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At least 55 records · Page 3Linked to original sources

PubMed1995

Preparation of carbon-fibre microelectrode for extracellular recording of synaptic potentials.

A method is proposed for rapid and effective forming of the recording tips of carbon-fibre microelectrodes by trimming and treating the tip with electric current pulses. The tip is trimmed to the required length. The signal-to-noise ratio of carbon-fibre microelectrodes is improved at low-frequency range (less than 100 Hz) after the treatment. The same microelectrode may be used for several experiments because of the possibility to trim and treat the tips repeatedly. This method also allows one to readily fabricate 2- or multi-channel carbon-fibre microelectrodes with the vertical distance between recording tips from few tens to hundreds of micrometres. As an example, the process of fabrication of a 2-channel microelectrode is described.

Carbon↗

PubMed2000

Technique for producing a carbon-fibre microelectrode with the fine recording tip.

A method for making a fine carbon-fibre microelectrode is suggested here. The diameter of the recording tip of the proposed microelectrode at the borderline of glass insulation is 2-4 microm. The method uses tapering and trimming the tip of a factory-made carbon-fibre with pulsed electric current. The treated fibre is introduced into a glass micropipette of desired parameters and is fixed in it. The proposed microelectrodes have good characteristics for extracellular recording of action and synaptic potentials. The fine tip of the microelectrode can pick out a firing activity of a small single unit better and injures the nerve tissue less in comparison with the ordinary carbon-fibre microelectrode.

Action Potentials↗

PubMed2026

Choice of Anesthesia in Microelectrode Recording-guided Deep Brain Stimulation Surgery for Parkinson's Disease (CHAMPION): A Noninferiority Randomized Controlled Trial.

BACKGROUND: Deep brain stimulation for Parkinson's disease is often performed under conscious sedation or general anesthesia. However, anesthetic agents may influence intraoperative microelectrode recording, and the optimal anesthesia method for microelectrode recording remains unclear. This study compared general anesthesia and conscious sedation in preserving microelectrode recording signal intensity during deep brain stimulation. METHODS: In this prospective, noninferiority randomized controlled trial, patients with Parkinson's disease (United Kingdom Brain Bank criteria) undergoing elective bilateral surgery were randomized 1:1 to the conscious sedation or the general anesthesia group. During surgery, a desflurane anesthetic titrated against the quality of the electrophysiologic signal was applied in the general anesthesia group, whereas patients in the conscious sedation group received dexmedetomidine anesthesia. The primary outcome was the proportion of patients with high-quality microelectrode recording (normalized root mean square greater than 2.0), assessed postoperatively off-line. Secondary outcomes included operation and recording duration, 6-month clinical efficacy, and complication rates. RESULTS: Of 188 randomized patients (94 general anesthesia, 93 conscious sedation), desflurane anesthesia was noninferior for high normalized root mean square proportion (89.4% vs . 90.3%; difference, -0.96%; 95% CI, -9.62 to 7.70). The general anesthesia group had shorter operative time (difference, -9.07 min; 95% CI, -13.99 to -4.14; P < 0.001). At 6 months, changes in Unified Parkinson's Disease Rating Scale score (difference, -2.50; 95% CI, -7.20 to 2.20; P = 0.297), levodopa equivalent daily dose (difference, -58.4 mg; 95% CI, -133.56 to 16.75; P = 0.128), and complication rates (general anesthesia: 10.9% vs . conscious sedation: 8.9%; P = 0.655) were comparable between the groups. CONCLUSIONS: General anesthesia is noninferior to conscious sedation for microelectrode-guided subthalamic nucleus deep brain stimulation, providing equivalent signal intensity and clinical outcomes while improving procedural efficiency, supporting its use as a valid clinical option.

Humans↗

PubMed1994

Silicon-substrate microelectrode arrays for parallel recording of neural activity in peripheral and cranial nerves.

