Review of the theory of generalised dielectrophoresis.

Generalised dielectrophoresis (gDEP), including conventional dielectrophoresis (cDEP), electrorotation (ER) and travelling wave dielectrophoresis (twDEP), is an effective tool for particle (cell) manipulation and characterisation, even down to the level of nano-sized objects such as DNA, proteins and viruses. All the disciplines of gDEP are originated from the interaction of an applied electric field with its polarisation effect on the particle and can be studied systematically in a unified approach under electrostatics. In this review, the authors discuss both the quasi-static and transient theory of gDEP in an unbounded medium for both spherical and ellipsoidal particles. Then the quasi-static theory of wall effect is discussed on gDEP for a spherical particle. The wall effect is minor for ER, twDEP and cDEP parallel to wall(s), but could be significant for cDEP normal to wall(s). Force and torque expressions in terms of electric potential and its derivatives are provided and suggested for a robust calculation of the twDEP force and DEP torque. Discussions are provided for the application of the theory to nano-sized particles. The authors also illustrate some features of the Clausius-Mossotti factor using erythrocyte as an example, including both the crossover (DEP) and peak frequencies (ER) at low and high-frequency limits.

Reductions in the effects of damping on stress concentration in premolars by post-endodontic restorations: a non-linear finite element study.

The aim of this study was to measure the structural damping constants of premolars after treatment with a cast Co-Cr post-core system or permanent root filling, and to evaluate the stress damping effects of these restored premolars. Both the damping ratio and the natural frequency (NF) of the cast Co-Cr post-core restored premolars and the permanent root-filled premolars were detected by in-vitro NF testing experiments. Unprepared premolars served as the control. The damping constants beta of the samples were calculated from the measured damping ratios and natural frequencies. The measured damping constants beta of the test premolars were then used for dynamic finite element (FE) analyses. Stress contours and damping effects of stresses in each treated type of premolar were computed and compared using ANSYS. The measured damping constants beta were 0.75 x 10(-5) for the unprepared premolars, 0.69 x 10(-5) for the root-filled premolars with coronal restoration, and 0.72 x 10(-5) for the cast Co-Cr post-core restored premolars. The unprepared intact premolars demonstrated the highest stress dissipation effects with a ratio of 29.3 per cent at the middle root opposite to the loading side. However, no stress dissipation effects were found in the premolars that had been restored with the cast Co-Cr post-core system. The FE analysis showed that metallic post treatment attenuated the damping properties of the premolar. The effects of damping on stress concentration were significantly lower in restored premolars than in untreated vital premolars. These findings suggest that future research on post material should take the damping property into consideration.

A travelling wave dielectrophoretic pump for blood delivery.

The travelling wave dielectrophoretic pump studied here is essentially a rectangular straight micro-channel with an electrode array on part of its wall, and operated under an ac voltage with phase shift at neighbouring electrodes. The travelling wave dielectrophoretic force drives the cells, which drag the plasma, and after some sophisticated interaction between conventional dielectrophoresis, travelling wave dielectrophoresis and fluid mechanics, the whole blood is delivered. The pump was fabricated using MEMS techniques and studied in details for different parameters. It is found that the pumping velocity is maximized at an intermediate frequency around 20-30 MHz (varies with phase shift), and at an intermediate channel height at about 40 microm. The quasi-static average cell velocity can reach 15 microm s(-1) for a pump with 1 mm length and 16 electrodes (total array length 465 microm) operated at 5 V and 20 MHz with 90 degrees phase shift.

The differential effect of foreign-born status on preterm birth: a Taiwan population-based birth registry study.

Whether foreign-born status confers a protective effect on preterm birth in Taiwan was investigated using singleton live birth data from the 2004 Taiwan Birth Registry (n = 211,946). Newborns of foreign-born mothers (FBMs) comprised 13.7% of the population. The preterm birth rate of newborns of FBMs (5.9%) was significantly lower than that of newborns of Taiwan-born mothers (TBMs) (8.0%) (P < 0.0001). After having adjusted for predisposing maternal factors or adverse pregnancy conditions, newborns of FBMs still had a lower risk in preterm birth than that of TBMs, with an odds ratio of 0.74 and 95% confidence interval between 0.71 and 0.79. Selection was hypothesised to explain the low preterm birth rate in FBMs.

