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At least 991 records · Page 55Linked to original sources
PubMed2005

Electrophysiological and morphological properties of identified crossed tecto-reticular neurons in the rat superior colliculus.

Previously we classified randomly sampled neurons in the intermediate layer (SI) of the rat superior colliculus (SC) into six subclasses according to their firing responses to depolarizing current pulses and five subclasses based on their morphological properties in slice preparations. In the present study, we investigated properties of a major output cell group of the rat SC (PND 17-24), crossed tecto-reticular neurons (cTRNs), which project to the contralateral medial pontine reticular formation. The cTRNs were identified by retrograde labeling with a fluorescent tracer (n=112). We compared their properties with those of presumed interneurons (n=127). We found that a majority of cTRNs were regular spiking neurons with moderate firing frequency (73%) and were multipolar-shaped (66%). The cTRNs had larger membrane capacitance, larger soma size and lower input impedance than presumed interneurons. Electrical stimulation of the superficial gray layer induced oligosynaptic EPSPs in the cTRNs. When bicuculline was added to the extracellular solution, the EPSPs were markedly enhanced and bursting spike responses were induced. The bursting responses were suppressed by applying D-2-amino-5-phosphonovalerate. These results suggest that the cTRNs exhibit NMDA receptor-dependent bursting responses to visual inputs. These observations give insights into the neuronal mechanism of generating burst activity in cTRNs, which triggers orienting behaviors.

Animals↗
PubMed1999

Binding of the third Na+ ion to the cytoplasmic side of the Na,K-ATPase is electrogenic.

A new experimental setup was constructed to allow parallel measurements of total internal reflection fluorescence and of capacitance changes in Na,K-ATPase-containing membranes. Effects correlated with cytoplasmic sodium binding to Na,K-ATPase were investigated. Ion binding-induced fluorescence changes of the electrochromic dye RH421 in membrane fragments adsorbed on a transparent capacitative electrode corresponded perfectly to capacitance increases detected by a lock-in technique. From these electric measurements it was possible to estimate a dielectric coefficient of about 0.25 for the electrogenic binding of the third Na+ ion. Binding of K+ to cytoplasmic sites was electroneutral.

Animals↗
PubMed2003

Monitoring solid phase synthesis reactions with electrochemical impedance spectroscopy (EIS).

This work describes the use of electrochemical impedance spectroscopy (EIS) as a means to monitor solid phase synthesis on resin beads. EIS was used to track changes during the swelling of beads in various solvents, during three typical reactions and throughout cleavage of the final product from the bead. The impedance response was investigated in a chemical reactor and was found to be faintly sensitive to the resin swelling and solvent flow. The position of the electrode within the reactor was found to be critical as polystyrene based beads float or sink dependent upon the solvent used. However, by choosing electrode position it was possible to monitor reaction progress on beads or within the bulk reactant/product mixture. Of the three typical chemical reactions studied impedance spectroscopy successfully followed two. Fitting of the impedance data to an equivalent electrical circuit provided an estimate as to the relative contribution of capacitive and resistive components to the overall response. Kinetic data from two reactions were also modelled, in both cases complex kinetics was observed, in close agreement with other studies.

Journal Article↗
PubMed2006

Electrostatic modulation of the superfluid density in an ultrathin film.

By capacitively charging an underdoped ultrathin La2-xSrxCuO4 film with an electric field applied across a gate insulator with a high dielectric constant, relative changes of the areal superfluid density ns of unprecedented strength were observed in measurements of the film kinetic inductance. Although ns appears to be substantially reduced by disorder, the data provide, for the first time on the same sample, direct compelling evidence for the Uemura relation Tc proportional to ns(T=0) in the underdoped regime of copper-oxide superconductors.

Journal Article↗
PubMed1994

Silicon ribbon cables for chronically implantable microelectrode arrays.

