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Biomedical subjects

R G Kozhedub

Publications and source records attributed to R G Kozhedub.

At least 19 recordsLinked to original sources
PubMed2000

[EEG study of the anxiolytic effect of scopolamine].

Effect of the central M-cholinolytic scopolamine on spatial organization of the rat brain electrical activity was studied under conditions of high and low emotional-stress responses. The EEG changes were estimated by 840 parameters. A possibility of the EEG discrimination by means of interstrain differences in responses to scopolamine, was shown. A more obvious decrease in spectral power and potentials coherence was revealed in Maudsley Reactive rats (MR) as compared with the Maudsley Nonreactive rats (MNRA), in parieto-temporal and occipital areas of the right hemisphere, and the reverse interrelationship occurred in the anterior parts of the right and posterior parts of the left hemisphere. These findings suggest some specifics in the spatial distribution of the maximum scopolamine action foci depending on the initial emotional level. Changes occurring under the scopolamine effect in different EEG frequency bands are different in the MR and the MNRA rats. The findings are discussed in respect to the EEG indices of anxiolytic component of cholinergic regulation of the brain activity.

Animals↗
PubMed1989

[An increase in the excitability of the cortical neurons during reinforcing stimulation of the lateral hypothalamus].

Pyramidal tract response (PTR) was recorded from unanaesthetized rabbits. The following three experimental paradigms were used which imitated behavioural conditioning procedures: pairing of direct stimulation of two cortical points; similar pairing conjoint with stimulation of additional reinforcing the lateral hypothalamus (LH); LH stimulation in response to increased PTR in a manner similar to instrumental conditioning procedure. An increase in the monosynaptic wave was the most common result for all three paradigms. The direct wave increase was significantly larger for the second and third experimental paradigms in comparison with the first one. In general the data obtained suggest that an increase in the synaptic efficacy is the major mechanism of behavioural conditioning, while changes in the membrane excitability reflect a participation of motivational components of reinforcement resulted from the LH activation.

Animals↗
PubMed1982

[Effect of acetylcholine on hippocampal response during long-term post-tetanic potentiation and depression of the medial septum and dentate gyrus].

Evoked potentials (EPs) of the dorsal hippocampus were recorded in non-immobilized non-anaesthetized rabbits before and after tetanization of the medial septum and the dentate fascia. Changes of acetylcholine (ACh) efficiency were tested during long-lasting potentiation (LLP) and posttetanic depression (PTD). Increase in the amplitude of the EP fast component (population spike) during microiontophoresis of ACh was used as an index of ACh efficiency. In various tests both decrease and enhancement of ACh efficiency after tetanization were observed independent of the LLP or PTD appearance. "Relative" ACh efficiency in most cases decreased during LLP and enhanced during PTD. These changes were nonspecific since they were observed in response to the stimulation of both medial septum (cholinergic input), and dentate fascia (non-cholinergic input). Reactions to the stimulation of the control (non-tetanized) input were mainly depressed with diminution of ACh efficiency. The above experiments do not confirm the hypothesis that LLP and PTD are based on respective changes in the sensitivity of the subsynaptic membrane to the transmitter. The most probable LLP mechanism seems to be the enhancement of synaptic efficiency due to increased release of the transmitter. PTD mechanisms probably include changes at the level of the postsynaptic membrane and call for further analysis.

Acetylcholine↗
PubMed1980

[Changes in the sensitivity of septohippocampal responses to acetylcholine during prolonged post-tetanic potentiation].

Septo-hippocampal field evoked potentials were recorded in unanesthetized rabbits. Changes in the rapid negative component of evoked potentials (population spike) seen in acetylcholine microiontophoresis served as an index of acetylcholine sensitivity. A tendency to decreased sensitivity during long-term post-tetanic potentiation (LTPTP) and negative correlation between LTPTP and acetylcholine sensitivity were found. The evidence obtained does not support a hypothesis of changes in the mediator sensitivity as a mechanism of LTPTP. The decreased mediator sensitivity that can suppress the responses mediated through untetanized pathways is considered as an analogue of pavlovian differentiation.

Acetylcholine↗
PubMedDate not supplied

The functional role of an increase in cell excitability and synaptic efficiency in the new cortex during learning.

Data were obtained in experiments on nonimmobilized and nonanesthetized rabbits, during the development of an analog of a CR, with recording of the response of the pyramidal tract, suggesting temporal specificity in the manifestations of membrane and synaptic plasticity, the participation of these mechanisms in both representations of the combined stimuli, and primarily unidirectional changes in the degree of their participation in these points of the cortex. It is concluded that temporary membrane plasticity creates conditions through the mechanisms of synchronization and summation for the passage of excitation from the sensory link to the motor output of the new connection. The gradual reorganization of excitatory and inhibitory connections to the output elements of the conditioned reflex act, determined by the mechanisms of synaptic plasticity, determine and strengthen the specialized character of the developed reaction.

Animals↗
PubMedDate not supplied

Prolonged changes in synaptic efficiency and cellular excitability during learning.

A temporal analysis of changes in the response of the pyramidal tract using a model of prolonged potentiation revealed the substantial role of the mechanism of the heightening of total excitability of the cell at the initial stage of the formation of trace processes (an analog of the "dominant") which apparently promote the greater strengthening of the underlying mechanism of the CR, namely, the increase in the efficiency of synaptic associations. In the development of a CR in response to the stimulation of two points of the cortex, the increase in cell excitability was more marked in those experiments in which reinforcement was supplemented by the stimulation of the lateral hypothalamus, stimulation eliciting an alimentary reaction. These data make it possible to consider membrane plasticity as a cortical mechanism of the motivational component of reinforcement, a mechanism determining the dominant properties of the stage of generalization of the CR.

