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At least 1,117 records · Page 62Linked to original sources
PubMed1997

Microelectrode arrays for stimulation of neural slice preparations.

A planar 6 x 6 array of iridium electrodes with four reference electrodes has been developed for use with neural tissue preparations. Precise knowledge of the relative locations of the array elements allows for spatial neurophysiological analyses. The 10 microns diameter platinized iridium electrodes on a 100 microns pitch have been used to stimulate acutely prepared slices of spinal cord from free-ranging rodents. An intracellular recording from a single neuron in the substantia gelatinosa (SG) using the whole-cell, tight-seal technique allowed low noise, high resolution studies of excitatory or inhibitory electrical responses of a given neuron to inputs from the primary afferent fibers or from stimulation by individual electrodes of the array. The resulting maps of responses provide an indication of the interconnectivity of neural processes. The pattern emerging is that of limited interconnectivity in the SG from areas surrounding a recorded neuron but with strong excitatory or inhibitory effects from those oriented in a longitudinal (rostral-caudal) direction relative to the neuron. The observations to date suggest the neurons of the SG are arranged in sets of independent networks, possibly related to sensory modality and input from particular body regions.

Animals↗
PubMed1999

Multiple single unit recording in the cortex of monkeys using independently moveable microelectrodes.

Simultaneous recording from multiple single neurones presents many technical difficulties. However, obtaining such data has many advantages, which make it highly worthwhile to overcome the technical problems. This report describes methods which we have developed to permit recordings in awake behaving monkeys using the 'Eckhorn' 16 electrode microdrive. Structural magnetic resonance images are collected to guide electrode placement. Head fixation is achieved using a specially designed headpiece, modified for the multiple electrode approach, and access to the cortex is provided via a novel recording chamber. Growth of scar tissue over the exposed dura mater is reduced using an anti-mitotic compound. Control of the microdrive is achieved by a computerised system which permits several experimenters to move different electrodes simultaneously, considerably reducing the load on an individual operator. Neurones are identified as pyramidal tract neurones by antidromic stimulation through chronically implanted electrodes; stimulus control is integrated into the computerised system. Finally, analysis of multiple single unit recordings requires accurate methods to correct for non-stationarity in unit firing. A novel technique for such correction is discussed.

Animals↗
PubMed2000

Rabbit and monkey visual cortex: more than a year of recording with up to 64 microelectrodes.

In the visual cortex of rabbits and a marmoset monkey, 32 and 64 microwires, respectively, were chronically implanted by an indirect insertion method so that the cortex was penetrated from the white matter. For more than 1 year recordings of action potentials of good quality were obtained at most electrodes. Recording stability was judged by spike shape, spike train autocorrelograms, and spike rates: within recording sessions, stability was essentially perfect. Periods in which the signals of several electrodes were stable could last for several days. A method of in vivo reconstruction of the electrode locations by micro-X-rays and subsequent stereophotogrammetry is presented. The aspect of animal welfare is considered.

Action Potentials↗
PubMed1997

Selective disruption of neurotransmission by acetylcholinesterase antibodies in sympathetic ganglia examined with intracellular microelectrodes.

Antibodies to acetylcholinesterase (AChE) induce adrenergic dysfunction in rats by selective, complement-mediated destruction of preganglionic sympathetic nerve terminals. To analyze this phenomenon at the neuronal level, monoclonal antibodies to AChE (1.6 mg) were injected via the tail vein, and superior cervical ganglia (SCG) or inferior mesenteric ganglia (IMG) were studied in vitro. In control SCG, all impaled neurons generated action potentials during direct injection of depolarizing current or indirect stimulation through the preganglionic nerve. Current injection remained effective in ganglia from treated rats, but preganglionic stimulation was greatly impaired: at 12 h and 3 d, less than 10% of the neurons responded, even to a maximal stimulus (150 V); at 9 d, only 25% responded. By contrast, in IMG, synaptic transmission was much less affected by antibody exposure: 60% or more of examined neurons responded to preganglionic stimulation. Differences in antibody access did not explain differing sensitivities of SCG and IMG since immunohistochemistry showed rapid accumulation of IgG deposits in both ganglia. These results are believed to reflect widespread but subtotal preganglionic sympathectomy by AChE antibodies. Current information indicates that paravertebral ganglia are all antibody-sensitive, but some prevertebral ganglia are resistant, suggesting immunochemical differences between them.

