Analysis of spontaneous electrical activity in cerebellar Purkinje cells acutely isolated from postnatal rats

Whole-cell patch recording techniques were used to analyze spontaneous electrical activity in cerebellar Purkinje cells acutely isolated from postnatal rats. Spontaneous activity was present in 65% of the cells examined, and it included simple and complex firing patterns which persisted under conditions that eliminated residual or reformed synaptic contacts. Under voltage clamp, both spontaneous and quiescent cells displayed similar voltage-dependent conductances. Inward current was carried by Na⁺ through tetrodotoxin (TTX)-sensitive channels and by Ca²⁺ through P-type and T-type Ca channels. P-type current was present in all cells examined. T-type current was found in <50%, and it did not correlate with spontaneous activity. We found no evidence of a transient (A-type) potassium current or hyperpolarization-activated cationic current in either spontaneous or quiescent cells. Spontaneous activity did correlate with a lower activation threshold of the Na current, resulting in substantial overlap of the activation and inactivation curves. TTX reduced the holding current of spontaneous cells clamped between −50 and −30 mV, consistent with the presence of a Na "window" current. We were unable, however, to measure a persistent component of the Na current using voltage steps, a result which may reflect the complex gating properties of Na channels. An Na window current could provide the driving force underlying spontaneous activity, as well as plateau potentials, in Purkinje cells. © 1997 John Wiley & Sons, Inc. J Neurobiol 33: 18–32, 1997     

Rectification properties and pH-dependent selectivity of meningococcal class 1 porin

We studied the current rectification properties and selectivity of class 1 porin (PorA) from Neisseria meningitidis (strain H44/76 Δ3Δ4) reconstituted in planar lipid membranes varying salt concentrations and pH. PorA channel shows voltage gating with a characteristic time remarkably longer than other porins. Its current-voltage asymmetry, evaluated as the current rectification ratio, changes nonmonotonically with salt concentration. Interestingly, it reaches its maximum value at physiological concentration. Porin selectivity, quantified by reversal potential measurements, is also significantly asymmetric. Depending on the direction of the salt gradient, the channel becomes more or less selective (10:1 vs. 5:1 Na⁺/Cl⁻). Besides, the reversal potential measurements suggest that porin inserts directionally following the concentration gradient. Measurements over a wide range of pH show that although PorA is strongly cation selective at pH >6, its selectivity gradually changes to anionic in an acidic medium (pH < 4). We show that a continuum electrodiffusion model quantitatively accounts for conductance and reversal potential measurements at positive and negative applied voltages.     

Analysis of GABA-induced inhibition of spontaneous firing in chick accessory lobe neurons

It has been hypothesized that chick accessory lobes (ALs) contain functional neurons and act as a sensory organ of equilibrium. It was reported that neurons located in an outer layer of ALs showed γ-aminobutyric acid (GABA)- and glutamic acid decarboxylase (GAD)-like immunoreactivity more strongly than centrally located neurons, which were surrounded by the GAD-immunoreactive terminals. We investigated effects of GABA on the electrical activity of AL neurons. About 50% of embryonic AL neurons exhibited spontaneous firing. In the on-cell recording, GABA, muscimol, and GABA in combination with CGP35348 inhibited this firing. In whole-cell voltage clamp recordings, GABA and muscimol evoked a transient current. The mean reversal potential of GABA-evoked currents was close to the theoretical reversal potential of Cl⁻. These results indicate that GABA exerts the inhibitory effect on the firing through the activation of GABA_A receptors. In addition, the intracellular concentration of Cl⁻ was estimated to be about 16 mM in measurements with the gramicidin-perforated configuration, indicating the physiological reversal potential of the GABA current was about −60 mV. In conclusion, AL neurons have an intrinsic mechanism to evoke the spontaneous firing, which can be arrested by the inhibitory mechanism through the activation of the GABA_A receptors.     

The Potential Around Electrode Tips: Model Considerations

SUMMARY

As a new approach we considered the time and frequency depending electrical properties of biological material. Our model shows that in the near field around an electrode tip (distance < 15 μm) the spread of potential differs significantly from a model which denies time and frequency dependence of the biological material. On the other hand this effect decreases in the far-field (distance > 20 μm) due to the low-pass filtering characteristic of biological material. Furthermore it can be seen that the distortion of the signal in the near-field of an electrode tip depends on the inner resistance of the stimulus generator: current sources distort much more than voltage sources.     

