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PubMed1989

Thermocycling, silane priming, and resin/porcelain interfaces interfaces--an electrical leakage study.

High 24-hour tensile and shear bond strengths have been reported for silane-primed resin/porcelain interfaces, but bonds often failed after prolonged water storage. This study was designed to determine the influences of both a silane primer and thermocycling on interfacial leakage between a light-cured BisGMA resin and dental porcelain. Porcelain discs measuring 10 mm in diameter and 1.5 mm in thickness were fired. Axial cylindrical cavities were prepared through the discs with a diamond bur. Four groups of eight discs each were restored in the following modes: groups 1 and 2 with light-cured bonding agent and light-cured microfilled resin, and groups 3 and 4 with a silane primer followed by the same bonding agent and resin. Specimens were water-stored for 24 hr, after which those in groups 2 and 4 were thermocycled 200 times between 4 degrees C and 60 degrees C. Specimens were then sealed to steel anodes and placed in 1% KCl, maintained at 21 degrees C, around a stainless steel cathode. Leakage currents were recorded daily for 30 days and after six months, by application of a 10 V potential difference between the cathode and each anode. Positive and negative controls gave massive and nil readings, respectively. The mean leakages were consistently greatest in group 2 (being significantly greater than for the other groups). Results suggest that silane priming minimizes leakage at the resin/porcelain interface after thermal cycling.

Bisphenol A-Glycidyl Methacrylate↗
PubMed1995

Effect of mercury on corrosion of eta' Cu-Sn phase in dental amalgams.

OBJECTIVES: The eta' Cu-Sn phase is the most corrosion-susceptible major component of the microstructure in high-copper dental amalgams, even though metallurgically prepared specimens of the phase are corrosion-resistant. The purpose of this study was to determine if mercury is the cause of the degradation. METHODS: Specimens of metallurgically prepared eta' Cu-Sn phase were tested in synthetic saliva using electrochemical methods. Mercury was adsorbed on the surface by exposure to mercury vapor, and the changes in the corrosion potential and anodic polarization characteristics were determined. Galvanic currents between eta' specimens and a high-copper dental amalgam were measured for both Hg-free and Hg-contaminated eta' electrodes. RESULTS: The Hg-free eta' phase showed a wide region of passivity. Exposure to mercury made the eta' phase electrochemically more active, and current peaks appeared on the polarization curves. The Hg-free eta' electrode was a cathode to a high-copper dental amalgam. The Hg-contaminated eta' electrode started also as a cathode, but became anode after a period of exposure. SIGNIFICANCE: It was concluded that mercury destabilizes the protective passive film on the eta' phase, making the phase more susceptible to corrosion in the oral environment. The results of the galvanic current measurements seem to indicate that the galvanic interaction between eta' and the other phases facilitates the mercury-related degradation.

Chemical Phenomena↗
PubMed1980

Electrical stimulation with pt electrodes. IV. Factors influencing Pt dissolution in inorganic saline.

Trace analysis has shown that Pt electrodes can suffer appreciable dissolution when used to apply biphasic current pulses of the type used in neural stimulation. The dissolution occurs even under conditions where other irreversible faradaic reactions, e.g., H2O electrolysis, are avoided. In the present study, factors influencing the dissolution of Pt electrodes during biphasic pulsing in neutral inorganic saline have been examined. The findings are consistent with the behaviour of Pt electrodes reported in other inorganic media. In a given test, the quantity of Pt dissolved was found to be a linear function of the aggregate anodic or cathodic charge injected. Therefore, dissolution 'rates' can be conveniently expressed in terms of nanograms of Pt per coulomb injected, e.g., 100 ng C-1. Most of the Pt went into solution as Pt (II) species, so the above rate would correspond approximately to 100 p.p.m. of the anodic charge per pulse. For anodic-first (AF) pulses, charge density was the major factor controlling dissolution, whereas for cathodic-first (CF) pulses, pulse duration had the greater influence. Depending on the polarity (AF or CF), charge density, and duration of the biphasic pulse, the dissolution rate for smooth bead electrodes ranged from 30 to 300 ng C-1. Lower rates were achieved with platinized electrodes but in the absence of organic solutes, it is unlikely that Pt dissolution can be completely suppressed.