Acetylcholinesterase↗
PubMed2000

A new technique for implanting a fine-wire microelectrode for chronic recording of unit activity from freely-moving mice.

We report here a newly developed chronic implantation technique using an epoxy-coated fine-stainless steel wire (33 microm in diameter) to record single unit activity from the brain of freely-moving mice with as little tissue injury as possible. Since the fine-wire electrode is not capable of staying straight by itself or of penetrating into the brain, a pair of permanent neodymium magnets placed on a micromanipulator as well as below the animal's head was used for stereotaxic implantation to keep the fine-wire straight and strong by the magnetic fields. With those implanted electrodes recording of single units from the hippocampal CA1 of freely-moving mice was performed during sleep and wakefulness.

Action Potentials↗
PubMed2003

Comparison of the comet assay and the oxygen microelectrode for measuring tumor oxygenation in head-and-neck cancer patients.

PURPOSE: To compare the Eppendorf PO2 histograph and the alkaline comet assay as methods of measuring tumor hypoxia in patients with head-and-neck squamous cell carcinomas. MATERIALS AND METHODS: As part of a larger clinical trial, 65 patients with head-and-neck squamous cell carcinoma nodal metastasis underwent tumor oxygenation measurements with Eppendorf PO2 histographs and comet assays, performed on fine-needle aspirates at 1 and 2 min after 5 Gy. Fifty-four patients had sufficient tumor cells for comet analysis at 1 min and 26 at both 1 and 2 min. Individual cells were examined for DNA single-strand breaks by alkaline gel electrophoresis, and the distribution of values was quantified using median tail moment (MTM). Nonirradiated tumor cells from pretreatment fine-needle aspirates received 5 Gy in vitro to establish the oxygenated response. RESULTS: There was a significant correlation between the 1- and 2-min MTM (slope = 0.77 +/- 0.03). There was no relationship between DNA damage in tumor cells irradiated in vitro and in vivo. No correlation was found between Eppendorf PO2 measurements and comet MTM. There was a statistically significant correlation between the treatment response in the node studied and comet MTMs, whereas no correlation was observed between treatment response and Eppendorf measurements. CONCLUSIONS: Comet assays are reproducible, as shown by biopsies at 1 and 2 min. Intertumor variation in the MTM is not a result of intrinsic radiosensitivity but of tumor hypoxia. There was no correlation between Eppendorf PO2 measurements and comet MTM. Comet assays were better than Eppendorf in predicting treatment response as an end point for short-term outcome. Longer follow-up is needed to determine the role of the comet assay as a predictor for locoregional tumor control and survivals.

Adult↗
PubMed1981

A simple method for glass insulating tungsten microelectrodes.

A method for insulating tungsten wires with glass by collapsing a glass capillary tube around the wire is described. A common laboratory electrode puller can be used. A new method for removing the glass from the tip using hydrofluoric acid is also described.

Animals↗
PubMed1997

Characterization and optimization of microelectrode arrays for in vivo nerve signal recording and stimulation.

