Explore the vast range of titles available.

General anesthesia induced by etomidate, barbiturates and propofol is associated with positive modulation of synaptic [alpha][beta][gamma] GABA.sub.A receptors, inhibitory hetero-pentameric ligand-gated ion channels formed from homologous subunits arranged [beta]-[alpha]-[beta]-[alpha]-[gamma] around a central gated chloride channel. Approaches based on mutations, amino-acid level analysis of photolabel incorporation, and cryo-electron micrography (cryo-EM) all indicate that etomidate binds selectively in two outer transmembrane [beta]+/[alpha]- inter-subunit sites per receptor. These approaches also reveal that the potent barbiturate photolabel R-mTFD-MPAB binds selectively in homologous sites formed at [alpha]+/[beta]- and [gamma]+/[beta]- interfaces. The anesthetic photolabel, pTFD-di-iPr-BnOH, was proposed to bind selectively in [alpha]+/[beta]- and [alpha]+/[gamma]- homologs of the etomidate sites, based largely on functional analysis of only 5 point mutations in [alpha]1[beta]3[gamma]2L receptors. To further test the interactions of receptor-bound pTFD-di-iPr-BnOH with outer transmembrane inter-subunit sites, we used voltage-clamp electrophysiology in substituted cysteine modification and protection (SCAMP) experiments at 8 residues located in the five homologous sites, focusing on [alpha]+ and [gamma]- loci. Control SCAMP studies were performed using etomidate and R-mTFD-MPAB. Incorporation of single cysteine mutations ([alpha]1M236C, [alpha]1S280C, [alpha]1A291C, [beta]3L231C, [beta]3M286C, [gamma]2I242C, [gamma]2L246C, and [gamma]2S301C) produced functional GABA-responsive receptors that retained sensitivity to pTFD-di-iPr-BnOH modulation and displayed increased GABA sensitivity following exposure to the covalent sulfhydryl modifier p-chloromercuribenzenesulfonate (pCMBS). In the presence of pTFD-di-iPr-BnOH, pCMBS modification effects were reduced (evidence of steric protection) in receptors with cysteine mutations in [alpha]+, [beta]-, and [gamma]-, but not in [alpha]-, [beta]+, or [gamma]+ interfacial loci. Protection patterns with etomidate and R-mTFD-MPAB mirrored prior results. SCAMP results further support the hypothesis that pTFD-di-iPr-BnOH binds selectively in [alpha]+/[beta]- and [alpha]+/[gamma]- interfacial sites that are homologs of the [beta]+/[alpha]- etomidate sites.

The patch clamp technique has become the gold standard for neuron electrophysiology research in brain science. Brain slices have been widely utilized as the targets of the patch clamp technique due to their higher optical transparency compared to a live brain and their intercellular connectivity in comparison to cultured single neurons. However, the narrow working space, small scope, and depth of the field of view make the positioning of the operation’s micropipette to the target neuron a time-consuming task reliant on a high level of experience, significantly slowing down operation of the patch clamp technique in brain slices. Further, the current poor controllability in gigaseal formation, which is the key to electrophysiology signal recording, significantly lowers the patch clamp success rate. In this paper, a stepwise navigation of the micropipette is conducted to accelerate the positioning process of the micropipette tip to the target neuron in the brain slice. Then, a fuzzy proportional–integral–derivative controller is designed to control the gigaseal formation process along a designed resistance curve. The experimental results demonstrate an almost doubled patch clamp technique speed, with a 25% improvement in the success rate compared to the conventional manual method. The above advantages may promote the application of our method in brain science research based on brain slice platforms.

We previously reported that a single 5 ns high intensity electric pulse (NEP) caused an E-field-dependent decrease in peak inward voltage-gated Na.sup.+ current (I.sub.Na) in isolated bovine adrenal chromaffin cells. This study explored the effects of a pair of 5 ns pulses on I.sub.Na recorded in the same cell type, and how varying the E-field amplitude and interval between the pulses altered its response. Regardless of the E-field strength (5 to 10 MV/m), twin NEPs having interpulse intervals [greater than or equal to] than 5 s caused the inhibition of TTX-sensitive I.sub.Na to approximately double relative to that produced by a single pulse. However, reducing the interval from 1 s to 10 ms between twin NEPs at E-fields of 5 and 8 MV/m but not 10 MV/m decreased the magnitude of the additive inhibitory effect by the second pulse in a pair on I.sub.Na . The enhanced inhibitory effects of twin vs single NEPs on I.sub.Na were not due to a shift in the voltage-dependence of steady-state activation and inactivation but were associated with a reduction in maximal Na.sup.+ conductance. Paradoxically, reducing the interval between twin NEPs at 5 or 8 MV/m but not 10 MV/m led to a progressive interval-dependent recovery of I.sub.Na, which after 9 min exceeded the level of I.sub.Na reached following the application of a single NEP. Disrupting lipid rafts by depleting membrane cholesterol with methyl-[beta]-cyclodextrin enhanced the inhibitory effects of twin NEPs on I.sub.Na and ablated the progressive recovery of this current at short twin pulse intervals, suggesting a complete dissociation of the inhibitory effects of twin NEPs on this current from their ability to stimulate its recovery. Our results suggest that in contrast to a single NEP, twin NEPs may influence membrane lipid rafts in a manner that enhances the trafficking of newly synthesized and/or recycling of endocytosed voltage-gated Na.sup.+ channels, thereby pointing to novel means to regulate ion channels in excitable cells.