This paper describes the design, fabrication, and testing of miniature ultraflexible ribbon cables for use with micromachined silicon microprobes capable of chronic recording and/or stimulation in the central nervous system (CNS). These interconnects are of critical importance in reliably linking these microelectrodes to the external world through a percutaneous connector. The silicon cables allow the realization of multilead, multistrand shielded local interconnects that are extremely flexible and yet strong enough to withstand normal handling and surgical manipulation. Cables 5 microns thick, 1-5 cm long, and from 60 to 250 microns wide have been fabricated with up to eight leads. The series lead resistance is typically 4 k omega/cm for polysilicon and 500 omega/cm for tantalum, with shunt capacitance values of 5-10 pF/cm and an interlead capacitance below 10 fF/cm. Soak tests in buffered saline performed under electrical and mechanical stress have been underway for over three years and show subpicoampere leakage levels. Silicon microprobes with built-in ribbon cables have remained functional for up to one year in the guinea pig CNS, recording driven single-unit activity and maintaining impedance levels in the 1-7 M omega range.

Animals↗
PubMed2005

Piezoelectric ceramics with high dielectric constants for ultrasonic medical transducers.

Complex system ceramics Pb(Sc(1/2)Nb(1/2))O3-Pb(Mg(1/3)Nb(2/3))O3-Pb(Ni(1/2)Nb(1/2))O3-(Pb0.965,Sr0.035) (Zr,Ti)O3 (PSN-PMN-PNN-PSZT abbreviated PSMNZT) have been synthesized by the conventional technique, and dielectric and piezoelectric properties of the ceramics have been investigated for ultrasonic medical transducers. High capacitances of the transducers are desired in order to match the electrical impedance between the transducers and the coaxial cable in array probes. Although piezoelectric ceramics that have high dielectric constants (epsilon33t/epsilon0 > 5000, k'33 < 70%) are produced in many foundries, the dielectric constants are insufficient. However, we have reported that low molecular mass B-site ions in the lead-perovskite structures are important in realizing better dielectric and piezoelectric properties. We focused on the complex system ceramics PSMNZT that consists of light B-site elements. The maximum dielectric constant, epsilon33T/epsilon0 = 7, 200, was confirmed in the ceramics, where k'33 = 69%, d33 = 940 pC/N, and T(c) = 135 degrees C were obtained. Moreover, pulse-echo characteristics were simulated using the Mason model. The PSMNZT ceramic probe showed echo amplitude about 5.5 dB higher than that of the conventional PZT ceramic probe (PZT-5H type). In this paper, the electrical properties of the PSMNZT ceramics and the simulation results for pulse-echo characteristics of the phased-array probes are introduced.

Journal Article↗
PubMed1995

A Simple and Rapid Method of Transformation of Streptomyces rimosus R6 and Other Streptomycetes by Electroporation.

Usually plasmid DNA is introduced into Streptomyces strains by polyethylene glycol-mediated transformation of protoplasts. However, many Streptomyces strains are only poorly or not at all transformable via protoplasts. Therefore, we have optimized the parameters critical for the application of electrotransformation of plasmid DNA into Streptomyces species. The most critical parameters evaluated for electrotransformation of the model strain Streptomyces rimosus R6 were the pretreatment of mycelia, buffer composition, and electric field strength. The electrocompetent mycelia were prepared from 24-h-old cultures, treated mildly with lysozyme, resuspended in sucrose-glycerol-polyethylene glycol buffer, and stored in aliquots at -70 deg C. The electric field strength of 10 kV/cm at 400 (Omega) and a capacitance of 25 (mu)F was applied. The method is simple and rapid, yielding transformant colonies in 48 to 72 h. Efficiencies of 10(sup5) to 10(sup6) transformants per (mu)g of plasmid DNA were reproducibly achieved for S. rimosus R6 and its mutants, and these numbers were 10(sup2) to 10(sup3) higher than those attained by polyethylene glycol-assisted transformation of protoplasts. In addition, we show that electroporation can be applied to other Streptomyces species, such as S. lividans 66, S. coelicolor A3(2), and an S. venezuelae strain. This last one could not be transformed by the standard protoplast procedure. Our data suggest that, because of the diversity of streptomycetes, the conditions have to be optimized for each strain.

