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At least 1,153 records · Page 64Linked to original sources
PubMed2001

A voltammetric study of direct electron transfer to cytochrome c using a very large assembly of carbon microelectrodes.

A very large assembly of more than 8000 carbon fibre microdisk electrodes was used to study direct electron transfer to cytochrome c. Near steady-state cyclic voltammograms were observed, which exhibited excellent signal-to-noise ratios despite the low concentrations of cytochrome c employed (1-50 microM). The high resolution of the voltammograms allowed the formal potential of the native form of cytochrome c to be determined over a range of solution pH.

Carbon↗
PubMed2005

Immobilization of DNA on carbon fiber microelectrodes by using overoxidized polypyrrole template for selective detection of dopamine and epinephrine in the presence of high concentrations of ascorbic acid and uric acid.

The overoxidized polypyrrole (PPyox) film as a template for DNA immobilization has been demonstrated in this paper. The DNA molecules inserted into the micropores of the ultrathin PPyox matrix under the driving forces of an electric field and were firmly immobilized on the carbon fiber electrode (CFE). Such a DNA-PPyox biocomposite layer exhibited more effective rejection of anionic ascorbate (AA) and uric acid (UA) and more preferential collection of the cationic dopamine (DA) and epinephrine (EP) than pure PPyox and DNA coatings. The DPV peak currents increased linearly with increasing DA and EP concentrations in the range of 3.0 x 10(-7) to 1.0 x 10(-5) M and 5.0 x 10(-7) to 2.0 x 10(-5) M with the lowest detected concentrations of 8.0 x 10(-8) M and 6.0 x 10(-8) M, respectively. The electrochemical signal of AA could be totally suppressed under a concentration of 20 mM and beyond this concentration, the overlapped responses of AA, DA/EP and UA could be resolved into three well-defined voltammetric peaks. The selectivity factors k(DA/AA) and k(EP/AA) were about 5000 and 2000 for an equal concentration in the presence of 0.5 mM UA. The properties of the biocomposite film have been characterized by atomic force microscopy and electrochemical investigations.

Ascorbic Acid↗
PubMed1987

Intrathyroidal autonomic nerves can directly influence hormone release from rat thyroid follicles: a study in vitro employing electrical field stimulation and intracellular microelectrodes.

The role of the autonomic nervous system in the control of thyroxine release from the rat thyroid gland in vitro, has been investigated using electrical field stimulation as a device to induce intrathyroidal nerves to release their neurotransmitters. The effects of field stimulation on follicular cell membrane potential and input resistance have been investigated using continuous intracellular recordings from individual cells. Electrical field stimulation promotes up to an eightfold increase in throxine release from the thyroid gland in vitro. This effect is blocked by the neurotoxin, tetrodotoxin. Electrical field stimulation has no effect on follicular cell membrane potential or input resistance. This is consistent with the results of previous pharmacological experiments using this preparation. It is concluded that electrical field stimulation induces intrathyroidal nerves to release their neurotransmitters, and that the net effect of this is to cause thyroxine release from the thyroid follicles. The existence of a directly acting secretomotor innervation to the thyroid follicle is suggested.

Animals↗
PubMed1985

Microelectrode for measuring local cortical oxygen tension and blood flow in the same microareas of cat cortex.

The purpose of this study is to investigate the relationship between changes in cortical Po2 (bPo2) and cortical blood flow when inhalating different oxygen mixtures. Experiments were performed on 31 cats anaesthetized with N2O/O2 plus supplemental drugs for immobilization and analgesia. Cortical Po2 was measured by the polarographic method using 25 microns Pt electrode (coated) and a 250 micron Ag-AgCl2 indifferent electrode, especially designed to rest lightly on the cortex by means of coiled spring support. Using the same electrode but with opposite tip polarization; local cortical blood flow (lCoBF) was measured at the same site by the H2-clearance method. The change of bPo2 in going from FiO2 25% to FiO2 75% was measured at 58 different sites. (Table 2). At 25% FiO2 the mean bPo2 was 24 +/- 16 mm Hg, with a range from 4 to 92 mm Hg. With increased FiO2 to 75% local bPo2 responded quite differently at adjacent sites. At 75% FiO2 the mean bPo2 was 42.7 +/- 32 mm Hg with a range from 10 mm Hg to 198 mm Hg. The bPo2 and lCoBF were both measured at 44 of the 58 different sites. Cortical sites with a resting bPo2 greater than 30 mm Hg at 25% FiO2 had a lCBF = 57 +/- 12 ml/100g m; whereas sites with resting normoxic bPO2 less than 20 mm Hg had a mean ICoBF = 56 +/- 14 ml/100g min.(ABSTRACT TRUNCATED AT 250 WORDS)

Anesthesia, Endotracheal↗
PubMed2005

Microelectrode investigations of the visual system at the Department Of Clinical Neurophysiology, Freiburg i.Br.: a historical account of the first 10 years, 1951-1960.

