Direct Current Recordings Research Articles

Organellular imaging in vivo reveals a depletion of endoplasmic reticular calcium during post-ictal cortical spreading depolarization.

During cortical spreading depolarization (CSD), neurons exhibit a dramatic increase in cytosolic calcium, which may be integral to CSD-mediated seizure termination. This calcium increase greatly exceeds that during seizures, suggesting the calcium source may not be solely extracellular. Thus, we sought to determine if the endoplasmic reticulum (ER), the largest intracellular calcium store, is involved. We developed a two-photon calcium imaging paradigm to simultaneously record the cytosol and ER during seizures in awake mice. Paired with direct current recording, we reveal that CSD can manifest as a slow post-ictal cytosolic calcium wave with a concomitant depletion of ER calcium that is spatiotemporally consistent with a calcium-induced calcium release. Importantly, we observed both naturally occurring and electrically induced CSD suppressed post-ictal epileptiform activity. Collectively, this work links ER dynamics to CSD, which serves as an innate process for seizure suppression and a potential mechanism underlying therapeutic electrical stimulation for epilepsy.

Comparison between the AC and DC measurement of electrodermal activity.

Recording electrodermal activity is a well-accepted physiological measurement for clinical approaches and research. Historically, applying a DC (direct current) signal to the skin to measure the conductance is the most common practice for exogenous recordings. However, this method can be subject to error due to electrode polarization even with "nonpolarizing" electrodes-a problem that can be eliminated with alternating current (AC) methodology. For that reason, Boucsein et al. () called for research demonstrating an AC method that is validated by comparison to standard DC methodology. Additionally, the complex structure of human skin has electrical properties that include both resistance and capacitance, and AC recording enables the measurement of skin susceptance (associated with current flow through capacitors). Finally, AC recording permits the simultaneous recording of the endogenous skin potential. In this paper, the results from a direct comparison between both methods are presented, which has not been reported previously. The results demonstrated excellent agreement between a 20 Hz AC method and a standard DC method, supporting the validity of the AC recording methodology employed. The results also showed that an applied voltage of 0.2 V is sufficient for DC recordings.

Abstract 18408: Cortical Spreading Depolarizations After Cardiac Arrest in an Asphyxial Rat Model

Introduction: Delayed neuronal cell death is observed following cardiac arrest (CA). The exact mechanisms remain unknown. Cortical spreading depolarization (CSD) is characterized by depolarization of neurons and glia cells, spreading as a wave that travels across the cortex. CSDs are known to occur in peri-infarct tissue and have been associated with poor outcome after stroke, and might contribute to the progression of neuronal injury after CA. Objective: To investigate if spontaneous CSDs occur during the post resuscitation period following CA, and to describe the characteristics of induced CSDs. Methods: Isoflurane-anesthetized Sprague-Dawley rats were randomized into one control group observed for 90 min (n=8), and two CA groups observed for 90 min (CA90min, n=7) and 360 min (CA360min, n=7), respectively, before data collection started. Animals underwent 8 min of asphyxial CA. Electrophysiological recordings were obtained over the right hemisphere through a burr hole. Potassium chloride (KCL) was applied onto the cortex through a separate burr hole in order to induce CSDs. Direct current recordings were gathered using an AgCl glass electrode. Induced abnormal CSDs were defined as CSDs with prolonged duration, low peak value, altered propagation speed and/or epileptiform discharges. Data collection (210 min) was divided into two periods: 1) In the 1 st period no stimulation was applied in order to detect spontaneous elicited CSDs. 2) In the 2 nd period KCl was applied. Results: Spontaneous CSDs were observed in one CA360min animal with prolonged CPR and time to return of spontaneous circulation of 298 sec. Significantly fewer CSDs were induced following KCl application in CA animals when compared with healthy controls (median(IQR) Control: 6(5-7) CA90min: 2(1-4) CA360min: 1(1-3), p<0.05). Induced abnormal CSDs were seen in both CA groups but not in controls (control vs. CA90min p=0.004, control vs. CA360min p=0.054). KCl application elicited multiple CSDs in rapid succession in 50% of CA animals and none of the controls (p=0.052). Conclusion: CSDs can occur following prolonged CA and resuscitation, and may lead to additional neuronal injury. The appearance and number of induced CSDs were altered in CA animals in comparison with healthy controls.

