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PubMed2003

Coupling between sensory neurons in the olfactory epithelium.

Coupling of olfactory sensory neurons (OSNs) in the olfactory epithelium of Necturus maculosus was demonstrated by dye-transfer with Lucifer yellow CH; however, the incidence of dye-transfer was low. Immunocytochemistry and Western blot analysis indicated that connexin 43, a gap junction channel subunit, was widely expressed by cells in the olfactory epithelium. Electrical coupling by presumptive gap junctions was assessed using electrophysiological recordings, heptanol block, tracer-uptake through hemi-junctions, and tracer-injection into tissue whole-mounts. Coupling, which involved pairs of OSNs only, was detected in approximately 3-10% of the OSN population; there was no evidence that OSNs were coupled into extended neural syncitia. These results suggest that coupling of OSNs by gap junctions is unlikely to have a general role in olfactory responses by mature (odor responsive) OSNs. Instead, the incidence of inter-neuronal coupling was small, similar to the fraction of immature OSNs, suggesting a possible role of gap junctions in the continual turnover and development of OSNs or possibly their senescence.

Aging↗
PubMed2004

BDNF regulates NMDA receptor activity in developing retinal ganglion cells.

Brain-derived neurotrophic factor (BDNF) modulates glutamate receptors of the NMDA type in many areas of the brain. We assessed whether BDNF exerts an effect on NMDA receptor properties in retinal ganglion cells during early postnatal development. Electrophysiological responses to the glutamate agonist NMDA (500 microM-2 mM) in retinal slices of wildtype and BDNF deficient mice (bdnf-/-) were recorded using the whole-cell patch-clamp technique. Retinal ganglion cells of bdnf-/- mice displayed significantly smaller NMDA currents than those of age-matched wildtype mice. Remarkably, NMDA receptor activity was restored by incubating retinal slices of bdnf-/- mice in BDNF (50 ng/ml) for 1-3 h. We suggest that BDNF plays a role in the activation of functional NMDA receptors in early ganglion cell development.

Animals↗
PubMed2003

A field test of electret ion chambers for environmental remediation verification.

In 1999, the State of Idaho INEEL Oversight Program performed a field test to determine if electret ion chambers could be used as a replacement to soil sampling in field survey releases at a remediated radioactively contaminated site. This study compared exposure rates measured using electret ion chambers with gamma spectroscopic analysis results of soil samples collected at the remediated site. Exposure rate measurements were made in 1999 using electret ion chambers at the same locations that INEEL Oversight Program sampled soil in 1998 following MARSSIM protocol. The waste site was divided into nine survey units based upon site history including previous site surveys and physical boundaries. Exposure rate measurements at the remediation site compared well with exposure rate measurements made at reference background locations used for routine environmental monitoring by the State of Idaho indicating that the remedial action met cleanup criteria. A poor correlation between exposure rate measurements and 137Cs concentrations and other discrepancies were observed during this study with respect to measurements made during the 1998 final site survey.

Biodegradation, Environmental↗
PubMed2004

Capacity of oscillatory associative-memory networks with error-free retrieval.

Networks of coupled periodic oscillators (similar to the Kuramoto model) have been proposed as models of associative memory. However, error-free retrieval states of such oscillatory networks are typically unstable, resulting in a near zero capacity. This puts the networks at disadvantage as compared with the classical Hopfield network. Here we propose a simple remedy for this undesirable property and show rigorously that the error-free capacity of our oscillatory, associative-memory networks can be made as high as that of the Hopfield network. They can thus not only provide insights into the origin of biological memory, but can also be potentially useful for applications in information science and engineering.

Association↗
PubMed2002

Theoretical and numerical predictions of the electromechanical behavior of spiral-shaped lead zirconate titanate (PZT) actuators.

This paper presents a two-dimensional analytical model of a spiral-shaped PZT ceramic actuator. Developed using elasticity theory and a zero-stress assumption, the theoretical analysis has been formulated for a piecewise semicircular representation of the spiral-shaped actuator. Closed-form solutions of the tangential displacement of the equivalent spiral under applied electrical field in the poling direction have been obtained. To develop confidence in the theoretical model, results are compared with those obtained using finite element analysis (FEA). Results from both are then compared with previously reported experimental findings, and reasonable agreement is achieved.

