Half-height Duration Research Articles

Axonal sodium and potassium conductance density determines spiking dynamical properties of regular- and fast-spiking neurons

Compared with regular-spiking (RS) neurons, the action potentials (APs) of fast-spiking (FS) neurons are characterized by narrow spike durations and unusually fast decay dynamics of dV/dt process. However, quantitative measure of accurate sodium and potassium densities accounting for spike shape in the axon initial segment (AIS) where action potentials are initiated in both RS and FS cells is not well explored. Here, axonal recordings showed that the averaged axonal spike half-height duration of RS cells is significantly larger (Matlab anova1, $$p < 0.001$$ ) than that of FS cells. The averaged dV/dt ratio of RS cells is significantly lower (Matlab anova1, $$p < 0.001$$ ) than that of FS cells. We have reproduced axonal APs by cortical Hodgkin–Huxley axonal models constrained by a set of experimentally observed properties of RS and FS cells. The model predicts that sodium channel conductance $${g}_{\mathrm{Na}}$$ in RS AIS is in a range of 1000–4000 pS/ $$\upmu \text {m}^{2}$$ and potassium channel conductance $${g}_{\mathrm{K}}$$ is in a range of 30–200 pS/ $$\upmu \text {m}^{2}$$ in order to produce energy-efficient RS action potentials with major properties matching experimental observations of pyramidal cells. The model predicts that $${g}_{\mathrm{Na}}$$ is within 1000–2500 pS/ $$\upmu \text {m}^{2}$$ and $${g}_{\mathrm{K}}$$ ranges within 300–1000 pS/ $$\upmu \text {m}^{2}$$ for AIS of FS cells. The AP duration and efficiency are nonlinearly regulated by the ratio of $${g}_{\mathrm{Na}}/{g}_{\mathrm{K}}$$ . We performed patch-clamp recordings on both RS and FS cortical axons and observed that $${g}_{\mathrm{Na}}$$ was approximately $$1620.4\pm 770\,\hbox {pS}/\upmu \text {m}^{2}$$ for RS AIS and $$803.7\pm 351.5\,\hbox {pS}/\upmu \text {m}^{2}$$ for FS AIS. The $${g}_{\mathrm{K}}$$ was $$189.6\pm 75.8\,\hbox {pS}/\upmu \text {m}^{2}$$ for the RS AIS and $$524.6\pm 281.6\,\hbox {pS}/\upmu \text {m}^{2}$$ for the FS AIS. Partial drug-mediated inhibition of sodium or potassium channels significantly decreases or enlarges the AP duration and dV/dt ratio of both RS and FS cells, respectively, suggesting that sodium and potassium conductance density in cortical axons may be critical in determining the dynamical features of AP profiles in FS and RS cells.

Axon initial segment potassium channel density in cortical neurons

There is a growing interest in estimating actual density ranges of Na+ channels in the very thin axon, especially in the action potential (AP) initiation zone, i.e., the axon initial segment (AIS, 20-50 microns away from the cell body). Both immunostaining studies and patch-clamp recordings indicated a relatively high density of Na+ channels in AIS of either pyramidal regular-spiking (RS) cells [1] or fast-spiking (FS) GABAergic interneurons [2,3]. Here, we investigated potassium channel densities in AISs of both RS and FS cells in same recording conditions. Our axonal recordings directly revealed that there is a very lower potassium density gK = 185.8±19 pS/µm2 N = 16) for the RS AIS while a higher gK (495.7±108 pS/µm2, N = 11) for FS AIS, see Figure ​Figure1A.1A. For both the RS pyramidal cells and FS PV cells, partially blocking K+ channels by applying 4-AP broadened the spike duration and decreased the dV/dt ratio significantly (P < 0.05) (For RS cells: N = 5; For RS cells: N = 4). Interestingly, we observed that the AP dV/dt ratio is an exponentially decaying function of the spike duration for both RS- and FS-spikings (see Figure ​Figure1B),1B), such that y = 0.12+0.16EXP((0.5-x)/0.2), where y represents the dV/dt ratio and × represents the AP duration. These observations suggest strongly that potassium channel density is one of the major intrinsic factors dominating the spike shape properties, especially half-height spike duration and dV/dt ratio. Figure 1 A. The bar graph shows peak K+ conductance density recorded in axon initial segment of cells (16 recording axons for RS pyramidal cell, 11 for FS interneuron) by outside-out axon patch recording technique. B. Summary of the results from partially blocking ... In sum, the significant difference in potassium channel density in axonal initial segment where action potentials are initiated may play a critical role in controlling action potential properties of both RS- and FS-spiking cells in nervous system by the same general biophysical rule. These results may be important for constructing computational models of different types of cortical neurons.

