Input Resistance Research Articles

Kv7/M channel dysfunction produces hyperexcitability in hippocampal CA1 pyramidal cells of Fmr1 knockout mice.

Fragile X syndrome (FXS), the most frequent monogenic form of intellectual disability, is caused by transcriptional silencing of the FMR1 gene that could render neuronal hyperexcitability. Here we show that pyramidal cells (PCs) in the dorsal CA1 region of the hippocampus elicited a larger action potential (AP) number in response to suprathreshold stimulation in juvenile Fmr1 knockout (KO) than wild-type (WT) mice. Because Kv7/M channels modulate CA1 PC excitability in rats, we investigated if their dysfunction produces neuronal hyperexcitability in Fmr1 KO mice. Immunohistochemical and western blot analyses showed no differences in the expression of Kv7.2 and Kv7.3 channel subunits between genotypes; however, the current mediated by Kv7/M channels was reduced in Fmr1 KO mice. In both genotypes, bath application of XE991 (10μM), a blocker of Kv7/M channels: produced an increased AP number, produced an increased input resistance, produced a decreased AP voltage threshold and shaped AP medium afterhyperpolarization by increasing mean velocities. Retigabine (10μM), an opener of Kv7/M channels, produced opposite effects to XE991. Both XE991 and retigabine abolished differences in all these parameters found in control conditions between genotypes. Furthermore, a low concentration of retigabine (2.5μM) normalized CA1 PC excitability of Fmr1 KO mice. Finally, ex vivo seizure-like events evoked by 4-aminopyiridine (200μM) in the dorsal CA1 region were more frequent in Fmr1 KO mice, and were abolished by retigabine (5-10μM). We conclude that CA1 PCs of Fmr1 KO mice exhibit hyperexcitability, caused by Kv7/M channel dysfunction, and increased epileptiform activity, which were abolished by retigabine. KEY POINTS: Dorsal pyramidal cells of the hippocampal CA1 region of Fmr1 knockout mice exhibit hyperexcitability. Kv7/M channel activity, but not expression, is reduced in pyramidal cells of the hippocampal CA1 region of Fmr1 knockout mice. Kv7/M channel dysfunction causes hyperexcitability in pyramidal cells of the hippocampal CA1 region of Fmr1 knockout mice by increasing input resistance, decreasing AP voltage threshold and shaping medium afterhyperpolarization. A Kv7/M channel opener normalizes neuronal excitability in pyramidal cells of the hippocampal CA1 region of Fmr1 knockout mice. Ex vivo seizure-like events evoked in the dorsal CA1 region were more frequent in Fmr1 KO mice, and such an epileptiform activity was abolished by a Kv7/M channel opener depending on drug concentration. Kv7/M channels may represent a therapeutic target for treating symptoms associated with hippocampal alterations in fragile X syndrome.

Danshensu reduces neuronal excitability by enhancing potassium currents in bushy cells in the mouse cochlear nucleus.

Danshensu, also known as salvianic acid A, is a primary active compound extracted from a traditional Chinese herb Danshen (Salvia miltiorrhiza). While its antioxidative and neuroprotective effects are well-documented, the underlying mechanisms are poorly understood. In this study, we sought out to investigate if and how Danshensu modulates neuronal excitability and voltage-gated ionic currents in the central nervous system. We prepared brain slices of the mouse brainstem and performed patch-clamp recording in bushy cells in the anteroventral cochlear nucleus, with or without Danshensu incubation for 1 h. QX-314 was used internally to block Na+ current, while tetraethylammonium and 4-aminopyridine were used to isolate different subtypes of K+ current. We found that Danshensu of 100 μm decreased the input resistance of bushy cells by approximately 60% and shifted the voltage threshold of spiking positively by approximately 7 mV, resulting in significantly reduced excitability. Furthermore, we found this reduced excitability by Danshensu was caused by enhanced voltage-gated K+ currents in these neurons, including both low voltage-activated IK,A, by approximately 100%, and high voltage-activated IK,dr, by approximately 30%. Lastly, we found that the effect of Danshensu on K+ currents was dose-dependent in that no enhancement was found for Danshensu of 50 μm and Danshensu of 200 μm failed to cause significantly more enhancement on K+ currents when compared to that of 100 μm. We found that Danshensu reduced neuronal excitability in the central nervous system by enhancing voltage-gated K+ currents, providing mechanistic support for its neuroprotective effect widely seen in vivo.