Acoustics↗
PubMed2002

Hybrid organic-inorganic electrolytic capacitors.

Organic capacitors are among the most significant applications of conductive polymers, allowing the realization of lightweight and flexible dispositives. The main drawback of completely organic capacitors is the very low dielectric rigidity, due to irregular surface of the polymer-polymer interface. This paper describes our hybrid solution using aluminum electrodes, with the very important characteristic of easy connection between contacts of the discrete dispositive and electrodes. Chemical, technological, and functional tests have been conducted to estimate the effective values of this device, and natural properties of self-healing and nonpolarity have been investigated.

Aluminum↗
PubMed2002

Effects of a liquid layer on thickness-shear vibrations of rectangular AT-cut quartz plates.

Thickness-shear vibrations of a rectangular AT-cut quartz with one face in contact with a layer of Newtonian (linearly viscous and compressible) fluid are studied. The two-dimensional (2-D) governing equations for vibrations of piezoelectric crystal plates given previously are used in the present study. The solutions for 1-D shear wave and compressional wave in a liquid layer are obtained, and the stresses at the bottom of the liquid layer are used as approximations to the stresses exerting on the crystal surface in the plate equations. Closed form solutions are obtained for both free and piezoelectrically forced thickness-shear vibrations of a finite, rectangular AT-cut quartz in contact with a liquid layer of finite thickness. From the present solutions, a simple and explicit formula is deduced for the resonance frequency of the fundamental thickness-shear mode, which includes the effects of both shear and compressional waves in the liquid layer and the effect of the thickness-to-length ratio of the crystal plate. The formula reduces to the widely used frequency equation obtained by many previous investigators for infinite plates. The resonance frequency of a rectangular AT-cut quartz, computed as a function of the thickness of the adjacent liquid layer, agrees closely with the experimental data measured by Schneider and Martin.

Computer Simulation↗
PubMed2002

Characterization of MEMS transducer performance using near-field scanning interferometry.

Sophisticated ultrasonic transducer microarrays based on micro-electro-mechanical-systems (MEMS) technologies are quickly becoming a reality. A current challenge for many researchers is characterizing the dynamic performance of these and other micro-mechanical devices. In this work, the performance characteristics of a MEMS ultrasonic transducer array were successfully measured using a scanning heterodyne interferometer system. The dynamic response of the entire transducer array was measured, and the results were compared with theoretical predictions. Individual elements were found to vibrate with Bessel-like displacement patterns, and they were resonant at approximately 4 MHz. The full array showed variations in peak out-of-plane displacement levels across the device of 16%, and isolated elements that were dramatically overresponsive and under-responsive. The measured variations across the array may have an undesirable impact on the performance of the transducer and its radiated field.

Elasticity↗
PubMed2002

Anisotropy in domain engineered 0.92Pb(Zn1/3 Nb2/3)O3-0.08PbTiO3 single crystal and analysis of its property fluctuations.

The orientation dependence of slowness and electromechanical coupling coefficients of 0.92Pb(Zn1/3 Nb2/3)O3-0.08PbTiO3 (PZN-8%PT) domain engineered single crystal was analyzed based on the measured complete set of elastic, piezoelectric, and dielectric constants. There exist one quasi-longitudinal, one quasi-shear, and one pure shear wave in each of the [100]-[010], [010]-[001], and [001]-[110] planes. The slowness of the quasi-shear wave exhibits strong anisotropy in all three planes, and the coupling coefficient k33 and k31 reach their maximum in [001] and [110] directions of cubic axis, respectively. Because the composition of PMN-8%PT system is very close to the morphotropic phase boundary, the extraordinary large piezoelectric coefficients d31 and d33, and high coupling coefficient k33 are very sensitive to compositional variation. We have performed error analysis and proposed an improved characterization scheme to derive a complete data set with best consistency.

Anisotropy↗
PubMed2005

Piezoelectric micromachined ultrasonic transducers based on PZT thin films.

