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At least 631 records · Page 35Linked to original sources
PubMed2003

A microelectrode drive for long term recording of neurons in freely moving and chaired monkeys.

An electrode drive is described for recordings of neurons in freely moving and chaired monkeys during the performance of behavioural tasks. The electrode drives are implanted for periods of up to 6 months, and can advance up to 42 electrodes using 14 independent drive mechanisms. The drive samples 288 points within a 12 mmx12 mm region, with 15 mm of electrode travel. Major advantages are that recordings are made in freely moving monkeys, and these recordings can be compared with those in chaired experiments; waveforms of single neurons are stable, enabling prolonged recordings of the same neurons across periods of days; recordings can be made throughout the brain, including the dorsolateral prefrontal cortex and hippocampus; the drive accommodates both sharp microelectrodes and fine wire assemblies such as tetrodes.

Action Potentials↗
PubMed2003

Capabilities of a penetrating microelectrode array for recording single units in dorsal root ganglia of the cat.

The recording capability of a microelectrode array in the cat dorsal root ganglion (DRG) was studied in 11 acute experiments, 373 single, discriminable sensory units were recorded on 587 electrodes (0.64 units/electrode). Sensory action potentials as large as 1750 microV were obtained (mean=132 microV). These were comparable to literature reports of the best DRG extracellular recordings made with conventional electrodes. We were able simultaneously to activate and record over 50 discriminable, time-varying units from L6 and L7 DRGs during a cyclic ankle displacement. We also successfully recorded stable, phase dependent multiple sensory units with very little artifact or electromyographic (EMG) contamination during decerebrate walking. Thus, the array is capable of recording more effectively from more DRGs neurons than has been achieved by conventional recording techniques. The recording selectivity and stability of the array, coupled with the large number of neurons that can be recorded simultaneously, provide attractive features for better understanding sensorimotor control principles.

Action Potentials↗
PubMed2003

Cryopreserved rat cortical cells develop functional neuronal networks on microelectrode arrays.

Neurons growing on microelectrode arrays (MEAs) are promising tools to investigate principal neuronal network mechanisms and network responses to pharmaceutical substances. However, broad application of these tools, e.g. in pharmaceutical substance screening, requires neuronal cells that provide stable activity on MEAs. Cryopreserved cortical neurons (CCx) from embryonic rats were cultured on MEAs and their immunocytochemical and electrophysiological properties were compared with acutely dissociated neurons (Cx). Both cell types formed neuritic networks and expressed the neuron-specific markers microtubule associated protein 2, synaptophysin, neurofilament and gamma-aminobutyric acid (GABA). Spontaneous spike activity (SSA) was recorded after 9 up to 74 days in vitro (DIV) in CCx and from 5 to 30 DIV in Cx, respectively. Cx and CCx exhibited synchronized burst activity with similar spiking characteristics. Tetrodotoxin (TTX) abolished the SSA of both cell types reversibly. In CCx SSA-inhibition occurred with an IC50 of 1.1 nM for TTX, 161 microM for magnesium, 18 microM for D,L-2-amino-5-phosphonovaleric acid (APV) and 1 microM for GABA. CCx cells were easy to handle and developed long living, stable and active neuronal networks on MEAs with similar characteristics as Cx. Thus, these neurochips seem to be suitable for studying neuronal network properties and screening in pharmaceutical research.

Action Potentials↗
PubMed1987

A stepper motor-driven microelectrode positioner.

The mechanical elements and the electronic control system from a stepper motor-driven microelectrode positioner is described. The unit embodies a high-precision small step angle hybrid motor. The compact, rugged and totally concentric design of the mechanic, by a spindle mechanism achieves the necessary precision by translating the stepwise rotations of the motor into steps of linear movement. The system takes advantage of commercially available low friction parts such as ball bearings, ball bushings and axles with hardened surfaces. The related electronic control unit is designed around the most recent integrated circuitry which is both sophisticated and economical. Though the described system is designed to be built in an average departmental workshop it compares favorably with more expensive commercial units and in some aspects outperforms them.