Interleukin 1beta-secreting cells in inflamed gingival tissue of adult periodontitis patients.

Interleukin 1beta (IL-1beta) is a cytokine with a wide range of biological activities. It is produced by various cell types including macrophages, fibroblasts, and neutrophils. The inflammatory responses mediated by IL-1beta play an important role in periodontal tissue destruction. The purposes of this study were: (1) to determine the location of IL-1beta in inflamed human gingival tissues by the immunofluorescence method; and (2) to correlate this location to the concomitant presence of macrophage or neutrophils by immunohistochemistry. Five patients with moderate to advanced adult periodontitis receiving periodontal phase I therapy were included in this study. One month after phase I therapy, 15 sites with a probing pocket depth >/=5 mm and gingivitis index >/=1 were arranged for modified Widman flap operation. Another three sites with a probing pocket depth

Modulation of calcium by inhibitory systems in the developing auditory midbrain.

Inhibitory synaptic transmission is of fundamental importance during the maturation of central auditory circuits, and their subsequent ability to process acoustic information. The present study investigated the manner in which inhibitory transmission regulates intracellular free calcium levels in the gerbil inferior colliculus using a brain slice preparation. Inhibitory and excitatory postsynaptic potentials were evoked by electrical stimulation of the ascending afferents at the level of the dorsal nucleus of the lateral lemniscus. Pharmacologically isolated inhibitory synaptic potentials were able to attenuate a calcium rise in collicular neurons that was generated by depolarizing current injection. In addition, GABA(A) and glycine receptor antagonists typically led to an increase of calcium in collicular neurons during electrical stimulation of the ascending afferent pathway at the level of the dorsal nucleus of the lateral lemniscus. Bath application of GABA or muscimol, a GABA(A) receptor agonist, evoked a brief hyperpolarization followed by a long-lasting depolarization in inferior colliculus neurons. This treatment also induced a transient calcium increase that correlated with the membrane depolarization phase. Baclofen, a GABA(B) receptor agonist, had no effect on either membrane potential or calcium levels. Ratiometric measures indicated that the muscimol-evoked rise in calcium was approximately 150 nM above basal levels. The muscimol-evoked responses were completely antagonized by bicuculline and attenuated by picrotoxin. Together, these results suggest that inhibitory synaptic transmission participates in the regulation of postsynaptic calcium during the developmental period. Inhibitory transmission may attenuate a calcium influx that is evoked by excitatory synapses, but it can also produce a modest influx of calcium when activated alone. These mechanisms may help to explain the influence of inhibitory transmission on the development of postsynaptic properties.

Heterosynaptic suppression of developing neuromuscular synapses in culture.

Activity-dependent competition between two spinal neurons coinnervating an embryonic myocyte was studied in Xenopus cell culture. We have characterized in detail the phenomenon of heterosynaptic suppression by which tetanic stimulation of one neuron results in functional suppression of the synapse made by the untetanized neuron (Lo and Poo, 1991). Fluorescence labeling of the neurons using two different fluorophores revealed that the coinnervating nerve terminals on the spherical myocyte were in close proximity. Heterosynaptic suppression could be induced when the postsynaptic cell was held under either current-clamp or voltage-clamp conditions during the tetanic stimulation. This finding, together with the observation that repetitive postsynaptic depolarization of the myocyte by direct current injection was much less effective in inducing synaptic depression, suggests that postsynaptic ACh receptor activation plays a dominant role in the induction of heterosynaptic suppression. The heterosynaptic suppression appears to be mediated by a rise of Ca2+ levels in the postsynaptic cell, since it was not observed when the cytosolic Ca2+ concentration of the myocyte was buffered at a low level with intracellular loading of a Ca2+ chelator, 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetra-acetic acid (BAPTA). The dependence of heterosynaptic suppression on the pattern of tetanic stimulation was also studied. At a stimulation frequency of 2 Hz, detectable heterosynaptic suppression could be induced after 20 repetitive stimuli were applied to one of the presynaptic neurons and the suppression was more effective with increasing number of stimuli. Over the range of 0.5-5 Hz, the extent of suppression was independent of the frequency of tetanic stimulation and, in some cells, detectable suppression could be induced at a frequency as low as 0.05 Hz. Except for a few cases, heterosynaptic suppression was found to last for as long as the recording was made after tetanus (up to 1 hr). The fact that the mean amplitude of spontaneous synaptic currents remained the same before and after the suppression while the evoked synaptic currents exhibited higher fluctuation after suppression suggests that the observed synaptic suppression involves a reduction of evoked ACh release from the nerve terminal, although postsynaptic changes have not been excluded. Finally we found that spontaneous synaptic activity may also contribute in part to the synaptic competition between coinnervating nerve terminals. Taken together, these findings provide a quantitative basis for further understanding of activity-dependent competition between developing neuromuscular synapses.

