scholarly journals Focal seizures are organized by feedback between neural activity and ion concentration changes

2021 ◽  
Author(s):  
Damiano Gentiletti ◽  
Marco de Curtis ◽  
Vadym Gnatkovsky ◽  
Piotr Suffczynski
Keyword(s):  
Low Voltage ◽  
Ion Concentration ◽  
Elementary Processes ◽  
Focal Seizures ◽  
Fast Discharge ◽  
Eeg Data ◽  
Concentration Changes ◽  
Physical Laws ◽  
Rhythmic Burst ◽  
Animal Eeg

AbstractHuman and animal EEG data demonstrate that focal seizures start with low-voltage fast activity, evolve into rhythmic burst discharges and are followed by a period of suppressed background activity. This suggests that processes with dynamics in the range of tens of seconds govern focal seizure evolution. We investigate the processes associated with seizure dynamics by complementing the Hodgkin-Huxley mathematical model with the physical laws that dictate ion movement and maintain ionic gradients. We show that the disturbance of K+and Cl−homeostasis by the fast discharge of inhibitory interneurons is sufficient to initiate seizures, which are maintained by positive feedback between ion concentration changes and neuronal activity. Gradual Na+accumulation increases the rate of the Na+/K+-pump, creating negative feedback which slows down and terminates ictal discharges and contributes to the postictal state. Our results emphasize ionic dynamics as elementary processes behind seizure generation and indicate targets for new therapeutic strategies.

Ion concentration changes observed in drizzling rains

1997 ◽  
Vol 45 (3) ◽  
pp. 165-182 ◽  
Author(s):  
Hiroaki Minoura ◽  
Yasunobu Iwasaka
Keyword(s):  
Ion Concentration ◽  
Concentration Changes

scholarly journals Relationships between resting conductances, excitability, and t-system ionic homeostasis in skeletal muscle

2011 ◽  
Vol 138 (1) ◽  
pp. 95-116 ◽  
Author(s):  
James A. Fraser ◽  
Christopher L.-H. Huang ◽  
Thomas H. Pedersen
Keyword(s):  
Skeletal Muscle ◽  
Membrane Potential ◽  
Conduction Velocity ◽  
Electrical Response ◽  
Quantitative Description ◽  
Ion Concentration ◽  
Ionic Homeostasis ◽  
Voltage Gated ◽  
Concentration Changes ◽  
T System

Activation of skeletal muscle fibers requires rapid sarcolemmal action potential (AP) conduction to ensure uniform excitation along the fiber length, as well as successful tubular excitation to initiate excitation–contraction coupling. In our companion paper in this issue, Pedersen et al. (2011. J. Gen. Physiol. doi:10.1085/jgp.201010510) quantify, for subthreshold stimuli, the influence upon both surface conduction velocity and tubular (t)-system excitation of the large changes in resting membrane conductance (GM) that occur during repetitive AP firing. The present work extends the analysis by developing a multi-compartment modification of the charge–difference model of Fraser and Huang to provide a quantitative description of the conduction velocity of actively propagated APs; the influence of voltage-gated ion channels within the t-system; the influence of t-system APs on ionic homeostasis within the t-system; the influence of t-system ion concentration changes on membrane potentials; and the influence of Phase I and Phase II GM changes on these relationships. Passive conduction properties of the novel model agreed with established linear circuit analysis and previous experimental results, while key simulations of AP firing were tested against focused experimental microelectrode measurements of membrane potential. This study thereby first quantified the effects of the t-system luminal resistance and voltage-gated Na+ channel density on surface AP propagation and the resultant electrical response of the t-system. Second, it demonstrated the influence of GM changes during repetitive AP firing upon surface and t-system excitability. Third, it showed that significant K+ accumulation occurs within the t-system during repetitive AP firing and produces a baseline depolarization of the surface membrane potential. Finally, it indicated that GM changes during repetitive AP firing significantly influence both t-system K+ accumulation and its influence on the resting membrane potential. Thus, the present study emerges with a quantitative description of the changes in membrane potential, excitability, and t-system ionic homeostasis that occur during repetitive AP firing in skeletal muscle.