Electrophysiology↗
PubMed1997

A simple method for the construction of a recording-injection microelectrode with glass-insulated microwire.

A rapid method for the production of a glass-insulated microwire electrode is described. A microwire was threaded into a glass capillary which was then pulled on a vertical pipette puller. A conical tip of the microwire was formed when the strongly heated glass capillary broke together with the wire in it. A tight seal of the glass-insulated microwire electrode between the glass and the metal was accomplished with silicone glue. The manufactured electrode performed consistently at different immersion depths, and yielded stable recordings of single units in the cerebral cortex and the medulla of rats. The strength and low impedance characteristics of the glass-insulated microwire electrode may make it useful for the recording of single units in deep brain structures. Furthermore, the electrode can be easily combined with another glass micropipette to form a dual recording-injection microelectrode unit.

Animals↗
PubMed1997

A flexible perforated microelectrode array probe for action potential recording in nerve and muscle tissues.

Flexible perforated microelectrode arrays probes for the simultaneous recording of electrophysiological activity between cells have been manufactured using photolithographic thin film techniques. Polyimide was used as the substrate. Gold was used as the active metal with titanium to adhere the gold to the substrate. A coating of silicon nitride improves the electrode isolation. Perforations in the substrate ensure the position of the electrode in tissue and improve the stability of recording during movement. These electrodes were used for extracellular recording in nerve and muscle tissues. The use of a flexible substrate alleviates the mechanical problems associated with local damage caused by rigid substrates during movement.

Action Potentials↗
PubMed1997

A new design of carbon fiber microelectrode for in vivo voltammetry using fused silica.

Voltammetric probes were constructed from stainless steel and fused silica tubing sheathing carbon fibers. Electrochemical tests were carried out to compare these electrodes with commercially available glass-sealed IVEC-5 electrodes. Electrodes of both types displayed a similar declining baseline and calculated coefficients of stabilization (tangent of baseline during a stable period). There were no significant differences in sensitivity between the two designs of electrodes to norepinephrine (NE) and dopamine (DA). All tested electrodes showed linear current responses to increasing concentrations of NE and DA. Fused silica (FS type) electrodes are suitable for electrochemical measurements (in vivo voltammetry) and display characteristics similar to those of commercially available IVEC-5 glass-sealed carbon fiber microelectrodes. Manufacture of FS type electrodes in a biochemical laboratory is easy and does not require any special equipment (such as a micropipette puller) or glass-handling skills. An additional fused silica tube can be glued to the electrode for microinjections. The electrodes are very robust, easy to handle and can be mounted on the arms of standard stereotaxic instruments. The electrodes can be made long enough to reach the deepest parts of brain of large animals.

Microelectrodes↗
PubMed1997

Properties of electrolyte-filled glass microelectrodes: an experimental study.

The electrochemical and electrical properties of geometrically defined electrolyte-filled microelectrodes were studied at various transelectrode current passages, using radiotracer (38Cl and 42K) and electrical techniques. Geometrically, the electrodes were defined by their tip properties that, for standard (single-barrelled, 3.0 M KCl-filled, approximately 10 M[ohm]) electrodes implied a tip opening radius of 0.135 microm and a tip taper of 0.0215 microm/microm in the most distal (0-150 microm), and of 0.0105 microm/microm in the next most distal (150-1000 microm) tip regions. From the radiotracer studies it followed that (a) in the absence of transelectrode current passage, K+ and Cl- are leaking from the electrode tip in amounts corresponding to currents of +/- 3.8 nA, and (b) in the presence of transelectrode current passage, the flow of K+ and Cl- through the electrode tip changes with the transelectrode current in a statistically linear fashion so that K+ carries about 80% and Cl- about 20% of any electrode-injected current. From the electrical measurements it appeared that the standard electrodes are characterized by (a) a tip potential of -2.6 mV, and (b) a resistance that changes from an instantaneous, non-rectifying type to a steady state, outwardly rectifying type, within tenths of a second of constant current flow. The outward current rectification was seen to be reduced by raising [KCl] in the immersing solution, or by lowering it in the filling solution. Together, the observed electrode properties are consistent with the electrode electrolyte's solute and solvent turnover being governed by electro-osmotic as well as by electrodiffusion laws.

