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Journal of Magnetic Resonance (San... Sep 2022We review recent efforts to develop and apply an experimental approach to the structural characterization of transient intermediate states in biomolecular processes that... (Review)
Review
We review recent efforts to develop and apply an experimental approach to the structural characterization of transient intermediate states in biomolecular processes that involve large changes in molecular conformation or assembly state. This approach depends on solid state nuclear magnetic resonance (ssNMR) measurements that are performed at very low temperatures, typically 25-30 K, with signal enhancements from dynamic nuclear polarization (DNP). This approach also involves novel technology for initiating the process of interest, either by rapid mixing of two solutions or by a rapid inverse temperature jump, and for rapid freezing to trap intermediate states. Initiation by rapid mixing or an inverse temperature jump can be accomplished in approximately-one millisecond. Freezing can be accomplished in approximately 100 microseconds. Thus, millisecond time resolution can be achieved. Recent applications to the process by which the biologically essential calcium sensor protein calmodulin forms a complex with one of its target proteins and the process by which the bee venom peptide melittin converts from an unstructured monomeric state to a helical, tetrameric state after a rapid change in pH or temperature are described briefly. Future applications of millisecond time-resolved ssNMR are also discussed briefly.
Topics: Magnetic Resonance Spectroscopy; Molecular Conformation; Nuclear Magnetic Resonance, Biomolecular; Peptides; Proteins
PubMed: 35998398
DOI: 10.1016/j.jmr.2022.107285 -
Frontiers in Psychology 2022Random Dot Motion (RDM) displays refer to clouds of independently moving dots that can be parametrically manipulated to provide a perception of the overall cloud moving...
Random Dot Motion (RDM) displays refer to clouds of independently moving dots that can be parametrically manipulated to provide a perception of the overall cloud moving coherently in a specified direction of motion. As a well-studied probe of motion perception, RDMs have been widely employed to understand underlying neural mechanisms of motion perception, perceptual decision-making, and perceptual learning, among other processes. Despite their wide use, RDM stimuli implementation is highly dependent on the parameters and the generation algorithm of the stimuli; both can greatly influence behavioral performance on RDM tasks. With the advent of the COVID pandemic and an increased need for more accessible platforms, we aimed to validate a novel RDM paradigm on Inquisit Millisecond, a platform for the online administration of cognitive and neuropsychological tests and assessments. We directly compared, in the same participants using the same display, a novel RDM paradigm on both Inquisit Millisecond and MATLAB with Psychtoolbox. We found that psychometric functions of Coherence largely match between Inquisit Millisecond and MATLAB, as do the effects of Duration. These data demonstrate that the Millisecond RDM provides data largely consistent with those previously found in laboratory-based systems, and the present findings can serve as a reference point for expected thresholds for when these procedures are used remotely on different platforms.
PubMed: 36562063
DOI: 10.3389/fpsyg.2022.1035518 -
International Journal of Molecular... Dec 2020An action potential (AP) triggers neurotransmitter release from synaptic vesicles (SVs) docking to a specialized release site of presynaptic plasma membrane, the active... (Review)
Review
An action potential (AP) triggers neurotransmitter release from synaptic vesicles (SVs) docking to a specialized release site of presynaptic plasma membrane, the active zone (AZ). The AP simultaneously controls the release site replenishment with SV for sustainable synaptic transmission in response to incoming neuronal signals. Although many studies have suggested that the replenishment time is relatively slow, recent studies exploring high speed resolution have revealed SV dynamics with milliseconds timescale after an AP. Accurate regulation is conferred by proteins sensing Ca entering through voltage-gated Ca channels opened by an AP. This review summarizes how millisecond Ca dynamics activate multiple protein cascades for control of the release site replenishment with release-ready SVs that underlie presynaptic short-term plasticity.
Topics: Animals; Humans; Neuronal Plasticity; Neurotransmitter Agents; Presynaptic Terminals; Synaptic Transmission
PubMed: 33396919
DOI: 10.3390/ijms22010327 -
International Journal of Molecular... Aug 2020Serial crystallography (SX) using X-ray free electron laser or synchrotron X-ray allows for the determination of structures, at room temperature, with reduced radiation...
