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At least 811 records · Page 45Linked to original sources
PubMed1994

Mechanisms for electrical stimulation of excitable tissue.

Electric fields excite electrically active tissue by several mechanisms. A long, straight, uniform fiber is polarized by an activating function, proportional to the axial gradient of the axial electric field. During unipolar anodal stimulation, the activating function results in two areas of depolarization (virtual cathodes) that are responsible for anode-make stimulation. During unipolar cathodal stimulation, the virtual anodes can be exploited to produce unidirectional propagation and physiological recruitment of axons. Anode-break stimulation of nerves arises from the intrinsic properties of the sodium channel kinetics; cathode-break stimulation in nerves is anode-break stimulation at a virtual anode. The activating function applies to magnetic stimulation as well as to electric stimulation. Other important mechanisms of stimulation arise if the fiber is terminated, nonuniform, or curved. In the brain, cortical neurons are excited when the electric field is directed from the dendrites toward the axon. Possible mechanisms for cortical excitation are the impedance mismatch between the axon and dendritic tree, and the axon bending as it enters the white matter. Transcranial magnetic stimulation differs from transcranial electric stimulation because during magnetic stimulation the electric field is parallel to the brain surface, whereas during electric stimulation the electric field has components both parallel and perpendicular to the brain surface. Cardiac tissue can be represented by use of the bidomain model. This model predicts that a point-source stimulus results in adjacent areas of depolarized and hyperpolarized tissue. The presence of virtual anodes during cathodal stimulation is analogous to the creation of virtual anodes along a one-dimensional fiber by the activating function. Anode- and cathode-break stimulation both occur in cardiac tissue, but the mechanism may be different than for nerve and may depend on diffusion of depolarization into a previously hyperpolarized region. Electrical stimulation of cardiac tissue can cause reentry through a critical point mechanism. Two mechanisms for defibrillation have been hypothesized: (1) the relatively high junctional resistance between cardiac cells causes each cell to be depolarized on one side and hyperpolarized on the other; and (2) the fiber tracts within the heart behave like individual fibers, with fiber curvature providing a mechanism for polarization. Similarities among nerve, brain, and cardiac stimulation are emphasized.

Animals↗
PubMed1976

Coating evolution with an implantable biological battery.

A cathode of smooth platinum in a right endoatrial position and an anode of Domal magnesium were used to construct a hybrid bioelectric battery designed to power a pacemaker. In use the cathode is gradually covered by a coating consisting of a crystalline layer and a layer of connective tissue. This coating is responsible for the system change in the reduction process at the cathode level: the transfer from an oxygen to a hydrogen system. This system change causes a voltage drop in the bioelectric battery. This paper deals with oxygen diffusion across the tissue layer, as well as with various spectral and chemical analyses. A high level of calcium and phosphorus in the different analyses carried out seems to show that the presence of these elements is related to the coating of the cathode. The effect on the formation of the coating of the position of the cathode is also discussed.

Animals↗
PubMed2004

Synthesis of silver and gold nanoparticles by a novel electrochemical method.

Spherical silver and gold nanoparticles with narrow size distributions were conveniently synthesized in aqueous solution by a novel electrochemical method. The technological keys to the electrochemical synthesis of monodispersed metallic nanoparticles lie in the choice of an ideal stabilizer for the metallic nanoclusters and the use of a rotating platinum cathode. Poly(N-vinylpyrrolidone) (PVP) was chosen as the stabilizer for the silver and gold clusters. PVP not only protects metallic particles from agglomeration, but also promotes metal nucleation, which tends to produce small metal particles. Using a rotating platinum cathode effectively solves the technological difficulty of rapidly transferring the (electrochemically synthesized) metallic nanoparticles from the cathode vicinity to the bulk solution, avoiding the occurrence of flocculates in the vicinity of the cathode, and ensuring the monodispersity of the particles. The particle size and particle size distribution of the silver and gold nanoparticles were improved by adding sodium dodecyl benzene sulfonate (SDBS) to the electrolyte. The electrochemically synthesized nanoparticles were characterized by TEM and UV/Vis spectroscopy.

