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At least 217 records · Page 12Linked to original sources

PubMed2006

Evaluation of the stability of intracortical microelectrode arrays.

In order to use recorded neural activities from the brain as control signals for neuroprosthesis devices, it is important to maintain a stable interface between chronically implanted microelectrodes and neural tissue. Our previous paper introduced a method to quantify the stability of the recording microelectrodes. In this paper, the method is refined 1) by incorporating stereotypical behavioral patterns into the spike sorting program and 2) by using a classifier based on Bayes theorem for assigning the recorded action potentials to the underlying neural generators. An improved method for calculating stability index is proposed. The results for the stability of microelectrode arrays that differ in structure are presented.

Action Potentials↗

PubMed1989

Microelectrode study on the ionic mechanisms which contribute to the noradrenaline-induced depolarization in isolated cells of the rabbit portal vein.

1. Experiments were carried out to determine the identity of the ionic mechanisms which contribute to the noradrenaline-evoked depolarization recorded with microelectrodes in freshly dispersed rabbit portal vein cells. 2. In normal physiological salt solution with microelectrodes containing 1 M NaCl the reversal potential (Er) of the noradrenaline-induced response was -7.6 +/- 2.9 mV. When the external NaCl was replaced by equipmolar concentrations of NaI, NaBr and NaNO3, Er was -33 +/- 3.5 mV, -29.1 +/- 5.2 mV and -18.4 +/- 1.1 mV, respectively. 3. In physiological salt solution Er of noradrenaline-evoked responses recorded with electrodes filled with 1 M NaI or 1 M NaNO3 was +16.3 +/- 3.9 mV and +10.0 +/- 7.6 mV, respectively. These results suggest that an increase in anion conductance contributes to the depolarization to noradrenaline. 4. Data from experiments with organic anions indicated that glutamate behaves as a less permeant anion but that benzenesulphonate blocks the anion conductance to unmask another conductance mechanism activated by noradrenaline. 5. When external NaCl was substituted by choline Cl and Tris Cl Er was -21.3 +/- 3.7 mV and -20.5 +/- 2.8 mV, respectively. These results suggest that noradrenaline also activates a cation conductance mechanism in freshly dispersed rabbit portal vein cells. It is concluded that the depolarization to noradrenaline recorded with a microelectrode is produced by the simultaneous activation of an anion channel and a separate cation channel.

Animals↗

PubMed1987

Thirty years of ion-selective microelectrodes: disappointments and successes.

The need to know the intracellular activity of an ion and how it changes under controlled conditions is as important today as it was 30 years ago. In 1956, one could fabricate only a H+-selective microelectrode and with a tip size not much smaller than 100 micron. Today, one can fabricate microelectrodes selective to H+, Na+, K+, Cl-, HCO3-, Ca2+, or Mg2+ (plus others) and with active tips less than 1 micron. The reduction of active tip size can be attributed mainly to the introduction of liquid ion exchanger (LIX) and neutral carrier ligands. Unfortunately, the LIX microelectrodes, as currently fabricated, do not yet function optimally as reliable and stable electrochemical measuring devices. A durable bond between the active membrane and its insulated container continues to remain the major design problem even after 30 years of development.

Animals↗

PubMed1987

Ability of the Ca2+-selective microelectrodes to measure fast and local Ca2+ transients in nerve cells.

The ability of the Ca2+-selective microelectrode to measure fast Ca2+ transients intracellularly is reviewed. In vitro, Ca microelectrodes can respond to Ca2+ injections with time to peaks as small as 40 ms. We present methods to improve the dynamic response of Ca microelectrodes and to make Ca-buffered solutions in high ionic strength. Examples of measurements of intracellular free Ca2+ [( Ca2+]i) transients in Aplysia neurons and in Limulus photoreceptors are shown. To show the validity of those measurements, simultaneous recordings of the Arsenazo III (AIII) absorbance and of the Ca-selective electrode potential were made in voltage-clamped neurons of the abdominal ganglion of Aplysia californica. Pressure injection of AIII to a concentration of 300-500 microM induced a rise in resting [Ca2+]i; injection of higher [AIII] led to buffering of [Ca2+]i transients. Both techniques responded to changes in resting [Ca2+]i in the same direction except that AIII showed an increase in absorbance in 0 [Ca2+]o. Voltage-clamp pulses transiently increased both the AIII absorbance and the Ca2+ electrode potential. Reducing or increasing the driving force for Ca2+ entry changed the magnitude of both signals in the right direction. Examples of spatial localization of [Ca2+]i increases and Ca2+ gradients within the cytoplasm were demonstrated using the Ca electrode. The use of optical techniques to measure local [Ca2+]i changes is briefly reviewed.

