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Notes: A simple and selective method of flow injection (FI) using a micro-column packed with chelating resin YPA4 as solid phase extractant was developed for the preconcentration and separation of trace amount of noble metals, Au(III), Ag(I), Pd(II) and Pt(IV), followed by ICP-AES determination. In HNO3 media, the chelating resin was selective towards Au(III), Ag(I), Pd(II) and Pt(IV), and the analysed ions were readily desorbed quantitatively with 5 ml of 2.5% m/v thiourea. Effects of acidity, sample flow rate and concentration, elution solution and interfering ions on the recovery of the analytes were systematically investigated. Under optimum conditions, the adsorption capacities of YPA4 for Au(III), Ag(I), Pd(II) and Pt(IV) were 67.2, 43.1, 64.8 and 27.6 mg per gram of resin in HNO3 media, respectively. It was found that YPA4 could be used for more than eight runs in HNO3 media without loss of capacity. The proposed method was used for the determination of trace noble metals in geological and environmental samples, and the analytical results obtained were in good agreement with the recommended values.

Notes: Intra-operative micro-electrode stimulation of sensorimotor thalamus produces paraesthesia or tingling in various body regions and is used to map somatotopy prior to implantation of deep brain-stimulating electrodes in awake patients. The neural elements affected by such microstimulation are unknown. Using paraesthesia as the behavioural–physiological response threshold, we measured chronaxie times for microstimuli applied to both somatosensory thalamic nuclei (cellular region) and its axonal afferents, the medial lemniscus. White matter chronaxie times were relatively unimodal, whereas two different clusters of chronaxie times were identified in grey matter: one corresponding to that of the medial lemniscus and the other about five times longer and compatible with that obtained from cell somata. Therefore, excitations of local axons and/or cell bodies can both contribute to the paraesthesia evoked during intra-operative thalamic mapping.

Notes: Though most experimental evidence indicates that the corticothalamic (CT) pathway would exert a direct excitatory action on thalamic relay neurons, the electrophysiological features of this excitation have never been clearly described. A methodological problem in previous electrophysiological studies was that direct corticofugal effects on relay cells could not be separated from those mediated by collateral activation of reticular thalamic neurons. In the present study, the reticular complex was lesioned by kainic acid and the CT response of relay neurons of the ventral lateral nucleus was recorded intracellularly in cats under pentobarbital or urethane anaesthesia.Following reticular thalamic lesions, a prominent depolarization was triggered in thalamic relay cells by stimulation of the CT pathway. This depolarization strongly drove spike discharges, and its amplitude augmented when the stimulation rate exceeded 2 Hz. Tetanizing the CT input with short trains (100–200 Hz for 200–300 ms) produced a similar augmentation to test volleys for 15–30 s after the tetanos. The CT excitation and its frequency-dependent augmentation were depressed by ketamine injection or by local application of N-methyl-D-aspartate (NMDA) antagonists. The augmenting phenomenon appeared strictly homosynaptic. For instance, it did not appear during repetitive stimulation of the cerebellar input, nor did the CT input potentiate subthreshold synaptic potentials of cerebellar origin during a conditioning procedure. Conversely, the cerebellar excitation was depressed when it occurred during the CT depolarization.It is concluded that the direct synaptic responses induced by CT fibres in relay neurons are mediated at least partly by the activation of NMDA receptors. Moreover, the marked non-linear additivity of cerebellar and CT synaptic potentials raises questions concerning the presumed improvement of thalamic transmission of peripheral informations ensured by the CT input. Instead, both inputs could compete for control of the firing of thalamic neurons. The numerical importance of CT fibres and the strong augmenting mechanism operating at synaptic sites in the thalamus suggest that the role of the thalamus is not only to transfer peripheral informations toward the cortex, but also and mainly to feed back to the cortex a modified copy of its own neuronal constructs.