Although the technique of somatic voltage clamp is widely used, computational models have predicted that this controls voltage in the dendritic tree poorly. Williams and Mitchell directly quantify this error using simultaneous recordings from the soma and apical dendrites of rat neocortical pyramidal neurons. Spruston and Johnston also highlight this in an associated news and views. The somatic voltage clamp technique has revolutionized understanding of synaptic physiology and the excitability of neurons. Although computer simulations have indicated that the somatic voltage clamp poorly controls voltage in the dendritic tree of neurons, where the majority of synaptic contacts are made, there has not been an experimental description of the performance of the somatic voltage clamp. Here, we directly quantify errors in the measurement of dendritic synaptic input by the somatic voltage clamp using simultaneous whole-cell recordings from the soma and apical dendrite of rat neocortical pyramidal neurons. The somatic voltage clamp did not control voltage at sites other than the soma and distorted measurement of the amplitude, kinetics, slope conductance and reversal potential of synaptic inputs in a dendritic distance–dependent manner. These errors question the use of the somatic voltage clamp as a quantitative tool in dendritic neurons.

The authors isolated the refinement of auditory thalamocortical connectivity by in vivo recordings and day-by-day voltage-sensitive dye imaging in an acute brain slice preparation. They find that postnatal connectivity between thalamus and cortex determines a critical period for plasticity in the auditory system. Neural circuits are shaped by experience during periods of heightened brain plasticity in early postnatal life. Exposure to acoustic features produces age-dependent changes through largely unresolved cellular mechanisms and sites of origin. We isolated the refinement of auditory thalamocortical connectivity by in vivo recordings and day-by-day voltage-sensitive dye imaging in an acute brain slice preparation. Passive tone-rearing modified response strength and topography in mouse primary auditory cortex (A1) during a brief, 3-d window, but did not alter tonotopic maps in the thalamus. Gene-targeted deletion of a forebrain-specific cell-adhesion molecule ( Icam5 ) accelerated plasticity in this critical period. Consistent with its normal role of slowing spinogenesis, loss of Icam5 induced precocious stubby spine maturation on pyramidal cell dendrites in neocortical layer 4 (L4), identifying a primary locus of change for the tonotopic plasticity. The evolving postnatal connectivity between thalamus and cortex in the days following hearing onset may therefore determine a critical period for auditory processing.

The aim of this paper was to investigate the influence of four different external factors (acetylcholine, ethanol, temperature and lidocaine hydrochloride) on PC12 quasi-neuronal networks by multielectrode-array-based Voltage Threshold Measurement Method (VTMM). At first, VTMM was employed to measure the lowest amplitude of the voltage stimulating pulses that could just trigger the action potential from PC12 quasi-neuronal networks under normal conditions, and the amplitude was defined as the normal voltage threshold ( V Th ). Then the changes of the V Th of PC12 quasi-neuronal networks treated by the four external factors were tested respectively. The results showed the normal V Th of PC12 quasi-neuronal networks was 36 mV. The V Th has negative correlation with the concentration of acetylcholine and has positive correlation with the concentration of ethanol. The curves of the correlation of the V Th with temperature and the concentration of lidocaine hydrochloride were U-shaped and Λ-shaped respectively. Comparing with our earlier studies on hippocampal neuronal networks and hippocampal slices, PC12 quasi-neuronal networks not only had the same typical voltage threshold characteristic, but also had similar changes on electrical excitability when treated by the four external factors mentioned above. Therefore, the rapid-formed PC12 quasi-neuronal networks could replace neuronal networks in proper conditions, and VTMM could be used to analyze the influence of external factors on the electrical excitability of PC12 quasi-neuronal networks.

We provide here detailed electrophysiological protocols to study voltage-gated sodium channels and to investigate how wild-type and mutant channels influence firing properties of transfected mammalian dorsal root ganglion (DRG) neurons. Whole-cell voltage-clamp recordings permit us to analyze kinetic and voltage-dependence properties of ion channels and to determine the effect and mode of action of pharmaceuticals on specific channel isoforms. They also permit us to analyze the role of individual sodium channels and their mutant derivatives in regulating firing of DRG neurons. Five to ten cells can be recorded daily, depending on the extent of analysis that is required. Because of different internal solutions that are used in voltage-clamp and current-clamp recordings, only limited information can be obtained from recording the same neuron in both modes. These electrophysiological studies help to elucidate the role of specific channels in setting threshold and suprathreshold responses of neurons, under normal and pathological conditions.

Switching converters are used in electric drive applications to produce variable voltage, variable frequency supply which generates harmful large dv/dt and high-frequency common mode voltages (CMV). Multilevel inverters generate lower CMV as compared to conventional two-level inverters. This paper presents simple carrier-based technique to control the common mode voltages in multilevel inverters using different structures of sine-triangle comparison method such as phase disposition (PD), phase opposition disposition (POD) by adding common mode voltage offset signal to actual reference voltage signal. This paper also presented the method to optimize the magnitude of this offset signal to reduce CMV and total harmonic distortion in inverter output voltage. The presented techniques give comparable performance as obtained in complex space vector-based control strategy, in terms of number of commutations, magnitude, and rate of change of CMV and harmonic profile of inverter output voltage. Simulation and experimental results presented confirm the effectiveness of the proposed techniques to control the common mode voltages.