The bidirectional role of GABAA and GABAB receptors during the differentiation process of neural precursor cells of the subventricular zone.

The intricate process of neuronal differentiation integrates multiple signals to induce transcriptional, morphological, and electrophysiological changes that reshape the properties of neural precursor cells during their maturation and migration process. An increasing number of neurotransmitters and biomolecules have been identified as molecular signals that trigger and guide this process. In this sense, taurine, a sulfur-containing, non-essential amino acid widely expressed in the mammal brain, modulates the neuronal differentiation process. In this study, we describe the effect of taurine acting via the ionotropic GABAA receptor and the metabotropic GABAB receptor on the neuronal differentiation and electrophysiological properties of precursor cells derived from the subventricular zone of the mouse brain. Taurine stimulates the number of neurites and favors the dendritic complexity of the neural precursor cells, accompanied by changes in the somatic input resistance and the strength of inward and outward membranal currents. At the pharmacological level, the blockade of GABAA receptors inhibits these effects, whereas the stimulation of GABAB receptors has no positive effects on the taurine-mediated differentiation process. Strikingly, the blockade of the GABAB receptor with CGP533737 stimulates neurite outgrowth, dendritic complexity, and membranal current kinetics of neural precursor cells. The effects of taurine on the differentiation process involve Ca2+ mobilization and the activation of intracellular signaling cascades since chelation of intracellular calcium with BAPTA-AM, and inhibition of the CaMKII, ERK1/2, and Src kinase inhibits the neurite outgrowth of neural precursor cells of the subventricular zone.

Solution of the internal and external problems of electrodynamics for a symmetrical vibrator with a reflector made of parallel straight conductors

Background. The work is aimed at the development and research of rigorous methods for calculating multi-element emitting and re-emitting structures, consisting mainly of the same type of elements, as well as studying the physical processes occurring in them. An iterative approach to solving the internal problem is proposed, which allows minimizing the cost of computer time and computer memory. Aim. In this work, using the proposed approach, we solve the internal and external problems of electrodynamics for a symmetrical vibrator with a reflector made of parallel straight conductors. The convergence of the iterative process is studied, the currents on the elements of the structure, its input resistance and radiation characteristics are calculated. Methods. The research is based on a strict electrodynamic approach, within the framework of which, for the specified structure in the thin-wire approximation, an integral representation of the electromagnetic field is formed, which, when considered on the surface of conductors together with boundary conditions, is reduced to a system of Fredholm integral equations of the second kind, written relative to unknown current distributions on conductors (internal task). The solution of the internal problem within the framework of the method of moments is reduced to solving a SLAE with a block matrix. Results. A mathematical model of a radiating structure is proposed, which is a symmetrical vibrator with a reflector made of parallel straight conductors. The internal and external problems of electrodynamics are formulated and solved for given parameter values. An effective algorithm for calculating the block matrix of SLAEs is proposed. Recommendations are given for the selection of systems of projection functions within the framework of the method of moments. The convergence of the iterative process for solving an internal problem of electrodynamics has been studied. The input resistance of the structure and the basic characteristics of its radiation are determined. Conclusion. A rational choice of systems of projection functions, based on the properties of the structure and its constituent elements, makes it possible to significantly reduce the size of the SLAE matrix and, accordingly, reduce computational costs. Taking into account the properties of the structure and its constituent elements also makes it possible to construct effective algorithms for calculating the SLAE matrix. It is shown that the convergence of the iterative process may be absent near resonant frequencies, therefore, when solving the internal problem, a combined approach should be used, which involves the use of both rigorous and approximate methods for solving SLAEs. At non-resonant frequencies, the iterative approach demonstrates its effectiveness. It is concluded that for such structures it is advisable to distinguish between resonant and non-resonant operating modes. In the non-resonant mode, the current functions have a fairly smooth dependence on frequency; in the resonant mode, these dependences become quite sharp and difficult to predict. In this regard, the task of developing an iterative approach to solving the internal problem of electrodynamics in resonant operating modes seems relevant.

