Extracellular Electrodes Research Articles

Unbuckling the Buccal oscillator in the American Bullfrog

The American Bullfrog is a remarkable model organism to study rhythm generation underlying breathing. It exhibits a breathing pattern that can be divided into four distinct ventilatory phases: lung‐priming, lung‐powerstroke, buccal‐dilation, and buccal‐constriction. We recently established that lung‐priming and lung‐powerstroke are generated by two separate burst generating substrates in the brainstem—the Priming area and Powerstroke area—located in rhombomere 4–5. The neural origin of the two phases of buccal, on the other hand, remains elusive. Our previous experiments suggest that a Buccal area located in rhombomere 7 is responsible, at least in part, for generating the biphasic buccal rhythm; however, whether any additional burst generating substrates are involved is yet unknown.The objective of this study was to characterize areas in the frog brainstem that generate the biphasic buccal rhythm. We utilized the isolated frog brainstem preparation and recorded fictive respiratory motor output from the trigeminal and facial cranial nerves using extracellular suction electrodes. We progressively transected the brainstem in both directions (caudal‐to‐rostral, and rostral‐to‐caudal) to identify regions where transection eliminated one or both buccal burst phases.Our preliminary results suggest that both phases of the buccal rhythm are generated by substrates located at the same level as the previously identified Buccal area. Nevertheless, using our current methodology, we are unable to discern whether multiple substrates or a single substrate is generating the buccal rhythm. To address this question, we developed a ‘buccal slice’ preparation at the level of the Buccal area which, when exposed to 100nM AMPA, produces buccal‐like bursts. We continue to develop this preparation as it holds promise for further dissecting the properties of this system and exploring it at the cellular and molecular levels.Our analysis suggests that the Buccal area is an evolutionary homolog of the mammalian preBötzinger complex. Both are located in rhombomere 7, are resilient oscillators, being staunchly insensitive to CO2, and co‐opted for sniffing. We anticipate that having two comparable preparations, i.e. ‘buccal slice’ and ‘preBötC slice’, will allow for more direct comparisons between these oscillators, further testing their homology and thus take us closer towards understanding the evolution of breathing.Support or Funding InformationNational Science and Engineering Council of Canada (NSERC) and Alberta Innovates Health Solutions (AIHS) provided funding for this study.

Analytical solution for time-dependent potentials in a fiber stimulated by an external electrode.

This study provides an analytical solution for time-dependent potentials in a 3D cylindrical fiber stimulated by an extracellular point electrode. The membrane is passive and represented by surface resistance and surface capacitance. Separation of variables solution expresses intracellular and extracellular potentials as sums involving modified Bessel functions; the coefficients ([Formula: see text] and [Formula: see text]) depend on time. In contrast to previous analytical solutions, where [Formula: see text] and [Formula: see text] had to be determined numerically, here [Formula: see text] and [Formula: see text] are given by explicit formulas that resemble the formulas for potentials in a fiber stimulated by a transverse electric field. The comparison of the 3D analytical solution with the 1D cable model shows that the cable model approximates transmembrane potential with the error below 5% when the distance between the electrode and the fiber is 0.2-4mm and when the stimulus is longer than 3.3ms. For stimuli between 0.43 and 3.3ms, the range of fiber-electrode distances with error below 5% shrinks, and it disappears completely for stimuli shorter than 0.43ms. Thus, our study shows that the applicability of the 1D cable model may be more limited than previously considered.

Spatial synchronization of visual stimulus-evoked gamma frequency oscillations in the rat superior colliculus.

In the superior colliculus, visual stimuli can induce gamma frequency oscillations of neuronal activity. It has been shown that in cats, these oscillations are synchronized over distances of greater than 300 μm that may contribute toward visual information processing. We investigated the spatial properties of such oscillations in a rodent because the availability of molecular tools could enable future studies on the role of these oscillations in visual information processing. Using extracellular electrode array recordings in anesthetized rats, we found that visual stimuli-induced gamma and eta frequency (30-115 Hz) oscillations of the local field potential that were synchronized over distances of ∼ 600 μm. Multiple-unit events were phase locked to the local field potential signal and showed prominent oscillations during OFF responses. The rate of lower than 5 ms cross-electrode coincidences was in line with the response-corrected predictions for each electrode. These data suggest that the synchronized superior colliculus neuronal activity is largely network driven, whereas common synaptic inputs play a minor role.