The history of the first ten years of neurophysiological science (1951-1960) at the Department of Clinical Neurophysiology in Freiburg i.Br. (Germany) is described by some of the participants. We describe the concepts of Richard Jung for the development of an experimental neurophysiology, the technical conditions which helped to realize these ideas, and the integration of the newly emerging German neurophysiological science into the international community, through the large number of foreign visitors. A short account is given of the young scientists working at the Freiburg laboratory during this period, their main lines of research, as well as the results of their studies.

Germany↗
PubMed2003

Ion fluxes in giant excised cardiac membrane patches detected and quantified with ion-selective microelectrodes.

We have used ion-selective electrodes (ISEs) to quantify ion fluxes across giant membrane patches by measuring and simulating ion gradients on both membrane sides. Experimental conditions are selected with low concentrations of the ions detected on the membrane side being monitored. For detection from the cytoplasmic (bath) side, the patch pipette is oscillated laterally in front of an ISE. For detection on the extracellular (pipette) side, ISEs are fabricated from flexible quartz capillary tubing (tip diameters, 2-3 microns), and an ISE is positioned carefully within the patch pipette with the tip at a controlled distance from the mouth of the patch pipette. Transport activity is then manipulated by solution changes on the cytoplasmic side. Ion fluxes can be quantified by simulating the ion gradients with appropriate diffusion models. For extracellular (intrapatch pipette) recordings, ion diffusion coefficients can be determined from the time courses of concentration changes. The sensitivity and utility of the methods are demonstrated with cardiac membrane patches by measuring (a) potassium fluxes via ion channels, valinomycin, and Na/K pumps; (b) calcium fluxes mediated by Na/Ca exchangers; (c) sodium fluxes mediated by gramicidin and Na/K pumps; and (d) proton fluxes mediated by an unknown electrogenic mechanism. The potassium flux-to-current ratio for the Na/K pump is approximately twice that determined for potassium channels and valinomycin, as expected for a 3Na/2K pump stoichiometery (i.e., 2K/charge moved). For valinomycin-mediated potassium currents and gramicidin-mediated sodium currents, the ion fluxes calculated from diffusion models are typically 10-15% smaller than expected from the membrane currents. As presently implemented, the ISE methods allow reliable detection of calcium and proton fluxes equivalent to monovalent cation currents <1 pA in magnitude, and they allow detection of sodium and potassium fluxes equivalent to <5 pA currents. The capability to monitor ion fluxes, independent of membrane currents, should facilitate studies of both electrogenic and electroneutral ion-coupled transporters in giant patches.

Cell Culture Techniques↗
PubMed1989

Effects of barium and bicarbonate on glial cells of Necturus optic nerve. Studies with microelectrodes and voltage-sensitive dyes.

We have studied the effects of Ba++, a known K+ channel blocker, on the electrophysiological properties of the glial cells of Necturus optic nerve. The addition of Ba++ reversibly depolarized glial cells by 25-50 mV; the half maximal deplorization was obtained with a Ba++ concentration of approximately 0.3 mM. In the presence of Ba++, the sensitivity of the membrane to changes in K+ was reduced and there was evidence of competition between K+ and Ba++ for the K+ channel. These effects, which were accompanied by a large increase in the input resistance of the glial cells, indicate that Ba++ blocks the K+ conductance in glial cells of Necturus optic nerve. With the K+ conductance reduced, we were able to investigate the presence of other membrane conductances. We found that in the presence of Ba++, the addition of HCO3- caused a Na+-dependent hyperpolarization that was sensitive to the disulfonic stilbene SITS (4-acetamido-4'-isothiocyanostilbene-2, 2'-disulfonic acid). Removal of Na+ resulted in a HCO3- -dependent, SITS-sensitive depolarization. These results are consistent with the presence in the glial membrane of an electrogenic Na+/HCO3- cotransporter in which Na+, HCO3-, and net negative charge are transported in the same direction. In Cl- -free solutions, the Ba++-induced depolarization increased, suggesting a small permeability to Cl-. Using voltage-sensitive dyes and a photodiode array for multiple site optical recording, the distribution of potential changes in response to square pulses of intracellularly injected current were recorded before and after the addition of increased and the decay of amplitude as a function of distance decreased. Such results indicate that Ba++ increases the membrane resistance more than the resistance of the intercellular junctions.