A new process for the fabrication of regeneration microelectrode arrays for peripheral and cranial nerve applications is presented. This type of array is implanted between the severed ends of nerves, the axons of which regenerate through via holes in the silicon and are thereafter held fixed with respect to the microelectrodes. The process described is designed for compatibility with industry-standard CMOS or BiCMOS processes (it does not involve high-temperature process steps nor heavily-doped etch-stop layers), and provides a thin membrane for the via holes, surrounded by a thick silicon supporting rim. Many basic questions remain regarding the optimum via hole and microelectrode geometries in terms of both biological and electrical performance of the implants, and therefore passive versions were fabricated as tools for addressing these issues in on-going work. Versions of the devices were implanted in the rat peroneal nerve and in the frog auditory nerve. In both cases, regeneration was verified histologically and it was observed that the regenerated nerves had reorganized into microfascicles containing both myelinated and unmyelinated axons and corresponding to the grid pattern of the via holes. These microelectrode arrays were shown to allow the recording of action potential signals in both the peripheral and cranial nerve setting, from several microelectrodes in parallel.

Action Potentials↗

PubMed1989

The physical state of potassium in frog skeletal muscle studied by ion-sensitive microelectrodes and by electron microscopy: interpretation of seemingly incompatible results.

According to the commonly accepted membrane pump theory most of cellular K+ ions are freely dissolved in free cellular water; the alternative association-induction hypothesis postulates that the bulk of cellular K+ is adsorbed (weakly bound) to cellular proteins which are maintained in a specific labile state in the cytoplasm of a living cell. K+ activities measured with ion-sensitive microelectrodes in the cytoplasm of frog skeletal muscle seem to confirm the claim that most of cellular K+ ions are free in cellular water. On the other hand, it is evident from electron microscopic ion binding studies that in frog skeletal muscle most of cellular K+ ions are adsorbed to cellular proteins. The conflicting results can be explained with the assumption that a damage of the cytoplasm caused by the impaling microelectrode leads to a liberation of adsorbed ions. The possibility that microelectrodes damage the muscle cytoplasm is tested by using the light microscope. It is found that microelectrodes produce visible traumas which increase with time. Electron microscopic ion binding studies with damaged muscle support the view that monovalent cations are liberated in the disturbed area of a muscle fiber. It is concluded that a K(+)-sensitive microelectrode is not suited to determine the concentration of free K+ ions in intact frog skeletal muscle.

Animals↗

PubMed1980

Ion-selective microelectrodes: theory and technique.

This report reviews the use of ion-selective microelectrodes to measure intracellular ionic activities and ionic electrochemical potential differences across cell membranes. Particular emphasis is placed on the electrochemical characteristics of liquid ion-exchanger microelectrodes. Methods for assessing the effect of interfering ions on the electrode potential are discussed and analyzed. An equivalent electrical circuit model is proposed in which deviations from their theoretical values of the slopes and selectivities of liquid ion-exchanger microelectrodes are analyzed in terms of surface conductance phenomena. A quantitative expression is developed that permits the transmembrane electrochemical potential difference for an ion, which is measured with an ion-selective microelectrode, to be corrected for deviations from ideality in the slope of the electrode response. The effect of lipophilic anions, dissolved in the organic ion-exchanger solution, on the electrochemical characteristics of cation selective liquid ion-exchanger microelectrodes containing neutral ionophores is discussed.

Animals↗

PubMed1998

Correlation of magnetic resonance and oxygen microelectrode measurements of carbogen-induced changes in tumor oxygenation.