Leader-Broker Dynamics Within Rich-Club Networks Across DG-CA3, DG-DG, CA3-CA3, and Random Hippocampal MEA Cultures

Leader-Broker Dynamics Within Rich-Club Networks Across DG-CA3, DG-DG, CA3-CA3, and Random Hippocampal MEA Cultures

Time Evolution Of Spike Activity In Hippocampal Neurons During Paired-Pulse Stimulation Of DG-CA3 Reconstructed Networks

Time Evolution Of Spike Activity In Hippocampal Neurons During Paired-Pulse Stimulation Of DG-CA3 Reconstructed Networks

Measuring Gastrointestinal Electrical Activity With Extracellular Electrodes: Author's Reply.

TO THE EDITOR: In our recent paper1 we found that 2 points of intracellular microelectrode recording were insufficient to describe significant disruptions in gastric motor patterns that were caused by inhibition of acetylcholinesterase. Thus, we employed video imaging and analyzed data by image processing routines developed by Dr Hennig.1 The resulting motility maps described the aberrant patterns of gastric contractions when tissue cholinesterases were inhibited in much more detail that could be achieved using electrical recording. In describing our rationale for the technology chosen, we made reference to the unsuitability of extracellular electrical recording as a means to measure changes in slow waves, because movement artifacts dominate these measurements.2 In a previous study we found that when movements are blocked, under conditions in which slow waves are unaffected, the signals recorded with extracellular metal electrodes and many have attributed to electrophysiological events (slow waves), are inhibited.2 Thus the signals monitored by extracellular electrodes are largely artifacts of movement and do not represent authentic slow wave activity. In light of these observations, which have been reproduced in mouse, dog, monkey and human gastric muscles when movement is suppressed, it is important for studies utilizing extracellular electrical recording to be accompanied by rigorous tests insuring that the electrical signals claimed to be slow waves persist after movement is stabilized. O’Grady et al3 have invested a great effort in writing letters to editors when we have commented in several papers on the unsuitability of extracellular recording for electrophysiological measurements in GI muscles. We feel compelled to comment on the artifacts of extracellular electrical recording, because this technique has been used and continues to be used for research studies and for patient evaluations, yet adequate validation of the technique has not been provided. Extracellular array electrodes might be selected as a means to record integrated signals from slow waves, smooth muscle electrical activity and muscle contractions in the absence of other recording techniques, but the steps required to “deconvolute” these signals would be extremely complex. Modeling such signals as descriptions of gastric electrophysiology seems folly. In our view a better use of time than writing letters would be to perform rigorous and convincing control experiments that demonstrate unequivocally the degree to which movements contaminate extracellular signals. Neglecting such control experiments to exclude the possibility of movement artifacts will continue to cloud their results, and it was this skepticism about the validity of extracellular recordings and our own empirical tests that caused us to avoid this technique in our recent study.1 O’Grady et al3 claim they have performed adequate controls for movement4 but the tests they performed stopped well short of providing convincing evidence that their recordings are not the result of movement artifacts. As we have detailed previously, it may not be feasible to stabilize movements of muscular tissues in vivo to the extent required to remove any suspicion of movement artifacts from extracellular recordings in GI muscles.5 We have directly measured movement artifacts in smooth muscle sheets that are similar to the waveforms of the signals O’Grady et al3 consider as “ideal” electrical recording in response to movements of less than 50 μm. Respiratory movements, circulation of blood and muscle contractions uncontrolled by dihydropyridines are all possible sources of such tiny movements in the in vivo tests they performed.4 We have suggested that the best approach to make clear association between extracellular recording and authentic slow waves is rigorous stabilization of movements in vitro, as described in the addendum of our previous paper.2 If one is determined to monitor contraction by just looking at the tissue, then relatively high power objectives would be needed to allow observations of the tiny movements that cause significant signals (ie, several 10 seconds of μVs) to be picked up by extracellular electrodes. We fully realize the time, effort and resources that O’Grady et al3 have invested in extracellular recording and modeling the data derived from these measurements, and we sincerely hope new ideas might be developed to alleviate movement artifacts or amplify the field potentials caused by slow waves to a level where they can be captured by extracellular recording. But as things stand, this technique has not been validated as a measurement of the field potentials resulting from the transmembrane currents occurring during electrical slow waves, and as such, its authenticity in describing electrophysiological events in visceral smooth muscles will continue to be questioned. If, as claimed, extracellular recording is the “gold standard” for interpretation of slow wave frequency and patterns in gastrointestinal muscles, then how about providing a rigorous assay of the gold?