Animals↗
PubMedDate not supplied

Correlational association between changes in cell excitability and synaptic efficiency during posttetanic reorganizations in the cortex.

A positive linear association between the posttetanic changes in synaptic efficiency and the shifts in the cellular excitability observed at the same time was established using the method of calculation of the coefficient of correlation (CC) between the changes in the direct and synaptic components of the response of the pyramidal tract. The CC values found at the initial stages of the formation of the trace process decrease with time, and a significant correlational association between the changes in the components is absent by an hour after the tetanic stimulation. Such temporal specificity in the contingency of the mechanisms studied presupposes at a certain stage in the organization of the trace a communality of intracellular molecular substrate which determines the manifestation of these mechanisms. Correlation analysis carried out suggests that cortical plasticity is a complex dynamic system, the understanding of which requires not only the elucidation of the elementary cellular mechanisms forming it, but the study of the character of the interaction between them as well.

Animals↗
PubMedDate not supplied

Synchronization and cooperative interaction in brain activity.

A conception is advanced according to which synchronization and the cooperative interaction of plastic processes at the level of the individual cell and of cell units of varying degrees of complexity form a principle of cerebral integration. The triggering and unfolding of plastic reorganizations which take place with the participation of motivational-emotional structures are realized through the mechanism of alteration of cell excitability. These influences are widely distributed throughout the cerebral cortex, but are selective in relation to the current need of the organism.

Animals↗
PubMedDate not supplied

The correlation between changes in synaptic efficiency and cellular excitability during the development of a conditioned reflex analog.

The calculation of the coefficient of correlation between changes in the direct (D) and monosynaptic (I) components of the pyramidal tract (PT) response made it possible to establish the presence of a positive linear association between conditioned reflex changes in synaptic efficiency and the shifts in cellular excitability observed at the same time. The coincidence of the maximal strength of this association with the greatest increase in cellular excitability which is dependent on the activation of motivatiogenic structures points to the role of these subcortical structures in the launching of intracellular reactions which leads to the formation of the overall molecular substrate which underlies interaction of membrane and synaptic mechanisms. The preceding of the greatest enhancement of synaptic efficiency by the maximal manifestation of the interaction attests to the contribution of this process to the manifestation of the principal mechanism of the conditioned reflex (CR).

Animals↗
PubMedDate not supplied

Features of the coordinated activity functionally identified neurons in the hypothalamus in different motivational-emotional states.

Coordinated activity of hypothalamic neurons associated with motivational and reinforcing systems were studied in functional states arising from hunger, satiation following food deprivation, "victim" cries, and electrical stimulation of the emotionally positive (lateral hypothalamus, lateral preoptic region) and negative (dorsomedial tegmentum) reinforcing structures of the hypothalamus. Activity characteristics were reflected in the magnitude, sign, and dynamics of correlations, and depended on the ratio of motivational and emotional components of behavior. The reciprocal nature of the statistical significance of the activity of these neurons in conditions in which motivation and emotion dominated indicates that the differentiated motivational and emotional hypothalamic influences in cortical processes during learning are mediated via the coordinated activity of neurons in the motivational and reinforcing systems of the hypothalamus.

Animals↗
PubMedDate not supplied

Temporospatial organization of membrane-synaptic modifications and topograms of slow oscillations in cortical potentials during learning.

This report concerns the important question of the specificity of the organization of the different stages of formation of a conditioned reflex, considered at the level of membrane-synaptic modifications, which are compared with changes in the spatial organization of slow cortical potentials. A defined sequence of involvement of cellular mechanisms is demonstrated during learning, which may be responsible for various features of the spatial organization of slow cortical potentials. Changes in cellular excitability in cortical neurons are probably connected with oscillations in the overall level of instantaneous topograms and, thus, with the general level of spatial synchronization; the involvement of excitatory and inhibitory synaptic connections (with efficiencies corresponding to different stages in the reflex) may determine the formation of the relief seen in topograms. Parameters at both levels depend on the effects of the hypothalamus on the cortex.

Animals↗
PubMedDate not supplied

[The dynamics of neocortical modifications: the dependence on motivational and emotiogenic systems].

A concept is advanced according to which for complete and successive development of membrane and synaptic modifications in the neocortex during the conditioned reflex (CR) elaboration the differentiated changes in impulse flow structure of the motivation and emotion systems of the hypothalamus and reciprocal character of excitatory and inhibitory interactions between them are necessary. Motivation excitation coordinated with repeated activation of synaptic inputs by pairing stimuli contributes to temporary (lasting about hour) increase in somatodendritic electroexcitability of neocortical neurons. It is necessary for maintaining cells in the state of readiness for summation of polymodal excitations during the CR generalization stage. Emotion excitation contributes to long-lasting (about twenty-four hours) increase in synaptic efficacy of excitatory and inhibitory connections which determine a conditioned act during the stage of specialization. Hetero- and homosynaptic facilitation of synaptic transmission lead to global and local character of spatial synchronization of slow activity during these stages. These processes are mainly determined cooperative interaction glutamatergic system with modulator cholin- and monoaminergic (noradren- and serotonin-) systems activating during motivational and emotional behavior components, respectively.

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