This paper describes fabrication and characterization results of piezoelectric micromachined ultrasonic transducers (pMUTs) based on 2-microm-thick Pb(Zr0.53Ti0.47O3) (PZT) thin films. The applied structures are circular plates held at four bridges, thus partially unclamped. A simple analytical model for the fully clamped structure is used as a reference to optimize design parameters such as thickness relations and electrodes, and to provide approximate predictions for coupling coefficients related to previously determined thin film properties. The best coupling coefficient was achieved with a 270-microm plate and amounted to kappa2 = 5.3%. This value compares well with the calculated value based on measured small signal dielectric (epsilon = 1050) and piezoelectric (e3l,f = 15 Cm(-2)) properties of the PZT thin film at 100 kV/cm dc bias. The resonances show relatively large Q-factors, which can be partially explained by the small diameters as compared to the sound wavelength in air and in the test liquid (Fluorinert 77). A transmit-receive experiment with two quasi-identical pMUTs was performed showing significant signal transmission up to a distance of 20 cm in air and 2 cm in the test liquid.

Computer Simulation↗
PubMed2005

Fabrication and characterization of piezoelectric micromachined ultrasonic transducers with thick composite PZT films.

Ferroelectric microelectromechanical systems (MEMS) has been a growing area of research in past decades, in which ferroelectric films are combined with silicon technology for a variety of applications, such as piezo-electric micromachined ultrasonic transducers (pMUTs), which represent a new approach to ultrasound detection and generation. For ultrasound-radiating applications, thicker PZT films are preferred because generative force and response speed of the diaphragm-type transducers increase with increasing film thickness. However, integration of 4- to 20-microm thick PZT films on silicon wafer, either the deposition or the patterning, is still a bottleneck in the micromachining process. This paper reports on a diaphragm-type pMUT. A composite coating technique based on chemical solution deposition and high-energy ball milled powder has been used to fabricate thick PZT films. Micromachining of the pMUTs using such thick films has been investigated. The fabricated pMUT with crack-free PZT films up to 7-microm thick was evaluated as an ultrasonic transmitter. The generated sound pressure level of up to 120 dB indicates that the fabricated pMUT has very good ultrasound-radiating performance and, therefore, can be used to compose pMUT arrays for generating ultrasound beam with high directivity in numerous applications. The pMUT arrays also have been demonstrated.

Computer-Aided Design↗
PubMed2005

Additive impairment of the barrier function by mechanical irritation, occlusion and sodium lauryl sulphate in vivo.

BACKGROUND: The interaction between potential irritants in the workplace might be important because workers are not usually exposed to a single irritant, but to multiple potentially harmful substances. Physical irritant contact dermatitis caused by friction or mechanical abrasion is a common occupational dermatosis. Prolonged water exposure by occlusion is also common in the workplace. Several studies have revealed the negative effect of the common anionic detergent sodium lauryl sulphate (SLS) on permeability barrier function. OBJECTIVES: To study the additive impairment of permeability barrier function by mechanical irritation combined with 0.5% SLS or prolonged water exposure by occlusion, as models of mild irritation. METHODS: The volar forearms of 20 healthy volunteers were exposed to mechanical irritation and occlusion with water or 0.5% SLS for four consecutive days in a combined tandem repeated irritation test (TRIT). Permeability barrier function was measured with a Tewameter TM 210. Irritation was assessed with a Chromameter CR 300 and a visual score. RESULTS: Barrier disruption in our model was rated as follows: occlusion with SLS and mechanical irritation > occlusion with SLS > occlusion with water and mechanical irritation > mechanical irritation and occlusion with water > occlusion with a glove and mechanical irritation > mechanical irritation > occlusion with water. Barrier disruption caused by occlusion or mechanical irritation was enhanced by the tandem application. The choice of irritant under occlusion, time of occlusion and order of tandem application all affected the degree of barrier disruption. Evaporimetry was able to detect early stages in the development of an irritant reaction before it became visible. Chromametry was not able to detect this early response. CONCLUSIONS: Physical irritants (friction, abrasive grains, occlusion) and detergents such as SLS represent a significant irritation risk and should be minimized, especially when acting together, as shown in our TRIT model.

Adult↗
PubMed2004

Vulnerability to ventricular arrhythmias [corrected] and heterogeneity of action potential duration in normal rats.