Animals↗

PubMed1987

Qualitative measurements of the entry of L-lactate into single surface fibres of frog skeletal muscle using a lactate-sensitive microelectrode.

The present results demonstrate the sensitivity of the Corning chloride liquid ion exchanger 477913 to L-lactate. Microelectrodes filled with this exchanger showed responses to changes in L-lactate concentration in chloride-free solutions. In these experiments L-lactate replaced gluconate in equimolar amounts. Microelectrodes filled with this exchanger were used to qualitatively detect changes in intracellular anion in chloride-depleted frog sartorius muscle fibres during exposure to extracellular concentrations of L-lactate. The increase in intracellular anion concentration is consistent with the movement of L-lactate into the cell. This microelectrode enables one to qualitatively monitor changes in intracellular L-lactate in chloride-free experiments without incorporating selectivity coefficients.

Animals↗

PubMed1983

Microelectrode studies of Necturus antral mucosa: electrical potentials and resistances.

Intracellular microelectrode techniques were applied to Necturus antral mucosa. Stable intracellular impalements were obtained with 15-50 M omega microelectrodes filled with 3M KCl. It was possible to change rapidly the mucosal bathing solution while maintaining the microelectrode in the cell. With these techniques, we were able to measure the electrical potentials and resistances of the cell membranes and the shunt pathway. The transepithelial potential was -4.9 +/- 1.3 mV, serosal solution reference. Apical cell membrane potential was -43.9 +/- 0.6 mV, cell negative to the mucosal solution. Basolateral cell membrane potential was -48.8 +/- 1.3 mV, cell negative to serosal solution. Transepithelial resistance was 427 +/- 66 omega . cm2. The ratio of apical to basolateral membrane resistances was 3.4 +/- 0.3. The electrical resistances of the transcellular and paracellular pathway were determined by the measurement of the total transepithelial resistance and the ratio of apical to basolateral cell membrane resistances before and after blocking apical membrane sodium permeability with amiloride. The resistances of the apical cell membrane, basolateral cell membrane, and the shunt were 2,203 +/- 585, 1,296 +/- 384, and 604 +/- 81 omega . cm2, respectively (mean +/- SE). Calculations from these measurements indicate that the shunt contribution to transepithelial conductance was approximately 85%.

Amiloride↗

PubMed1984

Viewing the kidney through microelectrodes.

Electrical measurements with microelectrodes have proven of great value in the investigation of renal ion transport mechanisms. By virtue of their fine tips (less than 1 micron in diameter) and because of the ease of recording electrical transients, they provide measurements with unparallelled space and time resolution. Early electrophysiological work was done largely in amphibians, because of their larger cell size, whereas studies in mammals were restricted to transepithelial electrical parameters, which provided no insight into individual membrane mechanisms. However, recently techniques have been developed to impale individual tubular cells of mammalian kidneys successfully, both in vivo and in vitro. Such experiments allow us to identify ion transport properties of individual cell membranes from the response of the electrical potential to fast pertubations of the luminal and/or peritubular fluid composition or to applied currents. The power of this approach was greatly increased by the development of ion-selective microelectrodes, allowing us to measure intracellular concentrations of Na+, K+, Cl-, Ca2+, and HCO3- or pH directly and to follow quantitatively their changes in response to different experimental maneuvers. In the present paper our knowledge of ion transport mechanisms of mammalian proximal tubular cell membranes is summarized, with emphasis on the transport of Na+, K+, HCO3-, and Cl-. With the exception of transcellular transport of Cl-, which is quantitatively less important, the major transport mechanisms of all other ions have been identified in the brush border and in the peritubular cell membrane. Emphasis is given to the description of HCO3- exit across the peritubular cell membrane, which has not thus far been studied with other than electrophysiological techniques. Microelectrode techniques will probably continue to provide new insight when regulatory phenomena are studied on the cellular level and individual conductance channels in renal cell membranes are identified with the newly developed patch-clamp technique.

Animals↗

PubMed1980

Excursion of vibrating microelectrodes in tissue.