Key factors dominating the neural coding preference to 1/f signal

Experiments have demonstrated that cortical and sensory neurons prefer to response to signals with characteristics of long-term correlation or 1/f noise feature better than signals with no correlation like white-noise-type [1]. In order to study the underlying mechanism, we built up a cortical neuronal model [2] based on Hodgkin-Huxley theory to study the correlations between neuron kinetics and signal statistics. Interestingly, we observed that (see Figure 1a,b) white-noise-type signal (cutoff frequency >10000Hz) is hard to induce action potentials unless signals with very strong intensity while 1/f signal and low-pass filtered white noise type signal (cutoff frequency <1000Hz) can easily induce action potentials with high firing rate at low signal intensity (quantified by signal standard deviation STD), see Figure ​Figure1a.1a. Moreover, the half-height duration of action potentials is also varying with more sensitivity to 1/f signal or filtered white noise than pure white noise (Figure ​(Figure1b).1b). In addition, neural firing rate and spike duration are more sensitive to 1/f signal than filtered white noise. This is a clear positive evidence of neuronal coding preference to signals with long-term correlations. Figure 1 Interactions among neuron kinetics and signal statistics. a) Firing rate vs signal STD for white noise, filtered white noise and 1/f noise. b) Half-height duration of action potentials vs signal STD for white noise, filtered white noise and 1/f noise. ... To further reveal the key factors dominating the preference of neuronal dynamics to colored and white noise, we systematically varied the values of Na+ and K+ channel time constants and channel rate constants. Figure ​Figure1c1c showed that the firing rate doesn't change much as a function of sodium activation time constant (τm) for a given 1/f signal (STD = 1). However, the firing rate decrease dramatically with an increase of sodium inactivation time constant (τh) or potassium activation time constant (τn) for this signal. For very large τh and τn, neuronal response dynamics start to be saturate for all signals, see Figure ​Figure1d.1d. These results indicate that both sodium inactivation time constant (τh) and potassium activation time constant (τn) may be the key factors dominating neural coding preference to signals with different correlated statistic features. In sum, this study demonstrated that ionic channel time constant of sodium inactivation and potassium activation may be the dominating factors accounting for the neuronal spiking sensitivity favorable to signals with temporal correlations.

Gamma-4 electrophysical facility project

The paper presents the Gamma-4 four-module electrophysical facility project developed for radiation physics research. For this facility, we have developed and tested a typical module which, with a matched load, generates an electrical pulse with voltage and current amplitudes of up to 2 MV and 750 kA, respectively, and with a half-height duration of 60 ns. 700 shots were performed which conformed the operating parameters and reliability of the module. Layouts of the facility for the modes of synchronous (with accuracy of ±3 ns) operation of the modules with vacuum electron diodes and with a current summator to generate soft x-ray pulses have been developed.

How does a supercoiled DNA chain pass through a small conical glass pore?