Radio-frequency response of single pores and artificial ion channels

Intercellular communication relies on ion channels and pores in cell membranes. These protein-formed channels enable the exchange of ions and small molecules to electrically and/or chemically interact with the cells. Traditionally, recordings on single-ion channels and pores are performed in the dc regime, due to the extremely high impedance of these molecular junctions. This paper is intended as an introduction to radio-frequency (RF) recordings of single-molecule junctions in bilipid membranes. First, we demonstrate how early approaches to using microwave circuitry as readout devices for ion channel formation were realized. The second step will then focus on how to engineer microwave coupling into the high-impedance channel by making use of bio-compatible micro-coaxial lines. We then demonstrate integration of an ultra-broadband microwave circuit for the direct sampling of single α-hemolysin pores in a suspended bilipid membrane. Simultaneous direct current recordings reveal that we can monitor and correlate the RF transmission signal. This enables us to relate the open–close states of the direct current to the RF signal. Altogether, our experiments lay the ground for an RF-readout technique to perform real-time in vitro recordings of pores. The technique thus holds great promise for research and drug screening applications. The possible enhancement of sampling rates of single channels and pores by the large recording bandwidth will allow us to track the passage of single ions.

Direct microwave transmission on single α-hemolysin pores

We integrated an ultra-broadband microwave circuit for direct sampling of single α-Hemolysin pores in a suspended bilipid membrane. Simultaneous direct current recordings reveal that we can monitor and correlate the radio-frequency transmission signal, with correspondence between open-close states of the direct current and the RF signals. This proves the ability of an RF-readout technique to perform real-time in-vitro recordings of pores. The technique thus holds great promise for research and drug screening applications, since the sampling rate of single channels can be drastically enhanced and the recording bandwidth allows for tracking the passage of single ions.

Upward gaze–evoked nystagmus with organoarsenic poisoning

The authors report assessment of abnormal ocular movements in three patients after organoarsenic poisoning from diphenylarsinic acid. The characteristic and principal sign is upward gaze-evoked nystagmus. Moreover, vertical gaze holding impairment was shown by electronystagmography on direct current recording.

Possible control of intermittent cerebral ischemia by monitoring of direct-current potentials.

Neurosurgically induced temporary occlusion of intracranial arteries carries the risk of cerebral ischemic damage. Because negative shifts in the cortical direct-current (DC) potential indicate tissue depolarization and, thus, critical ischemic stress, the authors hypothesized that recordings of these potentials could help to determine the optimal duration and frequency of induced intermittent focal ischemia to prevent brain injury. The investigators related the results of DC recordings both to simultaneously recorded decreases in extracellular Ca++ concentration ([Ca++]o), which reflect Ca++ entry into cells, and to histological outcome. In cats anesthetized with halothane the effects of intermittent brief (10 minutes long, six times [6 x 10-min group]) and prolonged (20 minutes long, three times [3 x 20-min group]) episodes of middle cerebral artery occlusions were compared with those of a single continuous episode (1 x 60-min group). Laser Doppler flow probes and ion-selective microelectrodes were used to measure cerebral blood flow, DC potentials, and [Ca++]o in cortical tissues of ectosylvian gyri. Negative shifts in DC potential were evaluated in the three groups during the entire 60-minute-long period of ischemia and were smallest in the 6 x 10-min group, larger in the 3 x 20-min group, and largest in the 1 x 60-min group. Accordingly, infarct volumes were smallest in the 6 x 10-min group, intermediate in the 3 x 20-min group, and largest in the 1 x 60-min group. Decreases in ischemic [Ca++]o were significantly greater in the 1 x 60-min group than in the two groups in which there were repetitive occlusions, and recovery of [Ca++]o after reperfusion normalized only in the 1 x 60-min group. The DC potential may provide a reliable measure to optimize intermittent ischemia and to achieve minimal ischemic brain injury during temporary neurosurgical occlusion of cerebral arteries.