PURPOSE: The aim of this work was to test the hypothesis that decreases in the linewidth of magnetic resonance (MR) water signals in tumors caused by oxygenating treatments are due to increases in capillary and venous oxygen saturation of hemoglobin, which are tightly coupled to increases in extravascular oxygen tension (pO2). To establish this link, changes measured by MR were compared to changes in tissue pO2 measured directly by oxygen microelectrodes during carbogen (95% O2/5% CO2) inhalation. METHODS AND MATERIALS: Mammary adenocarcinomas (R3230AC) in nine rats were imaged at 4.7 Tesla. T1-weighted (TR = 200 ms, flip angle = 45 degrees) spectroscopic images of the water resonance in a single slice through each tumor were acquired with spectral resolution of 3.9 Hz and bandwidth of +/-1000 Hz. In the same slices in these tumors, microelectrode measurements were made using a non-Clark style oxygen electrode with a 350-micron tip. MR and microelectrode measurements were made during alternating periods of air and carbogen inhalation. RESULTS: Water resonance linewidth decreased significantly during carbogen-induced hyperoxia. Paired Student's t-test analysis of microelectrode data indicated that pO2 was significantly (p < 0.05) increased as a result of carbogen inhalation. MR and microelectrode data averaged over each tumor demonstrated that decreased MR water signal linewidth is strongly correlated (r = 0.92, p < 0.05) with increased tumor pO2 levels. CONCLUSION: Although tumor oxygenating agents increase response to radiation in rodent tumors, clinical studies have shown only marginal effects on the radiosensitivity of human tumors. This may be, in part, because the effects of tumor oxygenating treatments are highly heterogeneous both within each tumor and among a population of tumors. The noninvasive, high-resolution MR methods that are validated by the present work could guide the design of new and more effective tumor oxygenating agents and optimize treatments for individual patients.

Animals↗

PubMed1996

[Ion-selective microelectrodes: principle and application of in vivo measurements of ionic concentrations in cochlear endolymph].

OBJECTIVE: To introduce the method of making neutral carrier ion-selective microelectrode and use it for in vivo measurement of ionic concentrations in cochloear endolymph. METHODS: GG-17 glass capillaries with 1.85 mm O.D. were rinsed extensively and dried in an oven. Two capillaries were parallelly connected and pulled with microelectrode puller to make a double-barreled micropipette. One barrel was back-filled with ion exchanger and internal reference solution, which served as ionic potential electrode, while the other barrel filled with 150 mmol/L KCL as reference electrode. Each barrel of microelectrode was connected to differential electrometer via Ag-AgCl wire and output was recorded on a three-channel recorder. Every ion-selective microelectrode was calibrated in a series of standard solutions to determine the required characteristics. Twenty healthy guinea pigs with normal hearing were anesthetized and were artificially respired through the tracheal canal after the intramuscular injection of suxamethonium chloride. The tympanic bulla was exposed and a double-barreled ion-selective electrode was inserted into the scala media through the round window and basilar membrane. The ionic potentials and endocochlear potentials (EP) were simultaneously recorded from the basal turn of the cochlea. Ionic concentrations were then calculated by Nicolsky-Eisenman equation. RESULTS: The concentrations of potassium, sodium and calcium ions in the cochlear endolymph were 146.3 +/- 11.8 mmol/L, 0.36 +/- 0.22 mmol/L and 16.2 +/- 5.7 micromol/L, respectively. CONCLUSIONS: The neutral carrier ion-selective microelectrode made with the above method is reliable and therefore can be used for accurately measuring the ionic concentrations of microenvironment in vivo continuously and transiently.

Animals↗

PubMed1981

A liquid ion-exchanger alternative to KCl for filling intracellular reference microelectrodes.

We have developed a filling solution for silanised microelectrodes consisting of potassium tetrakis (p-chlorophenyl) borate in octanol. Microelectrodes filled with this reference liquid ion-exchanger (RLIE) have equal selectivities to Na and K, and give the same membrane potential as do KCl-filled microelectrodes. The RLIE microelectrodes are more stable, less damaging to the cell membrane and do not leak Cl- ions. Their high resistance, however, makes them unsuitable for recording rapid potential changes or for passing current.

Animals↗

PubMed1987

Intracellular neutral carrier-based Ca2+ microelectrode with subnanomolar detection limit.