Electric Stimulation↗
PubMed1995

Effect of temperature on electrochemical deposition of calcium phosphate coatings in a simulated body fluid.

Calcium phosphate coatings were deposited on titanium plate by an electrochemical method in simulated body fluid at 5-62 degrees C. X-ray diffractometry and FTIR studies demonstrated that the deposits at 5, 22 and 37 degrees C were amorphous and those at 52 and 62 degrees C contained Mg(OH)2, CaCO3 and carbonate apatite of low crystallinity. The calcium, magnesium and phosphorus contents of deposit increased in direct proportion to the square root of loading time of cathodic potential. Induction periods, which might be thought to be the time required to decrease the pH of the electrolyte around the cathode by the formation of H2 gas and to start deposition of calcium phosphate, were observed on all the regression lines. It is concluded that in the electrochemical synthesis of calcium phosphate in this temperature range the diffusion process is a rate-determining step.

Body Fluids↗
PubMed1983

Characterization of immunoglobulins from the brown bullhead (Ictalurus nebulosus) produced against a naturally occurring bacterial pathogen, Aeromonas hydrophila.

The primary immune response in the brown bullhead (Ictalurus nebulosus) to intramuscularly injected, chloroform-killed Aeromonas hydrophila reached an agglutination titer of 128 in 3 wk, and the response to the bacteria plus adjuvant reached a titer of 512 in 5 wk. Anti-Aeromonas hydrophila antibodies from brown bullheads were excluded from Sephadex G-200 and had an immunoelectrophoretic migration pattern toward the cathode. Cleavage of the macromolecule by 2-ME reduction and iodoacetamide alkylation yielded subunits that were resumptively heavy chains of about 50,500 daltons and light chains of about 22,500 daltons. Bullhead antibodies were assumed to be tetrameric in configuration and therefore to have an approximate molecular weight of 600,000 daltons assuming a J chain is present in both early (6 wk) and late (20 wk) immune sera. The agglutinating activity of the antibody was completely eliminated by exposure to 65 degrees C for 30 min. Immunoelectrophoresis showed a single antibody component that moved toward the cathode. The structure and molecular weight of bullhead antibodies appears similar to that observed in channel catfish and other closely related teleost fish.

Aeromonas↗
PubMed1988

Spreading depression and central nervous system pharmacology.

Spreading depression is a reversible response of brain tissue to a local insult. It has been postulated to be the physiological substrate for the aura phase of classic migraine. The properties and mechanisms of spreading depression were studied in the parietal neocortex of the alfentanil-anesthesized rat, by using a cup electrode that provided close control of the electrical stimulus while allowing specific ion (K+) and potential recordings to be made directly beneath the cathode, the region of origin of the stimulus-induced spreading depression. Cathodal stimulation caused the extracellular K+ concentration to rise, and spreading depressions were observed when this concentration exceeded 8-12 mM in the upper 100-200 microns of cortex. In some experiments extracellular [K+] continued to increase for 5-10 sec after termination of the stimulus, without detectable after-discharge in the potential record, before subsiding. While spreading depression could easily be induced by pressure on the cortex, local damage incidental to opening the dura rarely induced spreading depression. This suggests that a local (1-mm2) neurovascular injury is not likely to induce spreading depression--at least in normal cortex--and so is probably not the source of the spreading depression postulated to generate the aura of classic migraine. Mechanisms of spreading depression, and drugs that influence spreading depression, are reviewed, and possible uses of spreading depression in the pharmacology of the central nervous system are considered.

Animals↗
PubMed1985

Characterization of synthetic carrier ampholytes by repetitive scanning of the electric field during focusing.

