Modulation of cell function by electric field: a high-resolution analysis.

Regulation of cell function by a non-thermal, physiological-level electromagnetic field has potential for vascular tissue healing therapies and advancing hybrid bioelectronic technology. We have recently demonstrated that a physiological electric field (EF) applied wirelessly can regulate intracellular signalling and cell function in a frequency-dependent manner. However, the mechanism for such regulation is not well understood. Here, we present a systematic numerical study of a cell-field interaction following cell exposure to the external EF. We use a realistic experimental environment that also recapitulates the absence of a direct electric contact between the field-sourcing electrodes and the cells or the culture medium. We identify characteristic regimes and present their classification with respect to frequency, location, and the electrical properties of the model components. The results show a striking difference in the frequency dependence of EF penetration and cell response between cells suspended in an electrolyte and cells attached to a substrate. The EF structure in the cell is strongly inhomogeneous and is sensitive to the physical properties of the cell and its environment. These findings provide insight into the mechanisms for frequency-dependent cell responses to EF that regulate cell function, which may have important implications for EF-based therapies and biotechnology development.

Convection in a very compressible fluid: comparison of simulations with experiments.

The time profile DeltaT(t) of the temperature difference, measured across a very compressible fluid layer of supercritical 3He after the start of a heat flow, shows a damped oscillatory behavior before steady-state convection is reached. The results for DeltaT(t) obtained from numerical simulations and from laboratory experiments are compared over a temperature range where the compressibility varies by a factor of approximately 40. First the steady-state convective heat current j(conv) as a function of the Rayleigh number Ra is presented, and the agreement is found to be good. Second, the shape of the time profile and two characteristic times in the transient part of DeltaT(t) from simulations and experiments are compared, namely (1) t(osc), the oscillatory period, and (2) t(p), the time of the first peak after starting the heat flow. These times, scaled by the diffusive time tau(D) versus Ra, are presented. The agreement is good for t(osc)/tau(D), where the results collapse on a single curve showing a power-law behavior. The simulation hence confirms the universal scaling behavior found experimentally. However for t(p)/tau(D), where the experimental data also collapse on a single curve, the simulation results show systematic departures from such a behavior. A possible reason for some of the disagreements, both in the time profile and in t(p), is discussed.

Heat transfer and convection onset in a compressible fluid: 3He near the critical point.

Heat transport in 3He above its critical temperature Tc was studied along the critical isochore in a flat Rayleigh-Bénard cell (height h=1 mm, diameter D=57 mm). The range of the reduced temperature epsilon was 5 x 10(-4)< or = epsilon < or =2 x 10(-1). The temperature difference deltaT(t) across the fluid layer as a function of the time t was measured for different values of the heat current q until steady state was reached. The crossover was observed from the regime dominated by the Rayleigh criterion for the convection onset to that controlled by the adiabatic temperature gradient (ATG), or "Schwarzschild criterion," in good quantitative agreement with predictions. The slope of the convective heat current versus the reduced Rayleigh number was found to be independent of compressibility and the same as for still less compressible fluids. Plots of Nu versus Ra, both corrected for the ATG effect, are presented for early-stage convective turbulence (1 x 10(5)

Intercellular relationships in elementary neuronal ensembles.

The mechanisms of combination of cortical neurons into discrete modules or elementary ensembles, serving as functional units and forming a mosaic of activity in which incoming information is coded, have been investigated. Neurons activated primarily by terminals of specific afferents respond stably with a minimal latent period and become the centers of ensembles, whose periphery is formed by secondarily activated neurons, responding variably with a longer latent period. The stochastic participation of these neurons in the structure of the ensembles lies at the basis of plasticity of cortical mechanisms. Neurons inhibited intracortically, and possibly, via ascending inhibitory pathways, are concentrated at the periphery and near the output cells of the ensemble.

Role of inhibition in the formation of a dynamic mosaic of neuronal ensembles in the cerebral cortex.