In intracellular electrolyte solutions a Ca2+-selective microelectrode based on the synthetic electrically neutral carrier N,N,N',N'-tetracyclohexyl-3-oxapentanediamide (ETH 129) shows an improved detection limit when compared with the so far widely used Ca2+ microelectrodes based on the neutral carrier ETH 1001. Detection limits are found at pCa = 9.2 in Ca2+ buffers containing an intracellular background of K+ (125 mM). Selectivity studies in mixed solutions show a preference of Ca2+ over Na+ of 6 X 10(5), over K+ of 1.6 X 10(6), and over Mg2+ of 5 X 10(6). The microelectrode does not suffer from significant interference by inorganic and organic inhibitors and by lipophilic cations and anions. The low detection limit is unchanged at least during the first eight hours of continuous contact with Ca2+ solutions. The EMF drift during the first hour of use is between 5 and 10 mV and is then reduced to about 1 mV/h. The changes in EMF induced between solution of pCa = 7 and pCa = 8 are reproducible within 24.7 +/- 0.4 mV (SD, n = 8, about 3 h). These electrode characteristics were found for single-barrelled microelectrodes of one micrometer diameter front-filled with a PVC-containing membrane phase. In the absence of poly(vinyl chloride) in the membrane phase irregular EMF response curves were obtained throughout. Preliminary punctures of ferret ventricular muscle cells indicate that the Ca2+ electrode response is not disturbed by the contact of a cytosolic milieu.

Animals↗

PubMed1986

The sensitivity of liquid sensor, ion-selective microelectrodes to changes in temperature and solution level.

Current procedures for the manufacture of ion-selective microelectrodes using liquid ion sensors result in two kinds of electrode, one with a short (10-100 micron) column of sensor at the tip and one with a long column (greater than 1 mm). We report here that the signal from a long-column microelectrode is very sensitive to small fluctuations in bath temperature and solution level when a recording is made above room temperature. This sensitivity is explained by the effects of temperature on the potentials developed at the interfaces between the ion sensor and the bordering aqueous solutions (the internal filling solution of the electrode and the test solution). If the temperature at the two interfaces is changed by different amounts, these interfacial potentials will also change by different amounts resulting in a change in the output of the electrode. Such an effect occurs for long-column electrodes because the column of sensor is usually not completely immersed in the heated test solution. Hence fluctuations in solution temperature and level will induce fluctuations in temperature along the column of sensor producing variations in the electrical signal from the electrode. In contrast, sensitivity to temperature and solution level is virtually absent in short-column microelectrodes since their column of sensor is fully immersed in the test solution and thereby at uniform temperature. In conclusion, in order to produce noise-free recordings of ion activities, the use of short-column microelectrodes is recommended for experiments performed above (or below) room temperature.

Electrophysiology↗

PubMed1983

Piezoelectric translator. A simple and inexpensive device to move microelectrodes and micropipettes small distances rapidly.

A device is described that is capable of rapidly moving microelectrodes and micropipettes over distances up to 15 mu. This piezoelectric transLator uses the diaphragm from virtually any available piezoelectric buzzer in combination with simple physical support and drive electronics. All of the necessary details for the construction of this small device are presented. Each finished unit is about 2 cm long with a diameter of 2 cm and can be readily adapted to existing manipulators. The translator has been found useful in aiding the independent penetration by one or more microelectrodes of single cells or of more complicated multicellular preparations (including those that lie behind a connective tissue layer). This new device offers fine control of microelectrode motion that cannot be obtained by the other methods used to aid microelectrode and micropipette penetration of cell membranes (e.g. capacitance overcompensation--"ringing in"' or "tickling"--or tapping the manipulator base). Finally, the device described in this paper is extremely simple and inexpensive to build.

Cytological Techniques↗

PubMed1983

Microelectrode study of K+ accumulation by tight epithelia: I. Baseline values of split frog skin and toad urinary bladder.