Notes: A considerable amount of evidence has accumulated to support a role for excitatory glutamatergic transmission in the regulation of the hypothalamo-neurohypophysial system. Glutamate immunoreactivity has been found in axon terminals forming asymmetric synapses on to magnocellular neurosecretory cells and kynurenic acid, a broad spectrum glutamate receptor antagonist inhibits 1) spontaneous electrical activity in vivo, 2) excitatory postsynaptic potentials in hypothalamic slices, and 3) osmotically-evoked vasopressin release from hypothalamic explants. While this provides strong evidence for glutamatergic regulation of hypothalamic magnocellular neurosecretory cells, the subtypes of glutamate receptors expressed by these cells have not been defined. We have, therefore, obtained current and voltage clamp recordings from supraoptic magnocellular neurosecretory cells in vitro to investigate the functional and pharmacological properties of their glutamate receptors. Application of micromolar concentrations of L-glutamate, or of the agonists kainate, quisqualate and N-methyl-D-aspartate (NMDA), produced reversible and dose-dependent depolarizations in all cells tested. These responses were mediated by postsynaptic receptors since they persisted during chemical synaptic blockade with Ca2 + -free or tetrodotoxin-containing solutions. The inward current induced by NMDA showed a marked Mg2+-sensitive voltage dependence, and was blocked by D, L-2-amino-5-phosphonovalerate. In contrast, currents induced by kainate and quisqualate showed linear current-voltage properties and were antagonized by 6-cyano-7-nitroquinoxaline-2,3-dione. We conclude that both NMDA and non-NMDA receptors are expressed by magnocellular neurosecretory cells of the rat supraoptic nucleus.

Notes: We investigate the ultrafast electro-optic response and sensitivity of a poled side chain polymer film via the electro-optic sampling technique. A 760 fs rise-time electrical transient is observed corresponding to a bandwidth of 460 GHz. We believe this to be device limited and not due to limitations in the speed of response of the polymer.

Notes: We demonstrate a role for Qri2 in the essential DNA repair function of the Smc5/6 complex in Saccharomyces cerevisiae. We generated temperature-sensitive (ts) mutants in QRI2 and characterized their properties. The mutants arrest after S phase and prior to mitosis. Furthermore, the arrest is dependant on the Rad24 checkpoint, and is also accompanied by phosphorylation of the Rad53 checkpoint effector kinase. The mutants also display genome instability and are sensitive to agents that damage DNA. Two-hybrid screens reveal a physical interaction between Qri2 and proteins that are non-Smc elements of the Smc5/6 DNA repair complex, which is why we propose the name NSE4 for the open reading frame previously known as QRI2. A key role for Nse4 in Smc5/6 function is likely, as overexpressing known subunits of the Smc5/6 complex suppresses nse4ts cell cycle arrest. The nse4ts growth arrest is non-lethal and unlike the catastrophic nuclear fragmentation phenotype of smc6ts mutants, the nucleus remains intact; replicative intermediates and sheared DNA are not detected. This could imply a role for Nse4 in maintenance of higher order chromosome structure.

Notes: Abstract A method has been developed for the determination of trace impurities in silicon nitride (Si3N4) powders by fluorination assisted electrothermal vaporization (ETV) /ICP-AES using the slurry sampling technique. Polytetrafluoroethylene (PTFE) emulsion as a fluorinating reagent not only effectively destroys the skeleton of Si3N4, but also carries out selective volatilization between the impurity elements (Cu, Cr) and the matrix (Si). The experimental parameters influencing fluorination reactions were optimized. The detection limits for Cu and Cr are 1.05 ng/mL ( Cu) and 1.58 ng/mL (Cr), the RSDs are in the range of 1.9–4.2%. The proposed method has been applied to the determination of Cu and Cr in Si3N4 ceramic powders. The analytical results were compared with those obtained by independent methods.

Notes: Abstract A new method for the determination of trace rare earth impurities in high-purity La2O3 by HPLC combined with ICP-MS is proposed. The chromatographic retention behavior of La and Ce in HPLC was studied with 2-ethylhexyl-hydrogen-2-ethylhexylphosphonate (P507) resin as the stationary phase and inorganic acid (HNO3) as the mobile phase. The effects of acidity of the mobile phase, flow rate of eluent and column oven temperature on the separation of La and Ce were investigated in detail. The results of the effect of different ratios of La / Ce showed that a favorable separation of La and Ce could be obtained easily and rapidly with the method presented. Compared with the conventional open column method, the proposed separation system shows a good performance with regard to short separation time, low reagent consumption, and simple operation. The method has been applied to the analysis of real samples of high-purity La2O3 with satisfactory results.

Notes: Abstract A new method using nanoparticle TiO2 as solid-phase extractant coupled with ICP-AES was proposed for simultaneous determination of trace elements. The adsorption behavior of nanometer TiO2 towards Cu, Cr, Mn and Ni was investigated by ICP-AES, and the adsorption pH curves, adsorption isotherms and adsorption capacities were obtained. It was found that the adsorption rates of the metal ions studied were more than 90% in pH 8.0∼9.0, and 2.0 mol L–1 HCl was sufficient for complete elution. Nanometer TiO2 possesses a significant capacity for the sorption of the metal ions studied which is higher than the capacity of silica, the commonly used extractant. The method has been applied to the analysis of some environmental samples with satisfactory results.