Serial crystallography (SX) using X-ray free electron laser or synchrotron X-ray allows for the determination of structures, at room temperature, with reduced radiation damage. Moreover, it allows for the study of structural dynamics of macromolecules using a time-resolved pump-probe, as well as mix-and-inject experiments. Delivering a crystal sample using a viscous medium decreases sample consumption by lowering the flow rate while being extruded from the injector or syringe as compared to a liquid jet injector. Since the environment of crystal samples varies, continuous development of the delivery medium is important for extended SX applications. Herein, I report the preparation and characterization of a lard-based sample delivery medium for SX. This material was obtained using heat treatment, and then the soluble impurities were removed through phase separation. The lard injection medium was highly stable and could be injected via a syringe needle extruded at room temperature with a flow rate < 200 nL/min. Serial millisecond crystallography experiments were performed using lard, and the room temperature structures of lysozyme and glucose isomerase embedded in lard at 1.75 and 1.80 Å, respectively, were determined. The lard medium showed X-ray background scattering similar or relatively lower than shortenings and lipidic cubic phase; therefore, it can be used as sample delivery medium in SX experiments.
Topics: Crystallography, X-Ray; Lipids; Viscosity
PubMed: 32825186
DOI: 10.3390/ijms21175977 -
IScience Sep 2021Neurons in the visual cortex quickly adapt to constant input, which should lead to perceptual fading within few tens of milliseconds. However, perceptual fading is...
Neurons in the visual cortex quickly adapt to constant input, which should lead to perceptual fading within few tens of milliseconds. However, perceptual fading is rarely observed in everyday perception, possibly because eye movements refresh retinal input. Recently, it has been suggested that amplitudes of large saccadic eye movements are scaled to maximally decorrelate presaccadic and postsaccadic inputs and thus to annul perceptual fading. However, this argument builds on the assumption that adaptation within naturally brief fixation durations is strong enough to survive any visually disruptive saccade and affect perception. We tested this assumption by measuring the effect of luminance adaptation on postsaccadic contrast perception. We found that postsaccadic contrast perception was affected by presaccadic luminance adaptation during brief periods of fixation. This adaptation effect emerges within 100 milliseconds and persists over seconds. These results indicate that adaptation during natural fixation periods can affect perception even after visually disruptive saccades.
PubMed: 34485868
DOI: 10.1016/j.isci.2021.102986 -
JACC. Clinical Electrophysiology Dec 2022Takotsubo syndrome is associated with life threatening arrhythmias, and the apical ballooning pattern is characterized by a peculiar QT prolongation and particularly... (Review)
Review
BACKGROUND
Takotsubo syndrome is associated with life threatening arrhythmias, and the apical ballooning pattern is characterized by a peculiar QT prolongation and particularly high-risk of arrhythmias.
OBJECTIVES
The aim of the study was to determine the association of QT interval on electrocardiogram for ventricular arrhythmic complications in patients with apical ballooning Takotsubo syndrome in a diverse population at a large urban hospital in the U.S.
METHODS
We reviewed 105 cases of apical ballooning Takotsubo syndrome in patients admitted between 2011 and 2017. Two cardiologists reviewed the electrocardiograms to measure QT interval, adjusted for rate using the Fridericia formula (QTF), and ventricular arrhythmic complications during the hospitalization. Data are reported as median and interquartile range or number and percentage.
RESULTS
Of the 105 patients, 86 (82%) were female, and 34 (32%) were self-reported Black or African American. The mean age was 65 years (range: 58-72 years). Left ventricular ejection fraction was 25% (range: 25%-35%). Heart rate was 101 beats/min (range: 83-121 beats/min). Ten (11%) patients experienced a ventricular arrhythmic complication and had significantly longer QTF (470 [range: 422-543] milliseconds) than did those without complications (417 [range: 383-456] milliseconds, P = 0.031). The area under the curve for QTF was 0.708 (95% CI: 0.536-0.880; P = 0.031). Twenty-eight (27%) patients had a QTF ≥460 milliseconds and significantly more arrhythmic complications (21% vs 5%, odds ratio 4.997 [95% CI: 1.288-19.237], P = 0.021). QTF was an independent predictor of ventricular arrhythmias: odds ratio 1.090 for each 10-millisecond increase in QTF (95% CI: 1.004-1.183; P = 0.040, corrected for sex).