Adrenergic effects on the corneal and intraretinal direct-current electroretinogram and on the standing potential of albino rabbit eyes.

This study was undertaken to investigate further the responsiveness of the albino rabbit retinal pigment epithelium and the inner retina to adrenergic agents as reflected in changes of the direct-current electroretinogram and of the standing potential of the eye. After unilateral vitrectomy on albino rabbits, a continuous intraocular perfusion with a reference solution was established. The reference solution was then alternated with the test solution. The direct-current electroretinogram and the standing potential were recorded from both eyes with a scleral contact lens and a reference electrode connected to matched calomel half-cells. An in vivo experimental technique that allows intraocular perfusion of a test substance and simultaneous intraretinal microelectrode measurements was also used. The alpha-adrenergic agonist phenylephrine (0.04 microM, n = 8) produced a reversible increase in c-wave amplitude (48%, p < 0.001) and also a small increase in b-wave amplitude (12%, p < 0.002). There was no significant influence on the a-wave amplitude. The standing potential was elevated at 1694 +/- 362 microV (mean +/- SEM) (p < 0.002). The alpha 2-adrenergic agonist clonidine caused similar effects on the electroretinogram, although at a higher concentration (40 microM, n = 5), with an elevation of the c-wave (25%, p < 0.001) and a small b-wave increase (12% p < 0.002). No significant influence on the a-wave or on the standing potential was found. Intraretinal direct-current electroretinogram-recordings during intraocular perfusion with phenylephrine showed an increase in transepithelial potential (p < 0.004; n = 6), accompanied by a reduction of the slow PIII (p < 0.0035; n = 6). The c-wave increase resulting from alpha-adrenergic stimulation seems to be generated partly across the retinal pigment epithelium, with an increase in transepithelial potential, combined with a reduction of the slow PIII. The elevation of the b-wave amplitude, together with the influence on the slow PIII, suggests alpha-adrenergic effects also on the inner retina. The experimental technique used in this study with intraocular perfusion after vitrectomy and simultaneous intraretinal direct-current recordings seems to be a practicable method for studies of the influence of pharmacologic agents on the retina and the retinal pigment epithelium.

Scalp recorded direct current potential shifts associated with the transition to sleep in man

Cortical direct current (DC) potentials are considered to reflect the state of cortical excitability which may change characteristically from wakefulness to sleep. The present experiments examined changes in the scalp recorded DC potential in 10 healthy humans at the transition from wakefulness to nocturnal sleep. For each subject, DC recordings obtained from Cz were evaluated for a 15 min pre-sleep onset interval and for a 20 min post-sleep onset interval, on 2 separate nights. Sleep stages were determined from standard sleep recordings. The transition from wakefulness to sleep coincided with a significant ( P <0.05) shift in the DC potential of negative polarity. Maximum negative potentials of (mean ± S.E.M.) 500 ± 130 μV (first night) and of 760 ± 200 μV (second night) were reached at the end of the 20 min post-sleep onset interval. A number of possible technical and biological artifacts were controlled. It is reasonable to assume that the slow negative shift of the DC potential at the transition from wakefulness to sleep reflects increased cortical excitability. Whether the negative potential shift [ertains during sleep, or is of transient nature and closely linked to the process of falling asleep, remains to be clarified.

A new fabrication technique for directly coupled transmural cardiac electrodes.

Many current attempts at electrophysiological elucidation of cardiac arrhythmia mechanisms have centered around activation sequence mapping. This is most commonly performed with polarized unipolar or bipolar metal electrodes, which, because of unstable direct current (DC) base-line potentials, necessitate alternating current (AC)-coupled amplification. An ideal nonpolarizable unipolar electrode offers unhindered exchange of charge allowing for stable DC recordings of biological electrical activity. In addition to activation information, DC unipolar recordings enable quantitation of systolic and diastolic potentials, other low-frequency phenomena of interest such as repolarization, as well as rapid recovery from such rapid extreme potential shifts such as defibrillation. Previous attempts to apply nonpolarizable electrodes to transmural cardiac investigations required complex wick electrode techniques to prevent mechanical movement of the fluid-metal interface when chlorided silver wire was used. We have developed a technique to fabricate miniature sintered Ag-AgCl electrodes that are mounted at various locations on a 20-gauge stainless steel needle permitting stable transmural DC unipolar electrogram recordings in vivo. The electrodes are low noise, rugged, sterilizable, and reusable and should prove useful in three-dimensional electrophysiological characterization of the heart.