A multifunctional and reconfigurable memristive neuron circuit

AbstractA memristive neuron circuit which is capable of encoding input information via temporal and adaptive frequency methods within the same structure is proposed. Its multifunctionality allows switching between these modes by adjusting circuit capacitors. Furthermore, it is investigated how other parameters like input voltage and resistance influence output properties for different encoding methods. This research contributes to the development of more flexible neuromorphic computing systems.

Thermally Coupled NTC Chip Thermistors: Their Properties and Applications.

Negative temperature coefficient (NTC) chip thermistors were thermally coupled to form a novel device (TCCT) aimed for application in microelectronics. It consists of two NTC chip thermistors Th1 and Th2, which are small in size (0603) and power (1/10 W). They are in thermal junction, but concurrently they are electrically isolated. The first thermistor Th1 generates heat as a self-heating component at a constant supply voltage U (input thermistor), while the second thermistor Th2 receives heat as a passive component (output thermistor). The temperature dependence R(T) of NTC chip thermistors was measured in the climatic test chamber, and the exponential factor B10/30 of thermistor resistance was determined. After that, a self-heating current I1 of the input thermistor was measured vs. supply voltage U and ambient temperature Ta as a parameter. Input resistance R1 was determined as a ratio of U and I1 while output thermistor resistance R2 was measured by a multimeter concurrently with the current I1. Temperatures T1 and T2 of both thermistors were determined using the Steinhart-Hart equation. Heat transfer, thermal response, stability, and inaccuracy were analyzed. The application of thermally coupled NTC chip thermistors is expected in microelectronics for the input to output electrical decoupling/thermal coupling of slow changeable signals.

Aging-associated weakening of the action potential in fast-spiking interneurons in the human neocortex

Aging is associated with the slowdown of neuronal processing and cognitive performance in the brain; however, the exact cellular mechanisms behind this deterioration in humans are poorly elucidated. Recordings in human acute brain slices prepared from tissue resected during brain surgery enable the investigation of neuronal changes with age. Although neocortical fast-spiking cells are widely implicated in neuronal network activities underlying cognitive processes, they are vulnerable to neurodegeneration. Herein, we analyzed the electrical properties of 147 fast-spiking interneurons in neocortex samples resected in brain surgery from 106 patients aged 11–84 years. By studying the electrophysiological features of action potentials and passive membrane properties, we report that action potential overshoot significantly decreases and spike half-width increases with age. Moreover, the action potential maximum-rise speed (but not the repolarization speed or the afterhyperpolarization amplitude) significantly changed with age, suggesting a particular weakening of the sodium channel current generated in the soma. Cell passive membrane properties measured as the input resistance, membrane time constant, and cell capacitance remained unaffected by senescence. Thus, we conclude that the action potential in fast-spiking interneurons shows a significant weakening in the human neocortex with age. This may contribute to the deterioration of cortical functions by aging.

Selective KCNQ2/3 Potassium Channel Opener ICA069673 Inhibits Excitability in Mouse Vagal Sensory Neurons

The excitability of vagal sensory neurons is abnormally enhanced in inflammatory visceral diseases, contributing to the unproductive and diffcult-to-treat neuronally based symptoms such as non-cardiac chest pain and excessive coughing. Identification of targets and modulators capable of regulating the excitability of vagal sensory neurons may lead to novel therapeutic options. The KCNQ/KV7/M-channel is increasingly recognized as an intrinsic regulator of excitability in neurons, and several neuronal KCNQ2/3-selective M-channel openers have been developed. This study aimed to characterize the effects of one of these KCNQ2/3-selective activators, ICA-069673, on the M-current (IM) in mouse nodose neurons, and to determine its effects on excitability and action potential firings using perforated patch-clamp technique. The results showed that ICA-069673 enhanced IM density, accelerated the activation and delayed the deactivation of M-channels in a concentration-dependent manner. The EC50 of ICA-069673 in enhancing IM determined at -30 mV is 0.52 μM. ICA-069673 at 10 μM shifted the voltage-dependent activation of IM in hyperpolarizing direction by -25.5 ± 4.1 mV (p<0.001) and increased the maximal conductance from 8.1 ± 4.0 to 12.6±7.4 nS/pF (p=0.031). In a total of 48 nodose neurons studied on voltage-clamp mode, ICA-069673 enhanced IM in 41 neurons (~85%). Consistent with its effects on IM, ICA-069673 induced a marked hyperpolarization of resting potential and reduced the input resistance. The hyperpolarizing effect was more pronounced in partially depolarized neurons. Moreover, ICA-069673 caused a 3-fold increase in the minimal amount of depolarizing current needed to evoke an action potential, and significantly limited the action potential firings in response to sustained suprathreshold stimulations. These results indicate that opening KCNQ2/3-mediated M-channels is suffcient to suppress the excitability and enhance spike accommodation in vagal sensory neurons, and provide evidence supporting further investigation into the effcacy of ICA-069673 in normalizing the aberrant vagal visceral nociception. The study is supported by NIH Grant R35HL155671. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Obtaining the maximum power from the source using step-up and step-down type pulse regulators that work on battery