Exposure to 50Hz electromagnetic field changes the efficiency of the scorpion alpha toxin.

BackgroundExtremely low-frequency (50 Hz) electromagnetic field (ELF-EMF) is produced by electric power transmission lines and electronic devices of everyday use. Some phenomena are proposed as “first effects” of ELF-EMF: the discrete changes in the membrane potential and the increase of the calcium channel activity as well as the intracellular concentration of Ca2+. Interaction of the scorpion alpha toxin with the sodium channel depends on the orientation of the charges and may be perturbed by changes in the membrane polarization. The toxin induces overexcitability in the nervous system and an increase in the neurotransmitters released with different consequences, mainly the paralysis of muscles. We assumed that the exposure to ELF-EMF 0.7 mT will change the effects of the insect selective scorpion alpha toxin (recombinant LqhαIT from Leiurus quinquestriatus hebraeus) at the level of the cercal nerve function, the synaptic transmission and on the level of entire insect organism. Taking into account the compensatory mechanisms in organisms, we tested in addition ten times higher ELF-EMF on whole insects.MethodsExperiments were performed in vivo on cockroaches (Periplaneta americana) and in vitro – on isolated cockroach abdominal nerve cord with cerci. In biotests, the effects of LqhαIT (10−8 M) were estimated on the basis of the insect ability to turn back from dorsal to ventral side. Three groups were compared: the control one and the two exposed to ELF-EMF – 0.7 and 7 mT. Bioelectrical activity of the cercal nerve and of the connective nerve that leaves the terminal abdominal ganglion was recorded using extracellular electrodes. LqhαIT (5 × 10−8 M) induced modifications of neuronal activity that were observed in the control cockroach preparations and in the ones exposed to ELF-EMF (0.7 mT). The exposure to ELF-EMF was carried out using coils with a size appropriate to the examined objects.ResultsThe exposure to ELF-EMF (0.7 mT) modified the effects of LqhαIT (5 × 10−8 M) on activity of the cercal nerve and of the connective nerve. We observed a decrease of the toxin effect on the cercal nerve activity, but the toxic effect of LqhαIT on the connective nerve was increased. Biotests showed that toxicity of LqhαIT (10−8 M) on cockroaches was reduced by the exposure to ELF-EMF (0.7 and 7 mT).ConclusionsThe exposure to 50 Hz ELF-EMF modified the mode of action of the anti-insect scorpion alpha toxin LqhαIT at cellular level of the cockroach nervous system and in biotests. Toxin appeared as a usefull tool in distinguishing between the primary and the secondary effects of ELF-EMF.

The location of pacemakers in the uteri of pregnant guinea pigs and rats.