This paper reports the utilization of a potential gradient array detector for monitoring the dynamics of the electric field during isoelectric focusing. Transient and steady state electric field profiles are presented for synthetic carrier ampholyte mixtures with a wide (approximately 3-10) pH range. Two available commercial products (Ampholine and Pharmalyte) and a laboratory synthesized mixture (PEHA ampholytes) are compared. The formation of conductivity gaps and their migration toward the cathode in extended experiments (cathodic drift) can be visualized with this system.

Ampholyte Mixtures↗
PubMed1995

Activation of calcium-dependent chloride channels causes post-tetanic depolarization in rabbit parasympathetic neurons.

Intracellular recordings were made from neurons in rabbit and feline vesical parasympathetic ganglia in vitro. In response to cathodal current injection (0.1-1 nA for 2-20 ms) the majority of rabbit neurons (229 out of 250) exhibited a single action potential that was followed by a fast and slow after-hyperpolarization (sAHP neuron). The remainder of the cells exhibited an action potential followed by only a fast after-hyperpolarization (fAHP neuron). fAHP neurons did not exhibit anomalous rectification and a spontaneous rhythmic hyperpolarization, which were common membrane properties in sAHP neurons. In response to a train of cathodal current pulses (5-20 Hz for 0.1-10 s), fAHP neurons exhibited action potentials followed by a post-tetanic depolarization (PTD). The PTD was associated with a decrease in membrane input resistance. The amplitude and duration of the PTD were a function of the number of action potentials in the train. The amplitude of the PTD was increased by membrane hyperpolarization and its estimated reversal potential was approximately -30 mV. Low-chloride solution and intracellular injection of chloride ions augmented the amplitude and duration of the PTD, whereas low-sodium, high-potassium and low-potassium solutions did not affect them. Tetraethylammonium (5-10 mM) and barium (0.5-1 mM) increased the amplitude and duration of the PTD. Nominal calcium-free solutions and omega-conotoxin (500 nM) abolished the PTD. The data suggest that activation of chloride channels by calcium influx through omega-conotoxin-sensitive calcium channels mediates the PTD. Repetitive stimulation of the pelvic nerve evoked a train of orthodromic action potentials followed by the PTD of fAHP neurons. (+)-Tubocurarine (10 microM) and hexamethonium (200 microM), but not atropine (1 microM), abolished orthodromic action potentials and the PTD, whereas these cholinergic antagonists did not depress the PTD evoked by direct action potentials. In summary, the data suggest that the PTD may function as a slow synaptic potential in fAHP neurons. This appears likely because neither slow excitatory nor inhibitory postsynaptic potentials are present in neurons of rabbit vesical parasympathetic ganglia. In contrast, slow inhibitory and excitatory postsynaptic potentials were recorded from neurons in feline vesical parasympathetic ganglia.

Action Potentials↗
PubMed1983

Functional characterization of hemoglobins from South Brazilian freshwater teleosts--I. Multiple hemoglobins from the gut/gill breather, Callichthys callichthys.

The five main hemoglobins of the South Brazilian bimodal breathing teleost, Callichthys callichthys were separated, and their oxygenation properties and those of the unfractionated hemolysate were measured at 10, 20 and 30 degrees C. The cathodal Hb component had a higher O2 affinity than the other components and a lower Bohr effect (phi = delta log P 50/delta pH), which is reversed at low and high pH values (6.8 greater than pH greater than 7.8). The other, anodal hemoglobins had normal Bohr effects and similar functional properties. The erythrocytic cofactor ATP had no significant effects on the O2 affinities of the hemolysate and the isolated anodal components at physiological pH conditions, but decreased the affinity of the cathodal Hb over the entire pH range tested (6.5-8.2). All hemoglobins showed high thermal dependence of O2 affinity (delta H values between -62 and -74 kJ mol-1 at pH 8.0), which decreased with falling pH, in accordance with an inverse relation between the Bohr effect and temperature. The possible adaptive significance of the oxygenation patterns of the hemoglobins and their temperature dependences are discussed comparatively with special reference to the closely-related bimodal breather Hoplosternum littorale, and to breathing habit (gill breathing in winter when the fish is a benthic feeder and "gut" air breathing in the warm reproductive season when they nest at the surface).

