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V G Marchenko

Publications and source records attributed to V G Marchenko.

18 recordsLinked to original sources
PubMed2004

Intracortical synchronization of epileptic discharges at different stages of ultrastructural rearrangements in a completely neuronally isolated area of rat neocortex.

Cross-correlation functions were used to study the time delay (a measure of synchronization) in the appearance of epileptic discharges in distant areas of the cortex in the intact cortex and in neuronally isolated cortical strips in Wistar rats. Experiments were performed at different stages of axon sprouting 30 and 90 days after isolation of cortical areas and in intact cortex. Significant increases in the number of synapses in layer V of isolated cortical strips at 30 days correlated with significant decreases in the time delay, while decreases in the number of synapses at 90 days correlated with a significant increase in the time delay. This is evidence that newly formed synapses increase the extent of synchronization and thus affect epileptogenesis. The data obtained here suggest that large pyramidal cells in layer V of the rat neocortex form a neural network in pathological conditions, this supporting intracortical synchronization of epileptic discharges.

Animals↗
PubMed2000

[Structural basis of the intracortical synchronization of epileptic potentials in the sensomotor region of the rat neocortex].

In control rats, penicillin-induced epileptiform discharges were completely synchronous in the neocortex sites at a distance of up to 4 mm from each other. Number of the cells decreased by 45.5% during 90 days in isolated cortical slabs and the synchronisation disappeared. The data obtained show that the loss of large pyramidal neurones of the layer V entailed a loss of the spatial synchronisation. The main axonal collaterals of large pyramidal neurones of the layer V could be followed horizontally for a distance of up to 2 mm in the somatosensory cortex. The neuronal network formed by the large pyramidal neurones of the layer V seems to provide a spatial synchronisation in the neocortex.

Animals↗
PubMed1990

[Mechanisms of post-isometric relaxation of skeletal muscles as a method of rehabilitation].

The authors demonstrate that a merited place among the methods of manual therapy belongs to PIR--postisometric relaxation of the muscles. It is shown that the relaxation of the muscle converted to isometric regime of work is achieved on the basis of the anatomic and biomechanical principles of its action. The use of PIR is advisable, which is evident in the light of the theory of portal pain control.

Exercise↗
PubMed1986

[Ultrastructural aspects of the process of Salmonella typhi bacterial interaction with L929-line cells].

The study of the use of scanning electron microscopy and the analysis of the initial stages of interaction between S. typhi and eukaryotic cells by the method of three-dimensional reconstruction has revealed that the infective agent penetrates into the cytoplasm on the principle of internalization. The internalization of S. typhi occurs with the active participation of the eukaryotic cells which, at the beginning, envelopes the bacteria with its processes, and the infective agents firmly adhere to the glycocalyx of the host cell by means of special fimbria-like formations differing from fimbriae by their lesser rigidity and thickness; then the microbes fixed to the membrane penetrate inside the cell without destroying its cytoplasmic membrane. Differences in the processes of the interaction of eukaryotic cells with S. typhi initial strain 238 and its variant free from the plasmid with a molecular weight of 6 Md, characterized by its lower capacity for association with cells of continuous cell culture L929, have been revealed. The factors stimulating the ingestion of S. typhi by eukaryotic cells are under study at present.

Adhesiveness↗
PubMed1982

[Responses of cat visual cortex neurons to local stimulation of the center of the receptive field with varying intensity].

The on-responses of striate cortical neurons in paralyzed cats were examined at dark adaptation by local stimulation of the receptive centre with stimuli of scotopic and mesopic range of intensity. The responses of 16% of the total amount of cells involved included phasic activation (type I). The responses of 68% of cells consisted of phasic and sluggish activation with phasic inhibition between them (type II). The responses of 16% of cells showed only slow inhibition (type III). The thresholds of phasic activation covered the range of 0.7-2200 td and were the same as those for the activation of cat cones. The thresholds of sluggish activation covered the range of 0.02-9 td, and coincided with those for rod inputs. The inhibitory effects were observed as phasic inhibition, breakdown of the monotony of the stimulus-response curve and as slow inhibition in on-responses as well. All inhibition effect occurred in mesopic range (0.7-2200 td).

Animals↗
PubMed1980

[Receptive fields of cat visual cortex neurons when photic stimulation parameters are altered].

Spatial excitability reliefs of receptive fields of visual cortex units were investigated in acute experiments on immobilized cats by changing physical and physiological parameters of light stimulation under dark, mesopic and low photopic adaptation. Transition from dark to low mesopic adaptation results in no changes of the shape and size of the receptive fields, revealed by constant intensity test slits, whereas with transition to low photopic adaptation the receptive fields were narrowed in 72% of cases and acquired an elongated shape while the sharpness of their selectivity to direction of movement and orientation of stimuli increases. At a constant background the receptive fields narrowed with decreasing brightness of the test light slit. The excitability relief in the field estimated by the absolute threshold of the cell response and by the level of intensity needed to get a constant number of discharges in response, considerably narrowed with a rise in the threshold criterion and with transition from dark to light adaptation. At light adaptation, stimulation with physiologically equal intensity revealed narrower reactivity reliefs. than those at dark adaptation. The estimation of the receptive fields, taking into account a possible contribution of light scattering in the eye media and over the screen, shows that in most cases their size cannot be explained by this factor.

Animals↗
PubMed1979

[Characteristics of the responses of cat visual cortex neurons to photic stimulation of different areas of their receptive fields].