The pregnant uterus is a smooth muscle organ whose pattern of contraction is dictated by the propagation of electrical impulses. Such electrical activity may originate from one or more pacemakers, but the location of these sites has not yet been determined. To detect the location of the pacemaker in the gravid uterus, two approaches were used: 1) determine the site from where the contraction started using isolated uteri from the pregnant guinea pig, and videotape their contractions; and 2) record, in isolated uteri from pregnant term rats, with 240 extracellular electrodes simultaneously, and determine where the electrical bursts started. In both the contractile and electrophysiological experiments, there was not a single, specific pacemaker area. However, most contractions (guinea pig 87%) and bursts (rat 76%) started close to the mesometrial border (mean 2.7 ± 4.0 mm SD in guinea pigs and 1.3 ± 1.4 mm in rats). In addition, in the rat, most sites of initiations were located closer to the ovarial end of the horn (mean distance from the ovarial end 6.0 ± 6.2 mm SD), whereas such an orientation was not seen in the guinea pig. In both guinea pig and rat uteri at term, there is not one specific pacemaker area. Rather, contractile and electrical activity may arise from any site, with the majority starting close to the mesometrial border. Furthermore, in the rat, most activities started at the ovarial end of the horn. This may suggest a slightly different pattern of contraction in both species.

In This Issue

HomeCirculation ResearchVol. 117, No. 5In This Issue Free AccessResearch ArticlePDF/EPUBAboutView PDFView EPUBSections ToolsAdd to favoritesDownload citationsTrack citationsPermissions ShareShare onFacebookTwitterLinked InMendeleyReddit Jump toFree AccessResearch ArticlePDF/EPUBIn This Issue Originally published14 Aug 2015https://doi.org/10.1161/RES.0000000000000070Circulation Research. 2015;117:389Optogenetic Voltage Sensing in Cardiac Myocytes (p 401)Download figureDownload PowerPointLiao et al measure electrical activity of heart cells and whole hearts with a fluorescent reporter.Monitoring electrical activity of the heart or cardiomyocytes in culture provides important information about normal and pathological cardiac physiology. But each recording method has limitations. Extracellular electrodes are non-invasive but have poor resolution. Intracellular recordings provide good resolution but are time-consuming, invasive and resource-intensive. Genetically-encoded voltage indicators (GEVI), however, may provide the best of both. They have been used to non-invasively measure electrical activity in brain cells of the mouse and fly, and now Liao and colleagues have tested one GEVI—called VSFP2.3—in whole mouse hearts and heart cells. Similar to VSFP2.3’s behavior in neurons, the protein’s fluorescent signal altered upon heart cell membrane depolarization: yellow emission increased and cyan decreased. This measurable change in fluorescence enabled the team to perform optical cardiograms on whole ex vivo mouse hearts, and on live mice—via optical fibers inserted into the animals’ chests. Lastly, the team used VSFP2.3 to monitor electrical activity of induced pluripotent stem cell-derived cardiomyocytes in vitro. Together the results provide a proof of principle that the use of GEVIs can provide high resolution monitoring of cardiovascular activity in vitro and in vivo.Methods to Study Cardiac Myocyte Epigenomics (p 413)Download figureDownload PowerPointPreissl et al investigate the epigenetic code and transcription profile of cardiomyocyte nuclei.The identity of a cell does not just come down to the proteins it expresses but to the genetic and epigenetic mechanisms that regulate protein expression. A thorough understanding of the epigenetic landscape of cardiomyocytes and how that landscape changes during development and disease could thus offer valuable insights into heart physiology. To gain such an understanding, Preissl and colleagues first devised a method for isolating highly pure cardiomyocyte nuclei, which relied on cold conditions and avoided enzymatic digestion to preserve the structural integrity of the nuclei and chromatin therein. The team separated cardiomyocyte nuclei from those of other heart cell types on the basis of expression of a specific marker protein—PCM1—and then analyzed nuclear mRNA expression, cellular mRNA expression and a number of epigenetic marks. Their study revealed that the pattern of epigenetic marks correlated more closely with nuclear mRNA expression than cellular mRNA, confirming that the former is a more accurate reflection of the transcription activity of cells. The procedure described in this paper serves as a springboard for further epigenetic analyses of cardiomyocytes from different stages of development or under different pathological conditions, say the authors.Role of miR-34a Post-MI (p 470)Download figureDownload PowerPointMicroRNA-34a impairs heart regeneration after myocardial infarction, report Yang et al.The hearts of newborn mice can almost entirely recover from injury, but by one week of age this regenerative capacity diminishes and remains lost throughout adulthood. If researchers could understand what makes regeneration possible in young mice they might be able to recapitulate regeneration in human hearts after myocardial infarctions. To this end, Yang et al have now investigated the role of microRNA miR34a in mouse heart regeneration. Mir34a is a suppressor of cell proliferation known to increase in expression in the heart with age. Furthermore, suppression of miR34a reduces age-associated cardiomyocyte death. The team showed that levels of miR34a are low in the newborn mouse heart and rise to adult levels within a week of birth. Over-expression of miR34a in the newborn mice prevented heart regeneration, whereas inhibition of miR34a in the adult heart improved cardiac function after infarction. Lastly, the team identified direct targets of miR34a repression—Sirt1, cyclinD1, and Bcl2—which are known to be involved in cell aging, proliferation and survival. Inhibition of miR34a in adult hearts led to the upregulation of these genes. Together the results suggest that inhibiting miR34a, or boosting its targets, may offer therapeutic routes to improve heart recovery after myocardial infarction. Previous Back to top Next FiguresReferencesRelatedDetails August 14, 2015Vol 117, Issue 5 Advertisement Article InformationMetrics © 2015 American Heart Association, Inc.https://doi.org/10.1161/RES.0000000000000070 Originally publishedAugust 14, 2015 PDF download Advertisement