A work‐for‐food enrichment program increases exploration and decreases stereotypies in four species of bears

Zoo‐housed bears are prone to exhibiting stereotypic behaviors, generally considered indicators of negative welfare. We explored the effects of a variable‐time feeding enrichment schedule on behavioral indicators of welfare in four bear species at Cleveland Metroparks Zoo. We distributed the diets of eight bears in one of five enrichment items, for two consecutive days each, and monitored behavior throughout the day. In Experiment 1, we compared variable‐time to fixed‐time presentation of enrichment over two, 10‐day periods. Overall, bears performed more exploratory behavior when enriched (p < 0.0001). Furthermore, variable‐time enrichment was associated with a greater increase in exploratory behavior than fixed‐time enrichment when compared to baseline (p < 0.001). Both fixed‐time (p_unadjusted <0.05, p_adjusted = 0.07) and variable‐schedule (p_unadjusted <0.05, p_adjusted = 0.09) enrichment were also associated with similar decreases in abnormal behavior compared to baseline. For Experiment 2, we tested habituation to enrichment over 30 days using multiple items and a semi‐variable presentation schedule. Again during the enrichment period, bears exhibited increased exploratory behavior (p < 0.0001) and decreased abnormal behaviors compared to baseline (p_unadjusted = 0.05, p_adjusted = 0.09). We observed no habituation during the 30‐day sustained enrichment period for these behaviors. Collectively, these results suggest that daily, variable‐schedule feeding enrichment, with intermittent presentation of unique enrichment items, increases behavioral indicators of positive welfare and decreases behavioral indicators of negative welfare.     

SPONTANEOUS AND LIGHT-EVOKED DISCHARGE OF THE ISOLATED ABDOMINAL NERVE CORD OF CRAYFISH IN VITRO REVEALS CIRCADIAN OSCILLATIONS

We examined the well-known spontaneous discharge (SD) and lightevoked (PD) discharge of the crayfish caudal photoreceptor for the possible existence of a daily rhythm in spike frequency. To do this, we isolated the abdominal nerve cord in vitro and studied its discharge frequency in constant darkness. Single cosinor analysis revealed significant SD and PD circadian rhythms (P <. 05) with periods τ = 24.4h and 24.2h, respectively. These oscillations correspond to an endogenous circadian discharge of the caudal photoreceptor that is enhanced by light. The importance of this rhythm in the adaptive behavior of crayfish is discussed. (Chronobiology International, 18(5), 759–765, 2001)     

Use of the Hurst Exponent for Analysis of Electrocortical Epileptiform Activity Induced in Rats by Administration of Camphor Essential Oil or 1,8-Cineole

In this study, we investigated the presence of long-range correlation effects in the electrocortical activity of rats using the Hurst exponent (H) calculated by dispersion analysis (DA) and an aggregated variance method (AGV). A slow decline of the autocorrelation function during time expansion and the existence of a correlation between distant time points of electrocorticograms (ECoGs) were shown to be typical of various pathophysiological states. In these cases, the H values were within a 0.5 < H < 1 range. A particularly slow decay of the autocorrelation function is typical of a long-range dependence (LRD). We found that ECoGs after i.p. administrations of camphor essential oil or its main constituent, 1,8-cineole, included attacks of uncontrolled electrical discharges and showed the presence of long-range correlation effects. Such findings are in agreement with recent data obtained by other authors and suggest that initiation of seizures can be predicted by certain ECoG indices. We estimated the critical period where the H values for ECoGs containing uncontrolled electrical discharges continuously increased within a few minutes before the attack. We believe that the AGV demonstrates certain advantages over DA in calculations of the H.     

Bone cadmium and lead in the ancient population from El Hierro, Canary Islands

This study was performed to determine the levels of lead (Pb) and cadmium (Cd) in 63 bone samples of the prehispanic population of the island El Hierro, comparing them with the values obtained on 98 prehispanic samples from Tenerife, Fuerteventura, Gran Canaria, and La Palma, all of them in the Canary Islands, and with eight modern samples who served as controls. Prehispanic individuals from El Hierro showed the lowest bone Pb values of all the archipelago (0.72±1.01 mg/kg), significantly different (F=6.9, p<0.001) from the values obtained for the population of other islands such as Tenerife (4.87±5.36 mg/kg) or Fuerteventura (4.45±7.85 mg/kg) and also from those of the modern population (30.53±14.62 mg/kg). On the other hand, bone Cd, although slightly lower in the ancient population groups, was not significantly different when compared with the modern one. In addition, no differences were observed in bone Cd among the ancient population of the different islands. Bone lead—but not cadmium—kept an inverse significant relationship with the distance of the burial site both to south Spain (r=−0.31) and Atlantic Morocco (r=−0.28, p<0.001 in both cases).     