A vibrating microelectrode holder consisting of a support rod attached to the cone of a miniature loudspeaker facilitates electrode penetration into arterial wall tissue, eliminates surface dimpling, and relieves polarographic artifacts believed to be due to tissue compression. The longitudinal vibratory excursion of free microelectrode tips, measured with strobe illumination microscopy, varies from less than 0.9 to 137 micron depending on energizing voltage and frequency. Tissue penetration is achieved most effectively at the resonance frequency, about 200 Hz for the present system. Total tip excursion is not diminished when the electrode is penetrated into excised rabbit femoral artery, but tip motion relative to surrounding tissue is considerably attenuated because the arterial wall holds the electrode shaft rather firmly and follows its movements. This relative motion in tissue is only 2.7 +/- 0.8 micron at 200 Hz and 0.05 V and can be reduced further at higher frequencies without sacrificing the penetration advantages of the system. Thus under proper vibratory conditions microelectrodes can be easily inserted into the arterial wall with minimal tissue disturbance.

Animals↗

PubMed1997

Optimal target localization for ventroposterolateral pallidotomy: the role of imaging, impedance measurement, macrostimulation and microelectrode recording.

From October 1992 through December 1996, we performed 109 ventroposterolateral pallidotomies on 104 patients with Parkinson's disease. Throughout the series, we have used the basic imaging technique described by Laitinen, utilizing impedance measurement and macrostimulation to determine the optimal target position within with the pallidum and avoid the optic tract and the internal capsule. To take advantage of the high resolution of MR imaging while compensating for potential MR distortion, we have refined our stereotactic software to accomplish effective cross-registration and reformatting of CT and MR images. By 1995, several centers were suggesting that optimal target localization required microelectrode identification of pallidal neuronal firing patterns. During 1996, we performed microelectrode recording in 13 of the 25 patients undergoing pallidotomy. We have concluded that the basic technique of Laitinen, coupled with high-resolution imaging remains the foundation for achieving effective pallidotomy. Microelectrode recording is a useful adjunct to identify hyperactive firing patterns in the internal pallidum and, coupled with impedance measurements and macrostimulation, can define the lower border of the pallidum.

Brain Mapping↗

PubMed1997

Chronic microelectrode investigations of normal human brain physiology using a hybrid depth electrode.

Neurosurgeons have unique access to in vivo human brain tissue, and in the course of clinical treatment important scientific advances have been made that further our understanding of normal brain physiology. In the modern era, microelectrode recordings have been used to systematically investigate the cellular properties of lateral temporal cerebral cortex. The current report describes a hybrid depth electrode (HDE) recording technique that was developed to enable neurosurgeons to simultaneously investigate normal cellular physiology during chronic intracranial EEG recordings. The HDE combines microelectrode and EEG recordings sites on a single shaft. Multiple microelectrode recordings are obtained from MRI defined brain sites and single-unit activity is discriminated from these data. To date, over 60 HDEs have been placed in 20 epilepsy surgery patients. Unique physiologic data have been gathered from neurons in numerous brain regions, including amygdala, hippocampus, frontal lobe, insula and Heschl's gyrus. Functional activation studies were carried out without risking patient safety or comfort.

Action Potentials↗

PubMed1992

Use of palladium touch microelectrodes under field conditions for in vivo assessment of dental plaque pH in children.

The aim of this study was to assess the applicability of palladium touch microelectrodes, connected to battery-run pH meters, for in vivo plaque pH measurements in children. The pH was assessed in 20 7-year-old and in 19 14-year-old caries-active and caries-inactive rural Kenyan children. The resting pH was measured at non-carious interproximal and occlusal sites and in open dentine cavities. Independent repeated measurements were performed at given sites at intervals of 15 s and 5 min and on different days. The resting plaque pH varied widely among the children, and there was no significant difference between caries-active and caries-inactive groups. The most striking feature was the considerable erratic fluctuations of pH at a given site with time, both in resting and in sucrose-challenged plaque. These fluctuations were sensitively recorded by palladium touch microelectrodes. After a sucrose rinse, not all sites in the same mouth behaved in a similar fashion, and thus the classical 'Stephan curve' was not always apparent. In conclusion, the palladium touch microelectrodes are highly applicable for plaque pH measurements in children, even under extreme field conditions.

Adolescent↗

PubMed2005

Detection of electrophysiological indicators of neurotoxicity in human and rat brain slices by a three-dimensional microelectrode array.