Journal Article↗
PubMed1997

Effects of catholytes on the mobilization of proteins after capillary isoelectric focusing.

Purified proteins and human plasma proteins were separated by capillary isoelectric focusing and detected by cathodic mobilization, e.g. by replacing the cathodic sodium hydroxide solution by solutions containing another anion. The effect of catholyte anions on the resolution of mobilized proteins was examined. Compared with the chloride or phosphate anion, organic anions having small dissociation constants improved protein resolution, especially in the range of acidic proteins. Among the catholytes examined, acetic acid gave the best resolution for purified proteins and human plasma proteins. Measurement of the changes of electric current during the mobilization process indicated that organic anions with low mobility move slowly towards the anode and retard changes of pH gradient in the capillary. Isoelectric focusing, cathodic mobilization, and direct pH measurement in polyacrylamide gel columns (1.3 mm internal diameter and 38 mm long) also revealed these effects of low mobility anions. In order to visualize the behavior of human plasma proteins in the mobilization step, micro two-dimensional polyacrylamide gel electrophoresis was employed. The results indicated that the proteins migrate towards the cathode, preserving their relative positions attained during the isoelectric focusing step.

Acetic Acid↗
PubMed1983

Electrical osteogenesis by low direct current.

A constant direct current cathode was employed in the medullary canal of the rabbit tibia to investigate electrical osteogenesis at low current levels. Currents of 0.015 or 0.075 microA were delivered to the bone and the biological response was compared with contralateral controls receiving 20 microA. This investigation was performed to determine if electrical osteogenesis occurs at current levels below the previously studied range of 1-100 microA with stainless steel electrodes. New bone formed by 0.015 microA cathodes was statistically comparable with that found around inactive cathodes from an earlier pertinent study. The osteogenic response to 0.075 microA cathodes was significantly elevated above that to inactive ones, thus substantiating electrical osteogenesis for currents below 1 microA. However, it is evident that this does not demonstrate a further stimulatory range but that currents near 0.075 microA probably approach the lower significant limit for electrically induced bone growth with stainless steel electrodes.

Animals↗
PubMed1986

The bone growth chamber for quantification of electrically induced osteogenesis.

A dividable titanium implant was inserted in the tibial metaphysis of rabbits, which permitted a numerical evaluation of ingrowing bone. The implant on the test side was used as cathode and was connected to a subcutaneously located stimulator delivering constant current of either 5 microA, 20 microA, or 50 microA. A corresponding control implant was inserted in the other tibia of the same animal and treated likewise, but was not connected to the stimulator. Distally to each implant, a platinum-iridium screw was inserted into the cortex and connected on the test side to the stimulator to serve as the anode. The results showed a 2.4-fold increase in bone formation with 5 microA. In the 20-microA group, there was 2.6-fold more bone in the test chambers. Direct current (DC) stimulation with 50 microA caused a clear decrease of bone volume, with an average of 48% less bone in the test implants. The results indicate that 5 and 20 microA direct current enhance bone ingrowth into a titanium implant that is used as a cathode. The osteogenesis seemed to be more pronounced in the case where the chamber was used as a cathode compared to earlier experiments in which the cathode was placed at a distance of 5 mm from the implant.

Animals↗
PubMed1992

Bone formation near direct current electrodes with and without motion.

The osteogenesis induced in the medullary canal of rabbits by the implantation of moving and stationary wire electrodes was studied with and without the simultaneous application of 20-microA constant direct cathodic current. After 3 weeks, the formation of new trabecular bone in the canal was studied and measured microscopically. Electrically stimulated osteogenesis was not observed at stationary electrodes. As in previous studies with this model, a movable electrode alone stimulated new bone formation whose area was 7-10% of the canal area. The amount of this bone was not statistically increased by the addition of cathode current. Movable, electrically active cathodes were associated, however, with fluid-filled spaces incorporated within the new trabecular bone. When mechanical stimuli were controlled, we were not able to demonstrate that the direct current stainless steel cathode acts either as an inducer or a substantial enhancer of medullary osteogenesis.