Temperature-Dependent Electrical and Ultrastructural Characterizations of Porcine Skin upon Electroporation

The mechanism of high-voltage pulse-induced permeabilization of the stratum corneum, the outer layer of the skin, is still not completely understood. It has been suggested that joule heating resulting from the applied pulse may play a major role in disrupting the stratum corneum. In this study, electrical and ultrastructural measurements were conducted to examine the temperature dependence of the pulse-induced permeabilization of the stratum corneum. The stratum corneum resistance was measured using a vertical diffusion holder, with the stratum corneum placed between two electrode-containing chambers. The stratum corneum resistance was reduced manyfold during the applied pulse. The extent of resistance reduction increased with pulse voltage until reaching a threshold value, above which the resistance reduction was less dependent on the pulse voltage. The stratum corneum was more susceptible to permeabilization at high temperature, the threshold voltage being lower. The stratum corneum resistance recovered within milliseconds after a single 0.3-ms pulse. High-temperature samples had a more prolonged recovery time. Using time-resolved freeze fracture electron microscopy, aggregates of lipid vesicles were observed in all samples pulsed above the threshold voltage. The sizes and fractional areas occupied by aggregates of lipid vesicles at 4°C and at 25°C were measured at different time points after the applied pulse. Aggregates of vesicles persisted long after the electric resistance was recovered. After pulsing at the same voltage of 80 V, samples at 4°C were found to have slightly more extensive aggregate formation initially, but recovered more rapidly than those at 25°C. The more rapid recovery of the 4°C samples was likely due to a lower supra-threshold voltage. Viscoelastic instability propagation created by the pulse may also play a role in the recovery of the aggregates.     

Magnitude and modulation of pancreatic β-cell gap junction electrical conductance in situ

The parallel gap junction electrical conductance between a -cell and its nearest neighbors was measured by using an intracellular microelectrode to clamp the voltage of a -cell within a bursting islet of Langerhans. The holding current records consisted of bursts of inward current due to the synchronized oscillations in membrane potential of the surrounding cells. The membrane potential record of the impaled cell, obtained in current clamp mode, was used to estimate the behavior of the surrounding cells during voltage clamp, and the coupling conductance was calculated by dividing the magnitude of the current bursts by that of the voltage bursts. The histogram of coupling conductance magnitude from 26 cells was bimodal with peaks at 2.5 and 3.5 nS, indicating heterogeneity in extent of electrical communication within the islet of Langerhans. Gap junction conductance reversibly decreased when the temperature was lowered from 37 to 30°C and when the extracellular calcium concentration was raised from 2.56 to 7.56 mm. The coupling conductance decreased slightly during the active phase of the burst. Activation of adenylate cyclase with forskolin (10 m) resulted in an increase in cell-to-cell electrical coupling. We conclude that -cell gap junction conductance can be measured in situ under near physiological conditions. Furthermore, the magnitude and physiological regulation of -cell gap junction conductance suggest that intercellular electrical communication plays an important role in the function of the endocrine pancreas.The authors thank Dr. Arthur Sherman for sharing his insights on in situ coupling measurements, and for helpful discussions throughout the work. DM acknowledges partial support by a National Institutes of Health training grant to the Johns Hopkins University, Department of Biomedical Engineering (5 T32 GM7057). This work was supported in part by a National Science Foundation PYI award (ECS-9058419) to NFS.     

