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PubMed2006

Long term recordings with microelectrode arrays: studies of transcription-dependent neuronal plasticity and axonal regeneration.

Substrate integrated microelectrode arrays (MEAs) offer an alternative to classical electrophysiological methods like the patch clamp technique for recording the electrical activity from cells and tissue of neuronal or cardiac origin. Since its introduction 30 years ago, this technology has made possible the repeated simultaneous recording from multiple sites in a non-invasive manner. The MEA technology can be applied to any electrogenic cells or tissue (i.e., central and peripheral neurons, heart cells, and muscle cells), either as cultures or acute cell or slice preparations. The combination of culture techniques and MEAs offers the possibility to monitor the activity of a designed specimen over extended periods of time, up to several months. Furthermore, recording the electrical activity of distributed regions of a preparation yields information on spatial effects that might go undetected with other recording methods. Development, plasticity, and regeneration are examples of applications that could especially benefit from long term monitoring of neuronal activity, as they concern processes that develop over extended periods of time. Here we highlight recent MEA studies on signal regulation of neuronal network behavior and axonal regeneration. We illustrate the use of MEAs to study long term potentiation (LTP) and summarize the advantages of MEA technology over traditional electrophysiological methods for studies aimed at understanding the transcription-dependent late phase of plasticity.

Animals↗
PubMed2005

Detection of viable Salmonella using microelectrode-based capacitance measurement coupled with immunomagnetic separation.

In this study, we demonstrated the use of a general medium--brain heart infusion (BHI) broth that is not specifically formulated for impedance measurement, to achieve detectable impedance signals by using an interdigitated microelectrode (IME) with capacitance measurement at low frequencies. Anti-Salmonella antibody coated immunomagnetic beads were used to separate S. typhimurium from samples to provide the selectivity to this method. From analysis based on the equivalent circuit of the IME system, we found that the impedance change in BHI broth resulting from the growth of Salmonella was indeed the change in the double layer capacitance and could be monitored at 10 Hz using the IME. The results indicated that medium modification to improve impedance signal is not necessary with this IME system. However, effective immunological separation for the target organism is required for the selectivity when non-selective media are used. This finding provides a more flexible option of medium in impedance methods, which may provide opportunities to test those species of bacteria that have no suitable conductance growth medium. The detection time, t(d), was obtained from the impedance growth curve (impedance against bacterial growth time) at 10 Hz at the point where the impedance started to change. A linear relationship between the detection time and the logarithmic value of the initial cell number (N) was found in the Salmonella cell number ranging from 10(1) to 10(6) cfu/ml. The regression equation was t(d) = -1.22Log N + 8.90, with R2 = 0.95. The detection times for the initial cell number of 10(1) CFU/ml and 10(6) CFU/ml are 8 h and 1.5 h, respectively. This method is more sensitive than impedance methods using conventional electrodes.

Biosensing Techniques↗
PubMed2004

Quality index for the quantification of the information recorded along standard microelectrode tracks to the subthalamic nucleus in parkinsonian patients.

OBJECTIVE: To quantify the usefulness of the neuronal activity recorded on a standard microelectrode track to the subthalamic nucleus (STN) for the determination of the transition between the thalamus and the STN. METHODS: The study is based on analysis of 689 extracelullar single units recorded on 70 tracks passing through the thalamus and the STN. Using four neuron parameters that were correlated with electrode depth, a quality index (QI) for each track was computed and compared with the subjective assessment by the electrophysiologist of the track quality. RESULTS: Subjectively, the transition between the thalamus and the STN was detected in 49 tracks (usual track) and not detected on 21 tracks (unusual tracks). Objectively, spike frequency, cell burst index (BI), signal relative root mean square (RMS) and spike relative amplitude were correlated with electrode depth and used to compute track QI. The average QI index of usual and unusual tracks was 0.25 +/- 0.9 and 0.85 +/- 0.15 (mean +/- confidence interval at P < 0.001), respectively. In 20 patients, QI correlates with post-operative measurement of electrode length in the STN. CONCLUSION: These results demonstrate that simple statistical analysis taking into account the variation of single-unit characteristics with electrode depth can discriminate between useful and useless tracks for the determination of the STN localisation.

Electrophysiology↗
PubMed2005

Listening to the brain: microelectrode biosensors for neurochemicals.

Chemical signalling underlies every function of the nervous system, from those of which we are unaware, for example, control of the heart, to higher cognitive functions, such as emotions, learning and memory. Neurotransmitters and neuromodulators mediate communication between neurons and between neurons and non-neural cells such as glia and muscle. In the past, the means for studying the production and release of these signalling agents directly has been limited in its temporal and spatial resolution relative to the dynamics of chemical signalling and the structures of interest in the brain. Now microelectrode biosensors are becoming available that give unprecedented spatial and temporal resolution, enabling, for the first time, direct measurement in real time of the chemical conversations between cells in the nervous system.