Chlorides↗
PubMed2002

Theoretical simulation of oxygen tension measurement in the tissue using a microelectrode: II. Simulated measurements in tissues.

BACKGROUND AND PURPOSE: The objectives of this study were to make a computer simulation of tissues with different vascular structures and to simulate measurements of oxygen tension using an Eppendorf-like electrode in these tissues and to compare the response to radiation of the tissues with the real oxygen distributions (called input distribution) with the response to radiation of the tissues in which the oxygen distribution is given by the results of the simulated measurements (called output distribution). MATERIALS AND METHODS: The structure of various tissues and the measurements of oxygen tension using a microelectrode were simulated using a computer program. The mathematical model used combines the description of a gradient of tissue oxygenation and the electrode absorption process. RESULTS: We have compared the oxygen distributions resulting from diffusion (input) with those obtained from a simulation of measurements (output) for various tissues in the same points. Because the electrode measurement is an averaging process, the calculated oxygen distributions are different from the expected ones and the extreme high and low values are not detected. We have then calculated the survival curves describing the response to radiation if there is a small fraction of truly hypoxic cells (expected values) or a large fraction of cells at intermediate values (observed results) in order to determine the differences between them. CONCLUSIONS: The results of our study show that oxygen electrode measurements do not give the true distribution of pO(2) values in the tissue. However, our results do not contradict the numerous empirical correlations between the Eppendorf measurements of tumour oxygenation and the outcome of treatments. Measurement results will be misleading for modelling purposes since they do not reflect the actual distributions of oxygen tensions in the measured tissue. Decisions based on such modelling could be very dangerous, especially with respect to the clinical response of tumours to new treatments.

Cell Hypoxia↗
PubMed2001

High-resolution two-dimensional spatial mapping of cat striate cortex using a 100-microelectrode array.

Much of our understanding of the visuotopic organization of striate cortex results from single-electrode penetrations and serial recording of receptive field properties. However, the quality of these maps is limited by imprecision in quantifying electrode position, combining data from multiple laminae, and eye drift during the measurement of the receptive field properties. We have addressed these concerns by using an array of 100 closely spaced microelectrodes to investigate the two-dimensional visuotopic organization of layer IV in cat striate cortex. This array allowed simultaneous measurement of the receptive field properties of multiple single units on a regularly spaced grid. We found the relationship between cortical and visual space to be locally non-conformal: the receptive field locations associated with a closely spaced line of electrodes appeared randomly scattered in visual space. To quantify the scatter, we fitted a linear transformation of electrode sites onto the associated receptive field locations. We found that the distribution of the difference between the predicted receptive field location and the measured location had standard deviations of 0.59 degrees and 0.45 degrees in the horizontal and the vertical axes, respectively. Although individual receptive field positions differed from the predicted locations in a non-conformal sense, the trend across multiple receptive fields followed the maps described elsewhere. We found, on average, that the 13 mm2 of cortex sampled by the array mapped onto a 5.8-degrees) region of visual space. From the scaling of this map and a combination of the statistics of the receptive field size (2.7+/-1.5 degrees) and scatter, we have explored the impact of electrode spacing on the completeness and redundancy in coverage of visual space sampled by an array. The simulation indicated an array with 1.2-mm spacing would completely sample the region of visual space addressed by the array. These results have implications for neuroprosthetic applications. Assuming phosphene organization resembles the visuotopic organization, remapping of visual space may be necessary to accommodate the scatter in phosphene locations.

Animals↗
PubMed1999

Electrochemical behaviour of cytochrome c at electrically heated microelectrodes.

The structural changes in cytochrome c with temperature have been been followed using a recently developed electrically-heated microelectrode sensor. Differential pulse voltammetry was used to perform electrochemical measurements of cytochrome c oxidation at different temperatures at heated bare gold electrodes contained in phosphate-buffered cytochrome c solution at room temperature. The voltammetric response shows the onset of unfolding and a marked dependence of the signal on electrode temperature. This augurs well for applications of heated electrodes as local probes in the study of the temperature dependence of electron transfer processes of other redox proteins, avoiding problems of bulk deterioration.