An electronic device for accelerating bone formation in tissues surrounding a dental implant

A dental implant is a unique structure which can be used with a noninvasive method because it is inserted into the bone in part and extended extracorporally. This study presents an electronic device that is temporarily connected with the dental implant, and reports its effect on accelerating bone formation in the surrounding tissues in a canine mandibular model. A small sized and low power consumption biphasic electrical current (BEC) stimulator ASIC was developed and the surrounding tissue was exposed to continuous BEC stimulation for 7 days with the parameters of 20 µA/cm², 125 µs duration, and 100 pulses/s. After 2 (n = 5) and 5 weeks (n = 5), animals were sacrificed and the specimens were histomorphometrically evaluated. The newly formed bone area (BA) was 1.30 times (3 weeks, P < 0.05) and 1.35 times (5 weeks, P < 0.05) higher in the experimental group compared to the control group, respectively. Bone‐implant contact (BIC) in 3‐week specimens was 1.62 times (P < 0.05) greater in the experimental group, while there was no statistically significant difference in 5‐week specimens. Based on these results showing accelerated bone formation on and around the dental implant, it could be suggested that the latent time for osseointegration in dental implants can be reduced, and the success rate of implants in poor quality bone can be increased by using our device with BEC. Bioelectromagnetics 30:374–384, 2009. © 2009 Wiley‐Liss, Inc.     

Channel formation kinetics of gramicidin A in lipid bilayer membranes

Summary Previous studies have given evidence that the active form of gramicidin A in lipid bilayer membranes is a dimer which acts as an ion channel; it has been further shown that the mean lifetime of the channel strongly depends on the membrane thickness. As the thickness slightly decreases when a voltage is applied to the membrane, the equilibrium between conducting dimers and nonconducting monomers may be displaced by a voltage jump. From the relaxation of the electrical current after the voltage jump, information about the kinetics of channel formation is obtained. For a dioleoyllecithin/n-decane membrane the rate constant of association is found to be 2×10¹⁴ cm² mole^–1 sec^–1, which is by three orders of magnitude below the limiting value of a diffusion-controlled reaction in a two-dimensional system. The dissociation rate constant is equal to 2 sec^–1, a value which is consistent with the channel lifetime as obtained from electrical fluctuation measurements.     

Models of membrane resonance in pigeon semicircular canal type II hair cells

Pigeon vestibular semicircular canal type II hair cells often exhibit voltage oscillations following current steps that depolarize the cell membrane from its resting potential. Currents active around the resting membrane potential and most likely responsible for the observed resonant behavior are the Ca⁺⁺-insensitive, inactivating potassium conductance I _A (A-current) and delayed rectifier potassium conductance I _K. Several equivalent circuits are considered as representative of the hair cell membrane behavior, sufficient to explain and quantitatively fit the observed voltage oscillations. In addition to the membrane capacitance and frequency-independent parallel conductance, a third parallel element whose admittance function is of second order is necessary to describe and accurately predict all of the experimentally obtained current and voltage responses. Even though most voltage oscillations could be fitted by an equivalent circuit in which the second order admittance term is overdamped (i.e., represents a type of current with two time constants, one of activation and the other of inactivation), the sharpest quality resonance obtained with small current steps (around 20 pA) from the resting potential could be satisfactorily fit only by an underdamped term.     

Some Relations between Changes in the Linear Electrical Properties of Striated Muscle Fibers and Changes in Ultrastructure

Some of the linear electrical properties of frog sartorius muscle have been investigated in Ringer's fluid and in a Ringer fluid made hypertonic by the addition of sucrose or NaCl. Electrical constants were determined from measurements of the phase angle of the admittance of a fiber for an applied alternating current, from measurements of the voltage induced by an inward pulse of current, and from measurements of the conduction velocity of the action potential and the time constant of its foot. The dilation of the transverse tubular system induced by the sucrose hypertonic Ringer fluid was correlated with the change in the electrical constants. From this it is concluded that a two time constant equivalent circuit for the membrane, as proposed by Falk and Fatt, is in good agreement with our results. Both the area of the membrane of the transverse tubular system, and the capacity (c_e) attributed to it, increased in the sucrose hypertonic Ringer fluid. The resistance r_e, which is in series with c_e, did not fall when the transverse tubular system was dilated and probably is not located in that system.     

The coupling between extra- and intracellular electric potentials in Bidens pilosa L.

The extracellular electrical potential in Bidens pilosa has been compared with the transmembrane potential in hypocotyl cells. We found that variations in the extracellular electrical potential, induced by different KCI concentrations, were identical to the variations of the transmembrane potential. In order to explain the strong correlation between the extracellular potential and the transmembrane potential, an interpretative model based on the electrical diagram of the plant was tested. From our data, we found that: (1) the symplast behaves as a low resistance pathway compared with the apoplast; and (2) the cell wall contributes weakly (20% at the most) to the transmembrane potential. It is concluded that each hypocotyl cell is strongly coupled electrically with its neighbour. This property, together with the high apoplast resistance, accounts for the similarity in the extracellular and transmembrane potential measurements. These properties, which are characteristic of excitable organs, support the existence of action potentials in Bidens.     