Animals↗
PubMed2005

Microelectrode array recordings of cardiac action potentials as a high throughput method to evaluate pesticide toxicity.

The threat of environmental pollution, biological warfare agent dissemination and new diseases in recent decades has increased research into cell-based biosensors. The creation of this class of sensors could specifically aid the detection of toxic chemicals and their effects in the environment, such as pyrethroid pesticides. Pyrethroids are synthetic pesticides that have been used increasingly over the last decade to replace other pesticides like DDT. In this study we used a high-throughput method to detect pyrethroids by using multielectrode extracellular recordings from cardiac cells. The data from this cell-electrode hybrid system was compared to published results obtained with patch-clamp electrophysiology and also used as an alternative method to further understand pyrethroid effects. Our biosensor consisted of a confluent monolayer of cardiac myocytes cultured on microelectrode arrays (MEA) composed of 60 substrate-integrated electrodes. Spontaneous activity of these beating cells produced extracellular field potentials in the range of 100 microV to nearly 1200 microV with a beating frequency of 0.5-4 Hz. All of the tested pyrethroids; alpha-Cypermethrin, Tetramethrin and Tefluthrin, produced similar changes in the electrophysiological properties of the cardiac myocytes, namely reduced beating frequency and amplitude. The sensitivity of our toxin detection method was comparable to earlier patch-clamp studies, which indicates that, in specific applications, high-throughput extracellular methods can replace single-cell studies. Moreover, the similar effect of all three pyrethroids on the measured parameters suggests, that not only detection of the toxins but, their classification might also be possible with this method. Overall our results support the idea that whole cell biosensors might be viable alternatives when compared to current toxin detection methods.

Action Potentials↗
PubMed2004

Photosynthesis in sediments determined at high spatial resolution by the use of microelectrodes.

The present study investigated photosynthetic rates and their regulation by light within the upper 5mm of sediment in a tidal area of Niida River in Hachinohe, Japan. Steady-state concentration profiles of O(2), NH(4)(+), NO(2)(-), H(2)S, and pH in the sediment were measured with microelectrodes. Microzonation of O(2) respiration, denitrification and SO(4)(2-) reduction was found in the sediment. When light intensities exceeded 1050 micromol photons/m(2)/s, net photosynthetic activity was detected in the upper 0.5mm of the microbial mat colonizing on the sediment surface in the tidal area. In contrast, gross photosynthetic activity was detected in the upper 1.0mm of the microbial mat at 1900 micromol photons/m(2)/s. As light intensity increased, the net photosynthetic rate and O(2) penetration depth increased. The maximal net photosynthetic rate and O(2) penetration depth were 6.1 micromol O(2)/cm(3)/h and 2.2mm, respectively, at 1900 micromol photons/m(2)/s. Net photosynthetic rates in the microbial mat in the tidal area were lower than in the upstream sediment. The analysis of continuous O(2) concentration measurements in different layers of the microbial mat during artificial light-dark cycles demonstrated that the photosynthetic activity response to changes in light intensity was extremely fast (a few seconds) and the O(2) concentration in the microbial mat became stable within 200s. The measurement of physical and chemical parameters in river water revealed that the study site was relatively polluted and sunlight intensity significantly fluctuated temporally. These results suggested that the in situ microbial processes occurring in the sediment fluctuated in accordance with periodic fluctuations in sunlight intensity.

Bacteria↗
PubMed1997

Oxytocin enhances action potentials in pregnant human myometrium--a study with microelectrodes.

OBJECTIVE: Our purpose was to quantitatively assess the effects of oxytocin on membrane properties in the pregnant human myometrium. STUDY DESIGN: Specimens were obtained from the lower uterine segment during cesarean section at term. Electrical activity was recorded from individual cells by a conventional microelectrode method and the membrane functions were analyzed. RESULTS: Two types of spontaneous action potentials were seen: a long plateau potential and a spike-like action potential. With no change in the resting membrane potential, low concentrations of oxytocin either evoked an action potential with a plateau phase, increased the amplitude and duration of the plateau potential, or increased the frequency of generation of action potentials. Oxytocin also lowered the threshold for evoking an action potential. Higher concentrations depolarized the membrane with an associated reduction in membrane resistance. CONCLUSION: Oxytocin augments the excitability of pregnant human myometrial cells by multiple actions on the membrane, affecting both frequency and amplitude of action potentials.

Action Potentials↗
PubMed1997

Permeation of phloretin across bilayer lipid membranes monitored by dipole potential and microelectrode measurements.