In normal rats, we analysed the arrhythmogenic role of intrinsic action potential duration (APD) heterogeneity. In each animal, ventricular arrhythmic events (VAEs) occurring spontaneously and during the exposure to an acute social challenge were telemetrically recorded. Action potentials were recorded from isolated left ventricular myocytes, at a pacing rate of 5 Hz (patch clamp: current-clamp mode). APDs were measured at -20 mV, -30 mV, -40 mV, -50 mV and -60 mV. The difference between the shortest and the longest APD was also computed, as an index of individual APD heterogeneity. Animals predisposed to stress-induced arrhythmias showed higher values of APD and APD heterogeneity as compared with the remaining rats. We concluded that, in the normal heart, a large intrinsic APD heterogeneity resulting from specific electrophysiological properties of ventricular myocytes is not in itself arrhythmogenic, but can predispose towards arrhythmia development under certain conditions, such as autonomic activation.

Action Potentials↗
PubMed2003

Non-contractile cells with thin processes resembling interstitial cells of Cajal found in the wall of guinea-pig mesenteric arteries.

Arterial interstitial cells of Cajal (ICC)-like cells (AIL cells) with a multipolar, irregular, elongated shape and with numerous thin (often less than 1 microm), sometimes branching, processes with lengths up to approximately 60 microm were isolated enzymatically from 1st to 7th order branches of guinea-pig mesenteric artery. Some of the processes of AIL cells were growing (average speed approximately 0.15 microm min-1) and their growth was blocked by 10 microM latrunculin B, an inhibitor of actin polymerisation. Staining with BODIPY phalloidin, a fluorescent dye selective for F-actin, showed the presence of F-actin in the processes of AIL cells. Voltage clamp of single AIL cells revealed an inward current that was four times more dense than in myocytes and was abolished by 10 microM nicardipine, and an outward current carried exclusively by potassium ions that was reduced by 1 mM 4-aminopyridine and/or 100 nM iberiotoxin but unaffected by 10 nM dendrotoxin-K. Imaging of intracellular ionised calcium with fluo-4 using a laser scanning confocal microscope showed local or global calcium transients lasting several seconds in approximately 28 % of AIL cells. When membrane current was recorded simultaneously, the calcium transients were found to correspond to long-lasting transient outward currents, which occurred at potentials positive to -40 mV. Unlike myocytes, AIL cells did not contract in response to 1 mM caffeine or 5 microM noradrenaline, although they responded with a [Ca2+]i increase. The segments of intact arteries did not stain for c-kit, a marker of ICCs. Single AIL cells stained positive for vimentin, desmin and smooth muscle myosin. The presence of ICC-like cells is demonstrated for the first time in the media of resistance arteries.

Animals↗
PubMed2004

NMDA receptors induce somatodendritic secretion in hypothalamic neurones of lactating female rats.

Many neurones in the mammalian brain are known to release the content of their vesicles from somatodendritic locations. These vesicles usually contain retrograde messengers that modulate network properties. The back-propagating action potential is thought to be the principal physiological stimulus that evokes somatodendritic release. In contrast, here we show that calcium influx through NMDA receptor (NMDAR) channels, in the absence of postsynaptic cell firing, is also able to induce vesicle fusion from non-synaptic sites in nucleated outside-out patches of dorsomedial supraoptic nucleus (SON) neurones of adult female rats, in particular during their reproductive stages. The physiological significance of this mechanism was characterized in intact brain slices, where NMDAR-mediated release of oxytocin was shown to retrogradely inhibit presynaptic GABA release, in the absence of postsynaptic cell firing. This implies that glutamatergic synaptic input in itself is sufficient to elicit the release of oxytocin, which in turn acts as a retrograde messenger leading to the depression of nearby GABA synapses. In addition, we found that during lactation, when oxytocin demand is high, NMDA-induced oxytocin release is up-regulated compared to that in non-reproductive rats. Thus, in the hypothalamus, local signalling back and forth between pre- and postsynaptic compartments and between different synapses may occur independently of the firing activity of the postsynaptic neurone.

Action Potentials↗
PubMed2002

Protein kinase Calpha participates in activation of store-operated Ca2+ channels in human glomerular mesangial cells.