Introduction. Pulse regulators are widely used to match the output resistance of the source with the load resistance in order to ensure the possibility of taking maximum power when the value of the load resistance changes. Problem. In the case of using non-traditional and renewable sources of electrical energy, for a more uniform supply of energy to the load, a battery is often connected to the output of the pulse regulator, which works in buffer mode. In such cases, the load for the pulse regulator will be the battery itself, and the role of the source load will be performed by the input resistance of the regulator. To ensure the mode of operation of the pulse regulator, in which the maximum power will be transmitted from the source to the load, it is necessary to know the regulating characteristics of the regulator. There are works that analyze the regulating characteristics of step-up and step-down pulse regulators, which are used to match the load with the output resistance of the source. At the same time, for the same purpose, pulse regulators of the step-up and step-down type can be used. Goal. The purpose of the work is to analyze the features of the operation of step-up and step-down type pulse regulators in the mode of maximum power transmission from the source to the battery, as well as to determine the conditions under which it is possible and appropriate to use such regulators for the specified purpose. Methodology. The regulating characteristics of step-up and step-down type pulse regulators with sequential and parallel switching on of the controlled key were determined and analyzed, taking into account the presence of a battery at their output. Results. It is shown that the transfer of energy from the source to the battery is possible only under certain modes of operation of the regulator, which depend on the type of regulator, as well as the amount of voltage on the battery. The conditions under which it is possible to draw the maximum power from the source are determined. Originality. Since the output resistance of the source and the load resistance are of the same order in the maximum power selection mode, the internal resistance of the power source was taken into account when determining the regulating characteristics of the regulators. Practical value. The obtained results made it possible to formulate practical recommendations for a justified choice of the regulator’s operating modes, depending on its type and the value of voltage on the battery. References 15, tables 1, figures 4.

Progressive Circuit Hyperexcitability in Mouse Neocortical Slice Cultures with Increasing Duration of Activity Silencing.

Forebrain neurons deprived of activity become hyperactive when activity is restored. Rebound activity has been linked to spontaneous seizures in vivo following prolonged activity blockade. Here, we measured the time course of rebound activity and the contributing circuit mechanisms using calcium imaging, synaptic staining, and whole-cell patch clamp in organotypic slice cultures of mouse neocortex. Calcium imaging revealed hypersynchronous activity increasing in intensity with longer periods of deprivation. While activity partially recovered 3 d after slices were released from 5 d of deprivation, they were less able to recover after 10 d of deprivation. However, even after the longer period of deprivation, activity patterns eventually returned to baseline levels. The degree of deprivation-induced rebound was age-dependent, with the greatest effects occurring when silencing began in the second week. Pharmacological blockade of NMDA receptors indicated that hypersynchronous rebound activity did not require activation of Hebbian plasticity. In single-neuron recordings, input resistance roughly doubled with a concomitant increase in intrinsic excitability. Synaptic imaging of pre- and postsynaptic proteins revealed dramatic reductions in the number of presumptive synapses with a larger effect on inhibitory than excitatory synapses. Putative excitatory synapses colocalizing PSD-95 and Bassoon declined by 39 and 56% following 5 and 10 d of deprivation, but presumptive inhibitory synapses colocalizing gephyrin and VGAT declined by 55 and 73%, respectively. The results suggest that with prolonged deprivation, a progressive reduction in synapse number is accompanied by a shift in the balance between excitation and inhibition and increased cellular excitability.