We investigated the captioned question by a resistive pulse technique, in which a constant electrical potential was applied inside and outside of a conical glass capillary with its tip opening diameter (d) down to ∼10 nm. The insertion of a chain segment into the tip decreases the current (Ip). Our studies on transport dynamics of individual supercoiled DNA chains through such a tip with different openings at various potentials (V) reveal that when d ≈ 35 nm, they can pass through the conical glass capillary without much stretching; namely, the current pulse has a typical triangle shape and its half-height duration time (Δtd,1/2) decreases, but its occurring frequency (f) increases exponentially, as V increases. For a smaller tip opening (d ≈ 14 nm), we found that f strangely increases and then decreases with increasing V. In addition, the current pulse is significantly skewed with a long tail and its minimum occurs when V ≈ 200 mV. Typically, each current pulse is composed of four steps as follows: (1) Ip sharply decreases from its baseline (Io) when a DNA chain approaches the tip opening and inserts a segment to block the pore; (2) the inserted segment is stretched under the electric field gradient so that the pore is less blocked, resulting in a slight current increase; (3) then Ip slightly decreases once more, indicating that the pulling of the inserted segment is faster than the relaxation (unwinding) of the rest of the chain outside so that it clogs at the tip entrance; and (4) Ip gradually increases and finally returns to Io because more and more segments are gradually pulled in by the electrical field until the entire chain slips through the conical glass capillary. These steps can be well explained in terms of a big difference between times of pulling the first segment inside the tip and relaxing the rest of the segments outside.

Use of an CXP8 X-ray streak camera for measuring the time characteristics of X rays emitted by a laser plasma

The time dependence of the X-ray intensity from targets exposed to single-shot or successive picosecond laser pulses at the NEODIM facility was obtained by direct measurements. The measurements were taken using an CXP8 streak camera (produced by the Research Institute of Pulse Techniques) with a picosecond time resolution under different operating conditions of the facility. The observed X-ray pulses had a half-height duration of 15–50 ps and a rise time of 5 ps at a ∼1.5-ps duration of the effecting laser pulse. Under actual experimental conditions, it was ascertained that time dependences of the X-ray intensity could be recorded for more than 200 spatial elements on a single record at a sweep duration of 0.5 ns per frame and a time resolution of <5 ps.

Optimization of high-voltage devices for energy compression of nanosecond pulses

Designs of compact converters intended for compression of high-voltage pulses with durations of a few nanoseconds and operating in a traveling wave mode were examined. The energy compression unit contained two lines-high-impedance and forming-with a high -pressure gas spark discharger used as a switch. A traditional serial connection of lines was replaced by a parallel connection to increase the energy compression efficiency. The power of the initial pulse (amplitude, 145 kV; half-height duration, 4 ns; and rise time, 1.5 ns) at a load of 45 Ω was increased by a factor of 1.8, while the calculated value was 2.5. The amplitude was as great as -195 kV, and the power was 17% higher relative to the circuit with a serial connection of lines. When shaped, the pulse was compressed in time to 0.8 ns. Two modifications of devices converting the initial pulse with an amplitude of -160 kV and a rise time of 0.3 ns into pulses with amplitudes of -210 and -250 kV and durations of 0.80 and 0.45 ns, respectively, were tested. Waveguide components of the converters were developed, with which it was possible to minimize the dimensions of the device in order to avoid excitation of higher harmonics while maintaining the electric strength.

A high-voltage nanosecond pulse generator for exciting diffuse gas discharges at atmospheric pressure

A high-voltage nanosecond pulse generator intended for studying diffuse discharges in gases at pressures close or equal to atmospheric pressure is described. The generator produces pulses with an ∼50-ns (at half-height) duration, a >50-kV voltage amplitude, a 10- to 12-ns rise time, and a pulse repetition rate of up to 1 kHz across an equivalent load (1.3 kΩ, 15 pF). The generator is based on available cheap components, and the amplitude (energy) of output pulses and their repetition rate can be promptly regulated in a wide range. The generator is immune to noise and reliable.

Generation and measurement of subnanosecond electron beams in gas-filled diodes

The results of experimental studies of generation of supershort avalanche electron beams (SAEBs) in gas-filled diodes and the analysis of the techniques for measurements of their amplitude-time characteristics are presented. The optimal conditions for obtaining the maximum SAEB amplitudes are described. It is shown that, at a 6-mm-diameter cathode and a 10-mm interelectrode distance, a beam is detected over the entire foil area, the diameter of which is 50 mm, and equals the inner diameter of the gas diode. A half-height duration of the beam-current pulse shorter than 90 ps was measured with the use of a collector with a 3-mm-diameter receiving element. The SAEB amplitude measured behind the 10-μm-thick Al foil at this pulse duration was ∼50 A.