Local mechanisms of phase-dependent postsynaptic modifications of NMDA-induced oscillations in the abducens motoneurons: a simulation study

1996 ◽  
Vol 76 (2) ◽  
pp. 1015-1024 ◽  
Author(s):  
I. L. Kopysova ◽  
S. M. Korogod ◽  
J. Durand ◽  
S. Tyc-Dumont
Keyword(s):  
Synaptic Input ◽  
Pattern Generation ◽  
Ion Concentration ◽  
Extracellular Potassium ◽  
Pump System ◽  
Voltage Gated ◽  
Ion Concentrations ◽  
Concentration Changes ◽  
Transmembrane Currents

1. In vivo experiments have shown that extracellular microelectrophoretic application of N-methyl-D-aspartate (NMDA) induced oscillatory plateau potentials with bursts of action potentials in rat abducens motoneurons. The period of these slow NMDA oscillations could be altered by single trigeminal non-NMDA excitatory input delivered at low frequency during the NMDA oscillations. 2. A resetting of the oscillations was observed depending on the phase of slow oscillatory cycle during which the trigeminal excitation occurred. 3. We investigated local mechanisms responsible for the phase-dependent modifications of NMDA oscillations, including contributions of voltage and concentration transients, in the mathematical model of the isopotential membrane compartment equipped with voltage-gated Na+, K+, and Ca2+ channels, with Ca2+-dependent K+ channels, and with ligand-gated NMDA and alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor channels. The faithful model was constructed with the use of models described earlier, which were modified by increasing time constants of kinetic variables of all voltage-gated conductances and by including coupled dynamics of voltages and ion concentrations. The changes in ion concentrations were produced near the membrane by transmembrane currents and removal mechanisms (pumps, diffusion). 4. This work focuses on local arrangement of voltage- and ligand-gated conductances and on local ion concentration changes in two separate pools: the postsynaptic pool of AMPA receptors and the extrasynaptic pool. In terms of the electrotonic and diffusional length constants, these pools were electrotonically close but diffusionally remote. 5. It was found that the effect of resetting can be produced by a local interaction between plateau and spike-generating conductances and glutamate receptors. 6. In vivo phase-dependent interactions between NMDA oscillations and AMPA synaptic input were reproduced by the local model only when changes in intracellular sodium and extracellular potassium concentrations were taken into account and the mechanisms of ion removal from postsynaptic pools had slower kinetics than the fast pump system operating in the extracellular pool. 7. Postsynaptic changes in ion concentrations of Na+ and K+ in intra- and extracellular layers near the membrane shift of Nernst equilibrium potentials for these ions depending on the phase of activation of synaptic input. Thus Na+ and k+ components of all transmembrane currents involved in the pattern generation are differently affected by synaptic action during the oscillations. We conclude that slow postsynaptic changes in ion concentrations near the membrane play a key role in the resetting of the NMDA oscillations.

La Doped Layered Structure Low-Voltage ZnO Varistor

2012 ◽  
Vol 512-515 ◽  
pp. 1263-1267
Author(s):  
Xing Gao ◽  
Guo You Gan ◽  
Li Hui Wang ◽  
Ji Kang Yan ◽  
Jian Hong Yi ◽  
...  
Keyword(s):  
Layered Structure ◽  
Low Voltage ◽  
Ion Concentration ◽  
Secondary Phases ◽  
Electrical Measurements ◽  
Leakage Currents ◽  
Epma Data ◽  
Zno Varistor ◽  
Current Voltage ◽  
La Doped

A novel fabricated technique, by feeding two sets of different ZnO formulations powder in a die by parts, molded only once to produce layered structure(including layer A and layer B) low-voltage ZnO varistor. The samples are examined by using energy dispersive X-ray spectroscopy (EDS), electron probe microanalysis (EPMA), scanning electron microscope (SEM) and DC electrical measurements. EDS and EPMA data indicate that doped elements only exists in layer A, The results of SEM indicate that secondary phases are formed at grain boundaries in layer A, not found in layer B. It is found that the electrical properties of low-voltage varistor are improved without reducing thickness and changing energy absorption capabilities. The higher nonlinearity coefficients, lower breakdown fields and leakage currents of layered structure low-voltage ZnO varistor, as compared to those of ZnO varistor fabricated from the conventional route. The improved current-voltage properties are attributed to the band structure difference in both sides grains, due to the different ion concentration and species in both sides of grain boundary. Layered structure varistor also has more simpler prepared technology than multilayer chip varistor.