Toad bladder and split frog skin were impaled with fine-tipped single- and double-barrelled K+-selective microelectrodes. In order to circumvent membrane damage induced by impaling toad bladder, a null point method was developed, involving elevations of mucosal potassium concentration. The results suggest that intracellular potassium activity of short-circuited toad bladder is approximately 82 mM, twice as large as earlier estimates. Far more stable and rigorously defined intracellular measurements were recorded from short-circuited split frog skins. The intracellular positions of the micropipette and microelectrode tips were verified by transient hyperpolarizations of the membrane potential with mucosal amiloride or by transient depolarizations with serosal barium or strophanthidin. Simultaneous impalement of distant cells with separate micropipettes demonstrated that both the baseline membrane potentials and the responses to depolarizing agents were similar, further documenting that frog skin is a functional syncytium. Measurements with double-barrelled microelectrodes and simultaneous single-barrelled microelectrodes and reference micropipettes suggest that the intracellular potassium activity is about 104 mM, lower than previously reported. Taken together with measurements of intracellular potassium concentration, this datum suggests that potassium is uniformly distributed within the epithelial cells.

Animals↗

PubMed1978

Volume changes and potential artifacts of epithelial cells of frog skin following impalement with microelectrodes filled with 3 m KCl.

Cells of isolated frog skin epithelium were observed microscopically during impalement with standard microelectrodes of 5 to 20 Momega resistance, filled with 3 m KCl. Impaled cells, as well as some neighboring cells, were seen to swell 10 to 100 sec after impalement, while the negative potential recorded by the microelectrode depolarized (open circuit conditions). Apparently, osmotic swelling of small epithelial cells may be caused by diffusion of KCl from such electrodes. This conclusion is supported by calculations quoted from the literature of KCl loss from microelectrodes. Intracellular recordings from epithelia with destructed cellular membranes gave negative "pre-tip potentials" of up to mV. The potentials could be altered by electrode movement, by decreasing the ambient pH or the tip-pH and by modifying the fixed charges of the tissue chemically. It is shown that even a moderate loss of KCl, which will not result in appreciable swelling, can produce negative potentials in front of the electrode tip if the protoplasm has a high density of negative fixed charges. We suggest the use of 3 m KCl electrodes with resistances above 30 Momega if after impalement compression of intracellular material by the tip can be avoided. Where such compression cannot be avoided, it is best to fill the microelectrode with an isotonic solution which mimics the electrolyte composition of the cytosol.

Animals↗

PubMed1985

Comparative measurements of potassium and chloride with ion-sensitive microelectrodes and x-ray microanalysis in cultured skeletal muscle fibers.

Data of the intracellular electrolyte concentration of potassium and chloride in cultured muscle cells measured by x-ray analysis were compared by using the different activity coefficients with intracellular potassium and chloride activities measured with double-barrelled microelectrodes. By using an activity coefficient of 0.6, 95% of the potassium microelectrode measurements are in accordance with the x-ray analysis values, in spite of a scattering of the values. Membrane potential and intracellular potassium values are linearly related. x-ray analysis and ion-sensitive microelectrodes measured the cytoplasmic chloride in the same range. Taking into account known activity coefficients, an error of 25% must be assumed with the intracellular chloride measurements. However, x-ray analysis and ion-sensitive microelectrode investigations are reliable tools to study intracellular potassium and chloride changes, which play an important role in membrane characteristics.

Animals↗

PubMed1990

Biphasic voltage relaxation pattern observed in cells of Eremosphaera viridis after injection of charge-pulses of short duration: detection of tip clogging of intracellular microelectrodes by charge-pulse technique.