The transmembrane diffusion of phloretin across planar bilayer lipid membranes is studied under steady-state conditions. Diffusion restrictions and adsorption related effects are measured independently. The adsorption of aligned phloretin dipoles generates a change in the intrinsic dipole potential difference between the inner and outer leaflets of the lipid bilayer. It is monitored by capacitive current measurements carried out with a direct current (dc) bias. The variation of the intramembrane electric field indicates a saturation of the binding sites at the membrane interface. In contrast, pH profile measurements undertaken in the immediate membrane vicinity show a constant membrane permeability. If phloretin binding and transmembrane diffusion are treated as two competitive events rather than subsequent steps in the transport queue the contradictory results become explainable. A mathematical model is developed where it is assumed that diffusing phloretin molecules are randomly oriented, i.e., that they do not contribute to the intrinsic membrane potential. Only the dipoles adsorbing onto the membrane are oriented. Based on these theory the membrane permeability is calculated from the capacitive current data. It is found to agree very well with the permeability deduced from the microelectrode measurements.

Adsorption↗
PubMed2000

Solvent drag across gramicidin channels demonstrated by microelectrodes.

The competition of ion and water fluxes across gramicidin channels was assessed from the concentration distributions of both pore-impermeable and -permeable cations that were simultaneously measured by double-barreled microelectrodes in the immediate vicinity of a planar bilayer. Because water movement across the membrane led to accumulation of solutes on one side of the membrane and depletion on the other, the permeable cation was not only pushed by water across the channel (true solvent drag); it also flowed along its concentration gradient (pseudo-solvent drag). For the demonstration of true solvent drag, a difference between the bulk concentrations on the hypertonic and the hypotonic sides of the membrane was established. It was adjusted to get equal cation concentrations at both membrane/water interfaces. From the sodium and potassium fluxes measured along with membrane conductivity under these conditions, approximately five water molecules were found to be transported simultaneously with one ion through the channel. In diphytanoyl phosphatidylcholine membranes, a single-channel hydraulic permeability coefficient of 1.6 x 10(-14) cm(3) s(-1) was obtained.

Biophysical Phenomena↗
PubMed1988

K+-selective microelectrode study of internally dialyzed squid giant axons.

Intracellular potassium activity, (aK)i, and axoplasmic K+ concentration, [K+]i, were measured by means of K+-selective microelectrodes and atomic absorption spectroscopy, respectively, in squid giant axons dialyzed with K+-free dialysis solution and bathed in K+-free artificial sea water. (aK)i measurements indicated that axoplasmic free K+ could be depleted by dialysis, whereas [K+]i measurements on axoplasm extruded from these axons suggest substantial retention of K+ (15.5 +/- 1.7 mmol/kg axoplasm K+; n = 9). In comparison, [K+]i in axoplasm extruded from freshly dissected axons was 330 +/- 16 mmol/kg axoplasm (n = 6). These data suggest that approximately 5% of the axoplasmic K+ ions are not easily removed by dialysis and that these ions are either bound to macromolecular sites or sequestered into membrane-enclosed organelles.

Animals↗
PubMed1997

The effect of a transmembrane osmotic flux on the ion concentration distribution in the immediate membrane vicinity measured by microelectrodes.

The osmotically induced transmembrane water flow is accompanied by solute concentration changes within the unstirred layer adjacent to membranes. Experimental concentration profiles, measured by means of microelectrodes in the immediate vicinity of a planar lipid bilayer, are compared with theoretical ones predicted from the standard physiological model in which the osmotic advection is countered by back-diffusion of the solute only. An increase of the apparent osmotic flow rate is induced by an increase of the osmotic gradient and by rigorous stirring. The polarization effect decreases in the latter case due to an increase of the transfer rate of solutes between the bulk solutions and the membrane surfaces, whereas it increases in the former case. The observations show that the concentration profile is not well described by the standard approximation. The discrepancy becomes increasingly large with increased volume flow. Based on a modified theoretical description of the interaction between water flux and diffusion, the hydraulic conductivity of the bilayer is calculated from the measured uniexponential concentration profiles. The common approximation that there is a discrete boundary between the stirred and unstirred regions adjacent to the membrane is substituted by the model of a stagnant point flow that takes into account a gradual change of the stirring velocity in the immediate membrane vicinity. Supported by experimental observations, this approach predicts a shortening of the unstirred layer if the transmembrane osmotic gradient is increased under gentle stirring conditions.

Chemical Phenomena↗
PubMed1998

Streaming potentials in gramicidin channels measured with ion-selective microelectrodes.

Streaming potentials have been measured for gramicidin channels with a new method employing ion-selective microelectrodes. It is shown that ideally ion-selective electrodes placed at the membrane surface record the true streaming potential. Using this method for ion concentrations below 100 mM, approximately seven water molecules are transported whenever a sodium, potassium, or cesium ion, passes through the channel. This new method confirms earlier measurements (Rosenberg, P.A., and A. Finkelstein. 1978. Interaction of ions and water in gramicidin A channels. J. Gen. Physiol. 72:327-340) in which the streaming potentials were calculated as the difference between electrical potentials measured in the presence of gramicidin and in the presence of the ion carriers valinomycin and nonactin.