Journal Article↗
PubMed1979

Electrotonic coupling among neuroendocrine cells in Aplysia.

1. We have discovered and characterized direct electrotonic synaptic coupling among a population of neuroendocrine (bag) cells in the parietovisceral ganglion of the marine gastropod Aplysia dactylomela. Pairs of ipsilateral and contralateral bag cells were impaled in vitro with microelectrodes. Current pulses applied through the electrometer amplifier to either cell influenced the other cell via electrotonic connections. 2. The coupling between bag cells was relatively weak when measured at the somata; the mean ratio of postsynaptic/presynaptic response amplitudes is 0.0075. Junctional rectification was not detected. The latency between pre- and postjunctional responses was long, up to 50 ms, a delay comparable to that for chemical synaptic transmission among neurons in this ganglion. Low-Ca2+/high-Mg2+ bathing solutions did not block transmission between bag cells, but did block chemical synaptic potentials in other identified neurons. 3. Postjunctional electrotonic responses had markedly slow time courses compared to the prejunctional responses, a characteristic that permitted summation of otherwise undetectable electrotonic PSPs and the demonstration of coupling between the two (bilateral) clusters of bag cells. 4. Based on extracellular recordings of their compound action potentials, the neurites of A. dactylomela bag cells extended a shorter distance (approximately 3 mm) along the connective than the neurites of A. californica or A. brasiliana. 5. Electrolytic lesions made along the neurites during intrasomatic coupling measurements significantly shortened the duration of postjuctional electrotonic responses, indicating that the neurites are widely electrically interconnected and, as a population, have a large effective membrane capacitance. The lesions furthermore revealed that an important site of electrotonic coupling is at the base of the pleurovisceral connective just rostral to the bag cell cluster. 6. The small-amplitude, long-latency and prolonged time course of postjunctional responses are interpreted to indicate remote and widespread coupling sites among the bag cells. This electrotonic coupling underlies the synchronized firing of the bag cells.

Action Potentials↗
PubMed1984

Intracellular recording from pectoral fin motoneurons of the stingray Dasyatis sabina, an elasmobranch fish.

Intracellular recordings were made from antidromically identified pectoral fin motoneurons in unanesthetized, decerebrate stingrays (Dasyatis sabina). These recordings had the three all-or-none components seen in other vertebrate motoneuron recordings. About 25% of the impalements had resting membrane potentials that were greater than -80 mV, which is larger than those of motoneurons from other vertebrate species. A novel depolarizing afterpotential (DAP) is associated with the isolated action potential occurring at the first node of Ranvier of the axon (M-spike). Occlusion experiments exclude recurrent events as the source of this potential. A capacitive source for the DAP is postulated. Using morphological and passive electrical data on motoneurons from previous studies, calculations of the passive decay of the nodal spike indicate that the membrane resistance of the initial segment is low and nearly equal to that of nodal membrane. The soma-dendritic (SD) spike is followed by a prominent, humped delayed depolarization (DD). The DD is temporally associated with the onset of the action potential produced by the initial segment (IS spike). Sources of the long-lasting period of repolarization recorded with the IS spike, which may underlie the DD, are postulated. The afterhyperpolarization (AHP) of stingray motoneurons tends to be shorter and smaller in amplitude than that of other vertebrate motoneurons. A negligible conductance change was often found during the period following an SD spike. No significant correlation was found between AHP duration and axonal conduction velocity. The input conductance of stingray motoneurons ranged between 1.5 X 10(-7) and 13.3 X 10(-7) S. The relationship between input conductance and axonal conduction velocity was determined from 42 motoneurons. These data were fitted by a power function with an exponent of 1.7, indicating that, in terms of membrane conductance properties, large stingray motoneurons are simply scaled-up versions of the small motoneurons.

Animals↗
PubMed2006

Swelling-activated pathways in human T-lymphocytes studied by cell volumetry and electrorotation.