Light induced oscillations of the standing potential in achromatopsia.

In three children with achromatopsia light-induced oscillations of the standing potential and electroretinograms (ERGs) were recorded. A low drift direct current recording system was applied to monitor the changes of the standing potential under general anesthesia. In all children the scotopic ERG components were normal. No photopic components could be observed. The fast oscillations of the standing potential were normal under scotopic and photopic conditions. The light-induced slow increase of the standing potential displayed low amplitudes and normal peak latencies. The results of our study support earlier investigations suggesting that cone-mediated mechanisms in the retina contribute a significant component to the amplitude of the light peak in the electroretinogram.

Comparison between intracellular and extracellular direct current recordings of sinus node activity for evaluation of sinoatrial conduction time.

For evaluation of sinoatrial conduction time in humans, study of extracellular direct current (DC) electrograms from the sinus node has been proposed. To validate this method, we compared transmembrane potentials from multiple sites (40 to 60, "mapping" of sinoatrial activation by microelectrode technique) and extracellular DC electrograms of the sinus node in 12 isolated rabbit atria. Sinoatrial conduction time, measured by microelectrodes and by extracellular electrograms, was essentially the same if the DC electrode was positioned over the pacemaker center (35 +/- 15 and 33 +/- 15 msec, respectively; deviation less or equal to 2 msec). While in all experiments phase 4 and phase 0 depolarization of dominant pacemaker fibers was reflected in the DC electrogram, it shape was influenced by pacemaker location and duration of sinoatrial impulse propagation. If sinoatrial conduction time was long (greater than 25 msec) the transition from the diastolic to the upstroke slope was smooth and the sinus node potential was clearly separated from atrial activity. If sinoatrial conduction time was short (less or equal to 25 msec) the onset of the upstroke slope was well defined and the upstroke slope directly merged into atrial activity. Extracellular recordings 0.2 mm away from the pacemaker center were fairly unchanged in shape; however, sinoatrial conduction time was significantly underestimated. Underestimation also occurred when the tip size of the extracellular electrode was increased from 0.2 to 0.5 and 1.0 mm. Thus sinus node activity is reflected in extracellular DC recordings; however, measurement of sinoatrial conduction time by this technique requires exact localization of the electrode over the pacemaker center, which cannot be controlled in humans.

Mechanisms of ischemic ST-segment displacement. Evaluation by direct current recordings.

Mechanisms of ischemic ST-segment displacement. Evaluation by direct current recordings.

Specific Features of Tohoku Charge Spectrometer

This report describes the specific features of the Tohoku Charge Spectrometer(TOHOKU CS)which has been constructed for the study of chemical effects of the nuclear transformations in gases, especially of the charge distribution of the residual atoms and of ion-molecule reactions in order to elucidate the primary and elemental stages in hot-atom chemistry. The facility is available for a chargespectrometer with a large source volume and a double mass spectrometer connected in perpendicular. Ions can be produced by the electron impact, X-ray irradiation or nuclear decay processes in the source volume. Charge spectrum of the residual atom after the Auger process of the nuclear decay can be measured through the first stage mass spectrometer, and products of ion-molecule reactions in the reaction chamber can be separated through the second mass spectrometer and detected by an aid of a16stages Cu-Be electron multiplier. Pulse countings are applicable in the both cases as well as direct current recordings to estimate the charged atoms or the fragment distribution. The specific availabilities of this facility are shown in some typical results by the preliminary experiments.

Direct current recordings of eyeball movements in neurologic practice.

Direct current recordings of eyeball movements in neurologic practice.