The spatial-temporal organization of neuronal responses in the rat visual cortex was investigated during the action on the retina of light stimuli of various size. It was shown that a leading role in the formation of a dynamic mosaic of neuronal ensembles belongs to inhibition. Two systems of inhibition are distinguished, involved in differing degree in the organization of the operating mechanisms of the brain during the action of various stimuli.

Some mechanisms of central inhibition.

Central inhibition is viewed as the result of the interaction of processes at the level of the neuron, nerve center, and intercentral relationships. At all levels this involves activity for the reorganization of a functional structure that realizes a state of excitation under one organization and a state of inhibition under another. The results are presented of an investigation of subcellular reorganizations during the inhibition of a neuron, the reorganization of neuronal activity during the inhibition of nervous centers, and the subordination of the centers of an equivalent level during the inhibition of acts in systemic activity.

[Interneuronal relations in elementary neuronal assemblies]. / Mezhneironnye otnosheniia v élementarnykh ansambliakh neironov.

Mechanisms of integrating cortical neurons into discrete modules--elementary ensembles--as functional units involved in formation of mosaic activity, in which input information is coded, were studied. Neurons primarily activated by specific afferent terminals and consistently responding with minimal latencies form the center of the ensemble while its periphery consists of secondary activated cells with variable long-latency reaction. Probabilistic participation of the latter in the ensemble structure underlies the cortical mechanism of plasticity. Neurons inhibited intracortically and, probably, by ascending inhibitory ways are situated in the periphery and at output ensemble elements.

[Role of inhibition in the formation of the dynamic mosaic of the neuronal ensembles in the cerebral cortex]. / O roli tormozheniia v formirovaniia dinamicheskoi mozaiki neironnykh ansamblei v kore mozga.

Responses of neurons to local or diffused illumination studied in the rat visual cortex revealed the leading role of inhibition in formation of the dynamic mosaic of neuronal ensembles. Two systems of inhibition (recurrent and afferent) take part in a different way in organization of working brain mechanisms by different stimuli.

[Space-time organization of neuronal activity in the frog tectum and its transformation in response to different visual stimuli]. / Prostranstvenno-vremennaia organizatsiia neironnoi aktivnosti v tektume liagushki i ee perestroiki pri deistvii razlichnykh zritel'nykh razdrazhitelei.

The space and time organization of neuronal activity was studied in the frog tectum opticum under the action of different visual stimuli. It is shown that inhibition plays an important role in neuronal reactions. It is suggested that differences in the space time parameters of neuronal activity reflect differences in visual signals which bring optic information from the retina.

[Visual information coding in the frog midbrain tectum]. / Kodirovanie zritel'noi informatsii v kryshe srednego mozga liagushek.

Possible mechanisms of optic information encoding in the frog tectum are considered on the basis of the extracellular recording of the tectum neuron impulse activity. It is suggested that optic information is coded in the frog tectum by means of space coding and is made more precise with the help of different types of time-coding, the coding by latency difference being used more widely. This mechanism may function either independently or be a component of complex time-codings. A uniform distribution in the tectal structures of neurons processing optic information indicates that the mechanism of exact analysis of optic stimulus movement parameters should be a distribution function of the same structures.

[Role of functional asymmetry of the cerebral hemispheres in organization of an instrumental alimentary conditioned reflex in cats]. / Rol' funktsional'noi asimmetrii polusharii golovnogo mozga v organizatsii instrumental'nogo pishchevogo uslovnogo refleksa u koshek.

During instrumental alimentary conditioning in cats the speed of reflex stabilization depended on the correspondence between the dominant leg's lateralization and the side of the lever, which the animal had to press in response to the signal. When the lever was on the side of the dominant leg, the speed of the conditioning was greater than in the absence of such correspondence. Functional switching off (KCl) of the cortex of any hemisphere at the stage of reflex stabilization does not disturb the instrumental reaction. The switching off of the dominant hemisphere at the stage of stable reflex disturb the instrumental reaction, but has no effect on more simple forms of conditioned behaviour, e. g. run to the feeding through in response to the signal.