Electrophysiological techniques for the assessment of in vitro neurotoxicology have several advantages over other currently-used methods (for example, morphological techniques), including the ability to detect damage at a very early stage. Novel recording techniques based on microelectrode arrays are available, and could improve recording power. In this study, we investigated how a three-dimensional microelectrode array detects the electrophysiological endpoints of neurotoxicity. We conclude that electrophysiology sensitively reveals neurotoxic actions, and that three-dimensional microelectrode arrays could be proposed for use in neurotoxicology as recording tools that allow easy and sensitive multisite recording, from both rodent and human brain tissue.

Animals↗

PubMed2004

Cingulotomy for psychiatric disease: microelectrode guidance, a callosal reference system for documenting lesion location, and clinical results.

OBJECTIVE: To evaluate magnetic resonance imaging (MRI)- and microelectrode recording-guided cingulotomy for patients with psychiatric disorders and to develop a new method of mapping lesion location in anterior cingulate cortex that takes into account the significant interindividual variability in callosal morphometry. METHODS: MRI and microelectrode recording were used to guide placement of radiofrequency lesions in patients with obsessive-compulsive disorder (n = 21) or affective disorders (n = 5). Postoperative improvement was evaluated with the Yale-Brown Obsessive-Compulsive Scale in 15 of the 21 obsessive-compulsive disorder patients studied. From the postoperative MRI scans, we developed a coordinate system for position in the anterior cingulate cortex. The callosal line passes from the most anterior point of the corpus callosum (c = 0) to the most posterior (c = 100). We reconstructed the lesions onto a sagittal map from the Talairach and Tournoux atlas using the distance along the callosal line and the distance above the upper surface of the corpus callosum. RESULTS: The location of neuronal activity distinguished gray and white matter and was useful in delineating the upper and lower cortical banks of the cingulate gyrus, the cingulate bundle, and the corpus callosum. This information was used to place the lesions. Lesions typically were 6 to 8 mm in diameter on T2-weighted MRI scans. The inferior margins were along the corpus callosum from c = 16 to c = 38. Four of 15 patients with obsessive-compulsive disorder had a documented decrease of more than 35% on the Yale-Brown Obsessive-Compulsive Scale, but only one patient had a sustained benefit for more than 1 year. CONCLUSION: Microelectrode recording is useful for lesion placement. Our system for reporting location in anterior cingulate cortex normalizes for differences in callosal morphometry. These techniques may aid future study.

Adult↗

PubMed2005

Risk factors for hemorrhage during microelectrode-guided deep brain stimulator implantation for movement disorders.

OBJECTIVE: Although hemorrhage is a well-known complication of microelectrode-guided deep brain stimulation (DBS) surgery, risk factors for the development of hemorrhage have not been well defined. We analyzed the risk factors for symptomatic and asymptomatic hemorrhage in a large series of DBS implantations into the subthalamic nucleus, ventrolateral thalamus, and internal globus pallidus. METHODS: All DBS procedures performed by a single surgeon at our institution between June 1998 and May 2004 were included in this study. All patients had postoperative imaging (magnetic resonance imaging or computed tomography) 4 to 24 hours after surgery. Hematomas were noted and scored as symptomatic or asymptomatic. Statistical correlation of factors affecting risk of hematoma formation was performed by use of logistic regression analysis. RESULTS: The total number of lead implantations was 481. There were 6 symptomatic hematomas and 10 asymptomatic hematomas. Three of the symptomatic hematomas resulted in permanent new neurological deficit. The risk of hematoma (of any type) per lead implantation was 3.3%, whereas the risk of permanent deficit from hematoma was 0.6%. Patients who developed hematomas had a slightly greater number of microelectrode recording penetrations than patients who did not have hematomas, but this difference did not reach statistical significance. There was not a statistically significant relationship between risk of hematoma and patient age or diagnosis. There was a significant effect of brain target (P = 0.001), with only 1 hemorrhage detected after thalamic DBS. CONCLUSION: DBS is generally safe, with only 0.6% of implantations associated with permanent neurological deficit. The incremental risk of successive serial microelectrode penetrations is small.

Aged↗

PubMed1999

The self-referencing oxygen-selective microelectrode: detection of transmembrane oxygen flux from single cells.