Effect of Ethanol Exposure on Slow Wave Activity and Smooth Muscle Contraction in the Rat Small Intestine.

Ethanol ingestion causes a variety of gastrointestinal disturbances including motility alterations. Slow wave propagation coordinates gastrointestinal motility, and abnormal slow wave activity is thought to contribute to motility disorders. To date, however, little is known about the effect of acute ethanol on motility disturbances associated with slow wave activity. To investigate the effect of ethanol on small intestine slow wave activity. Segments (3-5 cm long) were isolated from the rat duodenum, jejunum, and ileum and mounted in an organ bath superfused with a normal Tyrode solution or with 1, 3, or 5% ethanol containing Tyrode. The electrical activities were recorded using an array of 121 extracellular electrodes, and motility recordings were performed using a digital video camera. The frequency and amplitude of slow wave activity were not altered at 1, 3, or 5% ethanol concentrations, but a significant drop in velocity was found at 3 and 5% ethanol. Furthermore, inexcitable areas appeared in a dose-dependent manner. Slow wave was sometimes also seen to propagate in a circular fashion, thereby describing a reentrant loop. Finally, in all duodenal, jejunal, and ileal segments, ethanol inhibited contractions and became fully quiescent at 3-5%. These studies for the first time demonstrate that ethanol significantly inhibits slow wave and spike activity in a dose-dependent manner and could also initiate reentrant activities. Intestinal contractions were also inhibited in a dose-dependent manner. In conclusion, ethanol inhibits both slow wave activity and motor activity to cause ethanol-induced intestinal disturbances.

Single-unit activity, threshold crossings, and local field potentials in motor cortex differentially encode reach kinematics.

A diversity of signals can be recorded with extracellular electrodes. It remains unclear whether different signal types convey similar or different information and whether they capture the same or different underlying neural phenomena. Some researchers focus on spiking activity, while others examine local field potentials, and still others posit that these are fundamentally the same signals. We examined the similarities and differences in the information contained in four signal types recorded simultaneously from multielectrode arrays implanted in primary motor cortex: well-isolated action potentials from putative single units, multiunit threshold crossings, and local field potentials (LFPs) at two distinct frequency bands. We quantified the tuning of these signal types to kinematic parameters of reaching movements. We found 1) threshold crossing activity is not a proxy for single-unit activity; 2) when examined on individual electrodes, threshold crossing activity more closely resembles LFP activity at frequencies between 100 and 300 Hz than it does single-unit activity; 3) when examined across multiple electrodes, threshold crossing activity and LFP integrate neural activity at different spatial scales; and 4) LFP power in the "beta band" (between 10 and 40 Hz) is a reliable indicator of movement onset but does not encode kinematic features on an instant-by-instant basis. These results show that the diverse signals recorded from extracellular electrodes provide somewhat distinct and complementary information. It may be that these signal types arise from biological phenomena that are partially distinct. These results also have practical implications for harnessing richer signals to improve brain-machine interface control.