A Mathematical Model of Spontaneous Action Potential Based on Stochastics Synaptic Noise Dynamics in Non-Neural Cells

We developed a mathematical model to simulate the dynamics of background synaptic noise in non-neuronal cells. By employing the stochastic Ornstein–Uhlenbeck process, we represented excitatory synaptic conductance and integrated it into a whole-cell model to generate spontaneous and evoke cellular electrical activities. This single-cell model encompasses numerous biophysically detailed ion channels, depicted by a set of ordinary differential equations in Hodgkin–Huxley and Markov formalisms. Consequently, this approach effectively induced irregular spontaneous depolarizations (SDs) and spontaneous action potentials (sAPs), resembling electrical activity observed in vitro. The input resistance decreased significantly, while the firing rate of spontaneous action potentials increased. Moreover, alterations in the ability to reach the action potential threshold were observed. Background synaptic activity can modify the input/output characteristics of non-neuronal excitatory cells. Hence, suppressing these baseline activities could aid in identifying new pharmaceutical targets for various clinical diseases.

Ferroelectric Domain Wall Delayer and Low-Dropout Regulator.

A switching-type power converter providing an accurate and stable switching output voltage against line/load variations and power supply ripple is mostly complicated in system-on-chip power management integrated circuits (PMICs) within a limited occupation area. Here we fabricated domain wall (DW) nanodevices using an X-cut LiNbO3 thin film on silicon. The domain switching event occurs after a delay time predicted by Merz's law under the applied voltage. But the output current is irrespective of the applied voltage and can be adjusted by conducting wall width as well as input resistance in the circuit. The regulating currents appear repetitively across the volatile interfacial domains between the nanodevice and electrode under intermittently applied voltages. A wall-current-limited domain switching model is developed to explain the phenomenon. The multifunctional DW nanodevices with smaller occupation areas can serve as compact low-dropout regulators in PMICs, time-domain delayers in energy-efficient neural network systems, and on-chip electrostatic discharge protection besides nonvolatile memories and selectors.

АНАЛІЗ РЕЗУЛЬТАТІВ ЕКСПЕРИМЕНТАЛЬНИХ ДОСЛІДЖЕНЬ НЕОДНОРІДНОСТІ МЕРЕЖІ ПОСТІЙНОГО СТРУМУ

The modes of breakage of one line of network sections with parallel lines in electrical distribution networks of power supply to consumers of direct current electric transport have been studied. An analysis of the experimental data was carried out, the results of which indicate the presence of a dependence of the value of the variable component in the rectified current on the distance to the damaged area. Mathematical modeling of the breakage mode of one of the line sections in the network with a serial connection of three sections, each of which has parallel lines, has been carried out. The obtained results of mathematical modeling of the modes of operation of a direct current network with heterogeneity of different sections also indicate the possibility of using the sixth harmonic of the current to determine the occurrence of heterogeneity and the section with this heterogeneity. To reduce the influence of load changes when determining an inhomogeneous section, it is proposed to control the input impedance of the network at a frequency of 300 Hz. It has been established that in these regimes the resistance angle changes the most. A method for determining the occurrence of local damage to a direct current line and the distance to this damage location is proposed, which is based on moni-toring the value of the line current and the input resistance of the line at a frequency of 300 Hz. References 7, Figures 4, Tables 2.

Electrophysiological Recording from a "Model" Cell.

The muscle cell or neuron membrane is functionally equivalent to a resistor-capacitor (RC) circuit with the membrane resistance and capacitor in parallel. Once inserted inside the membrane, an electrode introduces a serial resistance and small capacitance to the RC circuit. Through a narrow opening at its tip (∼0.1-μm), current can pass through the electrode, into the cell, and back to the outside (ground) across the membrane to complete the circuit. This arrangement enables a voltage difference between the outside and inside of the cell membrane to be recorded. To determine cell membrane properties, a current can be injected into the cell through the electrode. One complication with this approach, however, is that the voltage difference measured with the electrode includes the voltage drop across the cell membrane and that across the electrode. Furthermore, a small amount of current is drawn by the electrode capacitor, thereby slowing the current flow across the membrane. Fortunately, most amplifiers are equipped with bridge balance and capacitance compensation functions so that the effects of the electrode on cell membrane properties can be canceled out or minimized. This protocol describes the basics of setting up and conducting electrophysiological experiments using a model cell. For the novice, a model cell provides a way to learn the operation of electrophysiology equipment and software without the anxiety of damaging living cells. This protocol also illustrates passive membrane properties such as the input resistance, capacitance, and time constant.