Cold-induced cytosolic free calcium ion concentration changes in wheat

2009 ◽  
Vol 166 (17) ◽  
pp. 1955-1960 ◽  
Author(s):  
J. Nagel-Volkmann ◽  
C. Plieth ◽  
D. Becker ◽  
H. Lüthen ◽  
K. Dörffling
Keyword(s):  
Calcium Ion ◽  
Ion Concentration ◽  
Free Calcium ◽  
Cytosolic Free Calcium ◽  
Concentration Changes ◽  
Calcium Ion Concentration

scholarly journals Why Are Seizures Rare in Rapid Eye Movement Sleep? Review of the Frequency of Seizures in Different Sleep Stages

2013 ◽  
Vol 2013 ◽  
pp. 1-10 ◽  
Author(s):  
Marcus Ng ◽  
Milena Pavlova
Keyword(s):  
Eye Movement ◽  
Rem Sleep ◽  
Low Voltage ◽  
Sleep Stage ◽  
Sleep Stages ◽  
Seizure Freedom ◽  
Rapid Eye Movement ◽  
Focal Seizures ◽  
Generalized Seizures ◽  
Interictal Discharges

Since the formal characterization of sleep stages, there have been reports that seizures may preferentially occur in certain phases of sleep. Through ascending cholinergic connections from the brainstem, rapid eye movement (REM) sleep is physiologically characterized by low voltage fast activity on the electroencephalogram, REMs, and muscle atonia. Multiple independent studies confirm that, in REM sleep, there is a strikingly low proportion of seizures (~1% or less). We review a total of 42 distinct conventional and intracranial studies in the literature which comprised a net of 1458 patients. Indexed to duration, we found that REM sleep was the most protective stage of sleep against focal seizures, generalized seizures, focal interictal discharges, and two particular epilepsy syndromes. REM sleep had an additional protective effect compared to wakefulness with an average 7.83 times fewer focal seizures, 3.25 times fewer generalized seizures, and 1.11 times fewer focal interictal discharges. In further studies REM sleep has also demonstrated utility in localizing epileptogenic foci with potential translation into postsurgical seizure freedom. Based on emerging connectivity data in sleep, we hypothesize that the influence of REM sleep on seizures is due to a desynchronized EEG pattern which reflects important connectivity differences unique to this sleep stage.

scholarly journals Nutrient Dosing Framework for an Emission-Free Urban Hydroponic Production

2021 ◽  
Vol 12 ◽  
Author(s):  
Tae In Ahn ◽  
Jai-Eok Park ◽  
Je Hyeong Jung ◽  
Sang Min Kim ◽  
Gyhye Yoo ◽  
...  
Keyword(s):  
Nutrient Dynamics ◽  
Nutrient Management ◽  
Simulation Analysis ◽  
Root Zone ◽  
Management Practice ◽  
Nutrient Absorption ◽  
Ion Concentration ◽  
Controlled Environment ◽  
Concentration Changes ◽  
Nutrient Solutions

The urban hydroponic production system is accelerating industrialization in step with the potentials for reducing environmental impact. In contrast, establishing sustainable fertilizer dosing techniques still lags behind the pace of expansion of the system. The reproducibility of root-zone nutrient dynamics in the system is poorly understood, and managing nutrients has so far primarily relied on periodic discharge or dumping of highly concentrated nutrient solutions. Here, we assayed root-zone nutrient concentration changes using three possible nutrient dosing types. Three Brassica species were hydroponically cultivated in a controlled environment to apply the nutrient absorption and transpiration parameters to the simulation analysis. We found that nutrient dosing based on total ion concentration could provide more reproducible root-zone nutrient dynamics. Our findings highlight the nutrient absorption parameter domain in management practice. This simplifies conventional nutrient management into an optimization problem. Collectively, our framework can be extended to fertilizer-emission-free urban hydroponic production.

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