Small organic solutes, including sugar derivatives, amino acids, etc., contribute significantly to the osmoregulation of mammalian cells. The present study explores the mechanisms of swelling-activated membrane permeability for electrolytes and neutral carbohydrates in Jurkat cells. Electrorotation was used to analyze the relationship between the hypotonically induced changes in the electrically accessible surface area of the plasma membrane (probed by the capacitance) and its permeability to the monomeric sugar alcohol sorbitol, the disaccharide trehalose, and electrolyte. Time-resolved capacitance and volumetric measurements were performed in parallel using media of different osmolalities containing either sorbitol or trehalose as the major solute. Under mild hypotonic stress in 200 mOsm sorbitol or trehalose solutions, the cells accomplished regulatory volume decrease by releasing cytosolic electrolytes presumably through pathways activated by the swelling-mediated retraction of microvilli. This is suggested by a rapid decrease of the area-specific membrane capacitance C(m) (microF/cm2). The cell membrane was impermeable to both carbohydrates in 200 mOsm media. Whereas trehalose permeability remained also very poor in 100 mOsm medium, extreme swelling of cells in a strongly hypotonic solution (100 mOsm) led to a dramatic increase in sorbitol permeability as evidenced by regulatory volume decrease inhibition. The different osmotic thresholds for activation of electrolyte release and sorbitol influx suggest the involvement of separate swelling-activated pathways. Whereas the electrolyte efflux seemed to utilize pathways preexisting in the plasma membrane, putative sorbitol channels might be inserted into the membrane from cytosolic vesicles via swelling-mediated exocytosis, as indicated by a substantial increase in the whole-cell capacitance C(C) (pF) in strongly hypotonic solutions.

Cell Membrane↗
PubMed1988

[A model of the coronary vascular bed and its verification by a physiological experiment].

We analysed the relationship between artery pressure (AP) and coronary flow (F) in the canine coronary bed, using an electrical analog model of the coronary circulation. The model contained a capacitance of epicardial vessels, input and terminal resistances, diode, and the number of e.m.f., simulated the intramyocardial pressure and zero-flow pressure. These e.m.f. are assumed to be a linear functions of left ventricular and aortic pressure. The value of coronary blood flow was calculated from experimental curves of AP and LVP and setting parameters. Good agreement was obtained between theoretical and experimental curves of coronary blood flow.

Animals↗
PubMed2003

Evolution in impedance at the electrode-skin interface of two types of surface EMG electrodes during long-term recordings.

The evolution in impedance at the electrode-skin interface of Beckman and Red Dot electrodes was assessed during long-term recordings. Impedance was measured between each pair of electrodes, arranged in a bipolar configuration on tibialis anterior (n=13). A waveform constructed of sinusoids of known frequencies, evenly distributed on a log scale from 1-16,384 Hz, was applied through the electrodes, and the result recorded by a DAQ system. SEMG signals were recorded at 1000 Hz during isometric dorsiflexion contractions of 30 s, performed every 15 min for 2 h. Impedance data were acquired at 65,536 Hz immediately before and after SEMG recordings. Large individual differences in impedance levels were observed at low frequencies. At high frequencies, impedance values depended only on the electrode type. Impedance decreased steadily with time for Beckman electrodes (p < 0.05), but did not decrease significantly for Red Dot electrodes. The magnitude of the reduction over time varied widely between individuals, and was related to the initial impedance values. The impedance-bandwidth product remained constant for each electrode type (95% confidence intervals 146.2-148.2 and 126.1-127.8 for Beckman and Red Dot electrodes respectively). When skin impedance is electrically modelled with a simple network containing a resistor and a capacitor, the capacitance varies with the properties of the electrode used, whereas resistance is dependent on the subject. Furthermore, the EMG spectrum is unaffected by impedance provided skin preparation is sufficient to reduce the impedance below 55 komega.

Adult↗
PubMedDate not supplied

Measurement of intracellular calcium levels of human spermatozoa acrosome reacted by electropermeabilization.