An improved CMOS second‐generation current controlled conveyor with enhanced tunable range of RX and its applications

SummaryThis paper presents a new CMOS‐based second‐generation current controlled conveyor (CCCII), based on a mixed translinear cell composed of CMOS‐based translinear elements, which offers a wide tunable range of four decades for the X‐terminal input resistance RX. The current‐controlled grounded and floating tunable resistors and multifunction filter with tunable cut‐off frequency have been realized to show the practical utility of the proposed CCCII architecture. Various performance evaluations have been carried out through simulations conducted on Cadence Virtuoso software using 0.18 μm gpdk CMOS technology at a supply voltage of ±1.5 V. Simulation results show the effectiveness of the proposed CCCII in attaining a wide tunable Rx ranging from 130 MΩ to 13 kΩ, offering good linearity, nearly unity voltage and current transfer gains, high input impedance at port Y varying from 3.7 GΩ to 1.18 MΩ, high output impedance at port Z varying from 67.63 GΩ to 13.19 MΩ, with the power consumption in the range of 3.68 μW to 18.78 μW for variation in bias current (Io) from 100 pA to 1 μA.

Intelligent MPPT control for SEPIC-Luo converter in grid tied photovoltaic system

Grid connected solar photovoltaic (SPV) systems are becoming more and more common due to steadily rising energy demand. The advantages of photovoltaic power generation, such as its eco-friendliness, low maintenance requirements, and lack of noise, are making it as a significant renewable energy source (RES). This framework presents the modeling and control design of PV grid tied system implemented with integrated single ended primary inductance (SEPIC) Luo converter. The main goal of this work includes investigating solar PV system behaviour and creating an effective grid connected solar power. Solar PV module tracks maximum power, with an aid of chaotic cascaded fuzzy a maximum power point tracking (MPPT) has developed. The DC voltage obtained is fed to 1Φ voltage source inverter (VSI) for conversion of AC voltage. In comparison to typical PWM control, the spectrum performance of the examined voltages is improved by adjusting the nominal duty cycle of main switch of SEPIC-Luo converter. So that PV output impedance is equivalent to DC-DC converter's input resistance. Finally, the obtained AC voltage is supplied to 1Φ grid for further applications. With less THD, an efficiency of 96% is achieved when the implementation of the suggested system is carried out using MATLAB/Simulink.

Application of near infra-red laser light increases current threshold in optic nerve consistent with increased Na+-dependent transport

Increases in the current threshold occur in optic nerve axons with the application of infra-red laser light, whose mechanism is only partly understood. In isolated rat optic nerve, laser light was applied near the site of electrical stimulation, via a flexible fibre optic. Paired applications of light produced increases in threshold that were reduced on the second application, the response recovering with increasing delays, with a time constant of 24 s. 3-min duration single applications of laser light gave rise to a rapid increase in threshold followed by a fade, whose time-constant was between 40 and 50 s. After-effects were sometimes apparent following the light application, where the resting threshold was reduced. The increase in threshold was partially blocked by 38.6 mM Li+ in combination with 5 μ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\mu$$\\end{document}M bumetanide, a manoeuvre increasing refractoriness and consistent with axonal depolarization. Assessing the effect of laser light on the nerve input resistance ruled out a previously suggested fall in myelin resistance as contributing to threshold changes. These data appear consistent with an axonal membrane potential that partly relies on temperature-dependent electroneutral Na+ influx, and where fade in the response to the laser may be caused by a gradually diminishing Na+ pump–induced hyperpolarization, in response to falling intracellular [Na+].

Comprehensive Noise Modeling of Piezoelectric Charge Accelerometer with Signal Conditioning Circuit.

This paper reports on noise modeling of a piezoelectric charge accelerometer with a signal conditioning circuit. The charge output is converted into voltage and amplified using a JFET operational amplifier that has high input resistance and low noise. The noise sources in the whole system include electrical and mechanical thermal noises of the accelerometer, thermal noises of resistors, and voltage and current noises of the operational amplifier. Noise gain of each source is derived from small signal circuit analysis. It is found that the feedback resistor of the operational amplifier is a major source of noise in low frequencies, whereas electrical thermal noise of the accelerometer dominates the rest of spectrum. This method can be used to pair a highly sensitive sensor with a single JFET operational amplifier instead of a multi-stage signal conditioning circuit.