Animals↗
PubMed1982

Electrochemical reactions of horse heart cytochrome c at graphite electrodes.

The interaction of cytochrome c with a paraffin-wax-impregnated spectroscopic graphite electrode (WISGE) was studied in a medium consisting of 0.1 M potassium phosphate, pH 7.0, by means of differential pulse and cyclic voltammetry. Ferricytochrome c yields on voltammograms a single cathodic peak C around a potential of -0.3 V (vs. Ag/AgCl) and two anodic peaks AI and AII around the potentials of 0.66 and 0.89 V, respectively. Cathodic peak C corresponds to a catalytic reaction during which ferricytochrome c is reduced to ferrocytochrome c: ferricytochrome c is then regenerated by chemical oxidation of ferrocytochrome c by oxygen adsorbed at the WISGE surface. The first, more negative anodic peak AI corresponds to anodic electrochemical oxidation of tyrosine residues, whereas the second, more positive anodic peak (peak AII) corresponds to an anodic reaction of haemin. Voltammetry at a WISGE may provide a valuable technique for obtaining data about cytochrome c properties on electrically charged surface.

Animals↗
PubMed1985

An underestimated visual pathway in reptiles.

Field potentials evoked in the turtle general cortex by electric stimulation of the optic tectum were analyzed. Cathodal polarization and subtotal lesions of n. rotundus led to either facilitation or depression of later components of the cortical potential. On the contrary, cathodal polarization and lesions of n.geniculatus lateralis dorsalis similarly affected the initial component. After 21-23 months following eye enucleation or optic nerve section, the conduction of fast tectal volleys to the general cortex via n. geniculatus lateralis dorsalis was blocked, though the conduction of tectal impulses to the dorsal ventricular ridge via n.rotundus survived. It is concluded that in turtles one more visual channel, i.e., retino-tecto-geniculo-cortical, is functioning, in addition to well-known retino-tecto-rotundo-telencephalic and retino-geniculo-cortical channels.

Animals↗
PubMed1992

Automated 'pain drawing' analysis by computer-controlled, patient-interactive neurological stimulation system.

We have developed a new method for the collection and analysis of pain drawings, as part of a computer-controlled, patient-interactive system for use with implanted neurological stimulators. The system has been tested in 44 patients with permanently implanted spinal cord stimulators for the relief of chronic, intractable pain. Patients interact directly with the system, using a graphics tablet, to enter pain drawings and corresponding outlines of their perceptions of stimulation paresthesias, for different stimulating pulse parameters and electrode geometries. Image analysis software has been developed to examine these data quantitatively. This precludes the inter-rater inconsistencies reported for manual pain drawing scoring techniques. A highly significant correlation has been observed between patients' analog ratings of the overlap of pain by paresthesias and the results of our automated analysis of graphic data. This in turn has been found to correlate with clinical observations of pain relief. The contemporary implantable stimulation devices supported by our system permit non-invasive selection of stimulating anodes and cathodes from a linear array of 4 electrodes. The 50 possible electrode combinations have certain geometric features, which we have entered into a multivariate statistical analysis, to determine their relationship with the overlap of pain by paresthesias. One particular configuration (cathode(s) flanked by anode(s) above and below) is significantly better, by this measure, than all the alternatives. This is consistent with prior clinical observations that this configuration is favored by patients whose systems have been adjusted by conventional, manual methods. Pain drawing' entry and analysis by a computerized, patient-interactive system has been useful in this specialized setting and may have broader applications.

Adult↗
PubMed1995

Electrochemical reduction of the biliverdin-serum albumin complex as monitored by absorption and circular dichroism spectroscopy.