Revealing the complex signal-processing mechanisms and interconnection patterns of the nervous system has long been an intriguing puzzle. As a contribution to its understanding the optimization of the impedance behavior of implantable electrode arrays with via holes is discussed here. Peripheral axons will regenerate through these holes allowing for simultaneous nerve stimulation and signal recording. This approach is part of the ESPRIT project INTER and may eventually lead to devices driving sensory motor prosthesis with closed loop control. In the first set of experiments, micromachined platinum electrode arrays were prepared, characterized and optimized for nerve signal recording. The results of these studies are based on impedance spectroscopy and microscopic techniques. Equivalent circuits were modeled describing formally the electrical response behavior with ohmic resistances between 500 omega and 10 k omega. To attain low impedances for all electrodes on the INTER device, platinum from H2PtCl6 was electrodeposited, and sputter technology as well as electrochemical deposition from H2IrCl6 solution were used to produce thin iridium films. For the former, a lift-off process was established at one of the institutes to generate electrode structures with a line width of 5 microns. As a result in all three cases the electrodes showed almost constant impedances over the entire frequency range (10 Hz-1 kHz), which is relevant for nerve signal recording. In the second set of experiments, electrodes were optimized to allow for nerve stimulation. For this purpose, the charge delivery capacity (CDC) had to be increased and the impedance had to be decreased. Iridium oxide is the material of choice, because its CDC is much higher than the CDC of platinum at 75 microC/cm2 (Ziaie et al., 1991, IEEE Sensors & Actuators Transducers, 6, 124-127). A significant increase of the electrochemically active surface of the electrode structures could be observed by measuring the surface roughness. In first experiments, an activated iridium oxide film was formed with cyclic voltammetry and was evaluated using scanning force microscopy and impedance spectroscopy. The evaluation of the cyclic voltammograms showed a CDC up to 400 mC/cm2 for sputter deposited and oxidatively treated iridium films. Further investigations are directed towards increasing the stability of the iridium oxide electrodes with regard to long-term implants. Parallel experiments aim at the controlled axon adhesion without changing the impedance behavior of the described electrodes.

Electric Impedance↗
PubMed1999

Long-term neural recording characteristics of wire microelectrode arrays implanted in cerebral cortex.

This paper describes a detailed protocol for obtaining chronic, multi-site unit recordings in cerebral cortex of awake animals for periods of three months or more. The protocol includes details for making relatively simple and inexpensive implantable multichannel electrodes that consist of arrays of separate microwires. The results reported in this paper suggest that a viable implant will have discriminable unit activity on about 80% of the electrodes, resulting in, on average, the simultaneous unit recording of upwards of 60 units during a daily recording session. The active electrodes during one recording session tend to remain active in subsequent recording sessions for several weeks. Using the methods described here, implants have been constructed which incorporate several different electrode materials, coatings, sizes, and electrode separation within a single array. These microwire electrode arrays provide the basic technology for obtaining unit recordings for several months. This provides a model system for studying biocompatibility of neural implants, which is a critical component for the development of neural implants that have an indefinite working span.

Action Potentials↗
PubMed2002

Nitric oxide determination by amperometric carbon fiber microelectrode.

Nitric oxide (NO) amperometric microsensor was prepared by the modification of bare carbon fiber electrode by Nafion and cellulose acetate (CA). Detection limit, response time, reproducibility and influence of some possible interferences (nitrite, nitrate, arginine) were tested and evaluated. This sensor was used for in vitro determination of NO release from fresh porcine aorta induced by calcium ionophore A23187 (CI).

Animals↗
PubMed1982

Microelectrode studies of the tegument and sub-tegumental compartments of male Schistosoma mansoni: anatomical location of sources of electrical potentials.

Histological studies using horse-radish peroxidase (HRP) as a marker, injected iontophoretically through a recording electrode, have indicated the origins of potentials encountered upon advancement of the electrode into and beneath the dorsal surface of adult male Schistosoma mansoni. The first potential encountered, having a value of -51 +/- 0.6 mV originates across the outer tegumental membrane. The next potential has a value of -28 +/- 0.6 mV and originates in the muscle masses underlying the tegument. Finally, a potential having the value -10 +/- 0.5 mV originates within the basal lamina and the interstitial fibers and extracellular space surrounding the muscle. Altering ion concentrations in the bathing medium (i.e. high K+, low Na+, zero Ca2+, low Cl-, high Li+) depolarizes all three potentials. External applications of ouabain and the antischistosomal, praziquantel, also cause depolarization of the potentials. It appears that the muscle potential and the tegumental potential are primarily K+-dependent. The depolarizing effects of ouabain. LiCl and low Na+ suggest that active transport is important in the maintenance of the muscle potential, just as is the case for the tegumental potential. There appears to be a close correlation between changes in the tegumental, muscle and extracellular space potentials. The correlation between tegument and muscle potential changes might be explained by junctional complexes between tegumental cell bodies and muscle cell bodies.