Charge pulse experiments performed on the peat-bog alga Eremosphaera viridis revealed an unusual voltage relaxation behaviour. Injection of charge pulses of 1 microseconds duration resulted in an immediate charging of the membranes (time constant of the order of 40 ns). Nevertheless, the potential-measuring microelectrode recorded an exponential increase in membrane voltage with a time constant of about 1.3 ms. The maximum voltage value was recorded after about 3 ms, followed by an exponential decay with a time constant of about 9.6 ms. This biphasic time course was independent of the amplitude of the injected charge and of the location of the impaled microelectrodes in the vacuole. Centrifuged cells in which the chloroplasts and the other organelles were pelleted in one part of the cells showed the same electrical response. Electrical breakdown of the cell membranes resulted in the disappearance of the biphasic voltage response. In this case only the decaying relaxation process could be recorded with a time constant of 3 ms. After resealing of the membranes the original biphasic relaxation response was restored. Increasing concentrations of KCl in the bathing medium reduced both time constants almost correspondingly. The experimental findings were evaluated with an electrical equivalent circuit. Theoretical analysis with reference to the experimental data suggested that the delayed voltage response of the potential-recording electrode resulted from a membrane seal across the tip of this electrode. The resistance of this seal was calculated to be about 400 M omega. The specific resistances and capacitances of tonoplast and plasmalemma membranes were calculated from the decaying part of the biphasic relaxation curves. The average values were found to be 2.58 omega.m2 and 5 mF.m-2. The investigations reported here suggest that charge pulse experiments can be generally used for the detection of membrane and cytoplasmic material clogging of the tip of intracellular microelectrodes, a problem with which most electrophysiologists are faced when interpreting data obtained from impaled microelectrodes.

Cell Membrane↗

PubMed1986

Neuronal activity evoked by chronically implanted intracortical microelectrodes.

The averaged evoked compound action potentials (AECAPs) were recorded from the ipsilateral pyramidal tract of awake, unrestrained cats before, during, and after continuous electrical stimulation of the cerebral cortex via chronically implanted activated iridium or platinum-30% iridium (Pt30%Ir) microelectrodes. After stimulating 24 h at 20 pulses per second (pps), using charge-balanced, 200-microseconds pulse pairs of 40 to 80 microA (400 to 800 microC/cm2, 8 to 16 nC/phase (ph), 2 to 4 A/cm2), there was a transient elevation of the threshold of the early (direct) and of the alte (transynaptic) components of the AECAP. After cessation of continuous stimulation at 80 microA, the threshold of the early component of the AECAP remained elevated for as long as 24 h and the late component as long as 4 days, indicating significant but reversible depression of the electrical excitability of cortical neurons close to the microelectrodes. In three cats stimulated 23 h/day for 1 week, the AECAP also recovered to their prestimulus threshold. In contrast, pulsing for 24 h at 320 microA (3200 microC/cm2, 64 nC/ph, 16 A/cm2) produced marked elevation of the threshold of the AECAPs which was not reversed by 7 to 12 days after termination of intracortical stimulation. The electrical excitability of neurons adjacent to (unpulsed) microelectrodes 2 mm from the pulsed electrode was not affected. The observations reported here, in conjunction with the histologic results reported in the companion paper, indicate that both the Pt30%Ir and the iridium microelectrodes can be operated safely at currents to at least 80 microA, charge/ph of 16 A/cm2, and a charge density of 800 microC/cm2 X ph. However, on the basis of the electrophysiologic criteria, both types appear to be unsafe when pulsed at 320 microA (64 nC/ph, 3200 microC/cm2 X ph, 16 A/cm2).

Action Potentials↗

PubMed1994

A new method for manufacturing carbon-fibre microelectrodes.

A new, fast and low-cost method using a carbon-fibre microelectrode is proposed. The microelectrode is constructed by glueing one or more carbon fibres (5 mm in diameter) with a silver resin on a silver wire or stainless steel tube. The characteristics of that microelectrode have been measured and compared with those of commercially available glass carbon-fibre microelectrodes. According to our measures, the impedance, capacity and current noise were lowered which permits these electrodes to be used in voltammetry and in detection of very low currents generated during formation of antigen-antibody complex.

Carbon↗