Human spermatozoa readily undergo in vitro capacitation and the acrosome reaction when exposed to a single, brief, high-voltage electric pulse in a medium containing calcium. Using the fluorescent calcium indicator, Fura-2, the changes in the intracellular calcium concentration of human sperm following exposure to voltages in the range of 200-2000 V cm-1 were measured. The induction of the acrosome reaction by the electropermeabilization pulse was also monitored. In comparison, changes in calcium uptake during a standard capacitation procedure in which sperm samples were incubated for 7 h were analyzed. At hourly intervals, acrosome reaction induction and intracellular calcium uptake were measured. The results indicate that electropermeabilization rapidly and efficiently produces high populations of acrosome-reacted sperm and a corresponding and associated increase in the intracellular calcium concentration.

Acrosome↗
PubMed1992

Circuit analysis of transmembrane voltage relationships in V-ATPase-coupled ion movements.

The concept of electrical circuit analysis is extended to include components found in membrane ionic transport systems. As in classical electrical equivalent circuits, resistors and capacitors are used to represent ion channels and the membrane capacitances, respectively; batteries represent energy sources driven by chemical reactions. In the extensions proposed, energy stored in various ionic concentrations is treated as charges on compartmental capacitors; symporters and antiporters are treated as energy-coupling devices analogous to transformers in alternating current electrical circuits. Pumps are shown to be special cases of porters in which the input circuit derives its energy from a chemical reaction. Using these components, circuit diagrams are drawn for several examples of membrane ion transport systems. By applying appropriate circuit analysis techniques, these diagrams facilitate the quantitative description of the energy distributions throughout the system.

Adenosine Triphosphatases↗
PubMed1983

Problems of recordings of nervous activity with glass microelectrodes in the CNS of insects.

Extracellular single unit recordings with glass microelectrodes in the central nervous system of insects display action potentials of variable amplitude, polarity and time course. This phenomenon is due to capacitive influences at the electrode in contact with the tissue. This is demonstrated by an electrical model circuit simulating extracellular recording conditions. Extracellularly recorded potentials often are very similar to intracellularly recorded ones. Criteria for the decision whether the electrode is intracellularly or not are discussed. Action potentials and slow potentials were recorded simultaneously in the acoustic neuropiles of Locusta. Since slow potentials may not only be distorted by capacitive properties of both the tissue and the electrode, but also are influenced by the anatomical organization of the nervous tissue, their interpretation is ambiguous.

Action Potentials↗
PubMed1989

A dual-frequency electrical impedance tomography system.

An electrical impedance tomography (EIT) system has been constructed, operating at two frequencies, 40.96 and 81.92 kHz, for investigating the practicability of the dual-frequency imaging method discussed theoretically in a previous paper. For testing the system, a phantom with a frequency-dependent electrical conductivity was designed. The properties of the phantom can be adjusted to match the frequency dependence observed in a given type of tissue. Dual-frequency images were obtained from a phantom simulating liver and also from 200 g of porcine liver in a saline tank. Prior to image reconstruction, it was necessary to apply a correction to the data to cancel the effects of stray capacitance within the electronics.

Animals↗
PubMed1990

A model of the stimulation of a nerve fiber by electromagnetic induction.

A model is presented to explain the physics of nerve stimulation by electromagnetic induction. Maxwell's equations predict the induced electric field distribution that is produced when a capacitor is discharged through a stimulating coil. A nonlinear Hodgkin-Huxley cable model describes the response of the nerve fiber to this induced electric field. Once the coil's position, orientation, and shape are given and the resistance, capacitance, and initial voltage of the stimulating circuit are specified, this model predicts the resulting transmembrane potential of the fiber as a function of distance and time. It is shown that the nerve fiber is stimulated by the gradient of the component of the induced electric field that is parallel to the fiber, which hyperpolarizes or depolarizes the membrane and may stimulate an action potential. Finally, it predicts complicated dynamics such as action potential annihilation and dispersion.

Action Potentials↗