Cariprazine delays ouabain-evoked epileptiform spikes and loss of activity in rat hippocampal slices

In the only bipolar cycling in vitro model, rat hippocampal slices are treated with the sodium pump inhibitor ouabain, which induces epileptiform activity, followed by refractory activity loss that recovers and cycles back to epileptiform activity. Thus, clinical cycling seen in patients with bipolar disorder is modeled on a cellular level as alternating hyperactivity and hypoactivity interspersed with normal activity. In this study, we tested the ability of cariprazine a new antipsychotic candidate to block ouabain-induced changes in rat hippocampal slices. Cycling of population spikes and epileptiform bursts was evoked using an extracellular stimulation electrode located in the Schaeffer collaterals of 400-µm-thick rat hippocampal slices treated with ouabain (3.3μM) alone or in combination with cariprazine (1, 5, 25, and 50µM). Responses were recorded using an extracellular electrode placed in the cell body layer of the CA1 region. Cariprazine 25 and 50µM delayed ouabain-induced epileptiform burst onset and subsequent activity loss. Lower cariprazine concentrations were ineffective. Cariprazine delays the onset of ouabain-induced epileptiform bursts and the loss of spiking activity similarly to that previously demonstrated with the mood stabilizer lithium. These results suggest that cariprazine may have therapeutic potential for treatment of bipolar disorder.

Long-Term Dynamical Constraints on Pharmacologically Evoked Potentiation Imply Activity Conservation within In Vitro Hippocampal Networks.

This paper describes a long-term study of network dynamics from in vitro, cultured hippocampal neurons after a pharmacological induction of synaptic potentiation. We plate a suspension of hippocampal neurons on an array of extracellular electrodes and record electrical activity in the absence of the drugs several days after treatment. While previous studies have reported on potentiation lasting up to a few hours after treatment, to the best of our knowledge, this is the first report to characterize the network effects of a potentiating mechanism several days after treatment. Using this reduced, two-dimensional in vitro network of hippocampal neurons, we show that the effects of potentiation are persistent over time but are modulated under a conservation of spike principle. We suggest that this conservation principle might be mediated by the appearance of a resonant inter-spike interval that prevents the network from advancing towards a state of hyperexcitability.

Response: "Commentary: Comparison of spike parameters from optically identified GABAergic and glutamatergic neurons in sparse cortical cultures".