Analysis of Variance↗
PubMed1999

Effect of faradic products on direct current-stimulated calvarial organ culture calcium levels.

Calcium release from mouse calvarial organ cultures was used to analyse the well-described biological effects of constant direct current (20 microA) in combination with Faradic products generated at a titanium wire cathode. Constant 20-microA direct current stimulation alone, delivered by agar salt bridges, consistently lowered the media calcium levels. Direct exposure of calvariae to a titanium cathode and its faradic products resulted in further lowering of media calcium levels and also a significant increase in the media pH. Hydrogen peroxide is a faradic product of the titanium cathode, micromolar amounts being generated by our system over 24 hr. H(2)O(2) is pro-resorptive whereas elevated pH stimulates osteoblast activity. We propose that where bone tissue is in direct contact with metal wire cathodes, the faradic products, hydrogen peroxide and hydroxyl ion, are significant factors which, in their own right, further contribute to accelerated remodelling and improved clinical outcome.

Animals↗
PubMed1985

Unusual sialilation of three different rare genetic variants of serum DBP: Gc1A17, Gc1A16, and Gc1A11.

The proteins of three anodal Gc1 variants, Gc1A16, 1A11, and 1A17, are characterized by the most acidic isoelectric points observed so far among the different Gc mutants. Stepwise removal of N-acetylneuraminic acid (NANA) by treatment with neuraminidase was performed to estimate the degree of sialilation of these Gc variants. The results indicate that both proteins, the anodal and the cathodal component of these Gc1 mutants, carry sialic acid residues. This observation is remarkable in so far as usually only the anodal component of the Gc1 protein contains NANA and only a single residue. From the experiments carried out it can be deduced that Gc1A16 has two NANA residues in the anodal and one NANA residue in the cathodal component. Gc1A16 was found in four members of three generations in a Danish family; the variant segregated as a Mendelian trait. More difficult to interpret are the results obtained with the variants Gc1A11 and Gc1A17. Gc1A11 probably has three NANA residues in the anodal and two NANA residues in the cathodal component. Gc1A11 has been observed in two mother-child pairs and is presumably also a simple genetic trait. Gc1A17 has also several NANA residues in both Gc proteins; it is suggested that the anodal component has either three or four NANA residues and the cathodal component either two or three NANA residues. Family information on this variant is not yet available.

Alleles↗
PubMed2006

Potentially implantable miniature batteries.

All presently used batteries contain reactive, corrosive or toxic components and require strong cases, usually made of steel. As a battery is miniaturized, the required case dominates its size. Hence, the smallest manufactured batteries are about 50 mm3 in size, much larger then the integrated circuits or sensors of functional analytical packages, as exemplified by implantable glucose sensors for diabetes management. The status of the miniaturization of the power sources of such implantable packages is reviewed. Three microcells, consisting only of potentially harmless subcutaneously implantable anodes and cathodes, are considered. Because their electrolyte would be the subcutaneous interstitial fluid, the cells do not have a case. One potentially implantable cell has a miniature Nafion-coated Zn anode and a biocompatible hydrogel-shielded Ag/AgCl cathode. The core innovation on which the cell is based is the growth of a hopeite-phase Zn2+ conducting solid electrolyte film on the discharging anode. The film blocks the transport of O2 to the Zn, preventing its corrosion, while allowing the necessary transport of Zn2+. The second cell, with the same anode, would have a bioinert hydrogel-shielded wired bilirubin oxidase-coated carbon cathode, on which O2 dissolved in the subcutaneous fluid would be electroreduced to water. In the third cell, the glucose of the subcutaneous interstitial would be electrooxidized to gluconolactone at an implanted wired glucose anode, similar to that tested now for continuous glucose monitoring in diabetic people, and O2 in the subcutaneous fluid would be electroreduced to water on its wired bilirubin oxidase cathode.