CONCLUSIONS
In a diverse population of patients with apical ballooning Takotsubo syndrome admitted to a large urban hospital in the United States, QTF at admission ≥460 milliseconds identifies patients at high risk for in-hospital arrhythmic complications. Further studies are needed to determine strategies aimed at shortening QT interval to potentially prevent life-threatening arrhythmic events.
Topics: Humans; Female; Aged; Male; Takotsubo Cardiomyopathy; Stroke Volume; Ventricular Function, Left; Long QT Syndrome; Arrhythmias, Cardiac; Hospitals
PubMed: 36543499
DOI: 10.1016/j.jacep.2022.08.010 -
Journal of Neurophysiology Sep 2022Neurons are embedded in complex networks, where they participate in repetitive, coordinated interactions with other neurons. Neuronal spike timing is thus predictably...
Neurons are embedded in complex networks, where they participate in repetitive, coordinated interactions with other neurons. Neuronal spike timing is thus predictably constrained by a range of ionic currents that shape activity at both short (milliseconds) and longer (tens to hundreds of milliseconds) timescales, but we lack analytical tools to rigorously identify these relationships. Here, we innovate a modeling approach to test the relationship between oscillations in the local field potential (LFP) and neuronal spike timing. We use kernel density estimation to relate single neuron spike timing and the phase of LFP rhythms (in simulated and hippocampal CA1 neuronal spike trains). We then combine phase and short (3 ms) spike history information within a logistic regression framework ("phaseSH models"), and show that models that leverage refractory constraints and oscillatory phase information can effectively test whether-and the degree to which-rhythmic currents (as measured from the LFP) reliably explain variance in neuronal spike trains. This approach allows researchers to systematically test the relationship between oscillatory activity and neuronal spiking dynamics as they unfold over time and as they shift to adapt to distinct behavioral conditions. Statistical models that incorporate neural spiking history and relationships to the phase of ongoing oscillations in the local field potential robustly capture and predict neuronal engagement in rhythmic processes. These models constitute a powerful tool to systematically test explicit hypotheses regarding the specific rhythmic currents that constrain neural spiking activity over time and during different behaviors.
Topics: Action Potentials; Hippocampus; Models, Neurological; Neurons
PubMed: 35858125
DOI: 10.1152/jn.00423.2021 -
Proceedings of the National Academy of... Oct 2019Human speech comprehension is remarkable for its immediacy and rapidity. The listener interprets an incrementally delivered auditory input, millisecond by millisecond as...
Human speech comprehension is remarkable for its immediacy and rapidity. The listener interprets an incrementally delivered auditory input, millisecond by millisecond as it is heard, in terms of complex multilevel representations of relevant linguistic and nonlinguistic knowledge. Central to this process are the neural computations involved in semantic combination, whereby the meanings of words are combined into more complex representations, as in the combination of a verb and its following direct object (DO) noun (e.g., "eat the apple"). These combinatorial processes form the backbone for incremental interpretation, enabling listeners to integrate the meaning of each word as it is heard into their dynamic interpretation of the current utterance. Focusing on the verb-DO noun relationship in simple spoken sentences, we applied multivariate pattern analysis and computational semantic modeling to source-localized electro/magnetoencephalographic data to map out the specific representational constraints that are constructed as each word is heard, and to determine how these constraints guide the interpretation of subsequent words in the utterance. Comparing context-independent semantic models of the DO noun with contextually constrained noun models reflecting the semantic properties of the preceding verb, we found that only the contextually constrained model showed a significant fit to the brain data. Pattern-based measures of directed connectivity across the left hemisphere language network revealed a continuous information flow among temporal, inferior frontal, and inferior parietal regions, underpinning the verb's modification of the DO noun's activated semantics. These results provide a plausible neural substrate for seamless real-time incremental interpretation on the observed millisecond time scales.