We are pleased to note that our publication “Comparison of spike parameters from optically identified GABAergic and glutamatergic neurons in sparse cortical cultures” by Weir et al. (2015) raised some discussion on the feasibility of solely electrophysiological discrimination of distinct neuronal subpopulations in vitro. We agree with Becchetti and Wanke (2015) that their report and our study on the same question were conducted with different technical approaches and that this may explain the observed differences between both studies. Although we obviously recorded a reduced spontaneous neuronal activity under our sparse culture conditions, these conditions were necessary to enable the unequivocal identification of single units in recordings with extracellular electrodes. Our combined approach of extracellular single unit recordings and cellular calcium imaging analyses in sparse neuronal cultures from GAD67-GFP transgenic mice clearly allowed the definite identification of inhibitory GAD67-positive interneurons and excitatory GAD67-negative neurons. The ratio of excitatory to inhibitory neurons and thus also the relative density of inhibitory connections was carefully assessed in our study and comparable to data from the cerebral cortex in vivo. For technical reasons this unambiguous assignment of a single neuron to one recording electrode is not possible at high cellular densities. We performed additional experiments and now also analyzed Fano factors of spike counts recorded in culture medium and under different culture conditions (low density culture 15.6 ± 1.8 recorded neurons; medium density culture 54.3 ± 3.1 recorded neurons). Fano factors of these cultures were compared to those of clearly identified GFP-positive, inhibitory and GFP-negative, excitatory units published in our previous study (Weir et al., 2015). Fano factors were calculated for all units by dividing the variation by the average spike counts within a time window of 800 ms. Note, that Becchetti et al. previously used a time window of 6 s for calculation of Fano factors (Becchetti et al., 2012). However, our additional analyses revealed that this methodological difference in the bin width does not account for the different experimental outcome, since Fano factors calculated with 6 s and 800 ms bins were strongly correlated (Low density culture R2 = 0.596, p < 0.0001; High density culture R2 = 0.649, p < 0.0001). As shown in Figure ​Figure11 below, all four experimental groups show a similar distribution of Fano factors and no significant differences in average Fano factor in different conditions (low density cultures 2.91 ± 0.16, n = 204 cells; medium dense cultures 2.6 ± 0.17, n = 152 cells; GFP-negative neurons 2.83 ± 0.3, n = 81 cells: GFP-positive interneurons 3.23 ± 1.03, n = 20 cells; One-Way ANOVA R2 = 0.005, p = 0.54). Single unit recordings at culture conditions with 1000 cells per mm2 as suggested by Becchetti and Wanke are not possible because spike sorting algorithms under this condition revealed a high failure rate. Figure 1 Distribution of Fano factors (calculated as described in Weir et al., 2015) of single units in low and medium dense cultures recorded in culture medium. For comparison, Fano factors of visually-identified GFP-positive and GFP-negative units recorded in ... Thus, on the basis of our new and additional experiments and analyses we cannot confirm that the Fano factor represents a sufficient parameter to reliably discriminate under in vitro conditions between excitatory and GABAergic inhibitory neurons. However, we would like to point out that a number of previous studies (Bartho et al., 2004; Sirota et al., 2008; Sakata and Harris, 2009) and also our own analyses in adult rat cerebral cortex (Reyes-Puerta et al., 2014) were able to identify inhibitory interneurons recorded under in vivo conditions on the basis of their extracellular firing properties. Therefore, it cannot be excluded that a more immature functional state of neurons cultured under in vitro conditions hamper the identification of inhibitory interneurons on the basis of the extracellular spiking properties.

Electrochemical Detection of Circadian Redox Rhythm in Cyanobacterial Cells via Extracellular Electron Transfer.

Recent research on cellular circadian rhythms suggests that the coupling of transcription-translation feedback loops and intracellular redox oscillations is essential for robust circadian timekeeping. For clarification of the molecular mechanism underlying the circadian rhythm, methods that allow for the dynamic and simultaneous detection of transcription/translation and redox oscillations in living cells are needed. Herein, we report that the cyanobacterial circadian redox rhythm can be electrochemically detected based on extracellular electron transfer (EET), a process in which intracellular electrons are exchanged with an extracellular electrode. As the EET-based method is non-destructive, concurrent detection with transcription/translation rhythm using bioluminescent reporter strains becomes possible. An EET pathway that electrochemically connected the intracellular region of cyanobacterial cells with an extracellular electrode was constructed via a newly synthesized electron mediator with cell membrane permeability. In the presence of the mediator, the open circuit potential of the culture medium exhibited temperature-compensated rhythm with approximately 24 h periodicity. Importantly, such circadian rhythm of the open circuit potential was not observed in the absence of the electron mediator, indicating that the EET process conveys the dynamic information regarding the intracellular redox state to the extracellular electrode. These findings represent the first direct demonstration of the intracellular circadian redox rhythm of cyanobacterial cells.

Human Islets Exhibit Electrical Activity on Microelectrode Arrays (MEA)

This study demonstrates for the first time that the microelectrode array (MEA) technique allows analysis of electrical activity of islets isolated from human biopsies. We have shown before that this method, i.e., measuring beta cell electrical activity with extracellular electrodes, is a powerful tool to assess glucose responsiveness of isolated murine islets. In the present study, human islets were shown to exhibit glucose-dependent oscillatory electrical activity. The glucose responsiveness could be furthermore demonstrated by an increase of insulin secretion in response to glucose. Electrical activity was increased by tolbutamide and inhibited by diazoxide. In human islets bursts of electrical activity were markedly blunted by the Na(+) channel inhibitor tetrodotoxin which does not affect electrical activity in mouse islets. Thus, the MEA technique emerges as a powerful tool to decipher online the unique features of human islets.Additionally, this technique will enable research with human islets even if only a few islets are available and it will allow a fast and easy test of metabolic integrity of islets destined for transplantation.