Depression of developing neuromuscular synapses induced by repetitive postsynaptic depolarizations.

Effect of postsynaptic activity on the synaptic efficacy was studied in Xenopus nerve-muscle cultures. Repetitive postsynaptic depolarizations induced by injection of current pulses into singly innervated myocytes resulted in significant reduction in the frequency of spontaneous synaptic currents and the amplitude of nerve-evoked synaptic currents at the majority of synapses that showed immature synaptic properties. Repetitive hyperpolarizations and steady depolarizations of similar duration were without effect. The depolarization-induced synaptic depression appeared to result predominantly from a reduced ACh secretion from the presynaptic nerve terminal. Buffering the myocyte cytosolic Ca2+ at a low level with intracellular loading of a Ca2+ buffer, 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetra-acetic acid (BAPTA), significantly reduced the effect of the depolarizations. Thus postsynaptic electrical activity can regulate the synaptic efficacy of the developing neuromuscular synapases and the regulation may be mediated by retrograde transsynaptic interactions.

Xanthine oxidase inhibitors from the leaves of Alsophila spinulosa (Hook) Tryon.

Diploptene(1), beta-sitosterol(2), a mixture of 6'-O-(E-P-coumaroyl)-alpha-glucopyranose and 6'-O-(E-P-coumaroyl)-beta-glucopyranose(3), a mixture of 6'-O-(E-P-caffeoyl)-alpha-glucopyranose and 6'-O-(E-P-caffeoyl)-beta-glucopyranose(4), caffeic acid(5) and astragalin(6) were isolated from an ethanolic extract of the leaves of Alsophila spinulosa Hook Tryon (Cyatheaceae). The plant has been used in folk medicine for hepatitis, gout, rheumatism, and tumor and these compounds were tested for their inhibitory effect on xanthine oxidase. Caffeic acid was the most potent constituent (IC50 = 39.21 microM; Ki = 28.2 microM) and was an uncompetitive inhibitor of the enzyme with respect to the substrate xanthine.

Activity-dependent synaptic competition in vitro: heterosynaptic suppression of developing synapses.

The development and stability of synaptic connections in the nervous system are influenced by the pattern of electrical activity and the competitive interaction between the adjacent nerve terminals. To investigate this influence, a culture system of nerve and muscle cells has been developed in which a single embryonic muscle cell is coinnervated by two spinal neurons. The effect of electrical activity on the synaptic efficacy was examined after repetitive electrical stimulation was applied to one or both neurons. Brief tetanic stimulation of one neuron resulted in immediate functional suppression of the synapse made by the unstimulated neuron innervating the same muscle cell. This heterosynaptic suppression was largely absent when the tetanic stimulation was applied concurrently to both neurons. This result demonstrates that activity-dependent synaptic competition can be studied in vitro at a cellular level.

Repetitive impulse activity potentiates spontaneous acetylcholine secretion at developing neuromuscular synapses.

The effects of presynaptic impulse activity on the transmitter secretion at developing neuromuscular junctions were examined in Xenopus nerve-muscle cultures. Repetitive suprathreshold stimulation of the presynaptic neuron results in marked potentiation of spontaneous synaptic activity, as shown by whole-cell voltage-clamp recording of synaptic currents in the postsynaptic muscle cell. Our results are consistent with the notion that synaptic efficacy of the developing synapse is potentiated by the presence of electrical activity. Such activity-dependent synaptic modulation enables the early neuronal activity to play a regulatory role during the maturation of synaptic connections.