A collector assembly for measuring a subnanosecond-duration electron beam current

The design and test results of the collector assembly intended for recording electron beams of sub-nanosecond duration are presented. The collector assembly features a passband of up to 12 GHz and is capable of transmitting slightly-distorted voltage pulses with a half-height duration longer than ∼50 ps. The collector assembly was used to detect current pulses of a subnanosecond-duration electron beam generated in a gas-filled diode.

A hardware and software system for the laser time-of-flight mass spectrometer

The hardware and software system for a laser time-of-flight mass spectrometer is based on the double-level principle. At the upper level, the personal computer automatically controls online recording and processing of mass spectra with the highest priority. The monitoring and stabilization functions are fulfilled by controllers of the second control level. The exchange between the controllers and personal computer takes place in the periods between mass-spectrum recording and processing. The use of the hardware and software system has made it possible (i) to form short mass peaks with a half-height duration of up to 10 ns, (ii) to decrease a scatter of relative sensitivity coefficients from two or three down to one order of magnitude, and (iii) to increase a dynamic range of the recorded mass spectra up to 1−1 × 109.

A High-Current Nanosecond Electron Accelerator with Inductive Energy Storage

A nanosecond electron accelerator with an output energy as great as 600 keV, a beam current of 16 kA, and an accelerating voltage half-height duration of ∼180 ns is described. The accelerator is based on an inductive energy storage composed of two coils. A wire explosive current chopper is used in the inductive storage as a release. The circuit diagram of the accelerator is shown, the design for the accelerator is described, and results from its testing are presented.

An Ion Diode with External Magnetic Insulation

An ion diode with an orificed anode and an external radial magnetic field created by a pair of concentric windings is described. It is distinguished by the absence of devices for preliminary plasma production. The diode is powered from a high-current nanosecond-pulse accelerator with a matching output autotransformer. The use of ballistic focusing in a converging ion beam makes it possible to reach an ion-current density of 600 A/cm2 at an efficiency of ∼ 60%, relative to the energy stored in the accelerator's forming line, and at an anode potential of ∼350 kV for a half-height voltage-pulse duration of 50 ns.

A Vacuum Feedthrough Insulator at a Voltage of ∼1 MV

The design and results of tests of a vacuum feedthrough insulator for a pulsed electron accelerator with a voltage of ∼1 MV, a current of ∼20 kA, and a half-height voltage-pulse duration of ≥ 400 ns are presented. A method for distributing the voltage over the sections of the insulator due to an electron emission from specially created surfaces is proposed.

Amplification of exocytosis by Ca2+‐induced Ca2+ release in INS‐1 pancreatic β cells

Functional coupling between Ca(2+)-induced Ca(2+) release (CICR) and quantal exocytosis in 5-hydroxytryptamine-loaded INS-1 beta cells was assessed through the use of carbon fibre amperometry in combination with Fura-2. CICR was evoked by the glucagon-like-peptide-1 (GLP-1) receptor agonist exendin-4 (Ex-4) and was accompanied by quantal secretory events appearing as amperometric current spikes time-locked to the increase of [Ca(2+)](i). The action of Ex-4 was reproduced by treatment with caffeine, and the source of Ca(2+) serving as a stimulus for exocytosis originated from ryanodine and thapsigargin-sensitive Ca(2+) stores. Two distinct patterns of exocytosis occurred within 5 s following the initiation of CICR. Non-summating exocytosis (NS-type) was defined as multiple asynchronous current spikes, and the half-height duration of each spike was 12-48 ms. Summating exocytosis (S-type) was defined as a cluster of spikes. It generated a macroscopic current, the half-height duration of which was 243-682 ms. The release charge of S-type exocytosis was 3.2-fold greater than that of NS-type when measured 2 s following the initiation of secretion. NS-type exocytosis was observed frequently under conditions in which the basal Ca(2+) concentration ([Ca(2+)](B)) was low (75-150 nM), whereas S-type exocytosis predominated under conditions in which the [Ca(2+)](B) was elevated (200-275 nM). Depolarization-induced Ca(2+) influx triggered NS-type exocytosis in most cells tested, irrespective of [Ca(2+)](B). It is concluded that CICR is a highly effective stimulus for exocytosis in INS-1 cells. The increase of [Ca(2+)](i) that accompanies CICR stimulates the asynchronous release of a small number of secretory granules under conditions of low [Ca(2+)](B). When [Ca(2+)](B) is slightly elevated, CICR targets a much larger pool of secretory granules that undergo summating exocytosis. The transition from NS-type to S-type exocytosis may represent an amplification mechanism for Ca(2+)-dependent exocytosis.