The functions of intensity, thresholds of reactions, thresholds of inhibitory effects and differential sensitivity to intensity of local light stimulation of central and different peripheral regions of receptive fields of 96 units in the 17th field of visual cortex were investigated in immobilized and nonanesthetized cats in dark adaptation. Receptive fields of cells had wide threshold and superthreshold reliefs (3-30 degrees). Some of them had V-shape reliefs, while others--reliefs with alternating zones of high and low excitability. As a rule, sensitivity of excitatory and inhibitory inputs was maximal in the centre of the receptive field. In the investigated population of cells the inhibitory inputs were more standard in sensitivity and on the average of lower excitability. The threshold relief of the receptive fields was markedly narrowed under light adaptation mainly due to a decrease in the peripheral inputs sensitivity. The number of low-threshold units, the differential brightness sensitivity and sensitivity of the inhibitory system increased in the visual cortex as compared to the lateral geniculate and retinal units. The mechanisms of receptive field formation in the visual cortex and their plasticity depending on the adaptation level, the role of excitatory and inhibitory inputs in these effects and behavioral significance of the obtained data are discussed.

Animals↗
PubMedDate not supplied

Structural bases of intracortical processes underlying the synchronization of epileptic potentials in the sensorimotor areas of the neocortex in rats.

Studies in long-term isolated areas of the rat neocortex were performed to investigate the dynamics of the numbers and areas of nerve cell bodies in layer V and to compare these data with the degree of synchronization of epileptic discharges evoked by application of penicillin. Decreases in the number of pyramidal neurons with body areas of 200-350 microm2 in isolated strips after maintenance for 30 and 90 days led to decreases in the degree of synchronization of epileptiform potentials. Large pyramidal neurons are known to have long horizontal axon collaterals, spreading into layers V and VI of the neocortex. It is suggested that the neural networks formed by large pyramidal neurons by means of their long horizontal collaterals mediate the process of intracortical synchronization.

Animals↗
PubMedDate not supplied

[An improved method for isolating a section of the rat neocortex].

Neocortical island chronically isolated from surrounding cortical and subcortical structures with preserved pial blood supply has long been a model for research into the mechanisms of cortex functioning. To fully cut the cortex we improved the type of knife by using a retractable tungsten wire. The tip of a syringe needle was bent and cut away all but the beginning of the bend. In anesthetized rats the somatosensory cortex was exposed, the guide needle was lowered down to the desired depth into the cortex avoiding blood vessels. The wire then was pulled out through the curved needle tip until the tip of the wire touched the pia mater. The device was then raised, lowered, rotated to achieve complete separation of the cortical island from the surrounding tissues. The wire was retracted into the needle before withdrawal of the device. Analysis of neocortical slices 8 weeks later showed lesions of the white matter and transcortical cuts.

Animals↗
PubMedDate not supplied

[Intracortical synchronization of the epileptiform field potentials at different stages of ultrastructural reorganizations in neuronally isolates island in rats].

A temporal delay (parameter of synchronization) between the incidence of epileptiform discharges in cortical sited located at a distance of 4 mm from each other was studied in rat intact cortex and neuronally isolated cortical slab using the cross-correlation function. Experiments were carried out at different stages of axonal sprouting. By 30 days of isolation, a significant increase in the number of boutons in the V cortical layer coincided with a significant decrease in the delay, whereas a reduction of the number of boutons by 90 days corresponded to its increase. These findings convincingly testify that the newly formed boutons form a basis for increase in synchronization and thus affect the epileptogenesis. The results obtained in this work and literature data suggest that under pathological conditions large pyramids of the V layer form a neuronal network which provides exclusively cortical synchronization of epileptiform field potentials.

Animals↗
PubMedDate not supplied

[Formation and functional significance of the dark receptive fields of the cat visual cortex].

Receptive fields (RFs) of single units in the 17th field of the visual cortex of immobilized cat were investigated under dark adaptation. The mean RF size was equal to 67 degrees and varied from 3 degrees up to 120 degrees. The RFs with centres located near gaze were from 3 degrees up to 120 degrees in dia, but with growth of excentricity the number of small RFs decreased, and in the region of 70 to 100 degrees from gaze only RFs with diameters equal to 100 degrees were found. The shape of "dark" RFs was either ellipsoidal (in most cases) or round. Detector properties (orientational, directional, size and velocity selectivity) of the "dark" RFs were significantly less manifest or absent. Under photopic light adaptation the same units reorganized their RFs to well known sizes and configuration. The hypothesis is discussed of the formation of local detector RF in the visual cortex in light adaptation by selective cortical inhibition which is activated in darkness only slightly. This view is an alternative to the commonly-accepted scheme of local cortical RF formation by the hierarchical and selective excitatory convergence.

Animals↗
PubMedDate not supplied

[The spatial synchronization of the potentials in the background and evoked ECoG of a neuronally isolated strip of rabbit cortex].

Conditions of formation of potentials' spatial synchronization in the neuronally isolated cortical slab were studied in anaesthetized rabbits in acute experiments. Cortical potentials in all recording points of the slab were similar to each other. Seizure potentials induced by electrical stimulation spread over the slab and became synchronous in all points of recording. The neuronal division of the slab in two parts did not lead to a disturbance of initial synchronization of the background potentials in the isolated parts of the slab, while seizure potentials after electrical stimulation spread only over one part of the slab. These results suggest that the spatial synchronization of the EEG activity is a result of activity physically spreading from subcortical structures.

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