Protein kinase C (PKC) plays an important role in activating store-operated Ca2+ channels (SOC) in human mesangial cells (MC). The present study was performed to determine the specific isoform(s) of conventional PKC involved in activating SOC in MC. Fura 2 fluorescence ratiometry showed that the thapsigargin-induced Ca2+ entry (equivalent to SOC) was significantly inhibited by 1 microM Gö-6976 (a specific PKCalpha and betaI inhibitor) and PKCalpha antisense treatment (2.5 nM for 24-48 h). However, LY-379196 (PKCbeta inhibitor) and 2,2',3,3',4,4'-hexahydroxy-1,1'-biphenyl-6,6'-dimethanoldimethyl ether (HBDDE; PKCalpha and gamma inhibitor) failed to affect thapsigargin-evoked activation of SOC. Single-channel analysis in the cell-attached configuration revealed that Gö-6976 and PKCalpha antisense significantly depressed thapsigargin-induced activation of SOC. However, LY-379196 and HBDDE did not affect the SOC responses. In inside-out patches, application of purified PKCalpha or betaI, but not betaII or gamma, significantly rescued SOC from postexcision rundown. Western blot analysis revealed that thapsigargin evoked a decrease in cytosolic expression with a corresponding increase in membrane expression of PKCalpha and gamma. However, the translocation from cytosol to membranes was not detected for PKCbetaI or betaII. These results suggest that PKCalpha participates in the intracellular signaling pathway for activating SOC upon release of intracellular stores of Ca2+.

Antibodies↗
PubMed2002

VEGF-induced mobilization of caveolae and increase in permeability of endothelial cells.

Glomerular epithelial cells (GEC) are a known site of vascular endothelial growth factor (VEGF) production. We established immortalized rat GEC, which retained the ability to produce VEGF. The isoforms expressed by GEC were defined as VEGF-205, -188, -120, and -164. The electrical resistance of endothelial cells cultured on GEC-conditioned matrix, an indicator of the permeability of monolayers to solutes, was significantly increased by the treatment with the neutralizing polyclonal antibodies to VEGF and decreased by VEGF-165. Transfection of endothelial cells with green fluorescence protein-caveolin construct and intravital confocal microscopy showed that VEGF results in a rapid appearance of transcellular elongated structures decorated with caveolin. Transmission electron microscopy of endothelial cells showed that caveolae undergo rapid internalization and fusion 30 min after application of VEGF-165. Later (36 h), endothelial cells pretreated with VEGF developed fenestrae and showed a decrease in electrical resistance. Immunoelectron microscopy of glomeruli confirmed VEGF localization to podocytes and in the basement membrane. In summary, immortalized GEC retain the ability to synthesize VEGF. Matrix-deposited and soluble VEGF leads to the enhancement of caveolae expression, their fission and fusion, formation of elongated caveolin-decorated structures, and eventual formation of fenestrae, both responsible for the increase in endothelial permeability.

Animals↗
PubMed1998

Luminal L-alanine stimulates exocytosis at the K+-conductive apical membrane of Aplysia enterocytes.

In Aplysia intestine, stimulation of Na+ absorption with luminal alanine increases apical membrane K+ conductance (GK,a), which presumably regulates enterocyte volume during stimulated Na+ absorption. However, the mechanism responsible for the sustained increase in plasma membrane K+ conductance is not known for any nutrient-absorbing epithelium. In the present study, we have begun to test the hypothesis that the alanine-induced increase in GK,a in Aplysia enterocytes results from exocytic insertion of K+ channels into the apical membrane. We used the fluid-phase marker horseradish peroxidase to assess the effect of alanine on apical membrane exocytosis and conventional microelectrode techniques to assess the effect of alanine on fractional capacitance of the apical membrane (fCa). Luminal alanine significantly increased apical membrane exocytosis from 1.04 +/- 0.30 to 1.39 +/- 0.38 ng. min-1. cm-2. To measure fCa, we modeled the Aplysia enterocyte as a double resistance-capacitance (RC) electric circuit arranged in series. Several criteria were tested to confirm application of the model to the enterocytes, and all satisfied the model. When added to the luminal surface, alanine significantly increased fCa from 0.27 +/- 0. 02 to 0.33 +/- 0.04 (n = 10) after 4 min. There are two possible explanations for our findings: 1) the increase in exocytosis, which adds membrane to the apical plasma membrane, prevents plasma membrane fracture, and 2) the increase in exocytosis delivers K+ channels to the apical membrane by exocytic insertion. After the alanine-induced depolarization of apical membrane potential (Va), there is a strong correlation (r = 0.96) between repolarization of Va, which reflects the increase in GK,a, and increase in fCa. This correlation supports the exocytic insertion hypothesis for activation of GK,a.

Alanine↗