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R G Kozhedub

Publications and source records attributed to R G Kozhedub.

14 recordsLinked to original sources
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↗
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

[The functional role of enhanced cellular excitability and synaptic efficiency in the neocortex during learning].

In experiments with noncurarized and unanaesthetized rabbits was recorded pyramidal tract response in the course of conditioning of direct stimulations of the two points of the cortical surface. The data obtained point to temporary specificity in manifestation of the membrane and synaptic plasticity, to participation of these mechanisms in the processes proceeding in both cortical representations of paired stimuli, and to predominantly undirected changes of a degree of their involvement in both cortical areas. At the early stage of conditioning were demonstrated all the characteristics of the dominant state developing at this stage, and at the late one those of differential conditioning. A conclusion is drown that the reinforcement through the membrane plasticity leads to initial dominant increase of cellular excitability. On the background of the latter by means of summation mechanism the conditions are created for excitation transmission from the sensory link of a new bond to its motor output. Underlined by the mechanisms of synaptic plasticity gradual reorganization of the excitatory and inhibitory connections to the output elements of conditioned response determines and consolidates specialized character of the elaborated reaction.

Animals↗
PubMedDate not supplied

[Long-term changes in synaptic efficiency and cellular excitability during learning].

Temporal analysis of changes of pyramidal tract response on the model of prolonged potentiation revealed the significant role of the mechanism of increase of the cell general excitability at the initial stage of trace processes formation ("dominant" analogue) what probably contributes to better consolidation of basic CR mechanism--the increase of synaptic links efficiency. During the elaboration of CR to stimulation of two cortical points the increase of cellular excitability was more expressed in those experiments where the reinforcement was supplemented by stimulation of the lateral hypothalamus eliciting alimentary reaction. These data allow to consider the membrane plasticity to be a cortical mechanism of motivational reinforcement component determining dominant properties of CR generalization stage.

Animals↗
PubMedDate not supplied

[Effect of serotonin on cholinergic septo-hippocampal reactions in the rabbit].

In noncurarized and unanaesthetized rabbits, the unit activity and field potentials evoked by testing stimulation of the medial septum were studied before, during (3-10 min), and in different periods (up. to 0.5 h) after microiontophoretic serotonin (5-OT) application or n. Raphe stimulation. In most of the cases, just during 5-OT application or n. Raphe stimulation, cholinergic septo-hippocampal responses decreased. Trace facilitatory effect of native and exogenously applied 5-OT on these responses was found. Increase of efficiency of cholinergic excitatory input was considered as a confirmation of the role of the serotonergic system in hippocampal long-term posttetanic potentiation after the stimulation of the medial septum. On the whole the data obtained indicate a complex modulatory 5-OT influence on the cholinergic septo-hippocampal responses.

Animals↗
PubMedDate not supplied

[Changes in pyramidal tract response to direct stimulation of the sensomotor cortex of the rabbit during formation of a conditioned reflex].

Changes of pyramidal tract (PT) response were analyzed, reflecting the final result of cortical interaction in the process of combinations of direct stimulations of cortical surface in nonimmobilized and unanaesthetized rabbits. It has been shown that in a situation, modelling conditioning, changes take place of the first direct component--the D-component--of the PT response (reflecting the excitability of the PT neurones), as well as changes of the successive indirect synaptic component--I-component (reflecting the excitability of presynaptic cortical elements and of intracortical synaptic connections). I-component changes were significantly more expressed. In most cases the I-component of the response was increased. The obtained data testify to an increase of synaptic efficiency in the process of temporary connection formation and to possible change (increase or reduction) of excitability of PT neurones.

Animals↗
PubMedDate not supplied

[Duration of trace processes in the neocortex of rabbits].

Changes of pyramidal tract (PT) response after short tetanization, similar to natural stimulation conditions, were analysed in unanaesthetized and nonimmobilized rabbits. PT response recording revealed a long-term (1 h and more) potentiation of monosynaptic neocortical reactions. Predominant better expressed and more preserved increase of synaptic (N) component provides evidence to the conjecture that the basic mechanism of the long-term potentiation consists in the rise of efficiency of excitatory synaptic connections. Less protracted and differently directed changes of D-component permit to consider that excitability change of neurones may be only an additional mechanism of the long-term potentiation. Such features of neocortical long-term potentiation were revealed as its low-frequency depression (at test stimuli repetition) and its spontaneous restoration after depression.

Animals↗
PubMedDate not supplied

[Changes in the effect of acetylcholine on septo-hippocampal reactions after serotonin administration to rabbits].

Impulse activity and focal evoked potentials appearing in the hippocampus in response to testing stimuli applied to the septum medial nucleus were recorded in nonimmobilized and unanaesthetized rabbits. The efficiency of acetylcholine (ACh) action on septo-hippocampal reactions was tested before and after microiontophoretic administration of the serotonin (5-OT) or stimulation of the raphe nuclei. The 5-OT and raphe stimulation produced significant changes in the ACh action on septo-hippocampal reactions. In most cases, after microiontophoretic administration of 5-OT, the efficiency of ACh diminished, independently of excitatory or inhibitory effect of the 5-OT. Thus, the modulating action of 5-OT consists not only in protracted trace changes of the magnitude of septo-hippocampal reactions but also in trace reduction of septo-hippocampal responses to ACh.

Acetylcholine↗