Express method of estimating laser-induced surface damage threshold for optical components

The present measurements of the components' surface resistance to laser-induced damage has been completed to facilitate development and construction of the “Luch” laser system, a four-channel Nd-phosphate glass laser with a full output energy of E = 14–16 kJ. The study describes a method that, with a series of experimental data obtained from a single sample, allows us not only to estimate the threshold fluences, but to take into account the statistical nature of the surface damage. In a number of experimental situations this method makes it possible to estimate damaging fluences even from the result of a single exposure of the studied surface. Estimated threshold fluences for various optical elements are presented: K8 glass, experimental phosphate laser glass KGSS-0180, high-reflecting and antireflecting thin-film coating of elements. The 1.054-μm radiation pulse with half-height duration of 4 ns and the irradiation spot of ∼4 mm in diameter were used in the experiment.

A 1-kW/cm2 flash KrCl excimer lamp

The amplitude-time characteristics of the emission from a one-barrier flash KrCl excimer lamp and conditions for the maximum luminosity in the UV spectrum range are reported. The best result is achieved for a Ne: Kr: Cl2=50: 1: 1 (torr) mixture. When the lamp is excited by the combined Fitch circuit, the pulse half-height duration 107 ns and the power density E(0,0)=1.1 kW/cm2 are attained.

A semiconductor opening switch-based quasi-rectangualr pulse generator operating into a low-impedance load

A generator with a semiconductor opening switch (SOS-diode) operating into a low-impedance load of 4–5 Ω is studied. The amplitude of quasi-rectangular pulses is 50 kV at a half-height duration of 100 ns. The energy is applied from an intermediate storage via a spark gap to the output generator stage. The output pulse is formed by solid-state components.

Influence of phase self-modulation on the temporal characteristics of ultrashort pulses emitted by solid-state lasers

The kinetics of changes in the temporal profile and frequency modulation of pulses under conditions of phase self-modulation and allowing for the width of the gain profile was analyzed using a model which postulates that the fluctuation pattern of the radiation emitted by a passively mode-locked solid-state laser has the form of an intensity peak against a background which is constant over the resonator period. The rms duration and the half-height duration of the largest peak were compared and the fraction of the pulse energy in the largest peak was studied to analyze the degree of deformation of the pulse temporal profile. It was found that, for moderate values of the phase self-modulation parameters, ultrashort pulses with a small fraction of energy in the side satellites and almost linear chirp in the central peak can be generated by tuning the system to the second threshold in a train of giant pulses. For large phase self-modulation parameters, this can be achieved by using a spectrum-limiting filter in the resonator.

Energy characteristics of an XeO photochemical laser

A kinetic model of the physicochemical processes in an XeO laser is developed and used as the basis to explain the experimentally observed dependences of the laser output characteristics on the pressure of the active mixture components. An analysis is made of the energy balance in the active medium of an XeO laser. The maximum laser efficiency and the conditions required to achieve this are estimated. An output pulse with an energy of 2.2 J and half-height duration of 8 μsec was obtained in an N2O:Xe:He =1:75:170 mixture with a total concentration of 3 amagat at a temperature of 160°K. The specific output energy was ~3 J/liter, the gain at the pump pulse maximum was 3.6×10–3cm–1, and the absorbed photon quantum efficiency was approximately 10%.