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Biomedical subjects

I V Volkov

Publications and source records attributed to I V Volkov.

16 recordsLinked to original sources
PubMed2001

Platinum-containing hyper-cross-linked polystyrene as a modifier-free selective catalyst for L-sorbose oxidation.

Impregnation of hyper-cross-linked polystyrene (HPS) with tetrahydrofuran (THF) or methanol (ML) solutions containing platinic acid results in the formation of Pt(II) complexes within the nanocavities of HPS. Subsequent reduction of the complexes by H2 yields stable Pt nanoparticles with a mean diameter of 1.3 nm in THF and 1.4 nm in ML. The highest selectivity (98% at 100% conversion) measured during the catalytic oxidation of L-sorbose in water is obtained with the HPS-Pt-THF complex prior to H2 reduction. During an induction period of about 100 min, L-sorbose conversion is negligible while catalytic species develop in situ. The structure of the catalyst isolated after the induction period is analyzed by X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy. Electron micrographs reveal a broad distribution of Pt nanoparticles, 71% of which measure less than or equal to 2.0 nm in diameter. These nanoparticles are most likely responsible for the high catalytic activity and selectivity observed. The formation of nanoparticles measuring up to 5.9 nm in diameter is attributed to the facilitated intercavity transport and aggregation of smaller nanoparticles in swollen HPS. The catalytic properties of these novel Pt nanoparticles are highly robust, remaining stable even after 15 repeated uses.

Catalysis↗
PubMed1985

[Characteristics of monosynaptic connections between neurons of the callosal system and specific thalamic nuclei].

In the sensorimotor cortex of awake rabbits monosynaptic afferent and efferent connections of callosal neurons (CN) with ipsilateral specific thalamic nuclei (ventral posterolateral, ventral posteromedial, ventral lateral and anteroventral nuclei) were analyzed by electrophysiological method and compared with those of target-units of callosal fibres (TU). It was demonstrated that CN and TU differed in their monosynaptic inputs from the thalamus and in their axons projecting to these structures and/or being a part of the pyramidal tract. These differences were the following: a greater portion of TU had the descending projections (54%) as compared with CN (14%); 22% of TU responded by monosynaptic action potentials to the stimulation of specific thalamic nuclei, while CN never manifested such responses. TU could project to the thalamus through the main axon stem as well as through the collaterals of the pyramidal tract axons. It is supposed that the discovered differences evidence for the much greater convergence of the thalamic relay neuron effect on TU, thus revealing the mechanism underlying the differences both in receptive field properties and in the background and evoked activity of CN and neurons synaptically excited in response to the transcallosal stimulation.

Animals↗
PubMedDate not supplied

Influence of stimulation of the medial hypothalamus on the interaction of neurons of the rabbit neocortex.

The interaction of neurons of the visual and sensory motor areas of the neocortex of the rabbit before and after stimulation of some medial nuclei of the hypothalamus was investigated by plotting cross- and autocorrelation histograms. Stimulation through bipolar electrodes using bursts of biphasic pulses at a frequency of 100 Hz, current strength 50-200 microA, led to the appearance in freely behaving rabbits of the reaction of avoidance of the place of stimulation. Following stimulation, as compared with resting wakefulness, the number of pairs of neurons functioning in correlation increased to 45%; at the same time, discharges of neurons of the sensory motor area ran ahead of discharges of visual neurons in the pairs up to 120 msec; the periodicity of the coupled discharges was mainly in the theta frequency range. A conclusion regarding the reflection of defense motivation in certain indices of the interaction of the cortical cells in the presence of a tonic conditioned reflex is reached on the basis of a comparison of the interaction of neurons following stimulation of the medial hypothalamus and the midbrain reticular formation, in the intersignal periods during the development of a defense conditioned reflex as well.

Animals↗
PubMedDate not supplied

An expert system based on the principle of the functional asymmetry of the brain.

A general concept for automating the secondary processing of data is proposed. Starting information is accumulated in a database. During processing, a textual description is generated for each object, and all further manipulations consists of transformations of the database. The use of this approach allows different types of information to be accumulated and analyzed efficiently using a single scheme.

Brain↗
PubMedDate not supplied

Effect of stimulation of the lateral hypothalamus on the correlation of neuron spike activity in the rabbit neocortex.

Cross-correlation and autocorrelation histograms were constructed with the aim of studying correlated spike activity of neurons in the visual and sensorimotor regions of both hemispheres of the rabbit brain before and after stimulation of the right and left lateral hypothalamic regions, which generates food-motivated responses. Stimulation of the left hypothalamus produced larger rearrangements in correlated neuron firing than stimulation of the right hypothalamus. Stimulation of the left hypothalamus, unlike that of the right hypothalamus, was followed by significant increases in the numbers of pairs of left hemisphere neocortical neurons with linked activity, and also induced the sequential firing of neurons in a particular defined order: sensorimotor cortex cells fired first, followed by visual cortex neurons after delays of up to 120 msec. It is concluded that cortical interhemisphere asymmetry in conditions of hunger is associated with nonuniform functioning of the right and left lateral hypothalamic regions.