Anti-Bacterial Agents↗
PubMed1998

Hypoxia induced by Na2S2O4 increases [Na+]i in mouse glomus cells, an effect depressed by cobalt. Experiments with Na+-selective microelectrodes and voltage-clamping.

The intracellular sodium concentration ([Na+]i) and resting potential (Em) of cultured mouse glomus cells (clustered and isolated) were simultaneously measured with intracellular Na+-sensitive and conventional, KCl-filled, microelectrodes. Results obtained in clustered and isolated cells were similar. During normoxia (PO2 122 Torr), [Na+]i was 12-13 mM corresponding to a Na+ equilibrium potential (ENa) of about 58 mV. Em was about -42 mV. Hypoxia, induced by Na2S2O4 1 mM (PO2 10 Torr), depolarized the cells by about 20 mV, [Na+]i increased by 21 mM and ENa dropped to about 35 mV. One millimolar of CoCl2 depressed, or blocked, the effects of Na2S2O4 on [Na+]i but did not affect hypoxic depolarization. Voltage-clamping at -70 mV, while delivering pulses of different amplitudes, produced only small (about 10 pA) and slow TTX-insensitive inward currents. Fast and large (TTX-sensitive) inward currents were not detected. The cell conductance (measured with voltage ramps) was less than 1 nS. It was not affected by hypoxia but was depressed by cobalt. Voltage ramps elicited small inward currents in control and hypoxic solutions that were much smaller than those induced by barium (presumably enhancing calcium currents). Also, normoxic and hypoxic currents had lower thresholds and their troughs were at more negative voltages than in the presence of Ba2+. All currents were blocked by 1 mM CoCl2 suggesting that, at this concentration, cobalt exerted a nonspecific effect on glomus membrane channels. Hypoxia induced a large [Na+]i increase (presumably through inflow), but very small voltage-gated inward currents. Thus, Na+ increases (inflow) probably occurred by disturbing a Na+/K+ exchange mechanism and not by activation of voltage-gated channels.

Animals↗
PubMed1984

Effects of elastase and collagenase on microelectrode impalements in canine atria at different ages.

Mechanical activity in isolated canine atria hinders impalements of single cells with microelectrodes. However, when atrial contractility becomes diminished, a substantial obstacle to impalement remains. To investigate whether the remaining obstacle could be connective tissue, atria were removed from dogs of three age groups (less than 1 year old, 2.8 +/- 0.2 years old and 10.7 +/- 0.5 years old), perfused arterially, and then immersed in elastase (0.01%) or collagenase (0.1%) for 15 min. The following observations were made: (1) In the older atria, satisfactory cell impalements were attained only after they were treated with elastase or collagenase, (2) elastase was effective on the endocardial surfaces only, and (3) collagenase was effective on the epicardial surfaces only. Enzyme effects corresponded to the known anatomic distribution of elastin (endocardial surface) and collagen (epicardial surface). Therefore connective tissue may present a considerable obstacle to cell impalement, especially in hearts from older dogs.

Action Potentials↗
PubMed1987

Computer-assisted stereotactic ventralis lateralis thalamotomy with microelectrode recording control in patients with Parkinson's disease.

Stereotactic ventralis lateralis thalamotomy can be performed in selected patients with medically intractable parkinsonian tremor and rigidity. New technology, including computed tomography-based stereotaxis and microelectrode recording techniques, provides a data base for precise localization of thalamic lesions tailored to each patient and thus reduces the risk associated with such a procedure. At our institution, 12 patients with medically intractable parkinsonian tremor have undergone this procedure; all experienced alleviation or cessation of the tremor and no permanent disabling neurologic sequelae.

Adult↗
PubMed2005

Microelectrode for in vivo real-time detection of NO.

Nitric oxide (NO) is gaining importance with its diverse spectrum of clinic effects. However, there is still a need for an ideal sensor to monitor its concentration in tissue. An ideal sensor should not interfere with the ongoing physiological process, while making fast, reliable, and repeatable measurements. We have designed a microelectrode for electrochemical NO measurement from tissue with relatively low interference and reliable results upon calibration. Details of electrode preparation and calibration procedure are explained along with an experiment to monitor effects of photodynamic therapy.

Animals↗
PubMed1979

Measurement of tissue pH in skin by glass microelectrodes.

Alterations in metabolic activity may be used as an indicator of tissue perfusion and haemodynamic status in peripheral ischaemia. A new type of microelectrode was used to measure pH in the skin of patients with vascular disease, and a decrease in pH was demonstrated along the leg, commensurate with the severity of the disease. Measurement of skin pH by this technique is easy and may be useful for assessing tissue perfusion or skin viability in other conditions.

Glass↗