD8+ to CD4(-)CD8+ transition were seen both in MG-and non-MG-thymomas. Terminal thymopoiesis, i.e., CD45RA+ cells within the CD4+CD8(-)CD3+ and CD8+CD4(-)CD3+ subsets, was skewed towards the CD4+ compartment in MG-thymoma and CD8+ compartment in non-MG-thymoma, but thymic export was increased only in the latter in keeping with the hypothesis that CD8+ lymphocytes may play a role in the initial stages of autosensitization and in disagreement with the relevance of an increased output of CD4+ T lymphocytes in paraneoplastic MG. Treg level in normal thymus and MG-NNT and both MG- and non-MG-thymoma was similar, and TCRVbeta development in Treg cells was slightly altered in thymoma but irrespective of MG presence. Thus, the relevance of a defective Treg development in MG context remains to be established. Most alterations in thymopoiesis were corrected by therapeutic corticosteroid administration, and the effects of steroid administration may be mediated by thymic microenvironment.

Myasthenia gravis (MG) with antibodies against the muscle-specific tyrosine kinase (MuSK abs) is often a severe disease requiring aggressive treatment. Various immunosuppressive (IS) regimens have been employed; the efficacy of plasma exchange is unanimously recognized, while the indication for thymectomy is controversial. We evaluated the response to therapy in 57 MuSK-positive patients (12 M/45 F) comparing our experience with other authors' results. Disease severity and response to treatment were graded according to MG Foundation of America; follow-up ranged from 0.5-29 years. Owing to both MG severity and the unsatisfactory response to cholinesterase inhibitors, most patients (54/57) needed IS treatment, and 35 received one or more courses of plasma exchange and intravenous immunoglobulin. At the end of follow-up, the rate of complete remission was 8.8%, and IS treatment had been withdrawn in only 10/54 patients. The extent of therapeutic response varied considerably. With conventional IS therapy (prednisone alone or in combination with azathioprine or cyclosporine), most patients achieved good control of their disease, but 30% of them were left with permanent facial and bulbar weakness. In patients with refractory disease, the use of mycophenolate mofetil and rituximab proved very effective, as also reported by other authors. In our and others' experience, MuSK-positive MG markedly improves with IS therapy, although, in comparison with the AChR-positive disease, it is characterized by a lower remission rate, as a higher proportion of patients remain dependent on treatment. Thymectomy is mostly considered scarcely effective; however, at present, no firm conclusions can be drawn on its role in the treatment of this form of MG.

The Davies-Bouldin cluster validation technique has been utilized to determine the optimal time series parameters (model, order and number of coefficients) to be used in a myoelectric pattern recognition system based on intramuscular recordings. The data used in our longitudinal study were recorded intramuscularly (4 muscle channels) from an amputee subject over three different experimental days. During the recording sessions, the subject performed 4 wrist movements (pronation, supination, wrist flexion, wrist extension) in a way that was intuitive to her. The time series coefficients obtained from the EMG data (from AR, MA, and ARMA modeling) were used for generating feature spaces with 4 classes (1 per movement). The results showed that the optimal parameters didn't differ substantially (AR, order 4, 2 coefficients) for those obtained for other type of movements and surface EMG recordings. The use of the Davies-Bouldin technique during the analysis produced important information about the separability and consistency of the data across different days., Papers from 23rd Annual International Conference of the IEEE Engineering in Medicine and Biology Society, October 25-28, 2001, held in Istanbul, Turkey. See also ADM001351 for entire conference on cd-rom. The original document contains color images.

Multipolar nerve cuffs are being developed to apply to peripheral trunk nerves in an effort to limit the number of implanted components of an FES system, while at the same time allowing specific fascicles within the cuffed nerve to be independently activated. Because the electrode contact sites of a multipolar circumferential fitted cuff are positioned only at the surface of the cuffed nerve, it is difficult to activate fascicules that are located deep within the nerve. This situation might be improved if one or more additional electrode contacts were provided within the core of the nerve. An obvious choice for such a contact is to use an intrafascicular electrode (IFE) such as those described by Horch and his colleagues. In our present study we inserted a single IFE into a trunk nerve that subserves the forelimb muscles in an adult anaesthetized pig. An 18 pole multichannel nerve cuff was then applied to the nerve at the same site. We stimulated different combinations of the cuff contact sites with and without the IFE while monitoring the evoked EMGs from an array of innervated forearm and shoulder muscles to assess the ability to activate different fascicles independently. The results have shown that the use of the IFE in combination with the normal cuff contacts can afford modest improvements in the degree of selective muscle activation that is possible., Papers from the 23rd Annual International Conference of the IEEE Engineering in Medicine and Biology Society, October 25-28, 2001, held in Istanbul, Turkey. See also ADM001351 for entire conference on cd-rom.