Animals↗
PubMedDate not supplied

Neurotoxic effects of mercury on auditory cortex networks growing on microelectrode arrays: a preliminary analysis.

Mercury is known to cause sensorineural hearing loss and impaired speech perception. However, there is still a lack of a quantitative description of mercury toxicity on central auditory structures. This is a preliminary study using the novel technique of microelectrode array (MEA) recordings to evaluate acute and chronic neurotoxic effects of mercury on auditory cortex networks (ACNs) in vitro. Morphological and electrophysiological effects of mercuric chloride (HgCl(2)) were studied. Neurons dissociated from auditory cortices of 14-day-old mouse embryos were grown on photoetched MEAs containing 64 transparent indium-tin oxide (ITO) electrodes. For acute electrophysiological experiments, the spontaneous spiking and bursting activity from ACNs were compared before and after application of HgCl(2). For chronic electrophysiological experiments, auditory cortex cultures were treated with various concentrations of HgCl(2) from the day of seeding, and were tested 4 weeks later for the presence of spontaneous activity. Morphological analysis was conducted on 8-day-old ACNs treated with HgCl(2) for 3 days. Results of acute experiments indicated that <75 mM of HgCl(2) had an excitatory effect of variable magnitude on the spontaneous activity of ACNs; however, concentrations above 100 microM completely and irreversibly inhibited spike and burst activity. Chronic exposure of ACNs to 10 microM HgCl(2) completely blocked the spontaneous activity. Morphological analysis indicated that 10 microM HgCl(2) caused neuronal cell death in 3 days. It is concluded that HgCl(2) has a more toxic effect on auditory networks when exposed chronically, and the levels of mercury showing toxic effects on ACNs are within the dose range shown to cause neurologic symptoms in humans.

Action Potentials↗
PubMed2000

Application of stripping voltammetry and microelectrodes in vitro biocompatibility and in vivo toxicity tests of AISI 316L corrosion products.

Adsorptive stripping voltammetric procedures, using mercury film microelectrodes, were optimised and applied to quantify total iron, chromium and nickel in samples of osteoblast-like cells culture medium and mice organs (liver, kidney and spleen) obtained from, respectively, in vitro and in vivo 316L stainless steel corrosion products biocompatibility and toxicity studies. The methods were based on the pre-concentration of the iron-catechol complex by adsorption at the potential of -1.80 V (vs. Ag/AgCl), of the chromium-diethylenetriaminepentaacetic acid complex at -1.00 V or -1.15 V (vs. Ag/AgCl) and of the nickel-dimethylglyoxime complex at -0.70 V (vs. Ag/AgCl). The detection limits achieved for each metal ion (i) in the culture medium were 1.93x10(-8) mol/L Fe, 2.80x10(-10) mol/L Cr and 7.70x10(-9) mol/L Ni for a collection time of 30 s, 40 s and 10 s, respectively, and (ii) in the mice organ solutions were 1.37x10(-8) mol/L Fe, 1.54x10(-8) mol/L Cr and 1.58x10(-9) mol/L Ni for an adsorption time of 25 s, 25 s and 15 s, respectively. The accuracy of the proposed procedures was verified by comparison of the results obtained by adsorptive stripping voltammetry with those attained by atomic absorption spectrometry for the same set of samples and good agreement was found. The in vitro study showed that stainless steel corrosion products affect the expression of the osteogenic phenotype. The in vivo mice model, used to investigate the systemic effects provoked by the corrosion products per se, indicated that Fe, Cr and Ni are partially accumulated in the organs studied and that Ni induced the more significant morphological alterations.

Animals↗
PubMed1998

Adsorptive stripping measurements of iron accumulation in mice kidney using microelectrodes and histological features.