Topics: Adolescent; Adult; Auditory Perception; Brain; Comprehension; Electroencephalography; Female; Humans; Linguistics; Magnetoencephalography; Male; Semantics; Speech Perception; Young Adult
PubMed: 31570590
DOI: 10.1073/pnas.1903402116 -
PloS One 2021Recently, a new defibrillation modality using nanosecond pulses was shown to be effective at much lower energies than conventional 10 millisecond monophasic shocks in ex...
AIMS
Recently, a new defibrillation modality using nanosecond pulses was shown to be effective at much lower energies than conventional 10 millisecond monophasic shocks in ex vivo experiments. Here we compare the safety factors of 300 nanosecond and 10 millisecond shocks to assess the safety of nanosecond defibrillation.
METHODS AND RESULTS
The safety factor, i.e. the ratio of median effective doses (ED50) for electroporative damage and defibrillation, was assessed for nanosecond and conventional (millisecond) defibrillation shocks in Langendorff-perfused New Zealand white rabbit hearts. In order to allow for multiple shock applications in a single heart, a pair of needle electrodes was used to apply shocks of varying voltage. Propidium iodide (PI) staining at the surface of the heart showed that nanosecond shocks had a slightly lower safety factor (6.50) than millisecond shocks (8.69), p = 0.02; while PI staining cross-sections in the electrode plane showed no significant difference (5.38 for 300 ns shocks and 6.29 for 10 ms shocks, p = 0.22).
CONCLUSIONS
In Langendorff-perfused rabbit hearts, nanosecond defibrillation has a similar safety factor as millisecond defibrillation, between 5 and 9, suggesting that nanosecond defibrillation can be performed safely.
Topics: Animals; Electric Countershock; Electrodes; Electrophysiology; Electroporation; Female; Heart; Isolated Heart Preparation; Male; Propidium; Rabbits; Safety; Ventricular Fibrillation
PubMed: 34559811
DOI: 10.1371/journal.pone.0257287 -
Biophysical Journal Oct 2020Biological cells deform on a nanometer scale when their transmembrane voltage changes, an effect that has been visualized during the action potential using quantitative...
Biological cells deform on a nanometer scale when their transmembrane voltage changes, an effect that has been visualized during the action potential using quantitative phase imaging. Similar changes in the optical path length have been observed in photoreceptor outer segments after a flash stimulus via phase-resolved optical coherence tomography. These optoretinograms reveal a fast, millisecond-scale contraction of the outer segments by tens of nanometers, followed by a slow (hundreds of milliseconds) elongation reaching hundreds of nanometers. Ultrafast measurements of the contractile response using line-field phase-resolved optical coherence tomography show a logarithmic increase in amplitude and a decreasing time to peak with increasing stimulus intensity. We present a model that relates the early receptor potential to these deformations based on the voltage-dependent membrane tension-the mechanism observed earlier in neurons and other electrogenic cells. The early receptor potential is caused by conformational changes in opsins after photoisomerization, resulting in the fractional shift of the charge across the disk membrane. Lateral repulsion of the ions on both sides of the membrane affects its surface tension and leads to its lateral expansion. Because the volume of the disks does not change on a millisecond timescale, their lateral expansion leads to an axial contraction of the outer segment. With increasing stimulus intensity and the resulting tension, the area expansion coefficient of the disk membrane also increases as thermally induced fluctuations are pulled flat, resisting further expansion. This leads to the logarithmic saturation observed in measurements as well as the peak shift in time. This imaging technique therefore relates the structural changes in the photoreceptor to the underlying neurological function of transducing light into electrical signals. Such label-free optical monitoring of neural activity using fast interferometry may be applicable not only to optoretinography but also to neuroscience in general.
Topics: Action Potentials; Interferometry; Ions; Neurons; Photoreceptor Cells
PubMed: 33031739
DOI: 10.1016/j.bpj.2020.09.005