Optoelectronic Transimpedance Converter Based on MOS Photovaricap for High Resistive Gas Sensors

The gas detectors consist of two parts: metal-oxides gas sensor and transducer. The sensing material is made of a thin semiconductor layer. The transducer is responsible for converting the change in the several physical parameters of the thin sensitive layer into a measurable signal. Due to the high output resistance of high resistive gas sensors and the low input currents of amplifiers, electrometric cascades are employed, followed by the conversion of the gas sensors small direct current into an active current signal using a mechanical modulator (dynamic capacitor) to enhance sensitivity and stability. The aim of this research is to analyze the main characteristics of a novel type of dynamic capacitor that utilizes a surface metal-oxide-semiconductor (MOS) photovaricap (PV) as the regulating element when detecting signals from high resistive gas sensors. For the creation of surface MOS PVs, samples of p-Si with varying resistivity were chosen. A thin layer of SiO2 was deposited on these samples, onto which a translucent metallic electrode was applied. Modulation of the PV capacitance was achieved by illuminating it with a gallium arsenide LED. As a result, the capacitance of the PV is changed, producing a variable voltage across the load resistor, which was then amplified and recorded. It was observed that the settling time of the useful signal is determined by two factors. The first is the RC chain composed of the load resistance of the gas sensor and the input capacitance of the PV, and the second is slow relaxation phenomena in the structure of the MOS PV that lead to the screening of the induced charge. Characteristics of the MOS PV as a dynamic capacitor and the features of the photo capacitance as a semiconductor element, in turn, determine the transimpedance conversion coefficient. The conducted research showed that MOS PVs can be applied to register small DC currents and voltages from high resistive gas sensors. In this case, ordinary narrowband or wideband amplifiers with relatively low input resistance can be used instead of electrometric amplifiers with mechanical dynamic capacitors. The considered circuit has been experimentally tested with commercial resistors.

Excitatory action of low frequency depolarizing GABA/glycine synaptic inputs is prevalent in prenatal spinal SOD1G93A motoneurons.

Amyotrophic lateral sclerosis (ALS) is a fatal adult-onsetneurodegenerative disease characterized by progressive motor neuron degeneration and muscle paralysis. Recent evidence suggests the dysfunction of inhibitory signalling in ALS motor neurons. We have shown that embryonic day (E)17.5spinal motoneurons (MNs) of the SOD1G93A mouse model of ALS exhibit an altered chloride homeostasis. At this prenatal stage, inhibition of spinal motoneurons (MNs) is mediated by depolarizing GABAergic/glycinergic postsynaptic potentials (dGPSPs). Here, using an ex vivo preparation and patch clamp recording from MNs with a chloride equilibrium set below spike threshold, we report that low input resistance (Rin ) E17.5 MNs from the SOD1G93A ALS mouse model do not correctly integrate dGPSPs evoked by electrical stimulations of GABA/glycine inputs at different frequencies. Indeed, firing activity of most wild-type (WT) MNs with low Rin was inhibited by incoming dGPSPs, whereas low Rin SOD1G93A MNs were excited or exhibited a dual response (excited by low frequency dGPSPs and inhibited by high frequency dGPSPs). Simulation highlighted the importance of the GABA/glycine input density and showed that pure excitation could be obtained in SOD-like MNs by moving GABA/glycine input away from the cell body to dendrites. This was in agreement with confocal imaging showing a lack of peri-somatic inhibitory terminals in SOD1G93A MNs compared to WT littermates. Putative fast ALS-vulnerable MNs with low Rin are therefore lacking functional inhibition at the near-term prenatal stage. KEY POINTS: We analysed the integration of GABAergic/glycinergic synaptic events by embryonic spinal motoneurons (MNs) in a mouse model of the amyotrophic lateral sclerosis (ALS) neurodegenerative disease. We found that GABAergic/glycinergic synaptic events do not properly inhibit ALS MNs with low input resistance, most probably corresponding to future vulnerable MNs. We used a neuron model to highlight the importance of the GABA/glycine terminal location and density in the integration of the GABAergic/glycinergic synaptic events. Confocal imaging showed a lack of GABA/glycine terminals on the cell body of ALS MNs. The present study suggests that putative ALS vulnerable MNs with low Rin lack functional inhibition at the near-term stage.