The cathodic reduction at the mercury electrode of a biliverdin IX alpha-serum albumin complex at physiological pH in an aqueous buffer containing percentages of DMSO ranging from 4% to 20% is studied by cyclic voltametry and controlled potential coulometry. The progression of pigment disappearance and the (stereochemical) nature of the product are monitored by chromatography, UV-visible absorption and circular dichroism spectroscopy. Upon reduction, albumin-bound biliverdin IX alpha, with a slight preference for the P-helicity, affords the corresponding bound bilirubin IX alpha -with an M-chirality conformation. The complex is reduced at -0.64 V (vs. SCE; 8% DMSO), only a little shifted compared to reduction of free biliverdin IX alpha under the same conditions. In contrast, an analogous bilirubin IX alpha-serum albumin complex is essentially inert towards cathodic reduction under conditions where free bilirubin IX alpha is reduced, indicating a better shielding by the protein of the bilirubin IX alpha molecule from the electrode surface. The presence of relative position (as in the biliverdins IX alpha and XIII alpha) or absence (as in mesobiliverdin IX alpha) of vinyl groups in the pigment does not have a significant effect upon its electroreduction behaviour, indicating that the process is not sensitive to the subtle differences imposed by vinyl groups upon the structure of the corresponding biliverdin-albumin complexes.

Biliverdine↗
PubMedDate not supplied

Intracranial self-stimulation site specificity: the myth of current spread.

Locus-specificity of intracranial self-stimulation (ICSS) was determined for 78 electrode placements using monophasic stimulation. ICSS rate comparisons between each pole of a bipolar electrode when each served as cathode were made when the anodal source was either the other pole of the bipolar electrode or a skull screw. In hypothalamic areas, medial forebrain bundle electrode tips elicited significantly higher rates than electrode tips of the same bipolar electrodes located in perifornical or far-lateral diencephalic placements. In turn, perifornical electrode tips elicited higher rates than more dorsally or medially placed tips. In dorsal pontine areas, locus coeruleus electrode tips elicited significantly higher rates than more medially or laterally placed tips. In periaqueductal midbrain and substantia nigra placements, tips located along the midline or in the substantia nigra elicited significantly higher rates than tips located lateral to or ventral to those respective structures. Anodal locus did not change these results. These results suggest that ICSS behavior is delimited by and corresponds to neuroanatomically discrete entities and that cathodal, rather than anodal factors seem to most crucially determine ICSS integrity.

Animals↗
PubMed1993

Simultaneous measurement of serotonin, catecholamines and their metabolites in mouse brain homogenates by high-performance liquid chromatography with a microbore column and dual electrochemical detection.

A dual electrochemical detector with two working electrodes (anode and cathode) suitable for high-performance liquid chromatography with a microbore octadecylsilica column was applied for the simultaneous measurement of norepinephrine, epinephrine, dopamine, 3,4-dihydroxyphenylacetic acid, homovanillic acid, 5-hydroxyindoleacetic acid, 3-methoxytyramine and 5-hydroxytryptamine (serotonin) in mouse brain homogenates. Microbore high-performance liquid chromatography provides very good resolution of these analytes and offers selective detection of biogenic amines and their metabolites on the basis of their retention behaviour and electrochemical reversibility. The large early-eluting peak of brain homogenates was eliminated on cathodic detection, thereby providing reliable measurements of early eluates. The detection limit of this method was ca. 0.2-0.5 pg per injection for all components, at a signal-to-noise ratio of 3. Owing to the high sensitivity, the brain tissue samples could be kept very small (less than 10 mg). Isocratic separation of these analytes was achieved within 15 min; hence over 90 analyses could be performed in a single working day. This simple, efficient and sensitive method can be used as a basic research tool for the assaying of biogenic amines and their metabolites in brain homogenates.

Animals↗
PubMed1996

New dual electrochemical detector for microbore liquid chromatography. Determination of dopamine and serotonin in rat striatum dialysates.

A new type of liquid chromatographic (LC) dual thin-layer amperometric detector for the simultaneous measurement of trace levels of dopamine and serotonin in microdialysates is described. The concentrations of these analytes in rat dialysates are usually in the sub-nanomolar concentration range (typically, 0.10-5.00 pg in 5-microl dialysates). With this dual electrode, a glass-lined microbore column provides excellent sensitivity, selectivity, and separation. In addition, a three- to five-fold improvement in anodic current or cathodic responses over conventional dual electrodes in microbore LC can be achieved. Due to the irreversible electrochemical properties of some interference peaks, this dual electrode provides reliable measurement of dopamine based on the cathodic signal. The detection limit (signal-to-noise ratio = 3) of this assay is 0.02 pg per injection for dopamine or serotonin. This new dual electrode allows the simultaneous measurements of basal dopamine and serotonin in rat striatum dialysates without the use of re-uptake inhibitors in perfusion medium.