A self-referencing, polarographic, oxygen-selective microelectrode was developed for measuring oxygen fluxes from single cells. This technique is based on the translational movement of the microelectrode at a known frequency through an oxygen gradient, between known points. The differential current of the electrode was converted into a directional measurement of flux using the Fick equation. Operational characteristics of the technique were determined using artificial gradients. Calculated oxygen flux values matched theoretical values derived from static measurements. A test preparation, an isolated neuron, yielded an oxygen flux of 11.46+/-1.43 pmol cm-2 s-1 (mean +/- s.e.m.), a value in agreement with those available in the literature for single cells. Microinjection of metabolic substrates or a metabolic uncoupler increased oxygen flux, whereas microinjection of KCN decreased oxygen flux. In the filamentous alga Spirogyra greveilina, the probe could easily differentiate a 16.6% difference in oxygen flux with respect to the position of the spiral chloroplast (13.3+/-0.4 pmol cm-2 s-1 at the chloroplast and 11.4+/-0.4 pmol cm-2 s-1 between chloroplasts), despite the fact that these positions averaged only 10.6+/-1.8 microm apart (means +/- s.e.m.). A light response experiment showed real-time changes in measured oxygen flux correlated with changes in lighting. Taken together, these results show that the self-referencing oxygen microelectrode technique can be used to detect local oxygen fluxes with a high level of sensitivity and spatial resolution in real time. The oxygen fluxes detected reliably correlated with the metabolic state of the cell.

Animals↗

PubMed2000

Electrophysiological studies on the evaluation of absorption enhancers in Caco-2 cells using a microelectrode technique.

We developed a microelectrode technique to characterize the electrophysiological properties in Caco-2 cells, and used it to determine the mechanisms of absorption enhancers. The action of absorption enhancers on the apical membrane of Caco-2 cells was estimated by measuring the apical membrane potential (Vm) with the microelectrode. The Vm value of Caco-2 cells in Hanks' balanced salt solution containing 0.5 mM K+ was 18.9+/-0.8 mV (n=217), and the apical membrane resistance was 49.4+/-1.1 MOhms (n=160). In the electrophysiological study with absorption enhancers, laurylmaltoside (LM) markedly decreased the Vm value, while sodium glycocholate (NaGC) moderately reduced this value, and EDTA did not affect the value. These findings might be associated with their action sites, plasma membrane or tight junction in Caco-2 cell monolayers. In influx and transport studies with these absorption enhancers, LM enhanced the influx of furosemide, which is transported via both the transcellular and paracellular routes into Caco-2 cells, and enhanced its transport to the basolateral side of Caco-2 monolayers more than that of 5(6)-carboxyfluorescein (CF), a paracellular marker. EDTA did not increase the influx of furosemide, and enhanced the transport of furosemide and CF across Caco-2 cell monolayers to the same extent. In contrast, NaGC only slightly increased the influx of furosemide and did not enhance the transport of either furosemide or CF across the Caco-2 monolayers in this study. These findings were well correlated with the effects of these absorption enhancers on the electrophysiological parameters. Therefore, the microelectrode technique might be useful for evaluating the action of absorption enhancers in the plasma membrane at an intact cell level.

Caco-2 Cells↗

PubMed1997

Glass pipette-carbon fiber microelectrodes for evoked potential recordings.

Current methods for recording field potentials with tungsten electrodes make it virtually impossible to use the same recording electrode also as a lesioning electrode, for example for histological confirmation of the recorded site, because the lesioning procedure usually wears off the tungsten tip. Therefore, the electrode would have to be replaced after each lesioning procedure, which is a very high cost solution to the problem. We present here a low cost, easy to make, high quality glass pipette-carbon fiber microelectrode that shows resistive, signal/noise and electrochemical coupling advantages over tungsten electrodes. Also, currently used carbon fiber microelectrodes often show problems with electrical continuity, especially regarding electrochemical applications using a carbon-powder/resin mixture, with consequent low performance, besides the inconvenience of handling such a mixture. We propose here a new method for manufacturing glass pipette-carbon fiber microelectrodes with several advantages when recording intracerebral field potentials.

Animals↗

PubMed1980

Protein effect on the antimony microelectrode in application to biological fluid.

In order to examine the effect of protein on the Sb-microelectrode used for the pH measurement of biological fluids, bovine serum albumin (BSA) and plasma protein were used for test samples. It was found that, BSA, probably by binding to components in the electrode system, produced a marked deviation of both the electromotive force and slope constant of the microelectrode, resulting in an alkaline shift of pH of 0.1-0.7. But the shift of the pH reading could be empirically predicated within an error of +/- 0.03 from the cubic function of protein concentration. Use of Tris standard solution as the calibration buffer, together with corrections for the effects of temperature, ionic strength, Po2, etc. on the Sb-microelectrode, would reduce the alkaline shift to approximately less than 0.08 and 0.04 pH units in the pH measurement of blood plasma and whole blood, respectively.

Antimony↗