Animals↗
PubMedDate not supplied

A dissection of the electroretinogram from the isolated rat retina with microelectrodes and drugs.

The origins of the a- and b-wave of the ERG were studied using simultaneous recordings made across the receptor layer and the full thickness of a piece of isolated albino rat retina. An inwardly directed current flowing across the rod outer segments was eliminated from the recording when postsynaptic activity was blocked with cobalt or when current source density measurements were made along the length of the outer segments. Rod photovoltages were inferred by removing extraneous field potentials from the recordings made across the photoreceptor layer. The spatial properties of the photovoltage indicates the responses came from an area about 100 microm in diameter. The glutamate analog. APB, which blocks depolarizing bipolar cells, eliminated the b-wave but left the a-wave unaffected. The ERG component due to depolarizing bipolar cells was inferred by subtracting recordings obtained before and after APB. After treatment with APB a slow component remained. This component was completely blocked by barium (200 microM), which blocks potassium channels on Müller cells. Barium had virtually no effect on low-intensity photovoltages but did affect the amplitude and shape of the saturated responses. Barium increased the amplitude of the component of the ERG which underlies the b-wave. It was concluded that the depolarizing bipolar cells directly generate the b-wave of the ERG.

Aminobutyrates↗
PubMed1991

Enzyme-modified organic conducting salt microelectrode.

A miniaturized enzyme-modified electrode has been constructed and evaluated. The tip of a capillary-encased, carbon-fiber electrode is recessed, and tetrathiafulvalene-tetracyanoquinodimethane crystals are electrochemically deposited in the recessed tip. Flavoenzymes are placed in the recess by cross-linking with glutaraldehyde. The specific enzymes used are glucose oxidase to form a microbiosensor for glucose, and a combination of acetylcholine esterase and choline oxidase to form a microbiosensor for acetylcholine. The sensor is operated in an amperometric mode with Eapp = 150 mV versus a sodium saturated calomel electrode, and the response appears to be limited by the kinetics of the enzyme reaction. The effective maximum current density for the glucose electrode is greater than 600 microA/cm2. At low concentrations of glucose, oxygen provides a significant interference by attenuating the signal. The device is simple to prepare and has a rapid response time. Interference from ascorbate has been significantly reduced by the design and by addition of a layer of ascorbate oxidase. Although not yet suitable for use in tissue, the biosensors are suitable for detection in situations where oxygen concentrations do not frequently change.

Acetylcholine↗
PubMed1989

Signal-to-noise ratio in microelectrode-array-based electrochemical detectors.

The signal-to-noise ratio at an electrode array depends on the electrode area, the perimeter-to-area ratio of the electroactive portion of the surface, the mass transfer coefficient of the analyte-electrode combination, the measurement bandwidth, and the sources and magnitudes of the noises. Simple models for chronoamperometry with an array in quiescent solution and for hydrodynamic current at an array in one wall of a rectangular conduit through which analyte-containing solution is following are given. Noises from seven sources, including environmental noises, are considered in a noise model. The signal and noise models are combined to yield a model for signal-to-noise ratio at array-based electrochemical detectors. There exists an optimum array density for a given area that depends on the noise power, noise resistance, the current density at a sparse array, and the current density at a solid electrode of the same area. Approximations that lead to simple expressions for the optimum electroactive area fraction and noise resistance lead to results that are in good agreement with more complex and less approximate calculations. Electrodes of millimeter dimensions consisting of about 1% active surface with electroactive "pieces" of micrometer dimensions are anticipated to yield detection limits of about 1 fmol injected into a typical packed-column liquid chromatograph. This corresponds to about 10(-10) M analyte in the detector and about an order of magnitude improvement over solid electrodes.

Electrochemistry↗