Electricity↗
PubMed2001

Electrolytic hydride generation atomic absorption spectrometry for the determination of antimony, arsenic, selenium, and tin--mechanistic aspects and figures of merit.

This article deals with the electrocatalytic and electrochemical mechanisms of hydride formation and their dependence on hydrogen overvoltage. A three-electrode-arrangement was used to determine the hydrogen overvoltage of different cathode materials (Pt, Au, Ag, glassy carbon, Cd, Pb, amalgamated Ag). The applicability of these cathode materials was tested for hydride formation using As(III), As(V), Sb(III), Sb(V), Se(IV), and Sn(IV). Glassy carbon is the most suitable cathode material for hydride generation with As(III), Sb(III), Se(IV), and Sn(IV). Hg-Ag is well suited for the production of stibine and arsine. As(III), As(V), Sb(III), and Sb(V) were all converted into their hydrides with efficiencies > 90%. A detection limit in the range of 0.11-0.13 microg L(-1) for As and Sb (sample volume 200 microL) was obtained for cathode materials with a high hydrogen overvoltage. The precision of replicate measurements was better than 5% calculated as variation coefficient. The accuracy of the presented method was verified by analysis of certified reference materials and tissues of cancer patients. The recovery rates for As and Se were calculated to be 93-108%.

Journal Article↗
PubMed2004

Effects of transcranial direct current stimulation over the human motor cortex on corticospinal and transcallosal excitability.

Weak transcranial direct current stimulation (tDCS) can induce long lasting changes in cortical excitability. In the present study we asked whether tDCS applied to the left primary motor cortex (M1) also produces aftereffects distant from the site of the stimulating electrodes. We therefore tested corticospinal excitability in the left and the right M1 and transcallosal excitability between the two cortices using transcranial magnetic stimulation (TMS) before and after applying tDCS. Eight healthy subjects received 10 min of anodal or cathodal tDCS (1 mA) to the left M1. We examined the amplitude of contralateral motor evoked potentials (MEPs) and the onset latency and duration of transcallosal inhibition with single pulse TMS. MEPs evoked from the tDCS stimulated (left) M1 were increased by 32% after anodal and decreased by 27% after cathodal tDCS, while transcallosal inhibition evoked from the left M1 remained unchanged. The effect on MEPs evoked from the left M1 lasted longer for cathodal than for anodal tDCS. MEPs evoked from the right M1 were unchanged whilst the duration of transcallosal inhibition evoked from the right M1 was shortened after cathodal tDCS and prolonged after anodal tDCS. The duration of transcallosal inhibition returned to control values before the effect on the MEPs from the left M1 had recovered. These findings are compatible with the idea that tDCS-induced aftereffects in the cortical motor system are limited to the stimulated hemisphere, and that tDCS not only affects corticospinal circuits involved in producing MEPs but also inhibitory interneurons mediating transcallosal inhibition from the contralateral hemisphere.

Adult↗
PubMed1975

Elastolytic activity of human duodenal contents.

Elastolytic activity of human duodenal contents was determined using the new chromogenic substrate succinyl-trialanine-p-nitroanilide (Suc-Ala3-NAp). The mean output values after pancreatic stimulation with pancreozymin and secretin were significantly higher in controls than in subjects with impairment of other secretory values (volume, bicarbonate, amylase, lipase). Agar gel electrophoresis and chromatography on DEAE-Sephadex revealed one to two fractions which differed in mobility (cathodic and anodic fraction), elution with different NaCl concentrations (0.15 M, cathodic fraction; 0.3 M, anodic fraction), and in behaviour towards synthetic and natural substrate (Suc-Ala3-NAp) and elastin-Congo Red). The cathodic fraction cleaved both substrates, whereas the anodic fraction cleaved only Suc-Ala3-NAp. After trypsin and enterokinase treatment the anodic fraction behaved as the cathodic fraction on DEAE-Sephadex chromatography. The molecular weights (Sephadex G-100) and the Michaelis constants (Suc-Ala3-NAp) of both fractions were identical (24 500; 0.45 X 10(-3) M). These fractions represent probably diffenent activation forms of pancreatic elastase.