Dynamics of spontaneous activity in random networks with multiple neuron subtypes and synaptic noise

During slow-wave sleep, brain electrical activity is dominated by the slow (< 1 Hz) electroencephalogram (EEG) oscillations characterized by the periodic transitions between active (or Up) and silent (or Down) states in the membrane voltage of the cortical and thalamic neurons. Sleep slow oscillation is believed to play critical role in consolidation of recent memories. Past computational studies, based on the Hodgkin-Huxley type neuronal models, revealed possible intracellular and network mechanisms of the neuronal activity during sleep, however, they failed to explore the large-scale cortical network dynamics depending on collective behavior in the large populations of neurons. In this new study, we developed a novel class of reduced discrete time spiking neuron models for large-scale network simulations of wake and sleep dynamics. In addition to the spiking mechanism, the new model implemented nonlinearities capturing effects of the leak current, the Ca²⁺ dependent K⁺ current and the persistent Na⁺ current that were found to be critical for transitions between Up and Down states of the slow oscillation. We applied the new model to study large-scale two-dimensional cortical network activity during slow-wave sleep. Our study explained traveling wave dynamics and characteristic synchronization properties of transitions between Up and Down states of the slow oscillation as observed in vivo in recordings from cats. We further predict a critical role of synaptic noise and slow adaptive currents for spike sequence replay as found during sleep related memory consolidation.     

The Spatial Variation of Membrane Potential Near a Small Source of Current in a Spherical Cell

A theoretical analysis is presented of the change in membrane potential produced by current supplied by a microelectrode inserted just under the membrane of a spherical cell. The results of the analysis are presented in tabular and graphic form for three wave forms of current: steady, step function, and sinusoidal. As expected from physical reasoning, we find that the membrane potential is nonuniform, that there is a steep rise in membrane potential near the current microelectrode, and that this rise is of particular importance when the membrane resistance is low, or the membrane potential is changing rapidly. The effect of this steep rise in potential on the interpretation of voltage measurements from spherical cells is discussed and practical suggestions for minimizing these effects are made: in particular, it is pointed out that if the current and voltage electrodes are separated by 60°, the change in membrane potential produced by application of current is close to that which would occur if there were no spatial variation of potential. We thus suggest that investigations of the electrical properties of spherical cells using two microelectrodes can best be made when the electrodes are separated by 60°.     

Calcium-dependent sodium current in the marine ciliateEuplotes vannus

Summary Ca and Na inward currents were recorded upon depolarizations inEuplotes after the blockage of K outward currents with intracellular Cs ions. The Na current was analyzed under voltage clamp and had the following properties: it activated to a maximum within 150 msec and partly inactivated during sustained voltage steps. It had a positive equilibrium potential between 25 and 30 mV and could be carried by Na or Li ions but not by K, choline or Tris ions. The current revealed a prominent associated inward tail current which deactivated with a single-exponential time constant of 118 msec. Both the current and its tail were strongly reduced after reduction of the extracellular Na concentration. Externally applied K channel blocker tetraethylammonium chloride did not block the current. Either EGTA injection into the cell or nonlethal deciliation with ethanol eliminated the current and its tail. These results indicate the existence of a Na conductance within the membrane ofEuplotes which is activated by the intracellular level of free Ca²⁺.     

Do light-induced changes in the membrane potential ofNitella reflect the feed-back regulation of a cytoplasmic parameter?

Summary Kinetic studies of the linearized response of membrane potential inNitella to light have revealed the existence of a feedback loop in the pathway of light action. Its existence can hardly be seen in the time course of the responses to dark/light transitions. However, making use of sine waves as input signals and employing a computeraided evaluation has resulted in finding complex time constants in the transfer function of the light effect which point out the existence of a feedback loop. Besides, sometimes spontaneous oscillations with periods of about 1 hr have been observed. It is shown that this system is different from that one reported in literature to be related to cytoplasmic streaming. By measuring the electrical low-frequency impedance, it has been demonstrated that it is not the purpose of the system to control membrane potential, even though secondary effects of the injected current have been found. It seems to be reasonable to assume that this system is involved in the control of a biochemically relevant parameter like the cytoplasmic pH by means of adjusting the balance of counteracting transmembrane transport processes.