Animals↗
PubMed1988

Electrically-induced collagen calcification in pig skin. A histopathologic and histochemical study.

Deposition of calcium salts on collagen fibres in skin of fully anaesthetized pigs was induced by exposure to direct current (d.c.). In biopsies obtained from cathode areas successively from day 1 to day 7 after exposure the histopathologic and histochemical changes before and after the initial deposition of calcium salts have been examined. For comparison skin sites with intradermal injected calcium hydroxyapatite crystals were studied in addition. Small areas of calcified collagen and elastic fibres were noted in viable tissue 2 days after d.c. exposure. In succeeding days the calcified areas enlarged with new deposits always more superficial and closer to the epidermis than the original calcium deposits. Preconditions for calcification appear to be (1) a pH change in basic direction and/or the electrochemical processes specific to the cathode area and (2) a viable tissue. Elastic fibres appear to have a lower calcification threshold than collagen fibres. A positive staining for glycoproteins (PAS) and glycosaminoglycans (alcian blue pH 2.5) was noted in the calcified collagen fibres simultaneously with the calcification. In succeeding days the intensity of the staining reactions increased. Whether changes in the glycoproteins, collagen and its intimately bound glycosaminoglycans precede the calcification or the staining reactions develop secondarily to this deposition is not known. However, seven days after intradermal injections of Ca-apatite crystals in pig skin small and large crystals were observed ultrastructurally without any relation to collagen fibrils, but the calcified tissue presented a positive PAS and alcian blue reaction from day 2. Thus the PAS and alcian blue stainings in this model develop secondary to the deposition of calcium salts.

Animals↗
PubMed1988

The morphogenesis of electrically and heat-induced dermal changes in pig skin.

In order to establish pathological evidence in dermis for distinguishing between sequelae of electrical torture and those of other superficial injuries, the skin of eleven fully anaesthetized Danish Landrace pigs have been exposed to heat and electrical energy from either 50 Hz alternating current (a.c.) or direct current (d.c.) via 12 mm large contact knobs or via a pointed 0.5 mm large electrode (only 50 Hz a.c.). The lesions have been examined from 1 to 126 days after the injury. While heat lesions exposed to energy lower than 60 joule only gave minor changes, heat lesions exposed to more than 60 joule showed changes in both collagen fibres (basophilic or eosinophilic fibres without any birefringence or coarse cross-striation in polarized light, respectively) and dermal cells (granular cytoplasm). Areas exposed to 50 Hz a.c. via 0.5 mm. electrode showed basophilic collagen fibres and in a few biopsies on day 7 calcium salts on collagen fibres. Using 12 mm large electrodes the changes were minor, but basophilic and eosinophilic collagen fibres with no birefringence or with fine/coarse cross-striation respectively were seen. Even cells with 'vesicular nuclei' were seen on day 1 and 2 after the injury. The changes in the anode area showed resemblance to that of heat lesions (basophilic collagen fibres). Eosinophilic collagen fibres with fine densely spaced cross-striation in polarized light and 'vesicular nuclei' as well as collagen fibres with calcium salts were seen in the cathode lesions. It is concluded that the dermal changes in the cathode area are specific for electrical injury from day 1 to 14. However, earlier studies have demonstrated dermal changes specific for electrical injury at day 0 and the presence of calcified collagen fibres up to 2 months after injury. The dermal changes in anode lesions were non specific and could not be differentiated from those found in heat lesions. Alternating current lesions (50 Hz) were specific from day 1 to day 7, when the pointed electrode was used, but only in a few days when the energy was transferred via the 12-mm electrodes.

Animals↗