Cholecystokinin↗
PubMed1985

The substrates for self-stimulation of the lateral hypothalamus and medial prefrontal cortex: a comparison of strength-duration characteristics.

The directly activated substrates for self-stimulation of the lateral hypothalamus (LH) and medial prefrontal cortex (MPFC) were described by comparing their strength-duration characteristics. The current required to maintain a half-maximal rate of lever pressing was traded off against the pulse duration while all other stimulation parameters were kept constant. In this manner, cathodal strength-duration curves were obtained at four LH and eight MPFC sites; anodal curves were obtained at two of the LH and six of the MPFC sites. In general, the cathodal LH curves had lower rheobases than the cathodal MPFC curves and continued to descend after the MPFC curves had levelled off. At short pulse durations, the anodal curves lay above the cathodal curves, a finding more pronounced in the LH data. The two sets of curves converged at the longer pulse durations. The differences in the strength-duration curves are consistent with the notion that different directly stimulated neurons are responsible for the rewarding effects of LH and MPFC stimulation. Anatomical and physiological properties that could account for these differences are discussed.

Animals↗
PubMed1987

Antithrombin antigen of high molecular weight associated with neoantigen in hemophilic plasma after factor IX concentrate therapy.

These studies were performed to investigate the cause(s) of the cathodal shift of mobility seen in crossed immunoelectrophoresis of antithrombin antigen in plasma of hemophilic patients after factor IX concentrate therapy. These plasmas were shown to contain antithrombin neoantigen with apparent identity to the neoantigen present in normal serum but not present in normal plasma. Sephacryl S-200 gel chromatography of serum demonstrated that the neoantigen eluted with the first two, early eluting protein peaks; thus the neoantigen had a higher molecular weight than native antithrombin. When the chromatographic fractions containing the neoantigen were studied by crossed immunoelectrophoresis, they were found to contain antithrombin antigen of more cathodal mobility than normal. Sephacryl S-200 chromatography of factor IX concentrate-treated hemophilic plasma also showed an early eluting peak of antithrombin antigen of more cathodal mobility than normal in crossed immunoelectrophoresis. The mobility of this peak was identical to the cathodal peak found in normal serum and in early eluting fractions from chromatography of normal serum. These results support the conclusion that factor IX concentrate-treated hemophilic plasma contained a non-functional, high molecular weight form of antithrombin, associated with the presence of neoantigen, which may represent complexed and/or modified antithrombin produced by the action of the concentrates in vivo.

Antigens↗
PubMed1992

Purification of recombinant human growth hormone by isoelectric focusing in a multicompartment electrolyzer with Immobiline membranes.

Recombinant human growth hormone (r-hGH) expressed in Escherichia coli, was 70-80% purified by a combination of ion-exchange chromatography and metal ion affinity chromatography. For the last purification step, a multicompartment electrolyzer was used, containing three compartments delimited by isoelectric membranes and two additional anodic and cathodic chambers. The central compartment was situated between two membranes having isoelectric points (pI) of 5.08 (anodic) and of 5.16 (cathodic), i.e. equidistant from the pI value of hGH (pI 5.12). r-hGH was isoelectric between these two membranes and could not leave the central chamber, while more acidic and more cathodic impurities collected in the two lateral chambers under the influence of the electric field. The r-hGH, thus purified, exhibited a single band by isoelectric focusing (IEF) in immobilized pH gradients (IPG) and gave recoveries greater than 90%. The problem of isoelectric precipitation in a practically ion-free environment was alleviated by focusing in 30% glycerol added with 1% neutral detergent (Nonidet-P40). The latter was eliminated by passage through a Q-Sepharose column after collecting the pI 5.12 band from the electrolyzer. Also the pre-hormone (pre-hGH) can be purified in a similar manner (30% glycerol, 1% Nonidet P-40) between two membranes having pIs 4.77 (anodic) and 4.87 (cathodic) (pre-hGH pI 4.82). This paper demonstrates the possibility of purifying by a focusing process also poorly soluble proteins at the pI.