The toxic effects caused by iron in kidney was performed on experimental studies with mice following administration of a metallic solution of this species to simulate the iron corrosion products of a metallic implant. To quantify the total levels of iron present in this organ, an electrochemical method was chosen based on the application of square wave voltammetry using adsorptive collection of iron-catechol on a mercury film microelectrode (MFM). The optimal working conditions to produce a very stable and reproducible iron peak in the digested kidney samples were found to be pH = 7.2 provided by 8.0 mmol/L PIPES buffer, catechol concentration of 3.0 x 10(-4) mol/L, deposition potential -1.80 V and deposition time 20 s. These results were compared with those obtained by atomic absorption spectrometry (AAS) indicating a good performance of the electrochemical method used. The analytical results show an increase of iron concentration with treatment time, which indicates that this metal ion is partially accumulated in the kidney. This accumulation induces with time some morphological alterations as evidenced by the histological analysis.

Animals↗
PubMed1998

Chromium determination in osteoblast-like cell culture medium by catalytic cathodic stripping voltammetry with a mercury microelectrode.

A catalytic cathodic stripping voltammetric procedure for the determination of total chromium in osteoblast-like cell culture medium using a mercury film microelectrode (MFM) was optimised. The method is based on the pre-concentration of the Cr(III)-diethylenetriaminepentaacetic acid (DTPA) complex by adsorption at the potential of-1.00 V (vs. Ag/AgC1) in the presence of 10 x 10(-3) mol/L DTPA, 0.70 mol/L sodium nitrate, 0.04 mol/L sodium acetate and 1.0 x 10(-3) mol/L potassium permanganate at pH 5.9-6.0. The limit of detection obtained for a 40 s collection time was 2.80 x 10(-10) mol/L of chromium. The results achieved by stripping voltammetry using the MFM were compared to those obtained by atomic absorption spectrometry (AAS) to ensure the reliability of the electrochemical method. This procedure proved to be an alternative to AAS and valuable in biocompatibility studies performed in vitro using osteoblast-like cells.

Acetates↗
PubMed2000

Drug evaluations using neuronal networks cultured on microelectrode arrays.

We used spontaneously active neuronal networks derived from dissociated embryonic murine spinal cord and auditory cortex and grown on substrate-integrated thin-film microelectrodes to determine characteristic responses to the cannabinoid agonists anandamide (AN) and methanandamide (MA). AN and MA reversibly inhibited spike and burst production in both tissue types. Responses of 21 cultures ranging in age from 23 to 111 days in vitro (d.i.v.) showed high intra- and inter-culture reproducibility at all ages. However, responses were tissue and substance-dependent. AN and MA were equipotent in cortical cultures and terminated bursting and spiking at 2.5 +/- 0.9 microM (n = 10). Spinal cultures were shut-off by 1.3 +/- 0.7 microM (n = 15) AN, but required 5.8 +/- 1.2 microM MA for activity cessation. MA, but not AN, demonstrated a biphasic influence: excitation at 0.25-3.5 microM and suppression at 4-7.1 microM. Palmitoylethanolamide, a related lipophilic molecule with no reported binding to the CBI receptor (to which AN and MA bind in the central nervous system), did not affect network activity at concentrations up to 6.5 microM. Irreversible cessation of activity was observed after 30 min applications of AN or MA at > 7 microM.

Animals↗
PubMed2001

Electrical properties of a light-addressable microelectrode chip with high electrode density for extracellular stimulation and recording of excitable cells.

A light-addressable microelectrode chip with 3600 TiN electrodes was fabricated. Amorphous silicon (a-Si:H) serves as a photo conductor. The electrodes on the chip are addressed by a laser spot and electrical properties of the system are determined. DC measurements show a dark to bright dynamic of 10(6)-10(7). The AC impedance dynamic @ 1 kHz/100 mV and thus the signal-to-noise-ratio is determined to 60. This value is quite sufficient for electrophysiological measurements. For the first time, recordings from cardiac myocytes are reported using the principle of light-addressing. Measurements were done with a standard laser scan microscope (Zeiss LSM 410).

Electric Stimulation↗