Animals↗
PubMedDate not supplied

Real-time distribution of linked spike activity in cortical neurons during learning in the cat.

Analysis of the distribution of linked spike activity showed changes occurring within the structure of interneuron functional connections during learning. In an electric shock defensive reflex, concentration of linked spikes from cat motor cortex neurons was observed on signal presentation, while in a conditioned food-procuring reflex to time, this was confined to the moment at which reinforcement was provided. This can be regarded as the appearance of a reflex at the level of interneuron interactions. This conclusion is supported by the observation that in well-trained animals, concentrations of linked spikes could be seen at the place of the conditioned reflex response, even in the absence of defensive and food-procuring movements.

Action Potentials↗
PubMedDate not supplied

[A comparison of the efficiency of stimulation of the right and left lateral hypothalamus during a self-stimulation reaction].

Higher rate of the right-side self-stimulation of the lateral hypothalamus than of the left-side was found in freely behaving (30 +/- 8 versus 16 +/- 5 pressings per minute) and fixed rabbits (15 +/- 3 versus 10 +/- 2 pressings per minute, accordingly) under conditions of optimal current (current strength was leveled about the thresholds of food motivational reactions).

Animals↗
PubMedDate not supplied

[A spike "collector"].

Explore the source record for details and available documents.

Action Potentials↗
PubMedDate not supplied

[The effect of stimulation of the medial hypothalamus on the interaction of rabbit neocortical neurons].

By means of histograms of cross- and autocorrelation plotting the interaction of visual and sensorimotor neocortex neurons was studied before and after stimulation of some medial hypothalamic nucleus. The stimulation was provided by packages of bipolar impulses with frequency of 100 Hz and current value of 50-200 mcA from the bipolar electrodes and resulted in appearance of avoidance reactions to stimulation place at rabbits' free behavior. After stimulation as compared with calm wakefulness the number of pairs of neurons with correlated activity was increased by 45%, the discharges of sensorimotor neurons forestalled the discharges of the visual ones for up to 120 ms, the frequency of periodicity of correlated discharges was basically in the theta-range. By means of comparison the interaction of neurons after stimulation of medial hypothalamus and midbrain reticular formation and in intersignal interval during defensive conditioning the conclusion was made about manifestation of defensive motivation in definite indices of cortical neurons interaction during tonic conditioned reflex.

Animals↗
PubMedDate not supplied

[The distribution in real time of the spike train activity in the cortical neurons of cats during learning].

Analysis of the dynamics of distribution of coincident impulses in pairs of neurons revealed modifications in the structure of neuronal interaction in the process of learning. In electrodefensive sound conditioning coincident paired impulses of the neurons in cat's motor cortex were timed to the moment of the conditioned stimulus presentation. In food-procuring time conditioning coincident impulses were concentrated around the moment of the reinforcement administration. The described temporal pattern of coincident impulse distribution is considered as a manifestation of a conditioned reaction at the level of neuronal interaction. This conclusion is confirmed by the finding that coincident impulses may be grouped within the period of expected conditioned reaction even in the absence of the defensive or food-procuring movement in well-trained cats.

Acoustic Stimulation↗
PubMedDate not supplied

[The effect of stimulation of the lateral hypothalamus on the spike trains of the rabbit neocortical neurons].

Cross- and autocorrelation histograms of the impulse activity of the visual and sensorimotor cortical neurons were plotted before and after stimulation of the right (RH) and left lateral hypothalamus (LH) which provoked food motivation reactions. Reorganization in correlated activity of neocortical neurons was more expressed after the LH than the RH stimulation. Only after the LH stimulation the number of neuronal pairs with co-related activity in the left hemisphere increased by 41% and some order of priority appeared in the neuronal discharges. The visual neurons discharged after the sensorimotor ones with delays up to 120 ms. The conclusion was drawn that cortical interhemispheric asymmetry of electrical activity during hunger was associated with unequal operation of the right and left lateral hypothalamus.

Animals↗
PubMedDate not supplied

[An expert system based on the principle of brain functional asymmetry].

The generalized concept is proposed for automation of secondary data processing. Initial information is stored in the knowledge base. During processing the verbal description is generated for each object. All further operations are reduced to the transformation of the textual data. This approach makes it possible to accumulate information of diverse types and efficiently analyze it according to the universal scheme.

Brain↗