Animals↗
PubMed2005

Visualization of the intact interface between neural tissue and implanted microelectrode arrays.

This research presents immunohistochemical strategies for assessing the interactions at the immediate interface between micro-scale implanted devices and the surrounding brain tissue during inflammatory astrogliotic reactions. This includes preparation, microscopy and analysis techniques for obtaining images of the intimate contact between neural cells and the surface of implantable micro-electromechanical systems (MEMS) devices. The ability to visualize the intact interface between an implant and the surrounding tissue allows researchers to examine tissue that is unchanged from its native implanted state. Conversely, current popular techniques involve removing the implant. This tends to cause damage to the tissue immediately surrounding the implant and can hinder one's ability to differentiate inflammatory responses to the implant versus physical damage occurring from removal of the implant from the tissue. Due to advances in microscopy and staining techniques, it is now possible to visualize the intact tissue-implant interface. This paper presents the development of imaging techniques for visualizing the intact interface between neural tissue and implanted devices. This is particularly important for understanding both the acute and chronic neuroinflammatory responses to devices intended for long-term use in a prosthetic system. Non-functional, unbonded devices were imaged in vitro and in vivo at different times post-implantation via a range of techniques. Using these techniques, detailed interactions could be seen between delicate cellular processes and the electrode surface, which would have been destroyed using conventional histology processes.

Animals↗
PubMed2006

Nanoscale laminin coating modulates cortical scarring response around implanted silicon microelectrode arrays.

Neural electrodes could significantly enhance the quality of life for patients with sensory and/or motor deficits as well as improve our understanding of brain functions. However, long-term electrical connectivity between neural tissue and recording sites is compromised by the development of astroglial scar around the recording probes. In this study we investigate the effect of a nanoscale laminin (LN) coating on Si-based neural probes on chronic cortical tissue reaction in a rat model. Tissue reaction was evaluated after 1 day, 1 week, and 4 weeks post-implant for coated and uncoated probes using immunohistochemical techniques to evaluate activated microglia/macrophages (ED-1), astrocytes (GFAP) and neurons (NeuN). The coating did not have an observable effect on neuronal density or proximity to the electrode surface. However, the response of microglia/macrophages and astrocytes was altered by the coating. One day post-implant, we observed an approximately 60% increase in ED-1 expression near LN-coated probe sites compared with control uncoated probe sites. Four weeks post-implant, we observed an approximately 20% reduction in ED-1 expression along with an approximately 50% reduction in GFAP expression at coated relative to uncoated probe sites. These results suggest that LN has a stimulatory effect on early microglia activation, accelerating the phagocytic function of these cells. This hypothesis is further supported by the increased mRNA expression of several pro-inflammatory cytokines (TNF-alpha, IL-1 and IL-6) in cultured microglia on LN-bound Si substrates. LN immunostaining of coated probes immediately after insertion and retrieval demonstrates that the coating integrity is not compromised by the shear force during insertion. We speculate, based on these encouraging results, that LN coating of Si neural probes could potentially improve chronic neural recordings through dispersion of the astroglial scar.

Animals↗
PubMed2000

Relationship of lesion location to cognitive outcome following microelectrode-guided pallidotomy for Parkinson's disease: support for the existence of cognitive circuits in the human pallidum.

Current models of basal ganglia anatomy posit the existence of multiple parallel, anatomically segregated circuits. Anatomical data from non-human primates suggest that the circuits subserving motor functions are segregated from those subserving cognitive functions. Here we present data that demonstrate that, in humans, motor and cognitive frontosubcortical circuits are segregated. We studied a group of patients with Parkinson's disease undergoing surgical lesioning of the globus pallidus internus for relief of their symptoms. Lesion location along an anteromedial-to-posterolateral axis was found to be related to postsurgical outcome on both cognitive and motor measures. Performance on several neuropsychological measures, including the generation of category exemplars and continuous mental addition, was linearly related to distance along this axis, with anteromedial lesions leading to postsurgical impairment, intermediate lesions having little effect and posterolateral lesions leading to an improvement on several measures. The same relationship was found between memory performance under conditions of proactive interference and lesion location within the globus pallidus internus. In contrast, bradykinesia, assessed as the speed of finger-tapping, had a non-linear relationship to lesion location, intermediate lesions leading to greater postsurgical improvement than lesions in more extreme anteromedial or posterolateral locations. These data demonstrate that the cognitive effects of pallidotomy can be dissociated from the motor effects. These effects depend upon the placement of the lesions within the globus pallidus internus, supporting the segregation of functionally distinct circuits in the human pallidum.

Cognition↗