Variation potential influence on photosynthetic cyclic electron flow in pea.

Cyclic electron flow is an important component of the total photosynthetic electron flow and participates in adaptation to the action of stressors. Local leaf stimulation induces electrical signals, including variation potential (VP), which inactivate photosynthesis; however, their influence on cyclic electron flow has not been investigated. The aim of this study was to investigate VP's influence on cyclic electron flow in pea (Pisum sativum L.). VP was induced in pea seedling leaves by local heating and measured in an adjacent, undamaged leaf by extracellular electrodes. CO2 assimilation was measured using a portable gas exchange measuring system. Photosystem I and II parameters were investigated using a measuring system for simultaneous assessment of P700 oxidation and chlorophyll fluorescence. Heating-induced VP reduced CO2 assimilation and electron flow through photosystem II. In response, cyclic electron flow rapidly decreased and subsequently slowly increased. Slow increases in cyclic flow were caused by decreased electron flow through photosystem II, which was mainly connected with VP-induced photosynthetic dark stage inactivation. However, direct influence by VP on photosystem I also participated in activation of cyclic electron flow. Thus, VP, induced by local leaf-heating, activated cyclic electron flow in undamaged leaves. This response was similar to photosynthetic changes observed under the direct action of stressors. Possible mechanisms of VP's influence on cyclic flow were discussed.

Electron Extraction from an Extracellular Electrode by &lt;i&gt;Desulfovibrio ferrophilus&lt;/i&gt; Strain IS5 Without Using Hydrogen as an Electron Carrier

We report that an intensely iron-corroding microbe, Desulfovibrio ferrophilus strain IS5, is capable of extracting electrons from an indium tin-doped oxide electrode without consuming electrochemically generated hydrogen as an electron carrier. When sulfate was presented as a metabolic electron acceptor, significant cathodic current production was observed at an onset potential of−200mV vs. SHE, which was approximately 750mVmore positive than the onset for hydrogen evolution in our experimental condition. This finding indicates that hydrogen is not required for the cathodic reaction of IS5, suggesting that IS5 accelerates anaerobic iron corrosion through direct electron uptake. © The Electrochemical Society of Japan, All rights reserved.

Passive electrical properties of Lupinus angustifolius L. stem TV. The core-conductor theory parametres: space constant λ and time constant τ

On the basis of the core-conductor theory and the method described by Hodgkin and Rushton (1946) for the axon, the space constant K and the time constant T have been determined for the stem of &lt;i&gt;Lupinus&lt;/i&gt;. Electrotonic potentials were recorded in the extrapolar region in the vicinity of the cathode along the longitudinal axis of the stem. Extracellular recording electrodes were applied. It was found that the steady-state distribution of potential along the stem surface is of exponential character. The calculated space constant K has a value of 2.0 to 2.4 mm (average 2.1 mm) and is almost identical with the X values for nerves and muscles (mean 1.5-2.0 mm). The values of the time constants ("half-time") of electrotonic potentials increase linearly with the distance from the cathode. The time constant τ calculated on this basis is on the average 5.2 sec and as compared with τ for nerves and muscles is 103 times higher. The phenomena observed in the &lt;i&gt;Lupinus&lt;/i&gt; stem fulfill the equations of the core-conductor theory (Appendix). Their character is identical to that of the phenomena noted in nerves or muscles. It is probable that they occur on the membrane of excitable cells of the stem. The results here presented are a, convincing argument indicating that in higher plants an excitable system may exist, subjected to the same laws as that in animal organisms.

Multi-scale simulation of extracellular electrode stimulation in the dentate gyrus

Multi-scale simulation of extracellular electrode stimulation in the dentate gyrus