Growth Hormone↗
PubMedDate not supplied

A comparison of corticospinal activation by magnetic coil and electrical stimulation of monkey motor cortex.

The effects of different orientations of a Cadwell round magnetic coil (MC) were compared with each other and with surface electrical stimulation of motor cortex in monkeys anesthetized with pentobarbital or urethane. Recordings were made from within the lateral corticospinal tract, either from axonal populations or with a microelectrode from individual axons. A lateral-sagittally orientated MC directly excited corticospinal neurons at lower stimulus intensity than was required for indirect, i.e., transsynaptic excitation via inputs to corticospinal neurons. By contrast, in 2 out of 3 macaques tested, a vertex-tangential orientation could excite corticospinal neurons indirectly at lower intensities than were required for direct excitation; at higher intensities, direct excitation also occurred. The site of direct corticospinal excitation by a lateral-sagittally orientated MC was inferred by comparing the response variability and latency to MC and surface electrical stimuli. Cathodal stimuli elicited more variable corticospinal population responses and later individual axonal responses than were obtained with anodal stimuli. The variability in response is attributed to interaction between nearby, on-going synaptic bombardment and the stimulus, implying that surface cathodal stimuli directly activate corticospinal neurons at the spike trigger zone (presumably the initial segment). By contrast, the consistency and reduced latency of the corticospinal responses to surface anodal stimuli are attributed to the direct excitation of corticospinal fibers within the white matter. When the stimulus intensity is clearly above threshold, surface anodal and cathodal stimuli can activate corticospinal neurons both directly and indirectly. Direct corticospinal excitation by the MC can resemble the effects of either surface anodal or surface cathodal stimuli. We conclude that the MC can activate corticospinal neurons at the spike trigger zone or their fibers deeper in white matter. The findings in the monkey are used to interpret the effects of different MC orientations in the human.

Action Potentials↗
PubMed1994

Regeneration of rat sciatic nerves in silicone tubes: characterization of the response to low intensity d.c. stimulation.

Endogenous d.c. electric fields have been postulated to play a role in normal development and repair functions of a variety of living systems. The corollary hypothesis, that exogenous electric fields can alter development and repair mechanisms, has led to the use of d.c. electric fields as a means to enhance mammalian peripheral nerve regeneration. This study investigates the response of transected rat sciatic nerves within silicone tubes to low intensity d.c. stimulation. In 40 rats, the right sciatic nerves were transected and sutured into silicone tubes, leaving a 5.0 mm gap between the stumps. The nerves were either treated with 10 microA d.c., with the cathode at the midpoint of the tube and the anode distant, or received no exogenous current. Three weeks later, transverse sections from the center of the tissue bridging the two segments were analysed by sampling approximately 12% of the cross sectional area, using x 1000 magnification on the light microscope. All non-stimulated (control) nerves showed regeneration of myelinated axons at the center of the bridge, while only 35% of the nerves stimulated with 10 microA had such a response. Of the nerves with regeneration of myelinated axons at the center of the tube, the control nerves had significantly more myelinated axons (P = 0.0028) than treated nerves. Stimulated nerves showed bizarre regeneration responses, including formation of multiloculated cysts and neuroma-like formations. In control nerves there was a gradual tapering of axon number from proximal to distal in the regeneration bridge, while in the stimulated nerves there was a sharp decrease in the number of axons proximal to the cathode. We hypothesize that this effect is due to the accumulation of electrolysis products at the cathode, which inhibit regeneration through this region. Regeneration of transected rat sciatic nerves is not enhanced by electric currents applied in this manner. Previous work interpreted the increased number of axonal cross-sections in the tube as an increase in the absolute number of regenerating fibers. Our data suggest that the increased number of axonal cross-sections is due to neuroma formation, probably in response to the accumulation of electrolysis products at the cathode. This work brings into question claims of an enhancement of peripheral nerve regeneration by applied electric fields.

Animals↗